PTP: Cable applications
The Mobile Backhaul is intrinsically complex. It has to support legacy technologies like circuit switching to carry 2G/3G voice, as well as packet-based technologies and topologies to transport data. Today’s mobile networks are heavily data centric and as demand grows for real-time services and the streaming and downloading of video, Network Operators around the globe are increasingly migrating to an Ethernet-based IP backhaul. Not only is Ethernet compelling on economic and network scalability grounds, it can carry both frequency and time synchronization - essential to transporting a diverse traffic mix.
To accommodate the soaring demand for broadband data services, 4G/LTE-A is being rolled out to deliver more bandwidth within the limited frequency spectrum, reduce latency and improve seamless roaming. However, 4G/LTE-A base stations need highly accurate time and phase synchronization to ensure smooth handovers between neighboring cells which enable consumers to get the Quality of Service they expect.
Technologies exist to achieve this: Synchronous Ethernet (or SyncE) for physical-layer frequency synchronization, and 1588 Precision Time Protocol (PTP) and Network Time Protocol (NTP) for packet-layer frequency time synchronization. The accuracy requirements for time and phase synchronization are very strict, typically +/-50ppb for RF generation and clocking, and +/-3us for phase synchronization between neighboring cells. GPS can also be used for synchronization, however GPS installations need outside antennas with clear sight of satellites (often difficult to achieve in urban environments), and suffer from an inherent lack of security (susceptible to jamming and spoofing).