Computer_Network

A computer network :-> It is a group of two or more computers connected to each electronically. This means that the computers can "talk" to each other and that every computer in the network can send information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet.

A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communicationsand allows sharing of resources and information among interconnected devices.

Put more simply, a computer network is a collection of two or more computers linked together for the purposes of sharing information, resources, among other things. Computer networking or Data Communications (Dotcom) is the engineering discipline concerned with computer networks.

Computer Network

Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications computer science information technology and/or computer engineering since it relies heavily upon the theoretical and practical application of these scientific and engineering disciplines.

Networks may be classified according to a wide variety of characteristics such as medium used to transport the data, communications protocol used, scale, topology, organizational scope, etc.

Computer Network

Application of computer networks

Local networks use Ethernet or Wi-Fi. Most computer networks use Ethernet or Wi-Fi as the LAN technology. Wi-Fi is also know as IEEE 802.11. In the wide area, almost all networks use TCP/IP to connect between sites. TCP/IP packets are put inside Ethernet or Wi-Fi frames to transport them over the local area. Computer software uses TCP/IP to create connections between computers and share information.

The first application for computer networks was to share printers attached to a personal computer in a small office. Many modern printers attach directly to the network and no longer need a host computer to operate. Anyone connected on the network can use any printer on the network, providing they have correct permissions.

Print Sharing

Technology

Application of computer networks

The second common application for computer networking was to share files and disk space. Files created on one computer can be used by someone working on another computer accessing the file over the network. This is the simplest form of electronic collaboration. This concept has been extended to create file servers. These are computers with the main purpose of storing and sharing files.

File Sharing

Wide Area File Sharing

NFS and CIFS are systems that work well in a local area with high speed links between the computers. They do not work well over long distances where bandwidth between the computers may be limited. The File Transfer Protocol (FTP) was designed to transfer files over long distances at slow or unpredictable speeds. Transferring files is not as interactive as sharing files, but it still allows for collaboration.

Application of computer networks

In the late 1990s, the Hyper Text Transfer Protocol (HTTP) gained widespread acceptance. This allowed information to be posted on a server in a standard markup language called the Hyper Text Markup Language (HTML). HTML also provides a mechanism for input. This is one of the main applications of computer networks since the year 2000. Web pages can display information in a standard format and receive input from the users to create surveys, shopping on line and many other applications

As 2010 approached, there was more interest in using computer networks to provide voice and video services. IP phones and IP TV became an alternative to the traditional phone system and cable TV system. We can expect to see more of these applications as the network continually grows.

World Wide Web and Beyond

Real Time Applications

There are 2 basic categories of Transmission Media:

Transmission Media

Guided

Unguided.

Many transmission media are used as communications channels.For telecommunications purposes in the United States, Federal Standar 1037C, transmission media are classified as one of the following:

Guided (or bounded)—waves are guided along a solid medium such as a transmission line.

Wireless (or unguided)—transmission and reception are achieved by means of an antenna.

Guided Media

Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path. The data signals are bound by the "cabling" system. Guided Media is also known as Bound Media. Cabling is meant in a generic sense in the previous sentences and is not meant to be interpreted as copper wire cabling only.

There 4 basic types of Guided Media:

Open Wire

Twisted Pair

Coaxial Cable

Optical Fibre

→

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Un Guided Media

Unguided Transmission Media consists of a means for the data signals to travel but nothing to guide them along a specific path. The data signals are not bound to a cabling media and as such are often called Unbound Media.

Also called wireless communication. It transports electromagnetic Waves without using a physical conductor. Signals are broadcastthrough the air ( in some cases water). There are available to anyone who can receive them.

Radio Frequency Allocation – the selection of the electromagneticspectrum defined as radio communication is divided into 8 ranges,called bands, each regulated by government. These bands arerated from very low frequency (VLF) to very high frequency (EHF)

OSI Model

Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary standards for networking and for operating system involved in networking functions.

Layered approach to communications

Seven layers altogether Each layer performs a unique function Each layer has its own protocol Protocol messages in upper layer is data to layer below

Open Systems Interconnection

Standard model for data communications Specified by international standards organization (ISO) Adopted by CCITT/ITU Official model explained in X.200 series

10

Physical

Link

Network

Transport

Session

Presentation

Application

Unreliable Wire, Telco Line

Reliable Across Physical Line

Unreliable Thru Multi-Node Network

Reliable End to End

Sync Points and Dialogs

Data Representation & Syntax

User Level Processing

RS232, T1, 802.x

LAPB, HDLC

X.25 Pkt, IP

TCP

ISO Session

ISO Presentation

Telnet, FTP, Mail

Layer Name Description Examples

7 Layers

LAYER 7 – The APPLICATION Layer

• The top layer of the OSI model

• Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing

LAYER 6 – The PRESENTATION Layer

• Manages data-format information for networked communications (the network’s translator)

• For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand

• This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression

LAYER 5 – The SESSION Layer

• Responsible for initiating, maintaining and terminating sessions

• Responsible for security and access control to session information(via session participant identification)

LAYER 4 – The TRANSPORT Layer

• Manages the transmission of data across a network

• Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium)

• Reassembles chunks into their original sequence at the receiving end

LAYER 3 – The NETWORK Layer

• Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts

• Responsible for deciding how to route transmissions between computers• This layer also handles packet switching and network congestion control

LAYER 2 – The DATA LINK Layer

• Handles special data frames (packets) between the Network layer and the Physical layer

• At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer

LAYER 1 – The PHYSICAL Layer

• Converts bits into electronic signals for outgoing messages

• Converts electronic signals into bits for incoming messages

• This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.)

