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Chapter 45 VoIP

IES-1248-51V User’s Guide

318

• Media gateways (MGs) encode and decode voice data, transmitting it from one

network to another (for example, from the PSTN to an IP network, and vice

versa). The H.248-enabled VoIP line cards are MGs.

• Media gateway controllers (MGCs) are intelligent devices that manage the

media gateways. They set up, manage and tear down calls by providing

instructions to the MGs.

In the following example, the MG allows the users of analog telephone C and IP

telephone D to communicate by reporting events to the MGC 1 (for example, if

the user of phone C dials a sequence of numbers). The MGC 1 interprets the

information according to its programming and issues the relevant commands to

the MG (for example, telling the MG how to connect phones C and D in a call, or

telling the MG to play a busy tone to phone C). See Section 45.1.4 on page 319

for a detailed example of H.248 call progression. For increased reliability, the MG

can use a second MGC 2 if it cannot reach the MGC 1.

Figure 148 H.248 Network Example

45.1.2 Termination

A Termination is a logical entity representing a connection to a media stream. A

Termination sources and/or sinks connections to the media stream. Every

connection to the MG is uniquely represented by a Termination.

A Termination may represent either a physical connections (such as an analog

phone connection) or an ephemeral connection (such as an RTP stream).

Generally, ephemeral Terminations exist for only as long as they are in use. In

contrast, physical Terminations exist for as long as they are provisioned in the

gateway.

Each Termination is assigned a unique identity at the moment of its creation by

the MG.

MGC 1

IP NETWORK

ANALOG

MGC 2

1 2 ... 313 314 315 316 317 318 319 320 321 322 323 ... 653 654

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