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Cisco VISM Installation and Configuration Guide
Release 3.0, Part Number OL-2521-01 Rev. D0, June 2004
Chapter1 Overview of the VISM and VISM-PR Cards
VISM and VISM-PR Card Features
Operating Modes
The VISM/VISM-PR card performs in the following operating modes :
•Voice over IP (VoIP) switching/trunking
•Switched AAL1 switched virtual circuits (SVCs)
•Switched AAL2 SVC
•Switched AAL2 PVC—this mode is not supported in VISM Release 3.0
•AAL2 trunking
•VoIP and switched ATM AAL1 SVC
The VISM/VISM-PR card, in order to support the operating modes, supports connections to three major
interfaces:
•Voice TDM network
•ATM network
•Call agent—signaling (either CAS or CCS but not both) and call control
In VoIP switching, switched AAL2 PVC, AAL1 SVC, and AAL2 SVC modes, all three of these
interfaces are always present and active. In AAL2 tru nking mode, the inter face to the ca ll agent inte rface
is not present and the only active interfaces are to the TDM network and the ATM network.
The operating modes, combined with features you configure, are u sed by VISM cards in a wide variety
of telephony applications. For example:
•Provide many of the functions of a tandem (Class 4) switch. VISM can be used to replace, or
partially offload, a Tandem switch by directing calls over a packet network rather than the
conventional voice TDM network.
•Concentrate voice and data user services onto a single broadband circuit for transmission over the
packet network. In this application, VISM performs as a front end to a voice gateway.
•The VISM/MGX combination is used to concentrate voice (and fax/modem voiceband data) user
services over a preprovisioned AAL2 trunk. VISM passes bearer and signaling data across a p acket
network and does not perform call setup and teardown functions.

VoIP Switching and Switched AAL2 PVC Operating Modes

In VoIP switching mode and swi tched AAL2 PVC mode, VISM op erates und er the contr ol of a call agent
to set up and tear down calls. When a call is set up, VISM transports voice payloads over an ATM
network to the called station destination. VISM performs either as a voice gateway or as a multiservice
access front end to a voice gateway.
Note This document refers to the device that provides the interface between VISM and the telephone
Signaling System 7 (SS7) as a call agent. Other terms that describe the same device are Virtual
Switch Controller, Media Gateway Controller, and Gatekeeper.