Wireless Networks Routing

Wireless Networks Routing

國立屏東教育大學資訊科學系王朱福教授

Outlines

Wireless networks architectures

Routing protocols for wireless networksMobile ad-hoc Networks (MANETs)Wireless Sensor Networks (WSNs)Vehicle ad-hoc networks (VANETs)

Wireless Communications

Wireless networks use radio frequency channels as their physical medium for communications.

Each node in the network broadcast information which can be received by all nodes within its direct transmission range.

Wireless network architectures

Infrastructure-based wireless networksFixed base stations / access points are

used.Infrastructure-less wireless networks

(Ad-hoc networks)No fixed infrastructure support are

available.Hybrid wireless networking

architecture

Wireless network architectures (cont.)Infrastructure-based wireless networks

Uses fixed base stations / access points which are responsible for coordinating communication between the hosts.

Single-hop communication

Ad-hoc networksConsists of nodes which communicate with each other

through wireless medium without any fixed infrastructure.Multi-hop communications

Wireless network architectures (cont.)

Properties of ad-hoc networks

No pre-build infrastructure

All nodes are wireless capable

Base stations are not necessary

Ease of deployment

Quickly deploy

Some emerging types of wireless networks

MANETs (Mobile Ad-hoc Networks)

WSNs (Wireless Sensor Networks)

VANET (Vehicle Ad-hoc Networks)

WMN (Wireless Mesh Networks)

…

Routing protocols for wireless networks – MANETs

A dynamically reconfigurable ad-hoc network.

Main issues in the design and operation of MANETs.(1) MANETs are more unstable than wired-networks because

of the lack of a centralized entity.

(2) Mobility will cause network topology to change, which results in a great change in connection between two hosts.

(3) The connectivity between network nodes is not guaranteed, so intermittent connectivity is common.

Routing protocols for wireless networks – MANETs (cont.)

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The main routing problems for MANETs

Node mobility

Routing path broken frequently

Traditional ad-hoc routing protocols

Routing protocols for MANETs

Flooding-type routing protocol (flooding)

Table-driven routing protocol (proactive)

On-demand routing protocol (reactive)

Hybrid routing protocol

Flooding-type routing protocol (Flooding)

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Advantage: They do not need to maintain network

topology, or is looking for data transmission path, so

they can quickly transfer information.

Disadvantage: Node receives information after, must

repeat broadcast, making it fast consumes its battery energy, and produces broadcast storm.

Flooding-type routing protocol (Flooding)

Table-driven routing protocol (proactive):They maintain the global topology information in the

form of tables at every node.These tables are updated frequently in order to

maintain consistent and accurate network state

information.For example, DSDV, WRP, and STAR.

Routing protocols for MANETs (cont.)

The DSDV routing protocol is an enhanced version of the distributed Bellman-Ford algorithm where each node maintain a table that contain the shortest distance and the first node on the shortest path to every other node in the network.

Table-driven routing protocol—Destination Sequenced Distance Vector routing (DSDV)

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Dest NextNode Dist seqNo2 2 1 223 2 2 264 5 2 325 5 1 1346 6 1 1447 2 3 1628 5 3 1709 2 4 186

10 6 2 14211 6 3 17612 5 3 19013 5 4 19814 6 3 21415 5 4 256

Routing table for Node 1

Table-driven routing protocol – DSDV (cont.)

Example:


Each node, upon receiving an update, quickly disseminates it to its neighbors in order to propagate the broken-link information to the whole network. Thus a single link break leads to the propagation of table update information to the whole network.

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Routing table for Node 1

Dest NextNode Dist seqNo2 2 1 223 2 2 264 5 2 325 5 1 1346 6 1 1447 2 3 1628 5 3 1709 2 4 186

10 6 2 14211 5 4 18012 5 3 19013 5 4 19814 6 3 21415 5 4 256


Advantage： It can be applied to MANETs with few

modifications. The updates are propagated throughout the network in order to maintain an up-to-date view of the network topology at all the nodes.


Disadvantage：(1) The DSDV suffers from excessive control

overhead that is proportional to the number of nodes in the network and therefore is not scalable in MANETs, which have limited bandwidth and whose topologies are highly dynamic.


(2) In order to obtain information about a particular destination node, a node has to wait for a table update message initiated by the same destination node. This delay could result in stale routing information at nodes.


On-demand routing protocol (reactive):They execute the path-finding process and exchange

routing information only when a path is required by a node to communicate with a destination.

For example, AODV and DSR.

Routing protocols for MANETs (cont.)

