PAP and CHAP ; Authentication Protocols That Used in ADSL

PAP and CHAP is the two main authentication protocols that used in ADSL.

Advantages and disadvantages of PAP and CHAP

•  CHAP has a more secure procedure for connecting to a system than PAP.

Because after sending the challenge message to user, the user responds with a value that calculates with the use of a one-way hash function and send sends respond packet. The RADIUS checks the response against its own calculation of the expected hash value. CHAP uses encrypted massage that includes user name and password. But PAP uses password in clear text and is a one way step process. That can be unsecured, half way communication.

Another feature of CHAP is that it doesn't only require the client to authenticate itself at startup time, but sends challenges at regular intervals to make sure the client hasn't been replaced by an intruder, for instance by just switching phone lines.

CHAP requires that the secret be available in plain text form. Irreversibly encrypted password databases commonly available cannot be used. It is not as useful for large installations, since every possible secret is maintained at both ends of the link.

•   CHAP provide access to the server in every time

It sends challenge massages frequently to the user, Because of that the user is always connected to RADIUS. Therefore we can prevent the rick of another client replacement to the server using same line.   

Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you

Synchronization Technique Used in Analog FDM

 Frequency division multiplexing (FDM) is an analog modulation technique that combines analog signals. In FDM several frequencies bandwidths are carried through a single line. Then it is transmitted to the receiver. In this case, in FDM we use guard bands within two bandwidths. Using guard band is a technique that use in FDM for synchronization. We can see it in this figure.

 

When we transmit these 10 kHz bandwidths (signals) to receiver without guard (5 kHz) bands, the receiver cant identity what is the 1^st, 2^nd, 3^rd signal. It hasn’t any understand about the bandwidth of the signal.

               We can see in this figure, if we use a guard band between them the receiver can identify the signals. It can know the bandwidth of the signal.

               That’s how synchronization technique used in analog FDM.

Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.

Benefits of Modulation in Telecommunication

Modulation for efficient transmission

                                                         

                      Signal transmitting over appreciable distance always involves a traveling electromagnetic wave. The efficiency of any particular transmission method depends upon the frequency of the signal being transmitted. By exploit in the frequency translation property of modulation the message can be inserted into carrier which has the frequency selected for the desired transmission method.

Modulation to overcome hardware limitation

                                             

                      The design of the communication may be constrict by the cost availability of the hardware, performance of the hardware often depends on the frequencies involved. Modulation permits that designer to place a signal in some frequency range that avoids the hardware limitation.

Modulation to reduce noise and interferences

                      A method for overcoming noise and interferences is to increase signal power until it overcomes the contamination. But increasing power is costly and may damage the equipments. Fortunately FM and certain other types of modulations have a valuable property of suppressing both noise and interferences.

Modulation for frequency assignment

                      When we tune a radio or television, particular station we are selecting one of the many signals being received at that time. Since each station has a different assigned carried frequency that desired signal can be separated from the others by filtering.

    Throughout this article I hope you may get some thing. This provides very basic explanation and future will cover more. Comments are well come. Thank you.