Chapter 8. WAN Protocols and Technologies: Asynchronous Transfer Mode (ATM)

ISDN Configuration Basics

Now that the boring specifics of ISDN are behind us, it is time to dive into the more interesting topic of how to actually configure Cisco routers to use ISDN.

Unfortunately, there is currently no method of configuring ISDN in a lab environment without the use of actual ISDN circuits or a costly ISDN simulator. Nonetheless, ISDN is a core topic in the CCIE routing and switching lab exam, and the only way to learn the topic is through a great deal of hands-on practice.

To configure basic ISDN, only two things must be configured:

• ISDN switch type settings

• Service profile identifiers (SPIDs)

The SPID is a number assigned to a fully initializing ISDN terminal that enables the Stored Program Control Switching System (SPCS) to uniquely identify the ISDN terminal at Layer 3 of the D-channel signaling protocol.

A SPID is assigned to each B channel and usually resembles a phone number followed by some extra digits. For example, if your router is connecting to a Siemens ISDN switch, the SPIDs would typically be of the type aaabbbbbbbccdd, where

aaa is the three-digit area code

bbbbbbb is the seven-digit phone number

For national ISDN switches, the most frequently used SPID value is NPANXXXXXX0101, based on the configurations being installed today. The NPA/NXX is simply the carrier's term for the local area code/access number.

Not all ISDN switches actually require that the SPIDS be configured, but the majority of them do. The ISDN provider can provide you with the information that you need. Currently, Cisco routers support a number of different switch type options, as documented in Table 7-1.

Table 7-1. Supported ISDN Switch Types

Identifier	Description
basic-1tr6	German 1TR6 ISDN switches
basic-5ess	AT&T basic rate switches
basic-dms100	NT DMS-100 basic rate switches
basic-net3	NET3 ISDN and Euro-ISDN switches (UK and others), also called E-DSS1 or DSS1
basic-ni1	National ISDN-1 switches
basic-nwnet3	Norway Net3 switches
basic-nznet3	New Zealand Net3 switches
basic-ts013	Australian TS013 switches
None	No switch defined
Ntt	Japanese NTT ISDN switches (ISDN BRI only)
primary-4ess	AT&T 4ESS switch type for the United States (ISDN PRI only)
primary-5ess	AT&T 5ESS switch type for the United States (ISDN PRI only)
primary-dms100	NT DMS-100 switch type for the United States (ISDN PRI only)
primary-net5	NET5 ISDN PRI switches (Europe)
primary-ntt	INS-Net 1500 for Japan (ISDN PRI only)
primary-ts014	Australian TS014 switches (ISDN PRI only)
vn2	French VN2 ISDN switches (ISDN BRI only)
vn3	French VN3 ISDN switches (ISDN BRI only)
vn4	French VN4 ISDN switches (ISDN BRI only)

You need to contact your ISDN service provider to determine which switch type is being used. The switch type can be configured in both global and interface configuration modes. If it is specified in global mode, the switch type applies to all ISDN interfaces in the router. If it is placed in interface mode, it is applied to the interface only. If both are specified, the switch type that is configured in interface mode overrides the switch type set globally for that interface. For example, if you have a router with six ISDN interfaces and five of them connect to a DMS-100 switch, with the other connecting to an NI switch, you can use the isdn switch-type basic-dms100 command globally and then use the command isdn switch-type basic-ni in interface mode for the specific NI connected BRI interface.