WHITE PAPER February 2008
Use of MPLS technology
in mobile backhaul networks
CONTENTS:
Introduction
Introduction .............. 1
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 Market Trends
means that backhaul is able to transport mobile data from the end user to the internet (or and Challenges ......... 2
similar network), mobile networks and traditional telephone networks.
Overview of
The rapidly evolving telecoms marketplace has meant that mobile operators are facing a IP/MPLS Forum’s
significant spike in bandwidth demands in the backhaul due to the proliferation of 3G-based MPLS Mobile
data services and the emergence of high-speed air interface enhancements such as High Backhaul Initiative .... 3
Speed Packet Access (HSPA).
Business Benefits
At the same time, backhaul network operators are being required to significantly reduce opera- of IP/MPLS Forum’s
tional costs in order to compensate for declining Average Revenue Per User (ARPU) and to com- Mobile Backhaul
pete with a host of new competitors and technologies. Operators are also required to protect Initiative .................... 3
(or sufficiently emulate) core legacy services such as voice, which still account for a substantial
share of revenue. Architectural
Overview ................... 4
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. RAN Equipment
Synchronization ........ 5
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 OAM and
infrastructure. In addition to reducing operational costs, MPLS-based networks will also lay the Resiliency................... 6
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 Conclusion ................. 7
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.
The IP/MPLS Forum is tackling these backhaul challenges via its MPLS Mobile Backhaul Initiative
(MMBI). 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 White Paper 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.
IP/MPLS Forum White Paper 1
Market Trends and Challenges
Third-generation mobile networks have become a reality. By The access and aggregation networks are used for more than
November 2007 there were 190 3G networks in commercial just mobile backhaul and it increasingly being used to carry
service across 83 countries worldwide with over 800 different traffic for more than one mobile operator. This requires meth-
types of 3G devices launched into the market available ods of separating and securing multiple operator traffic while
from around 90 suppliers (source: Global Mobile Suppliers maintaining service level agreements. We estimate that as
Association. Dec 2007). There was forecast to be 252 million many as three-quarters of 2G and 3G cell sites are co-located.
3G subscribers worldwide by December 2007 (source: Informa
Telecoms & Media: Sept 2007). The access and aggregation networks can be used to host
multiple services as well as multiple operators. For example,
This trend allows mobile operators to generate revenues an ISP that has an IP/MPLS based network could provide
from a range of new “next generation” data services that services such as IPTV, broadband access and enterprise VPN
are designed to generate revenues in addition to those from as well as mobile backhaul services, generating further value
legacy voice services. from the network.
However, these new 3G-based services will also require a The new backhaul infrastructure must therefore meet three
substantial increase in bandwidth, which will in turn lead to main criteria: it must be flexible (to support both legacy and IP
greater mobile backhaul costs. It is estimated that backhaul services), scalable (to support emerging future technologies)
can account for as much as 30% of a mobile operator’s and cost-effective (to compensate for rising levels of backhaul
operating costs (Opex) (source: Yankee Group, 2005). traffic). It also needs to be a converged network, which means
the operator does not need to run two separate networks
If mobile operators were to expand the backhaul network (leased lines and IP).
to meet these new bandwidth requirements in the traditional
manner the move to 3G could represent a significant increase These market trends have made backhaul a strategic asset
in required bandwidth and associated opex. for mobile operators and one that is currently a major area
of investment; these trends will grow as further air interface
The cost of backhaul is not the only consideration in the enhancements (HSPA, EV-DO, Rev C, mobile WiMAX etc.)
migration to 3G. As well as extra traffic, backhaul will need are rolled-out. However, global ARPU trends remain only flat
to be able to handle a range of new functionality, including or negative, despite an uplift in the proportion of revenues
Quality of Service (QoS) and resiliency management. These relating to higher-bandwidth data services. This creates a
new elements will become increasingly important as mobile major business challenge with backhaul as a significant
operators migrate towards packet-based backhaul networks. bottleneck (see figure 1).
