
Configuring WAN Line Services
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Enabling or Disabling T1 Services
The router enables T1 line services when you add the circuit. You can enable or
disable this interface without moving the cables.
See the Enable parameter on page A-88 for information.
Setting the T1 Frame Type
T1 framing digitizes analog signals to a digital signal, level zero (DS0) with 8-bit
words. T1 uses two types of frame formats:
•D4 Format
• ESF Format
The frame format of the interface should match the frame format required by the
associated T1 equipment.
D4 Format
The D4 format, or superframe format (SF), is the original T1 frame format. A D4
frame consists of:
• 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 per second.
ESF Format
The D4 format (SF) does not allow testing of a digital line while the line is in use.
To allow such testing, you can use the extended superframe format (ESF).
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)
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