Cisco VG200 Using Manual

CHAPTER

1

Using the Cisco Voice Gateway 200

This chapter describes how to use the Cisco Voice Gateway 200 (VG200) with
Cisco CallManager 3.0 or later. It introduces the Media Gateway Control
Protocol (MGCP) and describes how MGCP supports redundant
Cisco CallManager servers. This chapter then provides an overview of the
configuration required to make this work. This chapter includes the following
topics:

• Voice over IP Overview, page 1-1

• Using the Cisco VG200 with Cisco CallManager, page 1-6

• Using the Cisco VG200 with MGCP, page 1-7

• Using a Cisco VG200 Gateway with H.323, page 1-8

• Where to Go Next, page 1-14

Voice over IP Overview

Voice over IP (VoIP)enables your gateway to carry live voice traffic(forexample,
telephone calls and faxes) over an IP network. VoIP can consolidate voice and
data traffic for more efficient use of bandwidth, reduce toll charges, and enable
alternatives to expensive and proprietary PBX systems.

The Cisco VG200 is an important component of a VoIP solution, providing a
simple and inexpensiveinterfacebetween an Ethernet data network and the Public
Switched Telephone Network (PSTN).

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Voice over IP Overview

This section covers the following topics, describing in a general way how VoIP
works and defining the standards supported by the Cisco VG200 used to
implement a VoIP network.

• Implementing a VoIP Network, page 1-2

• The H.323 Standard, page 1-3

• Media Gateway Control Protocol, page 1-5

Implementing a VoIP Network

To implement VoIP, you must firstestablish a working IP network and ensure that
the network is properly tuned to reduce congestion. Voice traffic is more sensitive
to congestion than data traffic, meaning that users will notice more congestion
when using VoIP telephones than when using IP for other purposes. For more
information about configuring IP, refer to the “Configuring IP” chapter in the
Cisco IOS 12.0 Network Protocols Configuration Guide.

You also need to thoroughly understand your company’s existing voice network
and dial plan, which is the pattern of dialed numbers that provides access to
different telephony endpoints. You can then begin the process of integrating your
voice and data networks, which should be done cautiously and systematically to
prevent disruption of existing telephone service.

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Chapter 1 Using the Cisco Voice Gateway 200

Figure 1-1 Typical VoIP Network

POTS phones

PSTN

Voice over IP Overview

Gateway

TCP/IP network

In a VoIPnetwork,illustrated in Figure 1-1, it is possible for IP telephony devices
to interoperate directly.However, to connect to the PSTN, an intermediary device,
called a gateway, is required. A VoIP gateway, such as the Cisco VG200, allows
users of IP phones and PC-based soft phones to exchange calls with users of plain
old telephone service (POTS) phones on the PSTN. The gateway translates
between the signals used on the PSTN and the IP packets used to transmit data on
a TCP/IP network.

The H.323 Standard

The H.323 standard describes a method for converting between voice and data
transmission formats and for managing connections between telephony
endpoints. H.323 is actually a collection of protocols that define standard methods
for interconnecting H.323 endpoints (sometimes called terminals) and POTS
devices.

IP phones Soft phones

33340

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Voice over IP Overview

Figure 1-2 The H.323 Standard

POTS phones

H.323 Gateway

PSTN

TCP/IP network

Chapter 1 Using the Cisco Voice Gateway 200

H.323 Proxy

Simple IP

telephony devices

H.323 end point

H.323 Gatekeeper

33341

H.323 endpoints can communicate among each other without the intervention of
any other devices, howevertoconnect them to the PSTN, to manage call setup and
network bandwidth, and to simplify administration, the following devices are
often used:

• H.323 gateway—Connects H.323 devices to POTS devices on the PSTN

• H.323 gatekeeper—Manages network bandwidth and provides a central point

for call administration

• H.323 proxy—An H.323 endpoint that acts as an intermediary between H.323

endpoints and other IP telephony devices

To standardize communication among these devicesand endpoints, H.323 utilizes
the following protocols:

• H.245—Used to negotiate channel usage and capabilities

• H.225—Used for call signaling and call setup

• Registration, Admission and Status (RAS)—Used to communicate with the

H.323 gatekeeper

• Real-Time Protocol/Real-Time Control Protocol (RTP/RTCP)—Used to

create and transmit audio packets on the IP data network

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Chapter 1 Using the Cisco Voice Gateway 200

H.323 is a peer-to-peer protocol, helping to establish and manage connections
among H.323 endpoints. As with other peer-to-peer protocols, the many-to-many
relationships become difficulttoconfigure and maintain in large networks. MGCP
was developed specifically to overcome the problem of scalability inherent in the
H.323 protocol.

Media Gateway Control Protocol

MGCP establishes a master-slave protocol which, when compared to H.323,
simplifies voice network administration and improves reliability and
performance. In particular, it makes configuration and administration of gateway
devices easy. With MGCP, gateways are defined by MGCP as slave devices in
relation to the master, referred to as a call agent, which manages connections
between endpoints and controls how gateways function.

Figure 1-3 MGCP

POTS phones

Voice over IP Overview

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MGCP call agent

MGCP Gateway

PSTN

TCP/IP network

MGCP-managed endpoints

33342

Because an MGCP gateway is a slave device, it derives most of the configuration
it requires from the call agent. Toconfigurean MGCP gateway,all you need to do
is to identify the call agent on the gateway and identify the gateway to the call
agent. In addition, MGCP optionally supports multiple call agents, which can
eliminate a potential single point of failure in the voice network.

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