RAD Data comm HCD-E1 ,

HCD-E1 Installation & Operation Manual Chapter 1 - Introduction

01/01/01 08:07 Functional Description 1-17

Time Slot 0 Time Slot 16 Time Slots 1-15, 17-31

FAS MAS

a. Even Frames (0,2,4-14)

b. ODD Frames (1,3,5-15)

a. Frame 0

b. Frames 1-15

Channel Data

10011011

I1 ANNNNN

0000XYXX

ABCDABCD 12345678

32 Time Slots/Frame

8 Bits/

Time Slot

16 Frames/Multiframe

Notes

ABCD

MAS

FAS

International Bit

National Bit

Alarm Indication Signal (Loss of Frame Alignment - Red Alarm)

Frame Alignment Signal, Occupies alternate

(but not necessarily even) frames

ABCD Signaling Bits

Extra Bit

Loss of Multiframe Alignment

Multiframe Alignment Signal

Figure 1-9 E1 (CEPT) Frame Format

The 256 bits consist of 32 time slots of eight bits each, that carry the data

payload. The frame repetition rate is 8,000 per second, and therefore the

data rate supported by each time slot is 64 kbps. The number of time slots

available for user data is maximum 31, because time slot 0 is always used for

frame synchronization.

Time Slot 0

Time slot 0 is used for two main purposes:

• Delineation of frame boundaries. For this purpose, in every second frame

time slot 0 carries a fixed pattern, called Frame Alignment Signal (FAS).

Frames carrying the FAS are defined as even frames, as they are assigned

number 0, 2, 4, etc. when larger structures (multiframes) are used.

The receiving equipment searches for this fixed pattern in the data stream

using a special algorithm, a process called frame synchronization. Once this

process is successfully completed, the equipment can identify each bit in the

received frames.

• Transmission of housekeeping information. In every frame without FAS

RAD Data comm HCD-E1 operation manual ,