Scalable Geographic Routing for Mobile Ad-hoc Networks

(Joint work with Xiaojing Xiang and Zehua Zhou)

Xin Wang Assistant Professor

Director, Wireless and Networking Systems Lab (WINS)[SUNY, Buffalo]

http://www.cse.buffalo.edu/~xwang8

… Tomorrow – Common Net, Common Apps

Core InternetBackbone

AuthenticationAuthentication

PresencePresenceLocationLocation

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AccessRouterAccessRouter

AccessRouterAccessRouter

3G CellularNetworks

RadioController

RadioController Access

RouterAccessRouter

UrbanNetworks

HomeNetworks

EnterpriseNetworks

4GRadios

Ad HocNetworks

4G AirInterface

4GRadios

• DSL/Cable• High Speed Internet Access• Community wireless networks

• Broadband Distribution Networks• High Speed Pico Cells• Broadband Wireless

• 802.11++• Local Mobility• Packet Voice• High Data Rates

• Outdoor Areas• High Mobility

• Allow Peer-to-Peer Communications• Self Configuring

Talk Overview

Background and motivationSelf-adaptive geographic unicast routingScalable geographic multicast routingOn-going and future work

Background

Mobile Ad Hoc Networks (MANET)– Self organized networks with no fixed infrastructure – Example applications: disaster area, military, sensor

networks, wireless mesh networks – May need to traverse many hops due to limited radio

range

Routing: find a packet delivery path– Unicast: one-to-one– Multicast: one-to-many

or many–to-many

Challenges of MANET Routing

Host mobility leads to dynamic topologyRate of link failure/repair increases with

moving speed Topology and routing path maintenance

become more difficult with the increase of path length and node density

Mobile devices have very limited energy, and small devices such as sensors have very limited per-node resources

Existing Unicast Routing Protocols

Proactive protocols (DSDV, OLSR)– Maintain routes continuously, large overhead when

there is no traffic– Actively track network topology changes, not suitable

for high mobility

Geographic routing protocols (GPSR, GFG) – Make use of location information to reduce routing overhead– Only need to be aware of local topology

Reactive protocols (DSR, AODV, TORA, FLR)– Maintain routes only if needed– May need network-wide flooding to discover routes, larger

delay due to searching for path before sending packet

Hybrid protocols (ZRP, SHARP) – Combine the proactive and reactive approaches

Information Required for Geographic Routing

The position of the destination: determined through some location service

A node’s own position: obtained through positioning service such as GPS

The positions of all neighbors: learned through periodic beacons sent by neighbors

Forwarding Formats (GPSR’00)

Greedy forwarding– Make local optimal forwarding

decision, choose the neighbor closest to the destination as next hop.

D

x

x

D

Perimeter forwarding – Calculate a planar sub-graph

(no crossed-edges exist) from the local topology

– Route around the perimeter of void area (that does not have neighbor closer to the destination) until greedy forwarding can be resumed

Problems with Classical Geographic Routing

Proactive fixed-interval beaconing for positions– Generate unnecessary overhead and consume energy – Create collisions with normal data transmissions

Beaconing interval affects accuracy of the local topology and routing performance– Outdated topology => non-optimal routing, transmission

failures => more network resource consumption

Continuous retransmissions due to inaccurate position – Reduce link throughput and fairness, and increase

collisions => further delay and energy consumption

Performance Improvement

Change Beacon Sending Interval– Send out beacons only after moving a certain distance– Send beacons more frequently, e.g. piggyback position

with packets (Are the sending nodes the best next hop? )

Does not consider traffic conditions.May generate unnecessary beacons.

Do not use Beacons (CBF’03, BLR’04) – Focus only on finding the forwarding node in a dense

network – No recovery strategy– Need to search for path for each packet forwarding

Our Contributions

Propose two geographic on-demand routing protocols: alleviate unnecessary overhead due to proactive beacons

Introduce more flexible position distribution mechanisms: more updated topology, more efficient routing and less failure

Introduce a self adaptive routing approach: robust to topology changes and adaptive to traffic

Importance of updated positions: some analysisPositions obtained may become

outdated– A mobile [delete: with outdated position] may

move out of transmission range before the position is timed out and removed from neighbor table.

