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Chapter 2 GPRS protocols Contents: 2.1 Signalling Protocols used in GSM 2.2 Control Plane and User Plane in GPRS overview 1. User Data and Signalling 2. GPRS User plane (Rel 99) 3. Protocol used on the air-summary 4. Protocols used on GB and Gn summary 5. User data handling 6. GPRS control plane (Rel 99) 2.3 Other Interfaces 1. The Abis interface 2. Nokia solution for the Dynamic Abis 3. SS7 Interfaces in GPRS CN 2.4 GPRS protocols Rel 5 1. Evolved user plane for PS (Rel 5) 2. Evolved control plane for iu PS (Rel 5) 2.5 The GPRS Service 1. QoS Parameter (Rel 97/98) 2. QoS Parameter (Rel 99) 3. QoS Parameter comparison

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Page 1: Chap02 gprs pro_03t_kh

Chapter 2

GPRS protocolsContents:2.1 Signalling Protocols used in GSM 2.2 Control Plane and User Plane in GPRS overview

1. User Data and Signalling2. GPRS User plane (Rel 99)3. Protocol used on the air-summary4. Protocols used on GB and Gn summary5. User data handling6. GPRS control plane (Rel 99)

2.3 Other Interfaces1. The Abis interface2. Nokia solution for the Dynamic Abis3. SS7 Interfaces in GPRS CN

2.4 GPRS protocols Rel 51. Evolved user plane for PS (Rel 5)2. Evolved control plane for iu PS (Rel 5)

2.5 The GPRS Service1. QoS Parameter (Rel 97/98)2. QoS Parameter (Rel 99) 3. QoS Parameter comparison

Page 2: Chap02 gprs pro_03t_kh

2.1 Signalling Protocols used in GSM

HLR AC VLR EIR

BTS

MS

MSC

MTP

ISUP

SCCP

MTP

SCCP

BSSAP

DTAPBSSMAP

L1LAPDm

RR

MM

CMCC SS SMS

L1

LAPD

RSL/O&M/L2ML

BSCISDN

L1

L2

L3

MTP

SCCP

TCAP

MAP

Abis

A

In GSM-PLMN phase 1/2 the Signaling System No. 7 (SS7) is used for the transmission of signalling information between the components of the network switching sub-system NSS (interfaces B-G), as well as between MSC and BSC (A-interface) and in direction of the external ISDN networks.

There are three layers defined for signalling on Um in GSM:Layer 1 serves for the physical transmission and includes aspects as e.g. logical channels, FDMA, TDMA, multiframes, channel coding, etc.)Layer 2 functions on Um are performed by a modified LAPD protocol (LAPDm).Layer 3 on the Um radio interface is subdivided into three sublayers: radio resource management RR (channel administration, power control and handover), mobility management MM and connection management CM. The connection management consists of: call control CC, supplementary services SS and short message services SMS

Um

Page 3: Chap02 gprs pro_03t_kh

Chapter 2

GPRS protocols2.2 Control Plane and User Plane in GPRS overview

1. User Data and Signalling2. GPRS User plane (Rel 99)3. Protocol used on the air-summary4. Protocols used on GB and Gn summary5. User data handling6. GPRS control plane (Rel 99)

Page 4: Chap02 gprs pro_03t_kh

User data and “Signalling”

GSM is a circuit switched technology. The Resources are split into Signalling Resources (e.g. signalling channels on the air) and resources for user data.

Because GPRS is by its structure a packet switched technology it is possible to separate signalling and user data logically but not physically. So user data and high layer signalling use partly common procedures, so the protocol stack should be spitted. Protocols used for user data and for signalling are finally distinguished in the CN. This allows a network evolution without the need to redesign the complete system. The high layer signalling is even reused for 3G.

A layered protocol structure was designed in GPRS to realize the transfer of user information. Associated with the information transfer, control procedures were designed in one or more levels such as•error correction,•error recovery, •flow control,•multiplexing and de-multiplexing, and•segmentation and re-assembly.

The transmission plane of the NSS is based on a packet switched IP network. It is kept independent from the BSS and the radio interface.

The signalling plane consists of protocols responsible both for control and support of the transmission plane functions:•controlling the GPRS network access connections, such as „attaching to“ and „detaching from“ the GPRS network.•controlling the attributes of an established network access connection, such as activation of a PDP address.•controlling the routing path of an established network connection in order to support user mobility.•controlling the assignment of network resources to meet changing user demands.•providing supplementary services.