AODV, a route is established only when it is required by a source node for transmitting data packets.

In AODV, the source node and intermediate nodes store the next-hop information corresponding to each flow for data packet transmission.

On-demand routing protocol – Ah-hoc On-demand Distance-Vector Routing Protocol (AODV)

The major difference between AODV and other on-demand routing protocol is that it uses a destination sequence number ( DestSeqNum) to determine an up-to-date path to the destination.

A node updates its path information only if the DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node.

On-demand routing protocol – AODV (cont.)

AODV utilizes routing tables to store routing information.

The routing table stores:

destination addr

next-hop addr

destination sequence

hop count life time


1. If a node wants to send a packet to some destination. At first, it checks its routing table to determine whether it has a current route to the destination or not.

=>If yes, it forwards the packet to next hop node of the route.

=>If no, it initiates a route discovery process.

The AODV routing procedure

The Route discovery process: It begins with the creation of a RouteRequest (RREQ) packet.

Broadcasting is done via flooding.Broadcast ID gets incremented each time a source node uses

RREQ.Broadcast ID and source IP address form a unique identifier for

the RREQ.Type Reserved Hop Count

Broadcast ID

Destination IP Address

Destination Sequence Number

Source IP Address

Source Sequence Number

Time Stamp

RREQ packet format

The AODV routing procedure (cont.)

2. Sender S broadcasts a RREQ to all its neighbors, each node receiving RREQ forwards RREQ to its neighbors.

*Sequence numbers help to avoid the possibility of forwarding the same packet more than once.

3. An intermediate node (not the destination) may also send a RouteReply (RREP) packet provided that it knows a more recent path than the one previously known to sender S.

Type Reserved Hop Count

Destination IP Address

Destination Sequence Number

Source IP Address

Life Time

RREP packet format


4. As an intermediate node receives the RREP packet, it sets up a forward path entry to the destination in its routing table.

5. The source node can begin data transmission upon receiving the first RREP.


Illustration of route establishment in AODV

1. Node S needs a routing path to node D.2. Node S creates a RREQ packet

RREQ [D’s IP addr, seq#, S’s IP addr, seq#, hopcount]Node S broadcasts RREQ to its neighbors.

S A

B

C

D

RREQ{D, D’seq, S, S’seq, 0}

2. Node A rebroadcasts RREQ to all its neighbors.

S A

B

C

D



Illustration of route establishment in AODV (cont.)

3. Since, node C known a route to D.Node C creates a RREP packet and unicasts RREP to A.Set forward path in node C’s routing table.

S A

B

C

D

RREP{D, D’seq, S, S’seq, 1}


C’s Routing table

dest nexthop hopcount

D D 1

3. Node A creates a RREP packet and unicasts RREP to S.

4. Set forward path in node A’s routing table.

S A

B

C

D


C’s Routing table


D D 1

RREP{D, D’seq, S, S’seq, 2}

A’s Routing table


D C 2

4. Set forward path in node S’s routing table.

S A

B

C

D


C’s Routing table


D D 1

A’s Routing table


D C 2

S’s Routing table


D A 3

1. If intermediate nodes or the destination move.

The next hop links break.

Routing tables are updated for the link failures.

All active neighbors are informed by RouteError (RRER) packet.

2. When a source node receives an RRER, it can reinitiate the route discovery process.

3. It can be also dealt with by a local fix scheme.

Route maintenance in AODV (Path broken due to host mobility)

Assume link between C and D breaks.Node C invalidates route to D in route table.Node C creates RRER packet and sends to its upstream

neighbors.Node A sends RRER to S.Node S rediscovers route if still needed.

S A

B

C

DRRER

Illustration of route maintenance in AODV

RRER

Advantage: The routes are established on demand and the destination

sequence number can find the latest route to the destination.

Disadvantage: The intermediate nodes can lead to inconsistent routes if

the source sequence number is very old. The periodic beaconing leads to unnecessary bandwidth

consumption.


DSR designed to restrict the bandwidth consumed

by control packets in ad hoc wireless networks by

eliminating the periodic table-update messages

required in the table-driven approach.

On-demand routing protocol – Dynamic Source Routing Protocol (DSR)

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<1,2> <1,3,5,7>

<1,4>

<1,4,6>

<1,3,5>

<1,3><1>

<1>

Source

Destination

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<1,4,6>

<1,4,6>

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Destination

<1,3,5, 7><1,3,5,

7>

<1,3,5, 7>

<1,3

,5, 7

>

<1,3,5, 7>

<1,3,

5, 7

>

Hybrid routing protocol – Zone Routing Protocol (ZRP)

A hybrid routing protocol which effectively combines the best features of both proactive and reactive routing protocols.

