Basic Communications Systems Class 2

Today’s Class Topics Finish up – Data and Signals Analog Data to Digital Signals Analog Data to Modulated Analog Signals Transmission Media Twisted Pair, Coaxial Cable, Fiber Optics, Wireless Making Connections Modem Operations Interfacing

Data Communications and Computer Networks Chapter 2 Converting Analog Data into Digital Signals To convert analog data into a digital signal, there are two basic techniques: Pulse code modulation Delta modulation

Data Communications and Computer Networks Chapter 2 Pulse Code Modulation The analog waveform is sampled at specific intervals and the “snapshots” are converted to binary values.

Data Communications and Computer Networks Chapter 2 Pulse Code Modulation When the binary values are later converted to an analog signal, a waveform similar to the original results is created, as long as enough samples are taken

Data Communications and Computer Networks Chapter 2 Pulse Code Modulation The more snapshots taken in the same amount of time, the better the resolution.

Data Communications and Computer Networks Chapter 2 Delta Modulation An analog waveform is tracked, using a binary 1 to represent a rise in voltage, and a 0 to represent a drop.

Data Communications and Computer Networks Chapter 2 Converting Analog Data into Analog Signals Many times it is necessary to modulate analog data onto a different set of analog frequencies. Broadcast radio and television are two very common examples of this. In this situation a data signal is modulated by a carrier signal to produce a composite signal that can be broadcast in a particular range of frequencies near the carrier frequency. For example: music (analog data signal) is modulated by a 91.5 MHz sine wave, which produces a composite signal with components between 91.4 MHz and 91.6 MHz. This is transmitted. You retrieve the original signal by demodulating (tuning into) frequency 91.5 MHz on your radio to get back the music

Data Communications and Computer Networks Chapter 2

Data Communications and Computer Networks Chapter 2 Spread Spectrum Technology A secure encoding technique that uses multiple frequencies or codes to transmit data. Two basic spread spectrum technologies: Frequency hopping spread spectrum Direct sequence spread spectrum

Data Communications and Computer Networks Chapter 2 Frequency Hopping Spread Spectrum

Data Communications and Computer Networks Chapter 2 Data Code The set of all textual characters or symbols and their corresponding binary patterns is called a data code. There are two basic data code sets plus a third code set that has interesting characteristics: ASCII EBCDIC Baudot Code

Data Communications and Computer Networks Chapter 2

Data Communications and Computer Networks Chapter 2

Data Communications and Computer Networks Chapter 2

Data Communications and Computer Networks Chapter 2 Data and Signal Conversions in Action Let us transmit the message “Sam, what time is the meeting with accounting? Hannah.” This message first leaves Hannah’s workstation and travels across a local area network.

Data Communications and Computer Networks Chapter 2 Data and Signal Conversions in Action

Data Communications and Computer Networks Chapter 2 Data and Signal Conversions in Action

Data Communications and Computer Networks Chapter 2 Data and Signal Conversions in Action

Chapter 3 The Media : Conducted and Wireless Data Communications and Computer Networks: A Business User’s Approach

Data Communications and Computer Networks Chapter 3 Introduction The world of computer networks and data communications would not exist if there were no medium by which to transfer data. The two major categories of media include: Conducted media Wireless media

Data Communications and Computer Networks Chapter 3 Twisted Pair Wire Two or more pairs of single conductor wires that have been twisted around each other. Twisted pair wire is classified by category. Twisted pair wire is currently Category 1 through Category 5e. Twisting the wires helps to eliminate electromagnetic interference between the two wires. Shielding can further help to eliminate interference.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Coaxial Cable A single wire wrapped in a foam insulation surrounded by a braided metal shield, then covered in a plastic jacket. Cable can be thick or thin. Baseband coaxial technology uses digital signaling in which the cable carries only one channel of digital data. Broadband coaxial technology transmits analog signals and is capable of supporting multiple channels of data.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Fiber Optic Cable A thin glass cable approximately a little thicker than a human hair surrounded by a plastic coating and packaged into an insulated cable. A photo diode or laser generates pulses of light which travel down the fiber optic cable and are received by a photo receptor.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 It is very common to mix fiber with twisted pair in LANs.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Wireless Media Radio, satellite transmissions, and infrared light are all different forms of electromagnetic waves that are used to transmit data. Note in the following figure how each source occupies a different set of frequencies.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Terrestrial Microwave Land-based, line-of-sight transmission Approximately miles maximum between towers Transmits data at billions of bits per second Popular with telephone companies and business to business transmissions

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Often the microwave antennas are on towers and buildings.

