Routing in Mobile Ad hoc Networks

Routing in Mobile Ad hoc Networks
Sayed Chhattan Shah
Department of Information Communications Engineering
Hankuk University of Foreign Studies Korea
www.mgclab.com

Acknowledgements
 Computer Networks, Routing protocols in ad hoc networks: A survey

Wireless Ad Hoc Network
 A decentralized type of wireless networks
 Ad hoc because it does not rely on a pre existing network
infrastructure such as routers or access points

Mobile Ad Hoc Network
 A type of wireless ad hoc network
 Infrastructureless network of mobile devices
 Nodes are free to move independently in any direction
o Links to other devices are changed frequently

Multi hop Mobile Ad Hoc Network
 Nearby users directly communicate not only to exchange their own
data but also to relay the traffic of other network nodes that cannot
directly communicate

Routing
 Routing process of selecting paths in a network along which to
send network traffic
 Routing algorithms determine the specific choice of route

Design elements that contribute to a routing strategy
Performance Criteria
Number of hops
Cost
Delay
Throughput
Decision Time
Packet (datagram)
Session (virtual circuit)
Decision Place
Each node (distributed)
Central node (centralized)
Originating node (source)
Network Information Source
None
Local
Adjacent node
Nodes along route
All nodes
Network Information Update Timing
Continuous
Periodic
Major load change
Topology change

Routing in MANET
 No dedicated router nodes
 Local node mobility
 Global node mobility
 Limited resources
 Dynamic network environment
 Limited power
 Uncertainty of path quality

Routing in MANET
 Basic goals of routing protocols
o Maximize
 throughput
 network capacity
 network lifetime
o Minimize
 packet loss and drop
 control overhead
 energy consumption
 delay

Reactive routing protocols
 Route is created only when the source requests a route to a
destination
o Route discovery process
o Route maintenance

 Dynamic source routing
 Route request
o Broadcasts a route request packet to its neighbors
o Every node within a broadcast range adds their node id to the route request
packet and rebroadcasts
o Every node maintains route cache - If a route is found in the route cache,
the node will return a route reply message to the source node rather than
forwarding the route request message further
o DSR assumes that the path obtained is the shortest since it takes into
consideration the first packet to arrive at the destination node

 Route reply messages
• Sent to the source which contains the complete route from the source to the
destination
• The source caches this route

o Route maintenance
 Route error and acknowledgements packets
• DSR ensures the validity of the existing routes based on the
acknowledgements received from the neighboring nodes
• Acknowledgement packets also include passive
acknowledgements as the node overhears the next hop neighbor is
forwarding the packet along the route to the destination
• A route error packet is generated when a node encounters a
transmission problem which means that a node has failed to
receive an acknowledgement

 Temporally ordered routing algorithm
o Finds multiple routes from a source to a destination in a highly dynamic
mobile networking environment
o Reduces communication overhead
 React only when necessary – not to every topological change
o The protocol has three basic functions
 Creation of a route from a source to a destination
 Maintenance of the route
 Deletion of the route when the route is no longer valid.
o TORA builds and maintains a Directed Acyclic Graph (DAG) rooted at a destination

 Directed Acyclic Graph
o A directed graph with no cycles
o A DAG is rooted at the destination if the destination is the only node
with no downstream nodes - no links lead out of the destination. Such a
DAG is often called a destination oriented DAG
o Creation of such a DAG from a source to a destination would contain
multiple routes to the destination

 Temporally ordered routing algorithm
o The idea is to first build a DAG from the source to the destination
o Then as links fail, it might be necessary to re-compute a DAG in
order to find a route
o If network gets partitioned, deletion of routes is required.
o TORA uses three kinds of messages
 The QRY message for creating a route
 The UPD message for both creating and maintaining routes
 The CLR message for erasing a route

 TORA protocol
o Multiple paths created
o Good in dense networks
o Not scalable by any means
o Does not use a shortest path solution

 Associativity-based routing
o Route stability as the most important factor in selecting a route
o To determine stability, each node maintains a tick value for each neighbors, which is
increased by one every time a HELLO message is received from the neighbor
 Preemptive routing in ad hoc networks
o Attempts to initiate the discovery process of an alternate route just before the probable
route failure
o Generates a preemptive warning when the signal power of the packet received drops
below a predefined preemptive threshold
o Correct setting of the preemptive threshold is the main challenge

 Ad hoc QoS on-demand routing protocol
o Objective is to provide QoS support in terms of bandwidth and end-to-end delay
o Supports following features
 Accurate measurement of bandwidth availability in the shared wireless channel
and accurate measurement of end-to-end delay
 Distributed routing algorithm that adapts with the dynamic environment
 Resource reservation that guarantees the available resources
 Efficient resource release upon route adjustment
 Instant QoS violation detection
 Fast and efficient route recovery

