Unicast Routing in Mobile Ad-Hoc Networks

1
Unicast Routing in Mobile Ad-Hoc Networks

• Sajith Balraj
• Sumesh John Philip
• on February 29, 2000

2
Overview

• Introduction
• MaNet Protocols
• Proactive Hybrid Protocols
• WRP/GSR/FSR/LAR
• ZRP
• Reactive Protocols
• DSR/DSDV/AODV
• Challenges in Ad-Hoc Networks
• References

3
Mobile Ad-Hoc Network

• Collection of mobile nodes forming a temporary
  network
• No centralized administration or standard support
  services
• Each Host is an independent router
• Hosts use wireless RF transceivers as network
  interface

• Conferences/Meetings
• Search and Rescue
• Disaster Recovery
• Automated Battlefields

4
MaNet Issues

• Lack of a centralized entity
• Network topology changes frequently and
  unpredictably
• Channel access/Bandwidth availability
• Hidden/Exposed station problem
• Lack of symmetrical links
• Power limitation
• Multipath Fading
• Doppler Effect

5
MaNet Protocols

• Proactive Protocols
• Table driven
• Continuously evaluate routes
• No latency in route discovery
• Large network capacity to keep info. current
• Most routing info. may never be used!

• Reactive Protocols
• On Demand
• Route discovery by some global search
• Bottleneck due to latency of route discovery
• May not be appropriate for real time commn.

6
Conventional Routing Protocols ???

• DBF shows a degradation in performance
• Slow convergence due to Count to Infinity
  Problem
• Creates loops during node failure, network
  partition or congestion
• Protocols that use flooding techniques create
  excessive traffic and control overhead

7
MaNet Protocol Considerations

• Simple, Reliable and Efficient
• Distributed but lightweight in nature
• Quickly adapt to changes in topology and traffic
  pattern
• Protocol reaction to topology changes should
  result in minimal control overhead
• Bandwidth efficient
• Mobility Management involving user location
  management and Hand-off management

8
Wireless Routing Protocol (WRP)

• A path-finding algorithm
• Utilizes information regarding the the length and
  the predecessor-to-dest in the shortest path to
  each destination
• Eliminates the Count to Infinity Problem and
  converges faster
• An Update message is sent after processing
  updates from neighbors or a change in link to a
  neighbor is detected
• Each route update from neighbor k causes route
  entries of other neighbors that use k to be
  re-computed

9
The Algorithm

• Each node i maintains a Distance table (iDjk),
  Routing table (Destination Identifier, Distance
  iDj, Predecessor Pj, the successor Sj and a
  marker tag), link cost table (Cost, Update
  Period) , message retransmission list (Seq. No.,
  Counter, Acknowledgement flag, Update List)
• Listen for updates/ACKs which include i in the
  response list. Acknowledge each update
• Process the Distance table entries. Compute
  Djb Dkb kDj . Update predecessor
  as reported by k
• Update own Distance and predecessor information

10

• Choose neighbor p such that the path from p to j
  does not include i and iDjp lt iDjx and iDyp lt
  iDyx
• Broadcast new update message. Delete stale
  entries from MRL for new updates. Decrement
  counter for all entries in list.
• Retransmit MRL entry when counter hits zero,
  setting response list of update message to those
  neighbors who have not yet acknowledged
• Lack of NULL updates for given HelloInterval
  indicate change in link to a neighbor.

11
WRP Example
12
Performance Measurements

• Comparison against DBF and ILS
• For a single resource failure, WRP outperforms
  DBF in terms of number of steps and control
  overhead
• Performance of WRP better for resource recoveries
  in terms of number of control messages
• Average number of control messages least for WRP
  with node mobility
• Average message length comparable to DBF and ILS
  in most cases

13
Global State Routing (GSR)

• Combination of Distance Vector and Link State
• Global Network Topology stored in a Table
• Topology Table broadcast to immediate neighbors
  only
• Link State/Changes updates are time triggered

14
The Algorithm

• Ad-Hoc Network modeled as an undirected graph
  G(V,E)
• L(i,j) formed when D(i,j) less than or equal to
  RTr
• A List and Three Tables are maintained at each
  Node i Neighbor list Ai, Topology Table TTi
  TTi.LS(j), TTi.SEQ(j), Next Hop Table Nexti and
  Distance Table Di
• Initialize Ai, TTi. Use pkt.SEQ(j) to update
  TTi.SEQ(j)
• Compute shortest path tree rooted at i. Rebuild
  the Routing Table
• Broadcast information to neighbors periodically

