SHEKHAR HMP Assistant Professor, Wireless Networking Laboratory, Department of Computer Science

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SHEKHAR HMPAssistant Professor,Wireless
Networking Laboratory,Department of Computer
Science Engineering,M S Ramaiah Institute of
Technology,Bangalore, INDIAE-mail
shekharhmp_at_msrit.edu
NETWORK LAYER
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AGENDA

• Network Layer Design Issues
• Routing Algorithms
• Congestion Control Algorithms
• Quality of Service
• Internetworking
• Internet Protocols (IP, ARP, RARP, DHCP, etc.)

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ROUTING ALGORITHMS

• Software responsible or deciding which output
  line an incoming packet should be sent.
• Done for every arriving packet (datagram subnet)
  
• Made only during connection setup (virtual
  circuit subnet) session routing

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ROUTING ALGORITHMS Contd.

• Router have two processes
• Routing - filling and updating of routing tables
• Forwarding looks for outgoing link in routing
  table and forwards the packet

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ROUTING ALGORITHMS Contd.

• Properties of Routing algorithm
• Correctness
• Simplicity
• Robustness
• Fairness
• Optimality

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ROUTING ALGORITHMS Contd.

• Principle of optimality states that if a router
  J is on the optimal path from router I to router
  K, the optimal path from J to K also falls along
  the same route.

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ROUTING ALGORITHMS Contd.
(a) A subnet. (b) A sink tree for router B.
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ROUTING ALGORITHMS Contd.

• Classification of Routing algorithms
• Nonadaptive or Static routing
• Adaptive or Dynamic routing

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ROUTING ALGORITHMS Contd.

• Classification of Dynamic Routing algorithms
• Distance vector, Link state, and Hybrid routing.
• Distance vector routing RIP, IGRP
• Link state routing OSPF

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ROUTING ALGORITHMS Contd.

• Classification of Dynamic Routing algorithms
• Interior gateway and Exterior gateway
• Interior gateway routing RIP, OSPF
• Exterior gateway - BGP

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ROUTING ALGORITHMS Contd.

• Classification of Dynamic Routing algorithms
• Hierarchical Routing
• Broadcast Routing
• Multicast Routing
• Routing for Mobile Hosts
• Routing in Ad Hoc Networks

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SHORTEST PATHROUTING

• Dijkstra's algorithm
• Metrics
• Number of hops
• Distance
• Delay
• Bandwidth
• Load

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SHORTEST PATHROUTING
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SHORTEST PATHROUTING
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SHORTEST PATHROUTING
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FLOODING

• Every incoming packet is sent out on every
  outgoing line except the one it arrived on.
• Problem too many packets
• Solution hop counter, sequence numbering
• Selective flooding
• Send incoming packets to only those lines that
  are promising.

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FLOODING

• Applications (where robustness is required)
• Military
• Distributed database applications
• Wireless LAN

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DISTANCE VECTORROUTING

• Every router maintain a table (i.e. a vector)
  which gives the best known distance to each
  destination and which line to use.
• Tables are updated by exchange of information
  with neighbors.
• Commonly known as Bellman-Ford routing and
  Ford-Fulkerson algorithm.
• Internet Routing Information Protocol (RIP)

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DISTANCE VECTORROUTING
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DISTANCE VECTORROUTING
Reacts quickly to good news
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DISTANCE VECTORROUTING
Reacts slowly to bad news Count to Infinity
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DISTANCE VECTORROUTING

• Solution Count to Infinity
• RFC 1058 Split Horizon with Poisoned Reverse
• The split horizon rule states that it is never
  useful
• to send the information about a route back in
  the
• direction from which it came, as the router
  sending
• you the information is nearer to the
  destination
• than you are

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DISTANCE VECTORROUTING

• Solution Count to Infinity
• RFC 1058 Split Horizon with Poisoned Reverse
• The poisoned reverse rule states that send
• updates to neighbors with a defined hop count
• (say 16) for the routes learned by those
  neighbors.

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LINK STATEROUTING

• Each router must do the following
• Discover its neighbors, learn their network
  address.
• Measure the delay or cost to each of its
  neighbors.
• Construct a packet telling all it has just
  learned.
• Send this packet to all other routers.
• Compute the shortest path to every other router.

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LINK STATEROUTING

• Learning about the neighbors
• HELLO Packets are used.
• Measuring line cost
• ECHO Packets are used.

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LINK STATEROUTING

• Building link state packets

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LINK STATEROUTING

• When a node receives an LSP
• Compare sequence number
• If less or equal, discard
• Else
• store new LSP
• forward on all links except the one on which it
  arrived
• Each node generates a new LSP periodically
• Increments sequence number
• Sequence numbers do not wrap (64 bits)

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LINK STATEROUTING

• LSP are acknowledged

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LINK STATEROUTING

• Computing routes
• Dijkstras shortest path algorithm
• Memory store required
• Subnet of n routers, each router with k neighbors
  requires k.n
• Internet OSPF
• IS-IS ( Intermediate system - Intermediate system
  

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COMPARISON