7.1 Chapter 7 Transmission Media Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7.2 Figure 7.1 Transmission medium and physical layer

7.3 Figure 7.2 Classes of transmission media

GUIDED MEDIA Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable Topics discussed in this section:

7.5 Figure 7.3 Twisted-pair cable Twisting reduces electromagnetic interference between wires

7.6 Figure 7.4 Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP) cables

7.7 Table 7.1 Categories of unshielded twisted-pair cables

7.8 Figure 7.6 UTP performance Note: as AWG increases, the wire gets smaller, and attenuation increases (AWG 24 standard)

7.9 Twisted Pair Wire 1 MHz typically equal to 1 Mbps, but 1 MHz can equal 2 Mbps at 10x cost! So Cat 5 can support 100 MHz, or 100 Mbps for 100 meters But Cat 5e can support 1000 Mbps for 100 meters. How?

7.10 Twisted Pair Wire 10BaseT uses 2 pairs – one pair receives and the other pair transmits (a pair of wires is needed because it is a balanced transmission); whether half or full duplex depends on NIC and switch (can’t use hub) 100BaseT (Fast Ethernet) one pair receives and the other pair transmits; almost always full duplex (see above) 1000BaseT uses 4 pairs; each pair carries 250 Mbps and can receive and transmit simultaneously. Since each pair is operating at 250 Mbps and Cat 5e is only 125 Mhz, a unique encoding technique is used (4D-PAM5).

7.11 Twisted Pair Wire Riser vs. Plenum Wire that is pulled through metal pipes (risers) has a plastic jacket that when burned, can produce noxious fumes. Wire that is installed in a plenum has a plastic jacket that when burned, will not produce noxious gases.

7.12 Installation of 1000BaseT Be careful! Don’t kink wire Avoid unnecessary bends Kinks and bends can cause delay skew (one wire transmitting faster than another, because it is longer, or because there are too many bends). Might have to use cable with air pockets instead of plastic spacers to minimize bending distance. Use top quality connectors and jacks

7.13 Figure 7.5 UTP connector

7.14 Figure 7.7 Coaxial cable

7.15 Categories of coaxial cables RG-675 OhmCable TV, satellite TV, cable modems RG-850 OhmOlder Ethernet LANs; being replaced with RG- 58 RG-1175 OhmBroadband Ethernet and other video apps RG-5850 OhmBaseband Ethernet LANs RG-5975 OhmClosed-circuit TV; cable television (RG-6 better) RG-6293 OhmIBM 3270 terminal connections

7.16 Figure 7.8 BNC connectors

7.17 Figure 7.9 Coaxial cable performance Note: As frequency increases, attenuation takes off

7.18 Figure 7.11 Optical fiber

7.19 Figure 7.10 Bending of light ray

7.20 Figure 7.12 Propagation modes

7.21 Figure 7.13 Modes

7.22 Table 7.3 Fiber types

7.23 Figure 7.14 Fiber construction

7.24 Figure 7.15 Fiber-optic cable connectors

7.25 Figure 7.16 Optical fiber performance Note: loss is relatively flat

7.26 Fiber Installation Support cable every 3 feet for indoor cable (5 feet for outdoor) Don’t squeeze support straps too tight. Pull cables by hand, no jerking, even hand pressure. Avoid splices. Make sure the fiber is dark when working with it. Broken pieces of fiber VERY DANGEROUS!! Do not ingest!

UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Radio Waves Microwaves Infrared Topics discussed in this section:

7.28 Figure 7.17 Electromagnetic spectrum for wireless communication

7.29 Figure 7.18 Propagation methods

7.30 Table 7.4 Bands

7.31 Figure 7.20 Omnidirectional antenna Broadcast systems are either omnidirectional (as above), or focused or narrow-beam.

7.32 Terrestrial Microwave Focused, land-based, line-of-sight transmission Approximately miles maximum between towers (depends on tower height) Transmits data at hundreds of millions of bits per second Popular with telephone companies and business to business transmissions

7.33

7.34 Typical Terrestrial Microwave Performance BandBandwidth (MHz)Data Rate (Mbps) Two basic devices: Parabolic dish and horn

7.35 Figure 7.21 Unidirectional antennas

7.36 Satellite Microwave Similar to terrestrial microwave except the signal travels from a ground station on earth to a satellite and back to another ground station. L band – mobile communications C band – TV, VSAT Ku band - HDTV Ka band - Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and HEO).

