4. ROUTING PROTOCOLS

WIRELESS MESH NETWORKSWIRELESS MESH NETWORKS

Ian F. AKYILDIZ* and Xudong Ian F. AKYILDIZ* and Xudong WANG**WANG**

* Georgia Institute of Technology* Georgia Institute of Technology BWN (Broadband Wireless Networking) Lab &BWN (Broadband Wireless Networking) Lab &

** TeraNovi Technologies** TeraNovi Technologies

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4. ROUTING PROTOCOLS4. ROUTING PROTOCOLS

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Features for Optimal Routing in Features for Optimal Routing in WMNsWMNs

ScalabilityScalability

Fast route discovery and rediscovery Fast route discovery and rediscovery (for reliability)(for reliability)

Mobile user support Mobile user support (for (for seamless and efficient seamless and efficient handover)handover)

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Multiple Performance MetricsMultiple Performance Metrics

minimum hop-countminimum hop-count ineffective!!ineffective!! e.g., link quality and round trip time (RTT)e.g., link quality and round trip time (RTT)

RobustnessRobustness(link failures or congestions, fault-tolerant, load balancing)(link failures or congestions, fault-tolerant, load balancing)

Adaptive Support of Both Mesh Routers and Mesh Adaptive Support of Both Mesh Routers and Mesh ClientsClients(support mobility and power efficiency)(support mobility and power efficiency)

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FlexibilityFlexibility– Work with/without gateways, different topologiesWork with/without gateways, different topologies

QoS SupportQoS Support– Consider routes satisfying specified criteriaConsider routes satisfying specified criteria

MulticastMulticast– Important for some applications (e.g., emergency Important for some applications (e.g., emergency

response)response)

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* Apply routing algorithms derived for Ad Hoc Networks

Prelim Routing Protocols for WMNs

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CLASSIFICATION OF ROUTING PROTOCOLSCLASSIFICATION OF ROUTING PROTOCOLSFOR AD HOC NETWORKSFOR AD HOC NETWORKS

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OVERVIEWOVERVIEW

FlatFlat– ReactiveReactive

DSR – Dynamic Source Routing AODV – Ad hoc On demand Distance Vector

– ProactiveProactive FSR – Fisheye State RoutingFSR – Fisheye State Routing FSLS – Fuzzy Sighted Link State OLSR – Optimized Link State Routing ProtocolOLSR – Optimized Link State Routing Protocol TBRPF – Topology Broadcast Based on Reverse Path

Forwarding

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OVERVIEWOVERVIEW

HierarchicalHierarchical– CGSR – Clusterhead-Gateway Switch RoutingCGSR – Clusterhead-Gateway Switch Routing– HSR – Hierarchical State RoutingHSR – Hierarchical State Routing– LANMAR – Landmark Ad Hoc RoutingLANMAR – Landmark Ad Hoc Routing– ZRP – Zone Routing ProtocolZRP – Zone Routing Protocol

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OVERVIEWOVERVIEW

Geographical RoutingGeographical Routing– DREAM – Distance Routing Effect Algorithm for DREAM – Distance Routing Effect Algorithm for

MobilityMobility– GeoCast – Geographic Addressing and RoutingGeoCast – Geographic Addressing and Routing– GPSR – Greedy Perimeter Stateless RoutingGPSR – Greedy Perimeter Stateless Routing– LAR – Location-Aided RoutingLAR – Location-Aided Routing

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Reminder: Ad Hoc Routing ProtocolsReminder: Ad Hoc Routing Protocols

Proactive Protocols Proactive Protocols (A(Actively seeks for routes/paths)– Determine routes independent of traffic patternDetermine routes independent of traffic pattern– Traditional link-state and distance-vector routing protocols are proactiveTraditional link-state and distance-vector routing protocols are proactive

Reactive Protocols Reactive Protocols ((Seek for routes/paths only when required)– Maintain routes only if neededMaintain routes only if needed

Hierarchical RoutingHierarchical Routing– Introduces hierarchy to the flat networkIntroduces hierarchy to the flat network

Geographic Position Assisted RoutingGeographic Position Assisted Routing– Why send packets North when the destination is South?Why send packets North when the destination is South?

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Routing Protocols from Ad Hoc Networks Used for Routing Protocols from Ad Hoc Networks Used for WMNsWMNs

– Dynamic Source Routing (DSR) Dynamic Source Routing (DSR)

in Microsoft mesh networksin Microsoft mesh networks

D.B. Johnson, D.A. Maltz, and Y.-C. Hu, “The dynamic source routing protocol for mobile ad hoc networks (DSR),” IETF Internet-Draft, 2004.

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– AODV (ad-hoc on-demand distance vector) routingAODV (ad-hoc on-demand distance vector) routing Used by Used by many other companiesmany other companies Major building block for the routing framework of Major building block for the routing framework of IEEE IEEE

802.11s802.11s

C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004.

IEEE 802.11s Task Group, “Joint SEE-Mesh/Wi-Mesh proposal to 802.11 TGs overview,” IEEE Doc: 802.11-05/0567r6, 2006.

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– Topology broadcast based on reverse path Topology broadcast based on reverse path forwarding forwarding

(TBRPF) protocol in (TBRPF) protocol in Firetide NetworksFiretide Networks

R. Ogier, F. Templin, and M. Lewis, “Topology dissemination based on reverse-path forwarding (TBRPF),” IETF RFC 3684, 2004.

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Dynamic Source Routing (DSR) Dynamic Source Routing (DSR) D. B. Johnson, D. A. Maltz, Y.-C. Hu, “Dynamic Source Routing Protocol for Mobile Ad Hoc Networks”, IETF Draft, April 2004.

Based on Based on Source Routing principle!Source Routing principle!

On-demandOn-demand

Route computation performed on aRoute computation performed on a per-connection per-connection basisbasis

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Dynamic Source Routing (DSR) Dynamic Source Routing (DSR)

Source, after route computation, appends each packet Source, after route computation, appends each packet with a source-route informationwith a source-route information

Intermediate hosts forward packet based on source Intermediate hosts forward packet based on source routeroute

TWO PHASES: ROUTE DISCOVERY &TWO PHASES: ROUTE DISCOVERY & ROUTE MAINTENANCEROUTE MAINTENANCE

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Dynamic Source Routing (DSR):Dynamic Source Routing (DSR):ROUTE DISCOVERYROUTE DISCOVERY

When node S wants to send a packet to node D, but When node S wants to send a packet to node D, but does not know a route to D, node S initiates a does not know a route to D, node S initiates a Route Route DiscoveryDiscovery

Source node S floods (broadcasts) Source node S floods (broadcasts) Route Request (RREQ) Route Request (RREQ) packet.packet.

RREQ packet containsRREQ packet contains * DESTINATION ADDRESS

* SOURCE NODE ADDRESS and * A UNIQUE IDENTIFICATION NUMBER.

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If the node is the receiver (i.e., has the If the node is the receiver (i.e., has the correct destination address) then returns the correct destination address) then returns the packet to the senderpacket to the sender

If the packet has already been received If the packet has already been received earlier (identified via ID) then discard the earlier (identified via ID) then discard the packetpacket

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Each node receiving the packet checks Each node receiving the packet checks whether whether

it knows of a route to that destination.it knows of a route to that destination.

If it does not, it If it does not, it appends/adds its own appends/adds its own

identifieridentifier (address) to the route record and (address) to the route record and

forwards the RREQ packet.forwards the RREQ packet.

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Dynamic Source Routing Dynamic Source Routing (DSR):(DSR):ROUTE DISCOVERYROUTE DISCOVERY

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Represents transmission of RREQ

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YBroadcast transmission

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[S]

[X,Y] Represents list of identifiers appended to RREQ

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Node H receives packet RREQ from two neighbors: Potential for collision

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[S,E]

[S,C]

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Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

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[S,C,G]

[S,E,F]

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• Nodes J and K both broadcast RREQ to node D• Since nodes J and K are hidden from each other, their transmissions may collide

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[S,C,G,K]

[S,E,F,J]

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• Node D does not forward RREQ, because node D is the intended target of the route discovery

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[S,E,F,J,M]

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Route/Path Discovery in Route/Path Discovery in DSRDSR

Destination D on receiving the first RREQ, sends a Destination D on receiving the first RREQ, sends a Route Reply (RREP)Route Reply (RREP)

RREP is sent on a route obtained by RREP is sent on a route obtained by reversingreversing the the route appended to received RREQroute appended to received RREQ

RREP RREP includes the routeincludes the route from S to D on which from S to D on which RREQ RREQ

was received by node Dwas received by node D

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Route/Path Discovery in Route/Path Discovery in DSRDSR

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RREP [S,E,F,J,D]

Represents RREP control message

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DATA DELIVERY IN DSRDATA DELIVERY IN DSR

