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Cisco VISM Installation and Configuration Guide
Release 3.0, Part Number OL-2521-01 Rev. D0, June 2004
Chapter 3 VISM Functional Description
ATM Voice Data Processing Function
Figure 3-9 shows the packetization process for AAL2 cells.
Figure 3-9 AAL2 Cell Packetization and Transmission
Transporting Voice Cells with AAL2 Trunking
The AAL2 trunking operating mode transports voice cells with up to 64 AAL2 trunks. The CID/virtual
channel identifier (VCI) for each DS1/DS0 pair is preprovisioned, which ensures that DS0 voice streams
are automatically transported over the appropriate trunk.
For CAS applications, voice cells and CAS signaling are transported across the AAL2 trunk. If a channel
is configured for CCS signaling, the signaling is transmitted by extracting HDLC frames and forwarding
them over preprovisioned AAL5 virtual circuits (the voice cells are still transmitted using AAL2).
VISM does not support any call control functions with the AAL2 trunking operating mode. VISM passes
signal traffic across the trunk.
Alarm and packetization handling are the same as in the switched AAL2 PVC operating mode. Refer to
the “Transporting Voice Cells with Switched AAL2 PVC” section on page 3-13.
Transporting Voice Cells with Switched AAL1 SVC
VISM interacts with a call agent using an xGCP protocol over AAL5 control PVCs. In the switched
AAL1 SVC operating mode, the bearer path is VoAAL1 and the bearer connections are SVCs. VISM
dynamically sets up and tears down bearer connections.
CID LI UUI HEC
CPS-INFO
(variable length - from SSCS)
CPS Packet Payload
CPS
Packet Header
OSF
S
N
P Contains zero, one or more (complete or partial) CPS Packets
Pad
Start
Field
CPS-PDU Payload
CPS - PDU
CPS - Packet
6 1 1 Bits
Bits
0 - 47 bytes
8655
1 - 45/64 bytes
ATM
Header
ATM
Header
ATM Payload
(CPS-Packet may overlap
one or two ATM cell boundaries)
ATM Payload
(CPS-Packet may overlap
one or two ATM cell boundaries)
5548 48
53240
. . . .