Control plane

User Plane

Page 5: Chap02 gprs pro_03t_kh

GPRS User plane (Rel 99)

MS BSS SGSN ExternalUm Gb Gn Gi

MAC

GSM RF

RLC

LLC

SNDCP

IP v 4/6

ApplicationTCP/UDP

MAC

GSM RF

RLC

NS

FR

L1

BSSGP

Relay

NS

FR

L1

BSSGP

LLC

SNDCP

L1

L2 L2

IP IP

UDP /TCP

UDP /TCP

GTP GTP

Relay

L1

SNDCP: SubNetwork Dependent Convergence ProtocolLLC: Logical Link ControlRLC: Radio Link ControlMAC: Medium Access Control

BSSGP: BSS GPRS ProtocolNS: Network ServiceFR: Frame Relay

GTP: GPRS Tunnelling ProtocolUDP: User Datagram ProtocolTCP: Transmission Control ProtocolIP: Internet Protocol

L2

IP v 4/6

L1

ApplicationTCP/UDP

GGSN

Page 6: Chap02 gprs pro_03t_kh

Protocol used on the air-summary

GSM RF The GSM RF is the physical radio channel used to transfer the data packets.MAC The Media Access Control layer provides the access to the physical radio resource. That means it is responsible for the physical allocation of a packet data channel. It is strong associated with the RLC layer. RLC The Radio Link Control layer provides an reliable link over the air interface that fits the block structure of the physical channel. Therefore it segments and re‑assembles the LLC frames.Additionally it performs a sub-multiplexing to multiplex several MS on one physical channel and a channel combining to provide up to eight physical channels to one MS. The RLC layer is strongly associated with the MAC layer and performs additionally signalling tasks.BSSGP The BSS GPRS Protocol is used to transfer the LLC frames together with related information between SGSN and PCU. Information as QoS and routing information. Additionally node management information are transferred by the BSSGP.LLC The Logical Link Control layer provides the service necessary to maintain the communication capability between the MS and the SGSN. From the point of the LLC layer there is an established connection between MS and SGSN even if the RLC/MAC layer does not provide any physical connection. The physical connection will be established by the RLC/MAC layer only if the LLC layer has data available to transmit. The LLC layer provides several access points to transfer different kinds of data and to distinguish between different QoS classes. Additionally the LLC performs the ciphering function.SNDCP The Sub-Network Dependent Convergence Protocol supports the following tasks:·                    compression·                    segmentation/re-assembling·                    multiplexing/de-multiplexing of data packets to one ore more LLC SAPs.If applicable user data and the header is compressed. The segmentation is necessary to delimit the amount of data which is transferred by the LLC over the air interface as a single unit.

Page 7: Chap02 gprs pro_03t_kh

Protocols used on GB and Gn summary

FRFrame Relay is the link layer protocol, which is used to connect the SGSN with the PCU. Alternatively Ethernet connections can be used as link layer protocol on the Gb interface as well (defined in Rel 4). NSThis layer transports BSSGP PDUs. Network Service is based on the Frame Relay (or IP) connection between BSS and SGSN, and may be multi-hop and traverse a network of Frame Relay (or IP) switching nodes.  

BSSGPThe BSS GPRS Protocol is used to transfer the LLC frames together with related information between SGSN and PCU. E.g. QoS and routing information. Additionally node management information are transferred by the BSSGP.

On Gn interface the IP payload is transported on behalf of so-called T-PDUs using a GPRS Tunnelling Protocol (GTP) tunnel. The transport layer for this tunnel can be based on different technologies, for instance Ethernet/Internet Protocol (IP) or Frame Relay as well. For reliable data transfer User Datagram Protocol (UDP) provides unacknowledged and Transport Control Protocol (TCP) provides acknowledged transfer services.The protocol suite on Gi interface is the same as known from the Internet or other kinds of packed data networks.

