Overview of the VISM and VISM-PR Cards

This section introduces the Voice Interworking Service Module (VISM/VISM-PR) cards and software modules. It includes the following topics:

New Features in Release 3.3

Table 1-1 summarizes the new features in VISM/VISM-PR Release 3.3 and provides links to the corresponding sections in the documentation.

Table 1-1 VISM/VISM-PR Release 3.3 Features
Feature	Summary
V.110	VISM-PR can support V.110 data traffic transport in AAL2 trunking mode. See the "V.110" section on page 9-6.
1560/980 Hz Modem Tone Detection	VISM-PR card can detect the 1560/980 Hz modem tone in the VoIP switching mode. See the "1560/980 Hz Modem Tone Detection" section on page 9-8.
Voice Quality Statistics	VISM-PR can collect real-time voice quality statistics to assist with network analysis and troubleshooting system performance. See the "Voice Quality Statistics" section on page 9-59.
ATM Fax Relay	VISM-PR can transport fax in AAL2 trunking mode using less bandwidth than fax pass through. See the "ATM Fax Relay" section on page 9-11.
Filtering Traps	To reduce the load on Cisco WAN Manager (CWM), you can filter the VISM-PR traps while the card is being configured. See the "Trap Filtering" section on page 9-83.
VISM-PR Bulk Statistics Upload to CWM	You can upload history statistics data collected on a VISM-PR card to CWM. See the "VISM-PR Bulk Statistics Upload to CWM" section on page 9-87.
Display History Statistics	VISM and VISM-PR can collect history statistics. See the "History Statistics Collection" section on page 9-62.
Display All Static Configuration	On the VISM/VISM-PR card, you can use the dspall command to display static configurations, run-time statistics, and real-time dynamic data. See the "Static and Real-Time Configuration Display" section on page 9-69.
TDM Companding Law	VISM-PR supports nonstandard law companding on the TDM interface. See the "TDM Companding Law Configuration" section on page 9-118.
G.729a Codec with 20 ms	VISM/VISM-PR cards contain a new custom profile, 210, with upspeed to support G.729a with a 20-millisecond (ms) packetization period. See the "G.729a Codec with 20 ms Packetization Period" section on page 9-5.
Preferred Routes	In a PNNI network with a large number of SPVCs, the Cisco MGX 8850 (PXM1E and PXM45) can route SPVCs and SPVPs over pre-defined trunk routes in a PNNI group. See the "Preferred Routes" section on page 9-17.
Priority Bumping	On the VISM-PR card, you can set up high-priority connections when the available resources on the links are not enough for the call to be routed. See the "Priority Bumping" section on page 9-23.
Bearer IP Address Ping	On the VISM/VISM-PR card, you can ping both the controller traffic IP address and the bearer traffic IP address. See the "Bearer IP Address Ping" section on page 9-41.
Call Throttling	VISM-PR card supports call throttling to maintain the stability of the card when the call rate exceeds the maximum allowable limit. See the "Call Throttling" section on page 9-42.
Programmable CAS Bit Mapping	The CAS mapping feature allows you to map the output ABCD bits to input ABCD bits on a signaling channel on the VISM-PR card instead of using a PBX or another external device. See the "Programmable CAS Bit Mapping (ABCD CAS bits)" section on page 9-119.
E1 Trunk Conditioning	You can enable and disable trunk conditioning on a T1 and an E1 line. See the "Line Trunk Conditioning" section on page 9-124.
Bandwidth Utilization Enhancements	Bandwidth utilization features include •ATM Bandwidth Reuse for Non-overlapping Traffic •Dynamic PVC Bandwidth Management •Channel Current Peak Rates See the "Bandwidth Utilization Enhancements" section on page 9-33.
AIS Propagation Control	The purpose of this feature is to prevent the CPE from dropping calls when a network link failure is temporary. See the "AIS Propagation Control" section on page 9-29.

Card Description

The VISM/VISM-PR card, in combination with a Cisco MGX 8000 Series platform, enables telephone calls on conventional time-division multiplexed voice circuits to be transported over Asynchronous Transfer Mode (ATM) and VoIP packet-switched networks.

