HP X.25/9000 Programmer's Guide

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Chapter 2 15

X.25 Addressing

Addressing Options for Servers

A server uses the X.25 socket address information to identify which calls

it will process. Each server uses the bind(2) system call to deﬁne the

addressing information for calls it will process. The bind() system call is

described in Chapter 3 , “Establishing and Terminating a Socket

Connection,” and in your HP-UX man pages.

The discussion of incoming call-matching methods includes:

• Call-matching by interface name. An X.25 interface name is speciﬁed

in the

x25ifname[]

ﬁeld of the x25addrstr structure. Only calls

arriving over that interface can be connected to the socket.

• Call-matching by called X.121 address. The called address (with

wildcards) is stored in the

x25_host

ﬁeld of the x25addrstr

structure. Only calls with the speciﬁed called address (or matching

wildcard address) can be connected to the socket.

• Call-matching by called X.121 address and a subaddress. The

subaddress is stored in the

x25_host

ﬁeld of the x25addrstr

structure. Only calls with the speciﬁed called address (or matching

wildcard address) and subaddress can be connected to the socket.

• Call-matching by protocol ID. The protocol ID is set in the

x25_pid[]

ﬁeld of the x25addrstr structure. Only calls with the correct protocol

ID can be connected.

• Addressing conﬂicts in bind() calls.

When a CALL REQUEST packet arrives, three tests are performed to

attempt to match the call to a listen socket:

• The name of the local interface over which the call arrived is matched

against the

x25ifname

ﬁeld speciﬁed in the bind().

• The called address ﬁeld is matched against the

x25_host

ﬁeld

speciﬁed in the bind().

• The ﬁrst bytes of the user data ﬁeld in the CALL REQUEST packet

are matched against the

x25pid

ﬁeld speciﬁed in the bind().

If all of these tests succeed, the call is connected to the socket. If the

incoming call does not match with any of the speciﬁed addresses, the call

is cleared.

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