Content uploaded by Khaled Elleithy
Author content
All content in this area was uploaded by Khaled Elleithy
Content may be subject to copyright.
Hierarchically Segmented Routing (HSR) Protocol for MANET
Sarosh Patel, Syed Rizvi and Khaled Elleithy
Department of Computer Science & Engineering
University of Bridgeport
Abstract
With the rapid advances in wireless and semiconductor
technologies, mobile connectivity became cheap and
ubiquitous. One of the major challenges facing Mobile
Ad-Hoc Networks (also known as MANETs) is the
absence of a proper routing protocol that provides good
scalability, low overhead, low end-to-end delays,
seamless connectivity and good quality of service. In this
paper, we propose a Hierarchically Segmented Routing
(HSR) approach to solve this problem, based on the two
well know routing protocols; the DSR and CGSR. The
paper provides a comparative analysis of the proposed
HSR protocol using a stochastic network simulation.
1. Introduction
Wireless devices are becoming ubiquitous, with the
ever increasing advances in wireless and mobile
computing. Improved protocols must be developed to
support these new mobile devices/ MANETs and to see
that these devices do not overload the existing
infrastructure network. The aim of this endeavor is to
provide anytime, anywhere connectivity for unlimited
mobile devices without overloading the associated
infrastructure networks.
Most protocols in place suffer from low quality of
service and overload the network with a large percentage
of overhead (control data) when compared to the data
packets. Any improvement in the routing protocol should
be an extendible architecture to support high number of
mobile units and at the same time ensuring a good quality
of service.
Mobile routing protocols have been attracting the
attention of a major section of the research community as
is evident from the large number of ongoing projects at
various universities and institutions on this topic.
Numerous architectures have been proposed such as the
ExScal project in OSU [1], the Terminodes project in
Switzerland [2], and the Roofnet project at MIT [3], the
Waypoint Routing Protocol [4].
2. Related work
Routing protocols form the heart of any MANET,
which haven’t evolved as much to support a large amount
of mobile units. The performance of most routing
protocols degrades with the increase in mobile nodes,
leading to higher end-to-end delay, more dropped packets
and low quality of service (QoS).
Existing routing protocols can be classified either by
their behavior or by their architecture. The existing
protocols can be broadly classified into three groups
based on their behavior; reactive protocols (on-demand),
proactive protocols (table driven) and hybrid protocols
that are a combination of reactive and proactive protocols.
If classified by architecture, the protocols are either flat or
follow a hierarchy.
2.1. Reactive and proactive protocols
Reactive protocols are passive protocols that deliver
the routing paths and topologies on-demand. Reactive
protocols only take corrective measures on reported route
failure. In contrast, proactive protocols issue topology and
route information at regular intervals, therefore taking
corrective measures before nodes encounter a dead end.
Studies have revealed that reactive protocols enjoy a
higher throughput and efficiency when compared to
proactive protocols. This is mainly due to the fact that the
proactive protocols usually flood the network with control
packets constantly issuing topology information. This
causes a lot overload on the network without delivering
much of the data. This has caused the research community
to mainly concentrate their effort on reactive protocols
more than the reactive ones.
The well known table driven (proactive) protocols are
the Dynamic Destination-Sequenced Distance-Vector
Routing Protocol (DSDV) [5], Wireless Routing Protocol
(WRP) [6], Global State Routing (GSR) [7], Fisheye State
Routing [8], Hierarchical State Routing (HSR) [10], Zone-
based Hierarchical Link State Routing Protocol (ZHLS)
[8], and Cluster Gateway Switch Routing Protocol
(CGSR) [11].
Cluster based Routing Protocol (CBRP) [8], Ad hoc
on-demand Distance Vector Routing (AODV) [12],
Dynamic Source Routing Protocol (DSR) [13],
Temporally Ordered Routing Algorithm (TORA) [15],
Associativity Based Routing (ABR) [16, 17], Signal
Stability Routing (SSR) [18] to name a few are reactive or
on-demand protocols.
