|Issue:||Asia-Pacific III 2011|
|Topic:||Mobile backhaul networks – the next generation|
|Author:||Robin Mersh & Nikhil B. Shah|
Chairman, International Development
Robin Mersh is Chief Executive Officer, Broadband Forum. Mr Mersh joined the Broadband Forum as Chief Operating Officer in July 2006, and was promoted to Chief Executive Officer in July 2010. Mr Mersh has worked in the telecommunications industry for over 18 years, starting at Cable & Wireless and then moving on to BT. He has also 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, Robin Mersh received a Bachelor of Arts degree with honours from Queen Mary and Westfield College, University of London in 1992.
Nikhil B. Shah is 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. He lived in the US for twelve years before moving to Asia. He is a frequent speaker at various industry conferences.
The backhaul network between the Radio Access Network and the mobile core must be expanded to meet the demand of bandwidth-hungry data services. It has to be flexible enough to cope with the transition period and co-exist with 2G, 3G and 4G technologies. The Broadband Forum proposes a framework for the backhaul that is based on IP MPLS, which has proven to be as reliable as current technologies. The framework recommends star shaped topology (instead of hub-&-spokes) and L2/L3 VPN. Using MPLS has also the advantage of existing, well-developed management tools.
A traditional TDM approach to mobile backhaul networks has its limitations, making it difficult to meet the evolving demands of mobile networks. IP/MPLS (Multi Protocol Label Switching) has proved itself in both fixed-line services and in mobile core network. The transitioning of mobile backhaul infrastructures to standard-based IP/MPLS solutions allows operators to evolve their networks 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 explosion in demand for data-rich mobile services.
Mobile network operators across the globe are experiencing enormous growth – although voice communications are growing in a linear fashion, the demand for data services is increasing exponentially, with consumers increasingly opting for bandwidth-hungry mobile services such as Internet access, photo sharing and music downloads. At the same time mobile operators are under economic pressure, and their backhaul networks are experiencing bottlenecks due to scalability, flexibility, and cost concerns. Operators are therefore looking for ways to future-proof their backhaul architecture to support 3G traffic, with the global wave of 4G LTE (Long term Evolution) and WiMAX adoption. They also want to be able to provide a clear migration path towards all-IP 4G networks.
More and more consumers are accessing 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 to maintain end-to-end user-experience. While many consumers are still migrating from 2G to 3G, operators are already exploring and adopting 4G (LTE).
LTE offers high data rates at a reduced price per bit, better spectrum efficiency and latency. LTE also offers expected throughputs in the range of 100Mbps and latency should be in the range of 20ms. This can offer a rich user experience, comparable to that of fixed connections. LTE will therefore enable new business models around emerging services such as real-time online gaming, HD video streaming, video blogging, and Peer-to-Peer file exchange.
Mobile Backhaul is a crucial part of the mobile network, linking 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 – in scalability, performance, cost and ease of migration from one generation to the next.
A new approach to mobile backhaul infrastructure
Cell sites are becoming increasingly complex as operators adopt 3G technologies such as High Speed Packet Access (HSPA) and Evolution Data Optimized (EVDO) and already look towards 4G technologies. Even as they migrate to these next-generation services and architectures, they realise that 4G technologies (IP/Ethernet) and emerging 3G (ATM) services will need to coexist with legacy 2G (TDM) for some time. However, as traffic for high-bandwidth data services continues to grow, operators must find ways to reduce the mobile backhaul costs. US mobile operators have typically used leased T1/E1 lines in their mobile backhaul networks. In Western Europe and the greater part of Asia-Pacific, microwave-based (with TDM encapsulations) backhaul is widely deployed. TDM is known for its reliability, but it is expensive and does not scale easily.
Clearly mobile operators need a new approach to scale their mobile backhaul networks cost-effectively and many are shifting to Ethernet-based connectivity at cell sites. This approach, in addition to being highly scalable and reliable, must bridge the gap between legacy and next-generation networks and services – and provide the flexibility to support both.
