 |
|
SPIDs and DNs. A SAPI/TEI pair identifies a particular
device on a given ISDN link, but has only local significance. For a
call to traverse an ISDN network, network-wide parameters need to be
defined. In concept, a SAPI/TEI pair are the same as an LCN in an
X.25 network, in that the LCN is significant between a DTE and DCE,
but an NUA is necessary to route traffic across an X.25 network. To
establish an ISDN connection, you need a directory number (DN), which looks identical to a regular
telephone number. With a DN, you know what number to use to call
another ISDN user. That is not enough, however. We know that an ISDN
connection may have many different types of devices attached, so to
inform the ISDN switch in the telephone company's network what you
have at your location, the telephone company will assign you one or
more service profile
IDs (SPIDs) that
identify the equipment you are using on your ISDN
connection. |
| |