• Mobility support such as Mobile IP, DHCP,
Cellular phone networks relies on existence of at
least some infrastructure.
• For example cellular phone network requires base
stations, infrastructure networks etc.
• Ad-hoc network is used in situations where users
of a network cannot rely on infrastructure, it is
expensive, or there is none at all.
• In these situations mobile ad-hoc network is used.
• Mobile ad-hoc networks should be mobile and use
• Single-hop: All partners max. one hop apart
• Bluetooth piconet, PDAs
in a room, gaming devices.
• Multi-hop: Cover larger distances,
• Bluetooth scatternet,
TETRA police network,
• Instant infrastructure: Unplanned meetings,
spontaneous interpersonal communication.
• Disaster relief: infrastructure break down in
disaster areas, hurricanes cut phone and power
lines. Flood destroy base stations. In these cases
extremely fast and reliable ad-hoc network can be
• Remote areas: can be used where
infrastructure is expensive to set up ex. Sparsely
Mobile Ad-hoc Networking
And mobile IP
Router End system
• Routing of data is most difficult issues in ad-
• In wireless network with infrastructure
support a base station always reaches mobile
nodes, but in ad-hoc network this is not the
• Destination node may be out of range of a
source node transmitting packets.
• In ad-hoc network each node must be able to
forward data for other nodes.
• This create additional problems, such as Link
don't have same characteristics in both
time = t1 time = t2
Difference between wired networks
and ad-hoc wireless networks.
1. Asymmetric links: Quality of connection in
both direction may be different
2. Redundant links: Many redundant links
4. Dynamic topology: frequent changes of
connections, connection quality, participants
Difficulties in design of ad-hoc routing
• Traditional algorithm know for wired network
may not work efficiently or fail completely
because these are not design with highly
dynamic topology, asymmetric links, or
interference in mind.
• Additional information such as connectivity or
interference is needed for finding best path.
• Centralized approach cannot be used.
1.) Destination sequence distance vector(DSDV)
• Enhanced version of distance vector routing
for ad-hoc network.
• DVR is used as routing information protocol in
• In DVR each node exchanges its routing table
periodically with its neighbor, this strategy is
not used in case of wireless ad-hoc networks,
due to rapidly changing topology.
• DSVR adds two things to distance vector
1. Sequence number :
2. Damping :
Part of routing table for DSDV
Destination Next hop Metric Sequence no. Instal time
N1 N1 0 S1–321 T4–001
N2 N2 1 S2–218 T4–001
N3 N2 2 S3–043 T4–002
N4 N4 1 S4–092 T4–001
N5 N4 2 S5–163 T4–002
2. Dynamic source routing
• DSR divide task of routing into two separate
1. Route discovery: A node only tries to discover a
route to a destination if it has to send something
to this destination and there is currently no
2. Route maintenance: If a node is continuously
sending packets via a route, it has to make sure
that the route is held upright. As soon as a node
detects problems with the current route, it has
to find an alternative
Working of DSR
• If a node needs to discover a route, it broadcasts a
route request with a unique identifier and the
destination address as parameters. Any node that
receives a route request does the following.
1. If the node has already received the request (which
is identified using the unique identifier), it drops the
2. If the node recognizes its own address as the
destination, the request has reached its target.
3. Otherwise, the node appends its own address to a
list of traversed hops in the packet and broadcasts
this updated route request.
• Using this approach, the route request collects a list
of addresses representing a possible path on its way
towards the destination.
• As soon as the request reaches the destination, it can
return the request packet containing the list to the
receiver using this list in reverse order.
• condition for this is that the links work bi-
directionally. If this is not the case, and the
destination node does not currently maintain a route
back to the initiator of the request, it has to start a
route discovery by itself.
• The destination may receive several lists containing
different paths from the initiator. It could return the
best path, the first path, or several paths to offer the
initiator a choice.
Applying route discovery to the example in fo a
route from N1 to N3 at time t1 results in the
time = t1
1. N1 broadcasts the request ((N1), id = 42, target = N3), N2 and
N4 receive this request.
2. N2 then broadcasts ((N1, N2), id = 42, target = N3), N4
broadcasts ((N1, N4), id = 42, target = N3). N3 and N5 receive
N2’s broadcast, N1, N2, and N5 receive N4’s broadcast.
3. N3 recognizes itself as target, N5 broadcasts ((N1, N2, N5), id
= 42, target = N3). N3 and N4 receive N5’s broadcast. N1, N2,
and N5 drop N4’s broadcast packet, because they all recognize
an already received route request (and N2’s broadcast reached
N5 before N4’s did).
4. N4 drops N5’s broadcast, N3 recognizes (N1, N2, N5) as an
alternate, but longer route.
5. N3 now has to return the path (N1, N2, N3) to N1. This is
simple assuming symmetric links working in both directions. N3
can forward the information using the list in reverse order.
