Chapter 4 - Making Connections

A)     Interfacing A Computer To Peripheral Devices

a.      Interfacing – the process of providing all the proper interconnections between a computer and a peripheral

b.      Characteristics of interface standards

                                                    i.     De facto standard – a protocol that, although not an official standard, becomes so popular that other companies start using it

                                                   ii.     Electrical component – deals with voltages, line capacitance, and other electrical issues

                                                  iii.     Mechanical component – deals with items such as the connector or plug description

c.      An early interface standard

                                                    i.     RS-232 – the classic example of one of the earliest interfaces

                                                   ii.     EIA-232F – an interface standard for connecting a computer or terminal (or DTE) to a voice-grade modem (or DCE) for use on analog public telecommunications systems

                                                  iii.     Data terminating equipment (DTE) – the computer or terminal end of an interface

                                                  iv.     Data communication equipment (DCE) – the modem

                                                   v.     Full-duplex connection – one in which both sender and receiver may transmit at the same time, EIA-232F is full-duplex

                                                  vi.     Half-duplex connection – one in which either sender or receiver may transmit

d.      Universal serial bus (USB) – modern standard for interconnecting may types of peripheral devices to computers

                                                    i.     Daisy-chaining – connecting a device to each subsequent device (instead of back to the computer)

e.      Other interface standards

                                                    i.     FireWire – type of interconnection between peripheral devices (such as wireless modems and high-speed digital video cameras) and a microcomputer

1.      Asynchronous – supports the more traditional peripheral devices such as modems and printers

2.      Isochronous – provides guaranteed data transport at a predetermined rate

                                                   ii.     Thunderbolt – uses same connector from mini-displayport and provides a 10-Gbps connection to peripheral devices

                                                  iii.     SCSI and iSCSI

1.      SCSI (Small Computer System Interface) (pronounced skuzzy) – technique for interfacing a computer to high-speed devices such as hard disk drives, tape drives, CDs and DVDs

a.      Designed for permanent nature

2.      iSCSI (Internet SCSI) – a technique for interfacing disk storage to a computer via the internet

                                                  iv.     InfiniBand and Fibre Channel

1.      InfiniBand – serial connection or bus that can carry multiple channels of data at the same time. It can support data transfer speed of 2.5 billion bits

a.      It can interconnect thousands of devices using both copper wire and fiber-optic cables

2.      Fibre Channel – serial, high-speed network that connects a computer to multiple input/output devices

a.      Can only support 126 devices only

B)     Data Link Connections

a.      Asynchronous connections – a single character, or byte of data, is the unit of transfer between the sender and receiver

                                                    i.     Sender prepares a data character for transmission, transmit that character, and then begins preparing the next data character for transmission

1.      Frame – small packet of data

2.      Start bit – always a logic of 0, is added to the beginning of the character and informs the receiver that an incoming data frame is arriving

a.      Start bit allows the receiver to synchronize itself to the character

b.      At the end of the data character, one or two stop bits, which are always logic 1s, are added to signal the end of the frame

c.      Finally, a single parity bit, which is inserted between the data bits and stop bit, may be added to the data. This parity bit can indicate either even parity or odd parity, and it performs an error check on only the data bits

                                                   ii.     Slow in data transfer for larger files since there are 3 check bits

b.      Synchronous connections – unit of transmission is a sequence of characters

                                                    i.     Includes a start sequence (flag), a control byte, an address, a checksum, and an end sequence (flag)

c.      Isochronous connections – used to support various types of real-time applications

                                                    i.     Data cannot be too slow or too slow as that could distort and cause buffering for the end user

C)     Terminal-to-Mainframe Computer Connections

a.      Point-to-point connection – single wire runs between two devices and no other terminals or computers share this connection

b.      Multipoint connection – single wire with the mainframe connected on one end and multiple terminals connected on the other end

                                                    i.     Polling – allows only one terminal to transmit at one time, successfully controls multiple terminals that share a connection to a mainframe computer

1.      Primary – a mainframe computer

2.      Secondary – name for each terminal

3.      Roll-call polling – polling method in which the mainframe computer (primary) polls each terminal (secondary), one at a time, in round-robin fashion

4.      Hub polling – polls only the first terminal, which then passes the poll to the second terminal, and each successive terminal passes the poll along

5.      Selection – the primary creates a packet of data with the address of the intended terminal and transmits the packet. Only that specific terminal recognizes the address and accepts the incoming data

D)     Making Computer Connections In Action

Chapter 3 - Conducted and Wireless Media

A)      Conducted Media

a.       Twisted pair wire – comes as two or more pairs of single-conductor copper wires that have been twisted around each other

