Cisco AS5350XM

Basic Configuration Using the Command-Line Interface
Configuring the D Channels for ISDN Signaling
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Cisco AS5350XM and Cisco AS5400XM Universal Gateways Software Configuration Guide
Configuring the D Channels for ISDN Signaling
The ISDN D channels carry the control and signaling information for your ISDN calls—for both
circuit-switched data calls, and analog modem calls.
The D channel notifies the central office switch to send the incoming call to particular time slots on the
Cisco gateway or router. Each one of the B channels carries data or voice. The D channel carries
signaling for the B channels. The D channel identifies whether the call is a circuit-switched digital call
or an analog modem call. Analog modem calls are decoded and then sent off to the onboard modems.
Circuit-switched digital calls are directly relayed to the ISDN processor in the gateway.
When you configured ISDN PRI on the T1 or E1 controller, you automatically created a serial interface
that corresponds to the PRI group time slots. This interface is a logical entity that is associated with the
specific controller. After the serial interface is created, you must configure the D channel serial interface
that carries signaling. The configuration applies to all the PRI B channels (time slots) for that PRI group.
Figure 3 shows the logical contents of an ISDN PRI interface used in a T1 network configuration. The
logical contents include 23 B channels, 1 D channel, 24 time slots, and 24 virtual serial interfaces (total
number of B + D channels).
Figure 3 Logical Relationship of ISDN PRI Components for T1
Note When you configure your T1 controller for an NFAS backup D channel, a serial interface is
automatically created only when your primary D channel fails.
B (data channel) 1 S0:0
B (data channel) 2 S0:1
B (data channel) 3 S0:2
B (data channel) 4 S0:3
•••
•••
•••
•••
•••
B (data channel) 21 S0:20
B (data channel) 22 S0:21
B (data channel) 23 S0:22
D (signaling channel) 24 S0:23
35765
Channel
type
Time slot
number
Logical
contents
of a PRI
interface
Virtual
serial
interface
number