Chapter - 3 Communication and Networking


Communication and Networking

3.1 Introduction
COMPUTER NETWORK:
 A system in which two or more computer is interconnected with each other is called Computer Network. The main purpose of computer networking is to share resources such as files, printers, scanners etc within a networks domain.
The connection method between two computers can be wired such as twisted pair, co-axial cable, optical fiber or wireless such as microwave, satellite, Bluetooth etc.
Advantages of computer Network
       i.            Cheap due to resource share
    ii.            Fast and real time communication
 iii.            Access to more resource through internet.
  iv.            Long distance communication/remote connection.
     v.            Increase storage capacity.
Disadvantages of computer network
       i.            Security issue
    ii.            Computer virus
 iii.            High installation cost.
  iv.            Dependency server can lead to network failure.



3.2 Analog and digital signal:
Signal is the electromagnetic representation of data.
Analog Signal
Digital signal
1.     The analog signal is continuously varying electromagnetic waves called sine wave.
1.     The digital signal is a sequence of discrete voltage pulses and called square waves.
2.     Diagram
 

                                                      time
                  
2.     Diagram
                                                                                                                                           
                                                       time
3.     It is suitable for long distance communication through bounded media.
3.     It is not suitable for long distance communication through bound media.
4.     Demodulator converts analog signal into digital signal.
4.     Modulator converts digital signal into analog signal.

3.3 Direction of Communication Flow:
a)    Simplex:
In a simplex mode the communication is unidirectional as on one way street. Only one of the two devices on a link can transmit, other can only receive. The simplex mode can use the entire capacity on the channel to send data in one directional. Eg: Radio, Keyboard etc.
b)    Half duplex:
In this mode each station can transmit and receive but not at the same time. When one device is sending the other can only receive and vice-versa. The half duplex mode is like a one lane road with traffic allowed in both direction. In this mode the entire capacity of a channel is taken over by whichever of the two devices is transmitting at a time. The half duplex mode is used in cases where there is no need of communication in both directions at the same time. Example: Walkie-talkie
c)    Full Duplex:
In this mode can transmit and receive data simultaneously. The full duplex mode is like two way street with traffic flowing in both direction at the same time. In full duplex signals going in one direction share the capacity of link with signals going in the other direction. This sharing can occur in two ways either the link must contain two physically separate transmission path. One for sending and another for receiving or the capacity of channel are divided between signals travelling in both directions. An example of full duplex communication is telephone network, mobile network etc.
3.4 Types of Network/Network Architecture
·        The theoretical concept behind the design of a computer network is called network architecture. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources.
·        The computer that provides resources to other computers on a network is called server.
·        In the network the individual computers, which access shared network resources are known as workstations or nodes.
3.4.1 Network Based on servers:
Based on how the computers in a network are configured and how they access information network are classified into two types: peer to peer and client-server.
a) Peer to Peer network:
- The technique of data transmission from node to fashion in which each node behaves like as server or host temporarily is called peer to peer architecture.
- There is no client or good and powerful server.
- In the peer network the network users simply share disk space and other resources.

 b) Client server architecture:
- The network in which the all workstations or nodes are connected with main server.
- The data sent by any computer, at first reaches to server, and then passed to each workstation.
- The server behaves like as distribution station.
- All the clients are busy at the time distribution by server.
- The star topology is the suitable example of client server architecture.

3.4.2 Network Based on Geographical Area:
According to it the network is of 3 types.
1) Local Area Network (LAN):
- LAN refers to a combination of computer hardware and transmission media that is relatively small.
- LAN is typically comprised of only one transmission media type such as coaxial cable or twisted pair cable but never both.
- Examples of LAN: Two computers connected together in an office or two building connected together by a high speed wire etc.
- LAN is characterized by comparatively high only one kind of cable, which generally is limited to 5 KM or less.
2) Metropolitan Area Network (MAN):
- MAN is a network that is larger than a LAN.
- It is called metropolitan since it normally covers the area of city (a few tens to about 100 KM).
- Different hardware and transmission media are often used in MAN because they don’t require complete access to location between the network sites.
- The main important characteristic of MAN is their diversity (range).
- Two most important components of MANs are security and standardization is necessary to ensure reliable data communication.


3) Wide Area Network (WAN):
- A WAN includes all networks larger than a MAN.
- WANs are characterized by the slowest data communication rates and the largest distance.
- The connections in WANs are done by the device called global WANs.
- An enterprise WAN connects an entire organization, including all LANs at various sites.
- Global WANs also span the world, but they don’t have to connect LANs within a single organization. Internet is an example of global WAN.
- Private WANs (Internet) are also available.

