routing in mobile ad hoc networks
TRANSCRIPT
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
Reactive routing protocols
Dynamic source routing
o Route discovery process
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
Reactive routing protocols
Dynamic source routing
o Route discovery process
Route reply messages
• Sent to the source which contains the complete route from the source to the
destination
• The source caches this route
Reactive routing protocols
Dynamic source routing
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
Ad hoc QoS on-demand routing
o Bandwidth estimation
In order to estimate available bandwidth, existing total channel traffic load is
calculated
Reactive routing protocols
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
Reactive routing protocols
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
Reactive routing protocols
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.
Reactive routing protocols
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
Reactive routing protocols
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
Table-driven routing protocols
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
Table-driven routing protocols
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
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
Hybrid routing protocols
Zone routing protocol
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
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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
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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
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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
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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
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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
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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
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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-d d
Power-aware source routing protocol for mobile ad hoc networks