The key concept employed in ZRP is to use a proactive routing scheme within a limited zone in the γ-hop neighborhood of every node, and use a reactive routing scheme for nodes beyond this zone.

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Routing Zone with Radius = 1


Routing Zone for Node 8

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Routing Zone for Node8

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RouteRequest

RouteReply


Advantage: By combining the best features of proactive and

reactive routing schemes, ZRP reduces the control overhead.

Disadvantage: But in the absence of a query control, ZRP tends to

produce higher control overhead than the previously schemes.

Hybrid routing protocol – ZRP (cont.)

Other routing issue for MANET –The Intermittent connected routing problem

In case of the nodes density of a MANET is sparse, it will cause the intermittent connected routing problem, and consequently the traditional routing protocols will be no longer fit.

Intermittent connected routing problem

Epidemic routing protocol

Epidemic is a simple routing protocol to resolve the intermittent connected routing problem.

The nodes adopt store-carry-forward communication scheme.A node can carry the messages in its cache if no any direct

routing path to the destination is available. If a node moves into the node’s transmission range, they

will exchange the carried messages between them.

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(Epidemic routing)

A sensor network is composed of a large number of multifunctional and small sensor nodes.

WSN allows random deployment in inaccessible terrains or disaster relief operations.

Sensor nodes are fitted with an onboard processor, it consists of sensing, data processing, and communicating components.

Routing protocols for wireless networks – WSNs

Internet orsatel i te

User

Task manager node

Sink

Sensor field

Sink

Satelite

The sensor nodes are usually scattered in a sensor field.

Sensor nodes can collect data and route data back to sink.

The sink may communicate with the task manager node via Internet or Satellite.

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Military applications

Homeapplications

Other commercialapplications

Environmentalapplications

Health applications

Applications

The number of sensor nodes in a sensor network can be several orders of magnitude higher.

Sensor nodes are densely deployed.

Sensor nodes are prone to failures.

Sensor nodes are limited in power, computational capacities, and memory.

Sensor nodes mainly use a broadcast communication paradigm, whereas most ad hoc networks are based on point-to-point communications.

Sensor nodes may not have global identification (ID) because of the large amount of overhead and large number of sensors.

Aqua node

Aqua node

Mobilizer Location Finding System Power Generator

Power Unit

Sensor ADC

Processor

Storage

Transceiver

Sensing Unit Processing Unit Transmission Unit

Production costs The cost of each sensor node should be much less

than US $1 in order for the sensor network to be feasible.

Transmission media In a multi-hop sensor network, communicating

nodes are linked by radio, infrared or optical media.

Environment Sensor network usually work unattended in remote

geographic areas, such as large machinery, ocean, biologically and chemically contaminated field.

Hardware A sensor node is made up of four basic

components: sensing unit, processing unit, transceiver unit, power unit, and also have additional application-dependent components.

Three phases of WSNs deployment Pre-deployment phase

Sensor nodes can be either thrown in mass or placed one by one in the sensor field.

Post-deployment phase After deployment, topology changes are

due to change in sensor nodes’ Position available energy malfunctioning

Re-deployment phase Additional sensor nodes can be re-deployed at

any time to replace the malfunctioning nodes or due to changes in task dynamics.

Addition of new nodes poses a need to re-organize the network.

Node deployment In manual deployment, the sensors are

manually placed and data is routed through predetermined paths.

Energy consumption without losing accuracy Sensor nodes can use up their limited energy

performing computations and transmitting information.

Data reporting method Data reporting can be categorized as either time-

driven, event-driven, query-driven, or a hybrid.

The time-driven method is suitable for applications that require periodic data.

Event-driven and query-driven methods, sensor nodes react immediately to sudden and drastic changes in the value of a sensed attribute

Coverage A given sensor’s view of the environment is

limited in both range and accuracy. Area coverage is an important design

parameter.

Quality of service Bounded latency for data delivery is another

condition for time-constrained applications. As energy is depleted, the network may be

required to reduce the quality of results in order to reduce energy dissipation.

Flat-based All nodes are typically assigned equal roles or

functionality.

Hierarchical-based Nodes will play different roles in the network.

Location-based Sensor node’s positions are exploited to route

data in the network.

Each node typically plays the same role and sensor nodes collaborate to perform the sensing task.

This consideration has led to data-centric routing, where the BS sends queries to certain regions and waits for data from the sensors located in the selected regions.

