1. Communications Systems
By
Dr. Muhammad Saleem Awan

7. twisted-pair cable twisted-pair wire

9. UTP Categories
• Cat 1
– Used for audio frequencies, speaker wire, etc. Not for
networking.
• Cat 2
– Up to 1.5Mhz, used for analog phones, not for networking
• Cat 3
– EIA 568-A Spec from here on up
– up to 16MHz
– Voice grade found in most offices
– Twist length of 7.5 cm to 10 cm
• Cat 4
– up to 20 MHz
– Not frequently used today, was used for Token Ring

10. UTP Categories Cont.
• Cat 5
– up to 100MHz
– Twist length 0.6 cm to 0.85 cm
– Commonly pre-installed in new office buildings
• Cat 5e “Enhanced”
– Up to 100Mhz
– Specifies minimum characteristics for NEXT (Near End Crosstalk) and
ELFEXT (Equal level far end crosstalk)
• Coupling of signal from one pair to another
• Coupling takes place when transmit signal entering the link couples
back to receiving pair, i.e. near transmitted signal is picked up by
near receiving pair
• Cat 6
– Proposed standard up to 250Mhz
• Cat 7
– Proposed standard up to 600Mhz

12. plastic outer coating
woven or braided metal
insulating material
copper wire

13. protective coating
glass cladding
optical fiber core
Optical FiberOptical Fiber
An optical fiber is a thin (2 to 125µm), flexible medium capable of guiding an optical ray.
Preferable because of,
• Large bandwidth, light weight, and small diameter
• Nonconductivity (no EMI & RFI)
• Longer distance signal transmission with lesser attenuation
• Security & greater repeater spacing
• Designed for future applications needs

14. Optical FiberOptical Fiber
Five basic categories of application have become important for
optical fiber:
• Long-haul trunks
• Metropolitan trunks
• Rural exchange trunks
• Subscriber loops
• Local area networks

15. Basic fiber optic communication systemBasic fiber optic communication system

16. Transmission WindowsTransmission Windows
• Optical fiber transmissions uses wavelengths in the near
infrared portion of the spectrum
• Both Lasers and LEDs are used to transmit light through fibers
• Lasers are used for 1310 nm or 1550 nm single mode
transmissions
• LEDs are used for 850- or 1300 nm multimode applications

17. Fiber Optic Loss CalculationsFiber Optic Loss Calculations

21. Fiber Optic TypesFiber Optic Types
• Step-index multimode fiberStep-index multimode fiber
– the reflective walls of the fiber move the light pulses to
the receiver
• Graded-index multimode fiberGraded-index multimode fiber
– acts to refract the light toward the center of the fiber
by variations in the density
• Single mode fiberSingle mode fiber
– the light is guided down the center of an extremely
narrow core
Three basic types of optical fibers are used in communication
systems

22. Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics
Optical Fiber Transmission Modes

23. Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics

24. Components - Optical Fiber CableComponents - Optical Fiber Cable

25. Components - Optical Fiber CableComponents - Optical Fiber Cable

26. Indoor Optical Fiber CableIndoor Optical Fiber Cable

27. Outdoor Optical Fiber CableOutdoor Optical Fiber Cable

28. Next Lecture TopicsNext Lecture Topics
Topics include,
•Dispersion in optical fiber
•Multiplexing
•Fiber Optic Sources
•Fiber Optic Detectors
•Fiber Optic System Design Considerations