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1 (86) Radio Transport PM LTE Transport Confidential
LTE Transport Tutorial
Nokia Siemens Networks
Radio Transport Product Management
Confidential
____________________________________________________________________________
Version Date Author
4.0 24-Jun-2010 Torsten Musiol ____________________________________________________________________________
2 (86) Radio Transport PM LTE Transport Confidential
Terminology .....................................................................................................................................5 Glossary of Acronyms ......................................................................................................................6
1. Introduction ..................................................................................................................................9 2. LTE Basics.................................................................................................................................12
2.1 Network Architecture Evolution ............................................................................................12 2.2 Protocol Stacks....................................................................................................................15
2.2.1 User Plane....................................................................................................................15 2.2.2 Control Plane................................................................................................................15
2.3 Intra-LTE Handover .............................................................................................................16 2.4 Transport Performance Requirements .................................................................................18
2.4.1 Throughput (Capacity) ..................................................................................................18 2.4.2 Delay (Latency), Delay Variation (Jitter)........................................................................23 2.4.3 TCP Issues ...................................................................................................................25
3. Mobile Backhaul Architecture for LTE ........................................................................................26 3.1 X2 Connectivity Requirements.............................................................................................26 3.2 Implementation Options .......................................................................................................28
3.2.1 L2 vs. L3.......................................................................................................................28 3.2.2 Ethernet Based Backhaul Network................................................................................29 3.2.2.1 E-Line .......................................................................................................................30 3.2.2.2 E-LAN .......................................................................................................................31 3.2.2.3 E-Tree.......................................................................................................................32 3.2.2.4 Comparison...............................................................................................................33 3.2.3 Implementation Examples.............................................................................................34
3.3 Transport Service Attributes.................................................................................................36 3.3.1 Capacity .......................................................................................................................36 3.3.2 Performance .................................................................................................................36
3.4 Traffic Differentiation with VLAN and IP Addressing ............................................................37 3.4.1 Generic eNB IP Addressing Model................................................................................37 3.4.2 Network Reference Configurations ...............................................................................41
3.5 Transport Redundancy ........................................................................................................44 3.5.1 General.........................................................................................................................44 3.5.2 SCTP Multi-homing.......................................................................................................45
3.6 Base Station Co-location .....................................................................................................46 4. LTE Transport Interfaces and Protocols .....................................................................................47
4.1 Ethernet ...............................................................................................................................47 4.2 IP.........................................................................................................................................48
4.2.1 General.........................................................................................................................48 4.2.2 MTU Size Issues...........................................................................................................49 4.2.2.1 Enforcement of lower MTU size ................................................................................50 4.2.2.2 IP Fragmentation and Reassembly ...........................................................................51 4.2.2.3 Ethernet Jumbo Frames............................................................................................52 4.2.3 IPv6 ..............................................................................................................................53
5. QoS............................................................................................................................................55 5.1 End-to-End QoS ..................................................................................................................55 5.2 Transport QoS Features ......................................................................................................56
5.2.1 Traffic Prioritization on IP Layer ....................................................................................56 5.2.2 Traffic Prioritization on Ethernet Layer ..........................................................................57 5.2.3 Packet Scheduling ........................................................................................................58 5.2.4 Traffic Shaping .............................................................................................................59
5.3 Mapping RRM QoS onto Transport QoS..............................................................................60 5.4 Congestion Control ..............................................................................................................61
3 (86) Radio Transport PM LTE Transport Confidential
6. Synchronization..........................................................................................................................62
6.1 Synchronization from GPS...................................................................................................62 6.2 Synchronization from Transport Network .............................................................................63
6.2.1 IEEE1588-2008 Precision Time Protocol (Timing-over-Packet) ....................................63 6.2.2 Synchronous Ethernet ..................................................................................................65
6.3 Solutions for Co-location with Legacy Equipment ................................................................66 6.3.1 Synchronization from PDH interface .............................................................................66 6.3.2 Synchronization from 2.048MHz signal.........................................................................67
7. Transport Security......................................................................................................................68 7.1 General................................................................................................................................68 7.2 X2 Issues.............................................................................................................................70 7.3 IPsec Tunnel Mode vs. Transport Mode...............................................................................72 7.4 Security Associations and IP Addressing .............................................................................72 7.5 Public Key Infrastructure (PKI).............................................................................................75
8. Transport Operability..................................................................................................................76 8.1 Ethernet OAM......................................................................................................................76 8.2 Transport Plug’n’Play (SON)................................................................................................77
8.2.1 Auto-Connection...........................................................................................................77 8.2.2 Auto-configuration.........................................................................................................79
9. Flexi Transport Sub-Modules for LTE.........................................................................................80 10. List of Features....................................................................................................................83 11. References ..........................................................................................................................84 12. Change History ....................................................................................................................86
4 (86) Radio Transport PM LTE Transport Confidential
How to Read this Document
This document is intended to support LTE pre-sales activities. It describes standardized techniques as well as NSN concepts, recommendations and solutions.
Any statements regarding release planning in this document are of informative character only and are subject to change. This document will be further revised as product planning progresses.
5 (86) Radio Transport PM LTE Transport Confidential
Terminology
Control Plane The protocols, functions and interactions that are related to the control of the system
DiffServ The Differentiated Services protocol which provides a mechanism for applying Quality of Service in IP [RFC2474], [RFC2475]
eNodeB A logical node responsible for radio transmission/reception in one or more cells to/from the User Equipment. It terminates the S1 interface towards the MME and Serving GW. This is usually abbreviated to eNB.
EPS Bearer An EPS bearer is the level of granularity for bearer level QoS control in the EPC/E-UTRAN. In the case of GTP-based S5/S8 an EPS bearer runs between a UE and a PDN GW; in the case of PMIP-based S5/S8 it runs between a UE and a Serving GW.
Long Term Evolution The name given to the work on the evolution of the UTRAN for the next 10 years and beyond working towards a high data rate, low latency and packet-optimized radio-access technology.
Mobility Management Entity The C-plane functional element in the EPC that manages and stores UE context (UE/user identities, UE mobility state, user security parameters). It is responsible for the management of identities, checking authorization, bearer management, mobility management and NAS termination.
Network Domain Security The security mechanism employed to protect IP traffic in 3GPP and fixed broadband core networks.
Packet Data Network Gateway The Packet Data Network (PDN) Gateway (P-GW) is one of the gateways that provide the U-plane gateway functionality for the EPC. The P-GW terminates the SGi interface to the PDN. Its functionality includes policy enforcement and charging support.
Quality of Service The concept of providing varying levels of service depending on a variety of factors such as resources available, priority of data, subscription paid.
Serving GW The Serving Gateway (S-GW) is one of the gateways that provide the U-plane gateway functionality for the EPC. The S-GW is the gateway to the E-UTRAN and serves as a mobility anchor point.
System Architecture Evolution This is name given to the work on the evolution of the core network system architecture for the next 10 years and beyond towards a high data rate, low latency and packet-switched system supporting multiple radio access networks.
Transport Plane The protocols, functions and interactions related to transport of C-plane and U-plane data over the interfaces between network nodes of the E-UTRAN and EPC (and within the E-UTRAN and EPC).
User Plane The protocols, functions and interactions related to the transport and manipulation of user data in the system.
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Glossary of Acronyms
AAA Authentication, Authorization and Accounting
AMBR Aggregate Maximum Bit Rate
ANR Automatic Neighbor Relation
ARP Allocation and Retention Priority
BTS Base Transceiver Station
BTSEM BTS Element Management application
BTSOM BTS OAM protocol
BTSSM BTS Site Manager
CA Certificate Authority
CAC Connection Admission Control
CAPEX Capital Expenditure
CBS Committed Burst Size
CDN Content Distribution Network
CESoPSN Circuit Emulation Service over Packet Switched Network
CIR Committed Information Rate
CoMP Cooperative Multipoint
DL Downlink
DSCP DiffServ Code Point
EBS Excess Burst Size
EIR Excess Information Rate
EMS Element Management System
eNB Evolved Node B (also abbreviated as eNodeB)
EPC Evolved Packet Core
EPS Evolved Packet System
E-UTRAN Evolved Universal Terrestrial Radio Access Network
EVC Ethernet Virtual Connection
FD Frame Delay
FDD Frequency Division Duplex
FDV Frame Delay Variation
FFS For Further Study
FLR Frame Loss Ratio
FM Fault Management
FTM Flexi Transport sub-Modules
GBR Guaranteed Bit Rate
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GGSN Gateway GPRS Support Node
GPS Global Positioning System
GTP GPRS Tunneling Protocol
HO Handover
IDU Indoor Unit
IETF Internet Engineering Task Force
IKE Internet Key Exchange
L2 Layer 2
LTE Long Term Evolution
MAC Medium Access Control
MBH Mobile Backhaul
MBMS Multimedia Broadcast/Multicast Service
MBR Maximum Bit Rate
MEF Metro Ethernet Forum
MEG Maintenance Entity Group
MEP Maintenance End Point
MIMO Multiple Input Multiple Output
MLO Multi-Layer Optimization
MME Mobility Management Entity
MTU Maximum Transmission Unit
MWR Microwave Radio
NDS Network Domain Security
NE Network Element
NGMN Next Generation Mobile Networks
NMS Network Management System
NRT Non Real Time
NTP Network Time Protocol
O&M Operations and Maintenance
OAM Operation, Administration, Maintenance
ODU Outdoor Unit
OPEX Operating Expenses
PD Packet Delay
PDCP Packet Data Convergence Protocol
PDN Packet Data Network
PDN-GW Packet Data Network (PDN) Gateway
PDU Protocol Data Unit
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PDV Packet Delay Variation
PKI Public Key Infrastructure
PLR Packet Loss Ratio
PRC Primary Reference Clock
PS Packet Switched
PSK Pre-Shared Key
PW Pseudo-Wire
QoS Quality of Service
RLC Radio Link Control
RNC Radio Network Controller
RNL Radio Network Layer
RRM Radio Resource Management
RT Real Time
RTT Round-Trip Time
SA Security Association
SAE System Architecture Evolution
SAE-GW System Architecture Evolution Gateway
SCTP Stream Control Transmission Protocol
SDF Service Data Flow
SDU Service Data Unit
SEG Security Gateway
SFN Single Frequency Network
S-GW Serving Gateway
SGSN Serving GPRS Support Node
SLA Service Level Agreement
SLS Service Level Specification
SPQ Strict Priority Queuing
SW Software
TDD Time Division Duplex
TNL Transport Network Layer
UE User Equipment
UL Uplink
UNI User Network Interface
VPLS-TE Virtual Private Line Services Transport Equipment
VPN Virtual Private Network
WFQ Weighted Fair Queuing
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1. INTRODUCTION
LTE refers to the Long Term Evolution of the 3GPP radio access technology and is considered the successor of the current UMTS system with the rollout anticipated to begin with trials in 2009. The work in 3GPP is closely aligned to the 3GPP System Architecture Evolution (SAE) study which examines the overall evolved 3GPP architecture and its operation in conjunction with the Evolved UTRAN (E-UTRAN). SAE work in 3GPP has been renamed into Evolved Packet Core (EPC). Together EPC and LTE form Evolved Packet System (EPS).
Whereas the Radio Network Layer (RNL) is being specified by 3GPP, the Transport Network Layer (TNL) for LTE is nowhere defined consistently. Contributing standardization bodies are:
• IETF
• IEEE
• ITU-T
• Metro Ethernet Forum (MEF)
TransportNetwork
Layer
RadioNetwork
Layer MMESAE-GW
O&M
eNB
UE
Figure 1 Standardization landscape
To some extent, the Next Generation Mobile Networks (NGMN) consortium of mobile operators aims at closing the gap. Naturally, there is a lot of room for innovation and a need for education.
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The following figures indicate a number of Frequently Asked Questions and corresponding misconceptions which deserve clarification.
eNB
What about performance
impact with IPSec?
Ethernet / IP
What transport capacity is required?
What transport delay is
acceptable?
What are the synchronization requirements?
Point-to-pointor
Multipoint-to-Multipoint Ethernet?
How to connect automatically(plug‘n‘play)?
How to implement
QoS?
How to share transport with a co-sited base station?
O&M
MME
SAE-GW
How should IP addresses and VLANs be used
Ethernet switch
orIP router?
Is Transport security needed?
Figure 2 FAQ’s
eNB
Ethernet / IP
Transport capacity has to be >500Mbit/s
per eNB Transport delay has to be <5ms
Subscriber security is sufficient
Phase synchronization is
always needed
All transport nodes have
to be IP routers
O&M
MME
SAE-GW
Adjacent eNBs need to have direct links
(fully meshed network)
Multipoint-to-Multipoint is more
suited to flat architecture
Figure 3 Common misconceptions
This document provides an overview of generic LTE transport concepts and issues with special focus on the E-UTRAN, i.e. mobile backhaul (MBH) solutions for LTE Base Stations. Related features and functionalities of the NSN LTE solution will be described. The document aims at providing answers to the questions above, while also indicating NSN recommendation if there are multiple implementation options.
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The NSN LTE FDD product roadmap comprises the following stages:
• RL09 provides basic connectivity functions (LTE protocol stack, IP/Ethernet interface)
• RL10 supports in particular transport QoS, transport security and a variety of synchronization options
• RL20 provides support for base station co-location and operability enhancements
• RL30 and beyond will focus on transport resilience, IPv6 and other optimizations
Features are also linked to TDD releases (RLxxTD) following a similar logic.
This document is focused on features planned until RL20 / RL15TD. However, some functionality intended for later releases is also included. In general, the functionality of a next release extends the functionality of the previous release rather than changing it. Where this is not the case it will be highlighted.
