HP X.25/9000 Programmer's Guide

Chapter 2 11

X.25 Addressing

Levels of Addressing

X.25 allows call addressing to use an interface’s programmatic access

name, the X.121 address and subaddress, and protocol ID. This

information is contained in the x25addrstr structure, described below.

• The application can specify which X.25 interface to use when

receiving and connecting calls. This level of addressing is only useful

when there is more than one X.25 interface (as with multiple-port

cards or systems with multiple cards) connected to the HP 9000

system.

• Applications can specify which X.121 address to use when the

connection is established. Each interface connected to an X.25 PSN is

assigned a unique X.121 address. When an interface is connected to a

PSN, the subaddress also designates the X.25 interface (for test

purposes in back-to-back conﬁgurations, it is possible to use a

different X.121 address than that speciﬁed for the PSN interface at

conﬁguration time).

• Applications can specify the X.121 subaddress to use in connecting

the call. The subaddress can be used to select a particular type of

application on the other end of the call.

• Applications can also use the protocol ID to further select the type of

application on the other end of the call. Protocol ID addressing is fully

described in the CCITT X.244 (1984) Recommendations and Chapter

6 of the X.25 (1980) Recommendations.

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