Cisco Unified CallManager System Guide, Release 4.2(3)
Understanding Cisco Unified CallManager Voice Gateways
Downloads: This chapterpdf (PDF - 397.0KB) The complete bookPDF (PDF - 5.08MB) | Feedback

Understanding Cisco Unified CallManager Voice Gateways

Table Of Contents

Understanding Cisco Unified CallManager Voice Gateways

Cisco Voice Gateways

Standalone Voice Gateways

Cisco VG248 Analog Phone Gateway

Cisco VG224 Analog Phone Gateway

Cisco Voice Gateway 200

Cisco Access Digital Trunk Gateways DT-24+/DE-30+

Cisco Access Analog Station Gateways

Cisco Analog Trunk Gateways

MGCP BRI Call Connections

Switch-Based Gateways

Cisco Communication Media Module

Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Module

Cisco Catalyst 6000 24 Port FXS Analog Interface Module

Cisco Catalyst 4000 Access Gateway Module

Cisco Catalyst 4224 Access Gateway Switch

H.323 Gateways

Cisco IOS H.323 Gateways

T.38 Fax Relay

Outbound FastStart Call Connections

Voice Gateway Model Summary

Gateways, Dial Plans, and Route Groups

Dependency Records for Gateways and their Route Groups and Directory Numbers

Gateway Failover and Fallback

MGCP Gateways

IOS H.323 Gateways

Cisco VG248 and VG224 Analog Phone Gateways

Cisco Unified CallManager T1 CAS Hookflash Transfer Support

MGCP T.38 Fax Relay Support

Transferring Calls Between Gateways

Configuring Transfer Capabilities Using Gateway Configuration

Configuring Transfer Capabilities by Using Call Classification Service Parameter

Blocking Transfer Capabilities by Using Service Parameters

Gateway Configuration Checklist

Where to Find More Information


Understanding Cisco Unified CallManager Voice Gateways


Cisco Unified Communications gateways enable Cisco Unified CallManager to communicate with non-IP telecommunications devices. Cisco Unified CallManager supports several types of voice gateways.

This section covers the following topics:

Cisco Voice Gateways

Gateways, Dial Plans, and Route Groups

Gateway Failover and Fallback

Cisco Unified CallManager T1 CAS Hookflash Transfer Support

MGCP T.38 Fax Relay Support

Transferring Calls Between Gateways

Gateway Configuration Checklist

Where to Find More Information

Cisco Voice Gateways

Cisco Unified CallManager supports several types of Cisco Unified Communications gateways. Gateways use call control protocols to communicate with the PSTN and other non-IP telecommunications devices, such as private branch exchanges (PBXs), key systems, analog phones, fax machines, and modems.

Trunk interfaces specify how the gateway communicates with the PSTN or other external devices by using time-division-multiplexing (TDM) signaling. Cisco Unified CallManager and Cisco gateways use a variety of TDM interfaces, but supported TDM interfaces vary by gateway model. Refer to Cisco Unified Communications Solutions Reference Network Design for more information about selecting and configuring gateways.

The following list provides available interfaces that Cisco Unified CallManager supports with MGCP gateways:

Foreign Exchange Office (FXO)

Foreign Exchange Station (FXS)

T1 Channel Associated Signaling (CAS) recEive and transMit, or ear and mouth (E&M)

Basic Rate Interface (BRI) Q.931

T1 PRI—North American ISDN Primary Rate Interface (PRI)

E1 PRI—European ISDN Primary Rate Interface (PRI)

The following list provides available interfaces that Cisco Unified CallManager supports with H.323 gateways:

FXO

FXS

E&M

Analog Direct Inward Dialing (DID)

Centralized Automatic Message Accounting (CAMA)

BRI Q.931

BRI QSIG—Q signaling protocol that is based on ISDN standards

T1 CAS FXS, FXO, and E&M

T1 FGD

T1/E1 PRI

T1 PRI NFAS

T1/E1 QSIG

E1 R2

J1

The following list provides available interfaces that Cisco Unified CallManager supports with SCCP gateways:

FXS

For information about IP telephony protocols, see the "Understanding IP Telephony Protocols" chapter.

The following sections provide additional Cisco Unified CallManager gateway support information:

Standalone Voice Gateways

MGCP BRI Call Connections

Switch-Based Gateways

H.323 Gateways

Standalone Voice Gateways

This section describes these standalone, application-specific gateway models that are supported for use with Cisco Unified CallManager.

Cisco VG248 Analog Phone Gateway

The Cisco VG248 Analog Phone Gateway has a standalone, 19-inch, rack-mounted chassis with 48-FXS ports. This product allows on-premise analog telephones, fax machines, modems, voice-messaging systems, and speakerphones to register with a single Cisco Unified CallManager cluster.

