On-Demand Routing Protocols · On-Demand Routing Protocols • Routes are established “on...
Transcript of On-Demand Routing Protocols · On-Demand Routing Protocols • Routes are established “on...
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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)
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On Demand Routing - Readings
• D. B. Johnson and D. A. Maltz, "Dynamic Source Routing in Ad-Hoc WirelessNetworks," Mobile Computing, 1994.
Charles E. Perkins and Elizabeth M. Royer. "Ad hoc On-Demand Distance VectorRouting." Proceedings of the 2nd IEEE Workshop on Mobile Computing Systemsand Applications, New Orleans, LA, February 1999, pp. 90-100.
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Existing On-Demand Protocols
• Dynamic Source Routing (DSR)• Associativity-Based Routing (ABR)• Ad-hoc On-demand Distance Vector (AODV)• Temporarily Ordered Routing Algorithm (TORA)• Zone Routing Protocol (ZRP)• Signal Stability Based Adaptive Routing (SSA)• On Demand Multicast Routing Protocol (ODMRP)
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Dynamic Source Routing (DSR)
• Forwarding: source route driven instead of hop-by-hop route table driven
• No periodic routing update message is sent• The first path discovered is selected as the route• Two main phases
–– Route DiscoveryRoute Discovery–– Route MaintenanceRoute Maintenance
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DSR - Route Discovery
• To establish a route, the source floods a Route RequestRoute Requestmessage 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
• Each node maintains a Route CacheRoute Cache which records routes it has learned and overheard over time
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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 ErrorRoute Error packet to original sender to perform new route discovery
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Ad hoc On-Demand Distance Vector Routing (AODV)
• Primary Objectives– Provide unicast, broadcast, and multicast capability– Initiate forward route discovery only on demand– Disseminate changes in local connectivity to those
neighboring nodes likely to need the information
• Characteristics– On-demand route creation
• Effect of topology changes is localized• Control traffic is minimized
– Two dimensional routing metric: <Seq#, HopCount>– Storage of routes in Route Table
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Route Table
• Fields:– Destination IP Address– Destination Sequence Number– HopCount– Next Hop IP Address– Precursor Nodes– Expiration Time
• Each time a route entry is used to transmit data, the expiration time is updated to current_time + active_route_timeout
Next Hop
Source
Source
APrecursor Nodes
Destination
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Unicast Route Discovery
<Flags, Bcast_ID, HopCnt, Src_Addr, Src_Seq#, Dst_Addr, Dst_Seq#>
• Node can reply to RREQ if– It is the destination, or– It has a “fresh enough” route
to the destination• Otherwise it rebroadcasts the request• Nodes create reverse route entry• Record Src IP Addr / Broadcast ID
to prevent multiple rebroadcasts
Source
Destination
Route Request Propagation
•Source broadcasts Route Request (RREQ)
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Forward Path Setup
• Destination, or intermediate node with current route to destination, unicasts Route Reply (RREP) to source<Flags, HopCnt, Dst_Addr,
Dst_Seq#, Src_Addr, Lifetime>• Nodes along path create
forward route• Source begins sending data
when it receives first RREP
Source
Destination
Forward Path Formation
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Path Maintenance
• Movement of nodes not along active path does not trigger protocol action• If source node moves, it can reinitiate route discovery• When destination or intermediate node moves, upstream node of break
broadcasts Route Error (RERR) message• RERR contains list of all destinations no longer reachable due to link break• RERR propagated until node with no precursors for destination is reached
Source
Destination1
2
3
4
3’
Source
Destination1
24
3’
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GloMoSim/Qualnet Simulation Layers
Application Processing
Propagation Model Mobility
Frame Processing Radio Status/Setup
CS/Radio SetupRTS/CTSFrame Wrapper
Ack/Flow Control
Clustering
Packet Store/Forward VC Handle
FlowControl Routing
IP Wrapper IP/Mobile IP
RSVPTransport Wrapper TCP/UDP Control
Channel
Radio
MAC Layer
Network
IP
Transport
Application
RTP Wrapper RCTP
Packet Store/Forward
Clustering
Routing
Link Layer
Application Setup
Data PlaneData Plane Control PlaneControl Plane
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Performance Evaluation Enviroment
• PARSEC simulation enviroment– 100 nodes– 1000mx1000m square area– transmission range: 100m– channel data rate: 2 Mbps– random mobility model– UDP traffic between randomly selected node pairs– cluster-token MAC layer protocol
• HSR – 2 level physical partition– 1 level logical groupings, number of logical subnets varies with
network size
• FSR– 2 level fisheye scoping– fisheye radius is 2 hops
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Control O/H vs. number of nodes
00.20.40.60.8
11.21.41.61.8
25 49 100 225 324 400
Number of nodes
Co
ntr
ol
O/H
(M
bit
s/C
luste
r)
On-demand DSDV HSR FSR
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Control O/H vs. Traffic Pairs
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Control O/H vs. Mobility (100 pairs)
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Average Delay (ms)
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Location-Aided Routing (LAR)
• Ko and Vaidya (Texas A & M)• Location assisted (requires GPS)• On-demand• No periodic messages• LAR works like DSR except it limits the flooded
area of Route RequestsRoute Requests using location information
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LAR (cont’d)
•Scheme 1– The source specifies a request zone which
includes the source and the area where the destination may reside
– Nodes within the request zone propagate Route Route RequestsRequests
•Scheme 2– The source specifies the distance between itself
and the destination– Nodes forward Route RequestsRoute Requests if their distances
to the destination is less than or equal to the distance indicated by the packet
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DREAM
• Besagni, et al. (U of Texas, Dallas)• Location assisted (requires GPS)• Node coordinates (instead of routes) are
recorded in the route table •• Distance EffectDistance Effect: Send location updates to nearby
nodes more frequently• Location update frequencies are adjusted to
mobility rate
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DREAM (cont’d)
• The source partially floods data to nodes that are in the direction of the destination
• The source specifies possible next hops in the data header using location information
• Next hop nodes select their own list of next hops and include the list into data header
• If the source finds no neighbors in the direction of the destination or has no fresh location information of the destination, data is flooded to the entire network
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Location Based Routing Simulation (LAR and DREAM)
• 50 nodes; 750m X 750 m space• Free space channel propagation model• Radio with capture ability• MAC: IEEE 802.11 DCF• 10 UDP data sessions with constant bit rate
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Simulation Results (cont’d)
• Packet delivery ratio
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Simulation Results• Number of data packets transmitted per data packet delivered
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Simulation Results (cont’d)• Number of control bytes transmitted per data byte delivered
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Conclusions
• Conventional (wired net) routing schemes suffer of O/H, mobility and scalability limitations
• Hierarchical routing reduces O/H and improves scalability (at the expense of accuracy).
• On Demand routing eliminates background routing control O/H. It introduces latency; it does not well suited for QoS routing