Issues: Routing in Ad-hoc Networks Mobility Bandwidth constraint - PowerPoint PPT Presentation

Issues: Routing in Ad-hoc Networks  Mobility  Bandwidth constraint  Error-prone and shared channel  Location-dependent contention  Other resource constraints TDDD36: Routing

Issues: Multicas routing ...  Robustness  Efficiency  Control overhead  Quality of service  Efficient group management  Scalability  Security TDDD36: Routing

Unicast Routing Protocols  Many protocols have been proposed  Some have been invented specifically for MANET  Others are adapted from previously proposed protocols for wired networks  No single protocol works well in all environments  some attempts to develop adaptive protocols TDDD36: Routing

The ideal protocol (p303)  Distributed  Localized (and scalable)  Adaptive  Minimal maintenance and overhead  Loop free (and free from stale routes)  Balance scares resources usage against performance (and/or QoS) TDDD36: Routing

Routing protocol classification  Route information mechanism  Proactive (table-driven)  Reactive (demand-driven)  Hybrid  Temporal information  Past vs. Future information  Routing toplogy  Flat vs. hierarchical  Specific reources  Geography or Power TDDD36: Routing

Route update mechanism  Proactive (or table-drive) protocols:  Determine routes independent of traffic pattern  Traditional link-state and distance-vector routing protocols • Destination Sequenced Distance Vector (DSDV) • Optimized Link State Routing (OLSR)  Reactive (or demand-drive) protocols  Route is only determined when actually needed  Protocol operates on demand • Dynamic Source Routing (DSR) • Ad hoc On-demand Distance Vector (AODV) • Temporally Ordered Routing Algorithm (TORA)  Hybrid Protocols:  Combine these behaviors (e.g., table in limited zone, and demand drive otherwise) • Zone Routing Protocol (ZRP) • Greedy Perimeter Stateless Routing (GPSR) TDDD36: Routing

Routing protocols for wireless ad hoc networks Sensor networks Mobile ad hoc networks Response time, Energy bandwidth Proactive Reactive protocols protocols Dynamic Optimized Link- Ad Hoc On-Demand Destination-Sequenced Source Geography- Cluster-based State Routing Distance-Vector Distance-Vector (DSDV) Routing based routing (or hierarchical ) (OLSR) (AODV) (DSR) routing GPSR TDDD36: Routing

Some general trade-offs  Latency of route discovery  Proactive protocols may have lower latency • Routes are maintained at all times  Reactive protocols may have higher latency • Route from X to Y will be found only when X attempts to send to Y  Overhead of route discovery/maintenance  Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating  Reactive protocols may have lower overhead • Routes are determined only if needed  Which approach achieves a better trade-off depends on the traffic and mobility patterns TDDD36: Routing

Ad hoc networks: terminology  Broadcast: message sent to all neighbors within range  Flooding: message sent to all nodes in the network by neighbors forwarding message to their neighbors etc.  Different from wired network! TDDD36: Routing

Dynamic Source Routing (DSR) [Johnson96]  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 Route Request (RREQ)  Each node appends own identifier when forwarding RREQ TDDD36: Routing

Reactive protocols – DSR  In a reactive protocol, how to forward a packet to destination?  Initially, no information about next hop is available at all  One (only?) possible recourse: Send packet to all neighbors – flood the network  Hope: At some point, packet will reach destination and an answer is sent pack – use this answer for backward learning the route from destination to source  Practically: Dynamic Source Routing (DSR)  Use separate route request/route reply packets to discover route • Data packets only sent once route has been established • Discovery packets smaller than data packets  Store routing information in the discovery packets TDDD36: Routing

Dynamic source routing (DSR)  Reactive routing protocol  2 phases, operating both on demand :  Route discovery • Used only when source S attempts to to send a packet to destination D • Based on flooding of Route Requests (RREQ)  Route maintenance • Makes S able to detect, while using a source route to D, if it can no longer use its route (because a link along that route no longer works) TDDD36: Routing

