Scalability Fast route discovery and rediscovery (for reliability) Mobile user support (for seamless and efficient handover) Features for Optimal Routing in WMNs
Features for Optimal Routing in WMNs • Multiple Performance Metrics minimum hop-count ineffective!! e.g., link quality and round trip time (RTT) • Robustness(link failures or congestions, fault-tolerant, load balancing) • Adaptive Support of Both Mesh Routers and Mesh Clients(support mobility and power efficiency)
Flexibility Work with/without gateways, different topologies QoS Support Consider routes satisfying specified criteria Multicast Important for some applications (e.g., emergency response) Features for Optimal Routing in WMNs
* Apply routing algorithms derived for Ad Hoc Networks Prelim Routing Protocols for WMNs
OVERVIEW • Flat • Reactive • DSR – Dynamic Source Routing • AODV – Ad hoc On demand Distance Vector • Proactive • FSR – Fisheye State Routing • FSLS – Fuzzy Sighted Link State • OLSR – Optimized Link State Routing Protocol • TBRPF – Topology Broadcast Based on Reverse Path Forwarding
OVERVIEW • Hierarchical • CGSR – Clusterhead-Gateway Switch Routing • HSR – Hierarchical State Routing • LANMAR – Landmark Ad Hoc Routing • ZRP – Zone Routing Protocol
OVERVIEW • Geographical Routing • DREAM – Distance Routing Effect Algorithm for Mobility • GeoCast – Geographic Addressing and Routing • GPSR – Greedy Perimeter Stateless Routing • LAR – Location-Aided Routing
Reminder: Ad Hoc Routing Protocols • Proactive Protocols (Actively seeks for routes/paths) • Determine routes independent of traffic pattern • Traditional link-state and distance-vector routing protocols are proactive • Reactive Protocols (Seek for routes/paths only when required) • Maintain routes only if needed • Hierarchical Routing • Introduces hierarchy to the flat network • Geographic Position Assisted Routing • Why send packets North when the destination is South?
Routing Protocols from Ad Hoc Networks Used for WMNs Dynamic Source Routing (DSR) in Microsoft mesh networks D.B. Johnson, D.A. Maltz, and Y.-C. Hu, “The dynamic source routing protocol for mobile ad hoc networks (DSR),” IETF Internet-Draft,2004. 12
Routing Protocols from Ad Hoc Networks Used for WMNs AODV (ad-hoc on-demand distance vector) routing Used by many other companies Major building block for the routing framework of IEEE 802.11s C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004. IEEE 802.11s Task Group,“Joint SEE-Mesh/Wi-Mesh proposal to 802.11 TGs overview,”IEEE Doc: 802.11-05/0567r6,2006. 13
Routing Protocols from Ad Hoc Networks Used for WMNs Topology broadcast based on reverse path forwarding (TBRPF) protocol in Firetide Networks R. Ogier, F. Templin, and M. Lewis,“Topology dissemination based on reverse-path forwarding (TBRPF),” IETF RFC 3684, 2004. 14
Dynamic Source Routing (DSR) D. B. Johnson, D. A. Maltz, Y.-C. Hu, “Dynamic Source Routing Protocol for Mobile Ad Hoc Networks”,IETF Draft, April 2004. • Based on Source Routing principle! • On-demand • Route computation performed on aper-connection basis
Dynamic Source Routing (DSR) • Source, after route computation, appends each packet with a source-route information • Intermediate hosts forward packet based on source route • TWO PHASES: ROUTE DISCOVERY & ROUTE MAINTENANCE
Dynamic Source Routing (DSR):ROUTE DISCOVERY • When node S wants to send a packet to node D, but does not know a route to D, node S initiates a Route Discovery • Source node S floods (broadcasts) Route Request (RREQ) packet. • RREQ packet contains * DESTINATION ADDRESS * SOURCE NODE ADDRESS and * A UNIQUE IDENTIFICATION NUMBER.
Dynamic Source Routing (DSR):ROUTE DISCOVERY • If the node is the receiver (i.e., has the correct destination address) then returns the packet to the sender • If the packet has already been received earlier (identified via ID) then discard the packet
Dynamic Source Routing (DSR):ROUTE DISCOVERY • Each node receiving the packet checks whether it knows of a route to that destination. • If it does not, it appends/adds its own identifier (address) to the route record and forwards the RREQ packet.
