Welcome to May 2011 issue of Creanord EchoNEWS. EchoNEWS aims to keep you informed of developments at Creanord and in the fields of SLA assurance, automated Ethernet service delivery and OAM (Operations, Administration and Maintenance).
In this issue we look at how the evolution towards LTE and 4G not only changes the mobile backhauls but also poses challenges for a crucial part of the backhauls - the clock synchronization.
IEEE 1588v2 and Ethernet in Mobile Backhaul Networks
The evolution towards LTE and 4G supporting higher bandwidths for mobile data and video applications is forcing mobile backhauls to adapt to new requirements. In order to support the growing bandwidth demands cost efficiently, mobile backhauls are in a transition from synchronized TDM networks to asynchronous Ethernet. This evolution is also impacting how the time synchronization is implemented within the backhaul networks.
Timing has traditionally been delivered very accurately and reliably over TDM, but the migration to Ethernet based networks caused a disruption since packet networks are inherently asynchronous and do not have any inherent mechanism for providing highly accurate synchronization. There are several approaches to addressing this challenge, with Precision Time Protocol (PTP) - IEEE 1588v2 currently leading the way. The standard has been deployed by over 50 major operators globally.*
The IEEE 1588v2 synchronizes the local slave clock on each network device with a system Grandmaster clock. It uses traffic time-stamping to deliver very high accuracies of synchronisation which is needed to ensure the stability of base station frequency and handovers. The timestamps between master and slave devices utilize specific PTP packets.
*Mobile Backhaul Equipment and Services Report, Infonetics Research. September 2010.
Benefits of the IEEE 1588v2
The transmission of the clock information over Ethernet network eliminates the need for alternative mechanisms, such as GPS. The 1588v2 solution transmits dedicated timing packets, which flow along the same paths with the data packets, reducing the cost of synchronization and simplifying implementation.
The number of cell sites will increase due to the need for higher signal-to-noise ratio to support the increase in bandwidth delivered to the customers - making this cost reduction welcome news for operators.
Despite that the IEEE1588v2 systems add a small amount of traffic to the network it has many advantages. For example the systems work in the data path, which is the most redundant and resilient part of the network. This makes the solution less vulnerable to disruptions. In addition multiple transmission paths automatically reduce redundant clock system costs.
Challenges resolved by EchoVault
The 1588 protocol works on the assumption that the connection between master and slave clock is symmetric (i.e. it expects that the Packet Delay from Master to Slave and Slave to Master is the same). If this is not the case, packet delay variation is easily introduced and deriving accurate frequency and phase information is a challenge.
GSM, WCDMA, and CDMA2000 require frequency accuracy of 0.05 ppm (parts per million) at the air interface. CDMA2000 requires time synchronisation at the ± 3 µs level (± 10 µs worst case) and WCDMA TTD (Wimax) mode requires accuracy of ± 1.25 µs between base stations.
Low latency network built with EchoVault let's you sleep well at night by providing highly accurate measurements for securing that your network KPI’s meet the IEEE 1588v2 requirements and the accuracy of the PTP. Contact us and we'll help you add performance and quality to your Ethernet based mobile backhaul.