 Ad hoc QoS on-demand routing
o Bandwidth control
 Because of the shared medium, a node can successfully use the channel only
when all its neighbors do not transmit and receive packets at the same time
 Neighborhood traffic and topology information
• B, the raw data rate of the node
• Total amount of traffic in node’s wireless channel
• The amount of bandwidth that should be reserved
o Assumes all the nodes have identical data rate and transmission range

 Ad hoc QoS on-demand routing
o Bandwidth estimation
 In order to estimate available bandwidth, existing total channel traffic load is
calculated

 The flow oriented routing protocol
o FORP aims to transmit real-time data streams
o Uses mobility information of nodes to determine future route changes
 Each node appends its own ID and the Link Expiration Time LET of the last
link in which the message was received before forwarding to the next hop
 Destination contains the list of all the routes travelled and the LETs for each
hop which is used to calculate route expiration time
 Intermediate nodes continue adding the LETs to the forwarded packets to
enable the destination to keep track of the RET prediction
 The nodes are assumed to have a common time reference from GPS

 QoS routing with traffic distribution
o QoS is a collection of characteristics or constraints that a connection must guarantee
to meet the requirements of an application
o Assumes heterogonous network environment
o Makes use of a mobile routing backbone to dynamically distribute traffic within the network
and to select the route that can support best a QoS connection between a source and its
destination
o Nodes are classified as either QoS routing nodes (QRN), simple routing nodes (SRN) or
transceiver nodes (TN)
 A mobile routing backbone is created using all nodes having routing capabilities
 QoS support is realized by relaying packets having special requirements to nodes rich
in resources and connected through stable links

 QoS routing with traffic distribution
o Four QoS support metrics are used to differentiate nodes in the network and
identify the ones that can take part in the MRB
 A node’s Static resources capacity SRC computed by the weighted sum of the
size of the node packet queues, speed of the CPU, power of the battery and the
maximum available bandwidth.
 Dynamic resources availability DRA indicates the current load in the resource
usage of a node. The usage rate of the static resources are used to calculate the
available dynamic resources.
 Neighborhood quality NQ the number of nodes in the neighborhood of a node
which can successfully forward packets.
 Link quality and stability LQS the power of signal received and the statistical
stability of its links.

 Source routing with local recovery
o Route discovery in on-demand routing is typically performed via network-
wide flooding, which consumes a substantial amount of bandwidth
o To address the problem three types of approaches have been proposed
 Limited broadcast: route discovery is initiated by relay nodes. The
broadcast range is limited and does not flood the whole network
 Multipath routing: Multiple routes are discovered and cached in a single
route discovery
 Local error recovery: Route errors are handled at a relay node instead
of relying on end-to-end error recovery at the sender

 Source routing with local recovery
 Utilizes both route caches and local error recovery
 To recover from a route failure, a node first salvages a route by searching its
route cache for an alternate route to the destination
 If the node is not able to repair the route from its route cache, it initiates bypass
recovery by querying its neighbors to see if they have a link to any nodes on the
downstream route to the destination

Table-driven routing protocols
 Maintain up-to-date information of routes from each node to every
other node in the network
 Routing information is stored in the routing table of each node and
route updates are propagated throughout the network to keep the
routing information as recent as possible

 Destination-Sequenced Distance-Vector
o Every mobile node maintains a routing table which contains the possible
destinations in the network together with their distance in hop counts
o Routing updates are periodically forwarded throughout the network
 A full dump sends the entire routing table to the neighbors
 Incremental updates are smaller and are used to transmit those entries
from the routing table which have changed since the last full dump
update
o When a network is stable, incremental updates are forwarded and full dump
are usually infrequent

 Optimized link state routing
o Each node selects a subset of nodes in its neighborhood, which
retransmits its messages
o These selected nodes are named Multi Point Relays - MPRs
o The selection condition is the following:
 Each two hop neighbor node must have at least one bidirectional link toward a node
inside the MPR set
 So the MPR nodes must permit to reach all the two hop neighbors
o A node retransmits a received message only if it is part of the MPRs

 Optimized link state routing

Hybrid routing protocols
 Zone routing protocol
o Proactive mechanism of node discovery within a node’s
immediate neighborhood while inter-zone communication is
carried out by using reactive approaches
o Each node individually creates its own neighborhood which it
calls a routing zone
 The zone is defined as a collection of nodes whose minimum distance in
hops from the node in question is no greater than a value that is called the
“zone radius”
 Note that routing zones of nodes might overlap heavily

o Local
o Remote
 Route request sent to border nodes
• Border nodes reply if they know a route
 Otherwise border node bordercasts to it's border nodes