Also some hybrid protocols exist such as the Waypoint
Routing Protocol [4].
2.2. Flat and hierarchical protocols
In the case of flat routing algorithms, all the
participating nodes have equal privileges and
responsibilities. Flat routing algorithms are very well
suited for small networks where the network is easily
manageable by equal functionality nodes. But, as the size
of the network increases flat routing algorithms fail to
keep up and their performance degrades with increase in
the number of nodes. This is because with the increase in
the network size it becomes increasingly difficult to have
updated routing tables. Examples of good flat routing
protocols are Ad-hoc On-demand Distance Vector
(AODV) [12] and Dynamic Source Routing (DSR) [13,
14].
In contrast, the hierarchical networks classify nodes
on a priority bases. The entire network is divided in to
sectors, similar to circles in a mobile network. In each of
the divided sectors of the networks one node is giving
higher responsibility and functionalities to maintain the
routing tables of that particular sector. Hierarchal
protocols address the important problem of scalability [8].
These sectors or clusters can be three dimensional in
practice. The Cluster Gateway Switch Routing (CGSR)
[11] protocol is a good example of this class of routing
protocols. Figure 2 shows an illustration of protocol where
the network is divided into a large number of sectors each
with a priority node.
On the downside side when the traffic increases these
high priority nodes, also known as cluster-heads, become
bottlenecks. Most data transfer and routing tables are
controlled by these cluster-heads. This also leads to
cluster-heads burning off power faster when compared to
other regular nodes.
Another advantage of hierarchical protocols is that in
case of a route failure the entire route doesn’t need to be
recalculated. Only the part of the route in the sector where
the route has been broken needs to be recalculated. But, in
case of flat networks if a route fails then the entire route
has to be recalculated from the source to the destination
which is not only time consuming but adds put a huge
load on the network. Therefore, hierarchical networks not
only address the problem of scalability, but also that of
route failure.
There are many other hierarchical routing protocols
such as the Hierarchical State Routing (HSR) [10], Zone-
based Hierarchical Link State Routing Protocol (ZHLS)
[8, 9], and Fisheye State Routing (FSR) [9] to name a few.
3. Proposed HSR protocol
Binding refers to keeping the network together,
issuing routing updates, keeping track of nodes entering
and exiting the network etc. As the size of the MANET
increases, the control traffic also increases. When nodes
are tasked with binding the network as well as data
transfer, bottlenecks are created within the network
leading not only to battery drain out but slow network
performance. Hence it is critically important to
disassociate both of these functionalities to prevent node
failures due to bottle necks and low power conditions as
seen in hierarchical models. We also have to solve the
problem of scalability. This can be done by dividing the
MANET into clusters with a cluster-head which tasked
with binding responsibilities.
Clustering within MANETs is essential as it
discourages large routing tables. Each sector can only
have a limited number of mobile nodes that the cluster-
head can support. If the number is exceeded another
cluster can be created with a cluster-head. This also limits
the control traffic within the sector. For more details on
cluster-head election mechanisms please refer [11]. The
cluster-head of each sector is connected with the cluster-
head of its immediate neighboring clusters through a
gateway node (see Figure 1). The scope of other nodes
within the cluster other than the cluster-head and the
gateway nodes is limited to the cluster itself.
Cluster-heads do not participate in data transfer as
their primary responsibility is to bind the cluster and keep
the routing tables updated. This also saves the cluster-
head from power drain and avoids the creation of
bottlenecks with the route path which would occur due to
handling of two tasks. However, the cluster-head can
Figure 1: Shows a hierarchical division of a network under
Cluster Gateway Switch Routing [11]
participate only under special conditions such as when it
is either source or destination or no other node is active
within the cluster. Also when, the participating node
within the route becomes inactive in between the data
transfer.
