Milano, 4-5 Ottobre 2004 IS-MANET

The Virtual Routing Protocol for

Ad Hoc Networks

ISTI – CNR

S. Chessa

Wireless Ad Hoc NetworksAutonomous system of mobile hosts connected by wireless links

The nodes are autonomous and independent

Battery poweredMobileCooperate in a peer-to-peer fashion

No fixed network infrastructurePure distributed systemNo centralized coordinators

Nodes communicate by exchanging packets via radio waves

Features:Rapidly deployableEasily configuredRobustness

Potential drawbacks

Distributed controlNeighbor knowledgeMobility is a challenge

Wireless Ad Hoc Networks

Applications:

communication in remote or hostile environmentsmanagement of emergenciesdisaster recoveryad hoc commercial installationssensor networks

Wireless Ad Hoc NetworksWireless communications:

Transmission range of the nodes is limitedObstacles may prevent direct communication between a pair of nodes

Point-to-point NetworkCommunication between non-adjacent nodes requires cooperation of other nodes

Obstacle

Wireless Ad Hoc Networks

Proactive Routing

Solution derived from wired networks (Proactive approach)

Table drivenLink state

Drawbacks:Updates overhead, especially in presence of high mobilityLarge routing tablesLow scalability

On Demand (Reactive) protocols

No information about routes is maintained proactivelyroutes established only when needed (on-demand routing)Route discovery process generally based on flooding:

A route request message (RREQ) is sent (flooded) to discover a path to the destinationUpon receiving the RREQ the destination sends a route reply message (RREP) back to the source

Virtual Routing Protocol (VRP)

The Virtual Routing Protocol (VRP):Designed to reduce the overhead of route discovery based on floodingDoes not assume any geographical information of the nodes. Hybrid routing algorithm

Exhibits features of both reactive and proactive protocolsCan be tuned to behave as a reactive or as a proactive

Three different priorities for messages

Virtual Routing Protocol (VRP)

Units are arranged in a Logical Structure :No relation with the physical position of the unitsUnits must proactively maintain routes to the units to which they are connected in the logical structureExamples:

Ring of RingsHypercubeCCC3d-Torus

Node u which proactively maintains a route to unit v is a scout for v

Node v is a peer of u

Three protocols:Route acquisition (Route Discovery)Route maintenanceScouts Update

Virtual Routing Protocol (VRP)

A example of Logical Structure:The Ring of Rings (RoR)

… Va+1 Va … Va–1

s–1

s–1

Mobiles peered by ui Scouts for ui

ui

Virtual Routing Protocol (VRP)

Route Acquisition (Route Discovery)Based mainly on unicast messagesHigh priorityVirtual path setup

Path on the logical structure from the source to the destination

Route setupTranslation of the virtual path into a real physical route

Route MaintenanceUsed when a previously established route gets broken during communication

Scouts UpdateBased on floodingLow priorityCan be completely Reactive or partially proactive

VRP – Route AcquisitionVirtual path setup

The source computes a virtual path between itself and the destinationThe virtual path is computed on the logical structureThe virtual path is computed recursivelyThe virtual path is a sequence of scouts

… Va+1 Va

u1

u0

u2

u3

…

VRP – Route Acquisition

Route setup - Virtual path translationVirtual path:

RTRANS route from source to destination:

u3

u0

u1u2

v

u0 u3u1 u2

VRP – Route AcquisitionRoute setup - Virtual path translation

Destination cuts the loops of the collected route and return to the source a loop-free route

u3

u0

u1u2

v

vzu0 u3

u3

u0

u1u2

v

zz

VRP – Route AcquisitionRoute setup - Virtual path translation

Shortcut to the destination

u3

u0

u1u2

v

z

Transmission range

VRP – Route Acquisition

u3

u0

u1u2

v

z

u4

u5

Route setup - Virtual path translationRTRANS detour

zu0 u4 u1 u5 u3

VRP – Route Acquisition

Route setup (cont.)Route Request

Used if a certain number of virtual path translations failedBased on floodingSimilar to the route request of the other reactive routing protocols

u3

VRP – Route Acquisition

Broken RouteDetourBroken link message to the last scout

zu0 u4 u1 u5

Route AcquisitionWhen translating a virtual pathUpstream unit detects the broken linkUpstream unit computes a detour to deliver the RTRANS to its destination (If possible)Upstream unit warns the last scout through which the RTRANS has passed that the route archived in this unit is brokenWhen the last scout receives the warnning it invokes the scout update phase of the protocol

