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Transcript of Ad Hoc Workshop 2004 L2
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Universit du Luxembourg
Facult des Sciences, de la Technologie et dela Communication
Ad-Hoc Workshop 2004Lecture 2:
Reactive Routing
Christophe Ronkar
E4A
9.11.2004
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IntroductionWhat is ad hoc?
An ad hoc wireless network consists of a set of mobile nodes (hosts)that are connected by wireless links. The network topology maykeep changing randomly. (Murthy & Manoj)
Problem?Much more tasks for the hosts in MANET
=> routing (pass on the packets etc)
MANET: Mobile Ad hoc NETwork
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Routing protocols in ad hoc
Table-driven routing protocol (Proactive)
DSDV, WRP, STAR
On-demand (source-initiated) routing protocol (Reactive)
DSR dynamic source routingABR associativity-based routing
SSA signal stability-based adaptive routing
PLBR prefered-link based routing Hybrid routing protocol (ZRP)
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On-demand routing protocol
Only execute the path-finding process andexchange routing information when a path isrequired by a node to communicate with the
destination Find a path between source node and
destination node without building up routing
tables
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Summary
DSR: Dynamic Source RoutingABR: Associativity-Based Routing
SSA: Signal Stability-Based AdaptiveRouting Protocol
PLBR: Preferred Link-Based Routing
Protocol
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Dynamic Source Routing DSRGeneral 1/2
DSR is a efficient and dynamic on-demand routingprotocol, designed specifically for use in MANETs
Sender dertermins the whole path up to the receiver(Source Routing) and desposits the information in the
packets Route will only be calculated if needed!
Based on the Link-State-Algorithmus
Each node knows his best way to a destination Changes will by sent to all the nodes by flooding
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Dynamic Source Routing DSRGeneral 2/2
Hop-by-hop routing with a Hop-limit (=>TTL)
Small diameter of MANET (between 5 & 10 hops)
Nodes can move around at a moderatspeed
Beacon-less (compared to other Reactive r.p.) Uni- & bidirectional links may be present in MANETs
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Dynamic Source Routing DSRImportant terms Source Route (Wegsequenz)
Sequence of hops that the packet has to follow on itsway to the destination node.
Route Cache
Route Cache = number of Source Routes every node in MANETs owns a Route Cache Route Cache saves the learned Source Routes routes are deleted after a execution time
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Dynamic Source Routing DSRRoute Discovery & Route Maintenance
DSR contains 2 phases:1) Find a path (Route Discovery)
A node only tries to find a path if relevant data is present andthere is no path known to the receiver.
2) Maintain a path (Route Maintenance)
A node sends data: node has to maintain this path. When onenode gets in trouble with the path, it needs to find a new path.
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Dynamic Source Routing DSRRoute Discovery & Route Maintenance
Each packet sent, carries in its header the complete ordered listof nodes through which the packet will pass
This allows the source node to select & control the routes used
for its packets Other nodes forwarding or overhearing any of these packets can
also easily cache this routing information for future use.
For example is the destination node able to try another cached
route if the one it has been using is broken
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Dynamic Source Routing DSRRoute Discovery
Route Discovery is the mechanism by which anode S wishing to send a packet to a destinationnode D obtains a Source Route to D
The source node is the initiator and thedestination node is the target
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Dynamic Source Routing DSRRoute Discovery 1/4 Example:
Reference: The Dynamic Source Routing Protocol for
Mobile Ad Hoc Networks (DSR), Internet-DraftJohnson Maltz Hu July 2004
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Dynamic Source Routing DSRRoute Discovery 2/4
If node A has in his Route Cache a route to node E, thisroute is used.
If not => Route Discovery:
Node A (initiator) transmits a RouteRequest (flooding) Each RouteRequest identifies the initiator and target and also
contains a unique request identification (id) determined by theinitiator of the Request
The RouteRequest also contains a Route Record, here theaddresses of each intermediate node through which the packetsof the RouteRequest has been forwarded are listed
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Dynamic Source Routing DSRRoute Discovery 3/4
If node B has recently seen another RouteRequest from the sameinitiator,
or if node Bs own address is already listed in the Route Record,then node B discards the Request (length of Route Record is limited).
If node B is the target of the Route Discovery, it returns aRouteReply to the initiator of the Route Discovery.
