Protocols and Layering

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24 Οκτ 2013 (πριν από 4 χρόνια και 15 μέρες)

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Copyright 2012 Jim Martin
1
Protocols and Layering
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Chapter 20
Copyright 2012 Jim Martin
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OSI Network Layer Model

Physical
Datalink
Network
Transport
Session
Presentation
Application
Data Transport
Application Transport
Copyright 2012 Jim Martin
3
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Physical Layer: covers the physical interface and defines the rules by
which bits are transferred.
Physical Layer

Copyright 2012 Jim Martin
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The data link layer provides reliable (or
unreliable) transit of data across a physical
network link.


Different data link layer specifications define
different network and protocol characteristics,
including ??


WAN examples ??


For a LAN, IEEE has defined layered
architecture:
Datalink Layer

Copyright 2012 Jim Martin
5
Preamble
(7)
Length
(2)
DSAP SSAP cntl code type
(1) (1) (1) (3) (2)
Data ( 1 - 1492)
CRC
(4)
Dest
Address
(6)
Data: IP, ARP, SNA
Maximum Transmission Unit
(MTU) defined by the physical
medium and the link layer
802.2/802.3 Frame Format

Source
Address
(6)
Copyright 2012 Jim Martin
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The network layer provides routing and related functions
that enable multiple data links to be combined into an
internetwork.



This is accomplished by the logical addressing (as opposed
to the physical addressing) of devices.


The network layer supports both connection-oriented and
connectionless service from higher-layer protocols.


Network-layer protocols typically are routing protocols
Network Layer

Copyright 2012 Jim Martin
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The transport layer implements reliable (or unreliable)
internetwork data transport services that are transparent to upper
layers.


Transport-layer functions typically include


Error detection


Error recovery (reliable transfer)




Acknowledgements


Timeouts


Retransmissions


Stream or datagram service


Flow control




Window flow control

Transport Layer

Copyright 2012 Jim Martin
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Transport Layer

A 4-packet window sliding through
An outgoing datastream.
a)When transmission begins
b)After two packets have been acked.
c)After eight packets have been acked.

Copyright 2012 Jim Martin
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Transport Layer


Messages required to send a sequence of four
packets using (a) stop-and-go flow control, and
(b) a 4-packet sliding window. Time proceeds
down the page, and each arrow shows one
message sent from one computer to the other.
Copyright 2012 Jim Martin
10
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A Protocol defines the rules and conventions that govern how
computers exchange information over a network medium.
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Examples:


Application protocols


Transport protocols


Network protocols


LAN/WAN protocols


Physical protocols
Ethernet
IEEE 802.2, PPP
IP, ICMP, RIP
TCP,UDP
HTTP, telnet,...
Protocols

Copyright 2012 Jim Martin
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Internetworking: a collection of individual networks connected
by intermediate networking devices that function as a single
large network.
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An internet approach hides lower layer details from the user via
network-level interconnection methods.

The
Internet
is an implementation of a
network based on the internet approach.
Introduction