15
Performance Measurements

• Routing Inaccuracy
• Link State reacts fastest to topology changes
  GSR still outperforms DBF
• Control Overhead
• Link State has maximum overhead since it is event
  triggered
• Overhead is constant for GSR DBF
  
  
  
• Mobility Impact
• No impact on control overhead for GSR DBF
• Routing inaccuracy increases for all schemes, but
  least for ILS

16
Performance Measurements cont.

• Update Interval
• Routing inaccuracy may be improved or degraded
  with change in update interval
• Radio Range
• Routing inaccuracy decreases for larger
  transmission ranges

17
Advantages/Disadvantages of GSR

• Advantages
• Avoids Flooding for disconnects/reconnects
• Updates are time triggered than event triggered
• Greatly reduces control overhead
• Disadvantages
• Hogs bandwidth since entire topology table is
  broadcast with each update
• Link state latency depends on update interval
• Can GSR be modified to rectify its drawbacks ?

18
Fisheye State Routing

• The network is logically divided into Fisheye
  circles with respect to each node. The scope of
  the circle may be defined in terms of number of
  hops
• Reduction in update message achieved by using
  different exchange periods for different entries
  in the table
• Creates larger latencies for stations that are
  far
• Routes become progressively accurate as the
  packet gets closer to the destination
• FSR scales well to large networks, by keeping the
  LS exchange overhead low

19
FSR cont.
20
Zone Routing Protocol

• A Hybrid Routing Protocol
• A Zone is defined for each node
• Proactive maintenance of topology within a zone
  (IARP) Distance Vector or Link State
• Reactive query/reply mechanism between zones
  (IERP) With Route Caching Reactive Distance
  Vector W/O Route Caching Source Routing
• Uses Bordercast instead of neighbor broadcast
• Neighbor Discovery/Maintenance (NMD) and Border
  Resolution Protocol (BRP) used for query control,
  route accumulation etc.

21
ZRP Example
1 Hop
2 Hops
Multi Hops
B
F
A
C
D
E
G
H
22
Zone Routing Protocol cont.

• Routing Zone and IntrAzone Routing Protocol
• Zone Radius may be based on hop count
• Identity and distance of each Node within the
  Zone is proactively maintained
• The Interzone Routing Protocol
• Check if destination is within the routing zone
• Bordercast a route query to all peripheral nodes
• Peripheral nodes execute the same algorithm

23
Zone Routing Protocol cont.

• Route Accumulation
• Provide reverse path from discovery node to
  source node
• May employ global caching to reduce query packet
  length
• Query Detection/Control
• Terminate Query thread in previously queried
  regions
• Intermediate nodes update a Detected Queries
  TableQuery Source, ID
• Route Maintenance may be reactive or proactive

24
Location Aided Routing (LAR)

• A Modified Flooding Algorithm
• Utilizes location information of mobile hosts
  using a GPS for route discovery
• Flooding is restricted to a request zone,
  defined by an expected zone
• A node forwards a route request only if it
  belongs to the request zone
• Tradeoff between latency of route determination
  and message overhead
• Resorts to flooding when prior information of
  destination is not available

25
LAR Schemes
D(xd,yd)
D(xd,yd)
R v(t-t0)
N
I
N
I
J
J
S (xs,ys)
S (xs,ys)
Scheme 1
Scheme 2
26
LAR cont.

• Scheme 1.
• Source calculates the expected zone, defines a
  request zone in the request packet and initiates
  route discovery
• Node I receiving the route request forwards the
  request if it falls inside the request zone,
  otherwise discards it
• When destination receives the request, replies
  with a route reply including current location,
  time and average speed
• Size of request zone is large at low and high
  node speeds

27
LAR cont.

• Scheme 2.
• Source calculates the distance Dists to
  destination (xd, yd) and initiates route
  discovery with both parameters
• Node I calculates its distance Disti from (xd,
  yd) and forwards the request only if Distilt
  Dists d, otherwise discards the request
• Node I replaces Dists with Disti before
  forwarding the request
• None zero d increases probability of route
  discovery

28
Performance Comparison

• Scheme 2 performs better than Scheme 1 and
  Flooding
• For low transmission ranges and degree of
  connectivity, LAR schemes are comparable to
  Flooding
• Routing overhead increases with increase in
  location error
• Impact of location error more on Scheme 2 than
  Scheme 1
• Local Search may be employed by intermediate
  nodes to reconstruct routes, thus reducing
  request zone area and thereby reducing routing
  overhead