                                                               i.      Each single-conductor wire is encased within plastic insulation and cabled within one outer jacket

                                                             ii.      Laws of physics

1.       A current passing through a wire creates a magnetic field around that wire

2.       A magnetic field passing over a wire induces a current in that wire

                                                           iii.      Crosstalk – a current or signal in one wire that is producing an unwanted current or signal

                                                           iv.      Types of twisted pair wire (Category 1-7)

1.       Category 1 – standard telephone wire and has few or no twists

2.       Category 2 – used for telephone circuits and some low-speed LANs and has some twisting

3.       Category 3 – designed to transmit 10 Mbps of data over a local area network for distances up to 100 meters (328 feet)

a.       Repeater – a device that generates a new signal by creating an exact replica of the original signal

4.       Category 4 – designed to transmit 20 Mbps of data for distances up to 100 meters

5.       Category 5 – designed to transmit 100 Mbps of data for distances up to 100 meters

a.       Category 5e – indicates four pairs of wires, patch cords, and other possible components that connect directly with a cable. Supports higher speeds of 100 Mbps

6.       Category 6 – designed to support data transmission with signals as high as 250 MHz for 100 meters

7.       Category 7 – designed to support 600 MHz of bandwidth for 100 meters

a.       Unshielded twisted pair (UTP) – the most common form of twisted pair, none of the wires in this form is wrapped with a metal foil or braid

b.       Shielded twisted pair (STP) – a shield is wrapped around each wire individually, around all the wires together, or both. Provides an extra layer of isolation from unwanted electromagnetic interference

b.       Coaxial Cable – single wire (usually copper) wrapped in a foam insulation, surrounded by a braided metal shield, and then covered in a plastic jacket

                                                               i.      Types of signal

1.       Baseband coaxial – uses digital signaling in which the cable carries only one channel of digital data

2.       Broadband coaxial – transmits analog signals and is capable of supporting multiple channels of data simultaneously

                                                             ii.      Thickness of cable

1.       Thick coaxial cable – ranges in size from approximately 6 – 18 mm in diameter

2.       Thin coaxial cable – approximately 4 mm in diameter

c.       Fiber-optic cable – thin glass cable, surrounded by a plastic coasting

                                                               i.      Photo diode – a light source

1.       Placed at the transmitting end and quickly switched on and off to produce light pulses

                                                             ii.      Photo receptor – optic sensor

1.       Placed on the receiving end and used to detect light pulses

                                                           iii.      Backbone – the main connecting cable that runs from one end of the installation to another

                                                           iv.      Photonic fiber – similar to a fiber-optic cable but instead has holes in the cable. This allows light to travel through air holes which move unhindered

                                                             v.      Characteristics for fiber-optic cable

1.       Reflection – when a light signal inside the cable bounces off the cable wall and back into the cable

2.       Refraction – when light signal passes from the core of the cable into the surrounding material

3.       Single-mode transmission – requires the use of a very thin fiber-optic cable and a very focused light sources, such as a layer. Labeled as 8.3/125 cable

4.       Multimode transmission – uses thicker fiber cable and an unfocused light source, such as a led. Labeled as 62.5/125 cable

              

                                                           vi.      Right-of-way – legal capability of a business or a person to install a wire or cable across someone else’s property

            

B)      Wireless Media

a.       Terrestrial microwave transmission – transmits tightly focused beans of radio signals from one ground-based microwave transmission antenna to another. Used in telephone communications and business intercommunication

                                                               i.      Line-of-sight transmission – each antenna must be in sight of the next antenna in order to receive or transmit a signal

b.       Satellite microwave transmission – signal travels from ground station on Earth to a satellite and back to another ground station on Earth. Achieves greater distance than Earth-bound line-of-sight transmissions

                                                               i.      Uplink – sending data to the satellite

                                                             ii.      Downlink – receive data from the satellite

                                                           iii.      Propagation delay – transmission time from ground station to satellite and back to ground station

                                                           iv.      Types of satellites

1.       Low-earth-orbit (LEO) satellites – closest to the Earth, can be round as close as 100 miles from the surface and as far as 1000 miles away

2.       Middle-earth-orbit (MEO) satellites – can be found roughly 1000 to 3000 miles from the Earth

a.       Global positioning systems (GPS) – system of 24 satellites that are used for identifying locations of Earth

3.       Geosynchronous-Earth-orbit (GEO) satellites (high earth orbit) – found 22,300 miles from Earth and are always positioned over the same point on Earth

4.       Highly elliptical orbit (HEO) satellite – used by governments for spying and by scientific agencies for observing celestial bodies

a.       When the satellite is at its perigee (closest point to the Earth), it takes photographs of the Earth

b.       When the satellite is at its apogee (furthest point from the Earth), it transmits the data to the ground station