The VISM card is a single height card designed to operate in the following platforms:

The VISM-PR card is a single height card designed to operate in the following platforms:

You can use the VISM-PR card in combination with any of the following MGX 8000 Series switch Processor Module cards:

Table 1-2 lists the configuration requirements for VISM/VISM-PR in combination with the MGX 8000 Series switches and supported processor modules.

Table 1-2 VISM/VISM-PR and MGX 8000 Series Switch Support
VISM Module	Cisco MGX 8230	Cisco MGX 8830 (PXM1E)	Cisco MGX 8250 with PXM1	Cisco MGX 8850 with PXM1	Cisco MGX 8850 with PXM1E	Cisco MGX 8850 with PXM45	Cisco MGX 8880 (PXM45)
MGX-VISM-8T1	Yes	No	Yes	Yes	No	No	No
MGX-VISM-8E1	Yes	No	Yes	Yes	No	No	No
MGX-VISM-PR-8T1	Yes	Yes	Yes	Yes	Yes	Yes	Yes
MGX-VISM-PR-8E1	Yes	Yes	Yes	Yes	Yes	Yes	Yes

For information on installing and maintaining the PXM1, PXM1E, and PXM45 cards, refer to the Cisco MGX 8850 (PXM1E/PXM45), Cisco MGX 8950, and Cisco MGX 8830 Hardware Installation Guide, Release 2 through 5.

Note You cannot use the VISM card in combination with either the PXM1E or the PXM45 card.

Card Types

VISM and VISM-PR cards are installed in Cisco MGX 8000 Series switches as front cards and corresponding back cards—card sets.

Note Other physical configurations are supported while using the Service Resource Module (SRM) and 1:N redundancy. For more details, see the "Card Features" section.

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AX-RJ48-8T1—Supports eight T1 lines using RJ-48 connectors; use with a T1 front card.

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AX-RJ48-8E1—Supports eight E1 lines using RJ-48 connectors; use with an E1 front card.

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AX-SMB-8E1—Supports eight E1 lines using SMB connectors; use with an E1 front card.

The VISM or VISM-PR card and MGX 8000 Series switch combination provides an interface, or voice gateway, between conventional TDM networks and packet-switched networks (see Figure 1-4).

Cisco MGX 8000 Series switch Processor Module cards—PXM1, PXM1E, and PXM45—connect to the packet network. These cards communicate with a VISM/VISM-PR card through the switch midplane cellbus. For more information on the MGX 8000 Series switch midplane cellbus, see the documents listed in the "Documentation" section on page xxiii.

Card Service Types

Note

CBR is not supported with a combination of a PXM1 and either an RPM card or external router.

VISM/VISM-PR card connections with the RPM-PR require the nrt-VBR3 service type.

Card Characteristics

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Flexibility that allows the incorporation of new or improved technology as it becomes available

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Application flexibility that allows VISM/VISM-PR to be used in a range of situations that provide interoperability with a wide variety of equipment types

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Modularity that allows equipment to be purchased and installed as it is needed for scalability

Figure 1-5 shows a simplified diagram of the VISM/VISM-PR architecture and major components.

The card is broadly divided into a TDM side and an ATM side. The T1/E1 framers, the array of DSPs, and the HDLC processor support the TDM side. The ATM adaptation layer (AAL) and the segmentation and reassembly (SAR) sections support the ATM side.

VISM/VISM-PR is under the control of two independent processors. The main processor performs the control tasks—configuration, call setup and teardown, and management. The second processor, the data mover, handles the moving and processing of the voice and voiceband data traffic through the system.

The VISM/VISM-PR card itself does not contain any ports for connecting management stations. Workstations, PCs, or terminals that are used to manage VISM/VISM-PR must be attached via the PXM card, which provides both serial EIA/TIA-232 and Ethernet ports.

Card Features

VISM/VISM-PR cards process high-density digital voice circuits and provide dynamic compression, echo cancellation, dejittering, silence suppression, and packetization. The VISM/VISM-PR card uses the following features, each of which you can configure:

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Voice over ATM (VoATM) using AAL2 cells—No Logical Link Control/Subnetwork Access Protocol (LLC/SNAP) encapsulation.

