Routing and Location Management in Mobile Ad-hoc Networks

1
Routing and Location Managementin Mobile Ad-hoc
Networks

• By
• Sumesh J. Philip
• (09/20/2001)

2
Contents

• Introduction
• Routing Protocols
• Table Driven (WRP, DSDV)
• On Demand (DSR, AODV, TORA)
• Performance Evaluation
• Geographic (LAR, DREAM)
• Location Management for Large Scale Networks
  (GLS, SLURP, SLALOM)
• References

3
Mobile Ad-Hoc Network

• Collection of mobile nodes forming a network
• No centralized administration or standard support
  services
• Highly co-operative, 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 Constraints and Issues

• Lack of a centralized entity
• Network topology changes frequently and
  unpredictably
• Routing and Mobility Management
• Channel access/Bandwidth availability
• Hidden/Exposed station problem
• Lack of symmetrical links
• Power limitation

5
Conventional Routing Protocols ?

• Not designed for highly dynamic, low bandwidth
  networks
• Count-to-infinity problem and slow convergence
• Loop formation during temporary node failures and
  network partitions
• Protocols that use flooding techniques create
  excessive traffic and control overhead

6
MaNet Protocols

• Proactive Protocols
• Table driven
• Continuously evaluate routes
• No latency in route discovery
• Large capacity to keep network information
  current
• A lot of routing information 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 communication

7
Wireless Routing Protocol (WRP)

• A Path finding algorithm uses predecessor to
  destination in the shortest path
• Eliminates the Count-to-infinity problem and
  converges faster
• Neighbor connectivity via periodic Hello
  messages
• Update messages sent upon detecting a change in
  neighbor link

8

• Each node i maintains a Distance table (iDjk),
  Routing table (Destination Identifier, Distance
  iDj , Predecessor Pj ,the successor Sj), link
  cost table (Cost, Update Period)
• Processing Updates and creating Route Table
• Update from k causes i to re-compute the
  distances of all paths with k as the predecessor
• For a destination j, a neighbor p is selected as
  the successor if p-gtj does not include i, and is
  the shortest path to j

9
Operation
(0, J)
J
10
(2, K)
B
X
5
10
I
1
1
(2, K)
1
K
(1, K)
(?, K)
(11, B)
10
Destination Sequenced Distance Vector (DSDV)

• Each Route is tagged with a sequence number
  originated by destination
• Hosts perform periodic triggered updates,
  issuing a new sequence number
• Sequence number indicates the freshness of a
  route
• Routes with more recent sequence numbers are
  preferred for packet forwarding
• If same sequence number, one having smallest
  metric used

11
Topology changes

• Broken links assigned a metric of 8
• Any route through a hop with a broken link is
  also assigned a metric of 8
• 8 routes are assigned new sequence numbers by
  any host and immediately broadcast via a
  triggered update
• If a node has an equal/later sequence number with
  a finite metric for an 8 route, a route update
  is triggered

12
DSDV Operation
13
Damping Fluctuations

• Routes preferred if later sequence numbers, or
  smaller metric for same sequence numbers
• Problem Table fluctuations if worse metrics are
  received first, causing a ripple of triggered
  updates
• Solution Use average settling time as a
  parameter before advertising routes
• Tantamount to using two tables, one for
  forwarding packets and another for advertising
  routes

14
Dynamic Source Routing (DSR)

• Each packet header contains a route, which is
  represented as a complete sequence of nodes
  between a source-destination pair
• Protocol consists of two phases
• route discovery
• route maintenance
• Optimizations for efficiency
• Route cache
• Piggybacking
• Error handling

15
DSR Route Discovery

• Source broadcasts route request (id, target)
• Intermediate node action
• Discard if id is in ltinitiator, request idgt or
  node is in route record
• If node is the target, route record contains the
  full route to the target return a route reply
• Else append address in route record rebroadcast
• Use existing routes to source to send route
  reply else piggyback

16
DSR Route Maintenance

• Use acknowledgements or a layer-2 scheme to
  detect broken links inform sender via route
  error packet
• If no route to the source exists
• Use piggybacking
• Send out a route request and buffer route error
• Sender truncates all routes which use nodes
  mentioned in route error
• Initiate route discovery

17
Optimizations for efficiency

• Route Cache
• Use cached entries for during route discovery
• Promiscuous mode to add more routes
• Use hop based delays for local congestion
• Must be careful to avoid loop formation
• Non propagating RREQs

18
Optimizations

• Piggybacking
• Data piggybacked on route request Packet
• Problem route caching can cause piggybacked
  route replies to be discarded
• Improved Error Handling
• when network becomes partitioned, buffer packets
  and use exponential back-off for route discovery
• Listen to route replies promiscuously to remove
  entries
• Use negative information to ignore corrupt replies

