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Abstract:
Mobile backhaul is a critical part of the mobile network that links the Radio Access Network (RAN) and the mobile core networks. Service providers are rapidly moving to next generation wireless technologies like 3G, Mobile WiMAX and LTE to satisfy the growing demand of bandwidth and marginal overall growth in average revenue per user. 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.
This paper provides an overview of IP/MPLS Forum‟s Mobile Backhaul Initiative, the challenges which operators are facing in current situation, proposed reference architecture and business benefits of using MPLS in the Mobile Backhaul.
MPLS Mobile Backhaul Initiative
(MMBI) for 3G/WiMAX/LTE
Authors:
Ankur Rawat and
Sasindran M. Prabhu
© Tech Mahindra Limited 2010 - 1 -
Table of Contents
Introduction to Mobile Backhaul.................................................3
Market trends and Challenges……………………………………………..4
IP/MPLS Forum‟s MPLS Mobile Backhaul Initiative (MMBI)…………6
MMBI Architecture Overview……………………………………………….9
Business Benefits of IP/MPLS Forum‟s MMBI………………………..11
Market Prospects and Vendor Offerings………………………………..12
Conclusion…………………………………………………………………….14
Tech Mahindra‟s Plan………………………………………………..........15
References......................................................................................16
© Tech Mahindra Limited 2010 - 2 -
Acronyms and Abbreviations
ATM Asynchronous Transfer Mode
BS Base Station
BSC Base Station Controller
BTS Base Transceiver Station
IP Internet Protocol
LTE Long Term Evolution
MMBI MPLS Mobile Backhaul Initiative
MPLS Multiprotocol Label Switching
MSC Mobile Switching Center
QoS Quality Of Service
RNC Radio Network Controller
RTP Real Time Protocols
SDH Synchronous Digital Hierarchy
SONET Synchronous Optical Network
TDM Time Division Multiplexing
TNL Transport Network Layer
WIMAX Worldwide Interoperability for Microwave Access
© Tech Mahindra Limited 2010 - 3 -
Introduction to Mobile Backhaul
Mobile backhaul network spreads from the first transport equipment
connecting cell sites (e.g., BTSs/Node Bs/eNBs sites) to the transport
aggregation equipment connecting central sites (e.g., BSCs/RNCs/aGWs
sites). The mobile backhaul is considered to be consisting of three segments,
i.e., access network, aggregation network and metro/regional network.
Fig 1: Mobile Backhaul Network Overview
The mobile backhaul must be capable of transporting diverse mobile services
including 2G, 3G and future LTE services. The logical interfaces and the
services transported through the mobile backhaul are summarized in Table 1.
Table 1: Interfaces and Services
© Tech Mahindra Limited 2010 - 4 -
The 2G Abis interface between BTS and BSC can be based on TDM. The 3G
Iub interface between Node B and RNC can be based on ATM/IMA and IP over
Ethernet. From a logical perspective, the Abis and Iub interfaces are purely
static point-to-point connections.
In the LTE network, the eNB has S1 and X2 interfaces. The S1 interface
terminates on the aGW. The X2 interface runs between eNBs and is used for
neighbor discovery, handovers and cell optimization. Each eNB needs to be
able to communicate with its direct neighbors. Based on LTE ongoing
standardization and implementation, most likely, the S1 and X2 interfaces will
be based on IP over Ethernet.
Two types of fundamental connections must be established in the mobile
backhaul. One is the point-to-point connection between the transport
equipment connecting the cell sites and the transport equipment connecting
the central sites for transporting Abis, Iub and S1. The other is the point-to-
point connection between the transport equipments/interfaces connecting two
eNBs for transporting X2.
Market Trends and Challenges
The mobile communications industry continues to grow at a significant pace.
Industry sources report the following facts and figures:
The number of worldwide mobile subscribers hit 3.3 billion in 2007 and
will grow to 5.2 billion by 2011*
2.9 million Backhaul connections worldwide in 2006, grown to 4.8
million by 2009*
Two out of every three towers already have more than one mobile
operator on it.
Evolving backhaul requirements per cell site: 2-16 T1/E1s in 2006; 2-8
T1/E1s and 10-30 Mbps Ethernet in 2010
Mobile operators pay incremental charges for 2x to 10x bandwidth*
© Tech Mahindra Limited 2010 - 5 -
Legacy backhaul networks are prohibitively expensive. In the U.S. alone,
mobile operators‟ transport costs have increased from $2 billion in 2006
to $16 billion in 2009
Fierce competition is squeezing margins while new data and video
appliances such as Apple‟s iPhone, Samsung‟s Instinct and LG‟s
Voyager are driving demand for more bandwidth
Growing dependence on mobile connectivity
Exponential traffic growth in parallel to flat or low growth of average
revenue per user (ARPU)
The bandwidth increase will primarily be on Best Effort data user
services and driven by „flat fee business models‟**
More technologies need to be supported: 2G/GSM, 2G/CDMA,
3G/UMTS, 3G/EVDO, HSDPA, WiMAX and LTE
Evolution towards Ethernet and IP-based backhaul solutions.