Node S on receiving RREP, caches the route included in the RREPNode S on receiving RREP, caches the route included in the RREP

When node S sends a data packet to D, the entire route is When node S sends a data packet to D, the entire route is included in the packet headerincluded in the packet header

– hence the name hence the name Source RoutingSource Routing

Intermediate nodes use the Intermediate nodes use the Source RouteSource Route included in a included in a packet to determine to whom a packet should be packet to determine to whom a packet should be

forwardedforwarded

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Data Delivery in Data Delivery in DSRDSR

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DATA [S,E,F,J,D]

Packet header size grows with route length

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DSR Optimization: DSR Optimization: Route CachingRoute Caching

Each node caches a new route it learns by any means

When node S finds route [S,E,F,J,D] to node D, node

S also learns route [S,E,F] to node F

When node K receives Route Request [S,C,G] destined

for K, it learns route [K,G,C,S] to node S

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DSR Optimization: DSR Optimization: Route CachingRoute Caching

When node F forwards RREP [S,E,F,J,D], node F learns route [F,J,D] to node D

When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D

A node may also learn a route when it overhears Data

packets

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Advantages of Use of Route Advantages of Use of Route CachingCaching

– can speed up route discoverycan speed up route discovery– can reduce propagation of route requestscan reduce propagation of route requests

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Use of Route CachingUse of Route Caching

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[x,y,w] Represents cached route at a node (DSR maintains the cached routes in a tree format)

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[S,E,F,J,D][E,F,J,D]

[C,S]

[G,C,S]

[F,J,D],[F,E,S]

[J,F,E,S]

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Use of Route Caching:Use of Route Caching:Can Speed up Route DiscoveryCan Speed up Route Discovery

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[C,S]

[G,C,S]

[F,J,D],[F,E,S]

[J,F,E,S]

RREQWhen node Z sends a route requestfor node C, node K sends back a routereply [Z,K,G,C] to node Z using a locallycached route

[K,G,C,S]RREP

RREQ

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Use of Route Caching:Use of Route Caching:Can Reduce Propagation of Route Can Reduce Propagation of Route RequestsRequests

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[C,S]

[G,C,S]

[F,J,D],[F,E,S]

[J,F,E,S]

RREQ

Route Reply (RREP) from node K limits flooding of RREQ.In general, the reduction may be less dramatic.

[K,G,C,S]RREP

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Dynamic Source Routing: Dynamic Source Routing: AdvantagesAdvantages

Routes maintained only between nodes who need to communicate

– reduces overhead of route maintenance

Route caching can further reduce route discovery overhead

A single route discovery may yield many routes to the destination, due to intermediate nodes replying from

local caches

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Dynamic Source Routing: Dynamic Source Routing: DisadvantagesDisadvantages

Packet header size grows with route length Packet header size grows with route length Flood of route requests may potentially Flood of route requests may potentially

reach all nodesreach all nodesCare must be taken to avoid collisions Care must be taken to avoid collisions

between route requests propagated by between route requests propagated by neighboring nodesneighboring nodes– insertion of random delays before insertion of random delays before

forwarding RREQforwarding RREQ

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Ad Hoc On-Demand Distance Vector Routing Ad Hoc On-Demand Distance Vector Routing (AODV) (AODV) C. E. Perkins, E. M. Belding-Royer, I. D. Chakeres, “Ad hoc On-Demand Distance Vector (AODV) Routing”, IETF Draft, Jan. 2004.

AODV attempts to improve on DSR by AODV attempts to improve on DSR by maintaining maintaining routing tables at the nodesrouting tables at the nodes, so that data packets , so that data packets do not have to contain pathsdo not have to contain paths

AODV retains the desirable feature of DSR that AODV retains the desirable feature of DSR that routes are maintained only between nodes which routes are maintained only between nodes which need to communicateneed to communicate

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AODV

– Hop-by-hop routing as opposed to source routing

– On-demandOn-demand

– When a source node wants to send a message to some destination When a source node wants to send a message to some destination node and does not already have a valid route to that destination, node and does not already have a valid route to that destination, it initiates a it initiates a Path DiscoveryPath Discovery ProcessProcess to locate the destination to locate the destination (as in DSR case)(as in DSR case)

– It broadcasts the RREQ packet to its neighborsIt broadcasts the RREQ packet to its neighbors

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AODVAODV

RREQs are forwarded in a manner similar to DSRRREQs are forwarded in a manner similar to DSR

When a node re-broadcasts a RREQ, it sets up a When a node re-broadcasts a RREQ, it sets up a reverse reverse pathpath pointing towards the source pointing towards the source

– AODV assumes symmetric (bi-directional) linksAODV assumes symmetric (bi-directional) links

When the intended destination receives a RREQ, it replies When the intended destination receives a RREQ, it replies by sending a Route Reply (RR)by sending a Route Reply (RR)

RR travels along the RR travels along the reverse path set-upreverse path set-up when RREQ was when RREQ was forwardedforwarded

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AODVAODV

– When RREQ propagates, routing tables are When RREQ propagates, routing tables are updated at intermediate nodes updated at intermediate nodes (for route to (for route to source of RREQ)source of RREQ)

– When RREP is sent by destination, routing tables When RREP is sent by destination, routing tables updated at intermediate nodes updated at intermediate nodes (for(for route to route to

destination),destination), and propagated back to source and propagated back to source

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AODVAODV

–Each node maintains its own sequence number and a broadcast ID.

–The broadcast ID is incremented for every RREQ the node initiates

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AODVAODV

– The node’s IP address and the broadcast ID The node’s IP address and the broadcast ID uniquely identify a RREQ.uniquely identify a RREQ.

– Along with its own sequence number and Along with its own sequence number and broadcast broadcast

ID, the source node includes in the RREQ the ID, the source node includes in the RREQ the most most

recent sequence number it has for the recent sequence number it has for the destination.destination.

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AODVAODV

– Intermediate nodes can reply to the RREQ only if Intermediate nodes can reply to the RREQ only if they have a route to the destination whose they have a route to the destination whose corresponding Destination Sequence Number is corresponding Destination Sequence Number is greater than or equal to that contained in the RREQ. greater than or equal to that contained in the RREQ.

– During the process of forwarding the RREQ, During the process of forwarding the RREQ, intermediate nodes recording their route tables with the intermediate nodes recording their route tables with the address of the neighbor from which the first copy address of the neighbor from which the first copy of the broadcast packet is receivedof the broadcast packet is received establishing a establishing a reverse path.reverse path.

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AODVAODV

– If more same RREQs are received later, they are If more same RREQs are received later, they are

discarded.discarded.

– RREP packet is sent back to the neighbors and the RREP packet is sent back to the neighbors and the routing routing

tables are accordingly updated.tables are accordingly updated.

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Route Requests in AODVRoute Requests in AODV

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Represents transmission of RREQ

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Broadcast transmission

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Represents links on Reverse Path

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Reverse Path Setup in AODVReverse Path Setup in AODV

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• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

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• Node D does not forward RREQ, because node D is the intended target of the RREQ

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Route Reply in AODVRoute Reply in AODV

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Represents links on path taken by RREP

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Forward Path Setup in AODVForward Path Setup in AODV

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Forward links are setup when RREP travels alongthe reverse path

Represents a link on the forward path

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Data Delivery in AODVData Delivery in AODV

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Routing table entries used to forward data packet.NOTE: Route is not included in packet header as in DSR.

