86 lines
3.7 KiB
Perl
86 lines
3.7 KiB
Perl
.\" Copyright (c) 1983, 1986, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)2.t 8.1 (Berkeley) 6/8/93
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.\"
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.nr H2 1
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.\".ds RH Overview
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.br
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.ne 2i
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.NH
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\s+2Overview\s0
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.PP
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If we consider
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the International Standards Organization's (ISO)
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Open System Interconnection (OSI) model of
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network communication [ISO81] [Zimmermann80],
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the networking facilities
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described here correspond to a portion of the
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session layer (layer 3) and all of the transport and
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network layers (layers 2 and 1, respectively).
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.PP
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The network layer provides possibly imperfect
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data transport services with minimal addressing
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structure.
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Addressing at this level is normally host to host,
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with implicit or explicit routing optionally supported
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by the communicating agents.
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.PP
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At the transport
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layer the notions of reliable transfer, data sequencing,
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flow control, and service addressing are normally
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included. Reliability is usually managed by
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explicit acknowledgement of data delivered. Failure
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to acknowledge a transfer results in retransmission of
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the data. Sequencing may be handled by tagging
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each message handed to the network layer by a
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\fIsequence number\fP and maintaining
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state at the endpoints of communication to utilize
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received sequence numbers in reordering data which
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arrives out of order.
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.PP
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The session layer facilities may provide forms of
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addressing which are mapped into formats required
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by the transport layer, service authentication
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and client authentication, etc. Various systems
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also provide services such as data encryption and
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address and protocol translation.
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.PP
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The following sections begin by describing some of the common
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data structures and utility routines, then examine
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the internal layering. The contents of each layer
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and its interface are considered. Certain of the
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interfaces are protocol implementation specific. For
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these cases examples have been drawn from the Internet [Cerf78]
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protocol family. Later sections cover routing issues,
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the design of the raw socket interface and other
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miscellaneous topics.
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