In case of a data transmission from one end of the
MANET to the other end spanning many clusters, a route
is established from the source to the destination. The
cluster-head of each cluster nominates active nodes from
within cluster to form a part of the route. The choice of
the participating nodes is based on the information about
the node with the cluster-head. Since MANETs and
therefore clusters are groups of non-homogeneous mobile
devices, the cluster-heads can choose mobile units
depending on what data rates the active nodes are capable
of supporting.
3.1. Routing in HSR protocol
Routes can be of two types; first spanning just one
cluster, and the second, spanning multiple clusters. In the
case of routes spanning multiple clusters, the entire route
is divided into segments. This active route is
hierarchically managed using two routing protocols; one
at the inter-segment level and the other at the intra-
segment level.
The entire route from the source to the destination has
nodes involving multiple clusters are divided into
segments. A segment is a part of a route that forms a part
of a definite cluster. It is the route between two gateway
nodes or the route between the gateway node and the
source node or the destination node. In other words, a
route is a connection of one or more segments and
segment has a segment-head. The routing information
needed to maintain the route is provided to the segment-
head node by the cluster-head of that cluster. The entire
route is reduced to a one dimensional connection of
segments spanning many clusters from the source to the
destination. As shown in Figure 2 cluster-head nodes do
not form a part of the routing path. The dark nodes shown
in the Figure 2 are cluster gateway nodes that interface
two neighboring clusters. Also note that there are no
Cluster-head nodes participating in the route. While DSR
specifies the complete route from source to destination,
hence the large overhead. In HSR only the addresses of
the gateway nodes is specified as shown in Figure 3.
Figure 3 shows a comparison of routing with header
between HSR and CGSR at the packet travels from
Source ‘S” to the destination ‘D’. Note that CGSR is
implemented at the intra-cluster level and DSR at the
inter-cluster level.
Hierarchically, managing routes can be advantageous
when it comes to packet overhead and minimizing the
end-to-end delay. In flat routing protocols, whenever a
participating node drops out or becomes inactive the
entire route needs to be established. As the size of the
MANET increases routes become longer and break more
often. This causes immense wastage of resources and
time. Where as in the case of the proposed solution,
whenever a node failure occurs for any reason it can be
locally repaired without having to discard the complete
route path. This saves a lot of time and greatly reduces the
unnecessary network overhead. Hence two protocols are
amalgamated in this hierarchy by implementing CGRP at
the intra-segment level is and DSR at the inter-segment.
Cluster-head Gateway Switch Routing (CGSR)
Protocol is a hierarchical protocol based upon the DSDV
Routing algorithm [5]. The algorithm works in a very
Figure 2: Route segmentation
DSR Route
1. At Source S – D R4 G3 R3 G2 R2 G1 R1
2. At G1 – D R4 G3 R3 G2 R2
3. At G2 – D R4 G3 R3
4. At G3 – D R4
HSR Route
1. At Source S – D G3 G2 G1 R1
2. At G1 – D G3 G2 R2
3. At G2 – D G3 R3
4. At G3 – D R4
Figure 3: An illustration of DSR protocol with respect to
the proposed HSR protocol and CGSR
simple manner. The source transmits the data to the
cluster-head of its cluster which in turn transmits it to the
gateway of the destination cluster. The destination cluster-
head transmits it to the destination node. There are
numerous optimized cluster-head election mechanisms
[11]. On receiving a packet, a node finds the nearest
cluster-head along the route to the destination according
to the cluster member table and the routing table. Then the
node consults its routing table to find the next hop in order
to reach the cluster-head selected in step one and transmits
the packet to that node. This causes the cluster-head node
to become a bottleneck in the network and rapidly lose
power.
The Dynamic Source Routing (DSR) Protocol is a
source routed reactive protocol. The DSR protocol is a
learning protocol it generates routes based on the reply to
the route packet request. The node updates its entry when
it learns about a new node. Each node implementing the
DSR maintains a cache of addresses. When the node
learns about a new node it stores its address in the cache.
The important feature of the DSR route is that it gives the
address of each node through which it should traverse to
reach the final destination. The packet header in the case
of DSR is usually large.