Early work on data centric routing were shown to save energy through data negotiation and elimination of redundant data.

ADV REQ DATA

ADV REQ DATA

A1. Data is described by meta-message (ADV).2. Send ADV to neighbors.3. If neighbor do not have the data, sends REQ; otherwise, do

nothing.4. As the REQ received by sender, then it sends the data to the

neighbor.

Advantage Each node only needs to know its one-hop

neighbors.

Disadvantage Data advertisement cannot guarantee the

delivery of data.

Hierarchical routing is two-layer routing where one layer is used to select cluster heads and the other for routing.

Higher-energy nodes can be used to process and send the information, while low-energy nodes can be used to perform the sensing in the proximity of the target.

The creation of clusters and assigning special tasks to cluster heads can greatly contribute to overall system scalability, lifetime, and energy efficiency.

Proactive clustering.

Node transmits sensed data only if both of the following conditions hold:

1. The sensed value is greater than a Hard Threshold.2. The sensed value differs from last transmitted value

by more than a Soft Threshold.

Node

1st cluster head

2nd cluster head

Sink

Cluster

S

D

Advantage Good for time-critical applications.

Disadvantage Inappropriate for periodic monitoring,

e.g., habitat monitoring. Ambiguity between packet loss and

unimportant data.

Hierarchical-based routing Flat-based routing

Reservation-based scheduling Contention-based scheduling

Collisions avoided Collision overhead present

Reduced duty cycle due to periodic sleeping

Variable duty cycle by controlling sleep time of nodes

Data aggregation by cluster headNode on multi-hop path aggregates incoming data from neighbors

Simple but non-optimal routingRouting can be made optimal but with an added complexity

Requires global and local synchronization

Links formed on the fly without synchronization

Overhead of cluster formation throughout the network

Routes formed only in regions that have data for transmission

Lower latency as multiple hops network formed by cluster heads always available

Latency in waking up intermediate nodes and setting up the multipath

The location of nodes may be available directly by communicating with a satellite using GPS if nodes are equipped with a small low-power GPS receiver.

Relative coordinates of neighboring nodes can be obtained by exchanging such information between neighbors.

To save energy, some location-based schemes demand that nodes should go to sleep if there is no activity.

Vehicular Ad hoc Network (VANET) is a special case of MANET.

The direct communication between vehicular using Ad hoc network.

Routing protocols for wireless networks –VANETs

Applications in a VANET fall into two categoriescomfort applications safety applications

Comfort applications aim to improve the driving comfort and the efficiency of the transportation systemon-board Internet accesshigh data rate content download driving through payment

Introduction to VANETs

Safety applications aim to provide driver’s information about future critical situations inter-vehicle danger warning intersection collision avoidance work zone safety warning

Introduction to VANETs (cont.)

Safety applications

VANETs provide the following three communications: Inter-Vehicle Communication (IVC) Roadside-to-Vehicle Communication (RVC) Hybrid-Vehicular Communication (HVC)

V2V

V2R

RSU

Emergency Event


Vehicles mobility is restricted to one-dimensional road geometry.

Factors affect the mobility of vehicles such as road configuration traffic laws safety limitsphysical limits


Vehicle mobility creates a highly dynamic topology.VANETs are potentially large-scale networks.Vehicles can provide more resources than other types of

mobile networks such as： large batteries antennasprocessing power


The connectivity of the network is affected by factors that include transmitter powerenvironmental conditionsobstaclesmobility


Factors such as the vast number of nodes that lack inherent organization, as well as frequent topological changes


To enhance the safety of drivers To provide the comfortable driving environment The message for different purpose need to be sent to

vehicles through the inter-vehicle communications.Unicast routingMulticast and GeocastBroadcast

Routing for VANETs

Unicast routing is a fundamental operation for vehicle to construct a source-to-destination routing in a VANET

From Reference 1.

Routing for VANETs -- Unicast

Routing objective: Min-DelayThe goal of min-delay routing protocols is to

transmit data packets to destination as soon as possible.

Relative routing protocols ： VADD 、 CAR 、 DIR

Routing for VANETs -- Unicast

Unicast routing example for VANETsVehicle-Assisted Data Delivery (VADD)

Carry-and-forward for data delivery from a moving vehicle to a static destination.

VADD is to select a forwarding path with the smallest packet delivery delay.

Two Paths ： (1) Ia => Ic => Id => Ib

(2) Ia => Ib

Disconnected due to sparse

Delayacdb < Delayab

Unicast routing example for VANETs The VADD (cont.)

