Alcatel-Lucent 7705 Service Manual page 142

Circuit Emulation VLL (Cpipe) Services
Structured Mode (CESoPSN)
Structure-aware circuit emulation is used for the transport of structured TDM, taking at least
some level of the structure into account. By selecting only the necessary n × 64 kb/s
timeslots to transport, bandwidth utilization is reduced or optimized (compared to a full DS1
or E1). Full DS1s or E1s can be transported by selecting all the timeslots in the DS1 or E1
circuit. Framing bits (DS1) or FAS (E1) are terminated at the near end and reproduced at the
far end.
The 7705 SAR supports CESoPSN with and without CAS for DS1 and E1.
When CESoPSN with CAS is selected, the ABCD bits are coded into the T1 or E1
multiframe packets, transported within the TDM PW, and reconstructed in the T1 or E1
multiframe at the far end for each timeslot.
Channel Associated Signaling (CAS) includes four signaling bits (A, B, C, and D) in the
messages sent over a voice trunk. These messages provide information such as the dialed
digits and the call state (whether on-hook or off-hook).
The mechanism for E1 CAS is described in ITU-T G.732. When configured for E1 CAS,
timeslot 17 carries the signaling information for the timeslots used for voice trunking. Each
channel requires four signaling bits, so grouping 16 E1 frames into a multiframe allows the
signaling bits for all 30 channels to be trunked.
As shown in
alignment, alarm indication, and CRC. For Frame 0, timeslot 17 is reserved for multiframe
alignment bits. For the remaining 15 frames, timeslot 17 contains ABCD bits for two
channels.
Note: For E1 CAS, timeslots are numbered 1 to 32 on the 7705 SAR.
For T1 CAS, the signaling bits are transferred using Robbed Bit Signaling (RBS), where the
least significant bit in the channel is used periodically to transport these bits instead of voice
data.
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Figure 20, timeslot 1 of all frames within the E1 multiframe is reserved for
7705 SAR OS Services Guide