29
Destination-Sequenced Distance Vector Routing

• Protocol Overview
• Route Advertisements
• Routing Table Entry Structure

30
Protocol Overview

• Each Routing Table List all destinations and
  number of hops to each
• Each Route is tagged with a sequence number
  originated by destination
• Updates are transmitted periodically and when
  there is any significant topology change
• Routing information is transmitted by broadcast

31
Route Table Entry Structure

• Destinations Address
• Number of hops required to reach the destination
• Destination Sequence Number

32
Responding to Topology Changes

• Broken links indicated by ?
• Any route through a hop with a broken link is
  also assigned ?
• ? routes are immediately broadcast
• Sequence number of Destination is incremented and
  information is broadcast
• Nodes with same or higher sequence number
  broadcast their metric information
• Limit broadcast by full dump and incremental

33
Route Selection Criteria

• Route broadcast are asynchronous events
• Fluctuations are caused due to possibility of
  receiving routes with worse metric first
• Solution is maintain routing tables, one for
  routing and one for broadcast

34
Example of DSDV
35
Example of DSDV
36
Example of DSDV
37
Example of DSDV
38
Example of DSDV
39
Ad-Hoc On-Demand Distance Vector Routing

• Protocol overview and objectives
• Path Discovery
• Reverse Path Setup
• Forward Path Setup
• Route Table Management
• Path Maintenance
• Local Connectivity Management

40
Protocol Overview and Objectives

• Pure on-demand protocol
• Node does not need to maintain knowledge of
  another node unless it communicates with it
• Broadcast discovery packets only when necessary
• Distinguish between local connectivity and
  general topology maintenance
• To disseminate Information about changes in local
  connectivity to those neighboring nodes that are
  likely to need it

41
Path Discovery

• Initiated whenever nodes want to communicate
• Route Request packets are broadcast
• RREQ format
• lt source_addr, source_sequence- , broadcast_id,
  dest_addr, dest_sequence_, hop_cnt gt
• RREQ uniquely identified by ltsource_addr ,
  broadcast_idgt

42
Path Discovery Cont.

• Broadcast id incremented with every RREQ
• Neighboring nodes satisfy RREQ by sending RREP or
  broadcast RREQ after incrementing hop_cnt
• Each intermediate node keeps following
  information
• Destination Address
• Source Address
• Broadcast_id

43
Path discovery Cont.

• Expiration time for reverse path entry
• Source nodes sequence number

44
Reverse Path Setup

• Source sequence number is used to maintain
  freshness about reverse route to source
• Destination number specified for freshness of
  route before accepted by source
• Reverse path setup by having link to neighbor

45
Forward Path Setup

• Node processing on reception of RREQ
• checks if the route is current by comparing
  dest_seq
• if route is current node unicasts RREP back to
  neighbor from which it received the RREQ
• RREP contains ltsource_addr, dest_addr,
  dest_sequence_, hop_cnt,lifetimegt
• Node propagates RREP back to source
• Updates information on reception of subsequent
  RREPs

46
Forward Path Setup
47
Route Table Management

• Route Request Expiration Timer for purging
  reverse paths which do not lie on
  source-destination route
• Route Caching Timeout for time after which the
  route is considered invalid
• Active_timeout Period used to determine if
  neighboring node is active

48
Route Table Management

• Route Table entry
• Destination
• Next Hop
• Number of hops (metric)
• Sequence numbers of Destination
• Active Neighbors for this route
• Expiration time for the route table entry

49
Path Maintenance

• When dest node or intermediate node moves a
  special RREP is sent
• When next hop become unreachable the upstream
  node sends propagates RREP with fresh sequence
  number and hop cnt ?
• restart route discovery process from source on
  receipt of RREP

50
Local Connectivity Management

• Node learn of their neighbors in following way
• on receipt of broadcast message
• on receipt of hello message

51
Dynamic Source Routing

• Overview
• Constructs a source route in packet header
  listing source route
• Each host maintains a route cache
• Route discovery used for routes not in cache

52
Route Discovery

• Route Request Packet
• Route Reply Packet
• Route Record
• Unique Request id

53
Route Discovery

• Possible scenarios on receipt of route request
  packet
• discard packet if ltinitiator address, request idgt
  already seen
• if host already listed then discard packet
• if target address is same as host address then
  obtain reverse route from route record and send
  route reply
• add host address in case of none of the above

54
Route Maintenance

• Route error packet sent on detection of break
  containing addresses on both sides of error, the
  host that detected the error and the host to
  which it was trying to send the packet
• All upstream node then deletes routes with that
  particular hop

