
Configuring WAN Line Services
6-4
117345-B Rev. 00
An ESF frame comprises 24 D4 frames. A D4 frame contains one framing bit. An
ESF frame contains 24 framing bits that it uses for the following purposes:
• Synchronization (6 bits)
• Error checking (6-bit CRC)
• Diagnostic data channel (12 bits)
By default, the T1 interface uses ESF format. Set the frame type for this interface.
See the Frame Type parameter on page A-74 for information.
Enabling or Disabling Bipolar with 8 Zero Substitution (B8ZS)
T1 uses bipolar format for signals. In bipolar format, alternating positive and
negative pulses on the digital line signify the number 1, and the absence of a pulse
signifies 0 (Figure 6-2).
Figure 6-2. Bipolar Format
In bipolar format, a negative pulse must always follow a positive pulse, and vice
versa. A long string of zeros on a T1 line would cause the line to lose
synchronization due to lack of pulses. Bay Networks offers B8ZS for T1
synchronization.
Line voltage
Data
11 10000
0
+3V
-3V
0
LS0009A
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