Wireless Ad hoc networks Routing

1. Wireless Ad hoc networks Routing

2. Proposed ad hoc Routing Approaches • Conventional wired-type schemes (global routing, proactive): • Distance Vector; Link State • Proactivead hoc routing: • OLSR, TBRPF • On- Demand, reactive routing: • DSR (Source routing), MSR, BSR • AODV(Backward learning) • Scalable routing : • Hierarchical routing: HSR, Fisheye • OLSR + Fisheye • LANMAR (for teams/swarms) • Geo-routing: GPSR, GeRaF, etc • Motion assisted routing • Direction Forwarding

3. Wireless multihop routing challenges • mobility • need to scale to large numbers (100’s to 1000's) • need to support multimedia applications (QoS) • unreliable radio channel (fading, external interference, mobility, etc) • limited bandwidth • limited power

4. Conventional wired routing limitations • Distance Vector (eg, Bellman-Ford, BGP): • Tables grow linearly with # nodes • routing control O/H linearly increasing with network size • convergence problems (count to infinity); potential loops (mobility?) • Link State (eg, OSPF): • link update flooding O/H caused by network size and frequent topology changes CONVENTIONAL ROUTING DOES NOT SCALE TO SIZE AND MOBILITY DV LS Intra-AS RIP OSPF Inter-AS BGP

5. Proactive ad hoc schemes– OLSR and TBRPF • Link State explodes because of Link State update overhead • Question: how can we reduce the O/H? • Answer: Link State with “Topology reduction” • (1) if the network is “dense”, use fewer forwarding nodes • (2) if the network is dense, advertise only a subset of the links • Two leading IETF Link State schemes enhance scalability in large scale networks: • OLSR : Optimal Link State Routing • TBRPF: Topology Broadcast Reverse Path Routing

6. 24 retransmissions to diffuse a message up to 3 hops Retransmission node LSR (Link State Routing) • In LSR protocol a lot of control msg unnecessary duplicated

7. 11 retransmission to diffuse a message up to 3 hops Retransmission node OLSR (Optimal Link State Routing) • In OLSR only a subset of neighbors (MPR-Multipoint Relay Selectors) retransmit control messages: • Reduce size of control message; • Minimize flooding

8. OLSR Overview • RFC 3626, October 2003 • In LSR protocol a lot of control messages unnecessarily duplicated • In OLSR only a subset of neighbors (MPR-Multipoint Relay Selectors) retransmit control messages • Reduce flooding overhead • Adapted for dense network • OLSR retains all the advantages of LSR: • stable; • Does not depend upon any central entity; • Tolerates loss of control messages; • Supports nodes mobility

9. On-Demand Routing Protocols • Routes are established “on demand” as requested by the source • Only the active routes are maintained by each node • Channel/Memory overhead is minimized • Two leading methods for route discovery: source routing and backward learning (similar to LAN interconnection routing)

10. Existing On-Demand Protocols • Dynamic Source Routing (DSR) -- CMU • Multipath Source Routing (MSR) – TJU • Backup Source Routing (BSR) – UofO+TJU • Ad-hoc On-demand Distance Vector (AODV) • Associativity-Based Routing (ABR) • Temporarily Ordered Routing Algorithm (TORA) • Zone Routing Protocol (ZRP) • Location assisted routing (LAR, DREAM) • Signal Stability Based Adaptive Routing (SSA) • On Demand Multicast Routing Protocol (ODMRP) – UCLA

11. Dynamic Source Routing (DSR) • RFC 4728 – February 2007 • Forwarding: source route driven instead of hop-by-hop route table driven • Mobility ? • No periodic routing update message is sent • The first path discovered is selected as the route • Two main phases • Route Discovery • Route Maintenance

12. DSR - Route Discovery • To establish a route, the source floods a Route Request message with a unique request ID • The Route Request packet “picks up” the node ID numbers • Route Reply message containing path information is sent back to the source either by • the destination, or • intermediate nodes that have a route to the destination • Each node maintains a Route Cache which records routes it has learned and overheard over time

