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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
Call Control Function
Call Control Function
Call control is used in the switched AAL2 PVC operating mode only and is managed by the call agents.
The call agent performs the following functions:
• Analyzes signaling received from VISM cards and other call agents to monitor the status of all
endpoints and connections.
• Signals VISM cards and other call agents to set up and tear down calls.
• Reacts to fax, modem, alarm and other line conditions and events.
• Maintains a dial plan to locate the remote call agent using the dialed number.
• Negotiates profiles and codecs between the called and calling locations.
These functions require call agent communication with the VISM cards under call agent control and peer
call agents. Figure 3-10 shows the call agent communications links.
Figure 3-10 Call Agent Communications Links
The interface between the call agent and VISM cards is a gateway call control protocol generically
known as xGCP. The following gateway call control protocols are supported:
• Media Gateway Control Protocol (MGCP) 0.1 and 1.0
• Simple Gateway Control Protocol (SGCP) 1.5
• Simple Resource Control Protocol (SRCP)
SRCP enables the VISM card and the call agent to resynchronize. Synchronization occurs when the call
agent first assumes control of VISM or after the call agent loses communication with VISM.
All protocols use a UDP/IP connection between the call agent and the VISM cards. The IP address of
the call agent can be resolved in the following ways:
• Internal table which you set up with the CLI
• External domain name server (DNS)
You can configure VISM to use the internal table and external DNS in the following ways:
• Internal table only
• External DNS only
• Internal first and external second
• External first and internal second
Signaling
Network
C-ISUP
or SS7
Other Call
Agents
Other
MGX 8850
s
VISMs
MGX 8850
with VISM
Call Agent
Packet
Network
IP (xGCP)
VV
53241