Computer Networking

Computer Networking

A computer network is a collection of interconnected computers and other devices which are able to communicate with each other. In this context, the term interconnected means that there exists a path through which data can be transmitted from one computer/device to another.

A few of these advantages are:

• Resource Sharing
• Cost saving
• Collaborative user interaction
• Time saving
• Increased storage

Wired Technologies

Co-axial Cable:

Coaxial cable conducts electrical signal using an inner conductor (usually a flexible solid or stranded copper wire) surrounded by an insulating layer and all enclosed by a shield layer, typically a woven metallic braid; the cable is often protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a voltage is applied to the center conductor to carry electrical signals. The advantage of coaxial design is that the electric and magnetic fields are confined to the dielectric with little leakage outside the shield. On the converse, electric and magnetic fields outside the cable are largely kept from causing interference to signals inside the cable.

Ethernet Cable:

An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly. Normal straight through or patch cables were used to connect from a host network interface controller (a computer or similar device) to a network switch, hub or router. A cable with connections that "cross over" was used to connect two devices of the same type: two hosts or two switches to each other.

Optical Fiber:

An optical fiber (or optical fibre) is a flexible, transparent fiber made of a pure glass (silica) not much thicker than a human hair. It functions as awaveguide, or “light pipe”[1], to transmit light between the two ends of the fiber.[2] The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces. Specially-designed fibers are used for a variety of other applications, including sensorsand fiber lasers.

Wireless Technologies

Bluetooth:

Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security.

Infrared:

Infrared (IR) light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74micrometres (µm), and extending conventionally to 300 µm. These wavelengths correspond to a frequency range of approximately 1 to 400 THz,[1] and include most of the thermal radiation emitted by objects near room temperature. Microscopically, IR light is typically emitted or absorbed by molecules when they change their rotational-vibrational movements.

Microwave:

Microwaves are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz.[1] This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries.[2] In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

Radio Waves:

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometer. Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or by astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may cover a part of the Earth very consistently, shorter waves can reflect off the ionosphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.

Satellite:

A satellite link is a communications subsystem that involves a link between a transmitting Earth station and a receiving Earth station via a communications satellite.

Network Topologies

When we have to connect computers/devices in a network, there may be certain conditions which have to be satisfied. Depending upon these conditions, there may be different ways of interconnecting the computers/devices. The way in which the computers/devices are physically interconnected to form a network is called a Topology.

Bus Topology

In bus topology all the nodes are connected to a main cable called backbone. If any node has to send some information to any other node, it sends the signal to the backbone. The signal travels through the entire length of the backbone and is received by the node for which it is intended. A small device called terminator is attached at each end of the backbone. When the signal reaches the end of backbone, it is absorbed by the terminator and the backbone gets free to carry another signal. This prevents the reflection of signal back on the cable and hence eliminates the chances of signal interference.

Characteristics of Bus topology

• It is easy to install.
• It requires less cable length and hence it is cost effective.
• Failure of a node does not affect the network.
• In case of cable (backbone) or terminator fault, the entire network breaks down.
• Fault diagnosis is difficult.
• At a time only one node can transmit data

Star Topology

In star topology each node is directly connected to a hub/switch (zoomed or blinking). If any node has to send some information to any other node, it sends the signal to the hub/switch This signal is then broadcast (in case of a hub) to all the nodes but is accepted by the intended node(s). In the case of a switch the signal is sent only to the intended node(s). Star topology generally requires more cable than bus topology.

Characteristics of Star topology:

• It is more efficient topology as compared to bus topology.
• It is easy to install
• It is easy to diagnose the fault in Star topology.
• It is easy to expand depending on the specifications of central hub/switch
• Failure of hub/switch leads to failure of entire network
• It requires more cable length as compared to bus topology

Tree Topology

Tree topology is a combination of bus and star topologies. It is used to combine multiple star topology networks. All the stars are connected together like a bus. This bus-star hybrid approach supports future expandability of the network.

Characteristics of Tree topology:

• It offers easy way of network expansion
• Even if one network (star) fails, the other networks remain connected and working.

Mac Address:

A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. A network node may have multiple NICs and will then have one unique MAC address per NIC.

IP Address

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."

Domain Name:

A domain name is an identification string that defines a realm of administrative autonomy, authority, or control on the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS).

Domain names are used in various networking contexts and application-specific naming and addressing purposes. In general, a domain name represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet.

Types of Networks

LAN

A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.

ARCNET, Token Ring and other technology standards have been used in the past, but Ethernet over twisted pair cabling, and Wi-Fi are the two most common technologies currently used to build LANs.

MAN

A metropolitan area network (MAN) is a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.

WAN

A Wide Area Network (WAN) is a telecommunication network that covers a broad area (i.e., any network that links across metropolitan, regional, or national boundaries). Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence this mode of telecommunication allows a business to effectively carry out its daily function regardless of location.

PAN
A personal area network (PAN) is a computer network used for communication among computerized devices, including telephones and personal digital assistants. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink). A wireless personal area network (WPAN) is a PAN carried over wireless network technologies such as IrDA, Bluetooth,Wireless USB, Z-Wave, ZigBee, or even Body Area Network. The reach of a WPAN varies from a few centimeters to a few meters. A PAN may also be carried over wired computer buses such as USB and FireWire.

Network Devices

HUB:
An Ethernet hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. The device is a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision.

Switch

A network switch or switching hub is a computer networking device that connects network segments or network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3) and above are often referred to as layer-3 switches or multilayer switches.

Repeater:

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.

Gateway:

A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes, while the nodes that connect the networks in between are gateways. For example, the computers that control traffic between company networks or the computers used by internet service providers (ISPs) to connect users to the internet are gateway nodes.

Network Security

Denial of Services

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DoS attack) is an attempt to make a computer or network resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted efforts of a person, or multiple people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely.

Intrusion Problem

Snooping, in a security context, is unauthorized access to another person's or company's data. The practice is similar to eavesdropping but is not necessarily limited to gaining access to data during its transmission. Snooping can include casual observance of an e-mail that appears on another's computer screen or watching what someone else is typing. More sophisticated snooping uses software programs to remotely monitor activity on a computer.