Review: LHA -Logical Hierarchical Addressing Protocol For Mobile Ad-hoc Networks

The LHA allocation scheme uses the private block (192.168.0.0 - 192.168.255.255) to assign addresses to hosts in a MANET. The Host address is divided to 2 parts:

• Extended MANET ID, (ExMaID) 6 bits.
• Host ID, 16 bits.

They also use a NetID based on MAC address to identify a network.

An AA node is an Address Agent which assigns new free addresses to requesters. A requester node chooses its AA node from its neighbors.
The AA node which provides an address to the requester is his predecessor, and the requester is the successor of the AA node.

Network initialization:
The node starts a network when no messages are received for address assignment request. To choose the first address, the node selects a random number in the range of [1-30] as Host ID then another number from 6 bits as ExMaID. The NetID is defined by using the node's MAC address.

Joining of a node:
When a node joins a network it requests a free address from its neighbors. It then chooses its AA node based on its address and the available free addresses at this node.
AA node uses the following equation to assign a new free address:
New_Ad = Root_Ad + k*(Agent_Ad - (Root_Ad - 1)) - Afa +1.
Afa is the number of the available free addresses at this node.
K is the number of direct successor a node can have.

If an AA node don't have any addresses left, it broadcasts a request to its neighbors asking for a free address, the new node will be a successor to the node who provided the free address.

If no addresses are available, the new node is a root node for a new network.

Departure of a node:
When leaving a network, the node broadcasts informing his departure. The predecessor nodes updates their informations.

Network Partitioning:
When an AA node fails to assign a free address it checks it ALN (the number of lost nodes), if ALN > Threshold then there is network partition.
One of the partitions with the root node will increment its ExMaID while the other partition decreases its ExMaID and assigns the address of the root node to the new joining node. NetID is also updated in this partition.
All nodes free their missed addresses of their successors.

Network Merging:
There is 2 types of network merging:

• Soft merging: when the ExMaID are different then there is no address duplicated addresses. One of the partitions updates it NetID and save the ExMaID
• Hard merging: when ExMaID are identical then there is a high probability of address conflict. One of the networks increment its ExMaID by 2 and save the NetID of the other network.
  

Results shows that this method reduces latency to obtain IP address by 50 % comparing to the Token-based address assignment.

This work claim to reduce latency by 50% comparing to another address assignment protocol.
However it leaves many unresolved or unexplained points such as:

• How to determine how much successors a node can have, the value of K in the equation of address assignment. This value will definitely impact the number of free address allocations because every node is an AA node.
• When the root node leaves the network, the NetID should be changed and another node should be the new root node. What if a root node left the network then decides to join but because it is out of the transmission range, this node will not receive further messages from other nodes in the network. This node can initiate a new network with the same NetID, ExMaID and assign addresses to new nodes. When the node goes back into the transmission range of the initial network there is a high probability of address conflict which can go undetected because the NetID, ExMaID are identical.
• In the network partitioning if (ALN > Threshold) this is not necessarily a network partition. It can be simply nodes left the network after crash, empty battery etc, though too much unnecessary effort is done by changing ExMaID and broadcasting it.
• Since the NetID and not the ExMaID is used to identify a network then all the routing is based on the NetID and not IP address. This method will have impact on routing.
• When Hard merging, ExMaID is incremented by 2, what if there was a partition before, this means that one of the partion will increase its ExMaID by 1 what if the same partition was partitioned its ExMaID will be incremented by 1 which means the sum of increments is 2, equal to incrementing ExMaID when hard merging. This will lead to more conflict when partitions merge with a network who just had a Hard merging.
  

link to the article