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2. LTE BASICS
2.1 Network Architecture Evolution
Two general trends can be observed which have a great impact on the architecture of mobile networks:
First, circuit switched (CS) connectivity services will be gradually replaced by packet switched (PS) services. This implies in particular that legacy voice services will sooner or later disappear and be replaced by Voice-over-IP (VoIP) service.
Secondly, mobile networks evolve towards flat architectures, leading to more favorable economies with the ever-increasing amount of user traffic. With 3GPP Rel.6 (WCDMA), both the Radio Access Network (RAN) and the Core Network (CN) were built hierarchically. The RAN was composed of the base station (NodeB, NB) and the Radio Network Controller (RNC) and the CN of the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN). In a first evolution step (3GPP Rel.7), the concept of “direct tunnel” between RNC and GGSN has been introduced, so that user plane (U-plane) traffic can bypass the SGSN (“flat” CN). In a next step, pioneered by NSN, RNC functions have been merged into the I-HSPA base station (iNB, “flat” RAN).
NB RNC SGSN GGSN
Internet
3GPP Rel. 6 / HSPA
Direct tunnel
3GPP Rel. 7 / HSPA
Internet
Direct tunnel
3GPP Rel. 7 / Internet HSPA
Internet
NB
iNB
Figure 4 Evolution towards flat network architectur e
The LTE network architecture (Figure 5) introduced with 3GPP Rel.8 is built upon the same principles. Consequently, the CS part has been eliminated completely.
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Direct tunnel
Internet
eNB SAE-GW
MME
3GPP Rel 8 / LTE/SAE
Figure 5 LTE network architecture
The LTE network elements are as follows:
• The Mobility Management Entity (MME) is the control plane (C-plane) functional element in EPC. The MME manages and stores the UE context, generates temporary identities and allocates them to UEs, authenticates the user, manages mobility and bearers, and is the termination point for Non-Access Stratum (NAS) signaling.
• The Serving Gateway (S-GW) is the user plane (U-plane) gateway to the E-UTRAN. The S-GW serves as an anchor point both for inter eNodeB (eNB) handover and for intra 3GPP mobility, i.e. handover to and from 2G or 3G.
• The Packet Data Network Gateway (P-GW) is the U-plane gateway to the PDN, e.g. the Internet or the operator’s IP Multimedia Subsystem (IMS). The P-GW is responsible for policy enforcement, charging support, and user’s IP address allocation. It also serves as a mobility anchor point for non-3GPP access.
• Most often, the S-GW and P-GW functions are combined in one network element, often called SAE Gateway (SAE-GW) .
• The E-UTRAN contains only the base station, eNB, which provides the air interface to the UE.
Evolved Packet System (EPS) reference points are specified in [TS36.300], [TS23.401] and [TS23.402]. The following ones apply to the E-UTRAN:
• S1-MME Control plane reference point between eNB and MME
• S1-U User plane reference point between eNB and the S-GW
• X2 Control & user plane reference point between two eNBs
eNBs can be connected to each other via the X2 reference point and connected to MMEs and S-GWs via the S1-MME/S1-U reference points. A single eNB can be connected to multiple MMEs and multiple S-GWs.
O&M traffic, a.k.a. Management plane (M-plane) is not specified by 3GPP, but yet to be considered.
A fourth functional plane shall be introduced here: The Synchronization plane (S-plane). Terminated by respective applications in the network (synchronization grandmaster) and in the base station (synchronization slave), this concept can easily be understood since synchronization traffic flowing over the IP transport network has its own set of QoS requirements and should be distinguished from U/C/M-plane traffic correspondingly (see chapter 6.2).
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Inter-eNBconnection
(X2) IP
NMS
X2U/C-Plane
M-Plane
S1 U-Plane
S1 C-Plane
MME
SAE-GW
eNB 2
eNB1
S-PlaneSynchronization
Grandmaster(optional)
Figure 6 LTE traffic types
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2.2 Protocol Stacks
All protocol stacks for user (U), control (C), management (M) and (optionally) synchronization (S) planes are based on IP. This section outlines the protocol stacks of the S1 and X2 interfaces.
2.2.1 User Plane
The U-plane service layer is IP. UE mobility is achieved through tunnels which originate from the PDN-GW and are anchored at the S-GW. Within the E-UTRAN, the GPRS Tunneling Protocol (GTP-U) is used as tunneling protocol.
PDCP
RLC
MAC
PHY
User IP
PDCP
RLC
MAC
PHY
Uu
UE eNB
S1-U
UDP
IP
L1/L2
GTP-U
S-GW
UDP
IP
L1/L2
GTP-U
eNB
X2
UDP
IP
L1/L2
GTP-U
eNB
UDP
IP
L1/L2
GTP-U
Figure 7 User-plane protocol stacks
2.2.2 Control Plane
Within the E-UTRAN, SCTP is used to carry the control plane protocols (“Application Protocols”) S1-AP and X2-AP. SCTP has been used previously to carry NBAP over IP (Iub/IP).
PDCP
RLC
MAC
PHY
RRC
PDCP
RLC
MAC
PHY
Uu
UE eNB
S1-MME
IP
L1/L2
MME
SCTP
IP
L1/L2
NAS
RRCS1-AP
SCTP
S1-AP
eNB
X2
IP
L1/L2
eNB
SCTP
IP
L1/L2
SCTP
X2-AP X2-AP
Figure 8 Control-plane protocol stacks
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2.3 Intra-LTE Handover
Intra-LTE handover (HO) can be performed over the S1 interface (“S1 handover”) or X2 interface (“X2 handover”). S1 handover is always required for MME relocation. With X2 handover, DL data forwarding between Source eNB and Target eNB will be optimized. Furthermore, most of the C-plane messages are exchanged directly between the involved eNB’s, so the MME processing load will be reduced significantly.
Implications on the Mobile Backhaul Network will be elaborated in the following. In principle, the considerations apply similarly to both S1 and X2 handover. Since the X2 interface is expected to be present in many cases (X2 is required for ANR), this will be analyzed in more detail.
During the handover procedure the radio link is interrupted for a short moment (30…50ms). DL packets arriving at the Source eNB will be forwarded to the Target eNB via the (logical) X2 interface until the S1 path has been switched to the Target eNB (Hard Handover).
S1-uS-GW
Target eNB
Source eNB
Before
S1-u
S-GW
Target eNB
Source eNB
After
S1-uS-GW
Target eNB
Source eNB
During
X2-u
Figure 9 Handover over X2 - Principle
In the first phase (1) of the handover (see Figure 10, left side), the DL traffic destined to the Source eNB fills the normally lightly used Source eNB UL path (asymmetric user traffic and symmetric backhaul capacity DL/UL assumed). The duration of phase (1) T1 is determined by C-plane processing (including transport latency) and may be significantly longer than the air interface interruption time.
In the second phase (2) (see Figure 10, right side), the Target eNB connection may be temporarily congested if many handovers are taking place simultaneously and DL packets are already arriving through the S1 path to the Target eNB while X2 packets are still in transit. This “overlap time” T2 is mainly given by the X2 transport latency, assuming S1 latency toward Source eNB and Target eNB are almost equal. If congestion occurs packets may be queued (and potentially QoS aware dropped) at the affected transport node(s). But even if the X2 traffic goes completely along with S1 traffic (T2 ~ S1 UL latency + S1 DL latency), the probability and duration of such bursts will be very limited.
As a conclusion, the capacity need for X2 is very small compared to S1. Analysis of the mobility model resulted in 2%…3% extra capacity.
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S1-uS-GW
Target eNB
Source eNB
During HO (1)
S1-uS-GW
Target eNB
Source eNB
During HO (2)
X2-u
Figure 10 Handover over X2 - Capacity
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2.4 Transport Performance Requirements
2.4.1 Throughput (Capacity)
Cell peak rates will increase dramatically with LTE. This is mainly due to larger available bandwidth (max 20MHz per cell compared to 5MHz with WCDMA). It should be noted, however, that HSPA evolution will also bring multi-carrier modes, leveling this advantage at least partly.
Maximum cell peak rates of 150Mbit/s downlink (64QAM 2x2 MIMO) and 75Mbit/s uplink (64QAM single stream) are available for a 20MHz configuration (ref. [LTE for UMTS], chapter 9.2, Table 9.3 and 9.4). DL/UL peak rates of 172Mbit/s / 58Mbit/s have often been used for marketing purposes, but are actually not achievable since the code rate 1/1 is not defined by 3GPP.
It should also be noted that the cell peak rates are achievable only under ideal air interface conditions, i.e. very close to the base station (up to 20% of cell range, corresponding to 4% of cell area) and without interference from other cells.
Max. peak data rate
Mbp
s
LTE 2x20 MHz (2x2 MIMO
LTE 2x20 MHz (4x4 MIMO
Downlink
Uplink
350
300
250
200
150
100
50
0
Figure 11 Cell peak capacity
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As important as the cell peak rate is the cell average capacity (Figure 12). Average downlink cell spectral efficiency has been determined as ~1.5…1.7 bit/s/Hz in macro cell deployment with three sectors and 2.4…2.9 bit/s/Hz in micro cells with one sector (based on 3GPP simulations, 10MHz bandwidth, ref. [LTE for UMTS], Figure 9.12). It should be noted that this describes the cell peak capacity under average conditions, not an averaging over time.
The spectral efficiency also varies with the available bandwidth. For further consideration in this chapter, macro cell configurations with a spectral efficiency of 1.7 bit/s/Hz downlink and 0.7 bit/s/Hz uplink are assumed which is a good approximation for 10MHz and 20MHz bandwidth.
Average throughput (macro cell, 20 MHz)
Mbp
s
LTE (2x2 MIMO), 20 MHz carrier
LTE 4x4 MIMO, 20 MHz carrier
60
50
40
30
20
10
0
Downlink
Uplink
Figure 12 Cell average capacity
The required transport capacity can be dimensioned with two different approaches:
1) Dimensioning based on user traffic profile (recommended)
2) Dimensioning based on air interface capabilities
Dimensioning based on the user traffic profile requires planning data from the operator. It can be tailored to the actual needs and allows QoS parameters to be taken into account. On the other hand, dimensioning based on air interface capabilities provides a simple and straightforward alternative if the traffic profile is not available and should be sufficient for initial planning considerations. This approach will be elaborated further in this chapter. Note that the considerations herein refer to the eNB backhaul interface only. Depending on the traffic profile, statistical multiplexing gain could reduce the total capacity requirements at aggregation points.
For “translating” the capacity at the air interface into an equivalent capacity need at the transport (backhaul) interface of the eNB, air interface overhead has to be subtracted, while transport overhead has to be added.
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GTP-U (without header extension) 8 bytesUDP 8 bytesIPv4 (transport) 20 bytesIPSec ESP Header (SPI/Sequence Number) 8 bytes AES Initialisation Vector 16 bytes
ESP Trailer (2-17 bytes, incl. 0-15 padding bytes, average 8 bytes) 10 bytesIPSec Authentication (HMAC-SHA-1-96) 12 bytesIPSec Tunnel mode IP header 20 bytesEthernet higher layer (incl. 4 bytes for VLAN) 22 bytesEth. Inter Frame Gap, Preamble/SFD 20 bytesTotal transport overhead 144 bytes
Table 1 Transport overhead (with IPv4 and IPsec)
For a typical traffic profile with 50% small (60 bytes), 25% medium-size (600 bytes) and 25% large (1500 bytes) packets, the transport overhead can be estimated as ~25% with IPv4 and IPsec (~15% without IPsec). After subtracting the air interface overhead (PDCP/RLC), 20% (with IPsec) has to be added to the data rate at the air interfaces to calculate the corresponding transport capacity (15% without IPsec).
If N is the number of cells of one eNB site and Cpeak and Cavrg denote the peak and average capacity of one cell, the following main concepts can be distinguished (example in Figure 13 with 3 cells):
• „All-Average“ The backhaul connection supports the aggregated average capacity of all cells. Ctrs = N x Cavrg
• „All-Average/Single-Peak“ The backhaul connection supports the aggregated average capacity of all cells and the peak capacity of one cell, whatever value is greater. Ctrs = MAX (N x Cavrg ; Cpeak)
• „All-Peak“ The backhaul connection supports the aggregated peak capacity of all cells (“non-blocking”). Ctrs = N x Cpeak
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C
ell p
eak
Cell average
eNB
tran
spor
t
All-Average
All-Average/Single-Peak
PeakRate!
All-Peak
Ove
rboo
king
Figure 13 Transport capacity dimensioning scenarios
In most cases, “All-Average/Single-Peak" is a reasonable trade-off between user service capabilities and transport capacity requirements, which may have a great impact on the operating costs. With that approach, advertised user service peak rates up to the cell peak rate can be (momentarily) supported in one cell. The advertised maximum user service (average) rate will be, however, only a fraction of the cell peak rate. It is mainly driven by fixed broadband user experience (xDSL service rates) and applications and will be enforced by LTE QoS parameters. This also means that multiple users can be supported with that rate simultaneously. With service differentiation, different maximum rates could be applied to different users, i.e. premium users could be served with highest rates. If the number of users is (initially) low, transport costs could be reduced even further if the maximum user service (average) rate will be applied for dimensioning instead of the cell peak rate. In summary, „All-Average/Single Peak“ is a good trade-off in general, but it may be under-dimensioned for hot spots where users are located close to the antenna in multiple cells of the same eNB, and it may be over-dimensioned for sites with low utilization.
The “All-Peak” concept will always lead to over-dimensioning, thus usually extra costs. However, if fiber is available at eNB sites, the incremental cost impact may be tolerable. So, there will be cases where the operator requires that the transport sub-system shall be no bottleneck at all.
As an example for the “All-Average/Single-Peak” concept, a 1+1+1 10MHz 2x2MIMO configuration is shown in Figure 14.