Cisco VG248 Analog Phone Connectivity

The Cisco VG248 Analog Phone Gateway communicates with Cisco Unified CallManager by using the Skinny Client Control Protocol to allow support for the following supplementary services features for analog phones:

Call transfer

Conference

Call waiting (with calling party ID display)

Hold (including switch between parties on hold)

Music on hold

Call forward all

Send all calls to voice-messaging system

Group call pickup

Voice-messaging system message waiting indication

Speed dial (maximum of 9 speed dials)

Last number redial

Cisco fax relay

Dynamic port and device status that is available from Cisco Unified CallManager

Cisco VGC Phone Device Types

All Cisco VG248 ports and units appear as distinct devices in Cisco Unified CallManager with the device type "Cisco VGC Phone." Cisco Unified CallManager recognizes and configures each port as a phone.

Fax and Modem Connectivity

The Cisco VG248 supports legacy fax machines and modems. When fax machines are used, the Cisco VG248 uses either the Cisco fax relay or pass-through/up speed technology to transfer faxes across the network with high reliability.

You can connect any modem to the Cisco VG248 by using pass-through mode.

Voice-Mail Connectivity

The Cisco VG248 generates call information by using the Simplified Message Desk Interface (SMDI) format for all calls that are ringing on any of the 48 analog lines that connect to it. It will also pass on SMDI call information from other Cisco VG248s, or from a legacy PBX, to the voice-messaging system. Any commands for message-waiting indicators get sent to Cisco Unified CallManager and to any other attached SMDI hosts.

This mechanism allows for many new configurations when SMDI-based voice-messaging systems are used, including

You can share a single voice-messaging system between Cisco Unified CallManager and a legacy PBX.

Voice-messaging system and Cisco VG248 can function remotely in a centralized call-processing model.

Multiple clusters can use a single voice-messaging system, by using one Cisco VG248 per cluster.

Configure multiple voice-messaging systems in a single cluster because the Cisco VG248 generates SMDI call information rather than the Cisco Unified CallManager.

Cisco VG248 Time Device

The Cisco VG248 contains a real-time clock that is persistent across power cycles and restarts. The real-time clock gets set for the first time when the device registers with Cisco Unified CallManager. The clock gets set by using the DefineDateTime Skinny message that Cisco Unified CallManager sends. After a power cycle or restart, the clock resets when the Cisco VG248 receives the DefineDateTime message from Cisco Unified CallManager and then resets no more than once per hour thereafter.

Cisco VG248 Configuration File Updates

The Cisco VG248 queries the TFTP server to access the configuration files for the device. The configuration files update whenever you modify the configuration of the Cisco VG248 via Cisco Unified CallManager.

Refer to the Gateway Configuration section and the Cisco Unified IP Phone Configuration section of the Cisco Unified CallManager Administration Guide and to the Cisco VG248 Analog Phone Gateway Software Configuration Guide for more information.

Cisco VG224 Analog Phone Gateway

The Cisco VG224 Analog Phone Gateway has a standalone, 17-inch, rack-mounted chassis with 24-FXS ports. This product allows on-premise analog telephones, fax machines, modems, and speakerphones to register with Cisco Unified CallManager.

Cisco Voice Gateway 200

The Cisco Unified Communications Voice Gateway (VG200) provides a 10/100BaseT Ethernet port for connection to the data network. The following list gives available telephony connections:

1 to 4 FXO ports for connecting to a central office or PBX

1 to 4 FXS ports for connecting to POTS telephony devices

1 or 2 T1 PRI or T1 CAS ports for connecting to the PSTN

1 or 2 E1 PRI ports for connecting to the PSTN

MGCP or H.323 interface to Cisco Unified CallManager

The MGCP VG200 integration with legacy voice-messaging systems allows the Cisco Unified CallManager to associate a port with a voice mailbox and connection.

Cisco Access Digital Trunk Gateways DT-24+/DE-30+

The Cisco Access Digital Trunk Gateways DT-24+/DE-30+ provide the following features:

T1/E1 PRI (network or user side)

T1 CAS connections (DT-24+) that support E&M signaling with wink or delay dial supervision

FXO with loop-start or ground-start circuit emulation

MGCP interface to Cisco Unified CallManager

Cisco Access Analog Station Gateways

Station gateways let you connect the Cisco Unified CallManager to POTS analog telephones, interactive voice response (IVR) systems, fax machines, and voice-messaging systems. Station gateways provide FXS ports. The AS-2, AS-4, and AS-8 models accommodate two, four, and eight voice over IP (VoIP) gateway channels, respectively.

Cisco Access AS gateways communicate with Cisco Unified CallManager by using Skinny Gateway Protocol.

Cisco Analog Trunk Gateways

Analog trunk gateways let you connect Cisco Unified CallManager to standard PSTN central office (CO) or PBX trunks. Trunk gateways provide FXO ports. The AT-2, AT-4, and AT-8 models accommodate two, four, and eight VoIP gateway channels. The signaling type specifies loop start.

Cisco Access AT gateways communicate with Cisco Unified CallManager by using Skinny Gateway Protocol.

