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  Intercomms Issue 17
Issue 17 Articles

Future-Proofing Next Generation Mobile Backhaul Networks

By Robin Mersh and Nikhil Shah, Broadband Forum

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Robin Mersh, Chief Executive Officer, Broadband Forum
Robin Mersh, Chief Executive Officer, Broadband Forum
Nikhil B. Shah, Chairman, 
International Development, Broadband Forum
Nikhil B. Shah, Chairman,
International Development, Broadband Forum

Robin Mersh,
Chief Executive Officer, Broadband Forum

Robin Mersh joined the Broadband Forum as Chief Operating Officer in July 2006, and was promoted to Chief Executive Officer in July 2010. Robin has worked in the telecommunications industry for over 18 years, starting at Cable & Wireless and then moving on to BT. Robin has worked in business development and alliance management for various OSS software companies in the United States, mainly in network and service provisioning and activation, where he negotiated and managed several large OEM agreements. Originally from Cambridge in the United Kingdom, he received a Bachelor of Arts degree with honors from Queen Mary and Westfield College, University of London in 1992.

Nikhil B. Shah, Chairman,
International Development, Broadband Forum

Mr. Shah is a Head of Wireless Segment Development, for Asia/Pacific region at Juniper Networks. He is responsible for developing wireless business, strategy, solutions, and partnership initiatives. He also served on the board of Broadband Forum from 2006 – 2010, where currently he is a Chair of International Development. Mr. Shah has over sixteen years of global telecom industry experience including living in US for 12 years before moving to Asia. He is a frequent speaker at various industry conferences.

The traditional TDM approach to mobile backhaul networks has limitations that make it difficult to meet the evolving demands of mobile networks. However, IP/MPLS has proven itself over the years in fixed-line service providers as well as in mobile core networks. By transitioning mobile backhaul infrastructures to standard based IP/MPLS solutions, operators can evolve their network from 2G to LTE at their own pace. This aims to reduce operating expenses for mobile operators, allows them to scale efficiently, and most importantly, to position themselves to compete effectively for the coming tidal wave of data-rich mobile services.

Operators of mobile networks worldwide are experiencing explosive growth. Voice is growing in a linear fashion, but the increase in demand for data services is exponential. The reason is obvious to see: consumers are increasingly choosing bandwidth-hungry mobile services such as Internet access, photo sharing and music downloads for example.

In today’s environment, the economics of mobile operators are under pressure, Their backhaul networks are increasingly becoming bottlenecked due to scalability, flexibility, and cost concerns. Operators are looking for ways to future-proof the backhaul architecture to support 3G traffic, with the global wave of 4G (LTE/WiMAX) adoption. They also want to be able to provide a clear migration path towards all-IP 4G networks, as defined by leading standard bodies.

More and more consumers are pushing an increasing number of applications via the mobile network rather than over wires, creating greater pressure on the backhaul network to meet the growing demand and still maintain end-to-end user-experience. While many consumers are still migrating from 2G to 3G, many operators are already exploring and adopting 4G (LTE).

A recent ABI Research study predicts there will be 44 billion mobile applications downloads by 2016 worldwide, which is one more trend to validate the wealth of data on next generation networks. Equally, the global market for LTE handsets is expected to grow from 50k units (2010) to 82m by 2014. Similar growth drivers are expected in other LTE consumer segments such as Netbooks (Source: ABI report on LTE).

Long Term Evolution (LTE) offers high data rates at a reduced price per bit, better spectrum efficiency and latency. In the LTE environment, the expected throughput is in the range of 100Mbps and latency should be in the range of 20ms. This can offer a rich user experience for consumers, which is very comparable to what they have at home today with fixed connections, and mobility will be an added advantage. LTE will enable new business models around emerging services such as real-time online gaming, HD video streaming, video blogging, Peer2Peer file exchange and so on.

The rapidly increasing consumer adoption of smart phones, 3G/4G tablets (iPADs and similar devices) and USB modems are the primary driving factor behind the mobile broadband penetration. Increased traffic should reflect higher revenues, though the average revenue per megabit for data service is far lower than for traditional voice and text messaging, yet consumers are demanding mobile broadband services at affordable prices. Due to the significant cost of providing mobile data service, the mobile data tariffs today are still relatively expensive compared to fixed line broadband pricing. This phenomenon has created an imbalance in mobile operator’s balance sheet as well as their network capacity planning. To support the traffic growth and maintain quality of user experience, the mobile operators are scrambling to build out their networks faster than ever before.