Note

Subcell multiplexing is not supported for AAL2 switched virtual connections (SVCs).

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Extended Superframe (ESF) framing with or without cyclic redundancy check (CRC).

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Programmable 24, 32, 48, 64, 80, 96, 112, or 128 ms tail delay near-end echo cancellation (ECAN).

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Voice activity detection (VAD) and comfort noise generation (CNG) using variable threshold energy (Cisco proprietary).

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Call agent Simple Gateway Control Protocol (SGCP), Version 1.0, 1.1, or 1.5; SGCP 1.1+ or 1.5; Media Gateway Control Protocol (MGCP) 0.1 and 1.0; and Trunking Gateway Control Protocol (TGCP) 1.0.

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Backhauling channel-associated signaling (CAS) to a call agent using xGCP (backhauling can be accomplished with any supported SGCP and MGCP protocol).

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Backhauling Primary Rate Interface (PRI) signaling through Reliable User Datagram Protocol (RUDP) to a call agent.

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Full continuity testing (COT). This testing supports origination and terminating loopback and transponder COT between VISM and the central office on the TDM side.

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1:N cold redundancy. In switching modes, calls do not persist during a switchover. In AAL2 or AAL5 trunking mode, calls are not persistent and are dropped during a switchover.

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Graceful shutdown of ongoing voice calls when the VISM/VISM-PR is taken out of service for maintenance or other reasons. Forced shutdown is also supported.

Redundancy and Bulk Distribution

With or without bulk distribution, redundancy allows for the spare VISM/VISM-PR card to automatically take over the functions of a failed VISM/VISM-PR card.

After a VISM/VISM-PR card switches from standby to active state, executing the dspcds command on the PXM shows the new active and standby cards.

For example, the VISM card in slot 1.1 (with a PXM1 card) went from standby to active.

However, when you change cards to the new active VISM/VISM-PR card using the cc command, the display shows the active card as standby.

When the failed card is repaired, switching back to the repaired card is not automatic. You must manually change the repaired card back to the active state with the command line interface.

Redundancy for VISM/VISM-PR cards with or without bulk distribution can be provided through the following Service Redundancy Module (SRM) card types:

VISM/VISM-PR redundancy is cold redundancy in which ongoing calls do not persist during switchover in switching modes. In AAL2 or AAL5 trunking mode, calls are not persistent and are dropped during a switchover.

See Table 1-3 for the support level for 1:N service module redundancy (N = 1 through 11).

Note With SRM-3T3/C cards, 1:N redundancy is supported for up to 9 cards only (slots 9 and 10 are not supported) on PXM1 with SRM bulk distribution active.

Table 1-3 Service Module Redundancy
Front Card Model Number	Redundancy Support
MGX-VISM-8T1	1:N redundancy (bulk mode support for T1 lines only)
MGX-VISM-8E1	1:N redundancy (bulk mode support for E1 lines only)
MGX-VISM-PR-8T1	1:N redundancy (bulk mode support for T1 lines only)
MGX-VISM-PR-8E1	1:N redundancy (bulk mode support for E1 lines only)

Note You can use a VISM-PR card as a redundant card for a VISM card, but a VISM card cannot be used as a redundant card for a VISM-PR card.

Redundancy with Bulk Distribution

Redundancy with bulk distribution requires a spare VISM/VISM-PR card to be installed. The system uses the three T3 ports of the SRM back card instead of the normal T1 lines on the VISM/VISM-PR back cards.

In a redundancy configuration VISM/VISM-PR cards in bulk distribution mode do not require any back cards.

The TDM voice data transmitted or received over the T3 ports is distributed to the VISM/VISM-PR card as if it had been received over T1 back card ports in the normal manner. This feature reduces the number of physical lines required for VISM support, but it requires that external equipment multiplex and demultiplex the T1 data onto the T3 lines.

Redundancy Without Bulk Distribution

Redundancy without bulk distribution also requires a spare VISM/VISM-PR card equipped with a VISM/VISM-PR T1 redundant back card. In this arrangement the VISM/VISM-PR cards require and use their normal T1 back cards.