MGCP BRI Call Connections

Previously, gateways used H.323 signaling to Cisco Unified CallManager to provide interfaces to the public switched telephone network (PSTN) for BRI ISDN connections.

Now, Cisco Unified CallManager can use an MGCP gateway to handle BRI ISDN connections to the PSTN and to provide a centrally administered gateway interface. Cisco Unified CallManager uses logical connections to exchange MGCP and ISDN Q.931 messages with the gateway. This connection uses a User Datagram Protocol (UDP) logical connection for exchanging MGCP messages and a Transmission Control Protocol (TCP) connection for the backhaul ISDN Q.931 messages.

Figure 36-1 shows a typical scenario that centralizes call processing for remote-site BRI trunk gateways that connect to the PSTN. When a call arrives from or goes to the PSTN over the BRI trunk, the Cisco Unified CallManager and the gateway (based on an IOS router) exchange ISDN Q.931 messages across the WAN.

Figure 36-1 Topology Shows a Scenario by Using MGCP BRI Interfaces

For more information about MGCP BRI with Cisco Unified CallManager, refer to the MGCP-Controlled Backhaul of BRI Signaling in Conjunction with Cisco Unified CallManager document on the Cisco.com website.


Note The BRI gateway supports MGCP BRI backhaul for BRI trunk only. It does not support BRI phone or station.


Switch-Based Gateways

Several telephony modules for the Cisco Catalyst 4000 and 6000 family switches act as telephony gateways. You can use existing Cisco Catalyst 4000 or 6000 family devices to implement IP telephony in your network by using the following voice gateway modules:

Install Catalyst 6000 voice gateway modules that are line cards in any Cisco Catalyst 6000 or 6500 series switch.

Install the Catalyst 4000 access gateway module in any Catalyst 4000 or 4500 series switch.

Cisco Communication Media Module

The Cisco Communication Media Module (CMM), which is a Catalyst 6500 line card, provides T1 and E1 gateways that allow organizations to connect their existing TDM network to their IP communications network. The Cisco CMM provides connectivity to the PSTN also. You can configure the Cisco CMM, which provides an MGCP or H.323 interface to Cisco Unified CallManager, with the following interface and service modules:

6-port T1 interface module for connecting to the PSTN or a PBX

6-port E1 interface module for connecting to the PSTN or a PBX

24-port FXS interface module for connecting to POTS telephony devices


Note The Cisco CMM fits in the Cisco 7600 platform chassis.


Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Module

The Cisco Catalyst 6000 8 Port Voice T1/E1 and Services Modules provide the following features:

8 ports for providing

Digital T1/E1 connectivity to the PSTN (T1/E1 PRI or T1 CAS with the same features as DT-24+/DE-30+)

Digital signal processor (DSP) resources for transcoding and conferencing

MGCP interface to Cisco Unified CallManager

Connection to a voice-messaging system (using T1 CAS)

Users have the flexibility to use ports on a T1 module for T1 connections or as network resources for voice services. Similarly, the E1 module provides ports for E1 connections or as network resources. The ports can serve as T1/E1 interfaces, or the ports will support transcoding or conferencing.


Note Either module supports DSP features on any port, but T1 modules cannot be configured for E1 ports, and E1 modules cannot be configured for T1 ports.


Cisco Catalyst 6000 24 Port FXS Analog Interface Module

The Cisco Catalyst 6000 24 Port FXS Analog Interface Module provides the following features:

24 Port RJ-21 FXS module

V.34/V.90 modem, voice-messaging system, IVR, POTS

Cisco Fax Relay

MGCP interface to Cisco Unified CallManager

The Catalyst 6000 24 Port FXS Analog Interface Module provides 24 FXS ports for connecting to analog phones, conference room speakerphones, and fax machines. You can also connect to legacy voice-messaging systems by using SMDI and by associating the ports with voice-messaging extensions.

The FXS module provides legacy analog devices with connectivity into the IP network. Analog devices can use the IP network infrastructure for toll-bypass applications and to communicate with devices such as SCCP IP phones and H.323 end stations. The FXS module also supports fax relay, which enables compressed fax transmission over the IP WAN and preserves valuable WAN bandwidth for other data applications.

Cisco Catalyst 4000 Access Gateway Module

The Cisco Catalyst 4000 Access Gateway Module provides an MGCP or H.323 gateway interface to Cisco Unified CallManager. You can configure this module with the following interface and service modules:

6 ports for FXS and FXO

2 T1/E1 ports for T1 PRI, T1 CAS, or E1 PRI

Cisco Catalyst 4224 Access Gateway Switch

The Cisco Catalyst 4224 Access Gateway Switch provides a single-box solution for small branch offices. The Catalyst 4224 provides switching, IP routing, and PSTN voice-gateway services by using onboard digital signal processors (DSPs). The Catalyst 4224 has four slots that you can configure with multiflex voice and WAN interface cards to provide up to 24 ports. These ports can support the following voice capabilities:

FXS ports for POTS telephony devices

FXO ports for PSTN connections

T1 or E1 ports for T1 PRI, E1 PRI, and T1 CAS services

The Cisco Catalyst 4224 Access Gateway Switch provides an MGCP or H.323 interface to Cisco Unified CallManager.