Analysis – assumptions– Node B sends beacons periodically to refresh

its position at A– Neighbor area of A: centered at A, within

transmission range R – Moving area of B: centered at B, within

maximum distance r Neighbor time-out interval t

[B’s speed relative to A]

Current distance between A, B

Maximum distance traveled by B after t

],0[ maxVv],0[ Rz

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Probability of Moving Out of Range

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Probability of the mobile moving out-of-range (expressed in percentages)

Vmax

4s 6s 8s 10s 12s 14s

10m/s 3.57 5.49 7.51 9.64 11.88 14.27

20m/s 7.51 11.88 16.80 22.43 29.19 38.26

30m/s 11.88 19.51 29.19 42.94 55.38 65.24

40m/s 16.80 29.14 47.37 62.22 72.89 80.07

50m/s 22.43 42.94 62.22 75.00 82.64 87.24

Timeout

Proposed Geographic Routing Protocols

Beaconless Interactive Geographic Routing (BIGR)

BTGR: Beacon-on-Trigger Geographic Routing

Route searching phase

Route optimization phase

– Forwarding decision made through the cooperation of forwarding node and its neighbors

– Forwarding path optimized jointly by sending node and its neighbors

Beaconless Interactive Geographic Routing (BIGR)

There is no beacon, routing path is built on-demand

How to find next hop without positions of neighbors?

Route Searching

After a route searching, a node keeps a record for next hop

Destination F

Dest’s position, time (x_F, y_F), t

NextHop C

New position, time (x_new, y_new), t_new

Old position, time (x_old, y_old), t_old

Transmission mode greedy or recovery

B

A F

C

Next hop table for node B

Nex

t-ho

p po

siti

on

How to find next hop?

When a node (C) does not have next hop information, broadcast REQ

REQ message with

A node that receives a packet for the first time

Dest DestPos SendPos

Hop

D XD, YD Xc, Yc 1

Within neighborhood

B

A

SE

H

J

D

C

G

I K

M

N

LF

Forwarding Node Selection Reply sending: nodes closer to destination respond after a

competition delay, and the delay is smaller for a node closer to destination

Reply suppression: a node cancels its reply if it overhears packet forwarding, or overhears reply sent by node closer to destination

Multiple replies: select the node closer to the destination as next hop

REPLY message Dest Sende

rSendPos

Hop

D G XG, YG 1

B

A

SE

H

J

D

C

G

I K

M

N

LF

Packet Sending

C’s next hop table

Destination D

Dest’s position, time (x_D, y_D), t

NextHop G

New position, time (x_new, y_new), t_new

Old position, time (x_old, y_old), t_old

Transmission mode greedy

B

A

SE

H

J

D

C

G

I K

M

N

LF

Recovery from Local Void

Without local topology, cannot use perimeter forwarding. How to recover?

B

A

S F

H

J

D

C

IK

M

N

L

G

REQ message with Dest DestPo

sSendPos

Hop

D XD, YD Xc, Yc 2

E

Broadcast REQ to N-hop neighbors

Finding Path in Recovery Mode Reply sending:

Dest Sender SendPos

Hop

D G XG, YG 2B

S F

H

J

D

C

IK

ML

G

E

Reply suppression: drop the REPLY if having forwarded/overhead one from the node closer to destination

– If one-hop neighbor is nearer to destination, it replies with Hop = 1; Otherwise continues broadcasting REQ

– A two-hop neighbor nearer to destination replies (reverse path), Hop = 2;

Multiple replies: select the node closer to destination

Reply message

Position Update and Route Optimization Update next hop position when overhearing packet

forwarding by next hop (carrying sending node position)

Validate next hop– Estimate next hop

If both old and new positions are fresh If only new position is available, it will be used as the estimated position

