Since the beginning of the end of the TDM network, carriers across the globe have been transitioning traditional telecommunications services to Ethernet and IP. And because those services are inherently connection oriented, as they had to be when the only network in town was circuit switched, it was necessary to find a method to make the Ethernet network behave like the TDM network. For T1’s that method is pseudowire. But even if the wire is virtual, the reliability and scalability of pseudowire is as real as that unobtrusive repeater housing on a dusty country road. Over the next three weeks we’re going to review three key features of a good T1 pseudowire system – synchronization, protection, and troubleshooting. With those three bases covered, your customers will never notice that you’re delivering SONET-grade T1’s via an Ethernet network.
For those in the know, synchronization is the first item of discussion when the topic of PWE comes up. Synchronization put the “S” in SONET, after all, and where lies synchronization in a world without SONET? There are exotic answers ranging from 1588v2 to Synchronous Ethernet (SyncE), but in Calix’ experience, simple timing options such as differential and adaptive timing are sufficient for delivery of SONET grade T1s through the access network. Adaptive timing is analogous to the “line timing” in the SONET world. The PWE system monitors timing differences between incoming PWE packets and forwards those packets at the same interval to ensure synchronization is preserved end to end. With differential timing, the system is synchronized by a local BITS clock and the timing of incoming PWE packets is synchronized to the BITS clock. Neither of these methods requires complex new timing mechanisms, and are interoperable with existing BITS infrastructure everywhere.
So keep it simple – look for low cost, proven solutions that transform your network with the least amount of work.
Next week: Service assurance. Making your PWE services as robust as possible.
