Day 9(2): Network Security, Multiple Access Protocols

Hello dear students.
   Hope you all are doing good....

So now we are going to cover the network security topic. This topic is supposed to be our last topic from networking, we will also conduct a test for you which will be available to you soon. 

Let's get started...

NETWORK SECURITY - Security refers to " Protecting the information from unintended access". So, in network, security is the major concern to protect the information. However, the information can be Data, Software, Hardware, Networks. etc. to be protected. 

MALWARE- Malware refers to software which is used to harm the information intentionally. It's types are- Viruses, Worms, Trojan Horses, Ransomware, Spyware, etc. 

To prevent from the malware there are various methods such as-

  • CRYPTOGRAPHY - Cryptography is a technique which provides message confidentiality. In Greek, it means "Secret writing". It basically involves the process of encryption and decryption. In this technique, the sender sends the plain text, the encryption algorithm key translates the plain text into Cipher-text over the network and then the decryption algorithm key translates the cipher-text into the plain text for the receiver. Some cryptography algorithms are as follows-
  1. Symmetric-key - The symmetric-key algorithms are the algorithms where there is same key for the encryption and the decryption. The same key is used to encrypt the plain text into cipher-text and same key is used to decrypt the cipher-text into plain text. It uses 128-bit keys.  
  2. Asymmetric key - The asymmetric-key algorithms are the algorithms where there is a pair of public key and private key. The public key can be used by anyone but private key is secure.
  3. DES - DES stands for Data Encryption Standard. DES is basically a cryptography algorithm in which the same key is used for encryption and decryption. In this, there is 64-bit of plain text and 64-bit of cipher-text from DES CIPHER, and then by DES REVERSE CIPHER you will get 64-bit plaint text from that 64-bit ciphet text. It uses 56-bit key.It was published by NIST(National Institute of Standards and technology.
  4. AES - AES stands for Advanced Encryption Standard. The Same key is used for encryption and decryption. In DES, we use 56-bit key but in AES we use basically 128-bit key. It is much stronger and faster than DES. 

  • ENCRYPTION - Encryption stands for the conversion of the plain text to be sent into some coded form so that it can be secured while transmitting over the network. Here are various encryption methods which are-
  1. Substitution- In this, each letter is replaced by another. For example, A is replaced by G, or 5 with 3, etc.
  2. Mono-alphabetic- In this, every occurrence of a letter is replaced by another. For example, every occurrence of A is replaced by G.
  3. Poly-alphabetic- In this, every occurrence can have different substitute. For example, in one time A is replaced by E then on other occurrence A is replaced by G, and so on.
  4. Transposition- In this, it does nor substitute character with another, it reorders the letters to change their locations. Example, BOENTIKA key.

  • DIGITAL SIGNATURES - The digital signatures are basically used for the security purposes. Unlike the physical signatures, the digital signatures are our login details, checksum, etc. where only the admin knows the details and if it gets misuse, then your data will be in danger. The name is digital signature but it actually not signatures on computer or else it is just a security mechanism. The digital signature is login details, the application asks for login information for security purpose if we fill correct details then we can access the information. Checksum is basically another digital signature example where it can detect that if the message is updated or modified when it transmits. There are public and private keys. Public key is for anyone but private key is more secure and for the specific user whom the data is transmitted. 


ERROR CODES - When data transfers from one machine to another, there is a chance of errors(change of bits). Errors can be Single bit and Burst Error.

Single bit error - In this, there is an error in a single bit i.e. change in only 1 bit.
Example-
 1
Data Sent

 1
Data Received

So here is one bit changed which is 1 instead of 0 in location 2.


Burst Error - In this, there is an error in 2 or more bit i.e. change in 2 or more bits.
Example-
 1
Data Sent

 1
Data Received


Now, we are going to cover the topic, Multiple Access Protocols,
RANDOM ACCESS PROTOCOLS- In this, there is no control station. It is called as random access because there is no scheduled time for the transmission, it transmits in random order. If there is collision, frames are either destroyed or modified. It consists of 4 types-
  • ALOHA - In this, station shares a common channel. If there is collision, then the frames are destroyed. It was used for ground based broadcasting. It is basically of 2 types which are- Pure Aloha and Slotted Aloha.
  • CSMA - CSMA stands for Carrier Sense Multiple Access. It is based on the "carrier sense" principle. In this, the station checks the channel that it is idle or busy before transmitting a frame. It is basically of 3 types- 
  1. 1-Persistent CSMA
  2. Non-Persistent CSMA
  3. p-Persistent CSMA
  • CSMA/CD - It stands for Carrier Sense Multiple Access with Collision Detection. In this, the station sense whether the channel is idle or busy. If the channel is busy, then it waits for it to be idle. It can also detect the collisions. The station then stops the transmission when it detects the collision.
  • CSMA/CA - It stands for Carrier Sense Multiple Access with Collision Avoidance. It is basically used in wireless networks because they cannot detect the collision , so the only solution is collision avoidance. It do avoids the collision with 3 techniques-
  1. IFS(InterFrame Space)
  2. Contention Window
  3. Acknowledgements

CONTROLLED ACCESS PROTOCOLS - In this, the stations consult with each other that which station has the right for transmission. A station cannot send unless it has been authorized by other stations.It consists of 3 types-
  • RESERVATION - In this, a station needs to make a reservation before sending the data. If there are n stations, then there are exactly N reservation mini slots. 
  • POLLING - There are 2 modes- Poll and Select. This basically works on those networks where primary and secondary stations exit. The primary is for the data exchange and controls the links. The secondary is for final destination.
  • TOKEN PASSING - In this, a special packet called "token" is circulated through the ring. The station being token has the right to access the channel. This basically works on those networks where stations are organized in logical ring. 

CHANNELIZATION - It is a method in which the bandwidth is shared in time, frequency, or code between the stations.
  • FDMA - FDMA stands for Frequency Division Multiple Access. In this, the bandwidth is divided into the frequency bands. It is an access method in data-link layer. Here, each station has a band to send data, this band is reserved for that station all the time. 
  • TDMA - TDMA stands for Time Division Multiple Access. It is basically the division based on time.
  • CDMA - CDMA stands for Code Division Multiple Access. It is divided on the basis of frequency spectrum. In this, each user is given a unique code.



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