WHITE PAPER

WHITE PAPER Use of MPLS technology 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. 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. 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. February 2008 CONTENTS: Introduction .............. 1 Market Trends and Challenges ......... 2 Overview of IP/MPLS Forum’s MPLS Mobile Backhaul Initiative .... 3 Business Benefits of IP/MPLS Forum’s Mobile Backhaul Initiative .................... 3 Architectural Overview ................... 4 RAN Equipment Synchronization ........ 5 OAM and Resiliency................... 6 Conclusion ................. 7 IP/MPLS Forum White Paper 1 Market Trends and Challenges Third-generation mobile networks have become a reality. By November 2007 there were 190 3G networks in commercial service across 83 countries worldwide with over 800 different types of 3G devices launched into the market available from around 90 suppliers (source: Global Mobile Suppliers Association. Dec 2007). There was forecast to be 252 million 3G subscribers worldwide by December 2007 (source: Informa Telecoms & Media: Sept 2007). This trend allows mobile operators to generate 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 will also 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). 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. 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 “futureproof” and will be able to support a new generation of networks and access technologies such as LTE. This requires the mobile backhaul network to support many different generations of technologies simultaneously. 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. 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. For example, 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. 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 an uplift in the proportion of revenues relating to higher-bandwidth data services. This creates a major business challenge with backhaul as a significant bottleneck (see figure 1). A study by Infonetics Research suggested that the global market for backhaul equipment grew to $3.5 billion in 2007 and is forecast to grow to $5.6 billion by 2010, including legacy emulation services. (source: “Mobile Backhaul Equipment, Installed Base, and Services”, Infonetics Research, 2007) Traffic Voice Dominant Cellular operator 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) 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. 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 synchronisation, Operations and Maintenance (OAM), and support for various Transport Network Layers (TNLs), LTE and mobile WiMAX. Transport network & Mobile Core Network Backhaul Transport 2G, 3G, LTE, WiMAX Access Network Tra ffic G room ing at Cell Site Aggregation Network IP/MPLS Forum • Focus Area for Backhaul RNC BSC SAE Core Network for 2G, 3G, LTE, WiMAX Tra ffic G room Access Network ing at Cell Site RAN Figure 2. Scope of MMBI Business Benefits of IP/MPLS Forum’s Mobile Backhaul Initiative This combination of rising traffic requirements coupled with declining revenues is a key motivation for operators migrating RANs to a converged, packed-based architecture (see figure 1). MPLS has been globally deployed in these types of networks and has been an important element by 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. This architecture will directly impact mobile operators’ bottom line 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, mobile backhaul among others. IP/MPLS Forum White Paper 3 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 technology 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 provide differentiated services for this aggregate so that QoS requirements are met while at the same time providing further improvements in scalability. 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). 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 GSM/GPRS (2G/2.5G) EDGE (2.5G) UMTS /HSDPA/HSUPA (3G) CDMA 1x-RTT (2.5G) CDMA 1x EV-DO (3G) Specification TNL TDM TDM ATM ATM IP HDLC or TDM IP Speed (approximate) 56 - 114 Kbps 236.8 Kbps – 473.6 Kbps ~384 Kbps (uplink) ~ 2 to 3.1 Mbps (downlink) 144 Kbps ~ 1.8 Mbps (uplink), ~ 3.1 Mbps (downlink) 50 Mbps R3, R99/R4 R99/R5, R6 IS-2000 IS-856 Mobile WiMAX Long Term Evolution (4G) WiMAX Forum Network Access Architecture R1.1 R7/R8 IP IP > 50 Mbps (uplink) > 100 Mbps (downlink) Legacy 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. 4 Use of MPLS technology in mobile backhaul networks Future In R5 3G, LTE and mobile WiMAX environments, the RAN equipment interfaces use the IP TNL – either at the Iub interface (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. For further details on the MMBI reference architecture please visit: http://www.ipmplsforum.org/ or e-mail info@ipmplsforum.org RAN Equipment Synchronization RAN equipment needs to be fully synchronised 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. For 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 synchronisation allows for tighter accuracies and reduced guard bands thereby ensuring higher capacity. In the case of legacy TNLs such as TDM, synchronisation also focuses on backhaul transport reliability (see figure 3). BSC ET 1: Radio Framing Accuracy BSC ET Node Mobile Core Network(s) RN 3: Backhaul Transport Reliability 2: Hand Off Control Node Figure 3: Clocking and synchronisation in RAN IP/MPLS Forum White Paper 5 The MMBI outlines the following methods for clock distribution over an IP/MPLS based backhaul network. In the case of 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 ATM, a dedicated 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, delivery via methods such as synchronous Ethernet or IEEE 1588 v2 or by deriving timing from the PDH/SDH transmission mechanisms used in the mobile access networks. In particular in order to support the 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 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. Other protocols enable fault diagnosis, fault isolation (eg: LSP Ping and LSP traceroute) and performance monitoring. MPLS protocols also provide tools for 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. 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. 6 Use of MPLS technology in mobile backhaul networks Conclusion The migration towards 3G networks and devices is expected to quicken over the next few years. Air interface enhancements such as HSPA, a relatively inexpensive network upgrade, will also continue to grow in popularity. Mobile operators have also begun to develop strategies and technology roadmaps that will enable them to launch “4G” services using technologies such as LTE and mobile WiMAX. The first commercial launches of these 4G networks are expected in 2008. As network speeds continue to improve the environment for innovative new data services will also prosper. If delivered successfully, these new services will provide a lucrative new revenue stream for operators. These new data services will encompass many elements: location-based services, mobile TV, social networking, mobile gaming and many more. But the increase in bandwidth requirements for these new services will mean that traditional backhaul networks based on legacy technologies such as ATM will no longer remain a cost-effective method for handling backhaul. Nor will they be sophisticated enough to cope with functions such as quality of service and resiliency management, which will be integral parts of this new service delivery environment. For these reasons, mobile backhaul is at risk of becoming the bottleneck in today’s mobile networks. 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 ability to support QoS, traffic engineering and resiliency features will ensure that new services can be successfully rolled-out, while mobile operators will be able to leverage further cost benefits by using an MPLS-based backhaul network to deliver many non-backhaul services. 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. For more information please visit: 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