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 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 [...]
After reading this article you will learn about the function and requirement of routing. Function of Routing: The function of a router is to switch messages. Router, which is a generic term used in Wide Area Networks, aids in transferring messages. Routers are specialised computers used to connect two or more transmission lines. When data arrives on an incoming line [...]
Although there are a large number of routing strategies that have been proposed and are being used, most routing strategies have evolved from the requirements of packet-switching networks. These are basically four strategies that have been used in routing: 1. Fixed Routing 2. Flooding 3. Random Routing 4. Adaptive Routing. 1. Fixed Routing: A single permanent route is configured and [...]