Mobile Backhaul is a crucial part of the mobile network that links the Radio Access Network and the mobile core network. In designing the end-to-end mobile infrastructure, no area of the mobile network feels the strain more than backhaul networks (From a viewpoint of scalability, performance, cost and ease of migration from previous generation to next. i.e. 2G to 3G, or 3G to 4G).

Mobile backhaul infrastructure – a new approach

Cell sites are getting increasingly complex as operators rapidly adopt 3G technologies such as High Speed Packet Access (HSPA) and Evolution Data Optimized (EVDO) and are already looking ahead to 4G technologies. Even as they migrate to these next-generation services and architectures, operators realize that the new 4G technologies (IP/Ethernet) and emerging 3G (ATM) services will need to coexist with existing legacy 2G (TDM) for quite some time. Operators and transport providers must maximize their investment in infrastructure and are always reluctant to take out and replace existing technology. In addition, voice and text are still the dominant revenue generators, and it is hard to justify the expense and disruption of moving subscribers to new handsets.

The mobile backhaul market is clearly expanding. The mobile backhaul equipment market grew 10.3% in 2010 over the previous year, to $6.84 billion worldwide. Cost is a dominant factor in the design of the next-generation backhaul infrastructure. Many mobile carriers spend as much as 30 percent of their operating budgets on backhaul. The addition of almost 1.5 billion mobile subscribers between 2011 and 2015 will require more base stations, more cell site connections, higher backhaul capacities, and equipment for each cell site connection. (Source: Infonetics, 2010).

As traffic for high-bandwidth data services continues to grow, this cost will increase exponentially. Operators must find a way to reduce the cost of mobile backhaul. A vast majority of US mobile operators have used leased T1/E1 lines in their mobile backhaul networks. In Western Europe and the greater part of Asia/pacific, microwave (Time-division Multiplexing [TDM] encapsulations) based backhaul are widely deployed. Although TDM is known for its high reliability, this legacy approach is expensive and does not scale easily, since the carrier must add an additional full T1/E1 line when existing capacity is exceeded.

Clearly mobile operators need a new approach to cost-effectively scale their mobile backhaul networks, and so many of them are shifting to Ethernet based connectivity at cell sites This new approach, in addition to being highly scalable and reliable, must bridge the gap between legacy and next-generation networks and services—providing the flexibility to support both.

Figure 1: Scope of MPLS in Mobile backhaul initiative
Figure 1: Scope of MPLS in Mobile backhaul initiative

The Broadband Forum – defining next-generation mobile backhaul networks

The Broadband Forum, a global standards organization focused on end-to-end IP network optimization, is tackling these backhaul challenges via its MPLS in Mobile Backhaul Initiative (MMBI). The initiative proposes a framework for the use of IP/Multiprotocol Label Switching (MPLS) technology to transport Radio Access Network (RAN) backhaul traffic over access, aggregation and core networks. It describes possible deployment scenarios and provides recommendations on how to deploy MPLS in each of these scenarios to design flexible, scalable and economical backhaul network.

The Forum has already published the MMBI Framework and Requirements technical specification and currently Forum’s members are working together for defining standards based, interoperable architecture framework for 1) 2G and 3G networks and 2) LTE networks.

The MMBI architecture allows operators to leverage their existing last mile access technology of their choice, such as TDM, Point to point microwave links, DSL, Satellite etc. It is flexible and offers various options that enable them to deploy MPLS as close to cell site (for example, all the way to cell site or to hub location), as it fits in their architecture. Satellite is an expensive technology, but essential and important (such as Africa and remote parts of India) where fiber or copper is not available and sometimes distances exceed economical business logic.

The mobile networking industry is recognizing an increasing role for IP/MPLS as the best strategic solution for backhaul. IP/MPLS offers the combination of cost, scalability and flexibility that mobile operators need to leverage existing investments while building out capacity for the burgeoning data traffic. IP/MPLS supports features such as:

  • Co-existence of TDM (2G), ATM (3G) and IP/Ethernet (4G) transport
  • Strong ATM-like Quality of Service (QoS) and Traffic engineering techniques
  • Rapid service restoration after failure detection by leveraging tools such as Fast-reroute, Operation Administration and Maintenance (OAM) etc.
  • Future-proof investment for migrating from 3G to all-IP based 4G/LTE

Many mobile carriers have adopted IP/MPLS in their core network, as it is a familiar and field-proven technology that can be easily extended to the cell site. The transition to IP in the backhaul network is already taking place and will track with the accelerating growth of data-based services.

