Cisco CallManager System Guide, Release 3.2(1)
Understanding Voice Gateways
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Understanding Voice Gateways

Table Of Contents

Understanding Voice Gateways

Gateway Control Protocols and Trunk Interfaces

Trunk Interfaces

Cisco Voice Gateways

Standalone Voice Gateways

Cisco Voice Gateway 200 Gateway

Cisco Access Digital Trunk Gateways DT-24+/DT30+

Cisco Analog Access Station Gateways

Cisco Access Analog Trunk Gateways

Cisco VG248 Analog Phone Gateway

Cisco Catalyst 4000 and 6000 Voice Gateway Modules

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

Cisco Catalyst 6000 AVVID Services Module

Cisco Catalyst 4000 Access Gateway Module

Cisco Catalyst 4224 Access Gateway Module

Cisco Catalyst 6000 24 Port FXS Analog Interface Module

ICS77XX Gateways

H.323 Gateways

Cisco IOS H.323 Gateways

Intercluster Trunks

Voice Gateway Model Summary

Gateways, Dial Plans, and Route Groups

Gateway Failover and Failback

MGCP Gateways

IOS H.323 Gateways

SGCP Gateways

Cisco VG248 Analog Phone Gateway

Gateway Configuration Checklist

Where to Find More Information


Understanding Voice Gateways


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

This section covers the following topics:

Gateway Control Protocols and Trunk Interfaces

Cisco Voice Gateways

Gateway Failover and Failback

Gateway Configuration Checklist

Where to Find More Information

Gateway Control Protocols and Trunk Interfaces

This section describes the gateway control protocols and trunk interface protocols that are supported for configuring gateways in Cisco CallManager.

Gateway control protocols provide the internal interface between the voice gateway and Cisco CallManager.

Trunk interfaces specify how the gateway interfaces with the PSTN or other external devices.

Gateway Control Protocols

Gateway control protocols provide communication and control between Cisco CallManager and the voice gateway.

The amount and type of information you configure in Cisco CallManager Administration versus what is configured on the gateway varies, depending on whether gateway control protocol is MGCP, H.323, or Skinny:

Media Gateway Control Protocol (MGCP)—Gateways that support MGCP as of Cisco CallManager Release 3.1 include the Cisco VG200, Cisco 3600 and 2600, Cisco Catalyst 6000 8 Port Voice E1/T1 and Services modules, Cisco Catalyst 4000 Access Gateway Module, Cisco DE-30+, and Cisco DT-24+.

When MGCP is used, the Cisco CallManager controls routing and tones and provides supplementary services to the gateway. MGCP provides call preservation (calls are maintained during failover and failback), redundancy, dial plan simplification (no dial peer configuration is required on the gateway), hookflash transfer, and tone on hold. MGCP-controlled gateways do not require an MTP to enable supplementary services such as hold, transfer, call pickup, and call park.

H.323—The Cisco IOS integrated router gateways use the H.323 protocol to communicate with Cisco CallManager. Intercluster trunks for connecting remote Cisco CallManagers across the IP WAN are also configured as H.323 gateways.

Compared to MGCP, H.323 requires more configuration on the gateway, because the gateway must maintain the dial plan and route patterns.

Skinny Gateway Protocol—Older Cisco voice gateways such as the AT-2, AT-4, AT-8, AS-2, AS-4, AS-8, and the Cisco Catalyst 6000 24 Port FXS Analog Interface Module.

Skinny Client Control Protocol—Cisco VG248 Gateway registers and communicates with the Cisco CallManager using the Skinny Client Control Protocol, which also allows support for enhanced features, such as Message Waiting Indication. The Cisco VG248 Gateway supports clustering and failover.

Trunk Interfaces

Device protocols specify the time-division multiplexing (TDM) signaling interface between the voice gateway and the PSTN or external non-IP telephony devices. Supported TDM interfaces vary by gateway model. The following list gives available interfaces:

Foreign Exchange Office (FXO)—Use FXO ports for connecting to a central office or PBX. You can configure loop-start, ground-start, and E&M signaling interfaces, depending on the model selected.

