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by Gaby Junowicz Director, Business Development RAD Data Communications
From the ‘on the move' businessman picking up his emails to music-lovers downloading songs to their mobile phones, High Speed Downlink Packet Access (HSDPA) driven applications are finally reaching public consciousness. Anyone who has tried to download content from his or her GPS or UMTS mobile phone will welcome HSDPA as it offers mobile broadband services at a much faster speed. With speeds of up to 14.4 Mbps per user, it will significantly shorten the time it takes to download files onto HSDPA enabled handsets by as much as 82%. HSDPA enabled services will undoubtedly be welcomed by UMTS operators too. Faster downloads are likely to lead to greater service adoption and increased usage. It will also allow also them to deliver more services using existing infrastructure and at a reduced cost. Although the scramble for 3G licenses hasn't seen the full-scale adoption of services that the operators would have hoped, times are changing and the amount of traffic is expected to grow faster than the average revenue per user. However, operators are all too aware that such high capacity performance means increased costs, as it also requires significant additional bandwidth in order to backhaul traffic. As a result, operators will soon be forced to look to alternative backhaul solutions which are not only cost effective and scalable but also don't compromise the quality of their ‘bread and butter' - voice services. Today backhaul, a broad term for the provision of connectivity in the service provider's core network, accounts for a healthy chunk of operator cost in building and maintaining a mobile network. In fact, it is one of the major contributors to the high costs of building and running a mobile network. On average, transport equipment accounts for 25% of the costs of private cellular backhaul infrastructure. Transport outlays, moreover, vary between 40-60% of the total cost of leased lines, with backhaul contributing 75% of that sum. Despite all the benefits that 3G adoption will bring to operators they will also have to keep a watchful eye on the increased infrastructure requirements of 3G traffic. Most mobile networks currently rely on SDH/SONET or ATM data transmission services with dedicated phone connection E1/T1 access lines. While one or two E1/T1 lines might be sufficient to handle the average number of links connected to 2G base stations, the introduction of HSDPA may increase this to anywhere between eight and 16 E1/T1s per 3G cellular site. This burden on operators is compounded by the need to support legacy 2G and 2.5G networks as well as emerging 3G operations. In particular, there's the cost and suitability of the access platform to handle increased bandwidth capacity and the complexities of voice and data in a converged network as operators make the transition from traditional telephone TDM circuit-switched networks to ATM and, eventually, Gigabit Ethernet, IP or MPLS packet switched networks. In meeting this backhaul challenge, mobile operators are faced with an array of backhaul technologies and network interface choices. Many have tended to compartmentalise their infrastructure by building out parallel networks, using a dedicated transport network for each different mobile generation. Ultimately however, going down this route offers neither long-term proficiency or cost-effectiveness and operators would be better served by looking to integrate diverse traffic streams over a single backhaul link. Quite simply, what's required is a converged backhaul access network solution that technologically and economically delivers on all fronts. One familiar method for reducing backhaul costs, traditionally implemented in high- density segments of the core network, such as the Base Station Controller (BSC) or the Mobile Switching Centre (MSC), is aggregating several E1/T1s together and utilising statistical multiplexing to transport them over STM-1 lines. Aggregation is an essential part of existing cellular network transport design because it allows for more efficient use of the transport bandwidth and simplifies network management. Statistical multiplexing, moreover, is quite appropriate for the new types of data services that 3G will introduce. With the introduction of 3G, the mobile world is evolving into a real multimedia environment. Instead of simply voice services, a wider range of services is available to subscribers. This range embraces delay-sensitive and high quality services like video streaming, which require a reserve backhaul bandwidth (constant rate) to best effort-type services like Internet surfing, back office services, mailing, data downloads, etc, which, by nature, are statistical also in terms of the air interface and backhaul bandwidth usage. These diversified services allow the operator to design its transport network so as to maximise efficiency by employing statistical techniques. This new era of 3G and HSDPA services presents additional challenges to network designers. Aggregation, therefore, which characterises existing core networks, now has become an essential building block in the radio access and transport networks. In other words, it's now implemented even at cell sites. An additional test for operators is convergence. Convergence of fixed and mobile networks will also present a test for operator infrastructures. Some providers have already announced the convergence of mobile and fixed line services, such as BT's “21st century programme”, 21CN, and the branding of France Telecom's internet and TV services as Orange. The challenge for network architects is that fixed line and mobile services such as e-mail or internet surfing should feel the same whether they're being provided over a WiFi connection or a 3G mobile handset. This will require a unified transport network, which is likely to be based on IP technology. Various standards bodies are already looking to a unified IP-based transport network such as IMS (IP Multimedia Subsystem). On the other side of the equation, 3GPP, the 3rd Generation Partnership Project, has defined an “all-IP” approach in all its standards. Traditionally mobile networks require a high degree of synchronisation to maintain a proper service quality because cellular traffic is extremely sensitive to latency and packet loss. This is achieved by distribution of a common clock to serve as a point of reference among the numerous base stations spanning the network. Data (packet based) networks such as IP, however, are statistical-based by nature and do not provide inherent timing information whatsoever. In a data network problems arise as a result of Packet Loss (PL), when packets do not arrive at their destination, and Packet Delay Variation (PDV), when packets arrive with random, unpredictable delay. Anyone who has used VoIP services will be all too aware of this issue. Sophisticated clock recovery mechanisms are required to reconstruct timing and achieve the desired timing accuracy in the presence of packet delay variation and packet loss. This kind of clock recovery mechanism results in a process that negates the effect of the random PDV and captures the average rate of transmission of the original bit stream. By applying pseudo wire technologies, mobile operators will be able to speedily deploy high capacity W-CDMA services and keep HSDPA operating costs to a minimum while increasing their revenues and profitability from media-rich 3G content. As an interim solution, those mobile operators should also consider a hybrid solution that will run all their existing and delay-sensitive traffic over the deployed TDM links, while only the aggregation HSDPA traffic will be connected employing pseudo-wire technologies and packet transport networks. In making the vision of 3G enabled networks work, mobile telephony's backhaul challenge has paved the way for new solutions to be incorporated in the transport network, such as packet-based technologies. Enablers of that migration such as pseudo-wire techniques will help to ease the transition to our 3G futures. RAD Data Communications is a leading developer of access solutions for data and telecommunications. Author Biography Mr. Gaby Junowicz joined RAD Data Communications in January 2000 as a Business Development Manager, and was promoted to Senior Business Development Manager in 2003 and Director of Business Development in 2005. In this role Mr. Junowicz is responsible for the company strategy and business development in the area of solutions for cellular and wireless networks. |
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