Computer Network | Types Of Network | Topology | Data Transmission

Parveena February 12, 2020

Computer Network

Computer Networking

 Computer Network can be defined as a group of independent computers possibly located at different physical locations interconnected with each other so that they can communicate with each other.

In 1949 cloudy unknown word for the best telecom company in US of America has propose a model of communication.
 The data communication  concerns itself with the transmission of information between two location. The transmission of broadly involves sending and receiving the information .This indicates sending information between machines that are connected together by physical wire or radio link. The machines maybe transmitters ,telephone, computers etc.

COMMUNICATION


Data is transmitted from computer terminal to the information processing Unit through data communication circuit.
 Two types of data transmission methods are used to carry data from its origin to the information processing Unit.

Offline computers are not connected by communication circuit data is transmitted between a terminal and information processing Unit through a magnetic tape and magnetic disk pack.
 Online computers connected by communication circuit data can be instantly transmitted between a terminal and information processing unit.

Purpose Of Networking

  • It allow users to share computer resources like files printer, Disk etc among each other.
  •  Have a centralized control on the other computers.
  • Allow user to work from a place away from their own computers.


Types of networking -
Networks have been classified on various bases. On basis of extended of geographical coverage area Computer Network are-
LAN
MAN
WAN

Local area network
A local area network is a computer network in which the participating computers and computing resource are all located in a small geographical area such as a building or University campus.It is open a private owned network. LANs interconnect computers and peripherals over common communication medium in order to that use might share access to connected computer's databases, File,Application and peripherals.
LANs also provide a connection to the network either through a computer which is attached to both network  a or throughd called is gateway.

  Hardware Used in LAN
  1. Nodes  or workstation usually PC.
  2. One or more related power full computer with large storage capacity to act as a server.
  3. Network interface card attached to each of the workstation or servers.
  4. Cables to connect the computers and peripherals.

Software Used in LAN

  •  Network software Management or network operating system .some popular network systems are -

1 NOVAL Netware
2.Window NT server
 3.Windows 2000
4.Linux etc
 Application Software  capable of supporting network access.
 Server Software -a file server is a server software that can process file related request from the client workstation.Print servers, similarly process print-related request from the client workstation.

Client Software- this software run on the client nodes and allowed requests to be sent to the server and to receive back the result.

Advantage of LAN
  • All the available peripherals and other expensive resource can be share among the workstations.
  •  Application software and data can also be shared among the workstations.
  • Users can communicate with each other through emails.

 Disadvantage of LAN

  • A required resource may be unavailable if the server is down.
  •  Having few workstations may be expensive due to the cost of additional hardware and software.
  •  If not handled properly that a security maybe may not be assured.


Metropolitan Area Network (MAN)
A network which is spread over a large area than LAN. For example computer network connected to the computers located at hospital in a city is a MAN.

 Wide Area Network -WAN
Networks covering large area than that of MAN connecting the participating computers via telecommunication and satellite link are called WAN.A WAN may span a  country or the entire world.
The common transmission media used in WAN are -
Radio Waves ,Microwaves ,Communication Satellites.

  Hardware used in WAN are-
 Bridge is that connects two similar networks.
 Router AND Gateway is hardware that connected to dissimilar  Computer Networks.

 WAN Types
 Public Networks- This network are controlled by the government .Public can use them by subscribing to the services. Examples-
Integrated Service Digital Network ISDN
 Public Switched Telephone Network PSTN
 Public Switched Data Network PSD
 Value Added Network VAN

 Private Network - These WANs are owned and control by particular party and not open for public use. For Example- A company may have branches  in many countries. A WAN may connect its branch office.The company own the WAN and it is not meant for public use.





Data Transmission

Data Transmission along a communication medium depend on manufacture such as

  • Channel Bandwidth
  •  Nature of Transmission 
  • Direction of Transmission 
  • Mode of Transmission 
  • Communication Protocol.

Channel bandwidth
 Bandwidth is a measure of speed of transmission through a communication channel or bits transmitted per second or bps.
 In terminology bandwidth is also referred to simple a band.

Types of Band
Narrow band -This is lowest slowest of all the band with transmission speed ranging between 40 to 100 bps. example telegraph.

Line Band-This channel can transmit data 110 BPS to 9600 BPS example telephone lines.

Medium band - The capacity of this channel is of the order of megabits per second .they are the channel provided with lease line .

Broadband - This channel are faster with data transmission rates of several MBPS and above. Microwave links, Coaxial Cable and Fibre Optical channel belong this category .

Nature of Transmission
 Serial Transmission- Bits  are transmitted across a single line as a series of BITs, one after the other. At the receiving end , the bits are assembled back to form Bytes. for example telephone line.

