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que. For how many hops this message should be forwarded every RREQ carries a time to live (TTL) value that. For the first transmission this value is set to a predefined value and for the retransmission the value is increased. Retransmissions take place if there are no replies received. Data packets that are that are not transmitted yet and waiting for there transmission (i.e. the packets that initiated the RREQ) should be transmitted by a FIFO principal when a route is set.

RREP - If the node that is receiving, is either the node using the requested address or it has a valid route to the requested address a route reply message is unicasted back to the originator of a RREQ. One can unicast the message back because every route forwarding a RREQ caches a route back to the originator.

RERR - In active routes, nodes monitor the link status of next hops. The RERR message notifies all the other nodes of the loss of the link when a link breakage in an active route is detected. Each node keeps a “precursor list”, which contains the IP address for each its neighbors that are likely to use it as a next hop towards each destination in order to enable this reporting mechanism.

Figure 2-3, illustrates an AODV route lookup session. Node A wants to communicate with node J and from A to there is no route so then A broadcasts the RREQ which will be flooded in the whole network to all the nodes then this request will be forwarded from H to J, where J will generate RREP. Then by using the cached entries in H,G and D this RREP will be unicasted to A.

2.2.2 Proactive protocols – OLSR

In the proactive routing approach used in MANET maintains a constantly update topology understanding (routes calculated in advance and constantly updated).

In theory it is necessary that the whole network must be known to all of the nodes. So the constant overhead of routing traffic occurs, but there will be no initial delay in communication. Where latency delay is not desirable one should use proactive protocols because they are suitable for that kind of situations.

The (OLSR) was described in RFC3626. It is a protocol that uses the link-state scheme in an optimized manner tp circulate the topology information and it is also a table-driven pro-active protocol. Link-state information is flooded throughout the network, in a classic link-state algorithm. OLSR is also a Table-Driven Protocol. The message flooding in OLSR is optimized to preserve bandwidth because the protocol runs in wireless multi-hop scenarios. Multi Point Relaying is the technique on which the optimization is based on a technique.

As I mentioned above that the OLSR is the table-driven protocol. So, it maintains and update the information in a variety of tables.

The data on these tables is based on received control traffic, and control traffic is generated based on information retrieved from these tables. The calculation of the routes is also driven by the tables.

OLSR defines three types of control messages:

I. HELLO – These are the messages that are transmitted to all the neighbors.

II. TC – These are the link state signaling which is done by OLSR. By using MPRs TC messaging is optimized in many ways.

III. MID – Nodes transmit these messages running on more than one interface. All the IP addresses are listed by these mess本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。