Packet data networks often engineer bridges using the 80/20 rule. They are configured
in such a manner that the bridge routes 20 percent of the traffic off-net, and 80 percent
on-net. Tandems, on the other hand, are specifically designed for interconnection of different
networks and network service areas.
The MGCF can be engineered in such a way as to route traffic between media gateways
within its own control, and a smaller percentage of traffic routing to other media
gateways outside of its control. They can also be implemented as more of a central function
providing a sort of tandem function within a network.
Moving from Legacy to Convergence 47
Either way, their function within the IMS is to manage the packetized voice that is
routed into the IMS domain, and to pass the control of these calls through the MGCF
up to the Call Session Control Function (CSCF). They are needed only when interconnecting
with the Public Switched Telephone Network (PSTN).
The Breakout Gateway Control Function (BGCF) We have talked about the BGCF some
already. The BGCF sits at the border of the network and controls interconnections between
two networks. This means that the BGCF must provide some security capabilities
to prevent unauthorized access into the network.
As shown in Figure 2.3, the BGCF interfaces with the various MGCF entities within
its own domain and then provides the connection to another network connecting into
the BGCF of that network.
Pages:
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127