– Search for new route If both old and new positions are outdated If estimated position is out of transmission range or no longer closer to

destination than current forwarding node

Optimize rerouting path: three cases– Assumption: current forwarding path is from B to C,

neighboring node A overhears from both node B and C

Case 1: A is the destination

As A is the destination, B should send packet directly to A, so A sends CORRECT to B

B C

A

Old position

CORRECT

Current position

Old path

New path

AMove

B sets its next hop to A

CORRECT

Case 2: Greedy Mode Forwarding

If A is closer to F than C is to F, A sends CORRECT to B

Old position

Current position

Old path

New path

B C

A

A

Move F

Greedy B compares A’s and C’s positions

to F, and sets its next hop to A if

it is closer to F

A

Case 3: Recovery Forwarding

If A is closer to F than it is from B and C, A sends CORRECT to B– If B is the first hop of recovery, if A

is closer to F than B is to F, then A is closer to F than both B and C

– If B is the last hop of recovery, if A is closer to F than C is to F, then A is closer to F than both B and C

F

D

CB

CORRECT

A

Move

Recovery mode

Greedy

Old position

Current position

Old path

New path

B compares A and C’s positions relative to F, if A is closer to F, B sets its next hop to A

If B is the first hop of recovery, change mode to greedy

Proposed Geographic Routing Protocols

Beaconless Interactive Geographic Routing (BIGR)

BTGR: Beacon-on-Trigger Geographic Routing

BTGR: Beacon-on-Trigger Geographic Routing

Position distribution: through beacons Packet forwarding

– Send packet through greedy forwarding to the neighbor that is closest to the destination

– Use planar sub-graph in recovery mode. Beacon generation: triggered by data traffic and

route optimization– Adaptive to traffic

Send beacon periodically when overhearing data forwarding or requested by neighbor

Stop beaconing if there is no traffic – Route optimization

Broadcast a beacon upon detecting non-optimal path Topology maintenance

– Only maintain positions of neighbors when there is traffic

Beacon Triggering by Non-optimal Path

Route validation– Delete invalid neighbors– Update the positions of other members based on

estimation

Route optimization: also three cases– The first two cases are similar to that of BIGR– Case 3: When A overhears forwarding from B to C

using perimeter mode If A is closer to the destination than the position where

the perimeter mode started, B should resume greedy forwarding earlier

A broadcasts a beacon to refresh its position, B will send future packets to A

Impact of Mobility

Delivery ratio Control overhead

BIGR and BTGR delivery ratios are not impacted by speedBIGR more actively updates the position as speed increases

Impact of Mobility (cont)

Total transmissions Average end-to-end delay

GPSR has significantly higher transmission redundancy and end-to-end delay due to outdated position.

Summary

Propose two self-adaptive on-demand geographic routing protocols– Alleviate unnecessary overhead due to

proactive beacons– More efficient position distribution and very

robust to topology change: packet transmission delay is reduced more than three times at high mobility as compared to GPSR

– Outperform existing geographic protocols in all test scenarios, including mobility, node density and traffic load

Talk Overview

Background and motivationSelf-adaptive geographic unicast routingScalable geographic multicast routingOn-going and future work

Existing Multicast Routing Protocols

Tree-based (AMRIS, MAODV, LAM)– Utilize network resources efficiently

Mesh-based (FGMP, CAMP, ODMRP)– Robust

Difficult to scale due to overhead for route searching, group membership management, and tree/mesh maintenance over dynamic topology

Geographic multicast (LGT, DSM, PBM)– Only consider packet forwarding scheme– Reduce topology maintenance overhead, but not scalable

Why Is Geographic Multicast Difficult to Scale?

Putting the information of all group members into packet header creates excessive overhead for large group

Relying on location service to obtain positions for all group members adds more overhead

Our Contributions

Design an efficient on-demand hierarchical group membership management scheme

Avoid the need to build and maintain tree/mesh structure

Avoid the need for periodical network-range flooding of source information, and frequent location searches for group members

Protocol Overview

Group membership management– Two-tiers through a zone structure

Location of group members– Combined with group membership management

Packet forwarding– At upper tier, the source sends a packet to member

zones; At lower tier, the first node in the zone that receives the data packet will forward it to the group members.