DATA

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* Special considerations

- WMN routers differ from MANET routers * Power supply * Mobility * Separation of WMN routers and clients

Routing Protocols for WMNs

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Routing Challenges in WMNsRouting Challenges in WMNs

Routing in WMNs is much more complicated than in Ad Hoc Routing in WMNs is much more complicated than in Ad Hoc NetworksNetworks

REASONS:REASONS:1) Network topology is variable and inconsistent (same as ad hoc 1) Network topology is variable and inconsistent (same as ad hoc

networks)networks)

2) 2) Depending on the performance goal in routing, it may not beDepending on the performance goal in routing, it may not be possible to determine a routing path solely based on network possible to determine a routing path solely based on network

topologytopology

3) There may not be an optimal solution for a given routing 3) There may not be an optimal solution for a given routing problemproblem

4) Routing traverses both mesh routers and mesh clients that 4) Routing traverses both mesh routers and mesh clients that havehave

different networking capabilitiesdifferent networking capabilities

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Design PrinciplesDesign Principles

1)1) Maintaining a consistent and stable network Maintaining a consistent and stable network topologytopology

2) Performing dynamic and adaptive routing2) Performing dynamic and adaptive routing

3) Developing new routing metrics3) Developing new routing metrics

4) Considering tradeoff between cross-layer design 4) Considering tradeoff between cross-layer design and single-layer solutionand single-layer solution

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Design PrinciplesDesign Principles

5) Deriving distributed algorithms for routing5) Deriving distributed algorithms for routing

6) Ensuring scalability in routing6) Ensuring scalability in routing

7) Adaptively supporting both mesh routers and mesh 7) Adaptively supporting both mesh routers and mesh clientsclients

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PERFORMANCE METRICS

Per-Flow Parameters: (e.g., delay, packet loss ratio, and delay jitter and other parameters such as hop-count, per-flow throughput, and intra-flow interference)

Per-Node Parameters: (computational complexity and power efficiency)

Per-Link Parameters: (e.g., link quality, channel utilization, transmission rate, and congestion)

Inter-Flow Parameters: (e.g., inter-flow interference and fairness)

Network-Wide Parameters: (e..g., total throughput or total delay)

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* Hop-Count * Per-Hop RTT

* Per-Hop Packet Pair Delay

* Expected Transmission Count (ETX)

OVERVIEW OF ROUTING METRICS

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* Expected Transmission on a Path (ETOP) * Expected Transmission Time (ETT)

* Weighted Cumulative ETT (WCETT) * Bottleneck Link Capacity (BLC)

* Expected Data Rate (EDR) * Airtime Cost Routing Metric

OVERVIEW OF ROUTING METRICS

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* Minimum hop counting (the link quality is binary)

* Simple and requires no measurements

Disadvantages: * Can lead to poor throughput * Link quality all links do not have the same quality * Does not take packet loss or bandwidth into account * Route that minimizes hop count does not necessarily maximize the throughput

Hop Count

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Per-Hop RTTPer-Hop RTT

Measured by sending unicast probe packets between Measured by sending unicast probe packets between neighboring nodes neighboring nodes

Then calculating the time spent on the probe-ack Then calculating the time spent on the probe-ack procedureprocedure

A weighted moving average is needed to get a A weighted moving average is needed to get a smoother measurement, because one sample cannot smoother measurement, because one sample cannot really reflect the actual link status.really reflect the actual link status.

Adya A, Bahl P, Padhye J, Wolman A and Zhou L, Adya A, Bahl P, Padhye J, Wolman A and Zhou L, ““A multi-radio unification protocol for IEEE 802.11 wireless A multi-radio unification protocol for IEEE 802.11 wireless networks”,networks”, Proc. IEEE BroadNets 2004Proc. IEEE BroadNets 2004

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Based on per-hop RTT, a routing protocol selects a Based on per-hop RTT, a routing protocol selects a routing path with the least sum of RTTs of all links routing path with the least sum of RTTs of all links on the path.on the path.

Per-hop RTT is able to capture Per-hop RTT is able to capture

* the packet loss ratio in a link* the packet loss ratio in a link

* the traffic load* the traffic load

* queuing delay in two nodes on the link, and * queuing delay in two nodes on the link, and

* contention status in all neighboring nodes.* contention status in all neighboring nodes.

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* Loss will cause RTT to increase due to ARQ

* If ARQ fails, RTT is increased by some percentage

* This metric is load dependent

* Channel contention increases RTT

Per-Hop RTT

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Its effectiveness is constrained by two problems:Its effectiveness is constrained by two problems:

PROBLEM 1:PROBLEM 1:Per-hop RTT is too much dependent on the traffic load/queuing delay, which Per-hop RTT is too much dependent on the traffic load/queuing delay, which

interferes interferes with the accuracy of per-hop RTT and thus, can easily lead to route instability.with the accuracy of per-hop RTT and thus, can easily lead to route instability.

If a separate queue is assigned to probe packets, then it can accurately If a separate queue is assigned to probe packets, then it can accurately measure the measure the

link quality but cannot reflect the traffic load. link quality but cannot reflect the traffic load.

A solution to this problem is to adopt a A solution to this problem is to adopt a link measurement link measurement scheme !scheme !

Kim K-H and Shin KG, “On accurate measurement of link quality in multi-hop wireless mesh networks,” Proc. ACM MOBICOM 2006

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PROBLEM 2:PROBLEM 2: Accuracy of per-hop RTT measurement totally relies on the Accuracy of per-hop RTT measurement totally relies on the

weighted moving average scheme. weighted moving average scheme.

For large variations in measurements cause unreliable values For large variations in measurements cause unreliable values for per-hop RTT for per-hop RTT

(no matter what weight is applied in the weighted moving average (no matter what weight is applied in the weighted moving average scheme.)scheme.)

Overhead of the probe-ack procedure Overhead of the probe-ack procedure

REMARK:REMARK: Per-hop RTT captures per-link performance parameters, Per-hop RTT captures per-link performance parameters,

although although measurement is actually carried out at the network layer.measurement is actually carried out at the network layer.

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Disadvantages:

* Does not take link data rate into account.

* High overhead.

* Load dependent metric may cause route flaps

* Need to insert probe at head of interface queue to avoid queuing delay

* Not scalable - every pair needs to probe each other

Disadvantages of Per-Hop RTT

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Per-Hop Packet Pair DelayPer-Hop Packet Pair Delay

Measured by sending two back-to-back probe packets from a node to Measured by sending two back-to-back probe packets from a node to its neighbor its neighbor

First First a small probe packet; Second a small probe packet; Second large large

When the neighbor receives these two packets, it finds the delay in-When the neighbor receives these two packets, it finds the delay in-between them and then sends such information back to the probing between them and then sends such information back to the probing nodenode

Since relative delay is used to measure the per-hop delay, per-hop PPD Since relative delay is used to measure the per-hop delay, per-hop PPD measurement is less impacted by queueing delays or traffic load in a measurement is less impacted by queueing delays or traffic load in a node node

Draves R, Padhye J and Zill B, “Routing in multi-radio, multi-hop wireless mesh networks,” Proc. ACM MOBICOM 2004.

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* However, impact by traffic load still exists, because whether or * However, impact by traffic load still exists, because whether or

not being able to send probe packets in a link of two nodes also not being able to send probe packets in a link of two nodes also

depends on the queuing delays of other neighboring nodes. depends on the queuing delays of other neighboring nodes.

EXAMPLE:EXAMPLE:when Node A sends a probe packet to B, if A’s neighbor C is also when Node A sends a probe packet to B, if A’s neighbor C is also

sending a very high traffic load to A, then A has to delay its probe to B.sending a very high traffic load to A, then A has to delay its probe to B.

Therefore, per-hop packet pair delay still has to captureTherefore, per-hop packet pair delay still has to capture

the route instability issue. the route instability issue.

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* Large overhead than per-hop RTT, due to the need * Large overhead than per-hop RTT, due to the need of more probe packetsof more probe packets

Its performance is also dependent on the weighted Its performance is also dependent on the weighted moving average scheme, and assumes the variation moving average scheme, and assumes the variation of measurements are small.of measurements are small.

Similar to per-hop RTT, per-hop PPD only captures Similar to per-hop RTT, per-hop PPD only captures per-link performance parameters. per-link performance parameters.

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Expected Transmission Count Expected Transmission Count (ETX)(ETX)

ETX of a link is the expected number of transmissions before a ETX of a link is the expected number of transmissions before a packet is successfully delivered on a linkpacket is successfully delivered on a link

For a route, the ETX is the sum of the ETXs on all linksFor a route, the ETX is the sum of the ETXs on all links

Captures the link quality and packet loss on both directions of Captures the link quality and packet loss on both directions of a link a link

The route ETX can detect interference among links of the The route ETX can detect interference among links of the same routesame route

the larger the route ETX, the more self-interference on the the larger the route ETX, the more self-interference on the route.route.

De Couto DSJ, Aguayo D, Bicket J, and Morris R, De Couto DSJ, Aguayo D, Bicket J, and Morris R, ““A high-throughput path metric for multihop wireless routing,”A high-throughput path metric for multihop wireless routing,” in Proc. ACM MOBICOM 2003in Proc. ACM MOBICOM 2003

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Every period of Every period of seconds a node sends a broadcast probe seconds a node sends a broadcast probe message to all its neighborsmessage to all its neighbors

Each neighbor records the number of received probe Each neighbor records the number of received probe messages (denoted by nmessages (denoted by nww) during a period of w seconds, ) during a period of w seconds, where w > where w >

Thus, the delivery ratio of sending a packet from the Thus, the delivery ratio of sending a packet from the probing node to its neighbor is:probing node to its neighbor is:

nw

w /

7474


If a probing node embeds the information of nIf a probing node embeds the information of nww from all its from all its neighbors to the probe packetneighbors to the probe packet

Then each of its neighbors can derive the packet delivery ratio Then each of its neighbors can derive the packet delivery ratio from the neighbor to the probing nodefrom the neighbor to the probing node

With the delivery ratio at both forward and reverse directions, With the delivery ratio at both forward and reverse directions,

denoted by ddenoted by dff and d and drr, respectively, ETX is calculated as:, respectively, ETX is calculated as:

ETX 1

d f dr

7575

Advantages ofAdvantages ofExpected Transmission Count Expected Transmission Count (ETX)(ETX)

Lower overhead because broadcast rather Lower overhead because broadcast rather than unicast is applied to probe messages.than unicast is applied to probe messages.

