Page 260 - Optical Switching And Networking Handbook

11_200023_CH10/Bates 1/17/01 9:06 AM Page 245

The Future of Optical Networking (Where Is It All Heading?) 245

nel. The add-drop multiplexer (ADM) was generally complemented
by a digital cross-connect system (DACS) that acts as the in-between
box for the channels as they travel across the backbone networks.
Figure 10-8 shows where the DACS sits in front of the ADM.

Legacy Systems

The older SONET multiplexers are transparent to the type of traffic
being carried. Therefore, they only act as they are programmed and
they operate on all traffic the same way. This means that these
legacy systems are somewhat inflexible and cannot differentiate the
type of services being carried. Consequently, the legacy multiplexers
are incapable of dynamically allocating bandwidth “on the fly,” cre-
ating some inconsistencies in the way the IP traffic is being gener-
ated. This lack of flexibility and integration in the network elements
limits the amount and type of traffic we can carry on the architec-
ture. Problems like this are common; however, they do get in the way
of progress.

Central Office
Figure 10-8
DACS in front of T1
the ADM

D
384 Kbps A SONET
C
S ADM

64K