Routing and Location Management in Mobile Ad-hoc Networks By Sumesh J. Philip (09/20/2001)
Jan 19, 2016
Routing and Location Managementin Mobile Ad-hoc Networks
By
Sumesh J. Philip(09/20/2001)
Contents
IntroductionRouting 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
Mobile Ad-Hoc Network
Collection of mobile nodes forming a networkNo centralized administration or standard support servicesHighly co-operative, each host is an independent routerHosts use wireless RF transceivers as network interface
Conferences/Meetings
Search and Rescue
Disaster Recovery
Automated Battlefields
MaNet Constraints and Issues
Lack of a centralized entityNetwork topology changes frequently and unpredictablyRouting and Mobility ManagementChannel access/Bandwidth availabilityHidden/Exposed station problemLack of symmetrical linksPower limitation
Conventional Routing Protocols ?
Not designed for highly dynamic, low bandwidth networks“Count-to-infinity” problem and slow convergenceLoop formation during temporary node failures and network partitionsProtocols that use flooding techniques create excessive traffic and control overhead
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
Wireless Routing Protocol (WRP)
A Path finding algorithm; uses predecessor to destination in the shortest pathEliminates the “Count-to-infinity” problem and converges fasterNeighbor connectivity via periodic “Hello” messagesUpdate messages sent upon detecting a change in neighbor link
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->j does not include i, and is the shortest path to j
Operation
J
K
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(0, J)
(2, K)
(2, K)
(1, K)
X1110
1
5
10
(, K)
(10, B)
(10, I)
(11, B)
Destination Sequenced Distance Vector (DSDV)
Each Route is tagged with a sequence number originated by destinationHosts perform periodic & triggered updates, issuing a new sequence numberSequence 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
Topology changes
Broken links assigned a metric of ∞Any route through a hop with a broken link is also assigned a metric of ∞“∞ routes” are assigned new sequence numbers by any host and immediately broadcast via a triggered updateIf a node has an equal/later sequence number with a finite metric for an “∞ route”, a route update is triggered
DSDV Operation
Damping Fluctuations
Routes preferred if later sequence numbers, or smaller metric for same sequence numbersProblem : Table fluctuations if worse metrics are received first, causing a ripple of triggered updatesSolution : Use average settling time as a parameter before advertising routesTantamount to using two tables, one for forwarding packets and another for advertising routes
Dynamic Source Routing (DSR)
Each packet header contains a route, which is represented as a complete sequence of nodes between a source-destination pairProtocol consists of two phases route discovery route maintenance
Optimizations for efficiency Route cache Piggybacking Error handling
DSR Route Discovery
Source broadcasts route request (id, target) Intermediate node action Discard if id is in <initiator, request id> 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
DSR Route Maintenance
Use acknowledgements or a layer-2 scheme to detect broken links; inform sender via route error packetIf 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 errorInitiate route discovery
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
Optimizations
Piggybacking Data piggybacked on route request Packet Problem : route caching can cause piggybacked
route replies to be discardedImproved 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
Ad-hoc On DemandDistance Vector (AODV)
On demand protocol that uses sequence numbers (DSDV) to build loop free routesKey difference from DSR is that source route is no longer requiredPath discovery Reverse Path setup Forward path setup
Table management and path maintenanceLocal connectivity management
AODV Reverse path setup
Counters : Sequence number, Broadcast idReverse Path Broadcast route request (RREQ) < source_addr,
source_sequence-# , broadcast_id, dest_addr, dest_sequence_#, hop_cnt >
RREQ uniquely identified by <source_addr , broadcast_id>
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
AODV Forward path setup
RREQ arrives at a node that has current route to the destination ( larger/same sequence number) unicast request reply (RREP)<source_addr, dest_addr, dest_sequence_#, hop_cnt,lifetime> to neighborRREP 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
AODV OperationD
S
X
X
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
AODV Maintenance
Path maintenance Upon link breakage, affected node
propagates an unsolicited RREP <dest_sequence_#+1, ∞> to all upstream nodes
Source may restart route discovery processLocal connectivity management Broadcasts used to update local
connectivity information Inactive nodes in an active path required to
send “hello” messages
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 nodeAdjust reference level to restore routes on link failureMultiple routes to destination; route optimality not importantQuery, Update, Clear packets used for creating, maintaining and erasing routes
Creating Routes
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A B