By hierarchically combining CGSR and DSR we can
exploit the advantages of both the protocols. The
scalability greatly increased in spite of the limitation of
DSR because DSR is used on an inter-segment level,
hence the maximum route that can be supported is one
spanning 200 clusters and not just 200 nodes. Also the
overhead is very low as CGSR is used on intra-segment
level which leads to the computation of the shortest route
within the cluster. For reducing the load on the cluster-
head node mapping of each node with respect to the
cluster node is not done. The cluster periodically
broadcast routing information for nodes with respect to
the nearest gateway node. Since there are always more
than one gateway node the load is also uniformly
distributed within the cluster.
4. Implementation of the proposed algorithm
If a data needs to be transferred from one end of the
MANET to the other, the source sends a request to its
respective cluster-head of that cluster. An implementation
of the proposed algorithm is illustrated in Figure 4. The
cluster-head then forwards the request to cluster-heads of
the neighboring nodes. The cluster-heads of clusters that
which to participate in the data transfer reply back with
node addresses of nodes that are active and willing to
participate in the route.
Propagation of the route establishment request is
between the cluster-heads only, which decide on the basis
of the instantaneous information able to them. By limiting
the propagation of the route request to the cluster-heads
only the traffic is greatly reduced, because as seen in other
protocol the request keeps on propagating due to
retransmission from nodes throughout the network until
the TTL of the request has expired causing considerable
traffic.
Before the source transmits data, it must setup proper
headers to be used by the respective protocols. Firstly,
depending upon the routing information received for its
cluster-head, the source node attaches the routing
information of participation inter-cluster gateway nodes
from the source to the destination. This header is utilized
by the inter-segment DSR protocol. Next the source adds
intra-segment routing information for the packet to reach
the first gateway node.
By adding headers in this fashion two purposes are
served. First CGRS gets the route to the nearest gateway.
Second the DSR protocol gets the next hop to inter-
segment gateway node. The inter-segment header gets
reduced with each hop where as the intra segment header
is renewed at each gateway node. A new inter-segment
header is appended while entering a new cluster. Inter-
segment routing (DSR) occurs at the gateway nodes while
the inter-segment routing occurs at both gateway nodes
and cluster nodes until the data packet reaches the
Figure 4: Routing in HSR protocol
destination.
If both the source and the destination are within the
same cluster, the entire route is just one segment hence
only CGSR is implemented. If a route spanning multiple
clusters is established, such that there is only one
participating node from each cluster, then only DSR will
be implemented.
5. Performance analysis of the HSR
algorithm
We have simulated the proposed protocol with
varying number of nodes using a stochastic model with
Gaussian distribution to generate network failure
conditions, such as node failures, route failure etc. The
simulation was implemented in C++. We examined
simulation one to test the scalability of the protocol and
the next to test the network overhead generated by the
protocol. These are the two main objectives we designed
the algorithm to meet; scalability and network overhead.
Figure 5 provides comparison among the HSR, DSR
and CGSR protocols for the number of control packets
generated for marinating the network. As shown in the
Figure 6, it is difficult to maintain the network with a non-
clustered architecture. DSR generates a lot of control
packets to bind the network. This proves the fact that flat
architectures can handle large amount of nodes.
But CGSR and HSR are far better that DSR due to
the fact that they are hierarchical protocols. HSR is the
same as CGSR when it comes to network maintenance, as
shown in Figure 6.
Figure 6 shows the percentage of packets delivered
by each protocol. HSR is the best of the three protocols.
As the number of nodes increases the DSR protocol fails
very badly. DSR being a flat protocol, with the increase in
the number of nodes the routing becomes extremely
difficult due to nodes failing randomly.
CGSR and HSR protocols perform equally well when
the numbers of nodes are small; there is no considerable
difference in performance. The only difference in HSR is
that routing tables are not with respect to the cluster-head
but with respect to the nearest gateway node. With the
increase in the number of nodes routing becomes
relatively easier with HSR protocol than CGSR.