3.5 LAN Topology
- A network topology is the arrangement of computers, cables and other components on a network. There are 5 basic topologies:
a) Bus Topology
- All the nodes are attached to a continuous cable in straight line.
- Cable or bus is terminated at either end.
- Data is transmitted to all network adapters through that cable.
Advantages:
-         It is simple, reliable, easy to use and easy to understand.
-         The bus requires the least amount of cable to connect the nodes; therefore, it is less expensive.
-         It is easy to extend a bus.
Disadvantages:
-         Heavy network traffic can slow a bus considerably.
-         It is difficult to trouble shoot a bus.
-         Each BNC barrel connector weakens the electrical signal.


b) Ring Topology:
-         Each computer is connected to the next computer with the last one connected to the first.
-         It provides equal access for all computers on the network.
-         A ring network usually needs more cabling then a bus network.
Advantages:
-         Every computer is given equal access.
Disadvantages:
-         Failure of one computer on the ring can affect the entire network.
-         Difficult to trouble shoot.
-         More cable is needed.

c) Star Topology:
-         The computers are connected by a device called hub in a central located computer.
-         Stars are used in concentrated networks.
Advantages:
-         It is easy to modify and add new computers to a star network without disturbing the rest of the network.
-         The center the star is a good place to diagnose network problems.
-           Single computer failures don’t necessarily bring down the whole star network.
Disadvantages:
-         If the central hub failure, the whole network stops.
-         It cost more to cable in star topology.







d) Mesh Topology
- The node is linked to each other through intermediate nodes with redundant paths.
- If you are using a WAN and routers to search among multiple active paths to determine the best path, then mesh topology will be best.
- The Internet is an example of a large mesh topology.
Advantages:
-         Fault tolerance.
-         Communication channel is guaranteed.
-         Easy to troubleshoot.
Disadvantages:
-          Difficult to install and reconfigure.
-         Cost of maintaining redundant lines.
e) Tree Topology:
- Each device is connected to it own port or hub just like a star topology.
- Tree or ‘star of star’ topology interconnects hubs in hierarchical fashion.
Advantages:
- easy to extend.
- Easy to add new nodes.
- Allows the network to isolate and prioritize communication from different computers.
Disadvantage:
-         If the main root or hub fails to operate then the entire networks fail to operate.
3.6 Transmission Media:
A path for a data communication between source and destination is called Transmission Media. It is of two types:
a) Guided Transmission Media
b) Unguided Transmission Media

a) Guided Transmission Media:
The electromagnetic waves or electrical signals are guided along the physical path. For examples: C0-axaial cable, twisted pair cable, optical fiber etc.
For guided transmission the bandwidth depends on distance and medium.

Mainly three guided media are used.
1. Twisted pair cable
2. Co-axial Cable
3. Optical Fiber

1. Twisted Pair Cable:
Physical description:
-         It consists of two conductors (insulated Cu-wire) twisted together spirally.
-         One of the wire is used to carry signal whereas the other wire is used as ground or reference.
-         Generally twisted length 5 to 15 cm. Thickness/diameter=0.4 to 0.9 cm.
Application:
1.     Telephone Network
2.     Communication within building
There are two types of twisted pair cable and these are:

i) Unshielded Twisted Pair (UTP)
- It provides reduced interference.
- It provides better work performance.
- The metallic shield is grounded at both ends.
ii) Shielded Twisted Pair (STP)
- Used for cheaper network.
- Used for small distance transmission.
- Subjected to noise and electromagnetic signals interference.



2.  Co-axial Cable:
- Co-axial cable is made of two conductors that share a common axis.
- The center of the cable is copper wire encased in insulating plastic form.
- The foam is surrounded by the second conductor.
- They are used in communication network.
- Each co-axial cable can provide more than 5000 links.
- There are two types of co-axial cable. They are: thin net and thick net.

3. Optical Fiber:
- Optical fiber cable is made of glass materials. The cable works on the principle of total internal reflection.
- There are three parts in an fiber. The inner part is called core. The core is surrounded by cladding and cladding by jacket.

Some advantages of optical fiber:
-It has a much greater bandwidth than metal cables.
-It is much thin and light.
-Data can be transmitted digitally.
-But the cables are expensive.


b) Unguided Transmission Media:

It provides a means for transmitting electromagnetic waves but don’t guide them. For example: Propagation through air, satellite, wireless media, microwave etc.

In this case, bandwidth signals is more important than medium itself.

1. Satellite:
- A communication satellite is a microwave relay station, linking two or more ground based on microwave transmitter or receiver known as earth station or ground station.
- Satellite receives transmission on one frequency band (uplink), amplifies or repeats the signals and transmits it on another frequency called downlinks.
2. Wireless Media:
-Wireless media are used when it is impossible to install cables.
Many wireless devices that access the WAP (Wireless Application Protocol) Example: Bluetooth, microwave, artificial satellite etc.

3. Microwaves:
- Microwaves are radio waves that provide high speed signal transmission.
-A microwave station is an earth-based reflective dish that contains the antenna, transceivers and other equipment necessary for microwave communications.
-Current users of microwave transmission include cable TV providers, telephone companies, Hospital etc.

