
Overview of Line Protocols
1-15
Figure 1-9. Bipolar with 8-Zero Substitution
T1 Frame Format
T1 uses two types of frame formats:
•D4
• Extended superframe (ESF)
D4
D4 is the original T1 frame format. A D4 frame (Figure 1-10) comprises
• One framing bit
•A DS0 timeslot for each channel on the line
A DS0 timeslot is an 8-bit sample from a channel.
A T1 line generates 8000 D4 frames/second.
Line Voltage
Data
11 100000
0000
Substituted Byte
Binary Polar
Violation
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