NS NetworkService

BSSGPBSS

GPRSProtocol

NS

BSSGP

GTP GTP

GbGn

Page 8: Chap02 gprs pro_03t_kh

User data handling in MS (UL)

SNDCP PDU (SN-PDU)

LLC-PDU

RLC Block

MAC Block

Network PDU (NPDU)e.g. IP-packet

LLC-PDU

RLC Block

Burst Burst Burst Burst

channel codingMAC

GSM RF

RLC

LLC

SNDCP

IP v 4/6

Application

LLC segmentation

compression/segmentation

Page 9: Chap02 gprs pro_03t_kh

GPRS control plane (Rel 99)

MS BSS SGSNUm Gb

MAC

GSM RF

RLC

LLC

GMM/SM/SMS

MAC

GSM RF

RLC

NS

FR

L1

BSSGPRelay

NS

FR

L1

BSSGP

LLC

GMM/SM/SMS

SGSN GGSNGn Gi

L1

L2 L2

IP IP

UDP /TCP

UDP /TCP

GTP-C GTP-C

L1

GTP-C (GPRS Tunneling Protocol-Control) to separate from GTP-U (user plane)

In LLC heade

r

Distinction between signalling and user data coming from the MS is done finally in the SGSN with the

help of the LLC protocol

Page 10: Chap02 gprs pro_03t_kh

Chapter 2

GPRS protocols2.3 Other Interfaces

1. The Abis interface2. Nokia solution for the Dynamic Abis3. SS7 Interfaces in GPRS CN

Page 11: Chap02 gprs pro_03t_kh

The Abis interface

GSM RF

MAC

RLC

GSM RF PCM

PCU Frames Dynamic

Abis

BSS

MAC

GSM RF

RLC

NS

FR

L1

BSSGPRelay

The functional part of the BSS has to be split up into functions performed by the BTS and the PCU. In between the two a vendor specific format is used. The PCU frames. RLC/MAC functions are performed by the PCU , Channel coding and RF generation are performed by the BTS. The increased throughput of especially CS 3 and 4 and EGPRS compared with GSM requires a new solution, a dynamic Abis. That means the resource on demand principle is as well realized on abis. In most vendors cases concatenated PCU frames can be found.

MS BTS SGSNUm Gb

MAC

RLC

PCM

PCU Frames

NS

FR

L1

BSSGP

Relay

NS

FR

L1

BSSGP

LLC

SNDCP

BSCAbis

Page 12: Chap02 gprs pro_03t_kh

Nokia solution for the Dynamic Abis

Abis PCM allocation

fixed poolCoding Scheme Bit rate (bps)

CS-1 8,000

CS-2 12,000

CS-3 14,400

CS-4 20,000

MCS-1 8,800

MCS-2 11,200

MCS-3 14,800

MCS-4 17,600

MCS-5 22,400

MCS-6 29,600

MCS-7 44,800

MCS-8 54,400

MCS-9 59,200

Slave Groups

GMSK

8-PSK

GMSK

EDGE

GPRS

9 TCH:TRX:5:1 TCH:TRX:5:2 TCH:TRX:5:3 TCH:TRX:5:410 TCH:TRX:5:5 TCH:TRX:5:6 TCH:TRX:5:7 TCH:TRX:5:811 TCH:TRX:6:1 TCH:TRX:6:2 TCH:TRX:6:3 TCH:TRX:6:412 TCH:TRX:6:5 TCH:TRX:6:6 TCH:TRX:6:7 TCH:TRX:6:813141516

EDGE Dynamic Abis Pool

1 2 3 4 5 6 7 8

TRXSIG:TRX:1 TRXSIG:TRX:2

In this solution each TS on the TRXs gets its fixed subslot on the PCM, a group of other subslots gives the Dynamic Abis Pool (DAP). Depending on the availability of subslots and the throughput on the air additional subslots (slaves) are allocated to the TS temporarilly.

Page 13: Chap02 gprs pro_03t_kh

Gc (GGSN-HLR) Interface is optional and usually not implemented. It would be required for an external networks initiated “Packet call’ (PDP context activation).

Gf (SGSN-EIR) Interface is optional. It allows the Equipment Identity check to verify the IMEI.

Gr (SGSN-HLR) Interface is mandatory! it is required to allow an MS to register in a GPRS PLMN via SGSN. For example Security information is provided, the Location in the HLR is updated, … the same procedures as known from the the D interface (MSC/VLR-HLR) take place.

