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Cisco Voice Gateways and Gatekeepers (paperback), 1st edition

  • David Mallory
  • Ken Salhoff
  • Denise Donohue

Published by Cisco Press (August 17th 2006) - Copyright © 2007

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Cisco Voice Gateways and Gatekeepers

ISBN-13: 9780132798358

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Cisco Voice Gateways and Gatekeepers


Understanding and configuring GW/GK in complex VoIP networks


Denise Donohue, CCIE® No. 9566

David Mallory, CCIE No. 1933

Ken Salhoff, CCIE No. 4915


Deployments of voice over IP (VoIP) networks continue at a rapid pace. Voice gateways are an essential part of VoIP networks, handling the many tasks involved in translating between transmission formats and protocols and acting as the interface between an IP telephony network and the PSTN or PBX. Gatekeepers and IP-to-IP gateways help these networks scale. Gatekeepers provide call admission control, call routing, address resolution, and bandwidth management between H.323 endpoints including Cisco IOS® voice gateways and Cisco® Unified CallManager clusters. IP-to-IP gateways allow VoIP calls to traverse disparate IP networks.


Cisco Voice Gateways and Gatekeepers provides detailed solutions to real-world problems encountered when implementing a VoIP network. This practical guide helps you understand Cisco gateways and gatekeepers and configure them properly. Gateway selection, design issues, feature configuration, and security and high-availability issues are all covered in depth. The abundant examples, screen shots, configuration snips, and case studies make this a truly practical and useful guide for anyone interested in the proper implementation of gateways and gatekeepers in a VoIP network. Emphasis is placed on the accepted best practices and common issues encountered in real-world deployments.


Cisco Voice Gateways and Gatekeepers is divided into four parts. Part I provides an overview of an IP voice network. Part II is dedicated to voice gateways, including discussions of Media Gateway Control Protocol (MGCP); H.323; Session Initiation Protocol (SIP); voice circuit options; connecting to the PSTN, PBX, and IP WAN; dial plans; digit manipulation; route selection; class of restriction; Survivable Remote Site Telephony (SRST) and MGCP fallback; digital signal processor (DSP) resources; and Tool Command Languaue (Tcl) scripts and Voice XML (VXML). Part III addresses voice gatekeepers, including detailed deployment and configuration. Part IV is dedicated to IP-to-IP gateways.


“With this book, the authors provide an in-depth look at the breadth of voice gateway features and capabilities, as well as providing voice gateway configuration guidance.”

–Christina Hattingh, Access Technology Group, Cisco Systems®


  • Understand the pros and cons of MGCP, H.323, and SIP, how they implement call signaling and describe call flow, and how to configure each protocol
  • Learn the various analog and digital voice circuit options used to connect a VoIP network to the PSTN
  • Configure and troubleshoot PSTN, PBX, and IP WAN connections
  • Build scalable dial plans and understand the different types of dial peers
  • Understand the various ways gateways control called and calling phone numbers
  • Examine call admission control (CAC) techniques
  • Configure Class of Restrictions (CoR) for both inbound and outbound calls
  • Deploy and troubleshoot SRST and MGCP fallback
  • Evaluate DSP considerations and resources
  • Support interactive voice response (IVR) and advanced call-handing applications using Tcl scripts and VXML
  • Deploy and configure basic and advanced gatekeeper functions
  • Configure and troubleshoot IP-to-IP gateways

Table of contents



Part I   Voice Gateways and Gatekeepers

Chapter 1   Gateways and Gatekeepers

The Role of Voice Gateways

    Types of Voice Gateways

The Role of Voice Gatekeepers

The Role of IP-to-IP Gateways

Introduction to Voice Protocols

    Media Gateway Control Protocol


    Session Initiation Protocol

    Skinny Client Control Protocol

    Real-Time Transport Protocol

Call Control Agents

    Cisco CallManager

    Cisco CallManager Express

    SIP Proxy Server

    Cisco Enterprise Gateway

    PBX with Toll Bypass

Deployment Scenarios

    Single Site Deployment

    Multisite with Centralized Call Control

    Multisite Deployment with Distributed Call Control

Case Study: Introduction

Chapter Review Questions

Part II   Gateways

Chapter 2   Media Gateway Control Protocol

Introduction to MGCP



MGCP Operation

    MGCP Messages

    Registering with CallManager

Call Flow with MGCP

    Call Flow Between Analog Phones

    ISDN Connections with Backhaul

    MGCP Fallback

Dial Plan Considerations

Implementing MGCP Gateways

    Basic MGCP Gateway Configuration

    Configuring MGCP Fallback

    Assigning an MGCP Source IP Address

    Configuring MGCP PRI and BRI Backhaul

    Enabling Multicast Music on Hold

    Configuring Cisco CallManager

    Configuring CallManager Redundancy

    Configuring DTMF Relay

Securing MGCP Gateways

Troubleshooting Tools

Case Study: Configuring an MGCP Gateway

Review Questions

Chapter 3   H.323

H.323 Specifications

H.323 Network Components

    H.323 Gateways

    H.323 Gatekeepers

    H.323 Terminals

    Multipoint Control Units

    H.323 Proxy Servers

Call Flow


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