Cisco CallManager assumes all loop start trunks lack positive disconnect supervision. We recommend that you configure trunks with positive disconnect supervision as ground start.

Foreign Exchange Station (FXS)—Use FXS ports to connect to any Plain Old Telephone Service (POTS) device such as analog phones, fax machines, and legacy voice-mail systems.

T1-PRI—Use this interface to designate North American ISDN Public Rate Interface with 23 bearer channels and one common channel signaling (CCS).

E1-PRI—Use this interface to designate European ISDN Primary Rate Interface with 30 bearer channels, one CCS channel, and one framing channel.

T1-CAS—Use this interface to designate T1 channel associated signaling (CAS), where each channel includes a dedicated signaling element. The supported signaling interface type is E&M.

Cisco Voice Gateways

Cisco CallManager supports several types of Cisco IP telephony gateways. These sections provide an overview of the following supported gateways:

Standalone Voice Gateways

Cisco Catalyst 4000 and 6000 Voice Gateway Modules

ICS77XX Gateways

H.323 Gateways

Standalone Voice Gateways

This section describes the standalone, application-specific gateway models supported for use with Cisco CallManager.

Cisco Voice Gateway 200 Gateway

The Cisco IP Telephony 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 CallManager

MGCP mode supports T1/E1 PRI (user side only), T1-CAS, FXS, and FXO.

H.323 mode supports E1/T1 PRI (user side only), E1/T1-CAS, FXS, and FXO, and E&M, fax relay, G.711 modem.

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

Cisco Access Digital Trunk Gateways DT-24+/DT30+

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

T1/E1 PRI (network or user side)

T1-CAS connections (DT-24+) supporting E&M signaling with wink, immediate, or delay dial supervision; and loop start FXO and ground start circuit emulation.

MGCP interface to Cisco CallManager

Cisco Analog Access Station Gateways

Station gateways let you connect the Cisco CallManager to POTS analog telephones, interactive voice response (IVR) systems, fax machines, and voice-mail 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 AS gateways communicate with Cisco CallManager using SGCP.

Cisco Access Analog Trunk Gateways

Analog trunk gateways let you connect the Cisco 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 is loop start.

Cisco AT gateways communicate with Cisco CallManager using SGCP.

Cisco VG248 Analog Phone Gateway

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

Cisco VG248 Analog Phone Connectivity

The Cisco VG248 Analog Phone Gateway communicates with the Cisco CallManager using the Skinny Client Control Protocol to allow support for the following 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 mail

Group call pickup

Voice mail message waiting indication

Speed dial (maximum of 9 speed dials)

Last number redial

Cisco fax relay

Dynamic port and device status available from Cisco CallManager

Cisco VGC Phone Device Types

All Cisco VG248 ports and units appear as distinct devices in the Cisco CallManager as the device type "Cisco VGC Phone." To the Cisco CallManager, each port is recognized and configured as a phone.

Fax and Modem Connectivity

The Cisco VG248 supports legacy fax machines and modems. When using fax machines, the Cisco VG248 uses the Cisco fax-relay technology to transfer faxes across the network with high reliability using less bandwidth than a voice call.

Any modem can be connected to the Cisco VG248.

Voice Mail Connectivity

The Cisco VG248 generates call information in an SMDI format for all calls ringing on any of the 48 analog lines connected to it. It will also pass on SMDI from other Cisco VG248s, or from a legacy PBX to the voice-mail system. Any commands for message-waiting indicators are sent to the Cisco CallManager and to any other attached SMDI hosts.

This mechanism allows for many new configurations when using SMDI-based voice-mail systems, including:

You can share a single voice-mail system between Cisco CallManager and a legacy PBX

Voice-mail and Cisco VG248 can function remotely in a centralized call-processing model

A single voice-mail system can be used by multiple clusters, by using one Cisco VG248 per cluster

Configure multiple voice-mail systems per single cluster, because SMDI is generated by the Cisco VG248 rather than Cisco CallManager

Cisco VG248 Time Device

The Cisco VG248 contains a real time clock that is persistent across power cycles and restarts. The clock is set form the time and date contained in the DefineDateTime skinny message received from the Cisco CallManager. The clock is set the first time a DefineDateTime message is received after a power cycle or restart and then not more than once per hour thereafter.

