Directing the Traffic (17)[detail]

Network layer

Deals with end to end transmission/choosing route a message should take/connecting networks

connectionless

preferred by internet community, routers just move packets, network inherently unreliable, hosts manage error and flow control

connection oriented

network should be reliable, quality of service vital, preferred by telephone companies

Routing table

managed by routing algorithm to determine where packets should go

Virtual circuit

path established between sender and receiver, packets carry identifier

Routing when?

datagram: for each packet, VC network: when new VC set up

Forwarding

looking up table to see where to send packet

Pouting

filling in and updating routing table

routing goals

correctness, simplicity, robustness, stability, fairness, efficiency

non adaptive routing

static routes, decisions made offline, downloaded to routers when booting

adaptive routing

dynamic routing, changes based on topology, traffic, etc, optimise for some measure

Sink tree

Shows optimal routes from all sources to a destination

Flooding

simple technique to send incoming packet out all outgoing links except the one it arrived on

Distance vector routing

each router maintains table, tables shared with each other until no change

dijkstras algo

start at one point and move along tree working out best path

Link state routing

complete topology distributed to every router

Load shedding

When a router has too many packets to handle it must drop some: drop new packets for file transfer and old packets for real time media