* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Link-State Routing
Survey
Document related concepts
Deep packet inspection wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Backpressure routing wikipedia , lookup
Computer network wikipedia , lookup
IEEE 802.1aq wikipedia , lookup
Multiprotocol Label Switching wikipedia , lookup
List of wireless community networks by region wikipedia , lookup
Peer-to-peer wikipedia , lookup
Airborne Networking wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Transcript
Routing - Circuit Switching Telephone switching was hierarchical with only one route possible — Added redundant routes — Evolved to full mesh Toll switches Central offices Subscribers EETS 8316/NTU CC725-N/TC/11-08-01 #1 Routing - Packet Switching Data networks have used various routing protocols — Flooding — Source routing — Distributed shortest-path routing • Distance-vector routing • Link-state routing Layered routing is used in Internet for scalability EETS 8316/NTU CC725-N/TC/11-08-01 #2 Flooding Packet is copied at every router and broadcast to neighbors — Useful when info must be shared at all routers, eg, routing updates Advantage: no knowledge of network topology is necessary — Well suited to highly dynamic networks, eg, battlefield Disadvantage: Number of message copies may be huge without additional mechanisms, eg: EETS 8316/NTU CC725-N/TC/11-08-01 #3 Flooding (Cont) — Messages have hop limit to restrict number of copies — Messages are uniquely identified so routers can stop unnecessary copies — Routers can establish minimum spanning tree that message copies will follow • Overlay tree that covers every router exactly once Example network EETS 8316/NTU CC725-N/TC/11-08-01 Example spanning tree #4 Source Routing Sender determines route and specifies it in packet header — Example: IP source routing option — Usually centralized route server maintains network topology info and collect updates from all routers Advantage: sender can select optimal route or test certain routes Disadvantages: — Centralized routing is not scalable to large networks — Difficult to carry long routes in packet header EETS 8316/NTU CC725-N/TC/11-08-01 #5 Distributed Shortest-Path Routing Distributed shortest-path routing: each router builds up routing table independently and shares routing updates with other routers — Routing table entries specify how to forward packets to destination addresses/networks Two main types of routing protocols known from Internet experience: — Distance-vector or Bellman-Ford — Link-state EETS 8316/NTU CC725-N/TC/11-08-01 #6 Distance-Vector Routing (Bellman-Ford) Example: RIP (routing information protocol) Each router maintains a table (vector) of reachable destinations and corresponding shortest distances to each destination — Periodically shares routing table with its neighbors Each router modifies its routing table with the received updates — Shortest distance to every destination is chosen — New reachable destinations are added, unreachable destinations are deleted EETS 8316/NTU CC725-N/TC/11-08-01 #7 Distance-Vector Routing (Cont) RIP was first routing protocol used in Internet but difficulties were found — Slow to propagate routing updates through large network — Routers can have inconsistent or even incorrect information — Scalability problem: vector of destinations becomes longer as network is larger routing updates are larger EETS 8316/NTU CC725-N/TC/11-08-01 #8 Link-State Routing Examples: OSPF (open shortest path first), ISIS (intermediate system - intermediate system) Each router maintains a graph representing complete network topology — Monitors state of its links with neighboring routers — Floods link-state updates to all routers periodically Each router receives link-state updates from other routers and revises its graph — Shortest routes can be computed systematically by Dijkstra’s algorithm EETS 8316/NTU CC725-N/TC/11-08-01 #9 Link-State Routing (Cont) Example: topology graph is given, minimum spanning tree generated by Dijkstra’s algorithm is all shortest routes from source node A (link labels are distances) 5 3 2 2 A 1 3 5 A 1 2 1 EETS 8316/NTU CC725-N/TC/11-08-01 #10 Link-State Routing (Cont) Advantages: — Every router should have consistent, complete topology info consistent, optimal route selection — Routing updates do not grow with size of network (link-state updates depend on number of links per router) Disadvantage: flooding link-state updates can result in large traffic volume and traffic oscillations — Limit updates to only significant changes — Flooding is limited by layered routing EETS 8316/NTU CC725-N/TC/11-08-01 #11 Layered Routing Internet is too large for routing as “flat network” where every router is aware of every other router Layered routing: routers are grouped together into “routing domains” or “areas” — At lowest layer, interior routers within each routing domain use an intra-domain routing protocol with each other — Exterior routers represent each routing domain in higher layer inter-domain routing protocol — Interior routers are aware only of routing domain EETS 8316/NTU CC725-N/TC/11-08-01 #12 Layered Routing (Cont) Routing domain Interior routers use intra-domain routing Exterior routers use inter-domain routing EETS 8316/NTU CC725-N/TC/11-08-01 #13 Ad Hoc Networks