H.323 Gateways

H.323 devices comply with the H.323 communications standards and enable video conferencing over LANs and other packet-switched networks. You can add third-party H.323 devices or other Cisco devices that support H.323 (such as the Cisco 2600 series, 3600 series, or 5300 series gateways).

Cisco IOS H.323 Gateways

Cisco IOS H.323 gateways such as the Cisco 2600, 3600, 1751, 1760, 7200, and VG200 provide full-featured routing capabilities. Refer to the documentation for each of these gateway types for information about supported voice gateway features and configuration.

T.38 Fax Relay

Transporting real-time Group 3 fax documents over internet protocol (IP) uses the International Telecommunications Union Telecommunication Standardization Sector (ITU-T) recommendation T.38 Fax Relay. The T.38 standard defines the IP network protocol that Internet-aware T.38 fax devices and T.38 IP fax gateways use. The T.38 Fax Relay for VoIP H.323 feature provides standards-based, fax relay protocol support for Cisco and other vendor gateways.

The T.38 Fax Relay feature provides a standards-based, fax relay protocol that is available on several Cisco gateways. Because the T.38 Fax Relay protocol is standards based, Cisco gateways and gatekeepers can interoperate with third-party T.38 enabled gateways and gatekeepers in a mixed vendor network that requires real-time fax relay capabilities.

Cisco Unified CallManager handles the T.38 fax call by using a voice connection. When the originating gateway sends a fax, the gateway establishes an initial voice call. The terminating gateway detects the fax tone that the answering fax machine generates. The VoIP H.323 call stack then starts a T.38 mode request by using H.245 procedures. If the opposite end of the call acknowledges the T.38 mode request, the initial audio channel closes, and T.38 Fax Relay channel opens. When the fax transmission finishes, the call disconnects.


Note Both H.323 and MGCP (IOS only) support T.38 Fax Relay. For T.38 Fax Relay interworking between H.323 gateways and MGCP gateways, ensure that MGCP gateways are configured to operate in CA-controlled mode.


Outbound FastStart Call Connections

Calls that are placed from IP phones over large WAN topologies can experience voice clipping when the called party goes off hook to answer the call. When H.323 trunks or gateways are separated from the Cisco Unified CallManager server, significant delays can occur because of the many H.245 messages that are exchanged when a call is set up.

With the FastStart feature, information that is required to complete a media connection between two parties gets exchanged during the H.225 portion of call setup, and this exchange eliminates the need for H.245 messages. The connection experiences one roundtrip WAN delay during call setup, and the calling party does not receive voice clipping when the called party answers the call.

Cisco Unified CallManager uses media termination points (MTP) for making an H.323 outbound FastStart call. Cisco Unified CallManager starts an outbound FastStart call by allocating an MTP and opening the receive channel. Next, the H.323 Fast Connect procedure sends the SETUP message with a FastStart element to the called endpoint. The FastStart element includes information about the receiving channel for the MTP.

The called endpoint accepts the H.323 Fast Connect procedure by sending a CALL PROCEEDING, PROGRESS, ALERT, or CONNECT message that contains a FastStart element. When Cisco Unified CallManager receives the FastStart element, it connects the media immediately and avoids the delays with the usual exchange of H.245 messages.

The called endpoint can refuse the H.323 Fast Connect procedure by not returning the FastStart element in any of the messages up to and including the CONNECT message. In this case, the Cisco Unified CallManager handles the call as a normal call and uses the MTP for subsequent media cut-through.


Note You cannot directly establish T.38 Fax Relay calls by using Fast Connect procedures.


The Outbound FastStart feature requires an MTP. If an MTP is not available when the call is set up, the call continues without FastStart and with no supplementary services. If you want all calls to use FastStart only, you can set the service parameter called "Fail call if MTP allocation fails," which is located under Cluster Wide Parameters (Device-H323). When you set this parameter to True, the system rejects calls when no MTP is available.

Related Topic

H.323 Gateway Configuration Settings, Cisco Unified CallManager Administration Guide

Voice Gateway Model Summary

Table 36-1 summarizes Cisco voice gateways that Cisco Unified CallManager supports with information about the gateway control protocols, trunk interfaces, and port types.

Table 36-1 Overview of Supported Voice Gateways, Protocols, Trunk Interfaces,
and Ports 

Gateway Model
Supported Signaling Protocols
Trunk Interface
Port Types
Cisco IOS Integrated Routers

Cisco 1751 and Cisco 1760

H.323 (H.225)

FXS

FXO

POTS

Loop start or ground start

Cisco 2801

MGCP

FXS

FXO

T1 CAS

T1 PRI

E1

BRI

 

Cisco 3810 V3

H.323 (H.225)

T1 CAS

E1 CAS

T1 CAS

E1 CAS

Cisco 2600 series

MGCP, H.323, or SCCP

(Only MGCP supports QSIG.)