55
Optimizations

• Full Use of Route Cache
• Piggy Backing on Route Discoveries
• Reflecting Shorter Routes
• Improved Handling of errors

56
Full Use of Route Cache

• Each forwarding host can add route information to
  cache
• Nodes can operate in promiscuous mode and add
  information to cache from any packets that they
  hear
• Each intermediate node having a route can send a
  route reply packet

57
Piggy Backing on Route Discoveries

• Data is piggybacked on Route Request Packet and
  Route Reply Packet (like SYN for TCP)
• While piggybacking on Route Request and
  intermediate node send Route Reply propagate
  Route Request with data

58
Reflecting Shorter Routes

• D on receipt of packet from B can modify cache
  and send route reply

59
Improved Handling of errors

• In scenario when network becomes partitioned
  buffer packets and use exponential backoff
• Use promiscuous mode to remove entries

60
Performance Comparison of AODV and DSR

• DSR has access to significantly greater amount of
  routing information than AODV by virtue of source
  routing and promiscuous listening
• DSR replies to all requests reaching a
  destination from a single request cycle whereas
  AODV only replies once thereby learning only one
  route
• In DSR no particular mechanism to delete stale
  routes unlike AODV
• In AODV the route deletion causes all the nodes
  using that link to delete it, but in DSR only
  the nodes on that particular part are deleted

61
Performance Comparison of AODV and DSR

• Both protocols do not perform any load balancing
• Routing load in DSR is less than AODV but in
  terms of bits the difference is less
• In AODV the path discovery is mostly due to RREQ(
  but in RREP RERRs but in terms of network load
  both of them are nearly the same)
• Both protocols use hop-wise determination of
  routes

62
Challenges in Ad-hoc Design

• Protocols still in Nascent Stage, analysis for
  which protocol does well in which scenario
• QOS issues in Ad-hoc
• TCP performance over Ad-hoc
• Integration of Ad-Hoc Networks in Internet
• Multicasting in Ad-hoc Networks

63
References

• S. Murthy and J.J Garcia Luna Aceves, A Routing
  Protocol for Packet Radio Networks, Proc. IEEE
  Mobicom, Nov. 1995
• A. Iwata, C.C. Chiang, G. Pei, M. Gerla and T. W.
  Chen, Scalable Routing Strategies for Ad-Hoc
  Wireless Networks, IEEE journal on Selected
  Areas in Communcations, Aug. 1999
• M. Gerla and T. W. Chen, Global State Routing
  A new routing scheme for Ad-Hoc wireless
  networks, Proc. IEEE ICC 98
• Z. J. Haas, M. R. Pearlman, The Zone Routing
  Protocol for Ad-Hoc networks, Internet Draft,
  Aug. 1998
• Y. B. Ko, N. H. Vaidya, Location Aided Routing
  in Ad-Hoc networks, Proceedings of ACM/IEEE
  Mobicom98, Dallas, TX, Oct. 1998

64
References

• Charles Perkin's Home Page
• http//www.srvloc.org/charliep/charliep.html
• Routing in Ad Hoc Networks of Mobile
  Hosts http//phantom.me.uvic.ca/clesiuk/thesis/rep
  orts/adhoc/adhoc.htmlE18E3
• Wireless Adaptive Mobility LAB,
  UCLAhttp//www.cs.ucla.edu/NRL/wireless/
• Monarch Project Research Papershttp//www.monarch.
  cs.cmu.edu/papers.html
• Papers on Mobile Computing http//db.nthu.edu.tw
  /paper/Mobile/
• Simulation Environment for an Ad-Hoc Wireless
  Network Running the AODV Routing Algorithm

65
References

• http//www.ctr.columbia.edu/angin/e6950/sameh/aod
  v_final.html
• ADHOC Networks Presentation http//www.ittc.ukans.
  edu/eshwar/eecs845/intro.html
• Mobile Ad hoc Networking http//www.varium.com/ps
  o/AdhocNetworking.html
• Paper Collection on Ad-hoc Networks http//147.46.
  59.102/imhyo/papers/papers.html
• Ad-Hoc Networking Resource Page http//147.46.59.1
  02/imhyo/papers/papers.html
• Papers on Mobile Computing http//www-sor.inria
  .fr/aline/mobile/biblio.html
• Papers on Ad-hoc Multihop Wireless
  Networks http//www.ics.uci.edu/atm/adhoc/paper-c
  ollection/papers.html