A gateway is a device that translates one type of signal into another type of signal. One type of gateway is the voice gateway. A voice gateway is a router or switch that converts IP voice packets to analog or digital signals that are understood by trunks or stations. Gateways are used in several situations, for example, connecting to a PSTN or PBX, or connecting individual devices such as an analog phone or fax.
This chapter provides an overview of the voice gateways that you can use with the Cisco CallManager system and describes their basic configuration. For more information on configuring voice gateways, refer to Authorized Self-Study Guide: Cisco Voice over IP (CVOICE), Second Edition (ISBN: 1-58705-262-8) or Cisco Voice Gateways and Gatekeepers (ISBN: 1-58705-258-X) from Cisco Press.
Analog and Digital Gateways
There are two types of Cisco access gateways: analog and digital. At a high level, the difference between these two types of gateways is their capacity. Analog gateways (and analog connections) receive one line per port. This port could be a connection to the PSTN, an end device such as a fax machine, or a link to a PBX. Regardless of the connection, analog ports only permit one voice path per line. There are two categories of analog gateways:
Depending on the cards you have installed into a gateway, it could fill both station (FXS) and trunk (FXO) roles.
On the flip side, digital gateways typically allow multiple calls per port. These gateways connect the Cisco CallManager to the PSTN or to a PBX via digital trunks, such as PRI common channel signaling (CCS), BRI, T1 channel-associated signaling (CAS), or E1. Digital T1 PRI trunks might also connect to certain legacy voice-mail systems. Regardless of the connection type, you will typically use a digital gateway to provide a high-capacity connection to an alternate network type.
Core Gateway Requirements
To support modern VoIP networks, your IP telephony gateways must meet these core feature requirements:
Any IP telephony gateway that you select for an enterprise deployment should support these core requirements. In addition, every IP telephony implementation has its own site-specific feature requirements, such as analog or digital access, DID, and capacity requirements.
Gateway Communication Overview
For Cisco CallManager to reach other networks (including the PSTN), it must be able to communicate with the gateways connected to these networks. Cisco CallManager 4.x supports these three types of gateway communication protocols:
Examples of Cisco gateway devices that support H.323 include the Cisco VG224 Analog Phone Gateway (FXS only), Cisco 2600, Cisco 2800, Cisco 3700, and Cisco 3800 devices.
Examples of Cisco gateway devices that support MGCP are the Cisco VG224 (FXS only), Cisco 2600, Cisco 2800, Cisco 3700, and Cisco 3800 devices. Examples of non-IOS devices that support MGCP are the Cisco Catalyst 6000 WS-X6608-T1 and -E1.
Examples of Cisco devices that support SCCP are the Cisco VG224 Analog Phone Gateway (FXS only) and the Cisco VG248 Analog Phone Gateway. The Cisco VG224 gateway is 24-port gateway for analog phones, fax machines, modems, and speakerphones using Cisco CallManager or Cisco CallManager Express. The Cisco VG248 device is a 48-port gateway.
SIP can also be used as a gateway control protocol. Most Cisco IOS images that support H.323 and MGCP also support SIP. Cisco CallManager 4.x supports SIP trunks to connect CallManager to distributed SIP networks.
Most gateway devices support multiple gateway protocols. Selecting the protocol to use depends on site-specific requirements and your installed base of equipment. You might prefer MGCP to H.323 because of the simpler configuration of MGCP or its support for call survivability during a Cisco CallManager switchover from a primary to a secondary Cisco CallManager. In addition, you might prefer H.323 to MGCP because of the interface robustness of H.323 or the ability to use it with call admission control or SRST. The Cisco-recommended best practices direct corporations to use MGCP unless they have a specific reason to choose another protocol.
Configuring Access Gateways
Part I: Cisco CallManager Fundamentals
Introduction to Cisco Unified Communications and Cisco Unified CallManager
Cisco Unified CallManager Clustering and Deployment Options
Cisco Unified CallManager Installation and Upgrades
Part II: IPT Devices and Users
Cisco IP Phones and Other User Devices
Configuring Cisco Unified CallManager to Support IP Phones
Cisco IP Telephony Users
Cisco Bulk Administration Tool
Part III: IPT Network Integration and Route Plan
Cisco Catalyst Switches
Configuring Cisco Gateways and Trunks
Cisco Unified CallManager Route Plan Basics
Cisco Unified CallManager Advanced Route Plans
Configuring Hunt Groups and Call Coverage
Implementing Telephony Call Restrictions and Control
Implementing Multiple-Site Deployments
Part IV: VoIP Features
Configuring User Features, Part 1
Configuring User Features, Part 2
Configuring Cisco Unified CallManager Attendant Console
Configuring Cisco IP Manager Assistant
Part V: IPT Security
Securing the Windows Operating System
Securing Cisco Unified CallManager Administration
Preventing Toll Fraud
Hardening the IP Phone
Understanding Cryptographic Fundamentals
Understanding the Public Key Infrastructure
Understanding Cisco IP Telephony Authentication and Encryption Fundamentals
Configuring Cisco IP Telephony Authentication and Encryption
Part VI: IP Video
Introducing IP Video Telephony
Configuring Cisco VT Advantage
Part VII: IPT Management
Introducing Database Tools and Cisco Unified CallManager Serviceability
Configuring Alarms and Traces
Using Additional Management and Monitoring Tools
Part VIII: Appendix
Appendix A. Answers to Review Questions