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AirInterface eNB
90
30
Ethernet layer, with IPsec
TransportInterface
3 cells, 10MHzDL 17 Mbit/s net PHY average rate per cellUL 7 Mbit/s net PHY average rate per cellDL 75 Mbit/s net PHY peak rate per cell (64QAM 2x2 MIMO) UL 25 Mbit/s net PHY peak rate per cell (16QAM)
75
25
+20%
Figure 14 Example: “All-Average/Single-Peak” 1+1+1 10MHz
The maximum configuration with Flexi Multiradio BTS is the “All-Peak” scenario with a 2+2+2 20MHz 2x2MIMO air interface as shown below. It should be noted that with a single Gigabit Ethernet interface at the eNB the DL transport capacity is limited to 1Gbit/s, so the theoretically possible air interface capacity cannot fully be utilized.
AirInterface eNB
1000
360
830
300
Ethernet layer, with IPsec
TransportInterface
+20%
6 cells, 20MHzDL 150 Mbit/s net PHY peak rate per cell (64QAM 2x2 MIMO) – transport capacity limited UL 50 Mbit/s net PHY peak rate per cell (16QAM)
Figure 15 Example: “All-Peak” 2+2+2 20MHz
As stated in chapter 2.3, the capacity need for Intra-LTE handover (over S1 or X2 U-plane) is very small compared to S1 U-plane traffic (2%…3%).
Also, M-plane (~1Mbit/s) and C-plane (~0.3Mbit/s) capacity requirements are negligible compared to S1 U-plane.
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2.4.2 Delay (Latency), Delay Variation (Jitter)
Delay requirements originate from both user services (U-plane end-to-end delay / delay variation for VoIP, web surfing, file transfer, gaming, streaming, email, etc.), radio network layer protocols (C-plane) and synchronization (S-plane).
U-plane
U-plane delay requirements are determined by user service quality expectations. Obviously, delay requirements are important for interactive services (impact on response time, see Figure 16). However, there is also a relationship between U-plane delay and throughput performance if the user service is based on TCP (see chapter 2.4.3).
Figure 16 U-plane latency requirements
With respect to LTE system performance, less than 15ms round-trip time (RTT) can be achieved with pre-allocated resources, ~20ms including scheduling (ref. [LTE for UMTS], chapter 9.7). This can be verified with ping delay measurements starting from the UE, where the server is located near the SAE-GW (ignoring processing delays in the IP stacks and ping application). In contrast to GSM and WCDMA, the relative contribution of the mobile backhaul delay to the RTT has become significant and thus should be treated with special care. It is important to note that each 500km one-way distance between a base station and a usually centralized SAE-GW contribute 5ms to the RTT. This is only taking into account the unavoidable fiber delay (~200,000km/s is the speed of light in glass). Including the delay introduced by intermediate transport nodes, the transport part of the RTT can easily exceed the radio part.
In addition to delay (latency), also delay variation (jitter) has to be considered. Both the LTE air interface (scheduler) and the transport network contribute to the end-to-end jitter. Real-time end user applications (e.g. VoIP, audio/video streaming) are usually designed so that they can tolerate jitter in the order of 10…20ms, using a properly dimensioned jitter buffer. Network dimensioning and in-built QoS
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mechanisms have to assure that the end-to-end delay and delay variation budget of supported applications are not exceeded.
In principle, the user service related considerations above apply to both S1 and X2. As described in chapter 2.3, DL packets during handover arriving at the Source eNB will be forwarded to the Target eNB, i.e. will take a longer route. Basically, implementing X2 latency significantly less than the radio link interruption time (30…50ms) would have no benefit since those packets would have to wait at the Target eNB anyway. Most user applications will tolerate such a very short-term delay increase.
C/M-plane
In contrast to WCDMA, where RNL related latency requirements are imposed by a number of RAN functions over Iub/Iur (e.g. Macro-Diversity Combining, Outer Loop Power Control, Frame Synchronization, Packet Scheduler), LTE transport latency requirements are mainly driven by user services (U-plane). In particular, most of the handover messaging is performed in the latency-insensitive preparation phase. C-plane protocol timers give implicitly an upper bound for the S1/X2 transport RTT (50ms default, configurable 10…2000ms).
S-plane
A specific requirement for delay variation (jitter) applies if Precision Time Protocol (PTP) based on IEEE1588-2008, a.k.a. Timing-over-Packet, is used for eNB synchronization (see chapter 6.2.1).
NSN recommendations on network performance can be found in chapter 3.3.2.
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2.4.3 TCP Issues
The Transmission Control Protocol (TCP) is designed to provide reliable transport for packet data. Today TCP is used for 80-90% of all packet traffic in the internet. TCP is typically used for applications and their respective protocols where reliability is important, e.g. web browsing (HTTP), Email (SMTP) and file transfer (FTP). Due to its acknowledgement mechanism, a single TCP connection is rate limited by the ratio between the TCP window size and the RTT. Given a standard 64KB TCP receive window size (RFC793), 20ms RTT would limit the achievable service data rate at ~25Mbit/s for a single TCP connection in the steady state (TCP flow control). This limitation could be mitigated with multiple concurrent TCP connections (typically the case for web browsing) and/or enlarging the receive window through TCP Window Scaling (RFC1323) which is supported by many web servers today. In particular large file transfers (music, video, SW download) will benefit from these measures, if high service rates would be offered by the operator.
20
25
Figure 17 TCP data rate in steady state vs. RTT (wi thout Window Scaling)
Apart from the steady state, also TCP connection start-up (“TCP slow start”) and behavior after packet loss (“TCP congestion avoidance”) is affected by the RTT. With today’s browsers and web sites (average page size <1MB), it can be assumed that most of the web traffic is transferred within the slow start phase, so TCP Window Scaling will not help that much here. In any case, the transport network should be designed for low latency.
Perhaps more important in the early days of LTE is the potential impact on cell throughput performance tests which are often based on FTP. The test set-up has to be planned carefully (using Window Scaling, running multiple FTP sessions in parallel). Otherwise the transport network could be a bottleneck and distort the test results.
Content Distribution Networks (CDN) such as Akamai do not only reduce the network load but also reduce the end-to-end RTT, thus having a positive impact on the file transfer performance. For CDN supported services, the mobile network related RTT will be dominating.
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3. MOBILE BACKHAUL ARCHITECTURE FOR LTE
3.1 X2 Connectivity Requirements
Mobile networks are commonly structured with respect to user densities (metropolitan areas vs. rural areas), topological requirements (highways, railways, etc.) and capacities of network elements. Respectively, eNBs should be assigned to groups (clusters) where the handover probability between eNBs belonging to the same group is high and the handover probability between eNBs belonging to the different groups is zero or low. Since all LTE protocols are built upon IP, all network elements which need to communicate with each other must be “IP reachable” (logical view). This includes in particular eNBs within the same group which have to be able to reach their adjacent eNBs via the (logical) X2 interface (Figure 18).
Backbone
NetworkMobile Backhaul
NetworkeNB Group
eNB 11
eNB 12
eNBs withhigh HO
probabilitywithin one
group
eNB 21
eNB 22
Small or no HO probabilitybetween eNB
groups
X2-u/c
S1-u/c
Edge router
MME
SAE-GW
Figure 18 End-to-end architecture and connectivity
X2 handover principles are explained in chapter 2.3. There is some common misconception with respect to the requirements on the transport network, which shall be analyzed here.
At a first glance, it seems obvious that it would be beneficial if the X2 “turning point” would be located close to the base stations (Near-End X2 connectivity, Figure 19). This can be implemented with Ethernet switching or IP routing functions, which implies additional CAPEX and OPEX in many cases. X2 latency would be low and X2 traffic wouldn’t load higher parts of the Mobile Backhaul Network. On the other hand, the S1 transport path should be optimized for low latency anyhow (see chapter 2.4.2). X2 latency significantly less than radio link interruption time (30...50ms) doesn’t add value. Furthermore, the amount of X2 traffic is marginal compared to S1 traffic, so the potential for savings is very limited.
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Mobile Backhaul Network Backbone NetworkeNB
eNB
MME SAE-GW
X2-u/c S1-u/c
Figure 19 Near-End X2 connectivity
Far-End X2 connectivity (Figure 20), on the other hand, can be built on existing topologies (hub & spoke). It requires IP routing at the Far-End (Edge Router or Security Gateway) in order to limit the size of L2 broadcast domains. Also this architecture meets the latency and capacity requirements analyzed earlier.
Mobile Backhaul Network Backbone NetworkeNB
eNB
MME SAE-GW
X2-u/c S1-u/c
Figure 20 Far-End X2 connectivity
It can be concluded that Near-End X2 connectivity is not advantageous for 3GPP Rel.8/9/10 LTE network architectures. In particular, direct physical connections between adjacent eNBs (fully meshed network) are not required. This conclusion has to be reviewed again if functional requirements change with the architectural evolution. This might be the case when inter-site Cooperative Multipoint (CoMP) technology will be introduced (not expected before 3GPP Rel.11).
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3.2 Implementation Options
3.2.1 L2 vs. L3
There is a common misconception that the mobile backhaul network for LTE requires an IP router at every transport node.
As a matter of fact, most LTE backbone networks will be IP/MPLS based. The borderline between backbone network and Mobile Backhaul Network, implemented by an Edge Router, deserves further consideration with respect to network security (Security Gateway, see chapter 7). If IPsec is applied, the Security Gateway (SEG) terminates the IP layer with the eNB at the other end, thus would be a natural termination point of the Mobile Backhaul Network.
Aggregation
Network
Mobile Backhaul Network
Backbone
NetworkeNB
eNB
MME SAE-GW
L2 or L3 L3
eNB
eNBMME SAE-
GW
Access
Network
L2
Figure 21 L2 vs. L3
Since the eNB supports an IP-over-Ethernet interface, both Ethernet (L2 VPN) and IP (L3 VPN) transport services would be adequate in the Mobile Backhaul Network.
In the following subchapter, an Ethernet based backhaul network implementation option shall be elaborated further.
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3.2.2 Ethernet Based Backhaul Network
An Ethernet transport service can be delivered by the mobile operator itself (self-built transport network) or by another operator (a.k.a. leased line service). In both cases, service attributes and parameters are usually stated in a Service Level Specification (SLS), which in the latter case is part of a Service Level Agreement (SLA). While this makes a big difference with respect to the operator business case, it will be treated here conceptually as equal.
The following Ethernet services types will be distinguished as defined by Metro Ethernet Forum [MEF6.1]:
• E-Line
• E-LAN
• E-Tree
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3.2.2.1 E-Line
The mobile backhaul network can be purely based on L2 (Ethernet) transport. Point-to-point Ethernet Virtual Connections (EVC) between a User Network Interface (UNI) at the eNBs and another UNI at the (redundant) edge router are the straightforward solution. EVC attributes can be well controlled (see [MEF10.1]) and commercial services are commercially available in many markets, known as E-Line services (“Ethernet leased lines”). At the UNI between Mobile Backhaul and Backbone Network, the VLAN ID identifies a specific eNB.
The Edge Router (or Security Gateway) performs routing of S1 traffic between eNBs and the core nodes as well as routing of X2 traffic between eNBs within one group and between eNBs belonging to different groups.
eNB Group
eNB 11
eNB 12
eNB 21
eNB 22
UNI
UNI
UNI
UNI
EVC 11 (E-Line)
EVC 12 (E-Line)
EVC 21 (E-Line)
EVC 22 (E-Line)
UNI
UNI
UNI
UNI
Far-End X2 routing between eNBs within
one group and between eNB groups
Figure 22 L2 mobile backhaul network with E-Line
Advantages
• Security (impact of DoS attacks is limited to one eNB)
• QoS assurance (simple traffic engineering)
• Operability (simple troubleshooting)
Disadvantages
• Scalability (high number of EVC’s)
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3.2.2.2 E-LAN
As an alternative, the Mobile Backhaul Network could be built based on multipoint-to-multipoint EVC’s (E-LAN service). Most appropriately, eNB’s belonging to one group should be assigned to one E-LAN (Figure 23). At the UNI between Mobile Backhaul and Backbone Network, the VLAN ID identifies an eNB group. Inside the eNB group, an eNB is identified by its MAC address.
The Edge Router (or Security Gateway) performs routing of S1 traffic between eNB’s and the core nodes as well as routing of X2 traffic between eNB’s belonging to different groups, but traffic between eNB’s within one group will be switched inside the (virtual) LAN.
eNB Group
eNB 11
eNB 12
eNB 21
eNB 22
UNI
UNI
UNI
UNI
UNIEVC 1 (E-LAN)
EVC 2 (E-LAN) UNI
Far-End X2 routing
between eNBgroups
Near-End X2 switching
between eNBsof one group
Figure 23 L2 mobile backhaul network with E-LAN
Advantages
• Scalability (low number of EVC’s)
Disadvantages
• Security (adjacent eNB’s can be attacked)
• QoS assurance (traffic engineering is more difficult)
• Operability (troubleshooting is more complex)
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3.2.2.3 E-Tree
Using an E-Tree service with its root at the Edge Router means in a way a restricted E-LAN service, where inter-eNB connectivity would not be possible. So, X2 traffic would go through the Edge Router. From that perspective, it corresponds to the E-Line service.
eNB Group
eNB 11
eNB 12
eNB 21
eNB 22
UNI
UNI
UNI
UNI
EVC 2 (E-Tree)
EVC 1 (E-Tree)
UNI
UNI
Far-End X2 routing between eNBs within
one group and between eNB groups
Figure 24 L2 mobile backhaul network with E-Tree
Advantages
• Scalability (low number of EVC’s)
• Security (impact of DoS attacks is limited to one eNB)
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3.2.2.4 Comparison
In the table below, E-Line, E-Tree and E-LAN services are compared.
