Final several design issues at network layer


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Final several design issues at network layer

  1. 1. Several Design Issues at Network layer<br /><ul><li>Implementation of Connectionless Services
  2. 2. Implementation of Connection oriented Services
  3. 3. Comparison of datagram subnet and virtual-circuit subnet</li></ul>AshishDubey(9)<br />Hansel Gonsalves(12)<br />KashyapDavariya(7)<br />
  4. 4. Implementation of Connectionless Services<br />In Connectionless Service, no need to establish connection<br />In this packets are injected into subnet and routed independently of each other.<br />No advance set up is needed<br />In this context the packets are frequently called datagram and subnet is called datagram subnet.<br />
  5. 5. Routing within a datagram subnet<br />
  6. 6. Let see the working of datagram subnet.<br />Suppose process p1 has long message for process p2.<br />It hands message with instructions to transport layer to deliver it to process 2 on host 2.<br />The transport layer code runs on H1,within an OS.<br />It prepends a transport header to the front of message and hands the result to the network layer.<br />
  7. 7. Assume that message is four times longer than maximum packet size.<br />The Network layer breaks it into four packets 1, 2 ,3 and 4 and sends all to router A using point-to-point protocol.<br />At this point carrier takes over.<br />Every router has an internal table that tells where to send packets for each possible destinations. <br />
  8. 8. Each table entry is a pair consisting of a destination and the outgoing line to use for that destination.<br />Only directly connected lines can be used.<br />For eg: A has only two outgoing lines - to B and C - so every incoming packet must be sent to one of these routers, even if ultimate destination is some other router.<br />
  9. 9. As packets arrived at A, packets 1, 2 and 3 were stored briefly(to verify their checksums).<br />Then each was forwarded to C according to A’s table .<br />Packet 1 was then forwarded to C according to A’s table.<br />Packet 1 was then forwarded to E and then to F and at F it was encapsulated in datalink layer frame and sent to H2 over the LAN. <br />
  10. 10. Packet 2 and 3 follow the same route.<br />However packet 4 was routed at different router(i.e at B) for some reason.<br />Perhaps it learned of traffic jam somewhere along the ACE path and updated its router table as “later”.<br />The algorithm that manages the tables and makes the routing decisions is called Routing Algorithm. <br />
  11. 11. Implementation of Connection Oriented Services<br />In this a connection is established.<br />A path from source to the destination router must be established before any packets can be sent. <br />This connection is virtual circuit with physical circuit set up by the telephone system <br />Subnet is called virtual circuit subnet.<br />The particular route choosen is used for all traffic flowing over the connection.<br />
  12. 12. With connection oriented service , each packet carries an identifier telling which virtual circuit it belongs.<br />
  13. 13. Routing within a virtual-circuit subnet.<br />
  14. 14. Here , host H1 has established a connection 1 with host H2.<br />It is remembered as the first entry in each of the routing tables.<br />The first lines of A’s table says that if a packet bearing connection identifier 1 comes from H1, it to be sent to router C and given a connection identifier 1.<br />Similarly, the first entry at C routes the packet to E, also with connection identifier 1.<br />
  15. 15. Now let consider what happens if H3 also wants to establish a connection to H2.<br />It chooses identifier 1(because it is initiating the connection and this is its only connection) and tells the subnet to establish the virtual circuit.<br />This leads to the second row in the tables.<br />Note that we have a conflict here because although A can easily distinguish connection 1 packets from H1 from connection 1 packets from H3 , C cannot do this.<br />
  16. 16. For this reason, A assigns a different connection identifier to the outgoing traffic for the second connection.<br />Avoiding conflicts of this kind is why routers need the ability to replace connection identifiers in outgoing packets.<br />In some contexts, this is called label swithing.<br />
  17. 17. Comparison of datagram subnet and virtual-circuit subnet<br />
  18. 18. Comparison of datagram subnet and virtual-circuit subnet<br />