Network LayerRouting Issues (I)

Infrastructure vs. multi-hop

Infrastructure networks:

◦ One or several Access-Points (AP) connected to

the wired network

◦ Mobile nodes communicate through the AP

Multi-hop network (Infrastructureless):

◦ Mobile nodes communicate directly with each

other

◦ Multi-hop networks: all nodes can also act as

routers

Adaptivity and Cooperation Multi-hop networks require more cooperation

between layers:

◦ Channel variation

◦ network topology changes affect the application

◦ Routing in a multi-hop considerably affects the

medium access control (MAC) performance

◦ Collisions and channel fading affect both the

physical layer and the MAC

Problems in Multi-Hop Networks

Routing◦ How to keep up-to-date information on the

network topology? ◦ How to determine number of hops◦ How to cope with network topology changes

Higher DelayResource LimitationsSecurity Issues (Unreliability)Complex and Large Structures (Routing tables)Hard-to-Control

Routing Protocols

Routing ClassificationUnicast Routing (one-to-one connection)Multicast routing (one-to-many connection)Broadcasting (one-to-all connection)

Routing Protocols

Routing (unicasting) ProtocolsProactive RoutingReactive RoutingHybrid Routing Geometric Routing

Routing Protocols

Proactive Routing (table-driven)• Keep routing information current at all times

• Route maintenance

• Good for static networks

• High overhead and low delay

• Route invalidity

• Examples: (DSDV)

Destination-Sequenced Distance Vector

Routing ProtocolsReactive Routing (on-demand routing)

◦ Finds a route to the destination only after a

request comes in

◦ Good for more dynamic networks

◦ Low overhead and high delay

◦ Higher delay

◦ examples: AODV(Ad hoc On-Demand Distance

Vector), dynamic source routing (DSR)

Routing Protocols

Hybrid Schemes• Combines the advantages of reactive and

proactive

• Performs better both under dynamic and static

conditions

• Reasonable delay compared to reactive

• Reasonable overhead compared to proactive

• example: Zone Routing Protocol (ZRP)

Routing Protocols

Geometric routing:

◦ Assume location-awareness

◦ Locating nodes by Global Positioning System (GPS)

◦ Forwarding the packets toward the node location

◦ Take advantage of the geometry of plane

◦ Example: Geographic-based routing protocols

Proactive vs Reactive Routing

Latency of route discovery

◦ Proactive protocols may have lower latency

since routes are maintained at all times

◦ Reactive protocols may have higher latency

because a route from X to Y will be found only

when X attempts to send to Y

Proactive vs Reactive Routing

Overhead of route discovery/maintenance

◦ Reactive protocols may have lower overhead since

routes are determined only if needed

◦ Proactive protocols can (but not necessarily) result in

higher overhead due to continuous route updating

Flooding for Data Delivery

Network-wide Broadcasting

Sender S broadcasts data packet P to all its neighbors

Each node receiving P forwards P to its neighbors for

the first time

Packet P reaches destination D provided that D is

reachable from sender S

Node D does not forward the packet

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Communication linkRepresents that the nodes are within each other’s transmission range

Z

Y

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Represents transmission of packet P

Represents a node that receives packet P forthe first time

Z

YBroadcast transmission

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

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

Z

Y

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Z

Y

• Node D does not forward packet P, because node D is the intended destination of packet P

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

• Flooding completed• Nodes unreachable from S do not receive packet P (e.g., node Z)• Nodes for which all paths from S go through the destination D also do not receive packet P (example: node N)

Z

Y

M

N

L

Flooding for Data Delivery

B

A

S E

F

H

J

D

C

G

IK

Broadcast Storm Problem• Flooding may deliver packets to too many nodes (in the worst case, all

nodes reachable from sender may receive the packet)

Z

Y

M

N

L

Flooding: Advantages

Simplicity (no complex control mechanism)

More efficient than other protocols ◦ In small networks◦ Under light load traffic conditions◦ Highly dynamic networks

Potentially higher reliability of data delivery◦ Because packets may be delivered to the

destination on multiple paths

Flooding: Disadvantages

Very high overhead◦ Data packets may be delivered to too many

nodes who do not need to receive themEnergy consumingBandwidth consumingCongestion

Flooding of Control Packets

Many protocols perform flooding of control packets,

instead of data packets

The control packets are used to discover routes

Discovered routes are subsequently used to send

data packet(s)

Flooding

Overhead reduction

Virtual Backbone Formation (VBF)

◦ Connected Dominating Set (CDS)

◦ Maximal Independent Set (MIS)

Forwarding Group (FG)

Network Clustering

Flooding

Scoped Flooding

Scope Limited Flooding

?

Routing Protocols

Link-state Routing Protocols

◦ Routes are constructed based on the selection

of the communication links

◦ Routes are optimized based on the link

characteristics

◦ Shortest Path Problem

◦ Spanning Tree (Steiner Tree)

Routing Protocols

Node-state Routing Protocols

◦ Routes are constructed based on the selection

of the nodes

◦ Routes are optimized based on the node

characteristics

◦ Connected dominating set (CDS)

Routing Protocols

Link-state Routing Protocols◦ Relative mobility◦ Link duration◦ Link Bandwidth, …

Node-state Routing Protocols◦ Node Failure Rate◦ Node Mobility◦ Node Energy◦ Nodal capacity