The real time clock is not set when the device leaves the factory. The clock only sets when the device first registers with the Cisco CallManager.

Cisco VG248 configuration file updates

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

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

Cisco Catalyst 4000 and 6000 Voice Gateway Modules

Several available telephony modules for the Cisco Catalyst 4000 and 6000 family switches act as telephony gateways enabling you to implement IP telephony in your network using existing Cisco Catalyst 4000 or 6000 family devices.

You can install Catalyst 6000 voice gateway modules that are line cards in any Cisco Catalyst 6000 or 6500 series switch. You can install the Catalyst 4000 access gateway module in any Catalyst 4000 or 4500 series switch.

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 feature as DT-24+/DE-30+)

DSP resources for transcoding and conferencing

MGCP interface to Cisco CallManager

Depending upon which port type is configured, the ports can serve as T1/E1 interfaces, or the ports will support transcoding or conferencing.


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


Users have the flexibility to use each port for T1/E1 connections or as network resources for voice services.

Cisco Catalyst 6000 AVVID Services Module

The Cisco Catalyst 6000 AVVID Services Module can be configured with the following interface and service modules:

6-port T1 interface module for connecting to the PSTN

6-port E1 interface module for connecting to the PSTN

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

Cisco Catalyst 4000 Access Gateway Module

The Cisco Catalyst 4000 Access Gateway Module provides the following telephony features:

6 ports for FXS, FXO or E&M

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

MGCP interface to Cisco CallManager

Cisco Catalyst 4224 Access Gateway Module

The Cisco Catalyst 4224 Access Gateway Module provides the following features:

8 ports for FXS

Supported protocols and interface types including

T1-PRI, E1-PRI, T1-CAS, E1-CAS R2, ISDN BRI, and FXO

MGCP interface to Cisco CallManager

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 mail, IVR, POTS

Cisco fax relay (T.38 Phase 2)

MGCP interface to Cisco CallManager

The Catalyst 6000 24 Port FXS Analog Interface Module provides 24 FXS ports for connecting to analog phones, conference room speaker phones, and fax machines. You can also connect to legacy voice-mail systems. Using SMDI, you can associate the ports with voice-mail extensions.

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

ICS77XX Gateways

The Cisco Integrated Communications System (ICS) 7750, an integrated communications platform, provides easy, rapid deployment and management of key data and converged voice/data applications and services, including IP telephony, content delivery networking, multiservice routing, and more.

The system provides businesses a cost-effective platform for quick deployment of powerful applications such as unified messaging, integrated web call centers, data/voice collaboration, and networked video.

The Cisco ICS 7750 has all the elements needed to deliver data, voice, and video in a single chassis: multiservice router/voice gateway cards based on Cisco IOS software, application server cards running core voice applications, call processing software, and integrated web-based system management software, a data switching interface card for connectivity to Catalyst 3524-PWR XL switches or other data switches, and a card that monitors system health.

The Cisco ICS7750 uses multiservice route processor (MRP) cards to provide the functionality of multiservice routers and H.323-compliant voice gateways. In release 2.0.0, Analog Station Interface (ASI) cards add support for high-density analog foreign exchange station (FXS) ports (8- and 16-port versions are available).

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). You can also configure H.323 intercluster trunks to connect Cisco CallManagers in different clusters.

Cisco IOS H.323 Gateways

Cisco IOS H.323 gateways such as the Cisco 2600, 3600, 1750, 3810 V3, 7200 7500, AS5300, and VG200 provide full-featured routing capabilities as well as VoIP gateway functions. Refer to the documentation for each of these gateway types for information about support voice gateway features and configuration.

Intercluster Trunks

Use an intercluster trunk, an H.323 device, to connect two Cisco CallManagers in remote clusters. For information about configuring gatekeeper-controlled H.323 intercluster trunks for routing intercluster calls across a remote WAN link, refer to the Cisco IP Telephony Network Design Guide.

