The seven layers identified by ISO in the OSI reference model from bottom to top are: 1. Physical Layer 2. Data Link Layer 3. Network Layer 4. Transport Layer 5. Session Layer 6. Presentation Layer 7. Application Layer. The physical layer is concerned with transmission of data through communication channels, these communication channels do not themselves form part of the [...]
This article throws light upon the top six methods of data transmission. The methods are: 1. Twisted Pair 2. Shielded Twisted Pair 3. Baseband Coaxial Cable 4. Broadband Coaxial Cable 5. Fibre Optics 6. IEEE Standards. Method # 1. Twisted Pair: As must be obvious from the example, transferring data by copying it onto magnetic tape or floppy disk or [...]
SMDS or Switched Multimegabit Data Service is another service being offered by telephone companies in many countries. This service, which had become popular in the USA in the 90s, was developed by Bellcore in 1980. Figure 6.6 indicates how normal leased line connections can be established between some LANs. Telephones: Other Issues: Other telephone services include items, such as Synchronous [...]
This article throws light upon the three main types of protocols. The types are: 1. Transmission Control Protocol 2. Internet Protocol 3. User Datagram Protocol. Type # 1. Transmission Control Protocol: Transmission Control Protocol or TCP is a transport layer protocol. Recall that while discussing the "layer cake" one of the layers in the OSI reference model was the transport [...]
After reading this article you will learn about the definition of protocols. The word protocol appears very frequently in any discussion about networking. While it has been used very frequently in the discussions, it has not been clearly explained. Almost all wide area networks utilise TCP/IP and they have become practically synonymous with Wide Area Networks. When we continue the [...]
This article throws light upon the top five aspects of network security. The aspects are: 1. Secrecy 2. Integrity Control 3. Authentication 4. Cryptography 5. Virtual Private Networks (VPNs). Aspect # 1. Secrecy: The standard case quoted above of keeping certain files secret (totally or in part) from some users, happens in most organisations. This can be easily handled by [...]
Encryption methods have historically been of two categories, namely, substitution ciphers and transposition ciphers. We discuss them below. Category # 1. Substitution Ciphers: While the above would be a simple method of coding—based on the belief that the enemy could not decipher the Navajo tongue—variations of this method was used in substitution ciphers. In this method (sometimes known as a [...]
After reading this article you will learn about the use of bridges in LAN. Organisations that use multiple LANs and of different designs generally need to connect them to each other. They do this by using bridges. Bridges operate in the data link layer. This means that bridges do not examine the network layer header and can, therefore, copy IP, [...]
There are several reasons why congestion is caused. For example, if a stream of packets begin arriving on some of the input lines and all need to be sent on the same output line a queue will build up. If there is not enough memory to store all of them, packets will start to get lost. Adding more memory may [...]
After reading this article you will learn about the principles of congestion control. A subnet may be a complex system and the solution to congestion control in a subnet may be treated as a control problem. The control problem may be either open loop or closed loop. Both have different approaches to the problem. Control system specialists will be familiar [...]