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%sccs.include.redist.man%
@(#)iso.4 6.1 (Berkeley) 05/30/90
Sockets bound to the OSI protocol family use the following address structure:
._f struct iso_addr { u_char isoa_len; /* length, not including this byte */ char isoa_genaddr[20]; /* general opaque address */ }; struct sockaddr_iso { u_char siso_len; /* size of this sockaddr */ u_char siso_family; /* addressing domain, AF_ISO */ u_char siso_plen; /* presentation selector length */ u_char siso_slen; /* session selector length */ u_char siso_tlen; /* transport selector length */ struct iso_addr siso_addr; /* network address */ u_char siso_pad[6]; /* space for gosip v2 SELs */ }; #define siso_nlen siso_addr.isoa_len #define siso_data siso_addr.isoa_genaddr
The fields of this structure are:
10 siso_len: Length of the entire address structure, in bytes, which may grow to be longer than the 32 bytes show above.
10 siso_family: Identifies the domain: AF_ISO.
10 siso_tlen: Length of the transport selector.
10 siso_slen: Length of the session selector. This is not currently supported by the kernel and is provided as a convenience for user level programs.
10 siso_plen: Length of the presentation selector. This is not currently supported by the kernel and is provided as a convenience for user level programs.
10 siso_addr: The network part of the address, described below.
An ISO transport address is similar to an Internet address in that it contains a network-address portion and a portion that the transport layer uses to multiplex its services among clients. In the Internet domain, this portion of the address is called a port. In the ISO domain, this is called a transport selector (also known at one time as a transport suffix). While ports are always 16 bits, transport selectors may be of (almost) arbitrary size.
Since the C language does not provide conveninent variable length structures, we have separated the selector lengths from the data themselves. The network address and various selectors are stored contiguously, with the network address first, then the transport selector, and so on. Thus, if you had a nework address of less then 20 bytes, the transport selector would encroach on space normally reserved for the network address.