ZyXEL Communications IES-1248-51A, User Manual

Page: 318 / 654

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.
C
D
MG
MGC 1
IP NETWORK
ANALOG
MGC 2