Wireless networks may be classified as — Infrastructured: cellular systems consist of fixed (wireline) network with mobile users attached to network edge through fixed base stations • Handoff is necessary and critical — Ad hoc: no fixed infrastructure • All nodes can be mobile and autonomous • Connections are dynamic and arbitrary • Examples: battlefield,, emergency rescue operations, WLAN, PAN EETS 8316/NTU CC725-N/TC/11-08-01 #14 Ad Hoc Networks (Cont) IETF (Internet Engineering Task Force) Mobile Ad Hoc Networks (MANET) working group is studying proposals — MANETs consist of mobile routers and mobile hosts (can be physically same) — Mobile hosts are temporarily or permanently attached to a mobile router — Inter-router connectivity can change frequently • Routing protocol must adapt to continually changing topology • Addresses cannot be based on location EETS 8316/NTU CC725-N/TC/11-08-01 #15 Ad Hoc Networks - Routing Routing protocols — Table driven: nodes maintain and update routing tables • Cost in overhead traffic for distributing routing updates • Routes are always ready when needed for data — On-demand (source initiated): routing tables are not maintained cont., routes are found only when needed for data transmission • Cost in overhead traffic only when data is ready for transmission • Routing tables are smaller EETS 8316/NTU CC725-N/TC/11-08-01 #16 Ad Hoc Networks - Table Driven Routing Destination sequenced distance-vector (DSDV) routing — As in Bellman-Ford, each node maintains routing table of reachable destinations and their distances (number of hops) — Routing table info. is periodically broadcast for consistency, using two packet types: • Full dump packets contain complete routing info. sent infrequently • Incremental packets contain only new routing info. EETS 8316/NTU CC725-N/TC/11-08-01 #17 Ad Hoc Networks - Table Driven Routing Clusterhead gateway switch routing — Nodes are grouped into clusters and elect a cluster head by a cluster head selection algorithm — DSDV routing is used within clusters — Between clusters, packets are routed to cluster head gateway cluster head • Gateways are nodes within communications range of 2 or more cluster heads — Packets may have to hop through multiple cluster heads and gateways to final destination EETS 8316/NTU CC725-N/TC/11-08-01 #18 Ad Hoc Networks - Table Driven Routing — Each node maintains “cluster member table” of cluster heads for every destination node • Nodes broadcast their cluster member table and update their own tables Gateway Packet Cluster head EETS 8316/NTU CC725-N/TC/11-08-01 Gateway Cluster head Cluster head #19 Ad Hoc Networks - Table Driven Routing Fisheye link-state routing — Similar to link-state routing but link-state updates are not broadcast to every node • Broadcast link-state updates to nodes one hop away every 1 sec, nodes 2 hops away every 10 sec, nodes 3 hops away every 50 sec,... — Routes are more accurate to nearby nodes, but approximate to distant nodes • Packets will converge to more accurate routes to destination as get closer to destination EETS 8316/NTU CC725-N/TC/11-08-01 #20 Ad Hoc Networks - Table Driven Routing Link state updates 10 sec Link state updates 1 sec Link state updates 50 sec EETS 8316/NTU CC725-N/TC/11-08-01 #21 Ad Hoc Networks - Source Initiated Routing Ad hoc on-demand distance-vector routing — Similar to DSDV routing — Source node with data ready to send initiates a path discovery process • Broadcasts route request (RREQ0 packet to its neighbors. they broadcast to their neighbors, and so on • Eventually, destination node responds with route reply (RREP) packet in reverse direction • Nodes build up routing tables EETS 8316/NTU CC725-N/TC/11-08-01 #22 Ad Hoc Networks - Source Initiated Routing D S RREQ RREP D S EETS 8316/NTU CC725-N/TC/11-08-01 #23 Ad Hoc Networks - Source Initiated Routing Dynamic source routing — Nodes maintain route caches — If route to destination is unknown in its route cache, node will initiate route discovery • Broadcasts route request packet with destination address and source address • Other nodes will add their address into packet and continue broadcast to other nodes • Route reply is returned by destination or a node that knows a route to destination EETS 8316/NTU CC725-N/TC/11-08-01 #24 Ad Hoc Networks - Source Initiated Routing Associativity-based routing — Routes are selected base on new metric: degree of association stability • Each node periodically generates a beacon to advertise presence • Neighboring nodes will increment associativity tick of this node in their associativity tables for each beacon received • Association stability is defined by connection stability between two nodes over space and time – High association stability may mean low node mobility EETS 8316/NTU CC725-N/TC/11-08-01 #25 Ad Hoc Networks - Source Initiated Routing — Route discovery: • Node will broadcast query (BQ message) to destination • Intermediate nodes will add their address and associativity ticks into message • Destination node receives packets with associativity ticks of nodes along routes taken, and chooses route with best degree of association stability • Destination node returns BQ-REPLY back to source along chosen route • Intermediate nodes will record this chosen route EETS 8316/NTU CC725-N/TC/11-08-01 #26