                                                             v.      Satellite configurations

1.       Bulk carrier facilities – satellite system and all its assigned frequencies are devoted to one user

2.       Multiplexed Earth station – many users use the satellite system but reserve time in order to use the station

a.       Centralized reservation – all reservations go to a central location and that site handles the incoming requests

b.       Distributed reservation – no central site handles the reservations, but individual users come to some agreement on the order of transmission

3.       Single-user earth station – each user employs his or her own ground station to transmit data to the satellite

a.       Very small aperture terminal (VSAT) – single-user Earth station satellite system with its own ground station and a small antenna (2 to 6 feet across)

c.       Cell phones

                                                               i.      Generations

1.       Analog cell phones

2.       Digital personal communications services (PCS)

a.       Generation 2.5 – convergence of data signals with voice signals

3.       Higher data transfer speeds

4.       Current 4^th generation of cell phones

                                                             ii.      Mobile service areas (MSAs) – markets, United states broken into more than 700 MSAs

                                                           iii.      Advanced Mobile Phone Service (AMPS) – first generation cell phone system

                                                           iv.      Digital-advanced mobile phone service (D-AMPS) – newer, digital equivalent of analog cell phone service

1.       Provides greater signal clarity and security than AMPS

                                                             v.      Personal communications services (PCS) – second-generation cell phones

1.       First PCS technology uses a form of time division multiplexing called Time Division Multiple Access (TDMA), technology to divide the available user channels by time, giving each transmitting cell phone a brief turn to transmit

2.       Second technology PCS uses is Code Division Multiple Access (CDMA) technology, which spreads the transmission of a cell phone signal over a wide range of frequencies

a.       CDMA networks were converted to an updated form of CDMA called CDMA2000 IxRTT

                                                                                                                                       i.      They were converted to 1xEV (I x Enhanced Version), a version of 1xEV called Evolution Data Only (EV-DO)

3.       Third PCS technology is Global System for Mobile (GSM) Communications, which uses a different form of TDMA technology

a.       GSM networks were converted to General Packet Radio Service (GPRS)

                                                                                                                                       i.      They were converted to Universal Mobile Telecommunications System (UMTS) technology

4.       Fourth-generation systems are currently based on LTE (Long Term Evolution) technology

d.       Broadband Wireless Systems and WiMax

                                                               i.      Broadband wireless system – known as the wireless local loop or fixed-point wireless, one of the latest techniques for delivering Internet services into homes and businesses

1.       Systems bypass the telephone company’s local hoop

                                                             ii.      WiMax – broadband wireless transmission technology that is based upon a series of IEEE standards

e.       Bluetooth – wireless technology that uses low-power, short-range radio frequencies to communicate between two or more devices

                                                               i.      Piconet – small network with eight or fewer devices

1.       Scatternet – multiple piconets can be interconnected to form a scatternet

f.        Wireless local area networks

                                                               i.      Wireless fidelity (Wi-Fi) – transmit data in the 2.4 GHz frequency range

g.       Free Space Optics, Ultra-wideband, infrared, near-field communications, and ZigBee

                                                               i.      Free optics – uses lasers, or, in some cases, infrared transmitting devices to transmit data between two buildings over short distances

                                                             ii.      Ultra-wideband systems – transmit data over a wide range of frequencies rather than limiting transmission to a narrow, fixed band of frequencies

                                                           iii.      Infrared transmission – uses a focused ray of light in the infrared frequency range

                                                           iv.      Near-field communications (NFC) – used in very close proximity data transfers, often with the two devices touching each other

                                                             v.      ZigBee – designed for data transmission between smaller often embedded, devices that require low data transfer rates and corresponding low power consumption

C)      Media Selection Criteria

a.       Factors in decision making for media selection – cost, speed, expandability and distance, environment, and security

                                                               i.      Cost – initial cost, maintenance, labor

                                                             ii.      Speed

1.       Data transmission speed – the number of bits per second that can be transmitted

a.       Maximum bits per second for a particular medium depends proportionally on the effective bandwidth of that medium, the distance the data must travel, and the environment through which the medium must pass (noise)

2.       Propagation speed – speed at which a signal moves through a medium

3.       Expandability and distance – how far can a cable go, how easy is it to extend length, right-of-way

4.       Environment – could be hazardous to certain media, wireless transmission being interrupted by electromagnetic noise and interference

5.       Security – how easily can it be wiretapped or intercepted

D)      Conducted Media In Action: Two Examples

a.       Passive device – a simple connection point between two runs of cable that does not regenerate the signal on the cable

E)      Wireless Media In Action: Three Examples