Conducted and Wireless Media

Transcription

1 Fundamentals of Networking and Data Communications, Sixth Edition 3-1 Conducted and Wireless Media Chapter 3 Learning Objectives After reading this chapter, students should be able to: Outline the characteristics of twisted pair wire, including the advantages and disadvantages Outline the differences among Category 1, 2, 3, 4, 5, 5e, 6, and 7 twisted pair wire Explain when shielded twisted pair wire works better than unshielded twisted pair wire Outline the characteristics, advantages, and disadvantages of coaxial cable and fiber-optic cable Outline the characteristics of terrestrial microwave systems, including the advantages and disadvantages Outline the characteristics of satellite microwave systems, including the advantages and disadvantages as well as the differences among low-earth-orbit, middle-earth-orbit, geosynchronous orbit, and highly elliptical Earth orbit satellites Describe the basics of cellular telephones, including all the current generations of cellular systems Outline the characteristics of short-range transmissions, including Bluetooth Describe the characteristics, advantages, and disadvantages of broadband wireless systems and various wireless local area network transmission techniques Apply the media selection criteria of cost, speed, right-of-way, expandability and distance, environment, and security to various media in a particular application Chapter Outline 1. Introduction 2. Conducted Media a. Twisted pair wire b. Coaxial cable c. Fiber-optic cable

2 Fundamentals of Networking and Data Communications, Sixth Edition Wireless Media a. Terrestrial microwave transmission b. Satellite microwave transmission c. Cellular telephones d. Infrared transmissions e. Broadband wireless systems f. Bluetooth g. Wireless local area networks h. Free space optics and ultra-wideband i. ZigBee 4. Media Selection Criteria a. Cost b. Speed c. Expandability and distance d. Environment e. Security 5. Conducted Media in Action: Two Examples 6. Wireless Media in Action: Three Examples 7. Summary Lecture Notes Introduction All communications media can be divided into two categories: physical or conducted media, such as wires, and radiated or wireless media, which use radio waves. Conducted media include twisted pair wire, coaxial cable, and fiber-optic cable. In wireless transmission, various types of electromagnetic waves, such as radio waves, are used to transmit signals. This chapter examines seven basic groups of wireless media used for the transfer of data: terrestrial microwave transmissions, satellite transmissions, cellular radio systems, personal communication systems, pagers, infrared transmissions, and multichannel multipoint distribution service.

3 Fundamentals of Networking and Data Communications, Sixth Edition 3-3 Conducted Media Twisted pair wire The oldest, simplest, and most common type of conducted media is twisted pair wires. Twisted pair is almost a misnomer, as one rarely encounters a single pair of wires. To help simplify the numerous varieties, twisted pair can be specified as Category 1-7 and is abbreviated as CAT 1-7. If you determine that the twisted pair wire needs to go through walls, rooms, or buildings where there is sufficient electromagnetic interference to cause substantial noise problems, shielded twisted pair can provide a higher level of isolation from that interference than unshielded twisted pair wire, and thus a lower level of errors. Note that CAT 1 3 is essentially extinct. CAT 4 may be used for telephone wire. Most LAN users are now installing CAT 6. Coaxial cable Coaxial cable, in its simplest form, is a single wire wrapped in a foam insulation, surrounded by a braided metal shield, then covered in a plastic jacket. The braided metal shield is very good at blocking electromagnetic signals from entering the cable and producing noise. Because of its good shielding properties, coaxial cable is very good at carrying analog signals with a wide range of frequencies. There are two major coaxial cable technologies, depending on the type of signal each carries: baseband or broadband. Coaxial cable also comes in two primary physical types: thin coaxial cable and thick coaxial cable. Fiber-optic cable Fiber-optic cable (or optical fiber) is a thin glass cable approximately a little thicker than a human hair surrounded by a plastic coating. A light source, called a photo diode, is placed at the transmitting end and quickly switched on and off. The light pulses travel down the glass cable and are detected by an optic sensor called a photo receptor on the receiving end. Fiber-optic cable is capable of transmitting data at over 100 Gbps (that s 100 billion bits per second!) over several kilometers. In addition to having almost error-free high data transmission rates, fiberoptic cable has a number of other advantages over twisted pair and coaxial cable. Since fiberoptic cable passes electrically nonconducting photons through a glass medium, it is immune to electromagnetic interference and extremely difficult to wiretap.