Advantages Disadvantages
QoS assurance
(simple traffic engineering)
Operability (simple troubleshooting)
E-Line
Security
(impact of DoS attacks is limited to one eNB)
E-Tree
Scalability
(high number of EVC’s)
Security
(adjacent eNB’s can be attacked)
QoS assurance
(Traffic engineering is more difficult)
E-LAN
Scalability
(low number of EVC’s)
Operability
(Troubleshooting is more complex)
Table 2 Comparison of Ethernet Services
In summary,
� If physical security is considered not sufficient
o E-Line or E-Tree type of Ethernet service are most suitable.
o E-LAN: The scalability advantage has to be balanced against the security disadvantage.
� If physical security is considered sufficient
o E-Line or E-LAN type of Ethernet service is recommended.
o E-Tree is possible but would require configuration of host routes for each eNB at the Edge Router.
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3.2.3 Implementation Examples
Figure 25 below illustrates the physical view where the Mobile Backhaul Network is further sub-divided into the Access Network and the Aggregation Network. In many cases, the Access Network is built upon a microwave radio infrastructure, whereas the Aggregation Network uses fiber rings.
The Access Network may be purely implemented on L2 (Ethernet). For scalability reasons (limiting broadcast domains), the network should be partitioned into different VLAN’s where bridging takes place at intermediate nodes (e.g. microwave radio hubs).
The Aggregation Network could also be built upon L2 (Figure 25). As one solution, VPLS-TE with one VPLS instance per VLAN can be provisioned. The logical point-to-point structure allows for sophisticated traffic engineering while high availability can be supported through physical ring or mesh topologies.
This concept is also known as Multi-Layer Optimization (MLO). It aims at saving network CAPEX and OPEX through optimized application of different types of network elements, working on L1, L2 or L3 at different locations in the network topology. NSN Carrier Ethernet Transport (CET) supports this approach completely.
Backbone
NetworkAccess Network Aggregation
NetworkeNB 11
eNB 12
eNB 21
eNB 22
Carrier Ethernet Transport
MME
SAE-GW
Ethernet switch at MWR hub
location
Fiber connection
L2 Access & Aggregation
IP/MPLS
L3 Backbone
Figure 25 Implementation example: Carrier Ethernet Transport for Access & Aggregation, IP/MPLS for
Backbone
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Alternatively, the Aggregation Network could be built upon L3 (Figure 26). It should be noted, however, that the IP layers in the Aggregation and Backbone Network will be separated by a Security Gateway in case IPsec is used.
Backbone
Network
Access Network Aggregation
NetworkeNB 11
eNB 12
eNB 21
eNB 22
CET
MME
SAE-GW
Ethernet switch at MWR hub
location
Fiber connection
IP/MPLS
L2 Access L3 Aggregation L3 Backbone
Figure 26 Implementation example: Carrier Ethernet Transport for Access,
IP/MPLS for Aggregation & Backbone
If an IP router is present at the base station site it can be used to provide routed connections between the eNB and the core nodes as well as between neighboring eNBs for X2 traffic. Alternatively, the router can be used for providing VPLS services. In this case the topology from the eNB point of view is similar to the E-Line architecture presented earlier.
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3.3 Transport Service Attributes
Transport service attributes are used to describe the requirements on the transport service for eNB backhaul. It should be noted that these attributes are defined end-to-end (between eNB and core network elements) on the IP layer (L3) and have to be allocated in general to multiple parts of the network. In particular, if the transport service is (partially) provided by Ethernet Virtual Connections (EVC), these attributes have to be translated into their L2 equivalents.
Ethernet service attributes are defined by Metro Ethernet Forum [MEF6.1]. Note that these attributes are optional and a subset can be fully sufficient to define an LTE transport service.
3.3.1 Capacity
Ethernet capacity requirements are described by the service attributes
• Committed Information Rate (CIR) / Committed Burst Size (CBS) and
• Excess Information Rate (EIR) / Excess Burst Size (EBS) (optional).
Dimensioning of eNB backhaul capacity (“last mile”) is described in chapter 2.4.1.
3.3.2 Performance
As explained in chapter 2.4, performance requirements on the transport service are primarily driven by user service aspects.
� NSN recommends the following performance values:
Service Attribute Value Comments
L3: Packet Delay (PD)
L2: Frame Delay (FD)
≤ 10 ms TCP based applications require low transport latency
L3: Packet Delay Variation (PDV)
L2: Frame Delay Variation
≤ +/- 5.0 ms If Timing-over-Packet (ToP) based on IEEE1588-2008) is applied (could be relaxed otherwise)
L3: Packet Loss Ratio (PLR)
L2: Frame Loss Ratio
≤ 10e-4
(0.01%)
May be different depending on user service
Table 3 Transport Service Attributes (Recommendatio n)
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3.4 Traffic Differentiation with VLAN and IP Addres sing
LTE132 “VLAN based traffic differentiation” (RL10, RL15TD)
LTE875 “Different IP addresses for U/C/M/S-plane” ( RL10, RL15TD)
The traffic differentiation capability is tightly coupled with VLAN support and IP addressing. So, these topics will be handled here together.
Traffic differentiation can be used for various purposes. First, there may be a need to separate traffic of different planes (eNB applications) from each other for network planning reasons. E.g. M-plane traffic may need to be separated from U/C-plane traffic. S-plane traffic may require further separation. In another network scenario, traffic may be split into multiple paths which have different QoS capabilities (path selection).
The destination IP address is used as differentiation criteria. Traffic differentiation could be performed on multiple layers:
• L3: Using different IP subnets
• L2: Using different VLANs (Note: Each VLAN is terminated with a dedicated IP address at the eNB)
• L1: Using different physical paths (Note: External equipment required. Support for multiple physical interfaces is an RL30 study item)
First, the generic eNB IP addressing model shall be explained. Based on that, typical network scenarios will be elaborated.
3.4.1 Generic eNB IP Addressing Model
The model is based on two basic components:
1. Binding of eNB applications to IP addresses
2. Assignment of interface IP addresses to eNB interfaces
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Binding of eNB applications to IP addresses
eNB applications (S1/X2 U-plane, S1/X2 C-plane, M-plane, S-plane) may be arbitrarily bound to
• eNB interface address(es) or
• eNB virtual address(es)
as illustrated in Figure 27 below. Interface addresses are “directly visible” at eNB interfaces, whereas virtual addresses appear behind an eNB internal IP router.
S1/X2 U-plane application
S1/X2 C-plane application
S-plane application
M-plane application
U
C
M
S
Binding to virtual address
Binding to interface address
Virtual IP address
eNB
Interface IP address
Figure 27 Binding of eNB applications to IP address es
Configurations where eNB applications are bound to virtual addresses are typically used in scenarios where the transport link (VLAN, IPsec tunnel) shall be terminated with one IP address (interface IP address) while application separation on L3 is also required.
Address sharing, i.e. configuration with the same IP address, is possible. In the simplest configuration, the eNB features a single IP address for U-plane, C-plane, M-plane and S-plane.
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Assignment of interface IP addresses to eNB interfaces
eNB interface IP address(es) may be assigned to different types of data link layer interfaces, which are provided by
• physical interface(s) or
• logical interface(s)
as illustrated in Figure 28. A physical interface is provided by an Ethernet port, whereas a logical interface is provided by a VLAN termination. RL10 supports one physical interface and max 4 logical interfaces. Different interfaces belong to different IP subnets.
Physical interface
(Ethernet)
VLAN(optional)
Interface address assigned to physical
interfaces
eNBInterface addresses assigned to logical
interfaces
eNB
VLAN2
VLAN3
VLAN4
VLAN1
Physical interface
(Ethernet)
Logical interface (VLAN)
Figure 28 Assignment of interface IP addresses to e NB interfaces
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Figure 29 and Figure 30 below illustrate the configuration flexibility.
Application(s) bound to interface address Application(s) bound to virtual address(es)
VLAN(optional)
U
C
M
S
No or single VLAN per eNB
VLAN2
VLAN3
VLAN4
VLAN1
M
S
U
C
Multiple VLANsper eNB
VLAN(optional)
No or single VLAN per eNB
U
C
M
S
Figure 29 IP addressing with VLAN examples (RL10)
Application(s) bound to virtual address(es)
VLAN2
VLAN3
VLAN4
VLAN1
Multiple VLANsper eNB
U
C
M
S
Figure 30 IP addressing with VLAN examples (RL20)
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3.4.2 Network Reference Configurations
The figures on the next pages illustrate the eNB addressing options with some typical network scenarios (Network Reference Configurations). Those are different with respect to the underlying transport services. Ethernet transport services may be implemented as “E-Line” or “E-LAN”. As per MEF definition, E-Line denotes an Ethernet transport service based on point-to-point Ethernet Virtual Connection (EVC), whereas E-LAN denotes an Ethernet transport service based on multipoint-to-multipoint Ethernet Virtual Connection (EVC).
The IP address concept is also related to the IPsec architecture (see chapter 7). Configurations where eNB applications are bound to virtual addresses are typically used in a scenario where the IP transport layer is separately administered (IPsec VPN). In that case, the IPsec tunnel is terminated with separate interface addresses at the eNB and SEG (Figure 34).
E-Line with single IP Address
• Simplest configuration for E-Line service
• 1 VLAN per eNB
VLAN(optional)
M
S
U
C
Ethernet
eNB
eNB
SAE-GW
~ToP
Master
O&M
IP Router
MME
Figure 31 E-Line with single IP address
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E-LAN with single IP Address
• Simplest configuration for E-LAN service
• 1 VLAN per eNB group
VLAN(optional)
M
S
U
C
eNB
Ethernet
eNB
SAE-GW
~ToP
Master
O&M
IP Router
MME
Figure 32 E-LAN with single IP address
E-Line with L2 Differentiation
• Supporting virtually separate networks for different planes
• 2 VLANs per eNB (max 4 VLAN’s possible)
VLAN2
VLAN1
M
S
U
C
Example configuration
eNB
eNB
Ethernet
SAE-GW
~ToP
Master
O&M
MME
IP Router
EVC/VLAN 11, 12
EVC/VLAN 21, 22
Figure 33 E-Line with L2 differentiation
L2 differentiation can be supported in the same way with E-LAN.
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IPsec VPN with L3 separation
• Single interface IP address for IPsec tunnel termination
IPsec Tunnel
S VLAN
InterfaceIP address
Application IP address
U
C
M
IP
eNB
eNB
MME
SEG
SAE-GW
~ToP
Master
O&M
IPsec VPN
Eth
erne
t
IP Router
Figure 34 IPsec VPN (separate interface IP address)
� S-plane binding to interface address is recommended to avoid additional jitter due to IPsec processing. It is required for on-path support to enable accurate phase synchronization (see chapter 6.2.1).
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3.5 Transport Redundancy
3.5.1 General
Transport redundancy can be applied on different layers. As a basic principle, if multiple redundancy features are present, the redundancy mechanism on the lower layer needs to be faster than another mechanism on an upper layer.
Layer 1 (physical layer) based redundancy
An example is 1+1 link redundancy with MWR equipment.
L1 based redundancy doesn’t require any specific support from Flexi Multiradio BTS.
Layer 2 (data link layer) based redundancy
Ethernet switching procedures apply in case of L1 failure. One of the following concepts may be utilized:
• Rapid Spanning Tree Protocol (RSTP), Multiple Spanning Tree Protocol (MSTP)
• IEEE802.3ad (Ethernet Link Aggregation)
• ITU-T G.8031 (Ethernet Protection Switching)
• ITU-T G.8032 (Ethernet Ring Protection)
• Ethernet APS (RFC3619)
L2 based redundancy is a study item for RL30.
Layer 3 (network layer) based redundancy
IP re-routing, optionally supported by a routing protocol such as OSPF, applies in case of L2 link failure. IP based load balancing mechanisms, e.g. Equal Cost Multi-Path (ECMP) routing, could be utilized if supported by a corresponding edge router.
L3 based redundancy is a study item for RL30.
Layer 4 (transport layer) based redundancy
SCTP multi-homing for the C-plane is supported with RL20. See chapter 3.5.2 below.
Layer 7 (application layer) based redundancy
Examples are:
• U-plane: Multiple S-GW’s available per eNB
• C-plane: Multiple MME’s available per eNB (S1 Flex)
• S-plane: Multiple clock sources available per eNB, e.g.
o Multiple IEEE1588 (ToP) Grandmasters
o Multiple Ethernet links supporting SyncE
o Simultaneous provision of multiple synchronization technologies (e.g. GPS and ToP)
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3.5.2 SCTP Multi-homing
LTE775 “SCTP multi-homing (MME)” (RL20, RL15TD)
Multi-homed nodes can be reached under several IP addresses. With this feature, the eNB supports two IP addresses at the MME for S1 C-plane termination.
SCTP (RFC4960) supports multi-homing for failover (no load-sharing). Associations become tolerant against physical interface and network failures. At the set-up of an SCTP association, one of the several destination MME IP addresses is selected as initial primary path. Data is transmitted over this primary transmission path by default. Retransmissions happen on other available paths. Path status and reachability is monitored at the SCTP layer (via data chunks and heartbeats).
The feature is primarily meant for MME interface redundancy, not path redundancy. So, C-plane termination with a single IP address at the eNB is sufficient.
eNB
IP
Dual interfaceDual IP address
MME
Single interfaceSingle IP address
Figure 35 SCTP Multi-homing
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3.6 Base Station Co-location
LTE649 “QoS aware Ethernet switching” (RL20, RL15TD )
At least initially, existing (macro) 2G/3G base stations sites will be reused for LTE in order to keep deployment costs reasonably low. As a consequence, there is a clear demand for 2G/3G/LTE common backhaul solutions. The most straightforward way is to upgrade legacy base stations with an Ethernet backhaul option and aggregate the traffic using an Ethernet switch. With the eNB integrated Ethernet switching function, Flexi Multiradio BTS eliminates the need for an external device.
