quartz/content/notes/20-network-layer-control-plane.md

title	aliases	tags
20-network-layer-control-plane		cosc203 lecture

per-router control vs SDN

per router

• each router runs a routing algorithm
• router communicate with each other
• and creates a forwarding table

SDN software defined networking

a remote controller computes, and install fowarding tables in routers

• much faster: less work for each router
• separate control and data plane

routing algorithms

• goal is to determine "good" paths from sending to recieving host through network of routers
• path: sequence of routers
• "good": least "cost", "fastest", "least congested"

graph abstraction

• nodes: set of routers
• edges: set of links

c_{a,b} cost the link directly connecting a and b. if there is no link the cost is ♾

algorithm classification

global: all routers have complete toplogy, link cost into

• link state algotihms

decentralized: interative process of computation, exchange of into with neighbors

• routers only know link costs to attacked neighbors
• "distance vecotr algorithms

static: routes change very slowly over time

dynamic: routes change more quickly

• periodic updates or in response to link cost changes

link state routing

centralized: network topology, link costs are known to all nodes

• each node gathers informatin on each link to its neighbors
• build link state packets and flood to all other nodes

computes least costs paths from one node to all other nodes

• gives a fowarding table for that node

iterative: after k interations, know least cost path to k destinations

notations

Dijkstra's algorithm

foward search algorithm

///initialization
N` = {u}
for all nodes v
	if v adjacent to u
		then D(v) = Cuv
	else D(v) = infinity
	
//loop
loop until all nodes in N`
	find W not in N` such that D(w) is a min
	add w to N`
	update D(v) for all v adjacent to w and not in N`:
		D(v) = min(D(v), D(w)+Cwv)
	//new least-path-cost to v is either old least-cost-path to v or known least-path-cost to w plus direct-cost from w to v

complexity:

• n nodes
• O(n)

routing in the internet

ICMP