19
Ad-hoc On DemandDistance Vector (AODV)

• On demand protocol that uses sequence numbers
  (DSDV) to build loop free routes
• Key difference from DSR is that source route is
  no longer required
• Path discovery
• Reverse Path setup
• Forward path setup
• Table management and path maintenance
• Local connectivity management

20
AODV Reverse path setup

• Counters Sequence number, Broadcast id
• Reverse Path
• Broadcast route request (RREQ) lt source_addr,
  source_sequence- , broadcast_id, dest_addr,
  dest_sequence_, hop_cnt gt
• RREQ uniquely identified by ltsource_addr ,
  broadcast_idgt
• Route reply (RREP) if neighbor is the target, or
  knows a higher dest_sequence_
• Otherwise setup a pointer to the neighbor from
  whom RREQ was received
• Maintain reverse path entries based on timeouts
  

21
AODV Forward path setup

• RREQ arrives at a node that has current route to
  the destination ( larger/same sequence number)
• unicast request reply (RREP)ltsource_addr,
  dest_addr, dest_sequence_, hop_cnt,lifetimegt to
  neighbor
• RREP travels back to the source along reverse
  path
• each upstream node updates dest_sequence_, sets
  up a forward pointer to the neighbor who transmit
  the RREP

22
AODV Operation
D
S
23
Protocol Maintenance

• Route Table management
• Route request expiration timer purges reverse
  paths that do not lie on active route
• Active neighbor relays a packet within
  active_route_timeout
• Route cache timer purges inactive routes
• New routes preferred if higher destination
  sequence number or lower metric

24
AODV Maintenance

• Path maintenance
• Upon link breakage, affected node propagates an
  unsolicited RREP ltdest_sequence_1, 8gt to all
  upstream nodes
• Source may restart route discovery process
• Local connectivity management
• Broadcasts used to update local connectivity
  information
• Inactive nodes in an active path required to send
  hello messages

25
Temporally OrderedRouting Algorithm (TORA)

• Link reversal algorithm
• Destination oriented Directed Acyclic Graph (DAG)
• Full/Partial reversal of links
• Assigns a reference level (height) to each node
• Adjust reference level to restore routes on link
  failure
• Multiple routes to destination route optimality
  not important
• Query, Update, Clear packets used for creating,
  maintaining and erasing routes

26
Creating Routes
A
B
QRY
E
C
D
G (DEST)
F
H
27
Route Maintenance
UPD
A
B
UPD
E
C
UPD
D
G (DEST)
X
F
H
28
Erasing Invalid Routes
29
Performance Analysis

• Simulation Environment
• Network Simulator, 50 nodes in a 1500x300m
  rectangular flat grid
• Random waypoint mobility
• Constant bit rate traffic
• Address resolution ARP implementation in BSD
  Unix
• Medium Access Control IEEE 802.11
• Physical Layer model combines both free space
  and two ray ground reflection model
• Protocols studied DSDV(SQ), AODV, DSR, TORA

30
Performance Analysis

• Metrics
• Packet Delivery Ratio Ratio of number of
  packets generated by CBR sources to that received
  by CBR sinks at destination
• Routing Overhead number of routing packets
  sent each transmission counts as one
  transmission
• Path Optimality Difference between length of
  actual path took and the length of the shortest
  path

31
Packet Delivery Ratio

• 95-100 in most cases for DSR, AODV
• Stale route entries in DSDV cause drops
• Short lived loops in TORA as part of link
  reversal
• All protocols perform well when there is low node
  mobility

32
Routing Overhead (packets)

• Route caching and non-propagating RREQs in DSR
• TORA
• Sum of mobility dependant, independent overhead
  for TORA
• Congestive collapse
• Nearly constant for DSDV due to periodic updates

33
Routing Overhead (Bytes)

• DSR more expensive than AODV except at high
  mobility
• Smaller packets in AODV, may be more expensive in
  terms of media access, power and network
  utilization

34
Path Optimality

• DSDV, DSR use routes close to optimal
• TORA not designed to find shortest path
• TORA, AODV use paths close to optimum when node
  mobility is low

35
Geographic Routing

• Not many invariants to play with (IP address,
  local connectivity)
• Nodes physically located closer likely to be
  connected by a small number of radio hops
• Possible to obtain node location via a GPS system
• Geographic forwarding
• Packet header contains the destinations location
• Most forward with fixed radius

36
Distance Routing EffectAlgorithm for Mobility
(DREAM)

• Proactively disseminate location information
• Distance Effect
• Closer nodes are updated more frequently
• age field in location update
• Mobility Effect
• rate of location update controlled by mobility
• No bandwidth wastage for no movement
• Geographic forwarding
• If no entry for destination in table, flood
• Otherwise forward data to m neighbors in the
  direction of destination

