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 bitsEg. Address used to identify the route to the destinationTiming: It refers to two characteristics; when and how much to send.

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.

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)

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.

Transmission medium

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

Types of Transmission medium

Types of Transmission medium

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

mediumEg., Radio waves, Microwave and Infra red

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

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

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

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.

Performance

• Attenuation is higher• Higher bandwidth• Signal weakens rapidly and requires frequent use of

repeaters.

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

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)

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.

Propagation modes

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.

Multimode fibres

Single mode fibre

• Uses step index fibre• Carries light pulses along single path

Fibre types

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)

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.

Performance

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

Applications

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

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.