Use of MPLS in Mobile Backhaul Networks

Introduction

Backhaul plays a vital role in mobile networks by acting as the link between Radio Access Network (RAN) equipment (Eg: radio basestation) and the mobile backbone network.

– This means that backhaul is able to transport mobile data from the end user to the internet (or similar network), mobile networks and traditional telephone networks.

The rapidly evolving telecoms marketplace has meant that mobile operators are facing a significant spike in bandwidth demands in the backhaul due to-

– The proliferation of 3G-based data services and – The emergence of high-speed air interface enhancements such as High

Speed Packet Access (HSPA). At the same time, backhaul network operators are being required to significantly reduce operational costs in order to compensate for declining Average Revenue Per User (ARPU) and to compete with a host of new competitors and technologies. Operators are also required to protect (or sufficiently emulate) core legacy services such as voice, which still account for a substantial share of revenue.

Addressing the bottleneck

In this new situation backhaul networks with many cell sites have become the “bottleneck” offering insufficient capacity to support higher bandwidths and often expensive to upgrade. To address the problem operators are migrating from existing separate, legacy ATM and TDM backhauling networks to a more cost-effective, converged, MPLS-enabled, and multi-purpose infrastructure. In addition to reducing operational costs, MPLS-based networks will also lay the foundations for the delivery of next generation mobile services, such as location-based services, mobile gaming and mobile TV, and for the use of future technologies such as Long Term Evolution (LTE) and mobile WiMAX. Ultimately, this fully consolidated network will be able to handle many different types of traffic on a single cell site, enabling the operator to offer many different services to many different types of customer.

MPLS Mobile Backhaul Initiative

MPLS Mobile Backhaul Initiative (MMBI) tackles these backhaul challenges.The initiative aims to leverage the benefits of MPLS technology in the backhaul by providing a framework for a single MPLS aggregation/backhaul network that is flexible, scalable and economical. This presentation outlines the market dynamics that are driving the need to deploy MPLS technology in Radio Access Network (RAN) backhaul and provides a brief overview of the MMBI.

Market Trends

Traffic Increasing but Revenues Shrinking

The combination of rising traffic requirements coupled with declining revenues is a key motivation for operators migrating RANs to a converged, packed-based architecture MPLS has been globally deployed in these types of networks and has been an important element in creating an environment for the delivery of new data services As these packet-based networks grow in popularity, MPLS must now also be extended into to the backhaul

Total Cell Sites & Mean Subscribers per Cell Site (2003-2013)

Market Trends & Challenges

Third-generation mobile networks have become a reality. – The total number of 3G subscribers stood at around 614

Million at the end of 2007 and the number is forecasted to grow at a CAGR of 34% in near future.

– Growing at a CAGR of over 27%, 3G market for mobile handsets will supersede 475 Million units (including HSDPA handsets) by 2010.

– The growing 3G market is expected to fuel demand for 3G-based Mobile TV market with subscriber growth forecasted at a CAGR of nearly 48% by 2012.

– Introduction of femtocells is expected to result in mass adoption of 3G technology across the world.

“3G Market Forecasts to 2010”, Market and Research 2008

Issues:Traditional Backhaul-Expensive

Mobile operators are generating revenues from a range of new “next generation” data services that are designed to generate revenues in addition to those from legacy voice services. However, these new 3G-based services require a substantial increase in bandwidth, which will in turn lead to greater mobilebackhaul costs. It is estimated that backhaul can account for as much as 30% of a mobile operator’s operating costs (Opex) (source: Yankee Group, 2005)If mobile operators were to expand the backhaul network to meet these new bandwidth requirements in the traditional manner, the move to 3G could represent a significant increase in required bandwidth and associated opex.

Issues cont.More sophisticated requirements

Backhaul needs to be able to handle a range of new functionality, including-– Quality of Service (QoS) and – Resiliency management.

These new elements will become increasingly important as mobile operators migrate towards packet-based backhaul networks. Mobile backhaul networks must support many different generations of technologies simultaneously. – Must protect existing legacy technology investments for

some years. – But need a backhaul strategy that is “future-proof” and will

be able to support a new generation of networks and access technologies such as LTE.

Issues cont.Access & Aggregation Diverse Traffic

The access and aggregation networks are used for more than just mobile backhaul and it increasingly being used to carry traffic for more than one mobile operator. This requires methods of separating and securing multiple operator traffic while maintaining service level agreements (SLAs). – We estimate that as many as three-quarters of 2G and 3G cell

sites are co-located. The access and aggregation networks can be used to host multiple services as well as multiple operators. An ISP that has an IP/MPLS based network could provide services such as-– IPTV– broadband access and enterprise VPN – as well as mobile backhaul services, generating further value from

the network.

MMBI meets the needsFlexible * Scalable * Cost Effective

Backhaul Infrastructure Requirements

The new backhaul infrastructure must therefore meet three main criteria; it must be-– Flexible

To support both legacy and IP services – Scalable

To support emerging future technologies – Cost-effective

To compensate for rising levels of backhaul traffic

It also needs to be a converged network, which means the operator does not need to run two separate networks (leased lines and IP).

