Communications Systems

By

Dr. Muhammad Saleem Awan

twisted-pair cable twisted-pair wire

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

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

plastic outer coating

woven or braided metal

insulating material

copper wire

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

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

Basic fiber optic communication systemBasic fiber optic communication system

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

Fiber Optic Loss CalculationsFiber Optic Loss Calculations

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

Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics

Optical Fiber Transmission Modes

Optical Fiber Transmission CharacteristicsOptical Fiber Transmission Characteristics

Components - Optical Fiber CableComponents - Optical Fiber Cable

Components - Optical Fiber CableComponents - Optical Fiber Cable

Indoor Optical Fiber CableIndoor Optical Fiber Cable

Outdoor Optical Fiber CableOutdoor Optical Fiber Cable

Next Lecture TopicsNext Lecture Topics

Topics include,

•Dispersion in optical fiber

•Multiplexing

•Fiber Optic Sources

•Fiber Optic Detectors

•Fiber Optic System Design Considerations