1. Transmit through wireless channels as much as possible.

2. If the packet has to be carried through certain roads, the road with higher speed should be chosen.


3. Due to the unpredictable nature of vehicular ad-hoc networks, so dynamic path selection should continuously be executed throughout the packet forwarding process.

− The routing cannot expect the packet to be successfully routed along the pre-computed optimal path


To overcome the limitation of the static destination.

The CAR protocol establishes a routing path from source to destination by setting the anchor points at intermediate junctions.

Unicast routing example for VANETsConnectivity-Aware Routing (CAR)

CAR protocol sends the searching packets to find the destination.

Each forwarding vehicle records its ID, hop count, and average number of neighbors in searching packets.

Once the searching packets reach the destination, the destination chooses a routing path with the minimum delivery delay time and replies it to the source.

Unicast routing example for VANETsThe CAR (cont.)

While destination sends the reply packet to the source, the junctions passed through by the reply packet are set as the anchor point.

After the path set up, data packets are forwarded in a greedy forwarding.

Greedy forwarding example: x: the current message holder.Assume y is the closest neighbor of x to D, then x sends the message to y.

y

D

x

Unicast routing example for VANETsThe CAR (cont.)

Vehicle VS tries to send data to vehicle VD, the anchor points are set at I1,1, I2,1, I2,2, I3,2, I3,3, and I3,4.

Data is forwarded according to order in the list of anchor points.

Unicast routing example for VANETsAn example for CAR (cont.)

To improve the CAR protocol.

DIR protocol constructs a series of diagonal intersections between the source and destination vehicles.

Auto-adjustability is achieved that one sub-path with low data packet delay, between two neighboring diagonal intersections, is dynamically selected to forward data packets.

Unicast routing example for VANETsDiagonal-Intersection-based Routing (DIR)

To reduce the data packet delay, the route is automatically re-routed by the selected sub-path with lowest delay.

DIR protocol constructs a series of diagonal intersections between vehicles VS and VD.

Unicast routing example for VANETsThe DIR (cont.)

DIR protocol may set the fewer number of anchors than CAR protocol.

DIR protocol can automatically adjust routing path for keeping the lower packet delay, compared to CAR protocol.

Unicast routing example for VANETsThe comparisons between CAR and DIR

Multicast is defined by delivering multicast packets from a single source vehicle to all multicast members by multi-hop communication.

Geocast routing is to deliver a geocast packet to a specific geographic region.

Geocast Routing

Routing for VANETs – Multicast and Geocast

Broadcast protocol is utilized for a source vehicle sends broadcast message to all other vehicles in the network.

Routing protocol type ： Broadcast methods for V2V communication

Advertisement Publicity Broadcast

Broadcast routing for VANETs

The purpose of emergency information is to announce an urgent event by broadcasting for surrounding vehicles.emergency-vehicle-approach traffic accident information dissemination

Broadcast outing for VANETs (cont.)

Emergency-vehicle-approachEmergency-vehicle-approach information is used to

announce the urgent event to those vehicles in front of the current vehicle, so the emergency information is only disseminated ahead.

Traffic accident information disseminationTraffic accident information is used to announce the urgent

event to those vehicles behind the current vehicle, the emergency information is only disseminated behind.

Broadcast routing for VANETs (cont.)

1. Vehicle VA broadcasts the emergency message to the restricted direction.

2. Vehicle VD does nothing.

Broadcast routing for VANETs (emergency message distribution)

3. Vehicle VB is located in the relay range, it re-broadcasts the emergency information.

4. Vehicle VC is located in notification range but not in relay range, VC just receives the emergency information and not to re-broadcast.

Broadcast routing for VANETs --emergency message distribution (cont.)

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J. N. Karaki, A. E. Kamal, "Routing techniques in wireless sensor networks: a survey", IEEE Wireless Communications, pp. 6-28, Dec. 2004.

J. Zhao and G.Cao, “VADD: vehicle-assisted data delivery in vehicular ad hoc networks,” IEEE Computer Communications, pp. 1-12, 2006.

V. Naumov and T. Gross, “Connectivity-aware routing (CAR) in vehicular ad hoc Networks,” in Proceedings of IEEE International Conference on Computer Communications, pp.1919-1927, 2007.

Y. W. Lin, Y. S. Chen and S. L. Lee, “Routing protocols in vehicular ad hoc networks: a survey and future perspectives,” Journal of Information Science and Engineering 26, pp.1-20, 2010.

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Wireless Networks Routing