FXS

FXO

T1/E1 PRI

T1 CAS

QSIG (Not all Cisco 2600 series gateways support QSIG. Refer to your gateway documentation.)

POTS

Loop start or ground start

T1/E1 PRI

E&M

T1/E1 PRI

MGCP BRI

SCCP BRI (including 269x)

Cisco 2811, 2821, 2851

H.323, MGCP, or SCCP

T1 CAS

T1 PRI

E1

FXS

FXO

Loop start or ground start

Cisco 3600 series

MGCP or H.323

(Only MGCP supports QSIG.)

FXS

FXO

T1/E1 PRI

T1 CAS

QSIG (Not all Cisco 3600 series gateways support QSIG. Refer to your gateway documentation.)

POTS

Loop start or ground start

T1/E1 PRI

E&M

T1/E1 PRI

MGCP BRI (364x and 366x only)

SCCP BRI (3625 and 3645)

2600, 3625 and 3645 also support SCCP BRI. We have only MGCP BRI mentioned there.

Cisco 3725 and Cisco 3745

MGCP, H.323, or SCCP

(Only MGCP supports QSIG.)

FXS (Only supported in SCCP mode)

FXO

T1/E1 PRI

T1 CAS

QSIG

POTS

Loop start or ground start

T1/E1 PRI

E&M

T1/E1PRI

MGCP BRI (Only supported in SCCP mode)

Cisco 3825, 3845

MGCP, H.323, or SCCP

FXS

FXO

T1 CAS

T1 PRI

Loop start or ground start

Cisco 7200

H.323 (H.225)

T1/E1 CAS

T1/E1 PRI

T1/E1 CAS

T1/E1 PRI

Cisco 7500

H.323 (H.225)

T1/E1 CAS

T1/E1 PRI

T1/E1 CAS

T1/E1 PRI

Cisco AS5300

H.323 (H.225)

T1/E1 CAS

T1/E1 PRI

T1/E1 CAS

T1/E1 PRI

Cisco Standalone Voice Gateways

Cisco VG248 Analog Phone Gateway

Skinny Client Control Protocol

FXS

POTS

Cisco VG224 Analog Phone Gateway

H.323, MGCP or SCCP

FXS

POTS

Cisco Voice Gateway 200 (VG200)

MGCP or H.323

(Only MGCP supports QSIG.)

FXO

FXS

T1/E1 PRI

T1 CAS

QSIG

Loop start or ground start

POTS

T1/E1 PRI

E&M

T1/E1 PRI

Cisco Access Digital Trunk Gateway DE-30+

MGCP

E1 PRI

QSIG

E1 PRI

E1 PRI

Cisco Access Digital Trunk Gateway DT-24+

MGCP

T1 PRI

T1 CAS

FXO

QSIG

T1 PRI

E&M

Loop start or ground start

T1 PRI

Cisco Access Analog Trunk Gateway (AT-2, AT-4, AT-8)

Skinny Gateway Protocol

FXO

Loop start

Cisco Access Analog Station Gateway (AS-2, AS-4, AS-8)

Skinny Gateway Protocol

FXS

POTS

Cisco Catalyst Voice Gateway Modules

Cisco Communication Media Module

(WS-X6600-24FXS)

(WS-X6600-6T1)

(WS-X6600-6E1)

MGCP or H.323

FXS

T1 PRI

T1 CAS

E1 PRI

POTS

T1 PRI

E&M

E1 PRI

Cisco Catalyst 4000 Access Gateway Module (WS-X4604-GWY)

MGCP or H.323

(Only MGCP supports QSIG.)

FXS

FXO

T1 CAS

T1/E1 PRI

QSIG

POTS

Loop start or ground start

E&M

T1/E1 PRI

T1/E1 PRI

Cisco Catalyst 4224 Voice Gateway Switch

MGCP or H.323

(Only MGCP supports QSIG.)

FXS

FXO

T1/E1 PRI

T1 CAS

QSIG

POTS

Loop start or ground start

T1/E1 PRI

E&M

T1/E1 PRI

Cisco Catalyst 6000 8-Port Voice T1/E1 and Services Module (WS-X6608-T1)

(WS-X6608-E1)

MGCP

T1/E1 PRI

T1 CAS

QSIG

T1/E1 PRI

E&M, loop start, ground start

T1/E1 PRI

Cisco Catalyst 6000 24-Port FXS Analog Interface Module (WS-X6624-FXS)

MGCP

FXS

POTS


Gateways, Dial Plans, and Route Groups

Gateways use dial plans to access or call out to the PSTN, route groups, and group-specific gateways. The different gateways that are used within the Cisco Unified Communications Solutions have dial plans that are configured in different places:

Configure dial plan information for both Skinny and MGCP gateways in the Cisco Unified CallManager.