When the initiator receives this RouteReply, it caches this route inits Route Cache for use in sending subsequent packets to this
destination Otherwise node B isnt the target and it fowards the
RouteRequest to his neighbors (except to the initiator)
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Dynamic Source Routing DSRRoute Discovery 4/4
Destination node (target) sends out a RouteReply with the list ofthe best paths
Bi-directional links: the target uses a route to send theRouteReply with the reverse sequence of nodes (piggybacking)
Unidirectional links: the destination node initiates a RouteDiscovery and then attaches the RouteReply packet
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Dynamic Source Routing DSRRouteRequest
Reference: TU Carolo-Wilhelmina Braunschweig
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Dynamic Source Routing DSRRouteReply
Reference: TU Carolo-Wilhelmina Braunschweig
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Dynamic Source Routing DSRRoute Maintenance
Each node is responsible for confirming that the next hop in aSource Route receives the packet
The packet is retransmited many times until a confirmation isreceived from the next node on the route
If retransmission results a failure: a RouteError message is sent tothe initator, so the initiator can remove that Source Route from itsRoute Cache
Initator checks his Route Cache for another route
if not => RouteRequest A node forwarding or overhearing any packets may take advantage
of Source Routes found from those packets
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Dynamic Source Routing DSRRoute Maintenance
Example:
Reference: TU Cottbus Aline Wetjen
Dynamic Source RoutingSeminar on Car-2-Car CommunicationC2CC
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Dynamic Source Routing DSRRoute Maintenance
Example (cont.)
If C does not receive an acknowledgement from D aftersome number of requests, it returns a RouteError to A
Then Node A removes this broken link from its cache
If A has in its Route Cache another route to E (fromadditional RouteReplies or from its earlier RouteDiscovery), then it can send the packet immediately
using the this new route Otherwise, it should perform a new Route Discovery for
this target
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Dynamic Source Routing DSRAdvantages & Disadvantages
Reactive: no need to peridically flood the network for updating therouting tables (like table-driven r.p.)
Intermediate nodes utilize the route cache information efficiently toreduce the control overhead
Initator only tries to find a route if actually no route is known
Route Maintanence does not locally repair the a broken link Only efficient in small (
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Summary
DSR: Dynamic Source RoutingABR: Associativity-Based Routing
SSA: Signal Stability-Based AdaptiveRouting Protocol
PLBR: Preferred Link-Based Routing
Protocol
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Associativity-Based Routing ABRGeneral
Invented & developed by C.-K. Toh at Cambridge University (1996) Source-initiated: no need for periodic route updates ABR selects routes based on the temporal stability of the links
The temporal stability => counting the number of beacons
Every node generates periodic beacons to signify its existence tothe neighbors (beacon-based) This beacons are used to update the associativity table of each node
Each node classifies each neighbor link as stable or unstable
The fundamentel objective of ABR: find longer-lived routes
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Associativity-Based Routing ABRMetrics
ABR takes up a few metrics such as: Link delay
Signal strength
Power life (battery) Route relaying load
Period of presence
Spatial and temporal characteristics
Metric = value for helping the routing protocol to compare the different routes with each other
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Associativity-Based Routing ABR3 Phases
3 Phases:
Route Discovery
Route Repair/Reconstruction RRCRoute Delete RD
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Associativity-Based Routing ABRRoute Discovery 2/3
After a time period, the target can select the best routeby examining the associativity ticks along each path
If more paths have the same overall degree of
association stability, then the shortest route with lesshops is selected
Once the route as been chosen, the target sends aReply packet back to the source along the same path
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Associativity-Based Routing ABRRoute Discovery 3/3
3 routes possible from 1 to 15:1. 1-5-10-14-15
2. 1-5-4-12-15
3. 1-2-4-8-13-15
ABR selects route 3:
highest percentage of stable links
Reference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj
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Associativity-Based Routing ABRRoute Repair/Reconstruction 1/3
Case: Broken link
Node closer to the source initiates a local route repairprocess
Repair process:
The node broadcasts a RouteRepair packet namedlocal query LQ with a limited TTL
Broken link is by passed locally without flodding a newbroadcast query
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Associativity-Based Routing ABRRoute Repair/Reconstruction 2/3
-Broken path: 8-13-15
-Node 8 initiates the LQbroadcast
-New path: 8-12-15
Reference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj
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Associativity-Based Routing ABRRoute Repair/Reconstruction 3/3
Case: Node is moving
First the last node before the destination erases its route
Then a LQ process is initiated to check if the node is still reachable If the target is reachable, it selects the best partial route and replies Otherwise the LQ process is forwarded to the next upstream node A Route Notification message is sent to the next upstream node to
erase the invalid route and inform this node that it should take over theLQ process
If this process results in backtracking more than halfway to the source,the LQ process is discontinued and the source initiates a new
broadcast query process
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Associativity-Based Routing ABRRoute Delete
If a discovered route is no longer needed, the source node initiates a
RouteDelete RD broadcast Every node on this route will then delete the route entry from their
routing cache
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Associativity-Based Routing ABRAdvantages & Disadvantages
Stable routes have a higher preference compared to