Voice Gateway Model Summary

Table 33-1 summarizes Cisco voice gateways supported by Cisco CallManager, with information about the gateway control protocols, trunk interfaces, and port types.

Table 33-1 Overview of Supported Voice Gateways, Protocols, Trunk Interfaces, and Ports 

Gateway Model
Gateway Control Protocol
Trunk Interface
Port Types
Cisco IOS Integrated Routers

Cisco 1750

H.323 (H.225)

FXS

FXO

POTS

Loop start or ground start

Cisco 3810 V3

H.323 (H.2250

T1-CAS

E1-CAS

T1-CAS

E1-CAS

Cisco 2600

MGCP or H.323

FXS

FXO

T1 PRI

T1-CAS

E1 PRI

POTS

Loop start or ground start

T1 PRI

E&M

E1 PRI

Cisco 3600

MGCP or H.323

FXS

FXO

T1 PRI

T1-CAS

E1 PRI

POTS

Loop start or ground start

T1 PRI

E&M

E1 PRI

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

Intercluster Trunk

H.323

Intercluster Trunk

Not applicable

Cisco Standalone Voice Gateways

Cisco Voice Gateway 200 (VG200)

MGCP or H.323

FXO

FXS

T1-PRI

T1-CAS

E1 PRI

Loop start or ground start

POTS

T1-PRI

E&M

E1 PRI

Cisco Access Digital Trunk Gateway DE-30+

MGCP

E1-PRI

E1 PRI

Cisco Access Digital Trunk Gateway DT-24+

MGCP

T1-PRI

T1-CAS

T1-PRI

E&M, loop start, ground start

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

SGCP

FXO

Loop start

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

SGCP

FXS

POTS

Cisco VG248 Analog Phone Gateway

Skinny Client Control Protocol

FXS

POTS

Cisco Catalyst Voice Gateway Modules

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

MGCP or H.323

FXS

FXO

T1 CAS

POTS

Loop start or ground start

E&M

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

MGCP

T1-PRI

T1-CAS

T1-PRI

E&M, loop start, ground start

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

MGCP

E1-PRI

E1-PRI

Cisco Catalyst 6000 24-Port FXS Analog Interface Module

MGCP

Foreign Exchange Station (FXS)

POTS

Cisco Catalyst 6000 AVVID Services Module

MGCP

FXS

T1-PRI

T1-CAS

E1-PRI

POT

T1-PRI

E&M

E1-PRI

Cisco ICS Gateways

Cisco  ICS77XX-MRP2xx

MGCP or H.323

FXS

FXO

T1-PRI

T1-CAS

E1-PRI

POTS

Loop start or ground start

T1-PRI

E&M

E1-PRI

Cisco ICS77XX-ASI81

MGCP or H.323

FXS

FXO

T1-PRI

T1-CAS

E1-PRI

POTS

Loop start or ground start

T1-PRI

E&M

E1-PRI

Cisco ICS77XX-ASI160

MGCP

FXS

FXO

POTS

Loop start or ground start


Gateways, Dial Plans, and Route Groups

Use dial plans to access or call out to the PSTN; route groups; and group specific gateways. Remote Cisco CallManagers across the IP WAN are configured as intercluster (H.323) gateways.

The different gateways used within the Cisco IP Telephony Solutions have dial plans configured in different places:

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

Typically configure H.323-based Cisco IOS software gateways dial plan configuration in Cisco CallManager to access that gateway and configure dial peers in the gateway to pass that call out the gateway.

The route group points to one or more gateways and can select the gateways for call routing based on preference. The route group can direct all calls to the primary device and then use the secondary devices when the primary is unavailable. This serves effectively as a trunk group. 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. Route groups can perform digit manipulation that will override what was performed in the route pattern.

Configuration information associated with the gateway defines how the call is actually placed.

You can configure an H.323 gateway to be gatekeeper-controlled. This means that before a call is placed to an H.323 device it must successfully query the gatekeeper. Multiple clusters for inbound and outbound calls can share H.323 gateways, but MGCP and SGCP-based gateways are dedicated to a single Cisco CallManager cluster.