– Both data and control packets are transmitted through geographic unicasting, except when some control packets need to be flooded

– Packets for a zone are sent towards the zone center

Track the addresses and Zone IDs of sources

Home zone

Some Concepts

Member Zone Group member

Zone leader

Source

Source Announcements

A source– At session initiation time, floods an

ANNOUNCE, with address, position, and group ID

– Later piggybacks its information with the multicast packets

A node interested in being a member– Records source information

Home Zone Management

Home zone information update– A source sends its zone ID to home zone when moving to new

zone– The first home zone node floods source info to whole zone

Home zone searching– Other nodes: search home zone with ring of increasing size.– Source: announces its current zone as home zone, and sets

sequence number to 0; Sequence number increases by one each time home zone changes.

Home zone election– Will be triggered when a node receives a message addressed to

home zone with ID different from record (due to zone update or zone announcement from a new source)

Home Zone Election

Home ZoneSEQ = 1

Home ZoneSEQ = 0

When a node receives a message carrying home zone ID different from that in its record– If the message has larger sequence number, update its home zone info; otherwise, forward the

message to recorded home zone

Forwardto home zone with larger SEQ

Membership report

SOURCEmessage

Membership Management within Zone

A member

A leader

– Sends REFRESH to leader periodically and when joining /leaving group, carrying its membership and position

– Floods LEADER periodically within the zone to announce its leadership, carrying its own position and the positions and group IDs of the multicast members

Membership Management at Upper Tier

Home Zone

Leader knows source location

Membership report

SOURCEmessage

Leader does not know source locationor

Source information is outdated

Source: records the member zones

Moving between Zones

When a node moves into a new zone– Clears old zone’s information

If the node is a group member– Will continue receiving packets forwarded by old zone– Sends REFRESH to new zone leader

When a leader is moving out of a zone– Hands leadership to other nodes

Empty Zone Problem

S

r p

2

:zone ain node afor y Probabilit

kNkN

k

ppk

NP

)1(1

1

dSN :networkin nodes ofNumber

2 :zone of Area r

S :network of Aread :density Node

20 40 60 80 100

100m 74.885 56.282 44.864 36.865 30.853

200m 36.857 19.208 10.985 6.5467 3.9951

400m 6.4964 0.9643 0.1605 0.0281 0.0051

600m 0.5930 0.0112 0.0002 5.4E-06 1.2E-07

m2400 x m2400S 2nodes/km:Density

Empty Zone Handling

Member zone– The departing leader notifies the source

Home zone – The last node announces the new zone it is moving to

as the home zone; floods source information within new home zone; sends ANNOUNCE to network with sequence number of home zone increased by one

Multicast Packet Delivery Source

– Sends packets to all member zones and members in its zone

– Aggregates transmissions and sends one copy if several members share next hop

Intermediate nodes – Take similar action– If the message includes their

current zone, replace zone ID in the message with the information of the members in the zone. Zone leader

Group member

Other nodes

Source

Impact of mobility

Delivery ratio Control overhead

SGMP has up to 35% higher delivery ratio and 20 % lower overhead at high mobility

Scalability

Group size Network size

SGMP has higher delivery ratio under all group sizes, and has more than 2.5 times higher delivery ratio for large network sizes.

Summary

Design a scalable geographic multicast routing scheme– Scalable and robust group membership

management and packet forwarding in terms of group size, network range and mobility

– Avoid the need to build and maintain the tree/mesh structure over dynamic topology

– Avoid network-range flooding of source information and location searches for the group members

On-going and Future Work

Cross-Layer Optimization and Design of Mobile and Wireless Systems– Create infrastructure and algorithms to enable more

optimal performance of the wireless system, by adopting an integrated, multi-layer approach

– On-going projects Power control and energy efficient transmissions in

mobile Ad Hoc networks Architecture design and cooperative resource

management for IP-based radio access network

On-going and Future Work (cont)

Next Generation Mobile Wireless Network Infrastructure and Service– Development of network infrastructure and services

over emerging radio and computing technologies.