Does not measure delays, so the Does not measure delays, so the measurement based on probe messages are measurement based on probe messages are not impacted by queueing delays in a node. not impacted by queueing delays in a node.

7676

Disadvantages of Disadvantages of Expected Transmission Count Expected Transmission Count (ETX)(ETX)

– Probe messages experience different packet loss ratios Probe messages experience different packet loss ratios than unicast messages than unicast messages

because broadcast messages use more robust because broadcast messages use more robust modulation and coding schemes, and thus have low modulation and coding schemes, and thus have low transmission ratestransmission rates

– ETX does not take into account the differences in ETX does not take into account the differences in packet size for different traffic flows and the different packet size for different traffic flows and the different capacities for different linkscapacities for different links

7777

Disadvantages of Disadvantages of Expected Transmission Count Expected Transmission Count (ETX)(ETX)

– Estimation method in ETX may not be accurateEstimation method in ETX may not be accurate

* It relies on the mean loss ratio; * It relies on the mean loss ratio;

* Wireless links usually experience bursty * Wireless links usually experience bursty losses. losses.

78

* ETX metric performs best in static scenarios

* It is insensitive to load

* RTT is most sensitive to load

* Packet-Pair suffers from self-interference on multi-hop paths

* Minimum hop count based routing seems to perform best in mobile scenarios

* Schemes based on measurements of link quality does not converge quickly

SO FAR

7979

Expected Transmission on a Path Expected Transmission on a Path (ETOP)(ETOP)

* When a routing path is selected in many routing protocols, * When a routing path is selected in many routing protocols, the position of a link is not considered in the routing metricthe position of a link is not considered in the routing metric

This is true if the link layer allows an infinite number of This is true if the link layer allows an infinite number of retransmissions, because a retransmitted packet has the retransmissions, because a retransmitted packet has the same impact on upper layer no matter at which link same impact on upper layer no matter at which link retransmission happensretransmission happens

However, if the link layer allows only a limited number of However, if the link layer allows only a limited number of retransmissions, end-to-end retransmission has to be carried retransmissions, end-to-end retransmission has to be carried out. out.

8080


Comparing two links, even if their ETX is the same, the one Comparing two links, even if their ETX is the same, the one closer to closer to

the destination can result in higher transport layer the destination can result in higher transport layer retransmissions, retransmissions,

i.e., this link can lead to worse performance if it would be i.e., this link can lead to worse performance if it would be selected.selected.

ETOP solves the above problem by taking into account the ETOP solves the above problem by taking into account the relative relative

position of a link on a routing path when the routing cost of position of a link on a routing path when the routing cost of the path is the path is

calculated.calculated.

Jakllari G, Eidenbenz S, Hengartner N, Krishnamurthy S and Faloutsos M, “Link positions matter: a non-commutative routing metric for wireless mesh networks,” Proc. IEEE INFOCOM 2008

8181


Consider a routing path with n links from node vConsider a routing path with n links from node v00 to node v to node vnn

its cost is denoted by Tits cost is denoted by Tnn

For a packet to be delivered end-to-end through this routing path, For a packet to be delivered end-to-end through this routing path, the needed number of end-to-end attempts is assumed to be Ythe needed number of end-to-end attempts is assumed to be Ynn..

In an end-to-end attempt j, the number of links that a packet has In an end-to-end attempt j, the number of links that a packet has been traversed before it is dropped by the link layer is denoted as been traversed before it is dropped by the link layer is denoted as MM

The number of link layer transmissions at node j is assumed to be The number of link layer transmissions at node j is assumed to be HHjj . .

8282


ETOP of a routing path is the expectation of TETOP of a routing path is the expectation of Tnn

Captures the total number of link layer transmissions of a given routing Captures the total number of link layer transmissions of a given routing path under all possible end-to-end attemptspath under all possible end-to-end attempts

Compared to ETX, ETOP can improve transport layer throughput, Compared to ETX, ETOP can improve transport layer throughput, because a routing path is selected with a least number of overall link because a routing path is selected with a least number of overall link layer retransmissions.layer retransmissions.

E[Tn ] K (E[H j | H j K ]j0

n 2

P[M j | M n])

E[Yn 1] E[H j | H j K ]

j0

n 1

83

Expected Transmission Time (ETT) and Weighted Cumulative ETT (WCETT)

Expected Transmission Time (ETT)– An extended version of ETX. – Based on ETX, ETT considers the impact of both packet

size and link quality

– ETT reflects the expected packet transmission time on a link.

B

SETXETT

Draves R, Padhye J and Zill B, “Comparisons of routing metrics for static multi-hop wireless Networks,” in Proc. ACM SigComm, 2004

S: packet size, B: link bandwidth.

84


– For a routing path, the expected transmission time can be the sum of ETTs of all links on the path.

– However, ETT does not take into account channel diversity in WMNs using multiple radios at some nodes

To resolve this issue, a routing metric called WCETT is proposed

85


Weighted Cumulative ETT (WCETT)

given routing path.

– First term considers the overall expected transmission time of the routing path.

– Second term captures the transmission time on the bottleneck channels. – In this way, WCETT takes into account the tradeoff between overall routing

delay and channel diversity utilization.

jkj

n

ii XETTWCETT

11

max)1( n: number of hops on a routing path, k: # of available channels for multi-radio

operation.

n

iiHOPij ETTX

channelon

jkjX

1max finds the bottleneck channel of aso

86


ETT enhances the performance of ETX by mapping packet size and link BW into the transmission time.

However, it uses a similar estimation scheme as that of ETX, so it has similar problems of ETX, i.e., inaccurate estimation, bottleneck routes, etc.

87


WCETT is not applicable to WMNs based on single-radio

multi-channel operation for two reasons:

1) broadcast probe messages cannot be sent on different channels of the same radio simultaneously;

2) the channel switching time can be comparable to ETT of a link.

88

Bottleneck Link Capacity (BLC)

BLC is derived based on the expected busy time (EBT) of transmitting a packet on a link.

EBT can be estimated by considering the packet loss rate (PLR) and transmission mechanism in the MAC layer. – If RTS-CTS-Data-Ack handshake is used for packet transmission as

in an IEEE 802.11 MAC,

Liu T and Liao W, “Capacity-aware routing in multi-channel multi-rate wireless mesh networks,” in Proc. IEEE ICC, 2006

Thandshake: Total transmission time of one RTS-CTS-Data-Ack

Ep: PLR. p

handshake

e

TEBT

1

89


Based on EBT, a residual capacity of a link considered as defined as the ratio between the idle time and EBT. – Considering a path P, if the residual capacity of link i is

LCi, then BLC is given by

K: Length of the routing path Pμ: fine-tuning parameter.K

iPiLC

BLC

min

90


Residual capacity of the bottleneck link of a routing path

Dividing the minimum residual capacity by a certain number is for penalizing a long routing path

Because busy time is considered in BLC, load-balancing in links has been taken into account

91


However, the self-interference of a routing path is not considered, as the minimum residual capacity is considered in BLC

– If two routing paths have different self-interferences, then the bottleneck link can have the same residual capacity.

– The same problem applies to interference from other routing paths.

92

Expected Data Rate (EDR)

EDR integrates the expected transmission count and expected transmission contention degree (TCD) into the same routing metric

– TCD of a link is the time that is spent on retransmitting non-

acknowledged packets over a given period.

– Considering link k on a routing path, if the sum of TCDs of links that interfere link k is Ik, then the the EDR of link k is

For EDR of a routing path, it is defined as the EDR of the bottleneck link.

Γ: maximum transmission rate of link k.

kkk ETXI

EDR

93

Problems of Expected Data Rate (EDR)

– EDR integrates two closely related parameters: ETX ad TCD.

– In fact, given the same packet length, if ETX is large, TCD is large too.

why ETX and TCD have to be combined like an EDR

equation remains a question.

94

Problems of Expected Data Rate (EDR)

– Even if the link rate is considered in the metric, it does not consider the fact that multiple rates instead of only the maximum rate are available in each link.

– Interference range of a given link k is difficult to determine, so Ik is hard to derive.

– EDR of a routing path cannot take into account the self-interference,

as the EDR of a bottleneck link is used as the EDR of the entire routing path.