Configure dial plans in Cisco Unified CallManager to access the H.323-based Cisco IOS software gateways. Configure dial peers in the H.323-based gateways to pass the call out of the gateway.

The route group points to one or more gateways and can choose the gateways for call routing based on preference. The route group can serve as a trunk group by directing all calls to the primary device and then using the secondary devices when the primary is unavailable. One or more route lists can point to the same route group.

All devices in a given route group share the same characteristics such as path and digit manipulation. Cisco Unified CallManager restricts the gateways that you can include in the same route group and the route groups that you can include in the same route list. For more information about routing, see the "Route Plan Overview" section.

Route groups can perform digit manipulation that will override what was performed in the route pattern. Configuration information that is associated with the gateway defines how the call is actually placed and can override what was configured in the route pattern.

You can configure H.323 trunks, not H.323gateways, to be gatekeeper-controlled trunks. This means that before a call is placed to an H.323 device, it must successfully query the gatekeeper. See the "Gatekeeper and Trunk Configuration in Cisco Unified CallManager" section for more information.

Multiple clusters for inbound and outbound calls can share H.323 trunks, but MGCP and Skinny-based gateways remain dedicated to a single Cisco Unified CallManager cluster.

Related Topics

Dependency Records for Gateways and their Route Groups and Directory Numbers

Cisco Voice Gateways

Dependency Records for Gateways and their Route Groups and Directory Numbers

To find route groups or directory numbers that a specific gateway or gateway port is using, click the Dependency Records link that is provided on the Cisco Unified CallManager Administration Gateway Configuration window. The Dependency Records Summary window displays information about route groups and directory numbers that are using the gateway or port. To find out more information about the route group or directory number, click the route group or directory number, and the Dependency Records Details window displays. If the dependency records are not enabled for the system, the dependency records summary window displays a message.

For more information about Dependency Records, refer to Accessing Dependency Records, Deleting Gateways, and Removing a Directory Number from a Phone in the Cisco Unified CallManager Administration Guide.

Gateways, Dial Plans, and Route Groups

Cisco Voice Gateways

Gateway Failover and Fallback

This section describes how these Cisco voice gateways handle Cisco Unified CallManager failover and fallback situations.

MGCP Gateways

IOS H.323 Gateways

Cisco VG248 and VG224 Analog Phone Gateways

MGCP Gateways

To handle Cisco Unified CallManager failover situations, MGCP gateways receive a list of Cisco Unified CallManagers that is arranged according to the Cisco Unified CallManager group and defined for the device pool that is assigned to the gateway. A Cisco Unified CallManager group can contain one, two, or three Cisco Unified CallManagers that are listed in priority order for the gateway to use. If the primary Cisco Unified CallManager in the list fails, the secondary Cisco Unified CallManager gets used. If the primary and secondary Cisco Unified CallManagers fail, the tertiary Cisco Unified CallManager gets used.

Fallback describes the process of recovering a higher priority Cisco Unified CallManager when a gateway fails over to a secondary or tertiary Cisco Unified CallManager. Cisco MGCP gateways periodically take status of higher priority Cisco Unified CallManagers. When a higher priority Cisco Unified CallManager is ready, it gets marked as available again. The gateway reverts to the highest available Cisco Unified CallManager when all calls go idle or within 24 hours, whichever occurs first. The administrator can force a fallback either by stopping the lower priority Cisco Unified CallManager whereby calls get preserved, by restarting the gateway, which preserves calls, or by resetting Cisco Unified CallManager, which terminates calls.


Note SCCP gateways handle Cisco Unified CallManager redundancy, failover, and fallback in the same way as MGCP gateways.


IOS H.323 Gateways

Cisco IOS gateways also handle Cisco Unified CallManager failover situations. By using several enhancements to the dial-peer and voice class commands in Cisco IOS Release 12.1(2)T, Cisco IOS gateways can support redundant Cisco Unified CallManagers. The command, h225 tcp timeout seconds, specifies the time that it takes for the Cisco IOS gateway to establish an H.225 control connection for H.323 call setup. If the Cisco IOS gateway cannot establish an H.225 connection to the primary Cisco Unified CallManager, it tries a second Cisco Unified CallManager that is defined in another dial-peer statement. The Cisco IOS gateway shifts to the dial-peer statement with the next highest preference setting.

The following example shows the configuration for H.323 gateway failover:

interface FastEthernet0/0
ip address 10.1.1.10 255.255.255.0
dial-peer voice 101 voip
destination-pattern 1111
session target ipv4:10.1.1.101
preference 0
voice class h323 1
dial-peer voice 102 voip
destination-pattern 1111
session target ipv4:10.1.1.102
preference 1
voice class h323 1
voice class h323 1
h225 timeout tcp establish 3


Note To simplify troubleshooting and firewall configurations, Cisco recommends that you use the new voip-gateway voip bind srcaddr command for forcing H.323 always to use a specific source IP address in call setup. Without this command, the source address that is used in the setup might vary and depends on protocol (RAS, H.225, H.245, or RTP).


