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CS62180B-IL

T1 Framer

Cirrus Logic 

CS62180B

The T1 format provides a 64 kbps channel for

each individual voice or data line. These PCM

voice channels consist of 8-bit samples which

are sampled at 8 kHz for a data rate of 64 kbps.

A T1 frame is constructed by multiplexing 24 of

these DS-0 channels and inserting a framing bit

at the beginning of the series. This results in 192

bits of channel data, plus an F-bit, for a total of

1.544 Mbps (193 bits/frame transmitted at 8

kHz). See Figure A3.

8 bits

Channel 1

Framing bit

64 kbps

each

Channel 24

193 bits

TDM

8 kHz Sampling

T1 Frame = 1.544 Mbps

f CH 1

CH 24

Figure A3. T1 Overveiw

Multiple T1 frames are then grouped into super-

frames of 12 or 24 frames to provide for framing

and signaling synchronization. The older 193S or

SF(D4®) format defines a superframe as 12

frames, with the F-bits carrying 2 channels of

synchronization signals. The emerging 193E, or

Extended Superframe Format (ESF) calls for 24

frames in a superframe. This allows the 24 F-bits

Frame 1 (F1)

f CH 1

CH 24

Frame 12 (F12)

f CH 1

CH 24

12 Frames = 193S Superframe

F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12

Frame 1 (F1)

f CH 1

CH 24

Frame 24 (F24)

f CH 1

CH 24

24 Frames = 193E Superframe

F1 F2 F3 F4 F5

F20 F21 F22 F23 F24

Figure A4. Framing Overveiw

to be divided into 3 separate channels for fram-

ing, CRC checks, and system messages.

Additional variations on T1 are used for Sub-

scriber Loop Carrier (SLC-96®) and Digital Data

Service (DDS®) T1DM.

193S Framing Format

Figure A5 shows the bit uses in the 193S fram-

ing format. The framing bits are divided into two

channels. The odd F-bits are designated as the

FT (terminal framing) channel, which always

carries a repeating pattern of "101010". This pat-

tern allows synchronization to the frame

boundaries, and distinguishes the even and odd

frames. The even F-bits are designated as the FS

(signaling framing) channel. This channel carries

a different synchronization code (001110) which

identifies superframe alignment. The FS channel

can alternately be used as a message channel for

system use, in which case there is no facility

provided for multiframe synchronization.

Signaling information associated with each indi-

vidual voice channel, such as on-hook/off-hook,

call progress, dialing digits, etc., is transmitted

within the voice channel itself. The signaling

data is transmitted in the LSB of each channel

193S

Frame

1

2

3

4

5

6

7

8

9

10

11

12

F-bits

FT FS

1

0

0

0

1

1

0

1

1

1

0

0

Signaling

Channel bits Options

Data Signaling T 2 4

1-8

1-7

Bit 8

- AA

1-8

1-7

Bit 8

- AB

Figure A5. 193S Framing Format

DS225PP2

45

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