OverviewMPLS Mobile Backhaul Initiative

In 2008, the IP/MPLS Forum, now part of the Broadband Forum, launched it’s MPLS Mobile Backhaul Initiative (MMBI).MMBI provides a framework for the use of MPLS technology to bring solutions to transport RAN backhaul traffic over access, aggregation and core networks. The specification provides possible deployment scenarios and recommendations on how to deploy MPLS in each of these scenarios. This is a valuable reference guide that allows vendors and operators to select the appropriate feature sets for their specific scenario.

What does MMBI address?

A shared network infrastructure that is able to support (emulate) existing legacy services (2G, 2.5G) as well as new services based on 3G and beyond (Eg: HSPA, LTE). – This will enable a migration path between existing legacy ATM and

TDM backhaul networks to a more cost-effective, converged, MPLS-enabled, and multi-purpose network.

The work is independent from the air interface technology wherever possible but allows for the possibility that some specific backhaul requirements related to the air interface may need to be considered. Areas covered: – QoS considerations (Eg; to support specific service types), – Resiliency capabilities, – Clocking and synchronization, – Operations and Maintenance (OAM), and – Support for various Transport Network Layers (TNLs), LTE and

mobile WiMAX.

Scope of MMBI

Internet

PSN

2 G3 G4 G

Access Network

Access Network

Core Network

Backhaul Transport & RAN

RNC

BSC

Aggregation Network

Transport network & Mobile Core Network

Focus Area for BBF

backhaul

RAN

2G SGSN 3G MSC

2G MSC

3G PDSN/ SGSN

GGSN

CSN WiMAX

PDN GWa GW

Business Benefits

MMBI will directly impact mobile operators’ bottom line by-– Simplifying operations, – Reducing Operating Expenses (OPEX) – Leveraging the cost benefits of backhaul technologies such as Ethernet. – Enabling operators to support “next generation” services such as location-

based services (LBS), mobile IPTV and mobile gaming, and – Providing flexibility to protect investments in new and emerging

technologies. This flexibility works in two ways:

– it will protect radio equipment investment legacy 2G/3G and – It will be able to be re-used again as mobile operators migrate to future

technologies such as LTE and mobile WiMAX.MPLS is an established technology with proven track record for providing-

– QoS, – traffic engineering (TE), – legacy layer 1 and layer 2 emulation (via pseudowires) and – resiliency features.

These advantages can be leveraged for use in a wide variety of network architectures and applications such as Enterprise VPN, IPTV, mobile backhaul among others.

Why is MMBI uniquely qualified as the Backhaul solution?

Amazing flexibility– Supports both legacy mobile backhaul networks as well as future

technologies such as LTE. For example, the same MPLS network infrastructure can be used to carry the legacy traffic pseudowires, may also be used to carry and provide QoS guarantees to next generation LTE traffic. Investments in MPLS technologies benefit the service provider by making it “future proof” and still applicable in the fast evolving mobile technology scenarios (eg: LTE and beyond).

– Deploys on any layer 2 technology capable of supporting MPLS labeled switching.

– Ideally suited to overcome the scalability limitations of traditional circuit based technologies such as ATM and TDM.

MPLS permits support of these technologies using pseudowires to protect existing investments in legacy equipment. For future IP and Ethernet based interfaces, it is possible to aggregate traffic over single TE tunnels and provide differentiated services for this aggregate so that QoS requirements are met while at the same time providing further improvements in scalability.

– Provides economies of scale. Leverages the MPLS network to meet the requirements of not only the diverse set of mobile backhaul technologies but also to those of other applications, the MPLS network also. This provides significant reduction of capital and operational costs.

Architectural Scenarios

> 50 Mbps (uplink)> 100 Mbps (downlink

IPR7/R8Long Term Evolution (4G)

50 MbpsIPWiMAX Forum Network Access Architecture R1.1

Mobile WiMAX

~ 1.8 Mbps (uplink), ~ 3.1 Mbps (downlink)

IPIS-856CDMA 1x EV-DO (3G)

144 Kbps)HDLC or TDMIS-2000CDMA 1x-RTT (2.5G)

IP

ATMR99/R5, R6

~384 Kbps (uplink) ~ 2 to 3.1 Mbps (downlink)

ATMR3, R99/R4UMTS /HSDPA/HSUPA (3G)

236.8 Kbps – 473.6 Kbps

TDMEDGE (2.5G)

56 - 114 KbpsTDMGSM/GPRS (2G/2.5G)

Speed (approximate)Transport Network Layers (TNLs)

Specification Network

Architectural Overview

Network architectures for RAN backhaul in the IP/MPLS Forum’s MPLS Mobile Backhaul Initiative are defined for various Transport Network Layers (TNL) and mobile network generations. These scenarios are grouped as follows and comprise two basic categories: – Legacy (TDM, ATM, HDLC) and – Future (IP/Ethernet).

