Network security and privacy

Security is needed in order to maintain privacy. Thus network must provide security to the data whenever transmitted from one end point to another end point. The desirable properties of secure communication are confidentiality, authentication, message integrity and non repudiation.

Cryptography technique is generally used in order to provide security to the data while transmitting over network. Thus cryptography keeps information secure from getting into the unauthorized hands or intruders . Basically, Cryptography is the process in which plain text is first encrypted and then transmitted over the network and is then recovered into plain text at destination by using decryption. Process of Cryptography is as shown in following figure.

Encrypted data is referred as cipher text. Various cryptography algorithms are available and are used for encryption as well as decryption of data transmitted over the communication channel. Algorithm uses one or more keys. there are two types of keys: Public key which is publicly available and private key which is known to belonging person only. Intruders may present in between the communication channel. Encryption or decryption algorithms are classified into two types as symmetric and/or asymmetric algorithms. These algorithms help in achieving confidentially and privacy.

Network security can also be achieved by using digital signature and digital certificate. Digital signature and digital certificate are useful in verification of records. A DSA (digital signature algorithm) is used to sign a digital document. Digital signature is used to identify the sender. It specifies that the particular document belong to the person who signed the document. Once a document is signed by a particular person then he cannot say that the document does not belong to him/her. Digital certificate is an electronic certificate issued by a certificate authority. Digital certificate includes digital signature.

In this manner, security is provided to data over the network.

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This article is the topic of unit " Communication Technologies-II " from RTMNU MBA 3 rd sem IT syllabus notes.Further topics will be covered in upcoming blogs For more notes you can also refer to other links as given below:

1.http://rtmnupervasivecomp.blogspot.com

2.http://rtmnuittrends.blogspot.com

3.http://www.rtmnunetworkingtechnology.blogspot.com

)

CDMA

Concept:

As per the previous discussion, CDMA stands for Code Division Multiple Access. It is a multiplexing access method in which multiple users are allocated different codes to access the same channel. Where channel is the set of frequencies and code is nothing but the sequence of n symbols (0 or 1). Mobile telephony systems which use CDMA are referred as CDMA systems.

CDMA uses cellular network and is used for long distance communication. The initial evolution of CDMA was as 2.5 G. Nowadays CDMA supports high data rate and is thus considered as 3G. It transmits not only voice but also data and multimedia streams.

Features:
The important features of CDMA systems are:
1. It is more robust for multi-path delay.
2. Signals from each mobile station are coded with two or three codes.
3. It gives higher quality voice and data transmission with small bit error rate.
4. It has soft handover.
5. It performs power control by open loop or close loop methods.

CDMA codes allow unique identification of signals from different sources and transmit these signals through the same time, space and frequency slots without interference. Thus it is necessary that CDMA codes should not correlate with each other. The various types of codes are used and are discussed below.

Types of Codes:

1. Autocorrelation Codes:
An autocorrelation code is a multi-bit code which is used for coding the symbols before transmitting, allows the receiver to correlate and extract the symbols automatically. Barker codes and Pseudo-noise (PN) codes are the examples of autocorrelation codes. Barker code gives strong autocorrelation where as PN code gives strong peak with few, low and non-zero values which may results in interference with the users using same spread. Long M-sequence PN code has strong autocorrelation and is used as scrambling code. A short PN code also has strong autocorrelation. for example, in WCDMA short PN code is used.

2. Orthogonal Codes:
Two codes used for coding are referred as orthogonal when there is no effect of interference between two sets of signals on the received output. Orthogonal code do not show the strong autocorrelation property and thus requires the synchronization between transmitter and receiver. It gives zero cross-correlation. Examples of this code are Best code and Walsh code.
Best codes are optimized codes which allows significant correlation and do not create interference in between different channels. Whereas Walsh code are generated from Hadamard matrix with all pairs of rows are orthogonal. Walsh code is used in IS-95/cdmaOne. This code is used for channelization due to orthogonality property. Following table gives information about the different CDMA standards.

Different CDMA standards:

Conclusion:
Here we discussed about concept, features, types of codes used in different CDMA standards and different CDMA standards with their properties and uses also.

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This article is the topic of unit " Communication Technologies-II " from RTMNU MBA 3 rd sem IT syllabus notes.Further topics will be covered in upcoming blogs For more notes you can also refer to other links as given below:

1. http://rtmnupervasivecomp.blogspot.com/

2. http://rtmnuittrends.blogspot.com/

3. http://www.rtmnunetworkingtechnology.blogspot.com/

)