These are not compatible with packet networks, however. Since there
Figure 2.2 The media gateway (MG) and the media gateway controller (MGC)
MG MG
MGCF SIP call control
BGCF BGCF
IP network
MGCF
SIP
SIP SIP
SIP
Voice Voice
46 Chapter 2
are no switches in the packet domain, there must not only be another function to generate
the various service tones we are all accustomed to hearing, there must also be a
controller for managing the various tones and recordings.
This function lies within the Media Resource Function (MRF). The MRF consists of
two distinct functions: the media resource processor (MRP) and the media resource
controller (MRC). The MRC can interface to multiple MRPs to generate all of the tones
and announcements needed within the IMS domain.
The MRP then is responsible for creating the tone or announcement based on instructions
from the MRC. The MRC uses SIP for communicating the requirements
(such as what tones or announcements are to be provided). This replaces the methods
used within the circuit-switched domain of routing calls over dedicated facilities to
recording or announcement devices. In this case the facilities are IP connections.
The Media Gateway Control Function (MGCF) The MGCF is widely used within VoIP
networks already, and its role within the IMS is the same. The purpose of the MGCF
is to provide connectivity at the control layer into the IMS, controlling all of the media
gateways that are managing the bearer traffic.
Pages:
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125