VRP – Route Maintenance

Data communication Upstream unit discovers the broken linkUpstream unit send a route error message to the sourceSource establishes a new route to the destination if desired

u0 u3

VRP – Scouts UpdateInvoked when:

A scout receives a broken link messageDuring the route acquisition phase the scout does not have a valid physical route to the next scout

Completely ReactiveScout updates the route just to the broken unit

Partily ProactiveScout updates the route to all of its peered unit

Use multiple destinations flooding

VRP – Scouts UpdateMultiple Destinations flooding

Message has a special character in the destination field to identify that it is for multiple destinationsIt is forwarded even by its destinationsEach unit forward the message just onceDestinations of a multiple destination flooding are always all peered units of the source

When a unit receives a multiple destination flooding:If it has already received this message:

It drops the message

ElseIt looks in the logical structure if it is a destination of the floodingIf it is a destination it sends a reply to the source of the floodingIt rebroadcast the message

VRP – Scouts UpdateIf each unit has k peered units, each multiple destination flooding generates k replies

The use of multiple destination flooding allows the scout to maintain their routes more up-to-date

The use of multiple destination flooding reduces the number of floodings perfomed for scouts update (demonstrated through simulation)

Multiple destination floodings increases the number of flooding replies (unicast messages) and reduces the number of flooding in the network

VRP – SimulationSimulation Model

Simplified MAC layerCSMA – Listen the medium before try to transmitRTS/CTS – When a unit is transmitting, its neighbors and the neighbors of the destination remain quietExponential Delay – If transmission is not possible because the medium is not emptyRoughest Approximation: the simulator does not consider collisions

Neighbors information – the MAC layer provides to the routing protocols information about the neighbors of the unitsOut Buffer of 300 messages with LRUThree routing protocols were implemented:

VRPDSR (draft version 9)ZRP with unicast and ZRP with multicast (draft version 4)

VRP – SimulationUnits: 75Network field: 1000m x 1000mTransmission Range: 250mRing of Rings:

3 rings25 units per ring5 scouts

Units’ velocity: 0m/s to 20 m/sUnits’ pause time: 0s to 600sSimultaneous CBR connections: 10 to 50Messages per second per CBR source: 2Duration of each CBR connection: 15s or 120s

VRP – Simulation

VRP versus DSR: Delivery ratio as a function of the units' speed for 20 simultaneous CBR connections.

VRP – Simulation

VRP versus DSR: Delivery ratio as a function of the units' speed for 40 simultaneous CBR connections.

VRP – Simulation

VRP versus DSR: Delay to build a route as a function of the units‘ speed for 20 simultaneous CBR connections.

VRP – Simulation

VRP versus DSR: Routing load as a function of the units' speed with 20 simultaneous CBR connections.

VRP without proactive scout setup

VRP – Simulation

VRP versus DSR: Routing load as a function of the units' speed with 40 simultaneous CBR connections.

VRP without proactive scout setup

VRP – Simulation

VRP versus DSR: Average size of the units' routing table.

VRP – Simulation

VRP versus ZRP: Delivery ratio as a function of the units' speed20 simultaneous CBR connections of at most 15 seconds duration.

VRP – Simulation

VRP(up) versus ZRP(right): Delay to build a route as a function of the units' speed

VRP – Simulation

VRP versus ZRP: Routing load as a function of the units' speed

20 simultaneous CBR connections.

VRP – ConclusionsDelivery ratio:

Light traffic conditions:VRP always above 95%DSR about 70%ZRP about 82%

Heavy traffic conditions:VRP never below 75%DSR about 50%ZRP around 80%

Route Acquisition Delay:VRP has a delay significantly higher than DSR and ZRP

Unit’s Routing Tables:DSR and ZRP: O(N) (N number of units in the system)VRP: O(k) (k number of scouts per unit – connectivity of the logical structure)

VRP – Improvements

Scout Update over Received Messages

Shortcuts in Virtual Path Translation

Avoiding High Priority Flooding

Proactive Zone

Avoid route acquisition by immediately sending data during virtual path translation