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5.3.4 HOPERAA Algorithm:

In this Module, Client executes the HOPERAA algorithm to adjust its hopping period. Roughly speaking, S and C attach timestamps in the contactinitiation messages during the contact-initiation part and the Hopping Period Alignment and Adjustment part. C uses the timestamps to estimate its clock drift. According to the estimation, C decides the next time to run the HOPERAA algorithm. C also adjust its hopping period according to the estimation to deal with its clock drift and thus avoid sending messages to closed ports.

The HOPERAA execution interval is initiated to 0. In the contact-initiation part, every contact-initiation message and reply message will be attached with the timestamp of its sending time. The reply message also includes the timestamp and the arrival time of the first contact-initiation message received by the server. When the client receives the reply message, it will store and and keep their values unchanged. When C executes HOPERAA, it will execute the same operations as in the contact-initiation part, the server will add a timestamp of the sending time to every reply message.The client will record the arrival time.

5.3.5 Multi client Connection:

The extension to multiple clients per server is based on a simple idea: since each client considers the server’s clock as the reference clock, it can interact with the server independently of the other clients. For scalability reasons it is desirable that the server has more than one worker ports open in each time period (but still a small constant number of those), so as to balance the load among them. Moreover, by having the same hopping period but different phases in the corresponding hopping sequences, such a method can manage to bound better the time it takes for each client to initiate contact with the server. In this phase, the server uses the multiple hopping sequences to transfer the data.

Problem Definition:

First,analyze a new ICMP message – the ICMP Caddie messages scheme – which provides a simple and straightforward solution for IP Trace back.It need router modification. The potential deployment strategy using such an algorithm based on overloading existing IP header fields and we have demonstrated that this implementation is capable of fully tracing an attack after having received only a few thousand packets.

In existing System,its only for single client server communication.An attacker can possibly launch aDoSattack by studying the flaws of network protocols or applications and then sending malformed packets.which might cause the corresponding protocols or applications getting into a faulty state.which is sending incorrect IP fragments to the target.The target machine may crash if it does not implement TCP/IP fragmentation reassembly code properly. This kind of attacks can be prevented by fixing the corresponding bugs in the protocols or applications. However,the attacker does not always have to do its best to study the service if it wants to make it unavailable.

To overcome these problem, port number dynamically change while transferring a data. Here HOPERAA algorithm is used fro single client server communication. The whole port hopping mechanism consists of some parts: the contact-initiation part,the data transmission part.In the first phase, a time interval is selected initially.After that the server initiates the contact with its clients by sending initiation message. The clients involved in this communication must be within the time-interval.The server divides the range of port numbers into k intervalsNext is the Data transmission phase in which Client sends data messages to the worker ports of Server.After receive the data from client server send reply message to the client. This will be implemented for multiple client single server communication by using bigwheel algorithm.