4 Fundamentals of Networking and Data Communications, Sixth Edition 3-4 Wireless Media All wireless systems employ radio waves at differing frequencies. The FCC strictly controls which frequencies are used for each particular type of service. The services covered in this section will include terrestrial microwave transmissions, satellite transmissions, cellular radio systems, personal communication systems, pagers, infrared transmissions, and multichannel multipoint distribution service Terrestrial microwave transmission systems transmit tightly focused beams of radio signals from one ground-based microwave transmission antenna to another. Satellite microwave transmission systems are similar to terrestrial microwave systems except that the signal travels from a ground station on earth to a satellite and back to another ground station on earth, thus achieving much greater distances than line-of-sight transmission. Satellites orbit the earth from three possible ranges: low earth orbit (LEO), middle earth orbit (MEO), and geosynchronous earth orbit (GEO). Infrared transmission is a special form of radio transmission that uses a focused ray of light in the infrared frequency range. A broadband wireless system is one of the latest techniques for delivering Internet services into homes and businesses. ZigBee is a short-range, low-power transmission system often employed in mesh networks to allow controlling equipment to talk to each other. Media Selection Criteria When designing or updating a computer network, the selection of one type of media over another is an important issue. The principal factors you should consider in your decision include cost, speed, expandability, distance, environment, and security. In Action Examples Three In Action examples are introduced in this chapter. The first demonstrates how conducted media might be used in a local area network installation. The second demonstrates possible solutions to running a wire between two buildings. The third example is a wireless media example of a company considering satellite microwave transmissions between two locations while a fourth example demonstrates a terrestrial microwave solution between two branch offices. Quick Quiz 1. What is the advantage of using twisted pair wiring? Coaxial cable? Fiber-optic? Twisted pair is inexpensive and easy to work with. Coaxial cable is good for wide bandwidth signals such as video applications. Fiber-optic carries high amounts of traffic and has much lower error rates.

5 Fundamentals of Networking and Data Communications, Sixth Edition List two major uses of terrestrial microwave. To major users include: long-haul telecommunications and building-to-building data transfer. 3. What are the different ways to categorize satellite microwave? LEO, GEO, MEO, HEO; bulk, single-user, multiplexed 4. List the different forms of wireless technologies. The different forms include: terrestrial microwave, satellite microwave, infrared, cellular, PCS, pager systems, Bluetooth, wireless LANs, ZigBee, and broadband wireless. Discussion Topics 1. Why did the Iridium mobile telephone system fail? 2. While most of Europe and Asia use one form of cellular telephone technology, why can t the U.S. decide on a single cellular protocol? 3. What is the potential for broadband wireless systems? Do you think it will ever really catch on here in the U.S.? Teaching Tips 1. Bring some wire samples to class when discussing conducted media. 2. Have students search the Internet to examine what wireless calling plans are available in their area. 3. Use as a wiring example a portion of a lab or building on campus. Maybe you can locate actual wiring schematics. Solutions to Review Questions 1. What is meant by right-of-way? Right-of-way refers to the ability to install your own cables or wires over yours or someone else s property.

6 Fundamentals of Networking and Data Communications, Sixth Edition What is the function of a cellular telephone switching office? A switching office handles all cellular telephone calls, assigns channels, makes connections, performs billing. 3. What is the difference between data transmission speed and propagation speed? Data transmission speed is the time between successive bits; propagation speed is the time for one bit to traverse from one end of the medium to the other end. 4. What is the sequence of events when placing a call from a cellular telephone? Phone turned on, phone locates nearest tower, phone number dialed, tower passes phone number to CTSO, CTSO checks account, phone number passed to central office (if necessary), connection established 5. What are the different costs of a conducted media? Initial cable costs, costs of supporting devices, and maintenance costs 6. List a few common application areas for each orbit level satellite system. LEO: mobile phones, pagers; MEO: GPS systems; GEO: cable and direct television; HEO for military and science 7. In what situation might we use free space optics? Between buildings, clear line of sight, high data transfer speeds 8. What are the four orbit levels for satellite systems? LEO, MEO, GEO, HEO 9. What are the different wireless local area network protocols? IEEE b, a, and g (bag) 10. List a few common applications for terrestrial microwave. Long haul telecommunications and building-to-building communications 11. List three possible application areas of Bluetooth. Automobiles, wireless home audio systems, wireless computer peripheral interconnections

