Mobile backhaul transition required for wireless services
Strain on Networks
As data delivery moves into a new paradigm of next-generation wireless networks that provide data, video, and voice services, one of the major challenges for service providers is provisioning enough mobile backhaul to fuel intense data demands.
Mobile backhaul (see Figure 1) is the network for transporting mobile traffic between cell sites (BTS/NodeBs) and radio controllers (BSC/RNCs). Backhaul is one of the major contributors to the high costs of building out and running a mobile network – estimated to be approximately 25-30 percent of total operating expenses. As demands to support increased mobile data traffic grow, it is important that operators optimize their networks with the most cost-efficient backhaul techniques.
The Problem with TDM Backhaul
TDM circuits have historically inter-connected base stations to regional network controllers, which worked fine for voice-only systems or with low-bandwidth data traffic. However, the rapid growth in mobile broadband traffic has overloaded TDM circuits and providers are now unable to keep up with the uptick in wireless traffic growth.
Adding more TDM circuits to address this challenge is not a viable option since the recurring monthly costs for legacy backhaul technologies (PDH, ATM over PDH, and SONET/SDH) increase linearly with traffic. The relatively flat average revenue per user (ARPU) that an operator can charge for enhanced services prevents carriers from passing these increased expenses on to consumers. Operators are thus looking to move to packet-based backhaul techniques using IP and Ethernet to gain a lower cost per bit. Using Carrier Ethernet for wireless backhaul allows operators to support large bandwidth increases from cell sites, while keeping operational costs in check. Operators can significantly reduce their cost per connection by moving from TDM to Ethernet (see Figure 2).
Making the Leap from TDM to IP/Ethernet Backhaul
In a recent survey of Global Service Providers by Infonetics, 100 percent of service provider respondents claimed to have already deployed IP/Ethernet somewhere in their backhaul network. Most deployments were "hybrid," retaining TDM for voice due to clock synchronization requirements. Service Providers are implementing a “phased” migration to IP/Ethernet (see Figure 3), due to the fact that unlike TDM, Ethernet was not designed to carry synchronous information, and cannot “natively” align clock frequency across devices in the network to the level of accuracy and stability required for the set-up, hand-over and reliability of mobile phone connections.
The first phase is a hybrid implementation where Carrier Ethernet is used for packet offload of data services, and TDM is retained for voice. This approach is not an ideal solution, as it forces carriers to maintain and pay for two separate networks. The ultimate goal is phase two, in which a single Carrier Ethernet network is used to backhaul all services. Infonetics' survey of global service providers indicated 79% of service providers plan to move to a single IP/Ethernet mobile backhaul for carrying all traffic. Before pursuing this final stage of migration, carriers must have confidence timing over packet (ToP) technologies can satisfy strict clock synchronization requirements of wireless standards.