Mobile operators will also be required to protect existing A study by Infonetics Research suggested that the global
legacy technology investments for some years. At the same market for backhaul equipment grew to $3.5 billion in
time operators will need a backhaul strategy that is “future- 2007 and is forecast to grow to $5.6 billion by 2010,
proof” and will be able to support a new generation of including legacy emulation services. (source: “Mobile
networks and access technologies such as LTE. This requires Backhaul Equipment, Installed Base, and Services”,
the mobile backhaul network to support many different Infonetics Research, 2007)
generations of technologies simultaneously.
Traffic Cellular operator
Voice Dominant revenue & traffic
decoupled
Quantity
Revenues
Data Dominant
Time
Figure 1: ARPU declines; bandwidth increases
2 Use of MPLS technology in mobile backhaul networks
Overview of IP/MPLS Forum’s MPLS Mobile Backhaul Initiative
The IP/MPLS Forum’s MPLS Mobile Backhaul Initiative (MMBI) TDM backhaul networks to a more cost-effective, converged,
proposes a framework for the use of MPLS technology to bring MPLS-enabled, and multi-purpose network.
solutions to transport RAN backhaul traffic over access, aggre-
gation and core networks. The framework describes possible The work is independent from the air interface technology
deployment scenarios and provides recommendations on how wherever possible but allows for the possibility that some
to deploy MPLS in each of these scenarios. This will create a specific backhaul requirements related to the air interface
reference guide that will allow vendors and operators to select may need to be considered.
the appropriate feature sets for their specific scenario.
Areas within the scope of the initiative include: QoS
The focus is on a shared network infrastructure that is able to considerations (Eg; to support specific service types), resiliency
support (emulate) existing legacy services (2G, 2.5G) as well as capabilities, clocking and synchronisation, Operations and
new services based on 3G and beyond (Eg: HSPA, LTE). This Maintenance (OAM), and support for various Transport
will enable a migration path between existing legacy ATM and Network Layers (TNLs), LTE and mobile WiMAX.
Transport network &
Backhaul Transport Mobile Core Network
2G,
3G,
LTE, RNC
WiMAX
BSC
Access Core Network for
Network
Aggregation SAE
Tra Network 2G,
ffic G Site 3G,
room ing at Cell IP/MPLS Forum
• Focus Area LTE,
for Backhaul WiMAX
Access
Network
Tra
ffic G Site
room ing at Cell
RAN
Figure 2. Scope of MMBI
Business Benefits of IP/MPLS Forum’s Mobile Backhaul Initiative
This combination of rising traffic requirements coupled with and mobile gaming, and will be sufficiently flexible to protect
declining revenues is a key motivation for operators migrating investments in new and emerging technologies.
RANs to a converged, packed-based architecture (see figure
1). MPLS has been globally deployed in these types of net- This flexibility works in two ways: it will protect radio
works and has been an important element by creating an equipment investment legacy 2G/3G and it will be able
environment for the delivery of new data services. As these to be re-used again as mobile operators migrate to future
packet-based networks grow in popularity, MPLS must now technologies such as LTE and mobile WiMAX.
also be extended into to the backhaul.
MPLS is an established technology with proven support for
This architecture will directly impact mobile operators’ bottom providing QoS, traffic engineering (TE), legacy layer 1 and
line by simplifying operations, reducing Opex and leveraging layer 2 emulation (via pseudowires) and resiliency features.
the cost benefits of backhaul technologies such as Ethernet. These advantages can be leveraged for use in a wide variety
It will also enable operators to support “next generation” of network architectures and applications such as Enterprise
services such as location-based services (LBS), mobile IPTV VPN, IPTV, mobile backhaul among others.