13. DSR - Route Maintenance • Route maintenance performed only while route is in use • Monitors the validity of existing routes by passively listening to acknowledgments of data packets transmitted to neighboring nodes • When problem detected, send Route Error packet to original sender to perform new route discovery

14. MSR - Multipath Source Routing • Direct Descendant of DSR • On-demand + Source Routing + Multipath • Probing-based adaptive load balancing among multiple paths • Motivation of MSR • Efficiently using the network resource • Alleviate the oscillation in adaptive single path routing • Fast re-routing • Reducing computing & storage requirement • Exploiting computing power of host instead of link capacity

15. Distributing Traffic among Multiple Paths • Quantities: A heuristic equation • Probing-based adaptive control • Decoupling between transport layer and network layer: SRPing • Cost effective • Scheduling: Packet Weighted Round Robin • TCP out-of-order (re-sequencing) problem

16. Distributing Traffic among Multiple Paths • Heuristic equation • Rationale: Autonomous system, homogeneous assumption, bandwidth-delay product constant where , is the delay of route with index i, is the maximum delay of all the routes to the same destination, R is a factor to control the switching frequency between routes. U is a bound value to insure that should not to be too large.

17. MSR Summary • Reduce network congestion • Improve throughput, delay, mobility, fault tolerance (CBR & FTP) • Acceptable routing overhead? • Little more than that of DSR • Route discovery • Route maintenance • Probing (unicast) add little O/H • Good candidate for QoS support • QoS-MSR, reliable-MSR • Acceptable packet out-of-order level ?

18. Backup Source Routing (BSR) • Establish and maintain backup routes that can be utilized after the primary path breaks • Define a new routing metric - route reliability, and use it to provide the basis for the backup path selection • Reduce the frequency of route discovery flooding, which is a major overhead in on-demand protocols • Can improve the performance significantly in more challenging situations of high mobility

19. Simulation Methodology • ns – Wireless extensions by CMU • Adopt methods used in [Broch98, Johnson99] • Two major files: • Movement pattern file • Communication pattern file • 50 mobile hosts placed randomly within a 1500m×300m area • 20 connections • Different traffic types: CBR & FTP • Two set of simulations: Max speed 20m/s & 1m/s

20. Performance Evaluation • MSR vs. DSR vs. BSR • Performance Metrics • Packet delivery ratio • Data throughput • End-to-end delay • Packet drop probability • Queue size

21. Simulation Results with UDP Traffic -- Packet delivery ratio for 20 sources 8

22. Simulation Results – CBR • End-to-end throughput

23. Simulation Results with UDP Traffic -- Average end-to-end delay for 20 sources 11

24. Simulation Results - CBR • Packets dropped at each node

25. Previous Work on Using Multiple Paths • Alternate use (primary and backup) • It works OK for CBR traffic (BSR, Bypass - DSR, Node Disjoint M-path AODV, etc) • TCP does not get much benefit. Backup path is used only after timeout; not efficient in mobility/errors.? • Concurrent use (ie, packet scattering) • MSR • TCP does well in a static, error free net with long paths (up to 50% improvement) • With mobility & errors, TCP suffers out-of-order problems because of RTT difference on the two paths

26. “TCP Performance on multiple paths in ad hoc nets..” Liaw et al ICC 2004 Static net, no errors, opt W: max improvement 50%; typical improvement between 8% and 18%

27. Multiple Path TCP with Packet Replicas • TCP data packet duplication on multiple paths • May introduce less O/H than repeated end to end retransmissions • Improve end-to-end route robustness when single route is not stable: • Replicate packet on multiple paths • Combat random, non correlated link losses • Combat path breakage

28. Variable Loss Rate[ 0.05;0.1;0.15;0.2] Total Throughput(bits/s) Mobility(m/s) Original TCP Multipath TCP

29. Where do we stand? • OLSR and TBRPF can dramatically reduce the “state” sent out on update messages • They are very effective in “dense” networks. • However, the state still grows with O(N) • Neither of the above schemes can handle large scale nets from 10’s to thousands of nodes • What to do?