DSR: Route discovery (1) K F H Q A E P S G D J B M R I L C N TDDD36: Routing

DSR: Route discovery (2) K F H Q A E P S G D (S) J B M R I L C N TDDD36: Routing

DSR: Route discovery (3) (S,A) K F H Q A (S,E) E P S G D J B M R I L C N TDDD36: Routing

DSR: Route discovery (4) K F H Q A (S,E,G) E P S G D J B M R I L C N (S,B,C) TDDD36: Routing

DSR: Route discovery (5) (S,A,F,H) K F H Q A (S,E,G,J) E P S G D J B M R I L C N TDDD36: Routing

DSR: Route discovery (6) K F H (S,A,F,H,K) Q A E P S G D J B M R I L C N TDDD36: Routing

DSR: Route discovery (7) K F H Q A E P S G D (S,A,F,H,K,P) J B M R I L C N TDDD36: Routing

DSR: Route discovery (8) K F H Q A E P S G D J RREP(S,E,G,J,D) B M R I L C N TDDD36: Routing

DSR: Route Discovery (9)  Route reply by reversing the route (as illustrated) works only if all the links along the route are bidirectional  If unidirectional links are allowed, then RREP may need a reverse route discovery from D to S  Note: IEEE 802.11 assumes that links are bidirectional TDDD36: Routing

DSR: Data delivery K F H Q A DATA(S,E,G,J,D) E P S G D J B M R I L C N TDDD36: Routing

DSR: Route maintenance (1) K F H Q A DATA(S,E,G,J,D) E P S G D X J B M R I L C N TDDD36: Routing

DSR: Route maintenance (2) K F H Q A RERR(G-J) E P S G D X J B M R I L C N When receiving the Route Error message (RERR), S removes the broken link from its cache. It then tries another route stored in its cache; if none, it initializes a new route discovery TDDD36: Routing

Route 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 TDDD36: Routing

Route Reply in DSR Y Z RREP [S,E,F,J,D] S E F B C M L J A G H D K I N Represents RREP control message TDDD36: Routing

Route Reply in DSR  Route Reply can be sent by reversing the route in Route Request (RREQ) only if links are guaranteed to be bi-directional  To ensure this, RREQ should be forwarded only if it received on a link that is known to be bi-directional  If unidirectional (asymmetric) links are allowed, then RREP may need a route discovery for S from node D  Unless node D already knows a route to node S  If a route discovery is initiated by D for a route to S, then the Route Reply is piggybacked on the Route Request from D.  If IEEE 802.11 MAC is used to send data, then links have to be bi-directional (since Ack is used) TDDD36: Routing

Dynamic Source Routing (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 TDDD36: Routing

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 TDDD36: Routing

When to Perform a Route Discovery  When node S wants to send data to node D, but does not know a valid route node D TDDD36: Routing

DSR modifications, extensions  Intermediate nodes may send route replies in case they already know a route  Problem: stale route caches  Promiscuous operation of radio devices – nodes can learn about topology by listening to control messages  Random delays for generating route replies  Many nodes might know an answer – reply storms  NOT necessary for medium access – MAC should take care of it  Salvaging/local repair  When an error is detected, usually sender times out and constructs entire route anew  Instead: try to locally change the source-designated route  Cache management mechanisms  To remove stale cache entries quickly  Fixed or adaptive lifetime, cache removal messages, … TDDD36: Routing

DSR: Optimization of route discovery: route caching  Principle: each node caches a new route it learns by any means  Examples  When node S finds route (S, E, G, J, D) to D, it also learns route (S, E, G) to node G  In the same way, node E learns the route to D  Same phenomenon when transmitting route replies  Moreover, routes can be overheard by nodes in the neighbourhood  However, route caching has its downside: stale caches can severely hamper the performance of the network TDDD36: Routing