IP/MPLS Forum White Paper 3
The same flexibility that lets MPLS be applied to these various it is possible to aggregate traffic over single TE tunnels and
applications allows it to be applied to legacy mobile backhaul provide differentiated services for this aggregate so that QoS
networks as well as future technologies such as LTE. For requirements are met while at the same time providing further
example, the same MPLS network infrastructure can be used improvements in scalability.
to carry the legacy traffic pseudowires may also be used to
carry and provide QoS guarantees to next generation LTE Because a single service provider can leverage the MPLS
traffic. Additionally, MPLS can be deployed on any layer 2 network to meet the requirements of not only the diverse
technology capable of supporting MPLS labelled switching. set of mobile backhaul technologies but also to those of
other applications, the MPLS network also provides economies
IP/MPLS - with its packet-switching advantages and of scale. This has a significant impact in reducing both a
pseudowire technology - is ideally suited to overcome the service provider’s capital and operational costs. Furthermore,
scalability limitations of traditional circuit based technologies investments in MPLS technologies benefit the service provider
such as ATM and TDM. MPLS permits support of these tech- by making it “future proof” and still applicable in the fast
nologies using pseudowires to protect existing investments in evolving mobile technology scenarios (eg: LTE and beyond).
legacy equipment. For future IP and Ethernet based interfaces,
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).
Network Specification TNL Speed (approximate)
GSM/GPRS (2G/2.5G) TDM 56 - 114 Kbps
EDGE (2.5G) TDM 236.8 Kbps – 473.6 Kbps
UMTS /HSDPA/HSUPA R3, R99/R4 ATM ~384 Kbps (uplink)
(3G) R99/R5, R6 ATM ~ 2 to 3.1 Mbps (downlink)
IP
CDMA 1x-RTT (2.5G) IS-2000 HDLC or TDM 144 Kbps
CDMA 1x EV-DO (3G) IS-856 IP ~ 1.8 Mbps (uplink),
~ 3.1 Mbps
(downlink)
Mobile WiMAX WiMAX Forum IP 50 Mbps
Network Access
Architecture R1.1
Long Term Evolution (4G) R7/R8 IP > 50 Mbps (uplink)
> 100 Mbps (downlink)
Legacy
In the legacy environment, RAN equipment communicates via can be performed either at the edge node, the access node,
either TDM or ATM TNLs and are connected with a T1/E1 the access gateway or directly in the RAN equipment. The
interface, or with an Ethernet interface (Fast Ethernet) if TDM HDLC layer features in CDMA 1x-RTT and covers RAN equip-
or ATM is encapsulated over Ethernet via IP or MPLS. The ment communicating by means of HDLC-encoded bit streams.
functionality necessary to transport legacy traffic over MPLS
4 Use of MPLS technology in mobile backhaul networks
Future
In R5 3G, LTE and mobile WiMAX environments, the RAN Various deployment scenarios arise depending on the location
equipment interfaces use the IP TNL – either at the Iub inter- (and the extent) of MPLS technology in the mobile backhaul
face (for 3G) or on R7/R8 for LTE or mobile WIMAX. Mobile network and whether it comprises both the access and aggre-
traffic over IP TNL can be transported either via Ethernet gation sections of the network or just the aggregation section.
pseudowires or regular IP/MPLS TE tunnels over MMBI’s
mobile backhaul network. IP termination can take place either For further details on the MMBI reference architecture
at the edge node, the access node, the access gateway or please visit: http://www.ipmplsforum.org/ or e-mail
directly at the RAN equipment. info@ipmplsforum.org
RAN Equipment Synchronization
RAN equipment needs to be fully synchronised to a common For example, in the case where the air-interface is based on Time
reference timing signal to ensure sufficient frequency stability, Division Duplexing (TDD), the base station clocks must be syn-
radio framing accuracy and handoff control for RF channels. chronized to ensure no overlap of their transmissions within the
Thus the mobile backhaul network needs to support distribu- TDD frames. Ensuring synchronisation allows for tighter accura-
tion of frequency from the Radio Network Controller (RNC) to cies and reduced guard bands thereby ensuring higher capacity.
the RAN equipment.
In the case of legacy TNLs such as TDM, synchronisation also
focuses on backhaul transport reliability (see figure 3).
