Services offered by ISDN carriers vary considerably from country to country or region to region. Like modems, each switch type operates slightly differently, and has a specific set of call setup requirements. Before the router can be connected to an ISDN service, it must be configured for the switch type used at the CO. This information must be specified during router configuration so the router can communicate with the switch, place ISDN network level calls, and send data.

In addition to knowing the switch type the service provider is using, it may also be necessary to know what service profile identifiers (SPIDs) are assigned by the telco. A SPID is a number provided by the ISDN carrier to identify the line configuration of the BRI service. SPIDs allow multiple ISDN devices, such as voice and data equipment, to share the local loop. SPIDs are required by DMS-100 and National ISDN-1 switches.

SPIDs are used only in North America and Japan. The ISDN carrier provides a SPID to identify the line configuration of the ISDN service. In many cases when configuring a router, the SPIDs will need to be entered.

Each SPID points to line setup and configuration information. SPIDs are a series of characters that usually resemble telephone numbers. SPIDs identify each B channel to the switch at the central office. Once identified, the switch links the available services to the connection. Remember, ISDN is typically used for dialup connectivity. The SPIDs are processed when the router initially connects to the ISDN switch. If SPIDs are necessary, but are not configured correctly, the initialization will fail, and the ISDN services cannot be used.

Web Links ISDN Switch Types, Codes, and Values http://www.cisco.com/en/US/products/sw/ iosswrel/ps1831/ products_command_reference_ chapter09186a00800eea24.html