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11_200023_CH10/Bates 1/17/01 9:06 AM Page 241

The Future of Optical Networking (Where Is It All Heading?) 241

voice side of the network and the data calls directly into the Internet,
then the bandwidth would be better utilized. As shown in Figure 10-
3, a front-end system was used to receive the dial-up telephone calls
and analyze them. The calls were routed into the network based on
the dialed digits or the modem tones preceding the call setup. This
worked for a while, but it was a stopgap measure that had a short
life span.
Next came the dedicated links for separate voice traffic and data
access. In Figure 10-4, a company may have a T1 circuit installed to
the building for voice communications multiplexed at 64-Kbps voice
Time-Division Multiplexing (TDM) calls. The second T1 was used as
a dedicated access link into the Internet (or a corporate private net-
work). This works, but it is expensive and inefficient.
The topology changed as the progression wore on. The Internet no
longer is a single network; it is made up of thousands of interlocking
networks each owned and operated by independent organizations
(ILEC, ISP, CLEC, and end-user). These multiple backbones carry
different types of traffic. The number of applications supported has
also grown exponentially.

Figure 10-3
The front-end on
the network Voice
decided where
traffic went.
Data
PSTN
10011000010010000011

10011000010010
Internet
10011000010010000011010010011000101
10011000010010000011010010011000101