• The bottom layer of the OSI model

Computer Networking device (Hard Ware)

Computer networking devices are units that mediate data in a computer network , Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment.

List of computer networking devices

•Bridge: A device that connects multiple network segments along the data link layer. Works on OSI layer 2.

•Switch: A device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. So unlike a hub a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. Works on OSI layer 2.

•Router: A specialized network device that determines the next network point to which it can forward a data packet towards the destination of the packet.unlike a gateway, it cannot interface different protocols. Works on OSI layer 3

•Hub: Connects multiple Ethernet segments together making them act as a single segment. When using a hub, every attached all the objects, compared to switches, which provide a dedicated connection between individual nodes.works on OSI layer1.

•Repeater: Device to amplify or regenerate digital signals received while sending them from one part of a network into another. Works on OSI layer 1.

Some hybrid network devices:

•Multilayer Switch : A switch which, in addition to switching on OSI layer 2, provides functionality at higher protocol layers.

•Protocol Converter: A hardware device that converts between two different types of transmissions, such as asynchronous and synchronous transmissions.

•Bridge Router : Combines router and bridge functionality and are therefore working on OSI layers 2 and 3.

Other hardware for establishing networks or dial-up connections:

•Multiplexer: Device that combines several electrical signals into a single signal

•Network Card: A piece of computer hardware to allow the attached computer to communicate by network

•Modem: Device that modulates an analog "carrier" signal (such as sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information, as a computer communicating with another computer over the telephone network

•ISDN terminal adapter : A specialized gateway for ISDN

•Line Driver: A device to increase transmission distance by amplifying the signal. Base-band networks only.

Networking Soft Ware

Network Software is a set of primitives that define the protocol between two machines. The network software resolves an ambiguity among different types of network making it possible for all the machines in the network to connect and communicate with one another and share information.

Network software is the information, data or programming used to make it possible for computers to communicate or connect to one another.

Network software is used to efficiently share information among computers. It encloses the information to be sent in a “package” that contains a “header” and a “trailer”. The header and trailer contain information for the receiving computer, such as the address of that computer and how the information package is coded. Information is transferred between computers as either electrical signals in electric wires, as light signals in fiber-optic cables, or as electromagnetic waves through space.

Types of Cable in Networking Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types.

The type of cable chosen for a network is related to the network's topology, protocol, and size.

Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.

Types of cables used in networks :-

Coaxial Cable Fiber Optic Cable Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable

1 ) Coaxial Cable :-

Fig. 1. Coaxial cable

Coaxial cabling has a single copper conductor at its center. A plasticlayer provides insulation between the center conductor and a braided metal shield (See fig. 1). The metal shield helps to block any outside interference .

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable.

The two types of coaxial :-

1) Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to

the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters.

2) Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters.

Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does

Coaxial Cable Connectors :-

Fig. 2. BNC connector

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 2).

Different types of adapters are available for BNC connectors, including a T- connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather

2 ) Fiber Optic Cable :-

Fig. 3. Fiber optic cable

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 3). It transmits light rather than electronic signals eliminating the problem of electrical interference.

This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services.

The center core of fiber cables is made from glass or plastic fibers (see fig 3). A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC.

3 ) Unshielded Twisted Pair (UTP) Cable :-

Fig.4. Unshielded twisted pair

Twisted pair cabling comes in two varieties :- shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 4).

The quality of UTP may vary from telephone-grade wire to extremely high- speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.

The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

Category Speed Use

1 1 Mbps Voice Only (Telephone Wire)

2 4 MbpsLocalTalk & Telephone (Rarely used)

3 16 Mbps 10BaseT Ethernet

4 20 Mbps Token Ring (Rarely used)

5100 Mbps (2 pair)1000 Mbps (4 pair)

100BaseT EthernetGigabit Ethernet

5e 1,000 Mbps Gigabit Ethernet

6 10,000 Mbps Gigabit Ethernet

Categories of Unshielded Twisted Pair

Unshielded Twisted Pair Connector :-

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig.5).A slot allows the RJ-45 to be inserted only one way.

RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

Fig. 5. RJ-45 connector

4 ) Shielded Twisted Pair (STP) Cable :-

Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.).

If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.

Fig.6. Shielded twisted pair

Shielded twisted pair cable is available in three different configurations :

Each pair of wires is individually shielded with foil.

There is a foil or braid shield inside the jacket covering all wires (as a group).

There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).