Page 77 - Optical Switching And Networking Handbook

04_200023_CH03/Batesx 1/17/01 9:42 AM Page 62

62 Chapter 3

strongest selling points. Additionally, in the past, many of the high-
speed multiplexing arrangements (DS-2 and DS-3) used bit inter-
leaving to multiplex the data streams through the multiplexers.
SONET uses a byte-interleaved multiplexing format.This is a strong
point because it keeps the basic DS-0 signal intact throughout the
network, making it easier to perform diagnostics and troubleshoot-
ing. Byte interleaving simplifies the process and provides better end-
to-end management.
The base level of a SONET signal is called the synchronous trans-
port signal level 1 (STS-1), operating at 51.84 Mbps. The first step in
using the SONET architecture is to create the STS-1. Other levels
exist in multiples of STS-n to create a full family of transmission
speeds. The SONET hierarchy is shown in Table 3-2. In SONET, the
higher-level line rates are direct multiples of the OC-1 rate (51.84
Mbps), which means that additional stuffing is not necessary in the
multiplexing procedures.

Table 3-2
Electrical Optical Speed Capacity
Summary of Signal Value
Electrical and
STS-1 OC-1 51.84 Mbps 28 DS-1 or 1 DS-3
Optical Rates for
SONET STS-3 OC-3 155.520 Mbps 84 DS-1 or 3 DS-3

STS-12 OC-12 622.08 Mbps 336 DS-1 or 12 DS-3

STS-24 OC-24 1.244 Gbps 672 DS-1 or 24 DS-3
STS-48 OC-48 2.488 Gbps 1,344 DS-1 or 48 DS-3

STS-192 OC-192 9.953 Gbps 5,376 DS-1 or 192 DS-3
STS-768 * OC-768 40 Gbps 21,504 DS-1 or 768 DS-3

Note: Other rates exist, but these are the most popularly implemented.
*The OC-768 and STS-768 rates are newly defined. As the capacities are increased, the rates
will follow.