Figure 5-2. Overhead Message Format

T.O. 31W2-2GSC24-2

TM 11-5805-688-14-1

NAVELEX 0967-LP-545-3011

5-13. OVERHEAD MESSAGE FORMAT.

23-bit stuff code, a 5-bit port number, and a sense bit.

5-14. As noted in the message format discussion in

5-15. The 23-bit stuff code is one of three different

paragraph 5-7, overhead data are inserted in the

forms, indicating positive, negative, or no-action stuffing

multiplexer output data stream. The overhead data

operations performed by the multiplexer. Frame

consist of a framing or synchronization pattern for the

synchronization circuits in the demultiplexer are designed

receiving demultiplexer, and information regarding

to detect and initially synchronize with any one of the

stuffing actions performed as part of the multiplexer's

three 23-bit stuff codes.

Other circuits in the

input rate buffering process. The latter information

demultiplexer, operating on the basis of the particular

enables the demultiplexer to properly perform its

stuff code (one of three) detected, control the

destuffing and smoothing operations.

A complete

demultiplexer destuffing and smoothing functions. Thus

overhead message is contained in each minor frame of

the 23-bit stuff code serves a dual purpose: it enables

the multiplexer's output message.

The overhead

initial demultiplexer frame synchronization and

message consists of a 29-bit word, with one bit located in

determines the type of destuffing and smoothing

the first bit position of each of the 29 data words

operation the demultiplexer is to perform.

comprising the minor frame. Figure 5-2 illustrates the

manner in which the overhead word is interleaved into

5-16. To enable the demultiplexer to fully synchronize

the multiplexer's output. The figure shows that the

with the transmitting multiplexer and properly perform its

overhead word conveys three types of information: a

Figure 5-2. Overhead Message Format

5-4