6. Conclusion
In this paper we have introduced a new hierarchically
segmented protocol for routing data within MANETs. The
new protocol is based on CGSR and DSR protocols for
segmented routing over gateway nodes. When compared
to other protocols, the new routing algorithm is highly
scalable due to its clustered hierarchical architecture,
provides excellent scalability, and generates less network
overhead and low end-to-end delays.
7. References
[1] ExScal Project, http://www.cast.cse.ohio-
state.edu/exscal/, 2005.
[2] Terminodes Project, http://www.terminodes.org/,
2005.
[3] Roofnet Project,” http://pdos.csail.mit.edu/roofnet/,
2005.
Figure 5: No of MANET Nodes Vs Control Packets
Figure 6: No of MANET Nodes Vs Percentage of packets
delivered
[4] Rendong Bai and Mukesh Singal, “DOA : DSR over
AODV Routing for Mobile Ad Hoc Networks”, IEEE
transactions on Mobile Computing, Vol. 5, No 10,
Oct. 2006.
[5] C.E. Perkins and P. Bhagwat, "Highly Dynamic
Destination-Sequenced Distance-Vector Routing
(DSDV) for Mobile Computers", Comp. Comm.
Rev., Oct. 1994, pp.234-244.
[6] S. Murthy and J.J. Garcia-Luna-Aceves, "An
Efficient Routing Protocol for Wireless Networks",
ACM Mobile Networks and App. J., Special Issue on
Routing in Mobile Communication Networks, Oct.
1996, pp. 183-97.
[7] Tsu-Wei Chen and Mario Gerla, "Global State
Routing: A New Routing Scheme for Ad-hoc
Wireless Networks" Proc. IEEE ICC'98.
[8] A. Iwata, C.C. Chiang, G. Pei, M. Gerla, and T.-W.
Chen, "Scalable Routing Strategies for Ad Hoc
Wireless Networks" IEEE Journal on Selected Areas
in Communications, Special Issue on Ad-Hoc
Networks, Aug. 1999, pp.1369-79.
[9] Mingliang Jiang, Jinyang Li, Y.C. Tay, "Cluster
Based Routing Protocol" August 1999 IETF Draft.
[10] M Joa-Ng and I.-T. Lu, "A Peer-to-Peer zone-based
two-level link state routing for mobile Ad Hoc
Networks" IEEE Journal on Selected Areas in
Communications, Special Issue on Ad-Hoc Networks,
Aug. 1999, pp.1415-25.
[11] C. C. Chiang, "Routing in Clustered Multihop,
Mobile Wireless Networks with Fading Channel"
Proc. IEEE SICON'97, Apr.1997, pp.197-211.
[12] Charles E. Perkins, Elizabeth M. Royer, Samir R.
Das, "Ad Hoc On-demand Distance Vector Routing",
October 99 IETF Draft.
[13] David B. Johnson, Davis A. Maltz, "Dynamic Source
Routing in Ad Hoc Networks", Mobile Computing, T.
Imielinski and H. Korth, Eds., Kulwer, 1996, pp. 152-
81.
[14] David B. Johnson, Davis A. Maltz, "The Dynamic
Source Routing Protocol for Mobile Ad Hoc
Networks”.
[15] VD Park and MS Corson "A highly adaptive
distributed routing algorithm for mobile wireless
networks", Proc. INFOCOM'97, Apr. 1997, 9 pages.
[16] Chai-Keong Toh, "A novel distributed routing
protocol to support Ad hoc mobile computing" Proc.
1996 IEEE 15th Annual Int'l. Phoenix Conf. Comp.
and Commun., Mar. 1996, pp. 480-86.
[17] C.K. Toh, "Long-lived Ad-Hoc Routing based on the
concept of Associativity" March 1999 IETF Draft.
[18] R. Dube et al., "Signal Stability based adaptive
routing for Ad Hoc Mobile networks", IEEE Pers.
Comm., Feb. 1997, pp. 36-45.