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Z S E F B C M L J A G H D K I N
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Broadcast transmission Z [S] S E F B C M L J A G H D K I N Represents transmission of RREQ [X,Y] Represents list of identifiers appended to RREQ
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Z S [S,E] E F B M L C J A G [S,C] H D K I N Node H receives packet RREQ from two neighbors: Potential for collision
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Z S E F [S,E,F] B C M L J A G H D K [S,C,G] I N Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Z S E F [S,E,F,J] B C M L J A G H D K I N [S,C,G,K] • Nodes J and K both broadcast RREQ to node D • Since nodes J and K are hidden from each other, their transmissions may collide
Dynamic Source Routing (DSR):ROUTE DISCOVERY Y Z S E [S,E,F,J,M] F B C M L J A G H D K I N • Node D does not forward RREQ, because node D is the intended targetof the route discovery
Route/Path Discovery in DSR • Destination D on receiving the first RREQ, sends a Route Reply (RREP) • RREP is sent on a route obtained by reversing the route appended to received RREQ • RREP includes the route from S to D on which RREQ was received by node D
Route/Path Discovery in DSR Y Z S RREP [S,E,F,J,D] E F B C M L J A G H D K I N Represents RREP control message
DATA DELIVERY IN DSR • Node S on receiving RREP, caches the route included in the RREP • When node S sends a data packet to D, the entire route is included in the packet header • hence the name Source Routing • Intermediate nodes use the Source Route included in a packet to determine to whom a packet should be forwarded
Data Delivery in DSR Y DATA [S,E,F,J,D] Z S E F B C M L J A G H D K I N Packet header size grows with route length
DSR Optimization: Route Caching • Each node caches a new route it learns by any means • When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F • When node K receives Route Request [S,C,G]destined for K, it learns route [K,G,C,S] to node S
DSR Optimization: Route Caching • When node F forwards RREP [S,E,F,J,D], node F learns route [F,J,D] to node D • When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D • A node may also learn a route when it overhears Data packets
Advantages of Use of Route Caching • can speed up route discovery • can reduce propagation of route requests
Use of Route Caching [S,E,F,J,D] [E,F,J,D] S E [F,J,D],[F,E,S] F B [J,F,E,S] C M L J A G [C,S] H D K [G,C,S] I N Z [x,y,w] Represents cached route at a node (DSR maintains the cached routes in a tree format)
Use of Route Caching:Can Speed up Route Discovery [S,E,F,J,D] [E,F,J,D] S E [F,J,D],[F,E,S] F B [J,F,E,S] C M L [G,C,S] J A G [C,S] H D K [K,G,C,S] I N RREP When node Z sends a route request for node C, node K sends back a route reply [Z,K,G,C] to node Z using a locally cached route RREQ RREQ Z
Use of Route Caching:Can Reduce Propagation of Route Requests Y [S,E,F,J,D] [E,F,J,D] S E [F,J,D],[F,E,S] F B [J,F,E,S] C M L [G,C,S] J A G [C,S] H D K [K,G,C,S] I N RREP RREQ Z Route Reply (RREP) from node K limits flooding of RREQ. In general, the reduction may be less dramatic.
Dynamic Source Routing: Advantages • Routes maintained only between nodes who need to communicate • reduces overhead of route maintenance • Route caching can further reduce route discovery overhead • A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches
Dynamic Source Routing: Disadvantages • Packet header size grows with route length • Flood of route requests may potentially reach all nodes • Care must be taken to avoid collisions between route requests propagated by neighboring nodes • insertion of random delays before forwarding RREQ
Ad Hoc On-Demand Distance Vector Routing (AODV) C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004. • AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain paths • AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate
AODV • Hop-by-hop routing as opposed to source routing • On-demand • When a source node wants to send a message to some destination node and does not already have a valid route to that destination, it initiates a Path DiscoveryProcess to locate the destination (as in DSR case) • It broadcasts the RREQ packet to its neighbors
AODV • RREQs are forwarded in a manner similar to DSR • When a node re-broadcasts a RREQ, it sets up a reverse path pointing towards the source • AODV assumes symmetric (bi-directional) links • When the intended destination receives a RREQ, it replies by sending a Route Reply (RR) • RR travels along the reverse path set-up when RREQ was forwarded
AODV • When RREQ propagates, routing tables are updated at intermediate nodes (for route to source of RREQ) • When RREP is sent by destination, routing tables updated at intermediate nodes (forroute to destination), and propagated back to source
AODV • Each node maintains its own sequence number and a broadcast ID. • The broadcast ID is incremented for every RREQ the node initiates
AODV • The node’s IP address and the broadcast ID uniquely identify a RREQ. • Along with its own sequence number and broadcast ID, the source node includes in the RREQ the most recent sequence number it has for the destination.
AODV • Intermediate nodes can reply to the RREQ only if they have a route to the destination whose corresponding Destination Sequence Number is greater than or equal to that contained in the RREQ. • During the process of forwarding the RREQ, intermediate nodes recording their route tables with the address of the neighbor from which the first copy of the broadcast packet is received establishing a reverse path.
AODV • If more same RREQs are received later, they are discarded. • RREP packet is sent back to the neighbors and the routing tables are accordingly updated.
Route Requests in AODV Y Z S E F B C M L J A G H D K I N
Route Requests in AODV Y Broadcast transmission Z S E F B C M L J A G H D K I N Represents transmission of RREQ
Route Requests in AODV Y Z S E F B M L C J A G H D K I N Represents links on Reverse Path
Reverse Path Setup in AODV Y Z S E F B C M L J A G H D K I N • Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once
Reverse Path Setup in AODV Y Z S E F B C M L J A G H D K I N