XRT84L38 Datasheet, PDF (194/451 Pages) Exar Corporation – OCTAL T1/E1/J1 FRAMER

XRT84L38
OCTAL T1/E1/J1 FRAMER
REV. 1.0.0
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3.0 THE DS1 FRAMING STRUCTURE
A single T1 frame is 193 bits long and is transmitted at a frame rate of 8000Hz. This results in an aggregate bit
rate of 193 bits X 8000/sec = 1.544 Mbits/sec. Basic frames are divided into 24 timeslots numbered 1 thru 24
and a framing bit, see Figure 20. Each timeslot is 8 bits in length and is transmitted most significant bit first,
numbered bit 0. This results in a single timeslot data rate of 8 bits x 8000/sec = 64 kbits/sec.
FIGURE 20. T1 FRAME FORMAT
Timeslot S Timeslot
24
bit
1
DS1 Frame
125µs
Timeslots
2 - 22
Timeslot Timeslot S Timeslot
23
24
bit
1
(1/1.544)µs
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
(8/1.544)µs
3.1 T1 SUPER FRAME 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 21 and Table 33.
The SF structure consists of a multiframe of 12 frames. Each frame has 24 timeslots, plus an F-bit and 8 bits
per timeslot. A timeslot is equivalent to one voice circuit or one 64kb/s 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 Fs bit (signalling framing bit). The Ft bit carries a pattern of alternating zeros
and ones (101010) in odd frames that defines the boundaries so that one timeslot may be distinguished from
another. The Fs bit carries a pattern of (001110) in even frames and defines the multiframe boundaries so that
one frame may be distinguished from another.
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