 Parallel Transmission- Many Bits are transmitted simultaneously  along separated lines.
 It is many times faster than serial transmission because of multiple communication line required .
It is more expensive than serial transmission due to  cost overhead.
 This type of transmission is used only in short distance transmission of data. Example-Transmission of data from a PC to printer printer .



Direction of transmission
Depending on the direction of flow of data the transmission can be of the following three types
Simplex
Half duplex
 Full duplex
Simplex -communication data flow only in one direction communication between a mouse and a computer is of this type data flow from mouse to computer not the other way around.
Half Duplex - communication data can flow from the both of direction but only in one direction at a time walkie-talkie.
 Full Duplex - communication data can flow in both the direction simultaneously. as a result it is comparatively faster and more efficient. Example Telephone line.

Mode of Transmission
Depending on the difference in the speed of transmission between centre and receiver data can be transmitted in two way
Synchronous 
 Asynchronous

 Asynchronous Transmission-
 In this mode of transmission ,one character is transmitted at a time is transmitted character is separated from other characters by a start pit and a stop bit the receivers filters out the start and stop bits to obtain the data transmitted data this model transmission is used in case where the difference the speed of centre and receiver is very large as in data logging system  .

Synchronous Transmission-
A large junk of character is sent at unit at carefully timed interval in this mode of transmission is data junk is separated by synchronising characters the receivers goes on reading the data until it comes across synchronised character that a transfer between computer take place in this manner.

Network Topology

Computer Network and also classified depend on the manner of participating nodes are connected to each other the manner in which nodes of a computer network are connected to each other is called topology network.

Topology are -
Bus topology
Star topology
Rring topology
Hybrid topology
Full connected topology.


Bus Topology
The Bus consists of a single communication channel. Each connected device is attached to the
media at an interface point. Each connected device has a unique hardware address. Data transfer
takes place using these hardware addresses. The bus will have more complex arrangements with
several interconnected segments.
Advantages
  • Simple layout.
  • Ease in connectivity..
  •  Locating cable faults is easy
  •  Ideal for one to many data transmissions since all connected devices see the traffic on the cable. The signal reaches all stations regardless of their position on the bus.
Disadvantage/Bottlenecks
  • There is no automatic acknowledgement of receipt by virtue of the topology. 
  • The signals stop on reaching the end of the cable and do not return by default to the sender. Therefore, the higher level protocols exists which can ensure that data is successfully exchanged.

Ring Topology
Unlike bus topology, in a ring configuration the data transmission is unidirectional. Data
transmissions are received by each station’s interface as the data passes through the interface
connection. Like bus topology, each interface only copies the data from the network. Thereafter
data communicates to the device connected to the network on basis of the packet’s destination
address. Each network interface connection has its own hardware address for identification.
Typical ring topology is generally used in the large network Fibre Distributed Data Interface
(FDDI).
In ring topology, each interface station allows data transmission to pass through the interface
with only a few bits delay. For instance, consider circulation of a data packet (say 128 bytes), the
start of data packet may well have circulated around the ring and arrived back at the originating
station before the end of the packet has left for circulation. There is always only one circulating
data packet on the ring.
Advantages
  •  No routing problems since everyone on the ring receives the data. The addressed node makes copy of the data for circulation.
  •  Every generated packet eventually returns to the node therefore the acknowledgment of successful data transmission is trivial
  •  Larger networks may be constructed from a number of interconnected rings.
Disadvantage
  • In case one of the nodes fails network comes to a halt.

Star Topology
 All load in this topology are joined at a single node. This single node is called as a Central node HUB or switch to which all other devices are attach directly. This topology is frequently used for network in which control of network is located in Central node.
 Asynchronous Transfer Mode ATM is an example of star topology .This topology is very stable in banking network system where is master controller computer system is connected with note spread all over the city.
 Advantages
 1.Network is very reliable .Unless the Hub fails, the network remains functional .
2.It allows better control and enhanced security.

 Disadvantage of star topology 
This is very expensive due to extra hardware needed.
 The network failed if the central computer system fail .

Hybrid Topology -
This network topology is a mixture of above of all the topology.A central computer is a attach with sub controller which in turn participate in a variety of topology.

 Advantages
 Extremely flexible.
 It is very reliable.

 Disadvantage
 It is expensive.
 Adding a note to it is not very easy .

Full Character Topology
All the nodes are connected to all other node with separate link .
Advantages
 It is extremely reliable.
Breakdown of only does not affect the network communication is faster.

 Disadvantages 
This very expensive .
Additional no require many link to be set up.