Networking Services (XNS) Issue 5
Copyright © 1997 The Open Group
This chapter gives an overview of the Sockets interfaces and includes
functions, macros and external variables to support portability at the
C-language source level.
The associated headers are documented in
All network protocols are associated with a specific protocol family. A
protocol family provides basic services to the protocol implementation to
allow it to function within a specific network environment. These services
can include packet fragmentation and reassembly, routing, addressing, and
basic transport. A protocol family can support multiple methods of
addressing, though the current protocol implementations do not. A protocol
family normally comprises a number of protocols, one per socket type. It is
not required that a protocol family support all socket types. A protocol
family can contain multiple protocols supporting the same socket abstraction.
A protocol supports one of the socket abstractions detailed
in the manual page for the
function. A specific protocol can be accessed either by creating a socket of
the appropriate type and protocol family, or by requesting the protocol
explicitly when creating a socket. Protocols normally accept only one type of
address format, usually determined by the addressing structure inherent in the
design of the protocol family and network architecture. Certain semantics of
the basic socket abstractions are protocol specific. All protocols are
expected to support the basic model for their particular socket type, but can,
in addition, provide nonstandard facilities or extensions to a mechanism. For
example, a protocol supporting the SOCK_STREAM abstraction can allow more than
one byte of out-of-band data to be transmitted per out-of-band message.
This specification covers local UNIX connections and Internet protocols.
Associated with each address family is an address format. All network
addresses adhere to a general structure, called a sockaddr. The length
of the structure varies according to the address family.
Sockets provides packet routing facilities. A routing information database is
maintained, which is used in selecting the appropriate network interface when
Each network interface in a system corresponds to a path through which
messages can be sent and received. A network interface usually has a hardware
device associated with it, though certain interfaces such as the loopback
interface do not.
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