– On-going projects Sensor Network Applications and Services Programmable Wireless Networking and Service

Infrastructure Design Scalable and Resilient Wireless Mesh Network Design Context-aware Mobile Computing and Wireless Services

Architecture and Design for Heterogeneous Networks

Q & A

Focus of Talk

Scalable geographic routing protocols for Mobile Ad Hoc networks

Membership Reporting in Local Zone

A group member sends REFRESH to leader to report its membership – If leader is known, unicast – If leader is not known, elect leader

Leader election (on demand)– Flood the REFRESH, indicating leader information is

requested A leader will send back a LEADER message If no LEADER is received, the member announces itself as

the leader and floods a LEADER message within the zone

Zone leader

Group member

Other nodes

… Tomorrow – Common Net, Common Apps

Core InternetBackbone

AuthenticationAuthentication

PresencePresenceLocationLocation

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AggregationRouter

AccessRouterAccessRouter

AccessRouterAccessRouter

3G CellularNetworks

RadioController

RadioController Access

RouterAccessRouter

UrbanNetworks

HomeNetworks

EnterpriseNetworks

4GRadios

Ad HocNetworks

4G AirInterface

4GRadios

• DSL/Cable• High Speed Internet Access

• Broadband Distribution Networks• High Speed Pico Cells• 802.11++

• Local Mobility• Packet Voice• High Data Rates

• Outdoor Areas• High Mobility

• Allow Peer-to-Peer Communications• Self Configuring

Unifies access technologies (wireless and wireline) End-to-end Internet Service

– common mobility management and control – common transport infrastructure– common services infrastructure

Architecture and Design for Heterogeneous Networks– Enable end-to-end communications over

heterogeneous networks: WPAN, WLAN, WMAN, W-WAN, and Internet.

Secure and Cooperative Routing over Ad Hoc Networks– Provide security and incentive to enable the relay-

based hop-by-hop transmissions.

Case 3: Recovery Forwarding

Suppose A overhears from B and C

Packet was forwarded for destination F from B to C using recovery mode– If B is the last hop of recovery

If A is closer to F than C, then A is closer to F than both B and C

– A sends COREECT to B– B compare A and C’s positions

to F– B sets its next hop to A if it is

closer to F– Remain in recovery mode, a

better path

Old position

Current position

Old path

New path

F

D

CB

CORRECT

Recoverymode

A

Overall, if A is closer to F than Both B and C, it sends CORRECT to B

A

Move

Beacon Triggering by Data Traffic

Three types of beacons (for position information)– BEACON message– REQ (Carrying position)– Data packets (Carrying position)

Beacon request – Receiving REQ– Overhearing data transmission

Beacon sending – Only if the request interval is smaller than threshold

For packet sending– Use local topology information for forwarding if request sent

interval is smaller than threshold– Otherwise, send REQ to neighbor

Route Optimization (cont)

Optimization procedure depends on scenarios– Case 1: A is the destination of the packet– Case 2: Packet was forwarded for destination F from

B to C using greedy mode– Case 3: Packet was forwarded for destination F from

B to C using recovery mode

B C

AF

A

BC

Greedy mode

F

D

CB

Recovery mode

A

Case 1 Case 2 Case 3

Route Searching

How to find a path without beacon?– Depend on forwarding states: greedy or

recovery

Greedy forwarding– Find a neighbor closest to the destination

Recovery forwarding– How to forward when there is no neighbor

closer to the destination?

Destination D

Dest’s position, time

(xD, yD), t

NextHop G

New position, time (xnew, ynew), tnew

Old position, time (xold, yold), told

Transmission mode greedy

Membership Management in Local Zone

Membership reporting by mobiles nodes Leader election Moving between different zones

Membership Management at Upper Tier

A source needs to record the member zones

Source announcementHome zone electionZone membership reporting