Cisco VG248 and VG224 Analog Phone Gateways

The Cisco VG248 and VG224 Analog Phone Gateways support the Skinny Client Control Protocol for clustering and failover.

Cisco Unified CallManager T1 CAS Hookflash Transfer Support

Hookflash transfer defines a signaling procedure that allows a TDM device, such as a voice-messaging system, to transfer a call to another destination. While the device is connected to Cisco Unified CallManager through a T1 CAS gateway, the device performs a hookflash procedure to perform the call transfer. Cisco Unified CallManager responds to the hookflash procedure by using a blind transfer to move the call. When the call transfer completes, the voice channel that connected the original call to the device gets released.

Cisco Unified CallManager supports hookflash transfer on the T1 CAS ports of all Media Gateway Control Protocol (MGCP) gateways (both IOS and non-IOS gateways). See Table 36-1 for a summary of gateway model information.

MGCP T.38 Fax Relay Support

Transporting real-time Group 3 fax documents over internet protocol (IP) uses the International Telecommunications Union Telecommunication Standardization Sector (ITU-T) recommendation T.38 Fax Relay. The T.38 standard defines the IP network protocol that Internet-aware T.38 fax devices and T.38 IP fax gateways use.

The T.38 Fax Relay feature provides a standards-based, fax relay protocol that is available on several Cisco gateways. Because the T.38 Fax Relay protocol is standards based, Cisco gateways and gatekeepers can interoperate with third-party T.38 enabled gateways and gatekeepers in a mixed vendor network that requires real-time fax relay capabilities.


Note Both H.323 and MGCP (IOS only) support T.38 Fax Relay. For T.38 Fax Relay interworking between H.323 gateways and MGCP gateways, you must ensure that MGCP gateways are configured to operate in CA-controlled mode.


Cisco Unified CallManager handles the T.38 fax call by using a voice connection initially. When the originating gateway sends a fax, the gateway establishes a voice call. The terminating gateway detects the fax tone that the answering fax machine generates. When the T.38 channel opens, the audio channel closes. No bandwidth adjustment occurs at that time. No reversion to voice mode occurs when the fax transmission completes.

Cisco Unified CallManager support of MGCP T.38 Fax Relay includes the following features:

Call agent (CA)-controlled only (as opposed to gateway-controlled). Cisco Unified CallManager serves as the call agent.

Fax calls use T.38 in CA-controlled mode if IOS enables T.38 (default).

Fax calls use fax pass-through (or Cisco Fax Relay) if IOS disables T.38.

The current default IOS configuration supports T.38 Fax Relay. Ensure that the IOS MGCP gateway is configured to operate in CA-controlled MGCP T.38 Fax Relay mode.

Refer to the Cisco IOS Fax and Modem Services over IP Application Guide for additional IOS configuration information.

Transferring Calls Between Gateways

Using Cisco Unified CallManager Administration, you can configure gateways as OnNet (internal) gateways or OffNet (external) gateways by using Gateway Configuration or by setting a clusterwide service parameter. Used in conjunction with the clusterwide service parameter, Block OffNet to OffNet Transfer, the configuration determines whether calls can be transferred over a gateway.

To use the same gateway to route both OnNet and OffNet calls, associate the gateway with two different route patterns. Make one gateway OnNet and the other OffNet with both having the Allow Device Override check box unchecked.

Configuring Transfer Capabilities Using Gateway Configuration

Using Cisco Unified CallManager Administration Gateway Configuration, you can configure a gateway as OffNet or OnNet. The system considers the calls that come to the network through that gateway OffNet or OnNet, respectively. Use the Gateway Configuration window field, Call Classification, to configure the gateway as OffNet, OnNet, or Use System Default. See Table 36-2 for description of these settings.

The Route Pattern Configuration window provides a drop-down list box called Call Classification, which allows you to configure a route pattern as OffNet or OnNet. When Call Classification is set to OffNet and the Allow Device Override check box is unchecked, the system considers the outgoing calls that use this route pattern as OffNet (if configured as OnNet and check box is unchecked, then outgoing calls are considered OnNet).

You can use the same gateway to route both OnNet and OffNet calls by associating the gateway with two different route patterns: one OnNet and the other OffNet, with both having the Allow Device Override check box unchecked. For outgoing calls, the outgoing device setting classifies the call as either OnNet or OffNet by determining whether the Allow Device Override check box is checked.

In route pattern configuration, if the Call Classification is set as OnNet, the Allow Device Override check box is checked, and the route pattern is associated with an OffNet gateway, the system considers the outgoing call OffNet.

Table 36-2 Gateway Configuration Call Classification Settings

Setting Name
Description

OffNet

This setting identifies the gateway as being an external gateway. When a call comes in from a gateway that is configured as OffNet, the outside ring gets sent to the destination device.

