363-206-295
A SONET Overview
Issue 1 December 1997 A-13
Two key points should be noted at this time. First, the SONET frame is a fixed time
(125 µs) and no bit-stuffing is used. Second, as shown in Figure A-7, the
synchronous payload envelope can
float
within the frame using byte-stuffing. This
is to permit compensation for small variations in frequency between the clocks of
the two systems that may occur if the systems are independently timed
(plesiochronous timing). The SPE can also drift across the 125-µs frame
boundary. SONET STS pointers are used to locate the SPE relative to the
transport overhead.
Figure A-7. STS-1 Synchronous Payload Envelope in Interior of STS-1 Frame
9 Rows
9 Rows
3 Columns
87 Columns
STS-1 SPE
at any byte boundary)
(SPE can start
STS-1 Frame Format
Start of STS-1 SPE
info
Pointer
STS-1 POH
90 Columns
Transport Overhead
info
Pointer
s125
STS-1 Synchronous Payload Envelope
s125
To Next Page
Loading...
Need help?
General
