Tuesday, June 22, 2010

Requirement of Synchronous Ethernet aka syncE

From the last two decades Ethernet is becoming the dominant technology in service provider as well as in Telecom domain. Being it’s asynchronous behavior, providers faced lot of issues to integrate it with the existing TDM technologies. TDM mainly works on clock which means synchronization is required among all the nodes.

Now service providers are moving towards the Next Generation Network aka NGN or Packet Converge Network aka PCN. The challenge which they are facing is the clock synchronization between the TDM networks over Ethernet network. By nature Ethernet doesn’t provide any clock mechanism but thanks to synchronous Ethernet aka syncE which helps to make communication possible between TDM to TDM cloud over packet core network.
In synchronous Ethernet frequency is transferred over physical level than using any upper layers. Every syncE network equipment contains an internal clock called Ethernet Equipment Clock aka EEC. By doing this master slave interconnected tree is built and clock is passed from one node to another.  One primary reference clock (PRC) is used which normally serves the clock to the equipments.

One more category of clock is used which is also known as Synchronous Supply Unit (SSU). SSU are mainly required for given three reasons:-
  1. Reduce the jitter in clock.
  2. Act as a node clock.
  3. Serve the clock in case of failure of PRC.

According to ITU-T Rec. 803 standard, maximum depth of EEC could go up to 60 EEC nodes. The hierarchy is shown in depicted picture:-

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