7 Fundamentals of Networking and Data Communications, Sixth Edition What kind of objects can interfere with terrestrial microwave transmissions? Trees, mountains, buildings, bad weather 13. What are the main advantages and disadvantages of Bluetooth? Advantages: wireless, reasonable data transfer speed, many possible applications Disadvantage: short distance 14. What is an average distance for transmitting terrestrial microwave? The average distance is the line of sight which is roughly miles depending upon intervening obstacles. 15. Broadband wireless service supports what kind of applications? Most popular right now is Internet access. 16. What is the difference between terrestrial microwave and satellite microwave? Terrestrial is land based; satellite is not. 17. What are the main advantages and disadvantages of ZigBee? Advantages: low power, mesh design; Disadvantages: short distance, low speeds 18. What are the advantages and disadvantages of fiber-optic cable? Advantages: High speeds, long distances, low noise; Disadvantages: cost 19. Infrared transmission can be used for which type of applications? Short distance device-to-device data transfer. 20. Why is fiber-optic cable immune to electromagnetic interference? The cable is made of glass. 21. What is the advantage of IEEE over IEEE e? is designed for moving vehicles; e for stationary transmitters 22. What is the difference between baseband coaxial and broadband coaxial cable? Baseband: digital signals; Broadband: analog signals

8 Fundamentals of Networking and Data Communications, Sixth Edition What are the WiMAX protocols used for? The protocols are used for high-speed wireless connections between users and the Internet. 24. What is the primary advantage of coaxial cable compared to twisted pair? Coaxial cable can carry a signal or signals with a wide range of frequencies and it has less noise. 25. What is meant by line-of-sight? Line-of-sight means the receiver has to physically be able to see transmitter. 26. What are the advantages and disadvantages of shielded twisted pair? Advantage: provides better level of isolation from noise; Disadvantage: cost 27. What are the differences between the 2.5 generation cell phone services such as GPRS and 1xRTT and the newer UMTS, 1xEV, and EV-DO? The most noticeable difference is the data transfer rates are higher in the newer technologies. 28. What are Category 1, 2, 3, 4, 5, 5e, 6, and 7 twisted pair wire used for? Cat 1, 2 and 3: telephone lines; Cat 3, 4, 5, 5e, 6 and 7: LANs 29. What is the primary difference between AMPS (or D-AMPS) cellular systems and the newer PCS mobile telephones? PCS is all digital 30. How does crosstalk occur in twisted pair wire? Crosstalk occurs when electromagnetic radiation is emitted from one wire which is picked up by a second wire. 31. What is the primary difference between AMPS and D-AMPS cellular systems? AMPS: older analog system; D-AMPS: newer digital features added onto AMPS 32. Why is twisted pair wire called twisted pair? Twisted pair wire very often contains one or more pairs of wires and they are twisted around each other.

9 Fundamentals of Networking and Data Communications, Sixth Edition 3-9 Suggested Answers to Exercises 1. You are considering replacing your terrestrial microwave transmission system with a free space optics system. What are the advantages and disadvantages of doing this? Free space optics can be very high data transfer rate and may be a simpler system to maintain. But free space optics, like microwave, is line of sight. Both are not cheap. 2. Terrestrial microwave is a line-of-sight transmission. What sort of objects are tall enough to interfere with terrestrial microwave? Buildings, trees and mountains. 3. A T-1 service offered by voice and data communications companies is capable of supporting 1.5 Mbps of continuous data transfer over a high-quality telephone wire. What are the advantages and disadvantages of such a service when compared to services such as WAP, Bluetooth, and terrestrial microwave? T-1 is installed by phone company, so they worry about right-of-way. Also you don t have to worry about obstructions of signal. Disadvantage of T-1 is relatively low speed and recurring monthly cost. 4. Using the same five media examples from the previous exercise, rank them in order from most secure transmission to least secure transmission. Fiber, satellite, microwave, coaxial, twisted pair; or satellite, microwave, fiber, coaxial, twisted pair 5. There is a company in your community that is starting to offer a WiMAX service for Internet access. The company promises 2-Mbps downloads. If the company predicts that this new service will attract 2000 customers, what is the bandwidth necessary to support this service? A big part of the answer depends on what type of signal encoding are they using. For example, to transmit 2 Mbps, what is the baud rate of the signal? As a simple example, let s assume the baud rate is one hundredth the data rate. That would require a baud rate of 20,000 Hz. To support 2000 customers, you will need to support 2000 times 20,000 baud. 6. Using the same five media examples from the previous exercise, rank them in order from least noisy transmission to most noisy transmission. Fiber, microwave / satellite, coaxial, twisted pair

