N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 5 - SONET, WDM, DWDM and B-ISDN Technologies                                                             Slide 35 of 76 _________________                                                                                  __________

                                               SONET Standard Signals

                                            STS-1

                                            Virtual Tributaries (VTs)

_________________                                                                                  __________

The basic building blocks for SONET signals are Synchronous Transport Signal Level 1 and Virtual Tributaries.

Level 1 SONET Signal - a 51.84 M bps signal used to transport DS-X hierarchy.

Virtual Tributaries - Developed to transport lower rate signals. VTs are mapped into STS-1 signal frame. Each VT envelope has its own overhead bits and function as a separate container within the STS-1 signal. Types of VTs are distinguished from each other by their bit rates e.g. VT1.5 for 1.544 M bps and Async DS3 for 45 M bps.