The assumption of bi-directional links holds for many ad-hoc
networks. However, if links are not bi-directional, the
scenario gets more complicated. The algorithm has to be
applied again, in the reverse direction if the target does not
maintain a current path to the source of the route request.
1. N3 has to broadcast a route request ((N3), id = 17,
target = N1). Only N5 receives this request.
2. N5 now broadcasts ((N3, N5), id = 17, target = N1),
N3 and N4 receive the broadcast.
3. N3 drops the request because it recognizes an
already known id. N4 broadcasts ((N3, N5, N4), id = 17,
target = N1), N5, N2, and N1 receive the broadcast.
4. N5 drops the request packet, N1 recognizes itself as
target, and N2 broadcasts((N3, N5, N4, N2), id = 17,
target = N1). N3 and N5 receive N2’s broadcast.
5. N3 and N5 drop the request packet
• Now N3 holds the list for a path from N1 to
N3, (N1, N2, N3), and N1 knows the path
from N3 to N1, (N3, N5, N4, N1). But N1 still
does not know how to send data to N3! The
only solution is to send the list (N1, N2, N3)
with the broadcasts initiated by N3 in the
reverse direction. This example shows clearly
how much simpler routing can be if links are
Route maintenance is DSR
• After a route has been discovered, it has to be
maintained for as long as the node sends packets along
this route. Depending on layer two mechanisms,
different approaches can be taken:
1. If the link layer uses an acknowledgement (as, for
example, IEEE 802.11) the node can interpret this
acknowledgement as an intact route.
2. If possible, the node could also listen to the next
node forwarding the packet, so getting a passive
3. A node could request an explicit acknowledgement.
Conclusion of DSR
Dynamic source routing offers benefits
compared to other algorithms by being much
more bandwidth efficient, problems arise if the
topology is highly dynamic and links are
Overview of ad-hoc routing protocols
• Hong (2002) separates routing algorithms into
1. flat routing,
2. hierarchical routing,
3. geographic-position-assisted routing.
Flat ad-hoc routing
• Flat ad-hoc routing protocols comprise those
protocols that do not set up hierarchies with
clusters of nodes, special nodes acting as the
head of a cluster, or different routing algorithms
inside or outside certain regions.
• All nodes in this approach play an equal role in
• The addressing scheme is flat.
• This category again falls into two subcategories:
proactive and reactive protocols.
• Proactive type of protocols maintains fresh lists
of destinations and their routes by periodically
distributing routing tables throughout the
• The main disadvantages of such algorithms are:
1. Respective amount of data for maintenance.
2. Slow reaction on restructuring and failures.
• Examples of proactive algorithms are:
1. Optimized Link State Routing Protocol (OLSRP)
2. Destination Sequence Distance Vector (DSDV)
• reactive protocols finds a route on demand by
flooding the network with Route Request
• The main disadvantages of such algorithms are:
1. High latency time in route finding.
2. Excessive flooding can lead to network clogging.
• Examples of on-demand algorithms are:
1. Ad hoc On-demand Distance Vector(AODV)
2. Dynamic Source Routing
3. Flow State in the Dynamic Source Routing
Hierarchical ad-hoc routing
• Algorithms such as DSDV, AODV, and DSR only
work for a smaller number of nodes and depend
heavily on the mobility of nodes.
• For larger networks, clustering of nodes and
using different routing algorithms between and
within clusters can be a scalable and efficient
• The advantage is that if the topology within a
cluster changes, only nodes of the cluster have to
be informed. Nodes of other clusters only need
to know how to reach the cluster.
Clustering of ad-hoc networks
• Clusters can be combined to form super clusters etc.,
building up a larger hierarchy.
• Using this approach, one or more nodes can act as
cluster heads, representing a router for all traffic
to/from the cluster.
• All nodes within the cluster and all other cluster heads
use these as gateway for the cluster.
• Figure shows an ad-hoc network with interconnection
to the internet via a base station. This base station
transfers data to and from the cluster heads. In this
example, one cluster head also acts as head of the
super cluster, routing traffic to and from the super
• Different routing protocols may be used inside and
• Some are
1. CGSR – Clusterhead-Gateway Switch
2. HSR – Hierarchical State Routing
3. LANMAR – Landmark Ad Hoc Routing
4. ZRP – Zone Routing Protocol
• If mobile nodes know their geographical position this can
be used for routing purposes.
• This improves the overall performance of routing
• One way to acquire position information is via the global
positioning system (GPS).
• Mauve (2001) gives an overview of several position-based
ad-hoc routing protocols.
• some of them are
1. DREAM – Distance Routing Effect Algorithm for Mobility
2. GeoCast – Geographic Addressing and Routing
3. GPSR – Greedy Perimeter Stateless Routing
4. LAR – Location-Aided Routing