Alcatel-Lucent 7705 Service Manual page 152

Circuit Emulation VLL (Cpipe) Services
Structured T1/E1 CES with CAS
Structured circuit emulation with CAS is supported for T1 and E1 circuits.
Structured CES with CAS service is configured by choosing cesopsn-cas as the
vc-type when creating a Cpipe service. The DS1 or E1 service on the port associated with
the Cpipe SAP should be configured to support CAS (via the signal-mode {cas}
command) before configuring the Cpipe service to support DS1 or E1 with CAS. Refer to
the 7705 SAR OS Interface Configuration Guide for information on configuring signal
mode.
For n × 64 kb/s structured circuit emulation with CAS, the implementation is almost
identical to that of CES without CAS. When CAS operation is enabled, timeslot 16 cannot
be included in the channel group on E1 carriers. The CAS option is enabled or disabled at
the port level; therefore, it applies to all channel groups on that E1 port.
The packet size is based on 16 frames per packet for E1 when CAS is enabled and is not
user-configurable. For example, if the number of timeslots is 4, then the payload size is
64 octets. This 16-frame fixed configuration is logical because an E1 multiframe contains 16
frames; therefore, proper bit positioning for the A, B, C, and D CAS signaling bits can be
ensured at each end of the pseudowire.
number of timeslots.
For CAS, the signaling portion adds (n/2) bytes (n is an even integer) or ((n+1)/2) bytes (n is
odd) to the packet, where n is the number of timeslots in the channel group. Note that you do
not include the additional signaling bytes in the configuration setting of the TDM payload
size. However, the operating system includes the additional bytes in the total packet payload,
and the total payload must be accounted for when setting the service-mtu size. Continuing
the example above, since n = 4, the total payload is 64 octets plus (4/2 = 2) CAS octets, or
66 octets. Refer to
CES fragmentation is not supported.
Note: If you configure the service-mtu size to be smaller than the total payload size (payload
plus CAS bytes), then the Cpipe will not become operational. This must be considered if you
change the service-mtu from its default value.
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Table 20
Figure 23 to see the structure of the CES with CAS payload.
shows the payload sizes based on the
7705 SAR OS Services Guide