The
circuit emulation service (CES) helps to solve the problem of insufficient
optical fiber resources in the access ring and allows TDM services to be
transparently transmitted across the pure packet mode.
At
the physical layer on the UNI side, the OptiX OSN equipment is interconnected
with a CE through the following physical channels for accessing CES services:
Channelized STM-1
E1
Figure 1 Networking
diagram of the CES
Emulation Mode
The
OptiX NG-SDH series equipment supports two types of CES services:
structure-aware TDM circuit emulation service over packet switched network
(CESoPSN) CES and structure-agnostic TDM over packet (SAToP) CES.
In
the case of CESoPSN CES:
The equipment senses the frame format, frame
alignment mode, and timeslot information in the TDM circuit.The equipment processes the overheads and
extracts the payloads in TDM frames. Then, the equipment loads timeslots to the
packet payload in a certain sequence. As a result, the services in each
timeslot are fixed and visible in packets.
In
the case of SAToP CES:
The equipment does not sense any format in the
TDM signal. Instead, it considers TDM signals as bit flows at a constant rate,
and therefore the entire bandwidth of TDM signals is emulated.The overheads and payloads in TDM signals are
transparently transmitted.
Service Type
CES
services are classified into UNI-UNI CES services and UNI-UNI CES services by
service implementation point.
UNI-UNI CES services
As shown in Figure
2, a single OptiX OSN NE completes access of TDM services.
Figure 2 UNI-UNI
CES services
UNI-NNI CES services
As shown in Figure
3, the OptiX OSN NEs set UNI-NNI CES services. In the case of a UNI-NNI CES
service, the OptiX OSN NEs access customer TDM services through E1 ports; CES
PWs are created between the OptiX OSN NEs to emulate end-to-end TDM services.
Figure 3 UNI-NNI
CES services