95

Airtime Cost Routing Metric

– To identify an efficient radio-aware path among all the candidate paths,

– A default routing metric in IEEE 802.11s draft

– Reflects the amount of channel resources consumed for transmitting a frame over a particular link.

IEEE 802.11s Task Group, Draft, Amendment to Standard for Information Technology – Telecommunications and Information Exchange Between Systems - LAN/MAN Specific Requirements – Part 11: Wireless Medium Access Control (MAC) and physical layer (PHY) specifications: Amendment: ESS Mesh Networking, IEEE P802.11s/D1.00-2006.).

96

Airtime Cost Routing Metric

– The path which has the smallest sum of airtime cost is the best path.

– The airtime cost Ca for each link is calculated as:

pt

tPcaa er

BOOC

1

1][

Oca, Op, and Bt depend on the used transmission technology.

Oca: channel access overhead,

Op: protocol overhead,

Bt: number of bits in a test frame.

r and ept : bit rate in Mbit/s and frame error rate for the test frame size Bt, respectively.

97

Comparison of Different Routing Comparison of Different Routing MetricsMetrics

Many routing metrics try to capture link-layer performance parameters by using a procedure in the network layer

In fact, these schemes can be enhanced by performing link-quality measurements directly in the link layer and then use such measurements in the network layer

This method implies that the routing metrics should involve cross-layer interactions

98


RoutingMetrics

LayersCaptured

Performance Parameters

Advantages Shortcomings

Hop-count Network Number of hops Simple and lowMinimum hop-count is usually not the performance goal

Per-hop RTT

Network

Packet loss, traffic load,queuing delay, contention

Multiple link metrics captured

high overhead in sending probes, estimation accuracy depends on traffic load

Per-hop PPD

NetworkPacket loss, transmission

DelayDelay

Multiple link metrics captured, less impacted by traffic load

High overhead in measuring delay, performance dependent on the measurement accuracy, no load balancing

ETXNetwork

Packet loss, retransmission, contention

Captured multiple link metrics, relative lower overhead by using broadcast

Measurement is not accurate due to differences between broadcast and unicast, no load balancing, cannot capture packet loss variations, can have bottleneck link

99


RoutingMetrics

LayersCaptured



ETOP Network, Link

End-to-end attempts, linkretransmission

Link position considered inrouting

Difficulty in deriving the metric

ETT &WCETT

Network

Same link metrics of ETXand also link bandwidth and packet size

Improve ETX by considering link bandwidth and packet size, channel diversity

Same problems of ETX, Not applicable to single-radio multi-channel operation

100


RoutingMetrics

LayersCaptured



BLC Network, Link

MAC handshake, time, packet loss rate, hop count

Residual capacity of a link is considered, so load-balancing is performed indirectly

Bottleneck link of a route does not consider self-interference

EDRNetwork

link metrics as that in ETX, contention time

Use contention time of all interfering links to considerinterference

Have the same problems as those in ETX, hard to find interfering links

Airtime Cost Link

Resource consumed bya packet on a linka link

Captures the impact of the dynamic environment to a link

Overhead in probing, Airtime cost captured by probe message may bedifferent from a packet

101

Remaining Issues

– The measurement or estimation method for a routing metric may not be accurate

– It may also cause large overhead, especially for a large scale network.

– Performance comparisons between different routing metrics need further research, although some work has been done for a few routing metrics.

102

Remaining Issues

– The design of many existing routing metrics is still “ad-hoc”,

* i.e., why the proposed routing metric can improve the network performance is not really justified;

* usually only simulation results are used to prove the

effectiveness of a routing metric.

* the side-effect of such a design is that the effectiveness of a routing metric may be limited to a certain type of WMNs.

– A routing metric may not be able to capture enough network parameters for a routing protocol to optimize the network performance.

103

OVERVIEW OF ROUTING ALGORITHMSOVERVIEW OF ROUTING ALGORITHMS

Hop-Count based Routing Link Level QoS Based Routing Interference Based Routing (IRMA) Routing with Load Balancing Routing Based on Residual Link Capacity End-to-End QoS Routing Reliability Aware Routing Joint Channel Assignment and Routing (Layer 2.5

Routing)

104

SET 1:Hop-Count based Routing Algorithms

Light Client Management Routing (LCMR) Protocol

Orthogonal Rendezvous Routing (ORR) Protocol

HEAT Protocol

105

Light Client Management Routing (LCMR) ProtocolWehbi B, Mallouli W and Cavalli A, Light client management protocol for wireless mesh networks.Proc. 7th Int. Conf. on Mobile Data Management (MDM), 2006

End-to-end routing path from a source to a destination client consists of

* proactive route among mesh routers and * reactive routes between clients and mesh routers

To find the best route from one client to another, hop-count is used as the routing metric.

LCMR does not require routing functionality in clients Mesh routers supporting clients take care of routing

106


Mesh routers need to maintain two tables:

1. MAC and IP addresses of local clients

2. IP addresses of remote clients as well as the IP addresses of remote mesh routers associated

with remote clients

107


Based on these two tables,

• When a local client needs to set up a routing path to a remote client,

• its associated mesh router can find out which remote mesh router is responsible for forwarding traffic to the remote client

• Based on such information, mesh routers can then set up a routing path between them using proactive routing and hop-count metric.

108

Disadvantages of Light Client Management Routing (LCMR) Protocol

LCMR has a high overhead of maintaining the two tables on each mesh routers,

as all clients’ IP addresses need to be collected and stored at each mesh router.

109

SET 1:Hop-Count based Routing Protocols



HEAT Protocol

110

Orthogonal Rendezvous Routing (ORR) ProtocolCheng B, Yuksel M and Kalyanaraman S, Orthogonal rendezvous routing protocol for wireless mesh networks. Proc. IEEE Int. Conf. on Network Protocols (ICNP), 2006.

Each node can define its neighbors’ directions relative to its local North.

Relying on such information, ORR can reduce the state information for routing, and it does not need flooding for route construction.

111


Compared to geographic routing, ORR does not need exact location of nodes.

Idea In 2-D Euclidean space two orthogonal lines can

have at least two intersect points with another group of two orthogonal lines,

if these two groups of orthogonal lines have different centers.

112


To construct routing paths, a source node sends route discovery in orthogonal directions,

while a destination node sends route dissemination in orthogonal directions.

Thus, there is at least one intersect point, called rendezvous point

where both route discovery and route dissemination messages are received.

113


In this way a routing path is established between the source and the destination

Also, routing path from the source to the rendezvous point is a reactive route and

the remaining path to the destination is a proactive route.

114

Shortcomings of Orthogonal Rendezvous Routing (ORR) Protocol

1. Direction of a node needs to be configured freely 2. Network is not really a 2-D space. (If a 3-D space is considered, the theory for ORR may not be valid)

3. ORR may not work if the node density is high or topology change frequently happens

4. Routing path selection procedure is based on hop-count. (However, other metrics such as link quality can be adopted to enhance the ORR).

115

SET 1:Hop-Count based Routing Protocols



HEAT Protocol

116

HEAT ProtocolBaumann R, Lenders V, Heimlicher S and May M,HEAT: scalable routing in wireless mesh networks using temperature fields. Proc. IEEE Int. Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM), 2007

Anycast routing protocol HEAT considers all nodesin a WMN as a temperature field

– Gateways have the highest temperature

– Temperature of a non-gateway node will be determined by hop-count to the gateways and the robustness of a routing path from this node to gateways.

117

HEAT Protocol

Once temperatures of all nodes are determined according to this procedure, the packets from any

node to gateways can simply follow the following method:

The node forwards the packets to its neighbor with the

highest temperature, and this neighbor will repeat the

same process until reaching gateways.

118

Problems of HEAT Protocol

Totally depends on the assumption that the traffic of WMNs only needs to be routed between gateways and non-gateways

For other scenarios, anycast routing is not supported.

Moreover, how to consider other routing metrics in HEAT remains an open problem

119



Routing)

120

Set 2:Link-level QoS based Routing Algorithms

– Link quality source routing (LQSR) protocol– Multi-radio LQSR (MR-LQSR) routing

protocol- ExOR Routing Protocol– AODV-spanning tree (AODV-ST) protocol

121

Link Quality Source Routing (LQSR) Protocol Draves R, Padhye J and Zill B,Comparisons of routing metrics for static multi-hop wireless networks. Proc. ACM SIGCOMM, 2004.

Based on Dynamic Source Routing (DSR)

Contains all basic DSR functionalities, such as * Route Discovery (Route Request and Route Reply

messages) and

* Route Maintenance (Route Error messages).

122

Link Quality Source Routing (LQSR) Protocol

However, LQSR holds two major differences compared to DSR.

– LQSR is implemented as layer 2.5 protocol instead of as a network layer protocol

– LQSR supports link quality metrics.