FTLB supports three Ethernet interfaces, while two Ethernet interfaces are usable with FTIB. The aggregated Ethernet traffic is shaped according to a configurable level with respect to the available uplink capacity.
eNB
UNI‘(1)
UNI‘(2)
UNI
QoS awareshaping
Ethernet
integrated Ethernet switch
high
low
other base station
EVChigh
high
low
low
high
low
Figure 36 QoS aware Ethernet switching
Synchronization solutions with co-located base stations are described in chapter 6.3
If a co-located 2G base station doesn’t support Ethernet, the Flexi Multiradio BTS integrated CESoPSN feature can be applied (RL30 study item).
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4. LTE TRANSPORT INTERFACES AND PROTOCOLS
4.1 Ethernet
LTE118 “Fast Ethernet (FE) / Gigabit Ethernet (GE) electrical interface” (RL09, RL05TD)
LTE119 “Gigabit Ethernet (GE) optical interface” (R L09, RL05TD)
LTE491 “FlexiPacket Radio Connectivity” (RL20, RL15 TD)
Ethernet based on the [IEEE 802.3] standard will be the main eNB backhaul technology. In many cases, a network terminating device (leased line termination equipment, MWR IDU, xDSL CPE, etc.) is present at the eNB site. Electrical connection is most economical in that case which connects to the eNB via Ethernet. Flexi Multiradio BTS supports suitable indoor and outdoor site solutions.
No such device is needed in case FlexiPacket Radio is used. This MWR ODU can be directly connected and managed through the Ethernet interface of the Flexi Multiradio BTS (“zero footprint" solution). Also, if fiber access is available at the site, it can be connected directly.
The following interface types are supported (see chapter 9 for details of different Flexi Transport sub-modules):
• Gigabit Ethernet (GE) 100/1000Base-T, electrical
• Gigabit Ethernet (GE) 1000Base-SX/LX/ZX through optional SFP module, optical
The Ethernet interfaces, based on the [IEEE 802.3] standard (with type interpretation of the type length field, Ethernet II/DIX frame), support the following features:
• Full-duplex transmission mode
• Auto-negotiation and forced mode for the duplex mode (only full duplex advertised)
• Auto-negotiation and forced mode for the data rate
• Auto-negotiation and forced mode for MDI/MDIX
• VLAN tagging according to [IEEE 802.1q]
• Ethernet priority bits (p-bits) according to [IEEE 802.1p]
• IPv4 over Ethernet [RFC894]
• Address Resolution Protocol [RFC826] (ARP)
• MEF UNI Type 1 [MEF11]
It should be noted that U-plane IP packets may exceed the maximum SDU size of the Ethernet backhaul link due to additional packet overhead (GTP-U, UDP, IP/IPsec). See chapter 4.2.2.
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4.2 IP
LTE664 “LTE transport protocol stack” (RL09, RL05TD )
4.2.1 General
All eNB applications (U/C/M/S-plane) are running on top of IP. Protocol stacks are explained in chapter 2.2.
User applications are hooked upon the user IP layer which is independent from the LTE application IP layer between eNB and SAE-GW. GTP-U is used as a tunneling mechanism in between. This traffic may optionally be put into yet another tunnel if IPsec (tunnel mode) is used for transport security purposes (see chapter 7). So, there may be up to three IP layers which are all independent from each other (Figure 37):
• User IP layer, terminated by user application at the UE and corresponding peer
• LTE application IP layer, terminated by LTE/SAE network element applications
• IPsec tunnel IP layer (optional), terminated by SEG (integrated in the eNB, external device at the other end)
The eNB terminates the LTE application IP layer (and optionally the IPsec tunnel IP layer). Thus, the U/C/M/S-plane address („application address“) type is in principle independent from the IPsec tunnel termination address („interface address“).
Note: The term “Transport IP layer” is ambiguous. It refers to the IP layer used by the transport network. If IPsec is not used, this would coincide with the LTE application IP layer; with IPsec it would coincide with the IPsec tunnel IP layer.
FlexiMultiradio
BTS
Eth MAC
Eth PHY
UDP
G TP-U
SAE-GW Server
Internet OperatorServices
Eth MAC
Eth PHY
User App
Eth MAC
Eth PHY
UDP
G TP-U
LTE PHY
User App
LTE PHY
UE
LTE MAC
PDC P
Eth MAC
Eth PHY
Security GW(optional)
Eth MAC
Eth PHY
Eth MAC
Eth PHY
LTE MAC
PDC P
IP
IP
IP
User IPUser IP
IPsec Tunnel IP
LTE App IP LTE App IP
IPsec Tunnel IP
Figure 37 IP layers
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4.2.2 MTU Size Issues
Both GTP/UDP/IP and (optional) IPsec tunneling add overhead to the user IP packet. If this has been generated with an MTU size of 1500 bytes, corresponding to the maximum SDU size of a standard Ethernet frame between Internet routers, it will not fit to the Ethernet interface SDU of the mobile backhaul network. In principle, there are three ways to solve this problem:
1. Enforcement of lower MTU size at the user IP layer
2. IP fragmentation & reassembly at the LTE application IP layer
3. Enlargement of Ethernet SDU using Jumbo Frames under the LTE application IP layer (or IPsec tunnel IP layer, respectively)
All solutions have their pros and cons. Lower MTU size cannot be enforced in all circumstances. Ethernet Jumbo Frames would solve the problem nicely but are not available everywhere. IP fragmentation & reassembly would always work but has performance issues.
In the following, the options will be elaborated more in detail.
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4.2.2.1 Enforcement of lower MTU size
The MTU size used for packets at the user IP layer can be determined through static or dynamic configuration of the IP protocol stack SW of the UE. Unfortunately, this approach will not solve the problem completely.
With one approach, the MTU size of the IP protocol stack in the UE could be configured to a lower value. There are UE vendor specific settings (e.g. 1400 bytes in Symbian) which support this idea, but this is not mandated by any standard.
In case of IPv6, the MTU size at the UE could be set with the Router Advertisement message that the PDN-GW sends after PDN connection establishment ([RFC4861], section 4.6.4).
Alternatively, the user IP layer MTU could also be enforced through Path MTU discovery with a lower MTU properly set in the PDN-GW. This approach has been adopted with [TS29.275 v8.4.0] where a default MTU of 1280 bytes is proposed (equivalent to the minimum MTU size defined for IPv6). Unfortunately, Path MTU discovery (IPv4: RFC1191, MTU ≥68, IPv6: RFC1981, MTU ≥1280) is not mandated for neither IPv4 nor IPv6 (though strongly recommended). It’s usually performed for TCP/SCTP, but not for UDP based applications.
The impact of a lower MTU size on the transport efficiency is negligible (<1%).
eNB
Eth MAC
Eth PHY
UDP
G TP-U
S-GW / PDN-GW Server
Eth MAC
Eth PHY
User App
Eth MAC
Eth PHY
UDP
G TP-U
LTE PHY
User App
LTE PHY
UE
LTE MAC
PDC P
Eth MAC
Eth PHY
Security GW(optional)
Eth MAC
Eth PHY
Eth MAC
Eth PHY
LTE MAC
PDC P IP
IP
IP
S-GW_MTU PDN-GW_MTUeNB_MTUUE_MTU
IP
Application IP layer Path MTU
User IP layer Path MTU
Tunnel IP layer Path MTU
User IPUser IP
IPsec Tunnel IP
LTE App IP LTE App IP
IPsec Tunnel IP
Figure 38 Path MTU Discovery
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4.2.2.2 IP Fragmentation and Reassembly
Without using IPsec, Fragmentation and Reassembly of LTE application IP layer packets is terminated at the eNB at one end and the SAE-GW at the other end. With IPsec, the same approach should be applied in order to avoid multiple fragmentation. In this case IPsec packets are carrying fragments, but are not fragmented themselves. The MTU size (S1-GW_MTU) would need to be set up to a maximum of 1438 bytes in order not to exceed a value of 1500 for the Ethernet SDU at the eNB (example with IPv4 S1-U over IPv4 IPsec tunnel, see Figure 39). While this is a well standardized and generic solution, there are potential drawbacks, such as additional processing delay and throughput degradation due to processing load at the end points. Anyway, the performance impact will be limited due to the countermeasures taken in the user IP layer as described above.
The impact on transport efficiency is minor (~2.5%). Large packets (~25%) will be fragmented, i.e. cause double transport overhead (~10% per fragment).
GTP-UUDP
168 1394
ESPIPsecTunnel
IP
2020
User IP Payload PL/NH AuthPadding
RANIP
24 0 2 12
1496 ≤ 1500
90 x 16 = 1440
GTP-UUDP
168 150020
User IP PayloadRAN
IP
1544
GTP-UUDP
168 139420
User IP PayloadRAN
IP
1438(1st fragment)
1438S-GW_MTU
1500eNB_MTU
1500UE_MTU
eNB_MTU S-GW_MTU
SAE-GWSEGeNB
UE_MTU
Figure 39 Fragmentation & Reassembly with IPv4
Flexi Multiradio BTS supports Fragmentation and Reassembly at the LTE application IP layer.
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4.2.2.3 Ethernet Jumbo Frames
This solution has no impact on user IP layer and a slightly higher transport efficiency. On the other hand, it is not standardized (vendor specific SDU sizes up to 9000 bytes are possible) and therefore not generally supported by Ethernet equipment and Ethernet transport services.
1544S-GW_MTU
1608eNB_MTU
1500UE_MTU
GTP-UUDP
168 1500
ESPIPsec
Tunnel
IP
2020
User IP Payload PL/NH AuthPadding
RANIP
24 6 2 12
1608
97 x 16 = 1552
GTP-UUDP
168 150020
User IP PayloadRAN
IP
1544
eNB_MTU S-GW_MTU
UE_MTU
eNB SAE-GWSEG
Figure 40 Ethernet Jumbo Frames with IPv4
Support for Ethernet Jumbo Frames is a study item for RL30.
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4.2.3 IPv6
The GTP-U tunneling concept allows for using private IP addresses in the LTE transport network (eNB backhaul) while user applications require a public IP address. Instead of assigning a public address directly to the UE, mobile operators often use NAPT for saving public IPv4 addresses.
There are more than 16M private IPv4 addresses available which are even reusable in distinct parts of the operator network if routing in between is not needed. This is particularly the case with respect to the transport network (LTE application IP layer, optionally IPsec tunnel IP layer). Nevertheless, some operators claim to face a shortage of private IP addresses already now. Migration to IPv6 in the transport network is seen as a solution. Sooner or later, IPv6 in the transport network will become an operational cost optimization topic for network elements that anyway have to have IPv6 addresses due to support for IPv6 in the User IP layer (PDN-GW). It can be expected that these network elements would be simpler to manage if the number of IPv4 addresses is minimized.
The network elements are typically connected to a separate O&M network which is logically or even physically separated. Private IPv4 addressing can be used here and there is no technical reason to transport O&M traffic over IPv6. Migration to IPv6 is a major step since several O&M system components (incl. NetAct, iOMS, DHCP server, CMP server, etc.) are typically also used for legacy mobile networks. Anyway, IPv6 for M-plane transport will probably become an operational cost optimization topic later when all other networks are running on IPv6. However, NetAct will support IPv6 in LTE M-plane applications, i.e. where IP addresses are handled (NetAct Top level UI, Object browser, NetAct Configurator, NetAct topology database, etc.).
QoS (DiffServ) and security (IPsec) mechanisms are basically the same for IPv4 and IPv6.
In the following the relevant scenarios will be analyzed.
User IPv4 over LTE transport IPv4
This is the basic scenario, supported already with RL09 (IPsec option with RL10).
FlexiMultiradio
BTS
Eth MAC
Eth PHY
UDP
G TP-U
SAE-GW Server
Eth MAC
Eth PHY
User IP
User App
Eth MAC
Eth PHY
UDP
G TP-U
LTE PHY
User App
LTE PHY
User IP
UE
LTE MAC
PDC P
Eth MAC
Eth PHY
Security GW(optional)
Eth MAC
Eth PHY
Eth MAC
Eth PHY
LTE MAC
PDC P IPv4
IPv4
IPv4
IPsec Tunnel IP
LTE App IP LTE App IP
IPsec Tunnel IP
Figure 41 User IPv4 over LTE transport IPv4
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User IPv4/IPv6 over LTE transport IPv4
Some user services are running on IPv6. This scenario is completely transparent to the eNB, thus also available with RL09 (if supported by the SAE-GW).
FlexiMultiradio
BTS
Eth MAC
Eth PHY
UDP
G TP-U
SAE-GW Server
Eth MAC
Eth PHY
User App
Eth MAC
Eth PHY
UDP
G TP-U
LTE PHY
User App
LTE PHY
UE
LTE MAC
PDC P
Eth MAC
Eth PHY
Security GW(optional)
Eth MAC
Eth PHY
Eth MAC
Eth PHY
LTE MAC
PDC P IPv4
IPv4
IPv4/IPv6 User IPUser IP
IPsec Tunnel IP
LTE App IP LTE App IP
IPsec Tunnel IP
Figure 42 User IPv4/IPv6 over LTE transport IPv4
User IPv4/IPv6 over LTE transport IPv4/IPv6
The transport network is (partially) based on IPv6 (RL30 study item).