SS7 Interfaces in the GPRS CN

HLR AC EIR

Gs (SGSN-MSC) is optional:

-Combined GPRS/IMSI attach and detach -Combined RA/LA update-Circuit switched services paging via GPRS network-Non-GPRS alerts-Identification procedure-MM information procedure

SGSN GGSN

MSC/VLR

Based on BSSAP+ Based on MAP Gr Gc GfGs

L1

L2

L3

MTP

SCCP

TCAP

MAP

GsL1

L2

L3

MTP

SCCP

BSSAP+

MTP may be replaced by

IP

Page 14: Chap02 gprs pro_03t_kh

Chapter 2

GPRS protocols2.4 GPRS protocols Rel 5

1. Evolved user plane for PS (Rel 5)2. Evolved control plane for iu PS (Rel 5)

Page 15: Chap02 gprs pro_03t_kh

Evolved user plane for PS (Rel 5)

PHY

RLC

PDCP

LLC

SNDCP

PHY

RLC

PDCP

SNDCP

LLC

BSSGP

NetworkService

Iu-ps

GbUm

Relay

/Ack UnackRLC

MACMAC

/Ack UnackRLC

FRIP

L2FR

BSSGP

NetworkService

IP

L2

L1L1L1

GTP-U

L2

UDP/IP

L1

GTP-U

L2

UDP/IP

Iu modeGb mode

PDCP Packet Data Convergence ProtocolRLC Radio Link ProtocolRANAP Radio Access Network Application Part

For Iu mode:Compression, Ciphering, celll level Mobility, buffer management

Common protocolsIu influenced protocolsGb Gb influenced protocols

IP option Rel 4

Layer 1,2, not further specified,IP option, ATM option

MS GERANGERAN SGSN

Page 16: Chap02 gprs pro_03t_kh

Evolved control plane for iu PS (Rel 5)

RLC RLC

RRC NetworkService

Iu-ps

MS

Relay

GERAN

MAC

Common protocolsIu influenced protocolsGb

FR FR

NetworkService

L1

IP

LAPDm LAPDm

RRC

RLC

PHY

RLC

RRC

NetworkService

GbUm

GERAN SGSN

MACMAC

Gb influenced protocols

FR

Se

LAPDm LAPDm

RRRRC

L2

L1

RANAP

SCCP

As Definedin Iu Specs

L3

L2

L1

RANAP

SCCP

As Definedin Iu Specs.

L3

Layer 1,2, 3 not further specified,IP option, ATM option

L1PHY

BSSGP

RR

LLCLLC

GMM/SMGMM/SM

BSSGP

IP

L2 L2

RLCAck/NACK RLC

Ack/NACK

Page 17: Chap02 gprs pro_03t_kh

Chapter 2

GPRS protocols2.5 The GPRS Service

1. QoS Parameter (Rel 97/98)2. QoS Parameter (Rel 99) 3. QoS Parameter comparison

Page 18: Chap02 gprs pro_03t_kh

Precedence Class1: high priority2: normal priority3: low priority

Delay Class mean transferdelay (sec)

95% delay(sec)

mean transferdelay (sec)

95% delay(sec)

1 < 0,5 < 1,5 < 2 < 72 < 5 < 25 < 15 < 753 < 50 < 250 < 75 < 3754 (Best Effort) unspecified unspecified unspecified unspecified

Delay Class

SDU size: 128 Byte 1024 Byte

Reliability Class1 - 5 (lowest):

• data loss probability• out of sequence probability

• duplicate probability• corrupt data probabilityprobabilities 10-9 - 10-2

peak throughput Class1 - 9: > 8 kbit/s - >2048 kbit/s

maximum data rateno guarantee for this data rates

over a longer period of time

mean throughput Classmedium, guaranteed data rate; Class 1 - 19:

1: best effort100 Byte/h (0,22 bit/s) / 200 / 500 / 1000 / ... /

50 Mio. Byte/h (111 kbit/s)

QoS Parameter (Rel 97/98)

A GPRS Subscriber profile describes a service in terms of QoS parameters. The GPRS subscription is stored in the HLR. When a Service is activated the network is requested to provide a bearer with the described characteristics. Corresponding the network will use Ack/Nack mode on the different interfaces for example. The indicated values shall reflect the network performance as seen by the end user.