37
Location Aided Routing (LAR)

• On Demand protocol used restricted flooding for
  locating destination
• 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

38
LAR 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

39
LAR 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
• Non zero d increases probability of route
  discovery

40
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
41
Issue of Scalability

• The number of packets each node has to forward
  and the amount of state kept at each node grow
  slowly with the size of the network
• Most existing protocols break down for large
  networks
• Table driven
• incur large overheads due to routing table
  maintenance
• On-demand
• flood the entire network with discovery packets,
  wastes network resources
• long latency for discovery
• Protocols which use geographic routing use global
  flooding to build tables or destination
  discovery may not be scalable

42
Location Management
Cs radio range
A
D
F
C
G
B
E

• A addresses a packet to Gs latitude, longitude
• C only needs to know its immediate neighbors to
  forward packets towards G.
• Geographic forwarding needs a location service!

43
Desirable Properties ofLocation service

• Spread load evenly over all nodes.
• Degrade gracefully as nodes fail.
• Queries for nearby nodes stay local.
• Per-node storage and communication costs grow
  slowly as the network size grows

44
Grid Location Service (GLS)

• s is ns successor in that square.
• (Successor is the node with least ID greater
  than n )

45
GLS Updates
...
Invariant (for all levels) For node n in a
square, ns successor in each sibling square
knows about n.
9
...
1
11
1
1
2
...
3
11, 2
9
6
...
23
29
2
16
...
23, 2
7
6
...
...
...
17
5
...
26
25
...
...
...
8
4
21
...
19
46
GLS Query
...
9
...
1
11
1
1
2
...
3
11, 2
9
6
...
23
29
2
16
...
23, 2
7
6
...
...
...
17
5
...
26
25
location table content

...
...
...
8
4
21
query from 23 for 1
...
19
47
Scalable Location based Routing Protocol (SLURP)

• Hybrid Protocol that has a deterministic manner
  of discovering the destination
• Each node selects a home region using
  , which maintains the nodes current location
• Nodes that wish to communicate with a node query
  its home region using
• Can use most forward with fixed radius without
  backward progression to send data, once location
  is known
• Routing overhead

48
Protocol Operation
12
10
49
Scalable Location Management (SLALOM)

• Define a hierarchy of grids Order(3), Order(2),
  Order(1)
• Assign a Order(1) home region for each node in
  an Order(2) grid
• Nodes that wish to communicate with another node
  query its home region in their Order(2) grid
• To reduce location update overhead, define far
  and near home regions near regions updated
  frequently
• Routing overhead

50
Protocol Operation
51
References

• S. Murthy and J.J Garcia Luna Aceves, A Routing
  Protocol for Packet Radio Networks, Proc. IEEE
  Mobicom, Nov. 1995
• Y. B. Ko, N. H. Vaidya, Location Aided Routing in
  Ad-Hoc networks, Proceedings of ACM/IEEE
  Mobicom98, Dallas, TX, Oct. 1998
• Josch Broch, David B. Johnson, and David A.
  Maltz. The Dynamic Source Routing protocol for
  Mobile Ad-Hoc networks, Internet-Draft,
  draft-ietf-manet-dsr-00.txt, March 1998.
• Charles Perkins, Ad-Hoc On Demand Distance Vector
  (AODV) Routing. Internet-Draft,
  draft-ietf-manet-aodv-00.txt, November 1997.
• Charles E. Perkins and Pravin Bhagwat, Highly
  dynamic Destination Sequenced Distance Vector
  (DSDV) for mobile computers, In Proceedings of
  the SIGCOMM '94 Conference on Communication
  Architectures, Protocols and Applications, pages
  234-244
• Josh Broch, David A. Maltz, David B. Johnson,
  Yih-Chun Hu, and Jorjeta Jetcheva. A Performance
  comparison of multi-hop wireless Ad-Hoc network
  routing protocols. In Proceedings ACM/IEEE
  MobiCom, pages 85-97, October 1998.
• Jinyang Li, John Janotti, Douglas S. J. De Couto,
  David R. Karger, and Robert Morris, A Scalable
  Location Service for Geographic Ad Hoc Routing,
  The Sixth Annual International Conference on
  Mobile Computing and Netwroking, pages 120-130,
  August 2000.
• Seung-Chul M. Woo and Suresh Singh, Scalable
  Routing in Ad-Hoc Networks, Technical Report,
  TR00.001, March 2000
• V. Park, S. Corson, A Highly Adaptive Distributed
  Routing Algorithm for Mobile Wireless Networks,
  IEEE Infocom97
• Basagni S. and Chlamtac, I. and Syrotiuk, V. R.
  and Woodward, B. A. A Distance Routing Effect
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  the Fourth Annual ACM/IEEE International
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  998