Gugrajah_Yuvaan_ Ramesh_2003.pdf

Routing Protocols for Ad Hoc Networks Chapter 2
There are three kinds of nodes in a cluster: cluster heads, gateways and internal
nodes. The cluster head maintains topological information of the nodes in the cluster
and acts as a local coordinator of transmissions within the cluster. The cluster head
also summarizes link state information within its cluster and propagates it to the
neighbouring cluster heads via the gateway nodes. The knowledge of connectivity
between neighbour cluster heads leads to the formation of the next higher cluster
level. A virtual link is formed between two cluster heads using the internal nodes and
gateways nodes between the cluster heads. Nodes within a cluster exchange virtual
link state information as well as summarized lower level cluster information.
The Hierarchical Identification (HID) is used to identify each node and consists of a
sequence of MAC addresses of the nodes from the top hierarchy to the node itself.
For example, in Figure 2-10, the HID of node 10 is . For the delivery of a
packet from node 5, with HID(5) = to node 10 with HID(10) =,
the packet is first forward to node 1 (top hierarchy) which uses the virtual link
(1,6,2,8,3) to deliver the packet to node 3. Node 3 then delivers the packet to node 10
along the downwards hierarchical path.
The drawback of HSR is that nodes have to maintain longer hierarchical addresses
and have to continuously update the cluster hierarchy and hierarchical address as
nodes move. Since a continuously changing hierarchical address makes it difficult to
locate and keep track of nodes, logical partitioning is used in HSR. Logical
partitioning involves using subnets of the network, each with its own home agent to
manage membership. The subnets correspond to a particular user group, for example,
students from the same class or tanks in the same battalion. Each member of a logical
subnet knows the HID of its home agent from the routing table and registers its own
HID with the home agent. The registration with the home agent is both event driven
and time driven. It is assumed [Iwata99] that since members of the same subnet
would move as a group, registration overhead is modest because the members will
tend to reside in neighbouring clusters. When a source node requires a route to a
destination it uses the logical address of the destination to send the packet to the
home agent of the destination. The home agent redirects the packet to the destination,
which can then continue communication using the newly acquired and current HID
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