|  | 5.1 | ISDN
| 5.1.4 | ISDN switches and SPIDs
For proper ISDN operation, it is important that the correct switch type is configured on the ISDN device. The most common type in the United States is AT&T's 5ESS and Nortel's DMS-100. The most common type in Japan is NTT. U.K.'s most common types are Net3 and Net5. ISDN service providers use a variety of switch types for their ISDN services. Services offered by carriers vary considerably from nation to nation and region to region. Just like modems, each switch type operates slightly differently and has a specific set of call setup requirements. As a result, before you can connect a router to an ISDN service, you must be aware of the switch types used at the CO. You specify this information during router configuration so the router can place ISDN network-level calls and send data. In addition to learning about the switch type your service provider uses, you also need to know what Service Profile Identifiers (SPIDs) are assigned to your connection. The ISDN carrier provides a SPID to identify the line configuration of the ISDN service. SPIDs are a series of characters (that can look like phone numbers) that identify you to the switch at the CO. After you're identified, the switch links the services you ordered to the connection.
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