Many equipment vendors offer MPLS features within their products; however the lack of commonly agreed framework, architectures and deployment scenarios often results in additional avoidable costs in deploying MPLS services. To address this, the Broadband Forum also offers a certification program for vendors that enables service providers to choose standards-based, deployment-ready products for their backhaul solutions, which empowers them to deploy backhaul solutions quicker.

Evolving from 2G/3G to 4G (LTE) in the backhaul network

Broadband Forum is defining two architecture frameworks, one for 2G/3G and other for 4G/LTE, corresponding to the 3rd Generation Partnership Project (3GPP) work. In 2G/3G RAN, base transceiver stations (BTS) or simply base stations handle the radio interface with the mobile station and the base station controller (BSC) manages one or more base stations to provide control functions such as radio-channel setup, handovers etc. A hub-and-spoke topology enables communication from base station to controller and controller to base station as shown in Figure 2. The topology in 2G/3G RAN is also known as centralized topology.sIn this architecture, T1/E1 connections (TDM for 2G and ATM for 3G) between BTS and the BSC are carried over IP/MPLS based packet backhaul using pseudo-wire technologies.

Figure 2 - 2G/3G RAN Topology
Figure 2 - 2G/3G RAN Topology

In LTE RAN, the base station itself consists of controller functionality and communicates with another base station directly via any-to-any topology. LTE base station communicates with access gateway (aGW) via a star topology as shown in figure 3.

Figure 3 – All-IP LTE RAN Topology
Figure 3 – All-IP LTE RAN Topology

Coexistence, interoperability, roaming, and handover between LTE and existing 2G/3G networks and services are inherent design goals, so that full mobility support can be given from day one. In LTE networks, IP is the only protocol used to support connectivity between the different mobile nodes as defined by 3GPP. To achieve, any-to-any topology for LTE backhaul, the Broadband Forum has recommended leveraging L2VPN (Layer 2 Virtual Private Networks) and L3VPN (Layer 3 VPN such as Virtual Private LAN Service [VPLS] and Border Gateway Protocol [BGP]/MPLS based VPNs).

Hybrid IP/MPLS and TDM backhaul architecture for 2G/3G

In a hybrid model, carriers can build out capacity to accommodate the data traffic growth without having to re-engineer the voice network (leave voice on existing TDM networks). Mobile operators can leverage cost-effective alternatives such as Metro-Ethernet networks or existing assets to support data traffic (for example, using the DSL infrastructure in Western Europe to offload the data traffic from the cell site). Deploying a hybrid model allows operators to develop greater familiarity with IP/MPLS technology and integrate voice traffic into the packet-based infrastructure at a later date. In a long run, All-IP backhaul network is going to be winner.

Timing Synchronization

Synchronization is critical to maintain good voice quality, reduce interference and manage call handovers between base stations. There are several approaches to achieve this timing synchronization, including Synchronous Ethernet, Adaptive Clock Recovery and IEEE 1588 v2. Network architects must consider which of these methods to use and ensure that their equipment vendors provide the necessary support while migrating to packet based backhaul.
To assist in this area, the Broadband Forum is assessing various requirements for supporting clock distribution to the base stations, including frequency, phase, and time synchronization. The Forum is looking at different clock distribution scenarios over mobile transport network, and provides recommendations in the context of QoS, resiliency, and efficient distribution based on topology (Point to point or point to multi-point).

Matching SONET/SDH type reliability with IP/MPLS

Synchronous optical networking and synchronous digital hierarchy (SONET/SDH) is known for its high reliability and fast recovery from failures, and therefore, carriers expect that new packet based backhaul will match that level of resiliency. IP/MPLS has already proved itself in core networks to be as reliable as SONET/SDH in many carrier deployments. The combination of Fast Re-Route (FRR) and carefully engineered primary and secondary Label Switched Paths (LSP) allows IP/MPLS-based network to recover in tens of milliseconds—on par with SONET-based networks.

Managing and troubleshooting IP/MPLS-based networks

In the past there was a misconception that IP/MPLS was difficult to manage and complex to troubleshoot, resulting in higher operating expenses. Carriers have been understandably reluctant to move to a new transport technology unless they were confident in its operation, administration and management (OAM) tools.

With years of successful service provider deployments around the world, IP/MPLS now includes a robust set of standards-based OAM tools that greatly reduce troubleshooting time, such as MPLS LSP-Ping, trace route, Virtual Circuit Connectivity Verification (VCCV) - test pseudo-wire state as well as Bidirectional Forwarding Detection (BFD) - a hello protocol to connectivity, amongst others.

The Broadband Forum continues to advance the specifications and certification of mobile backhaul technologies that enhance interoperability and ensure that next generation backhaul networks meet the future demands of the industry.

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