Legacy Options

In the legacy environment, RAN equipment-– Communicates via either TDM or ATM TNLs and – Are connected with a T1/E1 interface, or with an

Ethernet interface (Fast Ethernet) if TDM or ATM is encapsulated over Ethernet via IP or MPLS.

– The functionality necessary to transport legacy traffic over MPLS can be performed either at the edge node, the access node, the access gateway or directly in the RAN equipment.

– The HDLC layer features in CDMA 1x-RTT and covers RAN equipment communicating by means of HDLC-encoded bit streams.

IP/Ethernet Options

IP/Ethernet scenarios include:– In R5 3G, LTE and mobile WiMAX environments, the RAN

equipment interfaces use the IP TNL – either at the Iubinter-face (for 3G) or on R7/R8 for LTE or mobile WIMAX.

– Mobile traffic over IP TNL can be transported either via Ethernet pseudowires or regular IP/MPLS TE tunnels over MMBI’s mobile backhaul network.

– IP termination can take place either at the edge node, the access node, the access gateway or directly at the RAN equipment.

Various deployment scenarios arise depending on the location (and the extent) of MPLS technology in the mobile backhaul network and whether it comprises both the access and aggregation sections of the network or just the aggregation section.

RAN Equipment Synchronization

RAN equipment needs to be fully synchronized to a common reference timing signal to ensure-– sufficient frequency stability, – radio framing accuracy and – handoff control for RF channels.

Thus the mobile backhaul network needs to support distribution of frequency from the Radio Network Controller (RNC) to the RAN equipment. – Example: in the case where the air-interface is based on Time

Division Duplexing (TDD), the base station clocks must be synchronized to ensure no overlap of their transmissions within the TDD frames.

Ensuring synchronization allows for tighter accuracies and reduced guard bands thereby ensuring higher capacity.

Clocking and Sync in RAN

BTS

BTS

NodeB

NodeB

BSC

RNC

BSC

1: Radio FramingAccuracy

2 : HandoffControl 3 : Backhaul

Transport Reliability

Mobile CoreNetwork(s)

Synchronization is vital across many elements in the mobile networkIn the Radio Access Network (RAN), the need is focused in three principal areas

How does MMBI Address Timing?

The MMBI outlines the following methods for clock distribution over an IP/MPLS based backhaul network. – In RAN equipment with IP TNL (including LTE)

Packet based methods where the frequency reference is carried over packets (e.g., based on Network Time Protocol (NTP)) may be used to deliver frequency to address the frequency stability requirements of the radio equipment.

– For legacy TNLs, such as TDM and ATMDedicated timing stream implemented using a pseudowire may be used to carry the reference timing signal from the RNCs to the RAN equipment both for backhaul transport reliability as well as frequency stability requirements of the radio equipment

Other methods for distributing the reference timing signal to the RAN equipment include:– Synchronous Ethernet or IEEE 1588 v2 – PDH/SDH transmission mechanisms used in the mobile access

networks. – GPS is also widely used to support the strict synchronization

requirements of TDD systems

OAM & Resiliency

A key advantages of MPLS is that it provides a wide selection of flexible troubleshooting and OAM tools that enable the deployment of a truly carrier-grade backhaul network. These include-– Fault detection methods to drive protection switching mechanisms

such as MPLS Fast Reroute. – Fault diagnosis, fault isolation (eg: LSP Ping and LSP traceroute)

and performance monitoring. – Loopback and connectivity check.

Examples include VCCV for pseudowire-based MPLS backhaul solutions and BFD for IP based MPLS backhaul solutions.

These OAM tools will remain applicable for future LTE mobile backhaul networks implemented as either IP based or Ethernet pseudowire based solutions.– Note: For legacy TNLs and Ethernet pseudowire based solutions,

the MMBI initiative leverages previous specifications by the IP/MPLS Forum that support interworking between native Layer1/Layer2 OAM and MPLS OAM.

Conclusion

MPLS technology in backhaul is the solution to the bottleneck in today’s mobile network.

– Offers benefits and cost efficiencies in both legacy mobile backhaul and for future environments based on new technologies such as LTE.

– Protects existing technology investments– Ensures that the technology will remain sufficiently “future proof” and

scalable. – New services can be successfully rolled out, while mobile operators are able

to leverage further cost benefits by using an MPLS-based backhaul network to deliver many non-backhaul services.

MMBI provides guidelines on the architecture, scenarios and technology choices for IP/MPLS RAN backhaul within the various network environments (legacy, IP, converged).

– The MMBI framework is based on the mobile network definitions outlined by the industry standards organizations (3GPP, 3GPP2, WiMAX Forum etc.)

– The solution is based on MPLS specifications and protocols developed at the IETF.

– The MMBI initiative is also being coordinated with other mobile backhaul activities underway at industry organizations such as the Metro Ethernet Forum (MEF).

For more information Check out

http://www.broadband-forum.org/technical/ipmplstechspec.php