Page 86 - Optical Switching And Networking Handbook

04_200023_CH03/Batesx 1/17/01 9:42 AM Page 71

SONET 71

The SONET VT1.5 signal carries a 1.544-Mbps DS-1 signal plus
path overhead. This forms a 1.728-Mbps digital signal. In Figure 3-
13, the VT1.5 signals are inserted into the STS payload area. It is
easy to see that the VT1.5 signals are still visible within the STS-1
payload area.

SONET Multiplexing Functions

SONET can accommodate several different signal sizes within the
STS-1 (49.536 Mbps) payload. SONET then multiplexes together the
individual STS-1 signals to form larger signals for transport across
a fiber medium. SONET also has the ability to carry larger signals
than the STS-1 payload through a process called concatenation.
The primary principles of the SONET multiplexers are as follows:

Mapping the tributaries into the STS-n frame
Aligning the information by using the pointer information to
determine where the first byte of the tributary is located

Figure 3-13
VT1.5s are still
visible in the
payload of a VT1.5
VT1.5
SONET STS-1
signal.

VT 1.5

VT1.5