Books: 1. Data communications by William L Schweber 2. Data communication and Networking by Behrouz A F0rouzan

Twisted Pair cable Multiconductor flat cable

Advantages of Twisted Pair Cable Simplest to setup Cheapest Limitation of Twisted Pair Cable Small Bandwidth (few hundred khz) High Repeater Frequency (every 6 Km for analog signal and every 2 Km for digital signals) Fair Security

2. Coaxial Cable (Coax) Coax has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid

The outer metallic wrapping serves as as shield against noise as the second conductor This difference in construction makes coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted pair cable.

Coaxial Cable Standards Coaxial cables are categorized by their radio government (RG) ratings. Each RG number denotes a unique set of physical specifications, including the wire gauge of the inner conductor, the thickness and type of the inner insulator, the construction of the shield, the size and type of the outer casing.

Guided Media Coaxial Cable Categories of coaxial cables

Guided Media Coaxial Cable BNC Connectors Bayone-Neill-Concelman

Advantages of coax Higher Data rate (300-400 MHz) than twisted pair (2 MHz). More secure than Twisted pair Disadvantages of coax Attenuation is much higher in coaxial cables than in twisted-pair cable. (signal weakens rapidly and requires the frequent use of repeaters). Fairly costlier than Twisted pair cable A signal in a coaxial cable loses about one half of its original value after 1000 ft of travel, depending on signal frequency

Performance of Coaxial Cable

Performance Comparison between Twister Pair Cable and Coaxial Cable Twister Pair Cable Coaxial Cable

Applications Coax Telephone Network Coaxial cable was widely used in analog telephone networks where a single coaxial network could carry 10,000 voice signals. Later it was used in digital telephone networks where a single coaxial cable could carry digital data up to 600 Mbps. Cable TV networks Ethernet LANs Thin Ethernet - RG 58 10 Mbps Range (185 m) Thick Ethernet - RG 11 -- 10 Mbps Range (5000 m)

Disadvantages of Coaxial Cable High Attenuation Higher Data rate communication not possible

3.Guided Medium(Fiber Optic Cable) Idea is light is carrier of data. Fiber-optic cable is made of glass or plastic Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance suddenly enters another substance (of a different density), the ray changes direction. This bending of light when it moves from one medium to another medium is called as refraction.

Reflection

Refraction

Critical Angle

Principle: Total Internal Reflection 1. Light moves from denser medium to rarer medium 2. Incidence angle should be greater than critical angle Example Looking at the sky while under water

Critical angle is a property of the substance, and its value differs from one substance to another.

Fiber Construction

Optical Fiber Benefits Greater capacity Data rates of hundreds of Gbps Smaller size & weight Lowest attenuation Electromagnetic isolation Greater repeater spacing 10s of km at least More secure against unauthorized users Resistance to corrosive materials. Glass is more resistant to corrosive materials than copper.

Optical Fiber Limitations Fiber Installation and maintenance Terminate the optical fiber cable Straight line alignment Costlier than any other guided medium Unidirectional light propagation

Books: 1. Data communications by William L Schweber 2. Data communication and Networking by Behrouz A F0rouzan

Guided Media Fiber-Optic Cable Propagation Modes

Single Mode

Single-mode uses step-index fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal. The single mode fiber itself is manufactured with a much smaller diameter than that of multimode fiber

Multimode Step-Index

Multimode Step-Index In multimode step-index fiber, the density of the core remains constant from the center to the edges. A beam of light moves through this constant density in a straight line until it reaches the interface of the core and the cladding. At the interface, there is an abrupt change due to a lower density; this alters the angle of the beam's motion. The term step index refers to the suddenness of this change, which contributes to the distortion of the signal as it passes through the fiber

Multimode Graded-Index

Multimode Graded-Index A graded-index fiber, therefore, is one with varying densities. Density is highest at the center of the core and decreases gradually to its lowest at the edge

Comparison of various propagation modes of fiber optical cable

Guided Media Fiber-Optic Cable Optical fiber performance

Guided Media Optical Fiber Cable Applications: SONET Cable TV LAN (FAST Ethernet) 100Base-FX 100Base-X

Transmission Characteristics of Guided Media Twisted pair (with loading) Frequency Range Typical Attenuation 0 to 3.5 khz 0.2 db/km @ 1 khz Typical Delay 50 µs/km 2 km Repeater Spacing Twisted pairs (multi-pair cables) 0 to 1 MHz 0.7 db/km @ 1 khz Coaxial cable 0 to 500 MHz 7 db/km @ 10 MHz Optical fiber 186 to 370 THz 0.2 to 0.5 db/km 5 µs/km 2 km 4 µs/km 1 to 9 km 5 µs/km 40 km 1 THz = 10 12 Hz

Question 1 A light signal is travelling through a fiber. What is the delay in the signal if the length of the fiber-optic cable is 10 m, 100 m, and 1 Km (assume a propagation speed of 2 x 10 8 m/sec)? Delay : Length of cable / Propagation Speed : 100m / 2 x 10 8 m/sec : 0.5 usec

Question 2 A beam of light moves from medium 1 to medium 2. The critical angle of medium 1 is 60. Do we have refraction or reflection for a incident angles of 80? Ans : Cant be determined ( Information related to one of the criterion of Reflection (Total Internal reflection) is not specified)

Question 3 A beam of light moves from one medium to another medium with less density. The critical angle is 60. Do we have refraction or reflection for each of the following incident angles? Show the bending of the light ray in each case. a. 40 - > Refraction b. 60 - > Refraction c. 80 - > Reflection

Question 4 Find decibel values for following voltage (a) 100 = 20log100 =40 db (b) 20 = 20log20 = 20log10*2= 20log10+ 20log2= 26 db (c) 0.2 = (d) 0.03 Hint : For voltage -> db = 20log (X) where X is voltage in volts Log 2 =0.3010 Log 3 =0.6989

Question 5 Convert these power ratios to decibel (db) (a) 100 = 10log100 =20 db (b) 20 (c) 0.2 (d) 0.03 Hint : For Power -> db = 10log (X) where X is voltage in volts

Question 6 What is ratio of two signals with a 0 db SNR? 0=10log X X=10 0 X=1 What is ratio of two signals with a 3 db SNR?