OSI/TS Configuration and Management Manual

Background Information About Addressing

OSI/TS Configuration and Management Manual—424831-001

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SNPA Addresses Over X.25 WANs

In X.25 networks, the SNPA address is the DTE address plus the port number, if any.

The SNPA address is assigned by the X.25 network addressing authority, described later

in this section.

X25AM does not provide an SNPA address parameter that OSI/TS can use.

Conceptually, however, the SNPA address can be described as follows:

For more information on SNPA addresses in X.25 environments, see the appendix

“Netid and Remotenetid” in the X.25 Access Method (X25AM) Manual.

LSAP Selectors

An LSAP (link layer service access point) selector is used by the Data Link Layer to

identify the Network Layer user of its service. A system, therefore, can run multiple

protocols on the same controller by assigning each protocol (such as OSI or TCP/IP) to

a separate LSAP. (LSAPs are sometimes called “protocol identifiers”.) In a LAN

environment, an LSAP selector is the hexadecimal string FE described in IEEE and ISO

specifications. In X.25 WAN environments, LSAP selectors are not applicable.

NSAP Addresses

An NSAP address (sometimes called a network address or a global network address) is

used by the Network Layer to identify the Transport Layer user of its service. NSAP

addresses are globally unique values within the OSI network, and are administered by a

hierarchy of addressing authorities as established by a hierarchy of addressing domains

(discussed in the following subsections).

Network Addressing Authorities

A network addressing authority is a set of rules. The authority can be a set of national or

international standards (such as the ISO standards) or a set of local rules issued by a

single person (such as a network manager). The network addressing authority ensures

the uniqueness of all the NSAP addresses within a domain (discussed in the following

subsection). There can be a hierarchy of authorities, each authority governing its own

WAN (25.25) SNPA Address

Consists of ...

Local SNPA address: SRCADDR parameter of the X25AM

line followed by the X25PORT parameter

(the port or subaddress of a subdevice)

Remote SNPA address: X25DESTADDR parameter of the

X25AM subdevice (includes the remote DTE address and

possibly the port number)

(NOTE: The X.25 line address itself is not configured in an

OSI/TS subsystem.)

Configured

Using SCF ...

X25DESTADDR attribute, X25PORT attribute