123


Layer 2.5 architecture brings two significant advantages.

– On the one hand, no modification is needed for the higher layer software,

i.e., LQSR routing protocol is transparent to higher layer software.

– Also no modification is required for link layer software.

124


Performance of LQSR varies based on different routing metrics and network mobility:

– For stationary nodes in WMNs, the routing metric ETX, achieves the best

performance

125


For mobile nodes:Minimum hop count method outperforms the three

link quality metrics, i.e., per-hop RTT, per-hop packet pair delay, and ETX

REASON:As the sender moves, the ETX metric cannot quickly track the changes in the link quality.

126

Set 2:Link-level QoS based Routing Protocols

– Link quality source routing (LQSR) protocol

–Multi-radio LQSR (MR-LQSR) routing protocol

– ExOR Routing Protocol– AODV-spanning tree (AODV-ST) protocol

127

Multi-Radio LQSR (MR-LQSR) Routing ProtocolDraves R, Padhye J and Zill B,“Routing in multi-radio, multi-hop wireless mesh networks”, Proc. ACM MOBICOM, 2004.

Based on LQSR, and thus, also based on DSR

Major difference from LQSR is WCETT

To make LQSR perform well in a mesh network with multiple radios per node, WCETT is used as the routing metric in the routing protocol

128

Multi-Radio LQSR (MR-LQSR) Routing Protocol

WCETT takes into account both link quality metric and the minimum hop-count

Achieves good tradeoff between delay and throughput

because it considers channels with good quality and channel diversity in the same routing protocol

129


MR-LQSR assumes nodes are stationary

This is true for mesh routers, but obviously not applicable to mesh clients

Performance of MR-LQSR can also be degraded by the mobility of nodes, i.e., mesh clients.

130


In WMNs, multi-channel operation over a single radio is another alternative to increase the network capacity.

But MR-LQSR is not applicable because WCETT is limited to multi-radio mode.

131


– Link quality source routing (LQSR) protocol– Multi-radio LQSR (MR-LQSR) routing protocol

–ExOR Routing Protocol– AODV-spanning tree (AODV-ST) protocol

132132

ExOR Routing ProtocolExOR Routing ProtocolBiswas S and Morris RBiswas S and Morris R, “, “ExOR: opportunistic multihop ExOR: opportunistic multihop routing for multi-Hop wireless networksrouting for multi-Hop wireless networks,”,” iin Proc. ACM n Proc. ACM SIGCOMM, SIGCOMM, 20052005..

* Proposed to improve throughput based on * Proposed to improve throughput based on cooperative broadcasting packets from cooperative broadcasting packets from source to destination without explicitly source to destination without explicitly setting up a routing pathsetting up a routing path

133

Source’s behaviorSource’s behavior

Collects enough packets of the same destination to form a bCollects enough packets of the same destination to form a batchatch– ExOR operates on batches of packets for efficiencyExOR operates on batches of packets for efficiency

Selects a set of nodes to be candidate forwarders, and Selects a set of nodes to be candidate forwarders, and

includes the prioritized list in the overhead of every packetincludes the prioritized list in the overhead of every packet

134134

ExOR Routing ProtocolExOR Routing Protocol

* This priority of a forwarding node is * This priority of a forwarding node is determined by determined by

the cost to the destination, the cost to the destination,

which is evaluated by the accumulative ETX to which is evaluated by the accumulative ETX to the destination node. the destination node.

135135

ExOR Routing ProtocolExOR Routing Protocol

Set of nodes that are selected for forwarding Set of nodes that are selected for forwarding packets are determined based on the packet packets are determined based on the packet loss ratio between the source and these loss ratio between the source and these nodes. nodes.

Although many nodes can receive packets Although many nodes can receive packets from the source node, only a subset of nodes from the source node, only a subset of nodes are selected as forwarding nodesare selected as forwarding nodes

in order to reduce the overhead.in order to reduce the overhead.

136

Forwarders’ BehaviorForwarders’ Behavior

How can a node know whether it is one of the How can a node know whether it is one of the forwarders or not?forwarders or not?

Check the forwarder list in the overhead of Check the forwarder list in the overhead of the received packetthe received packet– If the node finds itself in the list, buffer the If the node finds itself in the list, buffer the

packet and keep state of this batchpacket and keep state of this batch– If no, discard the packetIf no, discard the packet

137137

Forwarder’s BehaviorForwarder’s Behavior

Highest priority forwarding node sends its own Highest priority forwarding node sends its own batch of packets following the same procedure as batch of packets following the same procedure as done by the source node. done by the source node.

This process is repeated until 90% of packets in This process is repeated until 90% of packets in each batch are received by the destination node. each batch are received by the destination node.

The remaining 10% of nodes will rely on traditional The remaining 10% of nodes will rely on traditional minimum hop-count routing to deliver. minimum hop-count routing to deliver.

138

Forwarders’ BehaviorForwarders’ Behavior

How can a node know whether the packet it receives How can a node know whether the packet it receives has also been received by a node with higher priority has also been received by a node with higher priority or not?or not?

ExOR designs a “batch map” to record, for every paExOR designs a “batch map” to record, for every packet in the batch, the highest-priority node known to cket in the batch, the highest-priority node known to have received that packet.have received that packet.

139139

Advantages of ExOR Routing Advantages of ExOR Routing ProtocolProtocol

Most of packets are delivered without setting up Most of packets are delivered without setting up routing routing

paths, which is similar to anycast routing. paths, which is similar to anycast routing.

Moreover, ExOR can improve throughput for two Moreover, ExOR can improve throughput for two reasons. reasons. – It tries to use the best link to deliver packets through It tries to use the best link to deliver packets through cooperation of forwarding nodes. cooperation of forwarding nodes.

– Progress of packet forwarding can be continued even if Progress of packet forwarding can be continued even if some nodes some nodes

on a traditional path experiences bad link quality or out of on a traditional path experiences bad link quality or out of order. order.

140


– Link quality source routing (LQSR) protocol– Multi-radio LQSR (MR-LQSR) routing protocol

–ExOR Routing Protocol–AODV-spanning tree (AODV-ST) protocol

141

AODV-Spanning Tree (AODV-ST) ProtocolRamachandran K, Buddhikot MM, Chandranmenon G, Miller S, Almeroth K and Belding-Royer E,On the design and implementation of infrastructure mesh networks. Proc. IEEE WIMESH, 2005.

AODV ST is designed for multi-radio WMNs

ADOV-ST performs hybrid routing, i.e., for traffic inside the mesh network AODV is

used

where the spanning-tree based routing is used for traffic to/from gateways.

ETT is used as the routing metric

142

Drawbacks of AODV-Spanning Tree (AODV-ST) Protocol

AODV may not be efficient for intra-mesh traffic

The WCETT proposed for multi-radio WMNs is not applicable,

because AODV is a distance vector routing protocol

143



Routing)

144

TDMA instead of CSMA/CA as MAC

Based on the TDMA, an integrated routing and MAC scheduling algorithm (IRMA) is derived to find a routing path for each traffic flow

then determine slot allocation on each link considering

* BW allocation information * Link status, and * Topology information in the network.

Set 3:Interference Based Routing: IRMAWu Z, Ganu S and Raychaudhuri D, IRMA: integrated routing and MAC scheduling in multihopwireless mesh networks. Proc. IEEE WiMesh, 2006.

145

A centralized scheme

Relies on an existing solution to collect the node, link, and topology related information of the entire network and get traffic specifications of traffic flows.

Such signaling can be done in a global control plane (GCP) that can be implemented in a separate dedicated channel or a dedicated time slot

Interference based Routing: IRMA

146

Two routing mechanisms defined in IRMA:

– link scheduling with minimum-hop routing– link scheduling with bandwidth-aware routing

(preferred)

Interference based Routing: IRMA

147

Interference Based Routing: IRMALink Scheduling with Minimum-Hop Routing

A routing path is selected by shortest path using minimum hop-count.

Then time slots along this path are determined by the centralized algorithm by considering the latest flow information in the network.

may result in congested paths or links as the minimum hop-

count routing does not consider the available BW.

148

Interference Based Routing: IRMALink Scheduling with bandwidth-aware Routing

Available BW on each link is factored when a routing path is selected.

Based on the selection, time slots are then determined for each link on the path.

Thus, such a scheme can not only avoid contentions in traffic flows but can also avoid bottleneck or congested links.

149

Shortcomings of Interference Based Routing: IRMA

1. Not scalable with the network size (a centralized scheme)

2. Assumes an efficient scheme to collect all control information,

which is a challenging issue for all routing protocols.

3. MAC layer is assumed to have TDMA operation, which is not the

case for many WMNs.

