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(COMP361)FinalReview2.pdf
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Final Exam Review

COMP361 by M. Hamdi

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Network Layer

COMP361 by M. Hamdi

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Introduction

COMP361 by M. Hamdi

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Main Task of the network layer is to move packets from the source host to the destination host

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Lowest layer to deal with end-to-end issues!





Issues at the Network Layer

COMP361 by M. Hamdi

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Switching Technique:C
Datagrams

C
Virtual circuits




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outing:C
How to forward packets

C
How to calculate a path from source to destination?




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Traffic Control:C
Congestion control

C
Rate control




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Addressing (e.g., IP addressing)




Services of the Network Layer

COMP361 by M. Hamdi

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2 packet switching techniques are used:C
Datagrams

C
Virtual Circuits




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2 services are provided to the transport layer (reliable and unreliable):C
Connectionless Service

C
Connection-oriented Service







Summary

COMP361 by M. Hamdi

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The following implementations are feasible:




Network

Application

UDP/IPUDP/IP/ATM

TCP/IP ATM/ATM


Packet Routing

COMP361 by M. Hamdi

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There are two parts to the routing problem:C
1. How to pass a packet from an input interface to the output interface of a router (packet forwarding)?

C
2. How to calculate routes?.
Packet forwarding is done differently in datagram and virtual-circuit packet networks

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Route calculation is done in a similar fashion










Packet Forwarding of Datagrams

COMP361 by M. Hamdi

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Recall: In datagram networks, each packet carries the full destination address

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Each router maintains a routing table which has one row for each possible destination address





Packet Forwarding of Datagrams

COMP361 by M. Hamdi

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When a packet with destination node arrives at an incoming link, ...C
1. The router looks up the routing table

C
2. The routing table lookup yields the address of the next node (next hop)

C
3. The packet is transmitted onto the outgoing link that goes to the next hop




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Good:The router does not need to know about end-to-end flows

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Bad:Size of the routing table can grow very large




Packet Forwarding with Virtual Circuits

COMP361 by M. Hamdi

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Recall: In VC networks, the route is setup in the connection establishment phase

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During the setup, each router assigns a VC number (VC#) to the virtual circuit

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The VC# can be different for each hop

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VC# is written into the packet headers





Packet Forwarding of Virtual Circuits

COMP361 by M. Hamdi

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When a packet with VC_in in header arrives from router N_out, ...C
1. The router looks up the routing table for an entry with (VC_in , N_in )

C
2. The routing table lookup yields (VC_in, N_out)

C
3. The router updates the VC# of the header to VC_out and transmits the packet to N_out




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Good:Routing