30. Hierarchical Routing The previous schemes reduce control traffic O/H but do not significantly reduce routing table size Solution: use hierarchical routing to reduce table size In the process, reduce also control traffic O/H Proposed hierarchical schemes include: • Hierarchical State Routing (HSR) • Fisheye State Routing (FSR) • Landmark Routing • Zone routing (hybrid scheme)

31. Routing • Current MANET solutions have limitations: • (a) proactive routing solutions (eg, Optimal Links State -OLSR) do not scale because of table size and control traffic overhead • (b) on demand routing cannot handle high mobility and dense traffic patterns • (c) explicit hierarchical routing introduces excessive address maintenance O/H in high mobility • MANET protocols do not scale • UCLA approach: LANMAR • Exploit implicit hierarchy induced by group mobility

32. Logical Subnet Landmark Solution: Landmark Routing Overlay • Main assumption: nodes move in groups • Groups are predefined or dynamically recognized • Node address: < group ID , Host address> • Landmark elected in each group • Landmarks advertisements maintain the landmark overlay

33. Logical Subnet Landmark LANMAR Overlay Routing (cont) • Builds upon existing MANET protocols • (1) “local ” routing algorithm that keeps accurate routes within local scope < k hops (e.g., OLSR) • (2) Landmark routes advertised to all mobiles using DSDV

34. Logical Subnet Landmark LANMAR Overlay Routing (cont) • Packet Forwarding: • A packet to “local” destination is routed directly using local tables • A packet to remote destination is routed to Landmark corresponding to logical addr. • Once the landmark is “in sight”, the direct route to destination is found in local tables • Benefits: low storage, low update traffic O/H

35. Landmark Routing In action Landmark LM2 LM1 LM3 Logical Subnet dest source local routing Long haul routing • Node address = {subnet ID, Host ID} • Look up local routing table to locate dest  fail • Look up landmark table to find destination subnet  LM1 • Send a packet toward LM1

36. Link Overhead of LANMAR • Dramatic O/H reduction from linear to O(N) to O (sqrtN)

37. LANMAR enhances MANET routing schemes We compare: • MANET routing schemes: DSDV, OLSR and FSR; and (b) same MANET schemes, BUT with LANMAR overlay on top

38. LANMAR-DSDV LANMAR-FSR OLSR LANMAR-OLSR FSR DSDV Delivery Ratio • DSDV and FSR decrease quickly when number of nodes increases • OLSR generates excessive control packets, cannot exceed 400 nodes

39. Georouting - Key Idea • Each node knows its geo-coordinates (eg, from GPS or Galileo) • Source knows destination geo-coordinates; it stamps them in the packet • Geo-forwarding: at each hop, the packet is forwarded to the neighbor closest to destination • Options: • Each node keeps track of neighbor coordinates • Nodes know nothing about neighbor coordinates

40. Greedy Perimeter Stateless Routing for Wireless Networks (GPSR) • Greedy forwarding • Each nodes knows own coordinates • Source knows coordinates of destination • Greedy choice –“select” the most forward node

41. Finding the most forward neighbor • Beaconing: periodically each node broadcasts to neighbors own {MAC ID, IP ID, geo coordinates} • Each data packet piggybacks sender coordinates • Alternatively (for low energy, low duty cycle ops) the sender solicits“beacons” with “neighbor request” packets

42. Greedy Perimeter Forwarding D is the destination; x is the node where the packet enters perimeter mode; forwarding hops are solid arrows;

43. Got stuck? Perimeter forwarding > Greedy forwarding failure. x is a local maximum in its geographic proximity to D; w and y are farther from D.> Node x’svoidwith respect to destination D

44. GPSR vs DSR

45. TCP over GPSR, AODV, DSR and DSDV Throughput (Kbps) Speed(m/s)

46. GPSR commentary • Very scalable: • small per-node routing state • small routing protocol message complexity • robust packet delivery on densely deployed, mobile wireless networks • TCP is extremely sensitive to path breakage (timeout) -- It does very well with georouting • Outperforms DSR and AODV • Drawback: it requires knowledge of dest geo coordinates (explicit forwarding node address) • Beaconing overhead • nodes may go to sleep (on and off)