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11_200023_CH10/Bates 1/17/01 9:06 AM Page 244

244 Chapter 10

Figure 10-6 H.248 M H.323 NTP RTP
G
Changes in the Voice SAP SIP C
model add the RTP
to the application TCP UDP
layer

IP

ATM/FR/T1

Physical (Fiber)

400,000
Figure 10-7
The growth In the
350,000
volume of users
300,000
Users in ,000s 250,000

200,000
150,000

100,000

50,000
0
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Much of the decisions were based on the fact that the telecommu-
nications networks were built on TDM architectures and
SONET/SDH. SONET ran out of steam as the network grew beyond
the capacities that were well known and comfortable. In the normal
way of delivering the data speed communications, SONET devices
(specifically the add/drop multiplexers) were exclusively used to drop
off smaller subscriber circuits from a larger communications chan-