[unix-history] / usr / doc / smm / 15.net / 2.t

.\" Copyright (c) 1983,1986 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)2.t	6.3 (Berkeley) 6/5/86
.\"
.nr H2 1
.\".ds RH Overview
.br
.ne 2i
.NH
\s+2Overview\s0
.PP
If we consider
the International Standards Organization's (ISO)
Open System Interconnection (OSI) model of
network communication [ISO81] [Zimmermann80],
the networking facilities
described here correspond to a portion of the
session layer (layer 3) and all of the transport and
network layers (layers 2 and 1, respectively).
.PP
The network layer provides possibly imperfect
data transport services with minimal addressing
structure.
Addressing at this level is normally host to host,
with implicit or explicit routing optionally supported
by the communicating agents. 
.PP
At the transport
layer the notions of reliable transfer, data sequencing,
flow control, and service addressing are normally
included.  Reliability is usually managed by 
explicit acknowledgement of data delivered.  Failure
to acknowledge a transfer results in retransmission of
the data.  Sequencing may be handled by tagging
each message handed to the network layer by a
\fIsequence number\fP and maintaining
state at the endpoints of communication to utilize
received sequence numbers in reordering data which
arrives out of order.
.PP
The session layer facilities may provide forms of
addressing which are mapped into formats required
by the transport layer, service authentication
and client authentication, etc.  Various systems
also provide services such as data encryption and
address and protocol translation.
.PP
The following sections begin by describing some of the common
data structures and utility routines, then examine
the internal layering.  The contents of each layer
and its interface are considered.  Certain of the
interfaces are protocol implementation specific.  For
these cases examples have been drawn from the Internet [Cerf78]
protocol family.  Later sections cover routing issues,
the design of the raw socket interface and other
miscellaneous topics.
Commit	Line	Data
820fca5e	1	.\" Copyright (c) 1983,1986 Regents of the University of California.
66f1c552 KM	2	.\" All rights reserved. The Berkeley software License Agreement
	3	.\" specifies the terms and conditions for redistribution.
	4	.\"
95f51977	5	.\" @(#)2.t 6.3 (Berkeley) 6/5/86
66f1c552 KM	6	.\"
66f1c552 KM	7	.nr H2 1
820fca5e	8	.\".ds RH Overview
95c3c83a MK	9	.br
95c3c83a MK	10	.ne 2i
66f1c552 KM	11	.NH
	12	\s+2Overview\s0
	13	.PP
	14	If we consider
	15	the International Standards Organization's (ISO)
	16	Open System Interconnection (OSI) model of
	17	network communication [ISO81] [Zimmermann80],
	18	the networking facilities
	19	described here correspond to a portion of the
	20	session layer (layer 3) and all of the transport and
	21	network layers (layers 2 and 1, respectively).
	22	.PP
	23	The network layer provides possibly imperfect
	24	data transport services with minimal addressing
	25	structure.
	26	Addressing at this level is normally host to host,
	27	with implicit or explicit routing optionally supported
	28	by the communicating agents.
	29	.PP
	30	At the transport
	31	layer the notions of reliable transfer, data sequencing,
	32	flow control, and service addressing are normally
	33	included. Reliability is usually managed by
	34	explicit acknowledgement of data delivered. Failure
	35	to acknowledge a transfer results in retransmission of
	36	the data. Sequencing may be handled by tagging
	37	each message handed to the network layer by a
	38	\fIsequence number\fP and maintaining
	39	state at the endpoints of communication to utilize
	40	received sequence numbers in reordering data which
	41	arrives out of order.
	42	.PP
	43	The session layer facilities may provide forms of
	44	addressing which are mapped into formats required
	45	by the transport layer, service authentication
	46	and client authentication, etc. Various systems
	47	also provide services such as data encryption and
	48	address and protocol translation.
	49	.PP
	50	The following sections begin by describing some of the common
	51	data structures and utility routines, then examine
	52	the internal layering. The contents of each layer
	53	and its interface are considered. Certain of the
	54	interfaces are protocol implementation specific. For
	55	these cases examples have been drawn from the Internet [Cerf78]
	56	protocol family. Later sections cover routing issues,
	57	the design of the raw socket interface and other
	58	miscellaneous topics.