The Presentation Layer Of The Osi Model

THE PRESENTATION LAYER OF THE OSI MODEL Hi visitor, welcome to the page that TRIES to tell u about the presentation layer of the OPEN SYSTEMS INTERCONNECTION (OSI) model.First of all,for the IT EXPERT who’s got basic knowledge of the 7 layers of the OSI model, this page could be the much needed answer to the all similar concepts yet confusing definitions of the different layers of the model, and if u’re a novice/casual visitor, welcome to a website that hopes to offer very simple, detailed and interactive information. THE PRESENTATION LAYER The presentation layer is the sixth layer of the OSI model. It responds to service requests from the application layer and issues service request to the session layer. The presentation layer performs certain functions that are requested sufficiently often to finding a general solution for users, rather than letting each user solve the problems. In particular, unlike all the lower layers, which are just interested in moving bits reliably from here to there, the presentation layer is concerned with the syntax and semantics of the information transmitted. The presentation layer sometimes called the syntax layer in the OPEN SYSTEMS INTERCONECTION MODEL (OSI) is basically used to address and resolve data communication across the 7 layers. For example, a sending computer after receiving data from the application layer will need to convert such data from the receiving format(eg ASCII) to a format understood and accepted by other layers of the OSI model to ensure smooth file transfer. The presentation layer of the OSI model at the receiving computer is also responsible for the conversion of “the external format” with which data is received from the sending computer to one accepted by the other layers in the host computer. Data formats include postscript, ASCII, or BINARY such as EBCDIC (fully Extended Binary Coded Decimal Interchange Code). An example of data formating functions of the presentation layer is the conversion of an EBCDICcoded data to an ASCII style. However, the presentation layer has more duties other than data/file formatting. This includes data compression and security of transmitted information which is achieved through encryption. Encryption can be achieved with the use of cryptography-this function is however argued at times as the function of the session/network layer-(follow other web-links for suggestive reading) DATA SECURITY Another function of the presentation layer is found in the encryption or protection of data offered to transmissions/sessions within the layers. This can be achieved by cryptography. Cryptography is a data security science achieved by hiding information/data in transit. Although, there are other forms of cryptography such as the use of microdots or merging words with images, today’s computing world is largely concerned with encryption- the process of scrambling plaintext-e.g. everyday sentences and messages into ciphertext -a language understood by the machine or translator at the receiving end which is then interpreted into plaintext again i.e. decryption. This function is however debated as one not exclusive to the presentation layer alone but also other layers of the OSI such as the session, network ,transport layer.

DATA COMPRESSION The goal of data compression is to represent an information source (e.g. a data file, a speech signal, an image, or a video signal) as accurately as possible using the fewest number of bits. www.datacompression.com/index/shtml A simple characterization of data compression is that it involves transforming a string of characters in some representation (such as ASCII) into a new string (of bits, for example) which contains the same information but whose length is as small as possible. Data compression has important application in the areas of data transmission and data storage which inadvertently is the main concept behind the OSI layers. Many data processing applications require storage of large volumes of data, and the number of such applications is constantly increasing as the use of computers extends to new disciplines. At the same time, the proliferation of computer communication networks is resulting in massive transfer of data over communication links. Compressing data to be stored or transmitted reduces storage and/or communication costs. When the amount of data to be transmitted is reduced, the effect is that of increasing the capacity of the communication channel. Similarly, compressing a file to half of its original size is equivalent to doubling the capacity of the storage medium. It may then become feasible to store the data at a higher, thus faster, level of the storage hierarchy and reduce the load on the input/output channels of the computer system. So typically, in the presentation layer, the layout/structure of data in transit is set, language to be used in transmission is agreed on, security features are put in place to guarantee privacy and authentication, and the volume of data to be transmitted is decided through compression.