* Infonetics Research Mobile Backhaul Equipment, Installed Base and
Services,
** Lightreading.
The new 3G-based services will require a substantial increase in bandwidth,
which will in turn lead to greater mobile backhaul 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).
The cost of backhaul is not the only consideration in the migration to 3G. As
well as extra traffic, backhaul will need 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 operators will also be required to protect existing legacy technology
investments for some years. At the same time operators will 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. This requires the mobile
© Tech Mahindra Limited 2010 - 6 -
backhaul network to support many different generations of technologies
simultaneously.
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) and 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).
These market trends have made backhaul a strategic asset for mobile
operators and one that is currently a major area of investment; these trends
will grow as further air interface enhancements (HSPA, EV-DO, Rev C, mobile
WiMAX etc.) are rolled-out. However, global ARPU trends remain only flat or
negative, despite uplift in the proportion of revenues relating to higher-
bandwidth data services. This creates a major business challenge with
backhaul as a significant bottleneck
IP/MPLS Forum’s MPLS Mobile Backhaul Initiative (MMBI)
The IP/MPLS Forum is tackling the 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.
The IP/MPLS Forum‟s MPLS Mobile Backhaul Initiative (MMBI) proposes a
framework for the use of MPLS technology to bring solutions to transport RAN
backhaul traffic over access, aggregation and core networks.
The framework describes possible deployment scenarios and provides
recommendations on how to deploy MPLS in each of these scenarios. This will
create a reference guide that will allow vendors and operators to select the
appropriate feature sets for their specific scenario. The focus is on 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.
© Tech Mahindra Limited 2010 - 7 -
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 within the scope of the initiative include: 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.
Fig 2: Scope of MMBI
© Tech Mahindra Limited 2010 - 8 -
Also IP/MPLS forum has described the key requirements for mobile backhaul
in the following table.
Table 2: Mobile Backhaul Requirements
In addition, network clock and time synchronization plays a critical role when
making technology/vendor choice for mobile backhaul. It has particular
relevance for LTE, because this technology requires not only highly accurate
clock frequency synchronization, it needs time sync as well.
The following table depicts the requirement for frequency and time sync for
each of the major mobile technology:
Table 3: Network Clock and Time Sync Requirements
© Tech Mahindra Limited 2010 - 9 -
MMBI Architecture Overview The Broadband Forum has published the following technical specification:
MPLS in Mobile Backhaul Networks Framework and Requirements
Technical Specification
The Broadband Forum is currently working on the following technical
specifications
Mobile backhaul network for LTE
Mobile backhaul network for 2G and 3G
Figure 3 shows Broadband Forum‟s proposed reference architecture applied to
centralized mobile networks, depicting the Access, Aggregation and Core parts
of the mobile backhaul network according to the type of TNL used over the
Abis/Iub interface. This reference architecture corresponds to current and
near-term mobile 3G technologies (3GPP and 3GPP2).
Fig 3: Reference Architecture for centralized mobile networks with MPLS for transport
© Tech Mahindra Limited 2010 - 10 -
This reference architecture shows various MPLS use cases that are based
upon the type of the Transport network layer (TNL) carried over the MPLS
network. This reference architecture gives an overview of the functional
architecture without dealing with network node architecture. Four types of
TNL are considered in the work item (TDM TNL, ATM TNL, HDLC TNL and IP
TNL) according to the mobile network generation. TDM TNL is used for
2G/2.5G networks (GSM/GPRS, TDMA, and CDMA). HDLC TNL may be used
for CDMA networks. ATM TNL is used for UMTS-R99, R4 networks, and IP
TNL is used for UMTS R5, R6, R7, CDMA 2000, 3GPP2 networks. A detailed
listing of different TNL is provided in Table 4.
Table 4: Different RANs of Centralized Mobile Networks with Corresponding TNL
In the context of this work, the scenarios arising out of these TNLs are
hereafter referred to as TNL Scenarios since they refer to the transport service
provided by the MPLS network to the mobile network. Thus we have 4 TNL
scenarios, TDM TNL, ATM TNL, IP TNL and HDLC TNL.
© Tech Mahindra Limited 2010 - 11 -
Business Benefit of IP/MPLS MPLS Mobile Backhaul Initiative
This architecture will directly impact mobile operators‟ by simplifying
operations, reducing Opex and leveraging the cost benefits of backhaul
technologies such as Ethernet. It will also enable operators to support “next
generation” services such as location-based services (LBS), mobile IPTV and
mobile gaming, and will be sufficiently flexible 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 support 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, and mobile backhaul among others.
The same flexibility that lets MPLS be applied to these various applications
allows it to be applied to 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.
Additionally, MPLS can be deployed on any layer 2 technologies capable of
supporting MPLS labelled switching.
IP/MPLS - with its packet-switching advantages and pseudowire technology -
is 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 provides differentiated services for
this aggregate so that QoS requirements are met while at the same time
providing further improvements in scalability.
© Tech Mahindra Limited 2010 - 12 -
Because a single service provider can leverage 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 provides economies
of scale. This has a significant impact in reducing both a service provider‟s
capital and operational costs. Furthermore, 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).
