This is the responsibility of the
ISDN User Part (ISUP) protocol. The second function is for the connection and communication
with various databases within the network. This is the job of the Transaction
Control Application Part (TCAP).
Figure 2.1 Circuit-switched domain
EO EO EO
Tandem Tandem
EO EO EO
SS7 call control
network
TDM trunks
MG MG
MGCF
TDM trunks
SIP call control
BGCF BGCF
IP network
MGCF
42 Chapter 2
This signaling method works very well within today??™s circuit-switched networks but
is not compatible with packet networks, because the facilities have different attributes,
and the media being sent through these facilities have different requirements. For
example, in a packet network the amount of bandwidth is variable, and therefore the
amount of bandwidth required for a session must be identified. The method used to
packetize the voice (or whatever bearer traffic is being sent) must be identified so that
the packet can be disassembled at the destination.
There is much more information exchanged, of course, in both domains, as we will see
in the next few chapters as we break down the processes and procedures for the IMS
signaling. Remember throughout these discussions that we are talking primarily about
the signaling within each of these domains and not the bearer traffic.
When a subscriber initiates a call within the fixed circuit domain, that subscriber??™s
location is identified through the facility he or she uses to gain access.
Pages:
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116