1. Protocols and Standards
Protocols:
set of rules that governs data communications.
A protocol defines what is communicated, how it is
communicated and when it is communicated.
Key elements:
Syntax: it refers to the structure or format of data.
Semantics: it refers to the meaning of each section of bits
Eg. Address used to identify the route to the destination
Timing: It refers to two characteristics; when and how
much to send.

2. Standards
Standards:
• Provide guidelines to manufacturers.
Types of Standards:
• de facto [by fact]-Not approved by an organization but
spreaded widely for use.
• de jure [by law]-Approved by an organization.

3. Standard organizations
• International Organization for Standardization (ISO)
• International Telecommunication Union-
Telecommunication Standards (ITU-T)
• American National Standards Institute (ANSI)
• Institute of Electrical and Electronics Engineers
(IEEE)
• Electronic Industries Association (EIA)
• International Engineering Task Force (IETF)

4. Standard organizations(contd.,)
• Internet Standards
• Thoroughly tested specification
• Strict procedure and must be followed.
• Internet draft
• Working document with no official status
• 6-month life time.

5. Transmission medium
Transmission medium:
• physical path between transmitter and receiver.
• Carry the information from source to destination

6. Types of Transmission medium

7. Types of Transmission medium
2 Types of transmission medium are:
• Guided media(wired) :
 provide a service from one device to another
 waves are guided along a physical path
 Eg., twisted pair, coaxial cable and optical fiber
• Unguided media(wireless):
 Transport electromagnetic waves without Physical
medium
 Eg., Radio waves, Microwave and Infra red

8. Guided media-Coaxial cable
• Inner conductor –Central core
of solid or wire(copper)
surrounded by insulating
sheath-
• Outer conductor-Made up of
metal foil or braid or
combination of both
 Acts as a shield for noise and
completes the circuit.
 Enclosed in an insulting sheath
• Whole cable is protected by
plastic cover

9. Coaxial cable standards
• Categorized by their radio government (RG) ratings
• RG-Denotes the unique set of physical specifications
 Wire gauge of inner conductor
 Thickness and type of inner insulator
 Construction of shield
 Size and type of outer casting

10. Coaxial cable connectors
• For connecting coaxial cables to devices
• Commonly used connector-BNC(Bayone-Neill-Concelman)
• Three types of connectors are:
 BNC connector
 BNC T Connector
 BNC terminator

11. Types
• BNC connector-Connect the end of the cable to the devices.
Eg.TV set
• BNC T Connector-To branch out to a connection to a
computer or other device. Eg. Ethernet networks.
• BNC Terminator-Used at the end of the cable to prevent the
reflection of signal.

12. Performance
• Attenuation is higher
• Higher bandwidth
• Signal weakens rapidly and requires frequent use of
repeaters.

13. Applications
• Used in Analog telephone networks-Carry 10,000 voice
signals.
• In digital telephone networks-Carry digital data upto
600Mbps.
• Cable TV networks.
• Traditional Ethernet LANs
• Used in thin and thick Ethernet.
 10Base-2(Thin Ethernet)-Uses RG-58
 10BAse5(Thick Ethernet-Uses RG-11

14. Fibre optic cable
• Fiber-optic cable transmit signals in the form of light.
• Made up of Glass or Plastic
• Optical fibre uses reflection to guide light through a channel
• Glass or Plastic core is surrounded by Cladding(Dense Glass or
Plastic)

15. Bending of light rays
• I-Angle the ray makes with the line perpendicular to the
interface between 2 substances
• If the angle of incidence I is less than the critical angle, the ray
refracts and moves closer to the surface.
• If the angle of incidence is equal to the critical angle, the light
bends along the interface.
• If the angle is greater than the critical angle, the ray reflects
and travels again in the denser substance.

16. Propagation modes

17. Types of Multimode
Multimode step-index fiber
• Density of the core remains constant from the center to the edges.
• Beam of light moves in a straight line -Reaches the interface of the
core and the cladding.
• Light beam changes the direction at the interface between the core
and cladding
•Step index -suddenness of this change, which contributes to the
distortion of the signal
Multimode graded-index fiber
• Core Density decreases with distance from the center
• Results in carving of light beams.

18. Multimode fibres

19. Single mode fibre
• Uses step index fibre
• Carries light pulses along single path
 Fibre types

20. Cable Composition
• Outer Jacket- Either PVC or Teflon
• Inner Jacket-Kevlar Strands(To strengthen the cables)
• Kevlar-Strong material used in refraction of bulletproof
• Plastic coating- To cushion the fibre
• Fibre-Center of the cable(Consists of Cladding and core)

21. Fibre optic cable connectors
• Three types of connectors:
 SC connector(Subscriber channel)-Uses push/pull
locking system. Eg. Cable TV
 ST connector(Straight-Tip)-Used for connecting cables to
Networking devices. More reliable than SC
 MT-RJ connector-Same as coaxial cable connector.

22. Performance
• Attenuation is flatter than coaxial cable
• Need fewer repeaters.

23. Applications
• Often found in backbone networks
• cost-effective.
• With wavelength-division multiplexing (WDM), we can
transfer data at a rate of 1600 Gbps.

24. Advantages and Disadvantages
Advantages:
 Higher bandwidth.
 Less signal attenuation.
 Immunity to electromagnetic interference.
 Resistance to corrosive materials.
 Light weight.
 Greater immunity to tapping.
Disadvantages:
 Installation and maintenance
 Unidirectional light propagation
 Cost.