The Network Layer Computer Communication Course Computer - - PDF document

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The Network Layer Computer Communication Course Computer - - PDF document

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The Network Layer Computer Communication Course Computer Communication Course 15 February, 2001 1 Why do We Need Network Layer?

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15 February, 2001 1

The Network Layer

Computer Communication Course Computer Communication Course

2 15 February, 2001 The Computer Communications Course

Why do We Need Network Layer?

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3 15 February, 2001 The Computer Communications Course

Interconnection through Switching Elements

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15 February, 2001 The Computer Communications Course

Hosts and the Subnet

Subnet Router LAN Host

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5 15 February, 2001 The Computer Communications Course

The Network Layer Functions

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15 February, 2001 The Computer Communications Course

The Network Layer: End to End Service

Transport Network Data Link Physical Transport Network Data Link Physical

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7 15 February, 2001 The Computer Communications Course

Network Layer Design Issues

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15 February, 2001 The Computer Communications Course

The Network Layer Service Paradigms

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The Network Layer Service Paradigms

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Subnet Structure: Virtual Circuits

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Virtual Circuits: Signaling Protocols

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Routing in VC Subnets

  • The routing table of each intermediate node is a translation table

from the pair (Linein, VCin) to (Lineout, VCout)

  • When a packet arrives, the node puts VCout in the packet’s VC

field, and send the packet on the designated output line

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Routing Tables in VC Subnets

A B C D I B 1 C 1 A 1 C 2 A 2 D 1 A B C D I B 1 C 1 A 1 C 2 A 2 D 1

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Some VC Design Issues

  • Choosing connection number
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each router chooses VC numbers independently

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ambiguities should be avoided

  • When should VCs be released?
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Each process is required to indicate when it stops using VC

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In public networks VC release is enforced by charging for the connect time

  • How should the VC setup packet be routed?
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Use the datagram routing tables (see next slides)

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15 15 February, 2001 The Computer Communications Course

Choosing Connection Numbers for Full-Duplex Communication (III)

A B C D D 2 => B 1 B 1 => D 2 B 1 = > ??? 1 1 X Y C 3 => A 1 A 1 => C 3 A 1 => ??? 2 3

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Choosing Connection Numbers for Full-Duplex Communication (II)

A B C D 3 2 X Y D 2 => B 1 B 1 => D 2 C 3 => A 1 A 1 => C 3 1 1

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17 15 February, 2001 The Computer Communications Course

Choosing Connection Numbers for Full-Duplex Communication (III)

A B C D D 2 => B 1 B 1 => D 2 B 1 = > ??? 1 1 X Y C 3 => A 1 A 1 => C 3 A 1 => ??? 2 3

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Subnet Structure: Datagram Subnets

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Datagram Networks: the Internet Model

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C A B D E B B C E D B E E A A C E D D E E A E B B C E E E

Routing Tables in Datagram Subnets

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Datagram Subnets Design Issues

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15 February, 2001 The Computer Communications Course

VC vs Datagram

VC subnet Datagram subnet Initial Setup Required None Addressing During Setup (parsing) Short VC # on each packet On each packet State information One per VC none Routing Route is chosen at setup. All packets follow this route Each packet is routed independently Effects of Router failure All VCs passing through this router are terminated None Congestion control Simple: allocate enough buffers at setup Difficult

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Routing State vs. Bandwidth

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Service X Subnet Structure

Upper layer Type of Subnet UDP over IP UDP over IP over ATM TCP over IP ATM AAL1 over ATM

Connectionless Connection-oriented Datagram Virtual Circuit