SECTION I MESSAGE FORMAT AND BASIC EQUIPMENT CONCEPTS

T.O. 31W2-2GSC24-2

TM 11-5805-688-14-1

NAVELEX 0967-LP-545-3011

SECTION I

MESSAGE FORMAT AND BASIC EQUIPMENT CONCEPTS

5-5.

GENERAL.

messages. Each overhead message consists of a

framing pattern and stuffing information pertaining to one

Paragraphs 5-6 through 5-18 contain a description of the

of the multiplexer's 31 ports. A complete overhead

message format used in the transmission of digital data

message in each minor frame is designated as an

from the multiplexer in a multiplexer set to the

overhead word. The overhead message content is

demultiplexer in a far-end multiplexer set.

Basic

discussed in greater detail in paragraph 5-14.

equipment concepts are described in paragraphs 5-19

through 5-67 to introduce maintenance personnel to the

5-10

A minor frame contains 29 data words and one

unique equipment functions that are performed in the

complete 29-bit overhead word, and is the second

multiplexer set.

largest organized grouping in the output message

format. One bit of the overhead word is located in the

5-6.

MESSAGE FORMAT.

first bit position of each of the 29 data words comprising

the minor frame. Thus, it can be seen that overhead

5-7.

OVERALL MESSAGE FORMAT.

words appear in the output message format at a rate one

twenty-ninth that of data words.

5-8. Data leaving the multiplexer are arranged in a

predetermined format as shown in figure 5-1. The

5-11. Each data word contains a sampled channel

message format contains data bits sampled from the

data bit for each port being used in the multiplexer. As

multiplexer's channel data inputs interleaved with

previously noted, an overhead data bit occupies the first

overhead data bits generated within the multiplexer.

data word bit position.

The total number of bits

Overhead data are inserted for two purposes: to provide

contained in a data word is variable, depending upon the

a framing or synchronization pattern for use by the

number of multiplexer ports in use. Each multiplexer

receiving demultiplexer, and to inform the demultiplexer

configuration must use a minimum of 15 ports; therefore,

of stuffing actions taken by the multiplexer as part of its

the minimum data word length is 16 bits (overhead + 15

input rate buffering process. For purposes of enabling

channel data bits). The word length can range up to 32

proper demultiplexer operation in a high bit error

bits (overhead + 31 channel data bits when all 31 ports

environment, data bits comprising a complete overhead

are in use.

message are evenly inserted over the span of numerous

channel data messages, as described in paragraph 5-14.

5-12.

In summary, a major frame is comprised of 31

minor frames, with each minor frame containing one

5-9. The largest organized grouping in the output

overhead word. Each 29-bit overhead word consists of a

message format is the major frame. The significance of

demultiplexer framing pattern and stuffing information

this grouping is that in addition to sampled channel data,

pertaining to one of the multiplexer's 31 ports. One

it contains 31 complete overhead

overhead bit is located in the first bit position of the 29

data words comprising the minor frame. Remaining data

word bit positions, varying in number between 15 and 31,

contain a sampled channel data bit for each multiplexer

port in use.

5-2