In VoIP modes, redundancy can also be configured at the ATM permanent virtual circuit (PVCs) level. Two separate connections (PVCs) can be set up, each using a different destination physical port and each routed to a separate router. Configure one PVC as active and the other as standby. Both PVCs are monitored by heartbeat Operation, Administration, and Maintenance (OAM) F5 loopback cells every 200 ms. If three consecutive OAM cells are lost, the PVC fails, and only the remaining PVC is active. A PVC recovers automatically when five consecutive OAM cells are received while the PVC remains in standby mode (no automatic fallback to active state is provided).

Operating Modes

To support these operating modes, the VISM/VISM-PR card supports connections to the following three major interfaces:

In VoIP switching, switched AAL2 PVC, AAL1 SVC, and AAL2 SVC interfaces are always present and active. In AAL2 trunking mode, the interface to the call agent interface 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, can be used by VISM/VISM-PR cards to

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Provide many of the functions of a tandem (Class 4) switch. VISM/VISM-PR can be used to replace, or partially off load, a tandem switch by directing calls over a packet network rather than over the conventional voice TDM network.

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Concentrate voice and data user services onto a single broadband circuit for transmission over the packet network. In this application, VISM/VISM-PR performs as a front end to a voice gateway.

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Use the VISM/MGX combination to concentrate voice (and fax/modem voiceband data) user services over a preprovisioned AAL2 trunk. VISM/VISM-PR passes bearer and signaling data across a packet network and does not perform call setup and teardown functions.

VoIP Switching and Switched AAL2 PVC Operating Modes

In VoIP switching mode and switched AAL2 PVC mode, VISM/VISM-PR operates under the control of a call agent to set up and tear down calls. When a call is set up, VISM/VISM-PR transports voice payloads over an ATM network to the called station destination. VISM-PR 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/VISM-PR 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.

Figure 1-6 shows the major functional blocks and interfaces for the VoIP switching and switched AAL2 PVC operating modes.

Figure 1-6 VISM Block Diagram for VoIP Switching and Switched AAL2 PVC Operating Modes

The CAS path on the TDM side is embedded in the voice stream but is separated at the bearer processing function. CAS then joins the CCS path for CAS/CCS processing and is backhauled to the call agent. The path between the call agent and bearer processing, via a connection handling function, is for call setup and teardown.

Voice TDM Network Interface

The voice payload path is shown as a solid line along the bottom of Figure 1-6. All external TDM streams arrive and depart on the T1/E1 lines. Depending on the application, these streams consist of voice bearer channels (with or without CAS) and separate CCS channels (if CCS is used). The TDM line-handling function provides the physical layer interface, which includes framing, line codes, clocking, loopbacks, physical alarms, and so forth. Bearer channels, including CAS, are sent to the bearer processing function. CCS channels are sent to the CAS/CCS processing function.

Further processing of the bearer channels is performed by the DSPs. This processing provides echo canceling, compression, A/Mu law conversion, silence suppression, and fax/modem handling. If CAS is present, signaling bits are extracted at the DSP stage and sent to the CAS/CCS processing function.

ATM Network Interface

The ATM network interface receives the processed DS0 voice streams and prepares them for transport over a packet network. The voice streams are divided into specific sample periods (for example, 5 ms or 10 ms) and formatted into service-specific convergence sublayer (SSCS) packets appropriate for transport over the ATM network. The available transport methods are VoIP (using AAL5) and voice over AAL2. Processing of the ATM packets further segments the voice payload into ATM cells for transport over the network by means of a SONET port on the PXM card.

Call Agent Interface

The call agent interface consists of CAS or CCS and call control. The path between the call agent and bearer processing, through a connection handling function, is for call setup and teardown.

