1. Wireless Ad hoc networks – Routing

2. Proposed ad hoc Routing Approaches Conventional wired-type schemes (global routing, proactive): –Distance Vector; Link State Proactive ad 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. LSR (Link State Routing) In LSR protocol a lot of control msg unnecessary duplicated 24 retransmissions to diffuse a message up to 3 hops Retransmission node

7. 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 11 retransmission to diffuse a message up to 3 hops Retransmission node

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 Route RequestTo 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 ReplyRoute 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 Route CacheEach 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 Route ErrorWhen 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 Packet delivery ratio of every connection

23. Simulation Results – CBR Packet delivery ratio

24. Simulation Results – CBR End-to-end throughput

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

26. Simulation Results – CBR End-to-end delay

27. Simulation Results – CBR End-to-end delay

28. Simulation Results - CBR Packets dropped at each node

29. 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

30. “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%

31. 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

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

33. 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?

34. 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) Hierarchical Routing

35. 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

36. Solution: Landmark Routing Overlay Main assumption: nodes move in groups Groups are predefined or dynamically recognized Node address: Landmark elected in each group Landmarks advertisements maintain the landmark overlay Logical Subnet Landmark

37. 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 Logical Subnet Landmark

38. 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 Logical Subnet Landmark

39. Landmark Routing In action Logical Subnet Landmark LM1 LM2 LM3 source dest Long haul routing local routing 1.Node address = {subnet ID, Host ID} 2.Look up local routing table to locate dest  fail 3.Look up landmark table to find destination subnet  LM1 4.Send a packet toward LM1

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

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

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

43. 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

44. 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

45. 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

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

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

48. GPSR vs DSR

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

50. 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)