2.1 DSDV (Destination-Sequenced Distance-Vector Routing):
In DSDV [1], each node needs to follow a routing table. The routing table entry includes the destination node, hops and the destination sequence number, the destination sequence number assigned by the destination node, mainly for determining routing is outdated, and may prevent routing loops. Each node must periodically exchange routing information with neighboring nodes, of course, can also according to the routing table changes to trigger the routing table update.
Routing table update in two ways: one is to update all (Full dump), namely the topology update message will include the entire routing table, mainly applied to network changes rapidly. Another way is part of the update (Incremental update), contains only changes in the routing update message, usually applies to network changes slowly.Using only the sequence number of the highest routing in DSDV, if the two route with the same sequence number, then will choose the best routing (such as the shortest hops).
DSDV protocol update method still many deficiencies, have the following main points:
1. Poor scalability: Regardless of how network traffic, DSDV requires nodes
periodically broadcast updates. When adding more nodes of the network, the routing table corresponding increase in the capacity and bandwidth, which is the main drawback of DSDV. As long as topology changes, DSDV is unstable until update information in the whole network broadcasts. If a node's mobility is high, DSDV deal with them more difficult.
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2. Packet delivery low rate, throughput performance difference: Packet delivery rate refers to the number of packets received by the destination node and the source node sends the ratio of the number of packets. Table-driven DSDV routing protocol overhead as nodes, although the accelerated movement remained basically unchanged, but in the case of topology changes accelerate, not been able to converge, resulting in a large number of unreliable routing and routing loop, causing packet loss. When more severe when the topology changes, DSDV packet transmission rate declined sharply.
3. Broadcast large overhead: Since node periodically broadcasts update
information, Ad Hoc in bandwidth will be occupied, and some battery power is also used for maintenance broadcasts. Resulting in relatively large routing overhead, delay increases, throughput is low and some shortcomings, this initial charge of batteries for mobile Ad Hoc network is not too high, it is very much affected, and sometimes may lead to over-node early demise.
2.2 DSR (Dynamic Source Routing):
DSR [5] routing protocol is composed of two main mechanisms: Route Discovery mechanism and Route Maintenance mechanism.
Routing Discovery mechanism to use that the source node needs to the destination node sending a packet and also do not know when to reach the destination node path.
When the source node is using a path of arrived at the destination node, the source node can use the Route Maintenance mechanism to detected the cannot use path with topology changes.
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When the Route Maintenance mechanism that a source routing has been interrupted and no longer work path, in order to make the transmission of the data packet to the destination node, the source node will use a chance path, or to call Route Discovery mechanism to find a new path.
In DSR routing protocol, Routing Discovery mechanism and Route Maintenance mechanism operation is completely according to the requirements. Any situation will not affect the DSR routing protocol correct operation, because all the situation is established according to the demand, all situation in the loss if still needed can easily get quick recovery.
DSR protocol, there are still the following deficiencies:
1. Each data packet header needs to carry routing information packet overhead
is large, the network is not suitable for large diameter MANET.
2. Route request message using the flood way, the adjacent node route request
message transmission conflicts may occur and may generate duplicate broadcast.
3. As a result of the routing cache, expired route may affect the accuracy of
routing.
4. Not strong network scalability.
2.3 TORA (Temporally Ordered Routing):
TORA [4] defined as an area for each node. This area is involved some nodes, the node distance (or hops) in a limited range, this range is known as the zone radius.
Each node only needs to know the topology in routing area, and with the topology update to update. Although the network is very large, but update only in the local.
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If S wants to communicate with D, S sends a query message, it will be directly sent to the boundary node by node within the area. And broadcasts it, until you reach the D, D respond to this request.
TORA protocol summary:
1. TORA is a distributed routing algorithm based on reverse routing protocol. It
is designed to be used to find on-demand routing to the destination node provides multiple routes to quickly create routing and topology changes when possible through local algorithm to reduce the communication overhead.
2. TORA protocol to each node is assigned a priority burst through different
attributes. This method establishes a source node finally began destination node system. In essence, the packet is through this system from the source node to the destination node.
3. TORA the advantage of a high-density network can handle. Supports save
multiple routes and broadcast between two nodes.However, TORA algorithm is based on the synchronous clock, the clock time can lead to different routing failure.
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