7.37

7.38 Satellite Microwave LEO - Low Earth Orbit miles to 1000 miles. Used for pagers, wireless , special mobile telephones, spying, videoconferencing. MEO - Middle Earth Orbit to 22,300 miles. Used for GPS (global positioning systems) and government. GEO - Geosynchronous Orbit - 22,300 miles. Always over the same position on earth (and usually over the equator). Used for weather, television, and government operations.

7.39 Satellite Microwave HEO – Highly Elliptical Orbit A fourth type of orbit used by the military for spying and by scientific organizations for photographing celestial bodies. When satellite is far out into space, it takes photos. When satellite is close to earth, it transmits data.

7.40 Satellite Microwave Satellite microwave can also be classified by its configuration: Bulk carrier configuration Multiplexed configuration Single-user earth station configuration (e.g. VSAT)

7.41

7.42 Mobile Telephone Wireless telephone service, such as cellular telephone, cell phone, and PCS. To support multiple users in a metropolitan area (market), the market is broken into cells. Each cell has its own transmission tower and set of assignable channels.

7.43

7.44 Wireless LAN (IEEE ) This technology transmits data between workstations and local area networks using high speed radio frequencies. Current technologies (and protocols) allow up to 54 Mbps data transfer at distances up to hundreds of feet. More on this in a later chapter.

7.45 Free Space Optics Uses lasers, or more economically infrared transmitting devices Line of sight between buildings Typically short distances, such as across the street Newer auto-tracking systems keep lasers aligned when buildings shake from wind, transportation going by Current FSO speeds go from T-3 (45Mbps) up to OC-48 (2.5Gbps) with faster systems in the lab

7.46 Free Space Optics Major weakness is fog. A typical FSO has a link margin of about 20 dB. Under perfect conditions air reduces a system’s power by approx 1 dB/km. Heavy fog can cause a loss of 400 dB/km (rendering 20 dB system to 50 meters. Scintillation is also a problem (especially in hot weather).

7.47 Ultra-Wideband UWB not limited to a fixed bandwidth but broadcasts over a wide range of frequencies simultaneously. Many of these frequencies are used by other sources, but UWB uses such low power that it “should not” interfere with these other sources. Can achieve speeds up to 100 Mbps (unshared) but for small distances such as a wireless LAN.

7.48 Ultra-Wideband Proponents say UWB gets something for nothing, since it shares frequencies with other sources. Opponents say too much interferences. Cell phone industry really against UWB because CDMA most susceptible to interference. GPS (also uses CDMA) may be affected by UWB. One solution may be to have one type of system indoors (stronger signals) and another type outdoors (1/10 the power).

7.49 Infrared Transmissions Special transmissions that use a focused ray of light in the infrared frequency range. Very common with remote control devices, but can also be used for device-to-device transfers, such as PDA to computer.

7.50 Broadband Wireless Systems Delivers Internet services into homes and businesses. Designed to bypass the local loop telephone line. Transmits voice, data and video over high frequency radio signals.

7.51 Broadband Wireless Systems Originally two basic technologies: Multichannel multipoint distribution service (MMDS) – supports digital data, video, Internet access, millions bps, 2.5 GHz, miles Local multipoint distribution service (LMDS) – digital data, video, Internet access, millions bps, 28 GHz – 30 GHz, but only a few miles

7.52 Broadband Wireless Systems But it appears that both of those have died. WiMAX is the next hot standard here. Worldwide Interoperability for Microwave Access (IEEE ) Current WiMAX systems (802.16a) can deliver 10 Mbps over a span of 6 miles but require an outdoor antenna (can be pricey).

7.53 Broadband Wireless Systems Future d technology will enable users to access WiMAX directly from their laptops via PCMCIA. Future e will allow seamless handoffs between base stations, giving true mobile broadband connectivity. Should provide competition to Wi-Fi and current 3G cellular data standards such as EV-DO and HSPA but all three will probably co-exist.

7.54 Bluetooth Bluetooth is a Radio Frequency specification for short- range, point-to-multipoint voice and data transfer. Bluetooth can transmit through solid, non-metal objects. Its typical link range is from 10 cm to 10 m, but can be extended to 100 m by increasing the power.

7.55 Bluetooth Bluetooth will enable users to connect to a wide range of computing and telecommunication devices without the need of connecting cables. Typical uses include phones and pagers, modems, LAN access devices, headsets, notebooks, desktop computers, and PDAs.

7.56 Review Questions What are the limitations of Cat 5e/6? Two buildings in a city are separated by 100 meters. How do we interconnect them? Two buildings on a campus are separated by 100 meters. How do we interconnect them? Two buildings on a campus are separated by 400 meters. How do we interconnect them?