Table of Contents
A computer network is a group of hardware and computers that are interconnected by communication channels. These channels allow users to share information and resources. It can also be defined as a collection of connected devices. Networks can be classified into categories such as topology, scale, the used communication protocol and organizational scope. Communication protocols provide the root of networking program and define data rules and formats. It includes hardware, two Ethernet and link layer standard and ubiquitous in LAN and the internet protocol suite.
The OSI Model
According to the SANS Institute, the Open System Interconnection is an ISO standard for worldwide communications that define a networking framework for implementing protocols in seven layers (Aronoff, Chemick, Hsing, Mills, & Stokesberry, 1999). It affects the way computer networking protocols are designed by the IT industries. The layers are physical, data link, network, transport, session, presentation and application. The layers can only communicate with the layers below and above them. The layers are developing independently in order to allow flexibility and development without delays. Encapsulation takes place in each layer.
The Physical Layer
According to Jain & Agrawala (1993), the physical layer defines the physical properties of the network such as the cable types, the voltage levels and interface pins. The physical layer can be disrupted through physical processes such as interrupting with the power supply. Faulty power problems can be solved by installing the uninterrupted power supply (UPS). The UPS gives the user ample time to shutdown the computer orderly. Microwave Omission Analyser devices can cause network signal problems which can be solved though prevention by design.
The Data Link Layer
The data link layer is the layer that transmits and receives packets of information reliably across a uniform physical network. The data link layer is vulnerable because it was designed to be practical and functional. For computers to communicate with each other the Network Interface Cards (NIC) must be in existence. The Address Resolution Protocol (ARP) maps between the Media Access Control (MAC) and the Internet Protocol (IP) addresses on local networks.
The Network Layer
According to the Local Area Network Magazine (1990), the network layer routes data through various physical networks while travelling to a known host. Routers are machines which work is to decide on how information from one logical network to the other can be sent. Routers understand IP and make decisions depending on the information.
The Transport Layer
It is a layer that ensures reliable arrival; furthermore, provide error checking mechanisms and data control of messages. It provides services to connectionless-mode transmissions and connection-mode transmissions.
The Session Layer (Port Layer)
The layer manages to take down and setting up of a connection. A connection is the involvement between two communicating end points. In order to avoid cases of hacking in the session layer, authentication is installed at the beginning of the TCP session. Passwords are the type of authentication. For convenience purposes, passwords should consist of punctuations, numbers and letters.
The layer ensures that information passing through is in right from the recipient. The layer offers a binary code and a Unicode. The binary code ensures successful file transfers. The Unicode cover all universal languages. According to Andrew Brannan, Unicode vulnerabilities can be solved if a careful system administrator takes a few steps such as moving the web folder root off the logical drive that holds the system executables.
The Application Layer
The layer defines standards for interaction at the application or user program levels. The layer has application and user interaction. The greatest threat here is the Trojan horse. An example of a Trojan horse is an application that claims to solve virus problems but introduces viruses instead. Anti-viruses are installed to protect computers from Trojans worms and viruses. Viruses attach themselves to a program while worms are self-propagating.
The Media Access Address (MAC address) performs in the physical network segment for communication to network interfaces. This makes it a unique identifier. It’s mostly used in the IEEE 802 network technologies such as the Ethernet. The addresses are mainly used in the MAC protocol of the OSI reference model sub-layer. The manufacturers mostly assign the MAC addresses of a network interface card (NIC), which are stored in the cards read-only memory, the burned-in address and in its hardware. The MAC addresses are formed through the management of the Institute of Electrical and Electronics Engineers (IEEE). The formation follows one of the rules of the three numbering spaces: MAC-48, EUI-64 and, EUI-48. EUI is a trademark by the IEEE, which stands for Extended Unique Identifier.
IEEE 802 original MAC address originated from the Ethernet original Xerox addressing scheme. The Xerox potentially contains 248 or 281,474,976,710,656 possible MAC addresses. The numbering systems only differ in the identifier length and use of the same format. The addresses are either locally administered addresses or universally administered addresses. The manufacturer uniquely assigns a universally administered address to a device. Examples of technologies using the MAC identifier format are 802.11 wireless networks, Ethernet, Bluetooth, FDDI, IEEE 802.5 token ring, ATM, most other IEEE 802 networks, the Serial Attached SCSI and the Fibre channel, and the ITU-T G.hn standard. The ITU-T G.hn standard provides a way of creating high speed LAN using phone lines, power lines and coaxial cables. The G.hn APC layer accepts Ethernet frames using MAC-48 format and encapsulates them to G.hn MAC Service Data units (MSDUs).
It’s important to change MAC addresses in network visualization on most modern hardware. This can also be used in exploiting security vulnerabilities called MAC spoofing.
Local Area Network (LAN)
According to Dr. Massoud Maxwell Rabiee of the Allen-Braley brand, local area network (LAN) is a communication network that connects several devices and provides a means for information exchange among those devices (The Local Area Network Magazine, 1990). There is a way of physically connecting PLCs to computers in a LAN called the Network Connection Topology. LAN considers the way in which equipment in a network communicates which is called the network access control scheme.
LAN has three categories of media transmission named the coaxial cables, twisted pair wires and the Fibre Optic Cables. The shielded and unshielded twisted pair wires are commonly used due to the lower cost, the ease of installation and maintenance. LAN has network access control schemes known as Token-Ring, Master-slave and Career Sense Multiple Access with Collision Detection (CSMA/CD).
The CSMA/CD stations must keep ‘listening’ to ensure that there are no data collisions if several stations were transmitting data simultaneously. Moreover, this helps to solve the problem of re-transmitting data. The initiator station in the master-slave network scheme is called the master PLC will ‘poll’. The ‘polling’ action identifies a station in the ‘polling list’ trying to gain access in the network highway.
Networking has made communication easy in the current world by providing high speed communication. Running businesses through internet became possible because of availability of wire transfers of money and information. It also provides good ground loop noise immunity. Network providing companies are working hard and coming up with new technologies to limit data interruption. However, installation of the hardware that support internet comes with a high initial cost of installation. The speed of the internet is compromised when several connections are made for several computers, say in an office environment.