If both LTE application IP layer and IPsec tunnel IP layer are owned by the mobile operator, it is possible to use the same address for tunnel termination(s) and LTE applications (binding to interface addresses, collapsed “inner” and “outer” addresses, see chapter 3.4.1 and 7.4) in order to save IP addresses and reduce complexity.
FlexiMultiradio
BTS
Eth MAC
Eth PHY
UDP
G TP-U
SAE-GW Server
Eth MAC
Eth PHY
User App
Eth MAC
Eth PHY
UDP
G TP-U
LTE PHY
User App
LTE PHY
UE
LTE MAC
PDC P
Eth MAC
Eth PHY
Security GW(optional)
Eth MAC
Eth PHY
Eth MAC
Eth PHY
LTE MAC
PDC P IPv4/IPv6
IPv4/IPv6
IPv4/IPv6 User IPUser IP
IPsec Tunnel IP
LTE App IP LTE App IP
IPsec Tunnel IP
Figure 43 User IPv4/IPv6 over LTE transport IPv4/IP v6
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5. QOS
5.1 End-to-End QoS
In order to facilitate a certain end-to-end QoS for a user service, radio and transport QoS have to be considered consistently.
Radio interface resources are scarce, so strict control has to be applied. This means, capacity has to be reserved for Guaranteed Bit Rate (GBR) type of services through Connection Admission Control (CAC). Controlled overbooking with prioritization is the solution for non-GBR type of services. The resource situation in the access section (“last mile”) of the mobile backhaul network is similar, so the solution principles are similar: Committed Information Rate (CIR) guarantees continuation of GBR services, whereas Extended Information Rate (EIR) with overbooking and prioritization can be applied for non-GBR traffic. Nevertheless, it is recommended to reserve also a minimum capacity using CIR for non-GBR traffic.
In the aggregation section of the network the situation is more relaxed, so less strict control is required. Still, there might be a need for capacity reservation and traffic prioritization. If sufficient resources are available, this section may be ignored by the CAC.
The mobile network up to the SAE-GW is operator controlled, so with proper network dimensioning the service quality can be guaranteed. Naturally, CAC makes most sense here. This is not the case if the actual user service is provided by a server located anywhere in the Internet. Only Best Effort can be expected. If the user service is based on TCP (80…90% of the traffic), TCP congestion control mechanisms will assure a fair distribution of capacity.
eNB
Ethernet
SAE-GWInternet Server
IP
IP RouterInternetAggregation
CoreAccess
Best effort
Guaranteed
Ser
vice
qua
lity
Operator Server
IP
• No control• Scarce resources• Strict control (RRM)
• Reservation for GBR• Controlled overbooking
with prioritization for non-GBR
• Scarce resources• Strict control (Transport)
• Reservation (CIR)• Controlled overbooking with
prioritization (802.1p)
• Fair resources• Less strict control
• Reservation (MPLS TE)• Overbooking with
prioritization (DiffServ)
UE
• Radio & Transport CAC(CIR for GBR, EIR for non-GBR)
• Radio scheduling per UE (UL+DL)• Transport UL policing and
shaping per eNB• DL policing and shaping
per UE
QoS
feat
ures
• Flow & congestion control (TCP)
• Traffic marking• Flow &
congestion control (TCP)
• DL policing and shaping per eNB
Figure 44 End-to-End QoS
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5.2 Transport QoS Features
5.2.1 Traffic Prioritization on IP Layer
LTE131 “Traffic prioritization on IP layer” (RL10, RL05TD)
In order to avoid over-dimensioning in the backhaul network, Flexi Multiradio BTS supports QoS differentiation between user, control and management plane traffic as outlined in Figure 45. DiffServ is the most common way of traffic prioritization on IP layer [RFC2474], [RFC2475]. Traffic end points (eNB, S-GW, MME, O&M/NetAct) will set DSCP values, while intermediate network elements have to handle the packets accordingly. DSCP values for different U/C/M-plane traffic types are configurable.
Flexi Multiradio
BTS
Eth
L2
L1
Eth MAC
Eth PHY
UDP
IP
L2
L1
L2
L1
IP
BTSOM
SCTP
S1AP / X2AP
M-planeC-plane
GTP-U
(User) IP
U-plane
TCP
IP
Eth MAC
Eth PHY
IP
Eth MAC
Eth PHY
IP
UDP
GTP-U
(User) IP
M-planeC-planeU-plane
BTSOM
TCPSCTP
S1AP
IP
IEEE1588
UDP
S-plane
Eth MAC
Eth PHY
IP
IEEE1588
UDP
S-planeQoS marking(DSCP)
NetActSAE-GW
MME
IP Router(Security GW)
~ToP
Server
DSCP aware
Figure 45 Traffic prioritization on IP layer
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5.2.2 Traffic Prioritization on Ethernet Layer
LTE129 “Traffic prioritization on Ethernet layer” ( RL10, RL15TD)
If traffic aggregation is performed by Ethernet switching, not IP routing, the transport network may not be IP QoS (DiffServ) aware. In this case, Flexi Multiradio BTS supports traffic prioritization on the Ethernet layer, using frame marking methods (code points) applicable to Ethernet as illustrated in Figure 46. Ethernet priority bits (IEEE 802.1p) are set based on the DiffServ Code Point (DSCP). The mapping table is configurable.
Flexi Multiradio
BTS
Eth
Eth PHYEth PHY
Ethernet
NetAct
Ethermet Switching
SAE-GW
MME
IP Router(Security GW)
UDP
IP
L2
L1
BTSOM
SCTP
S1AP / X2AP
M-planeC-plane
GTP-U
(User) IP
U-plane
TCP
IEEE1588
UDP
S-plane
802.1p marking
Eth MAC
Eth PHY
IP
Eth MAC
Eth PHY
IP
Eth MAC
Eth PHY
IP
UDP
GTP-U
(User) IP
M-planeC-planeU-plane
BTSOM
TCPSCTP
S1AP
Eth MAC
Eth PHY
IP
IEEE1588
UDP
S-plane
~ToP
Server
802.1p aware
Figure 46 Traffic prioritization on Ethernet layer
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5.2.3 Packet Scheduling
Flexi Multiradio BTS performs packet scheduling using 6 queues with SPQ (Strict Priority Queuing) and WFQ (Weighted Fair Queuing).
Each Per-Hop-Behavior (PHB) is mapped to a queue. Expedited Forwarding (EF) is served with Strict Priority Queuing (SPQ). Assured Forwarding (AF1…4) and Best Effort (BE) PHBs are served with Weighted Fair Queuing (WFQ). The highest priority queue is rate limited by Connection Admission Control (CAC).
In case of queue overflow, packets are discarded according to the following strategies:
• Tail drop for EF queue
• Weighted random early discard (WRED) for AF1…4 queues
• Random Early Discard (RED) for BE queue
Shaping is performed per L2 interface(s) (either Ethernet or individual VLANs) with or without taking L2 overhead into account (i.e. L2 or L3 shaping).
PHB Q ueue EF
PHB Q ueue AF4
PHB Q ueue AF3
PHB Q ueue AF2
WAF4
WAF3
WAF2
SP
WFQ
PHB Q ueue AF1
PHB Q ueue BE
WAF1
LTE
Tra
ffic
Cl a
s se
s,m
arke
dw
it hD
SC
Ps
WBE
Layer 2Interface
+Shaper
WFQ_OUT
Packet Distribution
acc . to DSCPs
Figure 47 Packet scheduling
If multiple VLAN’s are configured for traffic separation, scheduling will be performed first per VLAN (one set of PHB’s / queues per VLAN), followed by WFQ scheduling for combining the traffic. Shaping can be applied per VLAN (supporting SLA related to VLAN/EVC) and for the aggregate traffic (supporting SLA related to the Ethernet UNI).
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5.2.4 Traffic Shaping
LTE138 “Traffic shaping” (RL10, RL15TD)
The Flexi Multiradio BTS Ethernet interface (FE or GE) supports data rates (100Mbit/s or 1000Mbit/s) and burst sizes which may be higher than the capacity of the Ethernet backhaul link (e.g. leased line or capacity limited microwave radio link). Traffic shaping is required to ensure conformance to the link capacity in order to minimize packet loss. This applies in particular to Ethernet leased lines where the link capacity is governed by a Service Level Agreement (SLA).
Traffic shaping reduces the burstiness of Ethernet or IP traffic in conformance with a given
• Maximum average output rate on Ethernet or IP layer
• Maximum burst size on Ethernet or IP layer
If packets need to be dropped despite shaping, this will be done based on priorities (QoS aware). Flexi Multiradio BTS performs single-stage traffic shaping in UL direction according to [MEF10.1] with a shaping granularity of 100kbit/s, exceeding the requirements of [MEF11].
Shaping can be applied per L2 interface, i.e. per physical Ethernet interface and per VLAN. That means, traffic can be shaped per traffic type (U/C/M/S-plane) if VLAN differentiation is used accordingly.
Shaping in DL direction is supported per bearer at the SAE-GW. eNB level shaping is recommended to be done by the Edge Router which routes the traffic into one or more VLAN’s (EVC’s) per eNB.
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5.3 Mapping RRM QoS onto Transport QoS
QoS has to be applied consistently to both the radio and the transport interface. As per [TS23.401], each U-plane Service Data Flow (SDF) is associated with a QoS Class Identifier (QCI). Table 4 illustrates an exemplary configuration, including M/C/S-plane traffic.
S-plane
C-plane
M-plane
ICMP
non-GBR
5IMS signaling
7Video (buffered streaming)
GBR
4Non-conversational Video
9
8TCP-based (e.g. www, e-mail, ftp, p2p file sharing, etc.
6Voice, video, interactive gaming
3Real Time Gaming
2Conversational Video
Resource TypeQCILTE Traffic Class
1Conversational Voice
LTE Radio domain
5EF46
4AF4134
5EF46
0BE0
5EF46
2AF2118
4AF4134
1AF1110
1AF1110
2AF2220
3AF3228
3AF3126
Ethernet p-bits
DiffServPHBDSCP
5EF46
LTE Transport domain
Table 4 Mapping RRM QoS onto transport QoS
Flexi Multiradio BTS supports configurable mapping between QCI, DSCP and Ethernet p-bits.
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5.4 Congestion Control
In contrast to the Iub interface in HSDPA, there are no standardized means for congestion control at the S1 interface in LTE. This has to be taken into account when designing the network. GBR traffic should be governed by CAC, so performance should be assured by SLA/SLS (CIR/CBS attributes) and traffic prioritization. Most of the user traffic is TCP based (web browsing, file transfer, email, etc.). In case of congestion, the load will be automatically reduced through TCP congestion control. So, not the eNB will address the load situation, but the UE and/or the application server. “Misbehaving” UDP based applications may require additional treatment at the SAE-GW, using Deep Packet Inspection (DPI). Further optimization techniques (e.g. ECN) may be applied in order to avoid that TCP need to resend lost packets and the radio interface (UL) will carry packets which will be dropped later.
Note: The HSDPA flow control algorithm was initially designed to control the air interface scheduler only. Since now often the transport network (Iub) is the bottleneck and inefficient RLC retransmission between RNC and UE shall be avoided, it was recognized that the transport network shall have its own congestion detection mechanism which contributes to the flow control. So, transport protocol independent information elements have been standardized, namely Frame Sequence Number (FSN) and Delay Reference Time (DRT). [TS25.435] defines the information elements for congestion detection, but not the congestion control algorithm itself. TCP cannot efficiently participate in HSDPA congestion control since RLC retransmission will hide congestion situations, both in the air interface and in the transport network.
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6. SYNCHRONIZATION
As per 3GPP requirement, the air interface at an eNB in FDD mode needs to be frequency synchronized with an accuracy of ±50ppb. In addition, phase (time) synchronization is required now for LTE TDD mode and in the future also for Single Frequency Network (SFN) Multimedia Broadcast Multicast Service (MBMS) and location based services.
6.1 Synchronization from GPS
Synchronization from GPS interface is a field-proven technology. The GPS antenna with integrated receiver is connected with a single-cable (power, sync, control) to the Flexi System Module. This is a site solution rather than a transport feature, but mentioned here for completeness reasons.
↑ Power and control to the GPS receiver
↓ PPS signal to BTS System Module
FYGA + mounting kit FYMA
FYHA or FYHB cable
FYEA GPS Surge Protector Kit (optional)
System Module
Figure 48 Synchronization from GPS
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6.2 Synchronization from Transport Network
6.2.1 IEEE1588-2008 Precision Time Protocol (Timing-over-Packet)
LTE134 “Timing-over-Packet” (RL10)
LTE891 “Timing-over-Packet with phase synchronizati on” (RL25TD)
Precision Time Protocol (PTP) based on [IEEE1588-2008] is a field-proven method to support synchronization through an IP transport network. It has to be noted that the network has to have sufficient quality (in particular low frame/packet delay variation).
