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1 | .\" Copyright (c) 1983 Regents of the University of California. |
2 | .\" All rights reserved. The Berkeley software License Agreement | |
3 | .\" specifies the terms and conditions for redistribution. | |
4 | .\" | |
f0c4290a | 5 | .\" @(#)2.t 6.1 (Berkeley) %G% |
66f1c552 KM |
6 | .\" |
7 | .nr H2 1 | |
8 | .ds RH Overview | |
9 | .NH | |
10 | \s+2Overview\s0 | |
11 | .PP | |
12 | If we consider | |
13 | the International Standards Organization's (ISO) | |
14 | Open System Interconnection (OSI) model of | |
15 | network communication [ISO81] [Zimmermann80], | |
16 | the networking facilities | |
17 | described here correspond to a portion of the | |
18 | session layer (layer 3) and all of the transport and | |
19 | network layers (layers 2 and 1, respectively). | |
20 | .PP | |
21 | The network layer provides possibly imperfect | |
22 | data transport services with minimal addressing | |
23 | structure. | |
24 | Addressing at this level is normally host to host, | |
25 | with implicit or explicit routing optionally supported | |
26 | by the communicating agents. | |
27 | .PP | |
28 | At the transport | |
29 | layer the notions of reliable transfer, data sequencing, | |
30 | flow control, and service addressing are normally | |
31 | included. Reliability is usually managed by | |
32 | explicit acknowledgement of data delivered. Failure | |
33 | to acknowledge a transfer results in retransmission of | |
34 | the data. Sequencing may be handled by tagging | |
35 | each message handed to the network layer by a | |
36 | \fIsequence number\fP and maintaining | |
37 | state at the endpoints of communication to utilize | |
38 | received sequence numbers in reordering data which | |
39 | arrives out of order. | |
40 | .PP | |
41 | The session layer facilities may provide forms of | |
42 | addressing which are mapped into formats required | |
43 | by the transport layer, service authentication | |
44 | and client authentication, etc. Various systems | |
45 | also provide services such as data encryption and | |
46 | address and protocol translation. | |
47 | .PP | |
48 | The following sections begin by describing some of the common | |
49 | data structures and utility routines, then examine | |
50 | the internal layering. The contents of each layer | |
51 | and its interface are considered. Certain of the | |
52 | interfaces are protocol implementation specific. For | |
53 | these cases examples have been drawn from the Internet [Cerf78] | |
54 | protocol family. Later sections cover routing issues, | |
55 | the design of the raw socket interface and other | |
56 | miscellaneous topics. | |
57 | .ds RH Goals | |
58 | .bp |