Market Prospects and Vendor Offerings in MMBI space
In the fixed-line network, the successful application of ADSL technology has
brought a 2Mbps bandwidth to the end user‟s home. The increasing growth of
broadband subscriber base results in huge demands for large bandwidth.
Data traffic transferred through the provincial backbone transport network
accounts for 90% of the total traffic. This indicates that the IP-based service
bearing has become the development trend in the industry. The future service
transport network tends to be intelligent, highly integrated and broadband-
enabled, which can be achieved by using the MPLS technology.
Leading network operators such as British Telecom (BT), France Telecom (FT)
and China Mobile have been actively participating in standardization of latest
flavors of MPLS like MPLS-TP and have planned to use the MPLS-TP
technology for service transport and mobile data backhaul. They have been
actively participating in and paying much attention to the development and
testing of related products by telecom equipment manufacturers.
Leading telecom equipment manufacturers, such as Alcatel-Lucent, Cisco,
Nortel, Nokia-Siemens, Ericsson, ZTE, Huawei, FiberHome, UTStarcom, etc.,
have been actively involved in the R&D of the MPLS-TP technology and related
standardization work. For example, ZTE has implemented MPLS-TP related
OAM and protection functions on its ZXR10 9000 and ZXCTN
6100/6200/6300 product series and successfully trialed them over the
networks of operators such as China Mobile and Telecom Malaysia. Huawei
has launched the PTN 912/OSN 3900/1900 series, FiberHome the CiTRANS
660/620 series, UTStarcom the TN 725/705 series, Alcatel-Lucent the 1850
TSS 320/40/5 series and Ericsson the OMS 2430/2450 series.
© Tech Mahindra Limited 2010 - 13 -
On all accounts, both telecom equipment manufacturers and network
operators have been actively engaged in the research and planning of the use
MPLS technology in Mobile Backhaul environment. This indicates that MPLS
has promising prospects and will play a key role in the future mobile backhaul
network.
Companies like Alcatel-Lucent, Cisco, Huawei and Juniper are offering
IP/MPLS forum certified MMBI products. Table shown below gives the details
of vendors, products and certified functionality.
Vendor Product Certified Services
ALU
7750 Service Router,
7705 Service Aggregation Router
TDM over MPLS (T1 and E1)
Cisco
7600 series Edge Router,
2941 Mobile Wireless Router
TDM over MPLS (T1 and E1)
Huawei
CX600 Series Metro Service
Platform
TDM over MPLS (E1)
Juniper BX7000 Multi-Access
Gateway TDM over MPLS (T1)
Axerra AXN1600/AXN800,
AXN10/AXN1 TDM over MPLS (T1 and E1)
Table 5: IP/MPLS Forum Certified Products
© Tech Mahindra Limited 2010 - 14 -
Conclusion
Wireless traffic volume is growing at a staggering pace, driven by new highspeed mobile services such as mobile video, multimedia messaging and web browsing. This traffic growth is made possible by new 3G deployments
such as CDMA EV-DO and UMTS HSDPA, and with 4G technologies like WiMAX and LTE on the horizon this trend is set to continue. The pressure for mobile operators to leverage their networks further, while at the same time
creating a cohesive and logical transformation path towards the next generation is at an all time high. Creativity and effective thinking "outside the
box" will be what distinguishes operators from one another. MPLS technology in the backhaul is the solution to this problem for a series of
reasons. The flexibility of the technology means it will offer benefits and cost efficiencies in both legacy mobile backhaul and for future environments based on new technologies such as LTE. This means existing technology investments
are protected and at the same time ensures that the technology will remain sufficiently “future proof” and scalable.
The goal of the IP/MPLS Forum is to provide 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) and the DSL Forum.
© Tech Mahindra Limited 2010 - 15 -
Tech Mahindra’s Plan
Based on the Capabilities in MPLS, WiMAX, 3G, LTE and other data-
communication technologies, Tech Mahindra will be able to contribute in the following areas.
Data plane module
Control plane module
OAM module
MPLS, 3G, Wimax and LTE specific features
EMS/NMS module
Based on the opportunity from the vendors, we will be able to select among these activities:
Requirement Analysis
Product Design and Development
Testing and Validation
Interoperability Testing
Network Design, Deployment and Maintenance for Telecom Service Providers.
© Tech Mahindra Limited 2010 - 16 -
References
IP/MPLS Forum MMBI Framework and Requirements Technical
Specifications
http://www.broadband-forum.org/downloads/MPLS-
MobileBackhaul.pdf
http://www.highbeam.com/doc/1G1-193324910.html
http://www.currentanalysis.com
http://www.lightreading.com
http://www.heavyreading.com
http://www.wikipedia.org
About Tech Mahindra
Tech Mahindra is part of the multi-billion (USD) Mahindra Group, in
partnership with British Telecommunications plc (BT), the world‟s leading
communications service provider. Focused primarily on the
telecommunications industry, Tech Mahindra is a leading global systems
integrator, Business Process Outsourcing provider as well as Business
transformation consulting organization. Tech Mahindra has recently expanded
its IT portfolio by acquiring the leading global business and information
technology services company, Mahindra Satyam (earlier known as Satyam
Computer Services).