The NSN PTP solution, a.k.a. Timing-over-Packet (ToP), consists of a Grandmaster (server) at the core site and Timing Slaves (client) implemented in the Flexi Multiradio BTS. The master and slaves communicate through the bidirectional protocol containing time stamps. The slaves use these timestamps to synchronize themselves to the grandmaster’s clock. Accurate frequency can be derived from that clock.
eNBEth IP / Ethernet MME
SAE-GW
Timing over Packet (IEEE 1588-2008)
Primary Reference
Clock
~Grandmaster
ToP Slave
~
Figure 49 Timing-over-Packet (IEEE1588-2008)
The following engineering rules apply:
• Maximum one way delay < 100ms
• Packet delay variation (jitter) < ±5 ms
• Packet loss ratio < 2%
• Timing packets (S-plane traffic) should have the highest priority or at least the same priority as the real-time traffic (should receive Expedited Forwarding (EF) QoS)
• High-priority traffic share of total traffic should be ~ 60 % or less
• Maximum 20 hops with packet switching
• Maximum 6 delay jumps (spontaneous, major change of delay, e.g. caused by re-routing or path switching) per day
LTE TDD mode requires accurate phase synchronization (±1.5us) in addition to frequency synchronization (±50ppb). While frequency synchronization can tolerate typical network jitter in the order
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of several milliseconds through long-time averaging, UL/DL delay asymmetry cannot be controlled with the required accuracy. In order to solve this problem, PTP has to be implemented at all intermediate nodes on the synchronization traffic path so that outgoing timing packets will be (re-)marked based on the local node clock (on-path support with IEEE1588-2008 boundary clock or transparent clock).
eNB
IP / Ethernet MME
SAE-GW
Timing over Packet (IEEE 1588-2008)
~Grandmaster
ToP Slave
~
Primary Reference
Clock
Figure 50 Timing-over-Packet for time/phase synchro nization
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6.2.2 Synchronous Ethernet
LTE713 “Synchronous Ethernet” (RL10)
Synchronous Ethernet (SyncE) as per G.8261/8262/8264 is an SDH like mechanism for distributing frequency at layer 1. In contrast to Timing-over-Packet, which is essentially a layer 3 technology, frequency synchronization will be extracted directly from the Ethernet interface at the Flexi Multiradio BTS. In contrary to packet based synchronization (IEEE1588-2008, NTP), the stability of the recovered frequency does not depend on network load and impairments. SyncE has to be implemented at all intermediate nodes on the synchronization traffic path.
eNBEth
Synchronous Ethernet
MME
SAE-GW
Primary Reference
Clock
~ ~~ ~Eth Eth Eth Eth Eth
Figure 51 Synchronous Ethernet
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6.3 Solutions for Co-location with Legacy Equipment
6.3.1 Synchronization from PDH interface
LTE710 “Synchronization from PDH interface” (RL10)
Synchronization from PDH interface is the conventional method applied for legacy base stations (2G, 3G). The synchronization signal is recovered from a selected E1/T1/JT1 line, the clock of which is traceable to a Primary Reference Clock (PRC). PRC synchronization is usually injected at the core site.
The co-located legacy base station forwards the clock through a spare E1/T1/JT1 interface to the Flexi Multiradio BTS.
BTSE1/T1
IP / Ethernet
TDM
Eth
E1/T1
eNB
~
Figure 52 Synchronization from PDH interface
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6.3.2 Synchronization from 2.048MHz signal
LTE711 “Synchronization from 2.048MHz signal” (RL10 )
Instead of forwarding the synchronization signal through an E1/T1/JT1 line, a co-located legacy base station may provide a 2.048MHz G.703 signal for synchronizing Flexi Multiradio BTS as illustrated in the figure below.
.
BTSE1/T1
IP / Ethernet
TDM
2.048MHzG.703
SYNC
eNB
Eth
SYNC
~
Figure 53 Synchronization from 2.048MHz signal
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7. TRANSPORT SECURITY
LTE689 “LTE IPsec Support” (RL10, RL15TD)
LTE564 “IPsec on FTIB” (RL20)
LTE150 “OAM Transport Layer Security (TLS) Support” (RL10, RL15TD)
7.1 General
As compared to TDM and ATM, IP based protocols enable lower transport cost and easier planning and configuration. On the other hand, mobile backhaul traffic becomes more vulnerable to hacker attacks. Attack methods have evolved rapidly with cheap HW providing high processing power and better tools which are widely available. In addition, base stations which were traditionally located in secure, locked sites are increasingly set up in public places or homes.
Furthermore, there are two major differences compared to WCDMA with respect to transport security (see Figure 54):
1. Air interface encryption of user plane traffic is terminated at the eNB, thus user plane traffic in the LTE mobile backhaul network is not secured by Radio Network Layer protocols.
2. Since the LTE network architecture is flat, adjacent base stations and core nodes (MME, S-GW) become directly IP-reachable from base station sites. If physical access to the site cannot be prohibited, a hacker could connect his device to the network port and attack aforementioned network elements.
Transport security features are seen mandatory if not both the mobile backhaul network and the eNB site can be regarded as secure. IPsec provides a comprehensive set of security features (data origin authentication, encryption, integrity protection), solving both problems above. The 3GPP security architecture, based on IPsec and Public Key Infrastructure (PKI), is outlined in following specifications: [TS33.210], [TS33.310] and [TS33.401].
This chapter gives an overview of the transport aspects of LTE mobile backhaul security. More details, in particular addressing the operability issues, can be found in [SDI].
� NSN recommends using IPsec.
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NB ServerUE
3GRNC
Core
eNB
ServerUE
LTE
U-plane security
Core nodes and adjacent eNBscan be attacked
User traffic can be can be
compromised
3GPP U-plane security
Mobile Backhaul
Figure 54 Security with WCDMA and LTE
IPsec is applied between Security Gateways (SEG). Each eNB site instantiates one SEG function. One or more Security Gateways (SEG) should be located at the edge of the operators “Security Domain” (as per 3GPP Network Domain Security). Typically, the Security Domain includes the backbone network. Connectivity provided by a 3rd party (leased lines) is usually treated as outside the Security Domain. The SEG is effectively hiding the core nodes (MME, SAE-GW, Network Management System) from the mobile backhaul network. Since the traffic itself is transparent to the SEG, various core network configurations can be supported (e.g. MME/SAE-GW pooling, S1-flex, etc.).
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eNB
Server
Core
SecurityGateway
(SEG)
SecurityGateway
(SEG) integrated in
Flexi BTS
Figure 55 Security Gateway functions in the network
3GPP recommends re-using IPsec also for O&M (M-plane) traffic. In addition to that, NSN has developed an M-plane security solution based on TLS. TLS provides end-to-end security since the session secured by TLS is terminated at the O&M equipment (Element Manager, Network Management System). Optionally, both concepts could be combined (TLS-over-IPsec). In this case, all traffic (U/C/M/S-plane) may flow through one single IPsec tunnel.
Flexi Multiradio BTS has an integrated Security Gateway function, supporting all options above.
The SEG at the core side may be a separate equipment or integrated within the Edge Router.
7.2 X2 Issues
In the simplest scenario, all S1 and X2 traffic of an eNB could pass through a single IPsec tunnel. That means that X2 traffic would need to be routed back through an SEG, i.e. passing this SEG function twice (“IPsec X2 Star” architecture, Figure 56). Alternatively, X2 traffic (U/C-plane) may be secured directly between eNB integrated SEG’s (“IPsec X2 Mesh” architecture, Figure 57).
There is a common misconception that the “flat” LTE architecture implies the „IPsec X2 Mesh“ architecture. In reality, the advantages are minor. The amount of backhaul traffic which can be saved in the aggregation network is very small. Even though X2 latency will be reduced, the effect will be insignificant since the transport path used for S1 should be designed for low latency anyhow (see also chapter 3.1).
� NSN recommends the “IPsec X2 Star” architecture.
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IPsec Tunnel
S* VLAN
U
C
M
MME
SAE-GW
O&MeNB
X2-u/c
SEG
IPsec VPN
IPsec tunnel: “outer” IP layer
IPsec tunnel: “inner” IP layer
Figure 56 “IPsec X2 Star” architecture
X2 Tunnel
X2 Tunnel
S1 Tunnel
SVLAN
U
C
M
...
MME
SAE-GW
O&M
IPse
cV
PNeNB
eNB
X2-u/c
SEG
Figure 57 “IPsec X2 Mesh” architecture
It should be noted that the 3GPP Rel.8/9 X2 self-configuration as per [TS36.300] does not fully support the “X2 Mesh” architecture. The TNL Address Discovery procedure determines the C-plane application address only, which is not sufficient in case the eNB application IP addresses shall be different from the interface IP address which terminates the IPsec tunnel layer.
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7.3 IPsec Tunnel Mode vs. Transport Mode
[TS33.210] requires IPsec Tunnel Mode. Transport Mode is declared as optional. With Tunnel Mode, the payload IP frame is encapsulated with an extra IP header (IPv4: 20bytes).
IPsec Transport Mode doesn’t need that extra IP header, so the transport efficiency is slightly better. However, a Transport Mode SA is defined as a security association between two IP hosts (see RFC2401). So, if a centralized SEG is applied, Tunnel Mode is the only choice. In turn, IPsec Transport Mode would only be applicable to direct X2 connections. For a more generic network design, NSN recommends to use only tunnel mode, for both S1 and X2. Due to the very low amount of X2 traffic, the transport efficiency impact is negligible.
If IPsec Tunnel Mode is used, the transport QoS mechanism (DiffServ) will not be affected. Flexi Multiradio BTS copies the application layer (“inner”) DSCP values into the IPsec tunnel (“outer”) DSCP’s, so that each packet will be treated properly. Correspondingly, an edge router should do that in DL direction.
� NSN recommends the IPsec Tunnel Mode.
7.4 Security Associations and IP Addressing
In case of the “X2 star architecture” (see chapter 7.2) each eNB has to build up Security Associations (SA) to one (or very few) SEG(s) only. SA’s are established and maintained automatically by the Internet Key Exchange (IKE) protocol. Flexi Multiradio BTS supports both IKEv1 (RFC2409) and IKEv2 (RFC4306)
The IP address for IPsec tunnel termination (interface IP address) may be different from the IP addresses which eNB U/C/M/S-plane applications are bound to (virtual IP addresses). This is important if IP addresses in the mobile backhaul network are managed separately, i.e. by another operator (IP transport service). See Figure 58.
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• Application(s) bound to interface address• Collapsed "inner" and "outer" address
• Application(s) bound to virtual address(es) ("inner“) address)
• Tunnel terminated at the interface address ("outer“ address)
VLAN1Tunnel3
VLAN1Tunnel4
VLAN1Tunnel2
VLAN1Tunnel1
M
S
U
C
Multiple tunnels per eNB
VLAN(optional)
IPsectunnel
U
C
M
S
Single tunnel per eNB
VLAN optional
Tunnel
Single tunnel per eNB
U
C
M
S
VLAN optional
Figure 58 IP addressing with IPsec Tunnel Mode
A typical configuration is shown in Figure 59. Here, the U/C/M-planes are bound to virtual addresses and forwarded via an IPsec tunnel. The S-plane is bound to the physical interface address, bypassing the IPsec tunnel. All traffic is going through a single VLAN.
IPsec Tunnel
S VLAN
InterfaceIP address
Application IP address
U
C
M
Figure 59 Mixed IP addressing
Traffic of different eNB applications (planes) may be routed through different SA’s (Figure 60) or even through different IPsec tunnels, based on a set of rules. For example, U/C-plane traffic and M-plane traffic may be terminated in different SEGs, belonging to different IP subnets. Source and destination IP addresses or IP subnets can be used for making the routing decision.
In order to keep the number of SA’s to be managed at the SEG reasonably low, it is recommended to assign eNB’s of the same group (adjacent eNB’s) to the same subnet. This assignment can be done per plane (U/C/M). Typically, the corresponding core nodes will belong to different subnets, so X2 traffic will need its own SA(s). In the simplest scenario, S1 and X2 traffic is passing through a single IPsec tunnel containing two (pairs of unidirectional) Security Associations: one IKE SA and two Child SA’s for the traffic to be protected. With U/C/M-plane separation, this would result in one IKE SA and 5 Child SA’s:
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• IKE
• S1 U-plane
• S1 C-plane
• M-plane
• X2 U-plane
• X2 C-plane
Neighbor eNB (via X2)
C
U
M
S
C
U
M
S
eNB SEG
User planeU
Control planeC Management planeM Application address (inner IP address)
Interface address (outer IP address)Synchronization planeS
IKE_SA 1 CHILD_SA 1.1
CHILD_SA 1.2 CHILD_SA 1.3
CHILD_SA 1.4
CHILD_SA 1.5
CHILD_SA 1.6
U
C
~
Figure 60 IPsec “Tunnels” and Security Associations
.
Flexi Multiradio BTS supports all those scenarios.
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7.5 Public Key Infrastructure (PKI)
For secure transport of information, mutual authentication of both sender and receiver and robust encryption of the information, which provides confidentiality and integrity, is needed. Both functions are based on secret credentials. Basically, there are two approaches with respect to the distribution of these in the context of the LTE network:
1. Pre-shared key (PSK) In the simplest way, all eNB’s would share the same key. If this key is compromised, security is completely gone. Thus, this is not an acceptable solution. Alternatively, each eNB could have a unique key assigned. This would provide better security, but has scalability issues. Each time an eNB will be added, removed or replaced, the key database of its communication partners need to be updated. In particular, this would be very difficult in case of direct X2 tunnels between adjacent eNB’s (“X2 mesh architecture”).
2. Digital certificate, Public Key Infrastructure (PKI) PKI is the solution recommended by 3GPP. It is based on digital certificates and public/private key pairs. The eNB certificate including the public key is sent openly to the other party in order to prove authenticity. The eNB private key is securely stored inside the eNB. PKI provides good flexibility for network changes. However, it requires investments into the security infrastructure.
Flexi Multiradio BTS supports PKI with X.509 certificates.
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8. TRANSPORT OPERABILITY
8.1 Ethernet OAM
LTE140 “Ethernet OAM” (RL20, RL15TD)
Ethernet OAM (Operation, Administration, Maintenance) features support management of Ethernet (L2) networks in terms of Fault Management (FM), Performance Management (PM) and Configuration Management (CM). This is beneficial for detection and localizing faults, examining and reporting network status, monitoring network performance, and provisioning and configuring parameters. Ethernet OAM functions and protocols are standardized as follows:
• Link Layer OAM (IEEE 802.3ah)
• Ethernet Service OAM (IEEE 802.1ag / ITU-T Y.1731), a.k.a. “Service Layer OAM”
Due to different objectives, these protocols complement each other.
