Cisco ASR 900 Series Configuration Guide

STS-1 and STS-3 Frames
A standard STS-1 frame is nine rows by 90 bytes. The first three bytes of each row represent the Section and
Line overhead. These overhead bits comprise framing bits and pointers to different parts of the SONET frame.
Figure 2: STS-1 Frame Structure
There is one column of bytes in the payload that represents the STS path overhead. This column frequently
"floats" throughout the frame. Its location in the frame is determined by a pointer in the Section and Line
overhead.
The combination of the Section and Line overhead comprises the transport overhead, and the remainder is
the SPE.
Figure 3: STS-1 SONET Overhead
For STS-1, a single SONET frame is transmitted in 125 microseconds, or 8000 frames per second. 8000 fps
* 810 B/frame = 51.84 Mbs, of which the payload is roughly 49.5 Mbs, enough to encapsulate 28 DS-1s, a
full DS-3, or 21 CEPT-1s.
1-Port OC-192 or 8-Port Low Rate CEM Interface Module Configuration Guide, Cisco IOS XE Everest 16.7.x (Cisco
ASR 900 Series)
23
Configuring SONET
STS-1 and STS-3 Frames

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English