Data Communications and Computer Networks Chapter 3 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. Satellites can be classified by how far out into orbit each one is (LEO, MEO, and GEO).

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 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 and government. GEO - Geosynchronous Orbit - 22,300 miles. Used for weather, television, and government operations.

Data Communications and Computer Networks Chapter 3 Satellites – Do They Change Position? Geosynchronous Orbit Satellites appear stationary with respect to any location on the Earth’s surface. GEO satellite receivers never need to move once positioned. This is because GEO satellites are positioned directly above the Equator and they complete an orbit around the Earth at exactly the same rate that the Earth rotates. Both LEO and MEO satellites require receivers that move to track the motion of the satellite in the sky.

Data Communications and Computer Networks Chapter 3 Satellite Microwave Satellite microwave can also be classified by its configuration: Bulk carrier configuration Multiplexed configuration Single-user earth station configuration (e.g. VSAT)

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 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.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Mobile Telephone AMPS - Advanced Mobile Phone Service - First popular mobile phone service, uses analog signals and dynamically assigned frequency division multiplexing. D-AMPS - Digital Advanced Mobile Phone Service - Applies digital time division multiplexing on top of AMPS. PCS - Personal Communication Systems - Newer all- digital mobile phone service (2nd generation)

Data Communications and Computer Networks Chapter 3 Mobile Telephone Current PCS phones use one of three technologies (all incompatible with each other): TDMA - Time division multiple access CDMA - Code division multiple access GSM - Global system for mobile communications

Data Communications and Computer Networks Chapter 3 Cellular Digital Packet Data Technology that supports a wireless connection for the transfer of computer data from a mobile location to the public telephone network and the Internet. Can be used in conjunction with mobile telephones and laptop computers. All digital transfer but relatively slow at 19,200 bps. Emergency services make use of CDPD.

Data Communications and Computer Networks Chapter 3 Pagers Typically one-way communication service that uses ground-based and sometimes satellite-based systems. Some systems are two-way. Some systems can transmit small text messages.

Data Communications and Computer Networks Chapter 3 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.

Data Communications and Computer Networks Chapter 3 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.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Broadband Wireless Systems Two basic technologies: Multichannel multipoint distribution service (MMDS) Local multipoint distribution system (LMDS)

Data Communications and Computer Networks Chapter 3 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.

Data Communications and Computer Networks Chapter 3 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.

Data Communications and Computer Networks Chapter 3 WAP (Wireless Application Protocol) WAP allows wireless devices such as mobile telephones, PDAs, pagers, and two-way radios to access the Internet. WAP is designed to work with small screens and with limited interactive controls. WAP incorporates Wireless Markup Language (WML) which is used to specify the format and presentation of text on the screen.

Data Communications and Computer Networks Chapter 3 WAP (Wireless Application Protocol) WAP may be used for applications such as: - travel directions - sports scores - - online address books - traffic alerts - banking - news Possible short-comings of WAP include low speeds, security, and a very small user interface.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Media Selection Criteria Cost – Initial cost, maintenance/support cost Speed – Propagation speed, data transfer speed Distance and expandability Environment – Noise level Security – Wiretap possible? Need encryption?

Data Communications and Computer Networks Chapter 3 Conducted Media In Action How do we wire a local area network? Typical: twisted pair wire from office wall jack to a wiring closet hub and fiber optic cable between hubs. Remember : using Category 5 unshielded twisted pair, the maximum wire segment length is 100 meters. Hub to hub connections are often fiber optic cable to allow increased distance and protection against electromagnetic radiation noise sources.

Data Communications and Computer Networks Chapter 3

Data Communications and Computer Networks Chapter 3 Interconnecting Two Buildings Two buildings are separated by 400 meters. How do we interconnect them? Twisted pair? Coax? Fiber? Wireless?