ISDN PRI is delivered over a leased T1 or E1 line. The main PRI configuration tasks are as follows:

1. Specify the correct PRI switch type that the router interfaces with at the CO of the ISDN provider.
2. Specify the T1/E1 controller, framing type, and line coding for the facility of the ISDN provider.
3. Set a PRI group timeslot for the T1/E1 facility and indicate the speed used.

Because routers connect to PRI using T1/E1, there is no "interface pri” command. Instead, the physical interface on the router that connects to the leased line is called a T1 controller, or an E1 controller, if an E1 line is being used. This controller must be configured properly in order to communicate with the carrier network. The ISDN PRI D and PRI B channels are configured separately from the controller, using the interface serial command.

Use the isdn switch-type command to specify the ISDN switch used by the provider to which the PRI connects. As with BRI, this command can be issued globally or in interface configuration mode. The table shows the switch types available for ISDN PRI configuration:

Router(config)#isdn switch-type primary-net5

Configuring a T1 or E1 controller is done in four parts:

1. From global configuration mode, specify the controller and the slot/port in the router where the PRI card is located:

   Router(config)#controller {t1 | e1} {slot/port}
   Router(config-controller)#


 
2. Configure the framing, line coding, and clocking, as dictated by the service provider. The framing command is used to select the frame type used by the PRI service provider. For T1, use the following command syntax:

   Router(config-controller)#framing {sf | esf}

   For E1 lines, use the framing command with the following options:

   Router(config-controller)#framing {crc4 | no-crc4} [australia]

   Use the linecode command to identify the physical-layer signaling method on the digital facility of the provider:

   Router(config-controller)#linecode {ami | b8zs| hdb3}

   In North America, the B8ZS signaling method is used for T1 carrier facilities. It allows a full 64 kbps for each ISDN channel. In Europe, it is typically HDB3 encoding that is used.

3. Configure the specified interface for PRI operation and the number of fixed timeslots that are allocated on the digital facility of the provider:

   Router(config-controller)#pri-group [timeslots range]

   For T1, the range of timeslots used is 1-24. For E1 the range of timeslots used is 1-31.

4. Specify an interface for PRI D-channel operation. The interface is a serial interface to a T1/E1 on the router:

   Router(config)#interface serial{slot/port: | unit:}{23 | 15}

Within an E1 or T1 facility, the channels start numbering at 1. The numbering ranges from 1 to 31 for E1 and 1 to 24 for T1. Serial interfaces in the Cisco router start numbering at 0. Therefore, channel 16, the E1 signaling channel, is channel 15 on the interface. Channel 24, the T1 signaling channel, becomes channel 23 on the interface. Thus, interface serial 0/0:23 refers to the D channel of a T1 PRI.

Subinterfaces, commonly used with Frame Relay, are designated with a dot, or period. For example, Serial 0/0.16 is a subinterface. Do not confuse the channels of a T1 or E1 with subinterfaces. Channels use a colon instead of a dot to indicate the channel number:

• S0/0.23 refers to a Subinterface
• S0/0:23 refers to a channel

Web Links Configuring ISDN PRI http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_configuration_ guide_chapter09186a00800ca71d.html