This chapter presents the Cisco Voice Interworking Service Module (VISM) set of features and the solutions provided by this voice card, including Voice Over AAL2, Voice over ATM, and Voice over IP (VoIP) networks. This chapter shows you how to add, configure, display, and verify voice connections. It describes VISM clocking, including clocking options and configuration procedures.
Multiprotocol Label Switching (MPLS) is introduced, with the steps required to set up MPLS on the RPM. The MPLS section does not provide detailed configuration information; it is intended only as a guide for planning for MPLS in your network.
The RPM, including memory locations and port numbering, is also described, and the Cisco IOS command-line interface is introduced. Commands for configuring the RPM and for setting up the RPM ATM switch interface are explained. This chapter also discusses permanent virtual circuits (PVCs) on the RPM, including commands for creating and displaying these PVCs.
VISM Overview
The first key topic discussed in this chapter is the Cisco Voice Interworking Service Module (VISM). The VISM consists of a front and back card set designed to operate on the Cisco MGX 8250/8850-PXM1 switches for Releases 1.5 and 2.0. For VISM services on MGX 8230 switches, you must use VISM Release 2.0 or 2.1. The VISM provides interfaces to an ATM packet network and to TDM (time-division multiplexing) T1/E1 lines.
VISM Release 2.1 is a single-height Cisco MGX front card. As many as 24 cards can be installed in a Cisco MGX 8250 or Cisco MGX 8850 shelf, and as many as 8 cards can be installed in a Cisco MGX 8230 shelf. Each VISM supports either eight T1 lines or eight E1 lines. There are two hardware versions of the card—one for T1 lines and one for E1 lines. T1 and E1 lines cannot be mixed on a VISM card. (VISM is not supported on the Cisco MGX 8260 platform.)
A Cisco MGX 8850 Wide Area Edge Switch, when equipped with one or more VISM card sets, can transport digitized voice signals across a packet network. Thus, the VISM/MGX 8850 combination provides an interface or gateway between conventional voice TDM networks and networks based on packet-switching technology.
VISM employs the concept of operating modes, which permit it to be used in a variety of applications. Releases 1.5 and 2.0 have two operating modes—VoIP and AAL2 trunking. These modes support three major applications:
Switching—Using VoIP mode, this application provides the emulation of many of the functions of a tandem (Class 4) switch. In this application, VISM functions as voice gateway (also called a media gateway) to an IP network and performs call control in conjunction with a call agent. The call agent (also called a media gateway controller) initiates and controls the call control functions. VISM transmits the voice payload through a bearer circuit using VoIP and ATM AAL5 network protocols.
Multiservice Access with Call Control—This application also uses VoIP mode. In this application, the VISM/MGX 8850 combination is used to concentrate voice and user data services onto a single broadband circuit for transmission over the packet network, again using VoIP and ATM AAL5 techniques. As with the switching application, VISM can function with a call agent to perform call control. In this application, VISM can function as a front-end to a voice gateway.
AAL2 trunking—This application uses AAL2 trunking mode. In this application, a VISM/MGX 8850 combination is used to concentrate voice (and fax/modem) user services over a preprovisioned AAL2 trunk. VISM merely passes (tunnels) bearer and signaling data across a packet network. It plays no part in call setup and teardown.
VISM architecture provides the following benefits:
Technology flexibility that allows the incorporation of new or improved technology as it becomes available
Application flexibility such that it can be used in a range of situations, providing interoperability with a wide variety of equipment types
Modularity that allows equipment to be purchased and installed as it is needed in a step-by-step manner
Equipped with eight T1 or E1 ports, an array of Digital Signal Processors (DSPs), an HDLC (High-Level Data Link Control) framer, and a broadband interface to the packet network, VISM is ideally suited to processing high-density digital voice circuits providing compression, echo cancellation, dejittering, and packetization on-the-fly.