User guide

August 2001 43
Understanding T1 Trunks
A single bit at the beginning of each frame contains
synchronization information. This bit is also called the F-bit or
framing bit. Figure 10 shows a single T1 frame with the
24 timeslots and a single F-bit. The 24 64 Kb/s lines plus the
F-bit make up a DS1 signal.
Figure 10. A T1 Frame Carrying 24 8-bit Timeslots
Each frame has a period of 125 µs, or 8000 frames per second.
This means that each channel receives 8000 8-bit timeslots per
second, or 64 Kb/s:
8000 timeslots/second x 8 bits/timeslot = 64 Kb/s
01
2
3
232221
20
00101101
8-bit timeslot
F
2322
1
0
F
DS1 125 S
Line 0
-
-
-
Line 23
Line 0
-
-
-
Line 23