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OSI and Switching

The OSI model is the rules that ensure that two computers are communicating with each other on the same network. The OSI model consists of seven layers Physical, Data Link, Network, Transport, Session, Presentation, and Application. When one sees the OSI model, it displays from Application down. According to Fitzgerald and Dennis (2005), “Layers 4 through 7 occur at the end node, and Layers 1 through 3 are the most important to telecommunications networks”. Now let us discuss the seven layers of the OSI model.

First is the application layer. This layer handles services on a network and information between programs on the computer or laptop. File transfers though the use of the File Transfer Protocol (FTP) are processed at this level. Next is the presentation layer. The presentation layer is responsible for handling of information encoded in the same format. The session layer follows the presentation layer. According to Fitzgerald and Dennis (2005), “the session layer, supports connections between sessions and handles administrative tasks and security”. A notable protocol in the session layer is the Lightweight Directory Access Protocol (LDAP).

The Transport layer is the next layer in the OSI model. This layer is responsible for the reliability of information being delivered from point to point on a network. Next is the network layer. This layer is used to direct transfers over a network. It determines information flow between networks. Data Link is the followed by the network layer. It sees the information in binary making sure that the two devices are on the same network. Lastly, we have the physical layer. According to Fitzgerald and Dennis (2005), “The physical layer defines the types of cables or wireless interfaces that are allowed…and the types of transmission rates that are allowed”.

Now we will discuss Circuit and Packet Switching. First, is circuit switching. Circuit switching consists of networks on leased lines, and networks on ISDN. Leased lines have a distinct advantage of the devices always having a line to communicate. There are disadvantages of a network based on leased lines. According to Fitzgerald and Dennis (2005), “The disadvantage becomes pronounced…network starts to grow, either in number of devices or in distance between locations”. A multipoint-leased line is more resourceful when the networks begin to grow in size of distance.

ISDN networks are also circuit switched networks. According to Fitzgerald and Dennis (2005), “As the first generation of ISDN...give customers one access into the network…engage in circuit-switched, leased-line, or packet-switched options”. This was to give users one plug with the result of multiple alternatives.

Packet switching networks were developed to counteract high active and extremely busy data traffic over a network. According to Fitzgerald and Dennis (2005), “Packet switching involves the application of statistical multiplexing, whereby numerous conversations can make use of one common communications channel, which significantly increases transmission efficiency”.

There ae four types of packet-switched networks. X.25, Frame Relay, Asynchronous Transfer Mode (ATM) and Transmission Control Protocol/Internet Protocol (TCP/IP). X.25 is the first packet-switching network introduced in 1970. It is based on analog networks. According to Fitzgerald and Dennis (2005), “A big problem with analog networks is the accumulation of noise through the amplification points, which leads to the very high error rate”.

Frame Relay began use in 1991. Frame relay is much faster that X.25 networks. There is a comparable link between Frame Relay and ATM. According to Fitzgerald and Dennis (2005), “At the core of the Frame Relay network is ATM because ATM currently offers the strongest

suite of tools for traffic management…many networks, including IP backbones, the Internet, and Frame Relay, have ATM at their core…ATM supports…voice, IP, Frame Relay, X.25, and leased lines”. Therefore, it is a viable conclusion that ATM is the best type of switching network.

References

Fitzgerald, J., Dennis, A. (2005). Business Data Communications and Networking. (8th ed.). John Wiley & Sons, Inc..