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Networks and Services: Carrier Ethernet, PBT, MPLS-TP, and VPLS by Mehmet Toy

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Chapter 9: Circuit Emulation Services (CES)

9.1 Introduction

A pseudowire is an emulation of a native service over a packet switched network (PSN). The native service may be low rate TDM, SDH/SONET, while the PSN may be Ethernet, MPLS, or IP. Especially, in mobile backhaul locations, equipment with TDM and SONET/SDH interfaces are common. The CESoETH (CES over Ethernet) is the solution to provide low cost Ethernet transport to these locations.

The CESoETH is offered at UNI. As operators begin offering CESoETH at locations outside their footprints, the service will be offered at ENNI as well.

In CES, data streams are converted into frames for transmission over Ethernet. At the destination site, the original bit stream is reconstructed when the headers are removed, payload is concatenated, and clock regenerated, while ensuring very low latency. The MEN behaves as a virtual wire that is an application layer function as described in Chapter 5.

When the TDM data is delivered at a constant rate over a dedicated channel, the native service may have bit errors, but data is never lost in transit. All PSNs suffer to some degree from packet loss, and this must be compensated when delivering TDM over a PSN.

The standard TDM pseudowire operating modes are CESoPSN, Structure-Agnostic TDM over Packet (SAToP), TDMoIP, and HDLCoPSN (HDLC emulation over PSN).

In SAToP [3], TDM is typically unframed. When it is framed or even channelized, the framing and channelization structure are completely disregarded ...

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