The Broadband Forum – defining next-generation mobile backhaul networks
The Broadband Forum, a global standards organisation focused on end-to-end IP network optimisation, is tackling these backhaul challenges via its MPLS in Mobile Backhaul Initiative (MMBI). The Forum members are working together to define standards-based, interoperable architecture frameworks for 2G & 3G networks and for LTE networks. The MMBI proposes a framework for the use of IP/ MPLS technology to transport backhaul traffic over access aggregation and core networks. It describes possible deployment scenarios and provides recommendations on how to deploy MPLS in these scenarios, and how to design flexible, scalable and economical backhaul network.
Figure 1: Scope of MPLS in Mobile Backhaul Initiative
The MMBI architecture allows operators to leverage their existing last mile access technology, such as TDM, Point-to-Point microwave links, DSL and Satellite. It is flexible and offers various options that enable the deployment of MPLS as close to cell sites as will fit within their architecture. Satellite is expensive but essential in regions such as Africa and remote parts of India, where fibre or copper are unavailable or uneconomical.
IP/MPLS is increasingly seen as the best strategic solution for backhaul. It offers the combination of cost, scalability and flexibility that mobile operators need to leverage existing investments while building out capacity for growing data traffic, and it supports features such as:
• Co-existence of TDM (2G), ATM (3G) and IP/Ethernet (4G) transport
• ATM-like Quality of Service (QoS) and traffic engineering techniques
• Rapid service restoration after failure detection
• Future-proof investment for migrating from 3G to all-IP based 4G/LTE
Many equipment vendors offer MPLS features within their products, but the lack of a commonly agreed framework, architectures and deployment scenarios often results in additional, avoidable costs. To address this, the Broadband Forum now offers a Certification program for vendors, enabling service providers to choose standards-based, deployment-ready products and expediting the deployment of backhaul solutions.
Evolving from 2G/3G to 4G (LTE) in the backhaul network
The Broadband Forum defines two architecture frameworks, one for 2G/3G and the other for 4G/LTE, corresponding to the 3rd Generation Partnership Project (3GPP) work. In 2G/3G RAN (Radio Access Network), the base transceiver stations (BTS), or simply base stations, handle the radio interface with the mobile station. 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 stations to controller and controller to base stations, as shown in Figure 2. This topology is also known as centralised topology. In 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
In LTE RANs, the base station itself contains controller functionality and communicates with another base station directly via any-to-any topology. LTE base stations communicate with access gateways (aGW) via a star topology as shown in figure 3.
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 VPLS (Virtual Private LAN Service) and BGP (Border Gateway Protocol) in 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. Operators can leverage cost-effective alternatives such as Metro-Ethernet networks or existing assets to support data traffic (e.g. using the DSL infrastructure to offload data traffic from the cell site). They are thus able to develop greater familiarity with IP/MPLS technology and integrate voice traffic into the packet-based infrastructure at a later date.
Synchronisation is critical to maintain good voice quality, reduce interference and manage call handovers between base stations. There are several approaches to achieve this timing synchronisation, including Synchronous Ethernet, Adaptive Clock Recovery and IEEE 1588 v2. The Broadband Forum is currently assessing various requirements to support clock distribution to base stations, including frequency, phase, and time synchronisation and provides recommendations in terms of QoS (Quality of Service), resilience and efficient distribution based on topology (point-to-point or point-to-multipoint).
Matching SONET/SDH type reliability with IP/MPLS
SONET /SDH (Synchronous Optical Networking /Synchronous Digital Hierarchy) technology is known for its high reliability and fast recovery from failures, and carriers expect new packet-based backhaul to match this level of resilience. IP/MPLS has already proved itself in core networks to be as reliable as SONET/SDH. 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 a par with SONET-based networks.
Managing and troubleshooting IP/MPLS-based networks
In moving to a new transport technology, carriers need to feel confident in its Operation, Administration and Management (OAM) tools. With years of successful service provider deployments around the world, IP/MPLS 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 net