Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf
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Routing Protocols for Ad Hoc Networks Chapter 2<br />
There are three kinds of nodes in a cluster: cluster heads, gateways and internal<br />
nodes. The cluster head maintains topological information of the nodes in the cluster<br />
and acts as a local coordinator of transmissions within the cluster. The cluster head<br />
also summarizes link state information within its cluster and propagates it to the<br />
neighbouring cluster heads via the gateway nodes. The knowledge of connectivity<br />
between neighbour cluster heads leads to the formation of the next higher cluster<br />
level. A virtual link is formed between two cluster heads using the internal nodes and<br />
gateways nodes between the cluster heads. Nodes within a cluster exchange virtual<br />
link state information as well as summarized lower level cluster information.<br />
The Hierarchical Identification (HID) is used to identify each node and consists of a<br />
sequence of MAC addresses of the nodes from the top hierarchy to the node itself.<br />
For example, in Figure 2-10, the HID of node 10 is . For the delivery of a<br />
packet from node 5, with HID(5) = to node 10 with HID(10) =,<br />
the packet is first forward to node 1 (top hierarchy) which uses the virtual link<br />
(1,6,2,8,3) to deliver the packet to node 3. Node 3 then delivers the packet to node 10<br />
along the downwards hierarchical path.<br />
The drawback of HSR is that nodes have to maintain longer hierarchical addresses<br />
and have to continuously update the cluster hierarchy and hierarchical address as<br />
nodes move. Since a continuously changing hierarchical address makes it difficult to<br />
locate and keep track of nodes, logical partitioning is used in HSR. Logical<br />
partitioning involves using subnets of the network, each with its own home agent to<br />
manage membership. The subnets correspond to a particular user group, for example,<br />
students from the same class or tanks in the same battalion. Each member of a logical<br />
subnet knows the HID of its home agent from the routing table and registers its own<br />
HID with the home agent. The registration with the home agent is both event driven<br />
and time driven. It is assumed [Iwata99] that since members of the same subnet<br />
would move as a group, registration overhead is modest because the members will<br />
tend to reside in neighbouring clusters. When a source node requires a route to a<br />
destination it uses the logical address of the destination to send the packet to the<br />
home agent of the destination. The home agent redirects the packet to the destination,<br />
which can then continue communication using the newly acquired and current HID<br />
2-29