Gateway Failover and Failback

This section describes how Cisco voice gateways handle failover and failback.

MGCP Gateways

MGCP gateways receive a list of Cisco CallManagers according to the Cisco CallManager group, defined for the device pool assigned to the gateway. A Cisco CallManager group can contain one, two, or three Cisco CallManagers, listed in priority order, that the gateway uses there. If Cisco CallManager #1 goes down, then Cisco CallManager #2 is used. If #1 and #2 go down, then #3 is used.

Failback is the process of recovering a higher-priority Cisco CallManager when a gateway fails over to a secondary or tertiary Cisco CallManager. For Cisco MGCP gateways, higher priority Cisco CallManagers are periodically checked, statuses are taken and, when determined ready, marked as available again. The gateway then reverts to the highest available Cisco CallManager when all calls have gone idle, or within 24 hours, whichever occurs first. A failback may be forced by the administrator either by stopping the lower priority Cisco CallManager (calls are preserved), or by restarting the gateway (calls are terminated).

IOS H.323 Gateways

Using several enhancements to the dial-peer and voice class commands in Cisco IOS Release 12.1(2)T, Cisco IOS gateways can now support redundant Cisco CallManagers. A new command, h225 tcp timeout seconds, that has been added specifies the time 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 CallManager, it tries a second Cisco CallManager defined in another dial-peer statement. The Cisco IOS gateway shifts to the dial-peer statement with next highest preference setting.

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

interface Loopback0
ip address 1.1.1.1 255.255.255.0
voip-gateway voip bind srcaddr 1.1.1.1
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, we recommend 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 used in the setup might vary depending on protocol (RAS, H.225, H.245 or RTP).


SGCP Gateways

SGCP gateways are identical to MGCP gateways in terms of Cisco CallManager redundancy, failover and failback.

Cisco VG248 Analog Phone Gateway

The Cisco VG248 Analog Phone Gateway supports the Skinny Client Control Protocol for clustering and failover.

Gateway Configuration Checklist

Table 33-2 provides an overview of the steps required to configure gateways in Cisco CallManager, along with references to related procedures and topics.

Table 33-2 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 you are configuring.

Step 2 

Gather the information you need to configure the gateway to operate with Cisco CallManager and to configure the trunk interface to the PSTN or external non-IP telephony device.

Gateway Configuration Settings, Cisco CallManager Administration Guide

Port Configuration Settings, Cisco 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 you are configuring.

Step 4 

Add and configure the gateway in Cisco CallManager Administration.

Adding Gateways to Cisco CallManager, Cisco CallManager Administration Guide

Step 5 

Add and configure ports on the gateway.

Port Configuration Settings, Cisco CallManager Administration Guide

Step 6 

Add and configure the Cisco VG248 Analog Phone Gateway.

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

Cisco IP Phone Configuration, Cisco CallManager Administration Guide

Step 7 

For FXS ports, add directory numbers, if appropriate.

Adding a Directory Number, Cisco CallManager Administration Guide

Directory Number Configuration Settings, Cisco CallManager Administration Guide

Step 8 

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

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

Cisco IP Telephony Network Design Guide

Step 9 

Reset the gateway to apply the configuration settings.

Resetting and Restarting Gateways, Cisco CallManager Administration Guide



Tip To get to the default web pages for gateway devices, you can use the IP address of that gateway. Make your hyperlink url = http://www.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

Adding Gateways to Cisco CallManager, Cisco CallManager Administration Guide

Gateway Configuration Settings, Cisco CallManager Administration Guide

Port Configuration Settings, Cisco CallManager Administration Guide

Directory Number Configuration Settings, Cisco CallManager Administration Guide

Additional Cisco Documentation

Cisco  IP Telephony Network Design Guide

Configuring Cisco IP Telephony Voice Gateways

Implementing Fax Over IP on Cisco Voice Gateways

Cisco VG248 Analog Phone Gateway Software Configuration Guide

Cisco VG248 Analog Phone Gateway Hardware Installation Guide