BSC BSC
ET
1: Radio Framing Mobile
Accuracy ET Core
Network(s)
Node RN
2: Hand Off Control
3: Backhaul
Node Transport Reliability
Figure 3: Clocking and synchronisation in RAN
IP/MPLS Forum White Paper 5
The MMBI outlines the following methods for clock distribution the RAN equipment both for backhaul transport reliability as
over an IP/MPLS based backhaul network. In the case of RAN well as frequency stability requirements of the radio equipment.
equipment with IP TNL (including LTE), packet based methods
where the frequency reference is carried over packets (e.g., Other methods for distributing the reference timing signal
based on Network Time Protocol (NTP)) may be used to deliver to the RAN equipment include, delivery via methods such as
frequency to address the frequency stability requirements of the synchronous Ethernet or IEEE 1588 v2 or by deriving timing
radio equipment. For legacy TNLs, such as TDM, and ATM, a from the PDH/SDH transmission mechanisms used in the
dedicated timing stream implemented using a pseudowire may mobile access networks. In particular in order to support the
be used to carry the reference timing signal from the RNCs to strict synchronization requirements of TDD systems, the use
of GPS is a widely used option.
OAM and Resiliency
One of the main advantages of MPLS is that it provides a wide backhaul solutions and BFD for IP based MPLS backhaul
selection of flexible troubleshooting and OAM tools that enable solutions. These OAM tools will remain applicable for future
the deployment of a truly carrier-grade backhaul network. LTE mobile backhaul networks implemented as either IP
based or Ethernet pseudowire based solutions.
These include fault detection methods to drive protection
switching mechanisms such as MPLS Fast Reroute. Other For legacy TNLs and Ethernet pseudowire based solutions,
protocols enable fault diagnosis, fault isolation (eg: LSP Ping the MMBI initiative leverages previous specifications by the
and LSP traceroute) and performance monitoring. MPLS IP/MPLS forum that support interworking between native
protocols also provide tools for loopback and connectivity Layer1/Layer2 OAM and MPLS OAM.
check. Examples include VCCV for pseudowire-based MPLS
6 Use of MPLS technology in mobile backhaul networks
Conclusion
The migration towards 3G networks and devices is expected to quick- will offer benefits and cost efficiencies in both legacy mobile
en over the next few years. Air interface enhancements such as HSPA, backhaul and for future environments based on new technolo-
a relatively inexpensive network upgrade, will also continue to grow in gies such as LTE. This means existing technology investments
popularity. Mobile operators have also begun to develop strategies and are protected and at the same time ensures that the technology
technology roadmaps that will enable them to launch “4G” services will remain sufficiently “future proof” and scalable.
using technologies such as LTE and mobile WiMAX. The first commer-
cial launches of these 4G networks are expected in 2008. The ability to support QoS, traffic engineering and resiliency
features will ensure that new services can be successfully
As network speeds continue to improve the environment rolled-out, while mobile operators will be able to leverage
for innovative new data services will also prosper. If delivered further cost benefits by using an MPLS-based backhaul
successfully, these new services will provide a lucrative new network to deliver many non-backhaul services.
revenue stream for operators. These new data services will
encompass many elements: location-based services, mobile The goal of the IP/MPLS Forum is to provide guidelines on
TV, social networking, mobile gaming and many more. the architecture, scenarios and technology choices for IP/MPLS
RAN backhaul within the various network environments
But the increase in bandwidth requirements for these new (legacy, IP, converged).
services will mean that traditional backhaul networks based
on legacy technologies such as ATM will no longer remain a The MMBI framework is based on the mobile network defini-
cost-effective method for handling backhaul. Nor will they be tions outlined by the industry standards organizations (3GPP,
sophisticated enough to cope with functions such as quality 3GPP2, WiMAX Forum etc.) The solution is based on MPLS
of service and resiliency management, which will be integral specifications and protocols developed at the IETF. The MMBI
parts of this new service delivery environment. For these initiative is also being coordinated with other mobile backhaul
reasons, mobile backhaul is at risk of becoming the bottleneck activities underway at industry organizations such as the
in today’s mobile networks. Metro Ethernet Forum (MEF) and the DSL Forum.
MPLS technology in the backhaul is the solution to this problem For more information please visit:
for a series of reasons. The flexibility of the technology means it http://www.ipmplsforum.org/ or e-mail info@ipmplsforum.org
IP/MPLS Forum White Paper 7
48377 Fremont Blvd., Suite 117
Fremont, CA 94538
Phone: +1-510-492-4056
Fax: +1-510-492-4001
E-mail: info@ipmplsforum.org