10 Fundamentals of Networking and Data Communications, Sixth Edition What is one potentially serious problem with using your personal digital assistant and Bluetooth to unlock doors wirelessly? Explain. What is someone steals your Bluetooth enabled device? Will they be able to access your locked devices? Did you use some form of security code? 8. Rank the following five media examples twisted pair, coaxial cable, fiber-optic cable, microwave, and satellite in order from highest data transmission speed to lowest data transmission speed. Fiber, satellite, microwave, coaxial cable, twisted pair (satellite might be first under some conditions) 9. Why do cellular telephone systems only need seven sets of frequencies in a metropolitan area? If you draw a set of cells like a honeycomb pattern, you will only need 7 sets of frequencies before you can start to reuse them. 10. The local cable TV company has changed its mind. It is now going to replace all the existing coaxial cable with unshielded twisted pair. List the advantages and disadvantages of this plan. Bad choice too much noise 11. You are talking on your cellular telephone as you pass from one cell to another. Will your cellular telephone use the same set of frequencies in the new cell as it was using in the previous cell? Explain. No. Any two adjacent cells use different frequencies. 12. The local cable TV company is considering removing all the coaxial cable and replacing it with fiber-optic cable. List the advantages and disadvantages of this plan. Higher data rates, more channels, less noise 13. Which of the wireless technologies can transmit through solid objects. Which wireless technologies cannot? Can: Bluetooth, wireless LANs Cannot: Infrared, microwave, satellite, MMDS/LMDS

11 Fundamentals of Networking and Data Communications, Sixth Edition Can you transmit a video signal over twisted pair wire? Explain. Be sure to consider multiple scenarios. More than likely you can but noise is going to be a serious factor. The signal may be very fuzzy or distorted, making it impractical. 15. You are walking down the street and your cell phone rings. What was the sequence of events that allowed a person with a conventional telephone to call you on your cellular telephone? Your cell phone must be turned on, which means the system recognizes what cell you are currently in. Someone places a call, it goes to the cellular switching office, the call goes to the cell you are in and your cell phone rings. 16. What characteristics of Category 5/5e unshielded twisted pair make it the most commonly used conducted wire? Data transfer rates of Mbps per wire; reasonably low noise; inexpensive cost per foot 17. How long does it take a signal to reach a satellite in low earth orbit? 500 miles (average) / 186,428 miles per second = seconds 18. List three different examples of crosstalk that don t involve wires and electric signals. (Hint: look around you.) hearing the students or instructor in the next classroom; hearing traffic on the road outside; many separate conversations in the same room. 19. Given that a satellite signal travels at the speed of light, exactly how long does it take for a signal to go from the earth to a satellite in geosynchronous orbit, and back to Earth? Show your calculations. 22,300 miles / 186,428 miles per second = 0.12 seconds, times two 20. Table 3-1 shows Category 1 wire transmitting a signal for 5-6 kilometers (3-4 miles) but Category 5e for only 100 meters (328 feet). Is Category 1 the best wire for long distance transmissions? Explain. No. Cat 1 can go 2-3 miles but only at very low data transfer rates.

12 Fundamentals of Networking and Data Communications, Sixth Edition Your company has two offices located approximately one mile apart. There is a need to transfer data between the two offices at speeds up to 100 Mbps. List as many solutions as possible for interconnecting the two buildings. Is each solution technically feasible? Financially feasible? Politically feasible? Defend your position. Twisted pair and coax: too great a distance for 100 Mbps Fiber-optic: might work; expensive; do you have right-of-way? Microwave: might work; expensive; do you have a clear line of sight? Satellite: might work, but really expensive Bluetooth or infrared: too great a distance Thinking Outside the Box 1. Definitely needs to be shielded, or fiber-optic. Wireless might be an interesting solution. 2. First solution might be a small twisted pair small office home office LAN; secondly you might want to consider wireless. 3. Satellite microwave; GPS; cellular phones; other radio technologies 5. Wireless LAN would be first choice; could also consider running twisted pair (might be hard to do physically); also consider data transmission systems that send signals over electrical outlets in the walls. 6. Bluetooth peer-to-peer; wireless LAN peer-to-peer; infrared