A
Appendix A
A.1 Superframe Format (SF)
The Superframe Format (SF), is also referred to as the D4 format. The
requirement for associated signaling in frames 6 and 12 dictates that the frames
be distinguishable. This leads to a multiframe structure consisting of 12 frames
per superframe (SF). See Figure A-1 and Table A-1 and A-2.
The SF structure consists of a multiframe of 12 frames. Each frame has 24
channels, plus an F-bit, and 8 bits per channel. A channel is equivalent to one
voice circuit or one 64 kbps data circuit.
This structure of frames and multiframes is defined by the F-bit pattern. The
F-bit is designated alternately as an Ft bit (terminal framing bit) or an Fs bit
(signalling framing bit). The Ft bit carries a pattern of alternating 0s and 1s
(101010) in odd frames that defines the frame boundaries so that one channel can
be distinguished from another. The Fs bit carries a pattern of (001110) in even
frames, and defines the multiframe boundaries so that one frame can be
distinguished from another.
Figure A-1. T1 Superframe PCM Format
Signalling Information
B
A
8 Bits per Channel
3
Bit 8
During:
1
2
4
5
6
7
8
Frame 12
Frame 6
Ft
or
Fs
CH CH
CH
13
CH
24
24 Channels per Frame
Frame = 193 Bits
1
2
FR
1
FR
2
FR
7
FR
11
FR
12
Multiframe
SF = 12 Frames
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A-1
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