150


Hop-Count based Routing Link Level QoS Based Routing Interference Based Routing (IRMA) Routing with Load Balancing Routing Based on Residual Link Capacity End-to-End QoS Routing Reliability Aware Routing Scalable Routing Joint Channel Assignment and Routing (Layer 2.5

Routing)

151

Set 4:Routing with Load BalancingSong W and Fang X ,”Routing with congestion control and load balancing in wireless mesh networks,’Proc. Int. Conference on ITS Telecommunications, 2006

Routing is directly determined by considering network congestion

Given a source and its destination, a routing path is determined by using the route with the least congestion

If more than one paths have the same number of congested nodes, the route with minimum hop-count is selected

Congestion state of a link is determined by the number of retransmissions of RTS and ACK packets.

If the congestion exceeds a threshold, the congestion weight on this link increases

152

Routing with Load Balancing: CARLiu T and Liao W,Capacity-aware routing in multi-channel multi-rate wireless mesh networks. Proc. IEEE ICC, 2006.

A capacity-aware routing (CAR) protocol is proposed to balance load among links and channels in a multi-radio WMN

CAR assumes channel assignment on radios lasts long time and can be static.

With static channels on each radio in the network, CAR determines the BLC in a reactive manner for each traffic flow.

153

Routing with Load Balancing: CAR

Transmissions start on a routing path that is determined according to the best BLC metric.

However, this path can be switched to a new one if the source finds the new path has a higher BLC value.

154

Routing with Load Balancing: CAR

Due to the bottlenecked link capacity in routing, CAR improves throughput and delay performance.

CAR may not achieve optimal performance because the path selection on different flows affect each other but is not coordinated among such flows.

155


Hop-Count based Routing Link Level QoS Based Routing Interference Based Routing (IRMA) Routing with Load Balancing Routing Based on Residual Link

Capacity End-to-End QoS Routing Reliability Aware Routing Scalable Routing Joint Channel Assignment and Routing (Layer 2.5

Routing)

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Set 5:Routing Based on Residual Link CapacityRaniwala A, Gopalan K and Chiueh T ,”Centralized channel assignment and routing algorithms formulti-channel wireless mesh networks,” ACM Mobile Computing and Communications Review, 2005.

An alternative scheme to consider link capacity in routing is to get the information of residual link capacity

A protocol called Hyacinth is developed to perform routing and channel assignment for a multi-channel WMN.

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Routing Based on Residual Link Capacity

Hyacinth considers traffic from/to gateways in WMNs and thus uses tree-based routing for such traffic.

Each node advertises its costs of its path from/to the gateway

Based on such information, a neighbor that finds a lower value in the cost will leave its old parent node and selects the new node as the new parent node.

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Routing Based on Residual Link Capacity

With such a procedure, all nodes in the network build up routing paths to the gateway like a spanning tree

To reflect the cost of a path, residual capacity of a link the routing metric.

Links are selected which have the largest available capacity

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Routing)

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Set 6:End-to-End QoS Routing

Quality Aware Routing Protocol Ring Mesh Routing Protocol

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Quality Aware Routing ProtocolKoksal CE and Balakrishnan H,”Quality-aware routing metrics for time-varying wireless mesh networks,”IEEE Journal on Selected Areas in Communications, 2006.

End-to-end QoS can be considered in a routing protocol by ensuring end-to-end packet loss rate, delay, or bandwidth.

End-to-end packet loss rate is ensured where both ETX and ENT are used as routing metrics

ENT is used to determine what routing paths can be used

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Quality Aware Routing Protocol

−Allowed packet loss rate in a link is given

−Based on this packet loss threshold and the measurement of the

link, a positive number δ used by ENT is derived.

−With δ and an existing probe scheme, ENT of each link is determined.

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−ENT is then compared with the maximum number of transmissions of a packet before it is discarded at the link layer

−If ENT is larger than the link-layer value, the routing cost of the link will become ∞

−Otherwise, ETX is used for the routing cost of the link

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−As a result, all links that do not satisfy packet loss requirement will be excluded from routing paths

−After this step, routing path selection is performed by just choosing a path with smallest routing cost

One critical issue: How to determine the allowed packet loss rate of a link given the threshold of end-to-end packet loss

requirement?

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Set 6:End-to-End QoS Routing

Quality Aware Routing Protocol Ring Mesh Routing Protocol

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RingMesh Routing ProtocolLin D, Moh T and Moh M ,”A delay-bounded multi-channel routing protocol for wireless mesh networks using multiple token rings: extended summary,”Proc. 31st IEEE Conference on Local Computer Networks (LCN), 2006.

End-to-end delay

RingMesh is developed based on a token ring protocol proposed for wireless LANs

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RingMesh Routing Protocol

Multiple token rings are created and organized from the gateway to all other nodes like a spanning tree scheme

Different channels are used in neighboring rings

First ring containing the gateway is called a root ring

Next ring connected to the root ring is a child ring.

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RingMesh Routing Protocol

These two rings share a common node which is called a pseudo gateway

Following this process, other child rings are connected together all the way to the root ring

For a node in the network, which ring it can join depends on the delay from it to the gateway:

the node joins a ring that can satisfy the end-to-end delay requirement.

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Shortcomings of RingMesh Routing Protocol

−How to form multiple rings to support multiple gateways to improve the delay performance is not addressed?

−It is also unknown what happens if no ring can be joined by a node

−No mechanism is also available to determine the delay from a node to the gateway, which is not a trivial task

−Thus, end-to-end delay aware routing is still a challenging research topic

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Routing)

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Set 7:Resilient Opportunistic Mesh Routing (ROMER) ProtocolYuan Y, Yang H,Wong SHY, Lu S and Arbaugh W,”ROMER: resilient opportunistic mesh routing for wireless mesh networks,”Proc. IEEE WIMESH, 2005

ROMER creates forwarding mesh on the fly for each packet

ROMER assumes that there is an existing scheme that can find the minimum cost from each mesh router to the gateway

Then the credit is determined while a packet is forwarded on the fly

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Resilient Opportunistic Mesh Routing (ROMER) protocol

When a packet is to be delivered from a mesh router, e.g., Node S, to the gateway, the source mesh router needs to set a credit cost.

If the minimum cost from S to the gateway is Cmin,S and the credit cost is Ccredit,S,

then S has a budget cost of Cmin,S + Ccredit,S to the gateway.

When the packet is sent to the next mesh router, e.g., node A, the budget is reduced by the cost of the traversed link clinkSA

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At mesh router A, the needed credit is computed according to the requirement of

Ccredit,A + Cmin,A + ClinkSA <= Cmin,S + Ccredit,S,

i.e., the remaining credit at mesh router A is Ccredit,A = Cmin,S + Ccredit,S − Cmin,A − ClinkSA.

If the ratio of the remaining credit over the initial credit Ccredit,S is less than a threshold, e.g., (Cmin,A / Cmin,S)2

, then the packet at mesh router A shall be discarded;

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Otherwise, mesh router A forwards the packet according to a randomized opportunistic forwarding scheme.

The above process is repeated until the packet is delivered to the gateway

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Finally, when multiple intermediate routers receive the same packet from a mesh router and

all have enough credit to forward the packet,

they need to follow a randomized opportunistic forwarding scheme to forward packets.

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Probability that each intermediate router can forward a packet depends on the quality of the link to the parent router


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Intermediate router with the best link quality forwards the packet with probability 1,

while other intermediate routers forward the packet with a probability of (Rl / Rmax),

where Rl is the current rate of the considered link and Rmax is the current rate at the best link.


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ROMER has to rely on an existing scheme to find out the minimum cost from each mesh router to the gateway

What type of cost is the best for ROMER and how to dynamically update the cost to best serve ROMER remain open questions !