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G (DEST)
FH
D
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UPD
UPD
UPD
UPD UPD
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Route Maintenance
C
A B
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D
UPD
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UPD
UPD
Erasing Invalid Routes
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 UnixMedium Access Control : IEEE 802.11 Physical Layer model : combines both free space and two ray ground reflection modelProtocols studied : DSDV(SQ), AODV, DSR, TORA
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
Packet Delivery Ratio
95-100% in most cases for DSR, AODVStale route entries in DSDV cause dropsShort lived loops in TORA as part of link reversalAll protocols perform well when there is low node mobility
Routing Overhead (packets)
Route caching and non-propagating RREQs in DSRTORA
Sum of mobility dependant, independent overhead for TORA
Congestive collapse
Nearly constant for DSDV due to periodic updates
Routing Overhead (Bytes)
DSR more expensive than AODV except at high mobilitySmaller packets in AODV, may be more expensive in terms of media access, power and network utilization
Path Optimality
DSDV, DSR use routes close to optimalTORA not designed to find shortest pathTORA, AODV use paths close to optimum when node mobility is low
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 hopsPossible to obtain node location via a GPS systemGeographic forwarding Packet header contains the destination’s
location Most forward with fixed radius
Distance Routing EffectAlgorithm for Mobility (DREAM)
Proactively disseminate location informationDistance 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
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
LAR Scheme 1
Source calculates the “expected zone”, defines a “request zone” in the request packet and initiates route discoveryNode I receiving the route request forwards the request if it falls inside the “request zone”, otherwise discards itWhen destination receives the request, replies with a route reply including current location, time and average speedSize of request zone is large at low and high node speeds
LAR Scheme 2
Source calculates the distance Dists to destination (xd, yd) and initiates route discovery with both parametersNode I calculates it’s distance Disti from (xd, yd) and forwards the request only if Disti<= Dists + δ, otherwise discards the request
Node I replaces Dists with Disti before forwarding the requestNon zero δ increases probability of route discovery
LAR schemes
N
S (xs,ys)
I
J
D(xd,yd)
R = v(t-t0)
N
S (xs,ys)
I
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Scheme 1 Scheme 2
D(xd,yd)
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 networkMost existing protocols break down for large networksTable driven
incur large overheads due to routing table maintenanceOn-demand
flood the entire network with discovery packets, wastes network resources
long latency for discoveryProtocols which use geographic routing use global flooding to build tables or destination discovery; may not be scalable
Location Management
A
B
CD F
C’s radio range
E
G
A addresses a packet to G’s latitude, longitudeC only needs to know its immediate neighbors to forward packets towards G.Geographic forwarding needs a location service!
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
Grid Location Service (GLS)
n
s
ss
s
s
s
s
s s
• s is n’s successor in that square. (Successor is the node with “least ID greater than” n )
sibling level-0squares
sibling level-1squares
sibling level-2squares
... 1
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GLS Updates9
23, 2
11, 2
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292
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location table content
location update
2Invariant (for all levels):For node n in a square, n’s successor in each sibling square “knows” about n.
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location table content
query from 23 for 1
GLS Query
Scalable Location based Routing Protocol (SLURP)
Hybrid Protocol that has a deterministic manner of discovering the destinationEach node selects a ‘home region’ using , which maintains the node’s current locationNodes 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
)(vN 3/2
)(IDf
)(1 IDf
Protocol Operation
[12]
[10]
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) gridNodes that wish to communicate with another node query its ‘home region’ in their Order(2) gridTo reduce location update overhead, define ‘far’ and ’near’ home regions; ‘near’ regions updated frequentlyRouting overhead )(vN 4/3
Protocol Operation
References
S. Murthy and J.J Garcia Luna Aceves, A Routing Protocol for Packet Radio Networks, Proc. IEEE Mobicom, Nov. 1995Y. B. Ko, N. H. Vaidya, Location Aided Routing in Ad-Hoc networks, Proceedings of ACM/IEEE Mobicom’98, Dallas, TX, Oct. 1998Josch 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 234-244Josh 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 Algorithm for Mobility (DREAM), Proceedings of the Fourth Annual ACM/IEEE International conference on Mobile Computing and Networking, MobiCom'98, pp. 76-84, Dallas, TX, October 25-30, 998