Mobile operators are actively transforming their backhaul networks to a costeffective IP-over-Ethernet paradigm. Almost all service providers have deployed IP/Ethernet somewhere in their backhaul network. But many deployments are “hybrid,” retaining TDM for voice due to clock synchronization requirements. One of the last remaining hurdles to widespread acceptance of this transformation is demonstrating that packet networks can address the synchronization requirements for 2G, 3G, and 4G mobile networks.
The IEEE 1588v2 Precision Time Protocol (PTP) standard addresses frequency, phase, and time-of-day synchronization requirements, making it ideal for applications such as LTE FDD and TDD. Alcatel-Lucent and Ixia have been at the forefront in the implementation and testing of advanced synchronization capabilities, verifying that the IEEE 1588v2 standard can address the frequency and phase synchronization requirements of mobile networks.
Ixia’s mobile backhaul testing solution accelerates packet-based mobile backhaul adoption and migration by providing a comprehensive testing solution that assesses the performance, scalability, and reliability of the network infrastructure prior to equipment upgrades and service turn-up.
Ixia and Alcatel-Lucent have engaged in rigorous test exercises to validate the performance and robustness of 1588v2 boundary and transparent clock implementations under traffic load, network failover, and scaled mobile backhaul network conditions. The demonstrations included a state-of-the-art 1588v2 implementation on Alcatel-Lucent’s 7705 Service Aggregation Router (SAR). Ixia’s IxNetwork application, running on highdensity 1GE load modules, was used to emulate the grandmaster clock and hundreds of 1588v2 slave clocks, trigger network failover conditions, and perform traffic generation and analysis.
Test measurements verified that the network implementation successfully achieved synchronization across hundreds of clocks while meeting traffic forwarding performance and QoS guarantees. The stability of the 1588v2 implementation was also verified during negative conditions and network failovers to ensure the reliability of network services.
It was demonstrated that 1588v2 can address the time and phase requirements of LTE TDD and multimedia broadcast multicast services (MBMS); and also provide a capability that is the foundation for highly-accurate network SLA monitoring.
As the cellular network becomes more dense and small cells are increasingly deployed, the need for broad synchronization distribution remains a crucial factor in an effective mobile network’s operation.
The test results provide an industry-first demonstration that a packet-based backhaul network can satisfy both timing synchronization requirements, as well as traffic forwarding performance and QoS guarantees for wireless services, under high-scale and volatile network conditions.
With the next-generation wireless network providing media-intensive data, video, and voice services, one of the major challenges for service providers is provisioning enough mobile backhaul capacity.
In a survey, 79% of service providers plan to move to a single IP/Ethernet mobile backhaul for carrying all traffic, and 150 operators were actively deploying a single (no TDM) all-IP/Ethernet backhaul in 2011 (Infonetics’ Mobile Backhaul Equipment and Services Report, March 26, 2012). This has been a “phased” migration that is due to the fact that unlike TDM, Ethernet was not originally designed to carry synchronous information and basic Ethernet 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 of migration is a hybrid implementation where IP/Ethernet backhaul is used for packet offload of data services while 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 IP/Ethernet network is used to backhaul all services. Before pursuing this final stage of migration, carriers must have confidence that timing over packet (ToP) technologies can satisfy the strict clock synchronization requirements of wireless standards. Timing synchronization is also critical in other network deployments, such as “smart grid” utility infrastructure.
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