Your 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.
“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.”
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 1588v2 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, for RF generation and clocking, and 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).
The inability to maintain clock synchronization under heavy traffic loading increases the chances of failed call setups, failed handover, data re-transmission (leading to slow download and uploads) – in essence poor user experience of the network service.
Because of the explosion in data volumes from LTE, LTE-A and moving to 5G the Network needs a reliable and highly accurate method of transferring time, this is the 1588v2 Precision Time Protocol (PTP) mentioned above.
Standards in network timing have become so important, limitations have been implemented to ensure proper functionality. The IEEE Standard under G.8271.1 states that in your Mobile Backhaul Network the Total Time Limit (TE) from the GM (Grand Master Clock) all the way to the slave clock located at the BTS (Mobile Base Station), MUST NOT exceed 1.5µs and consequently the handover between the Boundary Clock to the last switch which MUST NOT exceed 1.1µs (this is because the BTS uses 400ns) and hence why the GM to the BTS is a total Time Limit of 1.5µs.
If the Total Time Limit does exceed 1.5µs, the slave clock at the BTS will not be able to recover the signal and lock the synchronization from the GM. If this occurs the slave clock at the BTS will be on holdover and the mobile network will be asymmetric – Not Synchronized!
CoverTel Services is a leader in Mobile Backhaul Asymmetric Testing. We have worked with one of Australia’s largest Mobile Operators to test their network after they had upgraded their network from NTP to PTP. This upgrade entailed a number of hardware & network changes including Switches, Boundary Clocks, Interconnections and Fibre Optic cable runs which, in turn, affected the PTP flow along the mobile backhaul network.
CoverTel Services worked with the Mobile Operator to test the Asymmetry in the Network and characterise individual error contributions — including cTE, dTE and max|TE| — to make it compliant with the IEEE standard and to ensure their network delivers the performance their customers demand.