1Routing Protocols I2RoutingRecall: There are two parts to
routing IP packets:1.How to pass a packet from an input interface
to the output interface of a router (packet forwarding) ? 2. How to
find and setup a route ?Packet forwarding is done different! in
datagram and "irtua#circuit packet networks$oute cacuation is done
in a simiar fashion Jrg Liebeherr, 1998,1999Routing
Algorithms%&'ecti"e of routing agorithms is to cacuate (good)
routes$outing agorithms for &oth datagrams and "irtua circuits
shoud satisf!: # *orrectness # +impicit! # +impicit!#
$o&ustness # +ta&iit!# ,airness # %ptimait! Impossi&e
to satisf! e"er!thing at the same timeFairness vs. maximum
throughput-.ampe: /ssume that stations /0 10 * wants to send to /)0
1)0 and *)0 each at 2 3&4s/ssume the capacit! of the network
inks is 15 3&4s.6 6)//)11)**)Stability vs. optimal delay-.ampe:
%ptimi7e dea! &! sending a packets o"er ink with the east
traffic.89pdate the routing decision e"er! 15 sec/1*6:; *ost? #
6ea! # Throughput6ecision Time:8%nce per session (@*s)8%nce per
packet (datagram)6ecision Pace:8-ach node (distri&uted
routing)8*entra node (centrai7ed routing)8+ending node (source
routing)ShortestPath Routing$outing agorithms genera! use a
shortest path agorithm to cacuate the route with the east costThree
components: !. "easurement #omponent=odes (routers) measure the
current characteristics such as dea!0 throughput0 and >cost?$.
Protocol =odes disseminate the measured information to other
nodes%.#alculation=odes run a east#cost routing agorithm to
recacuate their routes &oal ofShortest Path RoutingAoa: Ai"en a
network were each ink&etween two nodes i and 'is assigned a
cost.,ind the path with the east cost &etween nodes i and
'.Parameters:di'cost of ink &etween node i and node 'Bdi' C 0
if nodes i and ' are not connectedBdii C 5=set of nodesApproaches
to Shortest Path RoutingThere are two &asic approaches to
east#cost routing in a communication networkThere are two &asic
approaches to shortest#path routing:1. Dink +tate $outing2.
6istance @ector $outingApproaches to Shortest Path Routing!. 'in(
State Routing 8-ach node knows the distance to its neigh&ors8
The distance information (Cink state) is &roadcast to a nodes
in the network8-ach node cacuates the routing ta&es
independent!$. )istance *ector Routing8 -ach node knows the
distance (Ccost) to its direct! connected neigh&ors8 / node
sends a ist to its neigh&ors with the current distances to a
nodes8 If a nodes update their distances0 the routing ta&es
e"entua! con"erge11)istance *ector Routing)istance *ector-ach node
maintains two ta&es:8)istance +able: *ost to each node "ia each
outgoing ink8Routing +able:3inimum cost to each node and ne.t hop
node=odes e.change messages that contain information on the cost of
a route$eception of messagestriggers recacuation of routing
ta&e)istance *ector Algorithm: +ablesl (v,w)cost of link (w,v)C
d(v,w) cost from v to d via wDd(v) minimum cost from v to
dto*d("0n) *d("0w)n wnv , d("0w)dviato6d(") ncost"ia(ne.t
hop)d)istance +able Routing+ableNote: In the figure, Cd(v,w)