Link Layer OAM (IEEE 802.3ah) operates at a single link and is mainly targeting as "Ethernet in the first mile" application. Flexi Multiradio BTS supports the following functions:
• OAM Discovery: Identify peer device and its OAM capabilities (with active mode support)
• Remote Failure Indication: Mechanism to provide failure information to the peer. Includes Link Fault, Dying Gasp, Critical Events
• Remote Loopback: allows to check the quality of the link for diagnosis and troubleshooting (w/ active mode support).
• Link Monitoring: Event notifications, including diagnosis information (threshold alarms)
Service Layer OAM (IEEE 802.1ag / ITU-T Y.1731) covers Ethernet end-to-end- and network segment- connectivity as well as service guarantees. Flexi Multiradio BTS supports the following functions:
• Ethernet Continuity Check: Reports loss of continuity between two MEP’s (Maintenance Endpoints), within a MEG (Maintenance Entity Group) or unintended connectivity
• Ethernet Alarm Indication Signal: indicates alarms to next nodes and suppresses alarms to NMS if indicated alarms occurs on lower levels
• Ethernet Remote Defect Indication: Used by a MEP to communicate to its peer MEP that a defect condition has been encountered.
• Loopback: behavior in Ethernet similar to "Ping" on L3 (with optional troubleshooting extensions)
• Link Trace: behavior in Ethernet similar to "Trace Route" on L3
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8.2 Transport Plug’n’Play (SON)
Self-Organizing / Self-Optimizing Networks (SON) principles are essential to decrease operator OPEX. This chapter recapitulates transport related items.
8.2.1 Auto-Connection
LTE154 “SON LTE BTS Auto Connectivity” (RL10, RL15T D)
Flexi Multiradio BTS is delivered from the factory with an initial basic SW to perform the basic boot process, the auto-connectivity agent SW for the establishment of a connection to the IP backhaul network and the self-configuration agent SW. Auto Connection supports fast integration of new or re-located base stations by an automated process based on DHCP [RFC2131], [RFC2132].
The following steps have to be performed beforehand:
1. Site plan preparation
Transport planning data related to the new Flexi Multiradio BTS have to be prepared. This is not needed for the auto-connection phase itself, but for the unambiguous Flexi Multiradio BTS detection in the subsequent auto-configuration step.
2. DHCP server preparation:
DHCP servers have to be preconfigured with suitable options and Flexi Multiradio BTS specific data (vendor specific attributes):
• IP address of the Identity Management System (IDM) respectively another 3rd party PKI Certificate Server providing a CMPv2 interface
• IP address of the Security Gateway protecting the responsible O&M system (NetAct)
• IP address of the management peer of the responsible O&M system
• optionally an IP address of a dedicated LDAP server for Certificate Management
Auto-Connection comprises the following functions.
1. Establishment of IP connectivity
The Flexi Multiradio BTS transport sub-module is automatically configured to enable the following steps:
• L1/L2 auto negotiation
• IP Address Assignment
In order to retrieve all information necessary for the IP connection establishment between Flexi Multiradio BTS and NetAct the Flexi Multiradio BTS acts as DHCP client. DHCP requests are submitted first untagged. If not successful, the whole VLAN ID range is scanned (VLAN probing). The DHCP server assigns an IP address, netmask and the IP address of the default gateway to the Flexi Multiradio BTS and delivers in addition further information as vendor specific attributes as listed above.
2. Retrieval of operator certificates (optional)
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If the address of a PKI Certificate Server has been delivered in the previous step, Flexi Multiradio BTS retrieves a new certificate from the operator’s CA using the CMPv2 protocol.
3. Connection to the Security Gateway (optional)
If the address of a Security Gateway has been delivered in step 1, Flexi Multiradio BTS establishes a connection to the gateway and sets up Security Associations for the M-plane.
4. (Secure) O&M plane connection
Flexi Multiradio BTS starts the (secure) M-plane connection to the NetAct framework. In addition to the previously established IPsec tunnel to the SEG, security may be extended further to the O&M application using TLS (optional).
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8.2.2 Auto-configuration
LTE720 “SON LTE BTS Auto Configuration” (RL10, RL15 TD)
Based upon successful Auto-connection, the Flexi Multiradio BTS configuration plan file (RAML2.1 format) will be downloaded which also contains all transport related parameters. This configuration will be operationally available after an automatically performed reset of the base station.
To derive IP connectivity information of neighbor sites the following procedure is applied:
• During the auto-configuration process each Flexi Multiradio BTS registers itself with its eNB global ID and given IP configuration at NetAct.
• NetAct uses the eNB Global ID to access the related configuration plan file of the newly registered BTS
• NetAct searches for given pre-planned neighbor configurations (respectively for their eNB global IDs)
• NetAct checks if the listed neighbor sites are already registered. For all sites in operation NetAct queries the database for the assigned IP configurations.
• NetAct stores the found IP configurations into the neighbor cell configuration area within the configuration plan file of the newly registered Flexi Multiradio BTS.
• The updated configuration plan file is now ready to be downloaded automatically as part of the auto-configuration process.
The operator is able to start the neighbor site scan and configuration plan file update also manually on demand for a single Flexi Multiradio BTS or a list of BTS’s.
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9. FLEXI TRANSPORT SUB-MODULES FOR LTE
LTE800 “FTLB” (RL09, RL05TD)
LTE707 “FTIB” (RL10)
Flexi Multiradio BTS interfaces to the backhaul connection are provided by field-replaceable Flexi Transport sub-modules (FTM) which are mounted on top of the Flexi System Module (FSM) core. Out of the FTM product family, most recent variants FTIB and FTLB also support LTE. This allows for cost efficient migration from WCDMA to LTE through SW upgrade (Flexi System Module multimode capability).
RU20 On Top
20092008 2010
FTIAFTJA
4xE1/T13xEth
FTFA
2xFlexBus
FTPBFTEB
8xE1/T1
Mainstreamproduct
RU10
FTIBFTHA
16xE1/T1
Premium product
I-HSPA Rel.3
FTOA
1xSTM-1
FTIB
4xE1/T13xEth
FTLB
4xE1/T13xEth
LTE
RL10RL09
SW U
pgrade
SW
Upg
rade
Figure 61 Flexi Transport sub-Modules (FTM) family
FTIB is sufficient for many sites, whereas FTLB is positioned as premium product. FTLB supports the same features as FTIB, but additionally an increased IPsec throughput (HW acceleration) and I-HSPA adapter functionality. Thus, upgrading from I-HSPA to LTE can be done easily through SW download.
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Main features are listed here:
FTIB FTLB
GE 100/1000Base-T interface (electrical, RJ45) 22) 2
GE SFP receptacle, supporting 1000Base-SX/LX/ZX (optical) 12) 1
IPsec throughput performance (HW capability, DL + UL) 1) 160Mbit/s 2Gbit/s
Timing-over-Packet1) (IEEE1588-2008) yes yes
Synchronous Ethernet1) yes yes
Ethernet switching1) yes yes
Table 5 Field-replaceable Flexi Transport sub-modul e variants
Notes
1) The list above indicates HW support. Specific features may require a SW license to be enabled.
2) Two out of three GE ports are usable at the same time
If IPsec is not enabled, the eNB transport throughput performance is non-blocking, i.e. exceeding the air interface capacity.
With IPsec enabled, 160Mbit/s throughput as provided by the lower-cost Flexi Transport sub-module FTIB will be sufficient for many eNB sites. Based on an integrated IPsec HW accelerator, Flexi Transport sub-module FTLB can even support up to 2Gbit/s throughput (HW capability).
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Flexi Multiradio BTSSystem Module
withFlexi Transport sub-module
3 x GE 1)
4 x E1/T1/JT1 2)4)
High-capacity IPSec 3)4)
ToP (IEEE1588-2008), Sync Ethernet 4)
Ethernet switching 5)
1) 2 x GE electrical + 1 x GE optical via SFP module
2) E1/T1/JT1 interface for synchronization
3) IPSec HW capability: 2 Gbit/s DL+UL
4) SW support with RL10
5) SW support with RL20
Non-blocking throughput performance with IPSec
2 x GE 1)
4 x E1/T1/JT1 2)
IPSec 3)4)
ToP (IEEE1588-2008), Sync Ethernet
Ethernet switching 4)
1) 2 x GE electrical or 1 x GE electrical + 1 x GE optical via SFP module
2) E1/T1/JT1 interface for synchronization
3) IPSec HW capability: 160 Mbit/s DL+UL
4) SW support with RL20
Non-blocking throughput performance without IPSec
FTIB
FTLB
Figure 62 Flexi Transport sub-Modules for LTE
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10. LIST OF FEATURES
LTE132 “VLAN based traffic differentiation” (RL10, RL15TD) ............................................................37 LTE875 “Different IP addresses for U/C/M/S-plane” (RL10, RL15TD)................................................37 LTE775 “SCTP multi-homing (MME)” (RL20, RL15TD)......................................................................45 LTE649 “QoS aware Ethernet switching” (RL20, RL15TD) ................................................................46 LTE118 “Fast Ethernet (FE) / Gigabit Ethernet (GE) electrical interface” (RL09, RL05TD).................47 LTE119 “Gigabit Ethernet (GE) optical interface” (RL09, RL05TD) ....................................................47 LTE491 “FlexiPacket Radio Connectivity” (RL20, RL15TD) ...............................................................47 LTE664 “LTE transport protocol stack” (RL09, RL05TD)....................................................................48 LTE131 “Traffic prioritization on IP layer” (RL10, RL05TD) ................................................................56 LTE129 “Traffic prioritization on Ethernet layer” (RL10, RL15TD) ......................................................57 LTE138 “Traffic shaping” (RL10, RL15TD).........................................................................................59 LTE134 “Timing-over-Packet” (RL10) ................................................................................................63 LTE891 “Timing-over-Packet with phase synchronization” (RL25TD) ................................................63 LTE713 “Synchronous Ethernet” (RL10) ............................................................................................65 LTE710 “Synchronization from PDH interface” (RL10).......................................................................66 LTE711 “Synchronization from 2.048MHz signal” (RL10)...................................................................67 LTE689 “LTE IPsec Support” (RL10, RL15TD) ..................................................................................68 LTE564 “IPsec on FTIB” (RL20).........................................................................................................68 LTE150 “OAM Transport Layer Security (TLS) Support” (RL10, RL15TD) .........................................68 LTE140 “Ethernet OAM” (RL20, RL15TD) .........................................................................................76 LTE154 “SON LTE BTS Auto Connectivity” (RL10, RL15TD) ............................................................77 LTE720 “SON LTE BTS Auto Configuration” (RL10, RL15TD)...........................................................79 LTE800 “FTLB” (RL09, RL05TD) .......................................................................................................80 LTE707 “FTIB” (RL10) .......................................................................................................................80
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11. REFERENCES
[IEEE802.1p] IEEE 802.1p
[IEEE802.1q] IEEE 802.1q - 2005, Virtual Bridged Local Area networks
[IEEE802.1ad] IEEE 802.1ad - 2005, Virtual Bridged Local Area Networks - Amendment 4: Provider Bridges
[IEEE 802.3] IEEE 802.3 – 2004, "Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications"
[IEEE1588-2008] IEEE 1588 - 2008, IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems
[LTE for UMTS] LTE for UMTS - OFDMA and SC-FDMA Based Radio Access Harri Holma, Antti Toskala, Wiley, 1st edition, 2009
[MEF6.1] Metro Ethernet Forum, Technical Specification 6.1 Ethernet Services Definitions - Phase 2
[MEF10.1] Metro Ethernet Forum, Technical Specification 10.1 (Ethernet Services Attributes Phase 2)
[MEF11] Metro Ethernet Forum, Technical Specification 11 (User Network Interface (UNI) Requirements and Framework)
[RFC792] IETF RFC 792, Internet Control Message Protocol
[RFC793] IETF RFC 793, Transmission Control Protocol (TCP)
[RFC826] IETF RFC 826, Address Resolution Protocol (ARP)
[RFC894] IETF RFC 894, A Standard for the Transmission of IP Datagrams over Ethernet Networks
[RFC1191] IETF RFC 1191, Path MTU Discovery
[RFC1323] IETF RFC 1323, TCP Extensions for High Performance
[RFC1981] IETF RFC 1981, Path MTU Discovery for IP version 6
[RFC2131] IETF RFC 2131, Dynamic Host Configuration Protocol
[RFC2132] IETF RFC 2132, DHCP Options and BOOTP Vendor Extensions
[RFC2409] IETF RFC 2409, The Internet Key Exchange (IKE)
[RFC2474] IETF RFC 2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
[RFC2475] IETF RFC 2475, An Architecture for Differentiated Services
[RFC4306] IETF RFC 4306, Internet Key Exchange (IKEv2) Protocol
[RFC4861] IETF RFC 4861, Neighbor Discovery for IP version 6
[SDI] NSN, Secure Device Identity solution J. Kosonen, 20.03.2009, v.2.0
[TS23.401] 3GPP TS 23.401, GPRS enhancements for E-UTRAN access; Stage 2
[TS23.402] 3GPP TS 23.402, Architecture Enhancements for non-3GPP accesses; Stage 2
[TS33.210] 3GPP TS 33.210, 3G Network domain security (NDS), IP layer security
[TS33.310] 3GPP TS 33.310, Authentication Framework
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[TS33.401] 3GPP TS 33.401, Draft technical specification for LTE/SAE
[TS36.300] 3GPP TS 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Stage 2 overall description
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12. CHANGE HISTORY
v1.0 03-Jul-2009
v2.0 22-Oct-2009
v3.0 19-Feb-2010
v4.0 24-Jun-2010