 3.7 Networking connecting device
1. Modem (Modulation-Demodulation)
- Modem is a device that allows a computer to transmit information over a telephone line.
- Modem translates between the digital signals the computer uses and analog signals that the telephone uses.
- The modem modulates the digital data onto a carrier signal on the telephone line while transmitting.
- When receiving, the modem demodulates the carrier signal to digital data.
- The maximum bit rate of PSTN (Public Switched Telephone Network). Example: FAX (Facsimile).
2. NIC (Network Interface Card)
-It is also called network adaptor.
- It is a circuit board or card that is installed in computer so that it can be connected to a network.
-PC will contain the NIC such as Ethernet.
-Network interface card provides a dedicated, full-time connection to a network.
3. Switch
-A bridge is a device that passes data packets between multiple network segments that use the communications protocol.
-Switches are similar to bridge but often a more direct network connection between the source and destination computers.
4. Hubs
-Hubs are connectively devices that connect computers in a star topology.
-Hubs contain multiple ports for connecting to network components.
-Use of hub has become very common networking as its cost is lower and easier to install.

5. Router
-A router is a device that acts like a bridge or switch but provides more functionality.
-Routes enable all users in a network to share a single connection to the internet or a WAN.

6. Gate Way
- A Gate Way is a device that enables communication between different network architecture.
- A Gate Way takes the data from one network and repackages it , so that each network can understand the other network’s data.
- A Gate Way is like an interpreter.

7. Repeater
- A repeater is a physical layer device used to interconnect the media segments of an expanded network.
- A repeater receives signals and retransmits them at their original strength and definition.

8. Bluetooth
-A proposed radio frequency (RF) specification that many portable devices will uses for short-range wireless communication is called Bluetooth.
- To use Bluetooth device must include a transceiver chip and be within a specified range (about 10 meters).
-For example: Laptops computers, Cellular Telephones etc
9. IR (Infrared)
- Infrared is a type of electromagnetic wave of large wavelength and small frequencies than visible lights.
-Routine controls and IRDA (Infrared Data Association) uses infrared emitting nodes to emit infrared radiation.
- It is used in TV, Printers, and Wireless LAN etc.
10. Wi-Fi
- Wi-Fi is a trademark of the Wi-Fi Alliance that manufactures may use to brand certified products that belongs to a class of Wireless LAN devices.
- A Wi-Fi enabled device such as a PC, Video-game Console, mobile Phone, MP3 Player can connect to the internet when within a range of a wireless network connected to the internet.

3.8 OSI (Open System Interconnection) Reference Model
-ISO certified origination for standard model for a network communication, called the OSI Reference Model in 1982 AD.
-The OSI Model divides network communication into 7 layers.
-The 7 layers of OSI Reference Model can be divided into 2 categories. They are: Upper Layer and Lower Layer
- Upper Layers of the OSI Model deal with application issues and generally are implemented only in software.
- Lower Layer of the OSI Model handle data transport issue.

Layer
Protocols
Application  Layer
FTP, TFTP, Telnet, HTTP
Presentation  Layer
SMTP,NFS
Session  Layer
Telnet, SNMP
Transport Layer
TCP,UDP
Network  Layer
IP
Data Link  Layer
ARP,RARP,RIP
Physical  Layer
Ethernet, Token Ring

Figure: 7 Layers of the OSI Reference Model


3.9 Communication Protocol
- A set of rules which is used by computers to communicate with each other across the network is called Protocol.
- Protocol specifies the format of message and the rules for exchanging the message.
Some of the popular protocols are defined below:
a)    TCP/IP
-         The main task of IP is the best effort delivery of the packets.
-         The function of TCP is the reliable, ordered delivery of stream of stream of bytes from a program on one computer to another computer.

b)    SMTP ( Simple Mail Transfer Protocol)
-         It is an application layer protocol for sending email using underlying TCP transport layer protocol in TCP/IP network.
-         STMP is a complete text based protocol.
-         STMP is extended to send other types of information such as text, picture, videos and other multimedia, program and data files using an internet standard called (Multimedia Internet Mail Extension).
c)    POP (Post Office Protocol)
-         It is an application layer protocol to receive the email from a remote mail server using TCP as a transport layer of serves.
d)    FTP (File Transfer Protocol)
-         It is an application layer protocol to exchange files between computers on a TCP/IP network.
-         FTP uses the TCP of the transport layer to transfer the files.
-         FTP is reliable and secure file transfer protocol.



e)    HTTP (Hyper Text Transfer Protocol)
-         HTTP is one of the popular application layer protocols which specify the rules for interlinks documents called Hypertext Documents.
-         The hypertext documents are placed in special host computer called server and a server, usually called internet browser.
f)     Telnet (Terminal Network)
-         It is an application layer protocol that provides interactive text based interference to access the command shell of the remote computer through virtual terminal connection.
-         Telnet protocol uses the transport layer facilities through the TCP protocol. 

UNIT - 3 [HOMEWORK QUESTIONS]
1.     What is networking? List out the advantages and disadvantages of Networking?
2.      Explain any two transmission media with appropriate diagrams.
3.     Describe the types of Network Topologies with their clear diagrams.
4.     Define computer Network. Explain in about LAN and WAN.
5.     Write short notes on:
a)   Coaxial cable                          b)   satellite
6.     What are the types of LAN topology? Explain with diagram.

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