Location-aware routing protocols
 Location-aware routing schemes in mobile ad hoc networks assume
that the individual nodes are aware of the locations of all the nodes
within the network

Location-aware routing protocols
 Location-aided routing
o Utilizes location information to minimize the search space for
route discovery towards the destination node
o Relies on GPS
 Based on location of the destination node and its mobility characteristics
such as the direction and speed, source sends route requests to nodes only
in the expected zone of the destination node
 If the source node has no information about the speed and the direction of
the destination node, the entire network is considered as the expected zone

40
Basic Idea
 Route discovery using flooding algorithm:
C
D
B
S
E
A
X

41
Basic Idea
 Location information
o Minimize the search zone
o Reduce the number of routing messages
 Speed and direction information
o More minimization of the search zone
o Increases the probability to find a node

42
 Each node knows its current location
 Uses last known location information and average speed to create
o an expected zone for destination
 region where source node S thinks that the destination node D may
contained at some time t – only an estimate made by S
o a request zone for flooding of routing message
Basic Idea

43
 Expected zone
o S knows the location of D at time t0
o Current time is t1
o The location of D at t1 is the expected zone
Basic Idea

44
 Request zone
o For route request
o Node forwards a route request only if it belongs to the request
zone
o If a route is not discovered within the timeout period, S initiates a
new route discovery with expanded request zone
Basic Idea

46
LAR Scheme 1
 The request zone is rectangular in shape
 Assume S knows that the node D was at location (Xd, Yd) at time t0
 Assume S knows the average speed v with which D can move
 From above two, S defines the expected zone at time t1 with radius
R = v(t1- t0) centered at location (Xd, Yd)
 The request zone is the smallest rectangle that includes current
location S and the expected zone such that the sides of the rectangle
are parallel to the X and Y axes

Example 1
Network Space
Expected
zone
A (Xs, Yd+R)
(Xd, Yd)
Request
zone
B (Xd+R, Yd+R)
S (Xs, Ys)
D (Xd+R, Ys)
R
Source node outside the expected zone
I (Xi, Yi)J (Xj, Yj)
D

Example 2
Network Space
Expected
zone
A (Xd-R, Yd+R)
(Xd, Yd)
S (Xs, Ys)
Request zone
B (Xd+R, Yd+R)
C (Xd-R, Yd-R) D (Xd+R, Yd-R)
R
Source node within the expected zone
D

Multipath protocols
 Multipath routing protocols create multiple routes from source to
destination
 Ad hoc on-demand multipath distance vector routing AOMDV
o each route request and route reply packet arriving at a node is
potentially using a different route from the source to the
destination.

Hierarchical protocols
 Hierarchical ad hoc routing protocols build a hierarchy of nodes,
typically through clustering techniques
 Nodes at the higher levels of the hierarchy provide special services,
improving the scalability and the efficiency of routing
o Creation of cluster
o Election of cluster head

Geographical multicast protocols
 Geographical multicast routing is a variant of multicast where the
goal is to route the packets coming from a source to destinations
located within a specific geographical region

Power Aware Protocols
 Create a efficient route between source node and destination node
o Active
 Transmission power control
 Load distribution
o Inactive period
 Sleep mode or simply turns it off when there is no data to
transmit or receive

Energy aware routing protocol
 Aims to design an efficient energy aware routing scheme for MANETS
 Uses variable range transmission
 Friis equation: 𝑃𝑡=
𝑃𝑟
𝐺𝑟𝐺𝑡
4𝜋𝑅
𝜆
2
53
Receiving RREP
Store the location
N_hop x and N_hop Y (node 4)
1
2
3
4
D

PLR routing protocol
 Aims to minimize transmission power
 Assumes that a source node has neighbor node and destination’s
location
54

Power-aware source routing protocol for mobile ad hoc networks
 Based on DSR routing protocol
 Solves the problem of finding a route 𝝅 𝐚𝐭 𝐫𝐨𝐮𝐭𝐞 𝐝𝐢𝐬𝐜𝐨𝐯𝐞𝐫𝐲 𝐭𝐢𝐦𝐞 𝐭 𝐬𝐮𝐜𝐡 𝐭𝐡𝐚𝐭 𝐭𝐡𝐞 𝐟𝐨𝐥𝐥𝐨𝐰𝐢𝐧𝐠 cost
function is minimized
55

 Route discovery
o All nodes except the destination calculate their link cost
 Add it to the path cost in the header of the RREQ packet
a
b
c f
e
Min-cost=a-b-e
Timer
Min-cost=a-b-e-dd
Power-aware source routing protocol for mobile ad hoc networks

Routing in Mobile Ad hoc Networks

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