IST 126 Transmission Media

Characteristics of Transmission Media Cost Ease of installation Bandwidth capacity – the amount of data that can be sent in a given amount of time Node capacity – the maximum number of nodes per segment Attenuation – the decrease of a signal strength over a distance EMI – electromagnetic inteference

Network Media Types Coaxial – uses electrical signal to send data Twisted pair – uses electrical signals also Fiber optics – uses light signals Wireless –Infrared –Microwave –Radio

Coaxial Cable A solid copper core (or stranded) conductor runs down the center of cable This wire is surrounded by plastic foam insulation The foam is surrounded by a second conductor that may be a wire mesh or a metallic foil Plastic jacket covers the cable for protection

Commonly Used Coaxial Cables RG-8 and RG-11: used with Thick Ethernet RG-58: used with thin Ethernet RG-59: used with cable TV

Characteristics of Coaxial Cable Cost is relatively inexpensive Installation relatively simple Typical bandwidth of 10 Mbps Node capacity is 30 for thinnet; 100 for thicknet Attenuation much less that for twisted-pair Susceptible to EMI Plenum-grade must be used in ceilings and walls

Twisted Pair Cable One or more pairs of two twisted copper wires are used Wires are twisted to decrease the amount of crosstalk and outside EMI Twisting the wires causes the emitted signals from the two wires to cancel out each other and hence reduce crosstalk The pair are color-coded Used in telephone connections

Types of Twisted Pair Cable Unshielded – consists of a number of twisted pair with a simple plastic casing Shielded – contains an extra layer of shielding to reduce effect of EMI Category 1-5 –Cat 5 supports up to 100 Mbps Use RJ-45 connector

Twisted Pair Characteristics STP is fairly expensive UTP is very economical STP is rigid and bulky and can be difficult to install Typically a bandwidth of 10Mbps UTP normally restricted to length of 100 meters due to attenuation UTP very susceptible to EMI STP reduces the effect of EMI

Fiber Optic Cable Uses light signals to transmit data Each fiber has an inner core of glass or plastic that conducts light The inner core is covered with a layer of glass that reflects the light back into the core An outer plastic sheath surrounds the inner core The cable may contain one or more fibers

Characteristics of Fiber Optics More expensive than copper cable Associated equipment can be much higher Much more difficult to install Data rates in range of 100Mbps to 2 Gbps Much lower attenuation than copper wires Not subject to EMI No signal gets out of the cable so no eavesdropping can occur

See Summary of Characteristics of Cable Media Handout

Infrared Wireless Infrared light is used to transmit signals These signals are in the terahertz range of the electromagnetic spectrum Remote controls for televisions, VCRs use infrared signals These signals cannot penetrate walls and are diluted by strong lights Can be either line-of-site or broadcast that reflect off walls and ceilings

Microwave Wireless Use the lower gigahertz frequencies of the electromagnetic spectrum Can be terrestrial or use satellites Signals are line-of-site Cannot penetrate structures, so clear path needs to be established between source and destination

Radio Wireless Uses radio waves for transmission May use unregulated or regulated frequencies You cannot be guaranteed a clear channel if you use unregulated frequency Propagates in all directions Will pass through structures