Page 19: Chap02 gprs pro_03t_kh

QoS Parameter (Rel 99)

With the Release 99 the services are categorized according to Conversational class (Real Time services e.g. voice over IP, low delay and delay variation, preserved time relationship)Streaming class (Real Time audio- and video streaming, one direction only) Interactive Background class (request, response pattern, e.g. WWW browsing, telnet applications, Round Trip Time sensible) Background class (best effort, e.g. e-mail, file transfer, SMS, Bit error sensible)

New attributes are used to describe the required Quality of Service in Rel 99.

QoS Profile Rel 99SDU Error Ratio

Residual Bit Error Ratio

Delivery of erroneous

SDU’s

Max Bitrate

Deliveryorder

Guaranteed bitrateTransfer delay

Traffic HandlingPriority

Allocation /Retention

Priority

Page 20: Chap02 gprs pro_03t_kh

QoS Parameter (Rel 99)

Maximum bitrate (kbps) The Maximum bit-rate is the upper limit an application can accept or provide. The network does not guarantee the maximum bitrate.

Guaranteed bitrate (kbps) It indicates the guaranteed number of bits delivered by network within a period of time (provided that there is data to deliver), divided by the duration. Guaranteed bitrate is only used for real-time traffic.

Delivery order (y/n) Indicates whether the PDP context shall provide in- sequence SDU delivery or not.

Maximum SDU size (octets) Indicates the maximum allowed SDU size (used for Admission control and policing).

SDU format information (bits) Lists all possible exact sizes of SDUs. Used to achieve better spectral efficiency and reduce delay when RLC retransmission is not used.

SDU error ratioIt indicates the fraction of SDUs lost or detected as erroneous. For Conversational and Streaming the SDU error ratio performance is independent of the loading conditions, whereas in Interactive and Background classes SDU error ratio is used as a target value.

Residual bit error ratio It indicates the undetected bit error ratio in the delivered SDUs. If no error detection is requested it indicates the BER in the delivered SDUs.

Delivery of erroneous SDUs

Is used to decide whether error detection is needed and whether packets with detected errors shall be forwarded or not. Yes: error detection is employed and erroneous SDUs are delivered together with an error indication. No: error detection is employed and erroneous SDUs are discarded. Not in use: SDUs are delivered without considering error detection.

Transfer delay (ms)It indicates maximum delay for 95th percentile of the distribution of delay for all delivered SDUs during the lifetime of the PDP context. It is used to specify the delay tolerated by the application.

Traffic Handling Priority (THP)It specifies the relative importance for handling SDUs belonging to one PDP context compared to the SDUs of other PDP contexts. The THP is only used within the Interactive Traffic Class.

Allocation/Retention PriorityIt specifies the relative importance of a PDP context compared to other PDP contexts and can be used by the network when performing admission control and resource allocation. The Allocation/Retention Priority attribute is a subscription attribute set in the HLR which cannot be negotiated from the mobile terminal.

Page 21: Chap02 gprs pro_03t_kh

QoS Parameter comparison

Yes/No

Yes/No/-

< 2048 kbps

<2048 kbps

<=1500 octets

<100 ms

5*10-2…10-6

10-2…10-5

1, 2, 3

Yes/No

Yes/No/-

< 2048 kbps

<2048 kbps

<=1500 octets

<250 ms

5*10-2…10-6

10-1…10-5

1, 2, 3

Yes/No

Yes/No/-

< 2048 kbps-overhead

<=1500 octets

4*10-3…6*10-8

10-3…10-6

1, 2, 3

1, 2, 3

Yes/No

Yes/No/-

< 2048 kbps-overhead

<=1500 octets

4*10-3…6*10-8

10-3…10-6

1, 2, 3

Conversationalclass

Streamingclass

Interactiveclass

Backgroundclass

Delivery order

SDU formatinformation

Delivery oferroneous SDUs

Maximum bitrate

Guaranteed bitrate

Maximum SDU size

Transfer delay

Residual BER

SDU error ratio

Allocation/retentionpriority

Traffic handlingpriority

GPRS/UMTS R99/R4/R5 QoS parameters

Precedence class

Allocation/retention priority

Delay classInteractiveclass

Backgroundclass

Traffic handlingpriority

Reliability class

Delivery oferroneous SDUs

Residual BER

SDU error ratio

R97/R98 R99/R4/R5

Peak through-put class

Maximum bitrate