The CAS path on the TDM side is embedded in the voice stream (bearer DS0s) and is separated at the bearer processing function. CAS (robbed bits, digits, and tones) is passed to the CAS/CCS processing function where it is passed (backhauled) to the call agent under the control of the call agent. The mechanism for communicating between VISM/VISM-PR and the call agent is gateway control protocols:

The separate CCS path channels are passed to the CAS/CCS processing function and backhauled to the call agent. CCS is transported as ISDN Q.931 messages both on the TDM side and on the call agent side. On the TDM side, the messages are carried in the Q.921 layer protocol (which terminates at the VISM/VISM-PR card). On the call agent side, communication with the call agent consists of Q.931 messages encapsulated in RUDP/UDP/IP packets. The Q.931 connection is terminated at the call agent and not at the VISM/VISM-PR card.

The call control path uses MGCP, TGCP, SGCP, and SRCP for call setup and teardown. Because signaling and call control are so intertwined, both call control and CAS use the same path and protocol for the VISM/VISM-PR card-to-call agent communications.

AAL2 Trunking Operating Mode

In the AAL2 trunking operating mode, the VISM/VISM-PR card serves as an access to one or more trunks to preprovisioned locations. VISM/VISM-PR can be used at both ends of the trunk or at one end with a compatible device at the other.

In AAL2 trunking mode, VISM/VISM-PR plays no part in call setup and teardown. Other network elements handle call control while VISM/VISM-PR handles voice transport over the trunks. Figure 1-7 shows the major functional blocks for the AAL2 trunking operating mode.

The AAL2 trunking mode is less complex than the VoIP switching or AAL2 PVC switched modes because call control is not involved, and a call agent is not needed.

The voice bearer path is treated in the same manner as in the VoIP switching and AAL2 PVC modes, except that only preprovisioned AAL2 PVCs are available for transport of voice over the trunks. CAS data is transported over the ATM network in the same AAL2 trunk as Type 3 messages. The CCS data can also be transported over the ATM network in a separate AAL5 PVC.

VoIP Trunking Operating Mode

The Voice over IP (VoIP) trunking feature allows the VISM/VISM-PR to connect to the PBX, or central office digital systems, using T1/E1 digital interfaces. The TDM bit stream is converted into RTP packets after echo cancellation and compression. These packets are transported over the IP network.

No call agent is required for setting up and tearing down calls. You must configure the DS0 circuits. An ATM link joins VISM/VISM-PR card and the first router. After that, the connection is IP only. VISM/VISM-PR and the router can have one or more PVCs to transport the data. You have the option to configure a PVC for bearer or control. If the PVC is configured as bearer and no control PVC exists, then PRI signal traffic and bearer traffic go through this PVC. If you configure separate PVCs for control and bearer, PRI signaling goes through control traffic only. You can modify some of the connection parameters after the PVC is added.

CAS is transported to the far-end by means of a Cisco proprietary format, not named signaling events (NSEs). PRI is transported over RUDP to the far-end once the trunk is provisioned between the originating and terminating VISM/VISM-PR cards.

PRI transport is handled like PRI backhaul, except that the PRI traffic is sent to a remote gateway instead of to a call agent. You can configure one line for PRI trunking and another line for PRI backhauling.

You must provision the Link Access Protocol D Channel (LAPD) trunk when configuring one line for PRI trunking and another line for PRI backhauling.

You must configure a line number, remote gateway IP address, local UDP port, and remote gateway UDP port, and then open a trunk. You must then configure the D channel as a trunk or backhaul:

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To configure the D channel as trunk, use the addlapdtrunk command before the addlapd command. If the addlapd command has been previously executed for that line, the addlapd command is rejected.

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To configure the D channel as backhaul, use the addses command before the addlapd command. If you do not configure either trunk or session, the addlapd command is rejected.

AAL1/AAL2 SVC Operating Mode

The AAL1 and AAL2 switched virtual circuit (SVC) operating modes are supported for VISM-PR cards.

Each AAL1/AAL2 SVC operating mode requires you to use a PXM1E or PXM45 in your MGX 8000 Series switch chassis.

AAL1 SVC is supported with the G.711 codec and clear channel. VAD is not supported in combination with AAL1 SVCs. CAS is not supported in combination with SVCs.

AAL2 SVC is supported with the G.711, G.726, G.729a, and G.729ab codecs and profiles 1, 2, 3, 7, 8, 100, 101, 110, and 200.

Note In AAL2 SVC mode, the AAL2 subcell multiplexing capability is not supported.

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