shorter routes=> fewer pathes will break which reduces flooding
A broken link is repaired locally
Stability informations are only used during the routeselection process
Chosen path may be longer than the shortest path,
because of the preference given to stable paths LQ broadcasts may result in high delays during the route
repair
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Summary
DSR: Dynamic Source RoutingABR: Associativity-Based Routing
SSA: Signal Stability-Based AdaptiveRouting Protocol
PLBR: Preferred Link-Based Routing
Protocol
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Signal Stability-Based Adaptive Routing
Protocol SSA
On-demand routing protocol that uses signal strength
and location stability for finding stable routes Beacon-based: signal strength of the beacons is
measured for determining link stability between the
nodes The location stability defines paths which has existed for
a longer period of time
Every node maintains a signal stability table (SST)which is based on the signal strengths of its neighborsbeacons
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Signal Stability-Based Adaptive Routing
Protocol SSA
If a node has received strong beacons for the past few
beacons, the node classifies the link as a stable link
Otherwise its a unstable link
Main objective of SSA: choosing routes that have stronger connectivity
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Signal Stability-Based Adaptive SSARoute Establishment 1/2
A source node which does not have a route to the target floods the
network with RouteRequests Nodes that employ the SSA protocol, process a RouteRequest only
if it is received over a stable link
The destination selects the first RouteRequest packet received over
stable links Then the destination initiates a RouteReply packet to notify the
selected route to the source
Major difference to ABR:
The node which received the RouteRequest first has to check if thepacket was received over a stable or unstable link
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Signal Stability-Based Adaptive SSARoute Establishment 2/2
RouteRequest from node 1 is
only forwarded over stablelinks to the target:
2-4-8-13-15
Reference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj
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Signal Stability-Based Adaptive SSARoute Maintenance 1/2
Broken links:
The last node before the broken link notify the sourcenode of the broken link (node 2 -> node 1)
And the node after the broken links notifies thedestination node (node 4 -> node 15)
The source node, after receiving aRouteBreakNotification packet, refloods theRouteRequest to find another stable route to D
Older entries in cache are only deleted if the datapackets fail to reach the next node Only if no stable route is available ,then also unstable
link are beeing used
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Signal Stability-Based Adaptive SSARoute Maintenance 2/2
-The broken link 2-4 is
detected and bypassed:1-5-4-8-13-15
Reference: Ad Hoc Wireless Networks
Architectures & Protocols, Murthy Manoj
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Signal Stability-Based Adaptive SSAAdvantages & Disadvantages
SSA finds more stable routes compared to DSR(shortest path routing)
SSA is able to classify the links using the beacon
counts (stable or unstable links)
Multiple flooding of RouteRequest packets (bandwidth)
RouteRequest received through a weak link is droppedwithout being processed
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Summery
DSR: Dynamic Source RoutingABR: Associativity-Based Routing
SSA: Signal Stability-Based AdaptiveRouting Protocol
PLBR: Preferred Link-Based Routing
Protocol
P f d Li k B d R ti
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Preferred Link-Based Routing
Protocol PLBR
PLBR is a routing protocol with an efficientflooding mechanismus
Flooding impaired:
Wastage of bandwidth
Increase the number of collisions
Broadcast stroms (topological instability)
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Preferred Link-Based Routing Protocol PLBR
General 1/2
A node selects a subset of nodes from its
neighbors list (NL) This subset is referred to as the preferred list
(PL)
Every RouteRequest packets carries the list of aselected subset of neighbors
All neighbors receive RouteRequest packets(broadcast), but only neighbors present in thePL forward them further (JoinQuery)
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Preferred Link-Based Routing Protocol PLBR
General 2/2
Changes in the tables are updated with the
beacons Also a quick link break detection mechanism that
locally repairs broken links is available
3 Phases:
Route Establishment
Route SelectionRoute Maintenance
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Preferred Link-Based Routing Protocol PLBR
Used rates
NL Neihbors List
PL Preferred List PLT Preferred Link Table
K maximum number of neighbors allowed in PL
NNT Neighbors Neighbor Table TP Traversed Path
TTL TimeToLive
INL Include List (reachable nodes)
EXL Exclude List (unreachable nodes)
P f d Li k B d R ti P t l PLBR
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Preferred Link-Based Routing Protocol PLBR
2 Algorithms
Neighbor Degree-Based Preferred Link (NDPL)
Weight-Based Preferred Link (WBPL)
P f d Li k B d R i P l PLBR
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Preferred Link-Based Routing Protocol PLBR
NDPL / WBPL
63
2
1 4
5 7
8
RouteRequest
S
D
stableReference: Ad Hoc Wireless NetworksArchitectures & Protocols, Murthy Manoj
unstable
P f d Li k B d R ti P t l PLBR
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Preferred Link-Based Routing Protocol PLBR
Example
Destination is not present in NNT from the Source (=>RouteRequest)
Preferred Link Table PLT has to be calculated K=2, size of Preferred List PL
NDPL: node furthest away
PLT(node 5,node 1)
After node 1 is deleted, node 8 isnt in the neighbor list
Source sends RouteRequest only to node 5
WBPL:
neighbors of Source all in PLT Neighbors 1,4 & 2 deleted
Send RoutRequest (unicast)
P f d Li k B d R ti P t l PLBR
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Preferred Link-Based Routing Protocol PLBR
Advantages & Disadvantages
Example:
only 3 packets are transmitted for finding the path
Path lenght is 3
Higher scalability compared to other on-demand r.p.
Reduction of control overhead (collisions)
NDPL & WBPL are both computationally more complexthan other RouteRequest forwarding schemes
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Questions