OnNet

This setting identifies the gateway as being an internal gateway. When a call comes in from a gateway that is configured as OnNet, the inside ring gets sent to the destination device.

Use System Default

This setting uses the Cisco Unified CallManager clusterwide service parameter Call Classification.


Configuring Transfer Capabilities by Using Call Classification Service Parameter

To configure all gateways to be OffNet (external) or OnNet (internal), perform the following two steps:

1. Use the Cisco Unified CallManager clusterwide service parameter Call Classification.

2. Configure individual gateways to Use System Default in the Call Classification field that is on the Gateway Configuration window.

Blocking Transfer Capabilities by Using Service Parameters

Block transfer provides a way of restricting transfer between external devices, so fraudulent activity gets prevented. You can configure the following devices as OnNet (internal) or OffNet (external) to Cisco Unified CallManager:

H.323 gateway

MGCP FXO trunk

MGCP T1/E1 trunk

Intercluster trunk

SIP trunk

If you do not want OffNet calls to be transferred to an external device (one that is configured as OffNet), set the Cisco Unified CallManager clusterwide service parameter, Block OffNet to OffNet Transfer, to True.

If a user tries to transfer a call on an OffNet gateway that is configured as blocked, a message displays on the user phone to indicate that the call cannot be transferred.

Related Topics

Route Pattern Configuration, Cisco Unified CallManager Administration Guide

Gateway Configuration, Cisco Unified CallManager Administration Guide

Trunk Configuration, Cisco Unified CallManager Administration Guide

Gateway Configuration Checklist

Table 36-3 provides an overview of the steps that are required to configure gateways in Cisco Unified CallManager, along with references to related procedures and topics.

Table 36-3 Gateway Configuration Checklist 

Configuration Steps
Procedures and Related Topics

Step 1 

Install and configure the gateway or voice gateway module in the network.

Refer to the installation and configuration documentation for the model of gateway that you are configuring.

Step 2 

Gather the information that you need to configure the gateway to operate with Cisco Unified CallManager.

Gateway Configuration Settings, Cisco Unified CallManager Administration Guide

Port Configuration Settings, Cisco Unified CallManager Administration Guide

Step 3 

On the gateway, perform any required configuration steps.

Refer to the voice feature software configuration documentation or Cisco IOS documentation for the model of gateway that you are configuring.

Step 4 

Add and configure the gateway in Cisco Unified CallManager Administration.

Adding Gateways to Cisco Unified CallManager, Cisco Unified CallManager Administration Guide

Step 5 

Add and configure ports on the gateway or
add and configure the Cisco VG248 and VG224 Analog Phone Gateways.

Port Configuration Settings, Cisco Unified CallManager Administration Guide

Adding a Cisco VG248 Analog Phone Gateway, Cisco Unified CallManager Administration Guide

Cisco Unified IP Phone Configuration, Cisco Unified CallManager Administration Guide

Step 6 

For FXS ports, add directory numbers, if appropriate.

Adding a Directory Number, Cisco Unified CallManager Administration Guide

Directory Number Configuration Settings, Cisco Unified CallManager Administration Guide

Step 7 

Configure the dial plan for the gateway for routing calls out to the PSTN or other destinations.

This configuration can include setting up a route group, route list, and route pattern for the Gateway in Cisco Unified CallManager or, for some gateways, configuring the dial plan on the gateway itself.

Cisco Unified Communications Solution Reference Network Design

Cisco Unified CallManager Administration Guide

Step 8 

Reset the gateway to apply the configuration settings.

Resetting and Restarting Gateways, Cisco Unified CallManager Administration Guide


Tip To get to the default web pages for many gateway devices, you can use the IP address of that gateway. Make your hyperlink url = http://x.x.x.x/, where x.x.x.x is the dot-form IP address of the device. The web page for each gateway contains device information and the real-time status of the gateway.


Where to Find More Information

Related Topics

Understanding IP Telephony Protocols

Understanding Cisco Unified CallManager Trunk Types

Route Plan Overview

Gatekeepers and Trunks

Adding Gateways to Cisco Unified CallManager, Cisco Unified CallManager Administration Guide

Gateway Configuration Settings, Cisco Unified CallManager Administration Guide

Port Configuration Settings, Cisco Unified CallManager Administration Guide

Directory Number Configuration Settings, Cisco Unified CallManager Administration Guide

Additional Cisco Documentation

Cisco Unified Communications Solution Reference Network Design

Configuring Cisco Unified Communications Voice Gateways

Implementing Fax Over IP on Cisco Voice Gateways

Cisco IOS Fax and Modem Services over IP Application Guide

Cisco VG248 Analog Phone Gateway Software Configuration Guide

Cisco VG248 Analog Phone Gateway Hardware Installation Guide

Cisco Voice Gateway Router Interoperability with CallManager

Cisco IOS Voice Configuration Library

Cisco IOS H.323 Configuration Guide

Cisco IOS MGCP and Related Protocols Configuration Guide