Day 2: Data Communications and Networking( Transmission Modes and Transmission Media)


Hello Dear Students,
      Hope you all are doing good.

So today we are going to study the topics from data communications and computer networks. 


Lets get started....

Data Communications

  • Data Communication means the exchange of data between 2 devices via some transmission media such as wire cable. 
  • It is the combination of Hardware(Physical Equipment) and Software(Programs).
  • The effectiveness of data communication system depends on- Delivery, Accuracy, Timeliness and Jitter.
  • The components of data communication system are- Message, Medium, Protocol, Sender, Receiver.

Transmission Modes-

It defines the direction of the signal flow between 2 devices. The direction of the flow of information between 2 communication devices. 3 types-
  • Simplex Mode- In this, one device can only send and the other device can only receive. The information is sent in only 1 direction. There is no mechanism for information to be transmitted back to the sender. It is UniDirectional. The number of required wires are 2. For example, TV, Radio,Keyboard, etc.
  • Half Duplex Mode(HDX)- In this, each station can both transmit and receive, but no at the same time. When one device is sending, the other device can only receive, and vice-versa. The information cannot be sent and received simultaneously. The number of required wires are 2. For example, Walkie talkie.
  • Full Duplex Mode(FDX)- In this, both stations can transmit and receive simultaneously. It is also called Duplex and is BiDirectional. The number of required wires are 4. For example, the Telephone calls where both can talk at same time.
Transmission Medium-

It is the medium by which the information is being carried from the sender to the receiver. The information is being sent through the electrical and the electromagnetic signals. The electrical signals are in the form of current whereas the electromagnetic signals are in frequencies. broadly 2 types-
  • Wired or Guided Medium
  • Wireless or UnGuided Medium
Guided Medium-  Guided medium are those which provides a connection from one device to another, contained by physical limits of the medium. The guided media includes-
  • Twisted-pair cable- It uses the metallic (copper) conductors that transmit signals in form of electric current. It consists of 2 copper wires about 1mm thick, twisted together. One wire is used to carry signals to the receiver, and other is used only as ground reference. It is of 2 types-  
                   Unshielded Twisted pair cable(UTP) - It is most common twisted pair cable used in communications.
                 Shielded Twisted pair cable(STP) - IBM has produced STP. It has a metal shield which basically prevents from noise or crosstalk, it is                     bulkier and more expensive.
         Twisted-pair cables are used in telephone lines to provide data channels and voice. LANs such as 10Base-T and 100Base-T also uses                           twisted-pair cables.
  • Coaxial Cable- It is also known as Coax and is basically used to carry signals of higher frequency. It does not contains 2 wires but has a central core conductor of copper wire. It is encapsulated with outer metallic wrapping which prevents from noise. The whole cable is protected by plastic cover.  It is basically of 3 types-
                 RG-59- The impedance is 75 Ohm. Used in Cable TV.
                 RG-58- The impedance is 50 Ohm. Used in thin ethernet.
                 RG-11- The impedance is 50 Ohm. Used in thick ethernet.
         Coaxial cables are widely used in analog telephone networks where single coaxial network could carry 10,000 voice signals. Later it was used           in digital telephone networks where single coaxial network could carry digital data up to 600Mbps. Cable TV uses RG-59 coaxial cable.                     However, it is now replaced with fiber-optics cables.  Coaxial cables are also used in Ethernet LANs.
  • Fiber-optics Cable- It is made up of glass or plastic and it transmits the signals in the form of light. The components of fiber-optics cable are- Light Source, Transmission Medium, and Detector. The modes for propagating light are- Single mode and Multimode( Step-index or graded-index). Multimode refers to the multiple beams from light source move to different paths. The fiber-optics cable connectors are- SC connector(used for cable TV), ST connector(used for connecting cable to network devices), and MT-RJ connector. It is used in Cable TV and LANs.

UnGuided Medium-  The unguided medium also known as wireless media. As the name suggests, it is wireless means no physical conductor is there. It transport electromagnetic waves(frequency). Signals are broadcast through free space and is available to anyone receiving signals. 
  • Radio Waves- Is is Omni Directional where an Antenna transmits radio waves in all directions. Basically used for multicast communication. It's frequency is between 3kHz to 1GHz. It travels long distance. Examples are- AM and FM radio, television, Mari-time radio, paging, etc.
  • Micro Waves- It is Uni Directional where the sending and receiving antennas to be aligned. It's frequency is between 1GHz to 300 GHz. They are used in cellular phones, satellite networks, and wireless LANs.
  • Infrared- Infrared signals can be used for short-range communications in a closed area using line-of-sight propagation. It's frequency is between 300 GHz to 400 THz. Such a wide bandwidth can be used to transmit digital data with a very high data rate. Examples- Remote controls for TVs, Wireless mouse and keyboards for PCs, etc.

Referrence- Behrouz A Forouzan


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