Drawbacks of Resilient Opportunistic Mesh Routing (ROMER) Protocol

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Hop-Count based Routing Link Level QoS Based Routing Interference Based Routing (IRMA) Routing with Load Balancing Routing Based on Residual Link Capacity End-to-End QoS Routing Reliability Aware Routing Joint Channel Assignment and Routing

(Layer 2.5 Routing)

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Multichannel Protocols

Multi-channel operation is widely adopted in WMNs Multi-channel operation is widely adopted in WMNs to improve network capacityto improve network capacity

Single-channel routing protocols may be run in each Single-channel routing protocols may be run in each of the of the

channels of the WMNchannels of the WMN– Easy design but not optimal, and does not guarantee availability of spectrum in the routes

Multi-channel routing protocols are better suitedMulti-channel routing protocols are better suited

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Two types of multi-channel routing protocolsTwo types of multi-channel routing protocols

–Type 1: Consider the impact of multi-channel operation such as link quality, interference, packet loss, bandwidth

–Type 2: Conduct close routing/MAC cross-layer design such as joint channel allocation and routing

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Most existing protocols are of type 1Most existing protocols are of type 1

– As an example, in MQ-LSR ignores the close relationship between traffic distribution and channel allocation by assuming different radios are assigned non-overlapping channels

– It also incorrectly assumes that the channel assignment changes relatively infrequent, leading to the necessity of joint channel-route assignment

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Joint Channel Assignment and Joint Channel Assignment and RoutingRoutingAlicherry M, Bhatia R and Li LAlicherry M, Bhatia R and Li L, , ““Joint channel assignment and Joint channel assignment and routing for throughput optimization in multi-radio wireless routing for throughput optimization in multi-radio wireless mesh networksmesh networks,”,” iin Proc. ACM MobiComn Proc. ACM MobiCom, 2005, 2005

For infrastructure WMNs (IWMNs)For infrastructure WMNs (IWMNs)

Assumption:Assumption:

Aggregated traffic load at mesh routers and channels assigned Aggregated traffic load at mesh routers and channels assigned to to

each router is not changing frequentlyeach router is not changing frequently

Channels assigned to radios on a node are determined Channels assigned to radios on a node are determined together with routing paths together with routing paths

with an objective to with an objective to obtain interference-free link schedule and obtain interference-free link schedule and achieve maximum throughputachieve maximum throughput..

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Joint Channel Assignment and Joint Channel Assignment and RoutingRoutingTang J, Xue G and Zhang WTang J, Xue G and Zhang W, , ““Interference-aware topology Interference-aware topology control control and QoS routing in multichannel wireless mesh networksand QoS routing in multichannel wireless mesh networks,”,” ACM MobiHocACM MobiHoc, 2005., 2005.

Assumes the channel assignment can be static in Assumes the channel assignment can be static in WMNsWMNs

Goal:Goal: mathematical formulation of the joint design mathematical formulation of the joint design between between

channel assignment and routingchannel assignment and routing

However, no actual protocol is proposedHowever, no actual protocol is proposed

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Distributed Joint Channel and Routing Distributed Joint Channel and Routing ProtocolProtocolAvallone S and Akyildiz, IF and Ventre GAvallone S and Akyildiz, IF and Ventre G, , ““A channel and rate A channel and rate assignment algorithm and a layer-2.5 assignment algorithm and a layer-2.5 forwarding paradigm for forwarding paradigm for multi-radio wireless mesh neetworks,multi-radio wireless mesh neetworks,”” IEEE/ACM Transactions on IEEE/ACM Transactions on Networking, Networking, 20092009

It takes into account the It takes into account the number of flows number of flows that are possible to route on each linkthat are possible to route on each link

Amount of flows is obtained from a solution Amount of flows is obtained from a solution

to the joint channel assignment and routing to the joint channel assignment and routing problemproblem

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Distributed Joint Channel and Routing Distributed Joint Channel and Routing ProtocolProtocol

Objective Objective Enable every router to utilize each of its links in Enable every router to utilize each of its links in

proportion to their assigned flow ratesproportion to their assigned flow rates

Routing protocol only requires a Routing protocol only requires a partial knowledge partial knowledge of the network topology and does not make use of of the network topology and does not make use of a destination-based routing tablea destination-based routing table

Hence, the name Hence, the name Layer-2.5 (L2.5) Layer-2.5 (L2.5) given to the given to the

routing protocol.routing protocol.

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Layer-2.5 Routing AlgorithmLayer-2.5 Routing Algorithm

Each mesh router is configured with the set of pre-Each mesh router is configured with the set of pre-

computed flow rates associated with its linkscomputed flow rates associated with its links Packets are Packets are forwardedforwarded using such information (rather using such information (rather

than than routedrouted using routing tables) using routing tables)– Layer-2 information are used, hence the nameLayer-2 information are used, hence the name

Each mesh router attempts to keep the utilization of Each mesh router attempts to keep the utilization of

the outgoing links proportional to their pre-computed the outgoing links proportional to their pre-computed

flow ratesflow rates

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Channel Assignment & RoutingChannel Assignment & Routing

* An approximate solution:* An approximate solution: Determine pre-computed flow ratesDetermine pre-computed flow ratesA pre-computed flow rate is determined for every link based on theA pre-computed flow rate is determined for every link based on thegiven optimization objectivegiven optimization objective

Determine the channel assignmentDetermine the channel assignmentChannels are assigned to radios in the attempt to make such Channels are assigned to radios in the attempt to make such pre-computed flow rates schedulablepre-computed flow rates schedulable

Adjust the pre-computed flow ratesAdjust the pre-computed flow ratesThe pre-computed flow rates may be adjusted in order to obtain a The pre-computed flow rates may be adjusted in order to obtain a

setset

of schedulable flow rates given the computed channel assignmentof schedulable flow rates given the computed channel assignment

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Open Research IssuesOpen Research Issues

Performance BenchmarkPerformance Benchmark – Large number of routing metrics and routing protocols Large number of routing metrics and routing protocols

available for WMNs. available for WMNs.

– Considering routing protocols for other multi-hop wireless Considering routing protocols for other multi-hop wireless networks, the number is much bigger networks, the number is much bigger

– Confusion about which routing metric and what type of Confusion about which routing metric and what type of routing protocols can provide the best performance => routing protocols can provide the best performance => benchmark to investigate and compare different routing benchmark to investigate and compare different routing metrics and protocols. metrics and protocols.

190190


– It is expected to include theoretical analysis of performance It is expected to include theoretical analysis of performance bound, practical consideration of protocol design, and bound, practical consideration of protocol design, and performance evaluation either through simulations or testbeds.performance evaluation either through simulations or testbeds. In [1], a comparative study is carried out for different routing strategies for In [1], a comparative study is carried out for different routing strategies for

WMNs. WMNs. Some design guidelines are provided in Some design guidelines are provided in [2][2] for multihop wireless networks. for multihop wireless networks. However, such work is still far from providing a benchmark of selecting However, such work is still far from providing a benchmark of selecting

routing metrics and protocols.routing metrics and protocols.

[1] Wellons J, Dai L, Xue Y and Cui Y[1] Wellons J, Dai L, Xue Y and Cui Y, , ““Predictive or oblivious: a comparative study of Routing strategies for Predictive or oblivious: a comparative study of Routing strategies for wireless mesh networks under uncertain demandwireless mesh networks under uncertain demand,"," Proc. IEEE SECON Proc. IEEE SECON, 2008, 2008

[2] Yang Y and Wang J[2] Yang Y and Wang J, , ““Design guidelines for routing metrics in multihop wireless networksDesign guidelines for routing metrics in multihop wireless networks,”,”

PProc. roc. IEEE INFOCOMIEEE INFOCOM, 2008., 2008.

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New routing metricsNew routing metrics– How to integrate multiple routing metrics into the How to integrate multiple routing metrics into the

same routing protocol is another challenging issue. same routing protocol is another challenging issue.

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Scalable routingScalable routing – This is a This is a critical requirement critical requirement by WMNs, achieved by few by WMNs, achieved by few

routing protocols so far. routing protocols so far. – Hierarchical routing Hierarchical routing protocols can only partially solve this protocols can only partially solve this

problem due to their complexity and difficulty of problem due to their complexity and difficulty of management.management.

– Geographic routingGeographic routing needs GPS or similar needs GPS or similar cost, cost, complexitycomplexity. . Additional traffic by inquiry of destination position. Additional traffic by inquiry of destination position.

– Scalability is also related to MAC protocols. Thus, an eventual Scalability is also related to MAC protocols. Thus, an eventual scalable routing protocol must be closely integrated with the scalable routing protocol must be closely integrated with the MAC protocol.MAC protocol.

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Network coding and routingNetwork coding and routing– Can potentially improve the performance of WMNsCan potentially improve the performance of WMNs E.g., research to apply network coding to WMNs [1], [2],E.g., research to apply network coding to WMNs [1], [2], Benefits of network coding to a multichannel WMN in [2]Benefits of network coding to a multichannel WMN in [2]– However, as network coding is still in an early phase of being However, as network coding is still in an early phase of being

applicable to a practical networking protocol, integrating applicable to a practical networking protocol, integrating network coding with routing is still a new and challenging network coding with routing is still a new and challenging research directionresearch direction

[1] Omiwade O, Zheng R and Hua C[1] Omiwade O, Zheng R and Hua C, , ““Practical localized network coding in wireless mesh networksPractical localized network coding in wireless mesh networks,”,” Proc. of IEEE SECONProc. of IEEE SECON, 2008, 2008

[2] Zhang X and Li B[2] Zhang X and Li B, , ““On the benefits of network coding in multi-channel wireless networksOn the benefits of network coding in multi-channel wireless networks,”,” Proc. of IEEE SECONProc. of IEEE SECON, 2008, 2008

Documents

4. ROUTING PROTOCOLS