OBJECTIVES
- Describe the features of a contemporary corporate network infrastructure and key networking technologies
- Evaluate alternative transmission media, types of networks, and network services
- Assess the role of the Internet and the World Wide Web in a firm’s information technology infrastructure
- Identify and describe the most important tools for communication and e-business
- Identify and describe the challenges posed by networking and the Internet and management solutions
Telecommunications: Communication of information by electronic means themarriage of computers and communications: The 1996 TelecommunicationsDeregulation and Reform Act allowed telephone companies, broadcasters, andcable companies to enter each other’s markets.
The Information Superhighway: High-speeddigital telecommunications networks, accessible by the general public
TELECOMMUNICATIONS ANDNETWORKING IN TODAY’S BUSINESS WORLD
§Anetworking and communications revolution led by Internet-based technologies
§1billion instant messages per day
§4billion e-mails each day
§65million music files downloaded
§Estimated3.9 billion photos sent over the Internet
§$769billion spent in the United States on telecommunications equipment and services
§Today,networking and the Internet are synonymous with doing business.
§TheBusiness Telecommunications Environment
§Telecommunicationsenvironment provides connectivity by providing communication channels for text,voice, and video images.
§Thenetwork infrastructure for a large corporation consists of many different kindsof networks for both data and voice communication.
§Mostof these different kinds of networks are moving towards a common Internetfoundation.
Networkingand Communications Trends
Theseven major trends in telecommunications:
- Rapid technological innovation has resulted in a proliferation of new hardware devices and new alternatives for business communications.
- Continuing telecommunications deregulation has encouraged competition and created many alternatives.
- Distinctions between telephone, cable television, Internet, and satellite telecommunication are blurred.
- Growing dominance of Internet technologies in voice, video, and data communications
- Rapid growth in “last-mile” high-speed broadband connections to homes and businesses
- Rapid growth in wireless telephone, wireless computer networks, and mobile Internet devices
- Growing scope of communication-intense services and products
The Business Value of Telecommunications andNetworking
•Declining transaction costs
•Declining agency costs
•Increased agility
•Higher quality management decisions
•Declining geographical barriers
•Declining temporal barriers
•The extremely rapid growth inbusiness networking and telecommunications results from the extraordinary valueof participating in networks like the Internet.
Networks and Corporate Infrastructure
•Anetwork consists of two or more connected computers.
•Eachcomputer on the network contains a network interface device called a networkinterface card (NIC).
•Theconnection medium for linking network components can be a telephone wire,coaxial cable, or radio signal in the case of cell phone and wireless localarea networks.
•Thenetwork operating system (NOS) routes and manages communications on the networkand coordinates network resources.
•Networksalso contain a switch or a hub acting as a connection point between thecomputers.
•Hubsare very simple devices that connect network components, sending a packet ofdata to all other connected devices.
•Aswitch has more intelligence than a hub and can filter and forward data to aspecified destination. Switches are used within individual networks.
•Arouter is a special communications processor used to route packets of datathrough different networks, ensuring that the message sent gets to the correctaddress.
KeyDigital Networking Technologies
•Client/ServerComputing
•PacketSwitching
•TCP/IPand Connectivity
Client/ServerComputing:
Asimple definition of CS is “server software accepts requests for data fromclient software and returns the results to the client.”
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Client/servercomputing is a distributed computing model in which much of the processingpower is located within small, inexpensive client computers.
Thepowerful clients are linked to one another through a network that is controlledby a network server computer.
Theserver sets the rules of communication for the network and provides everyclient with an address so others can find it on the network.
PacketSwitching:
Inpacket-switched networks, messages are first broken down into small bundles ofdata called packets.
Thesepackets are sent along different communication paths and then the packets arereassembled once they reach their destinations.
Packetswitching makes more efficient use of the communications capacity of a network.
Thepackets include information for directing the packet to the right address andfor checking transmission errors along with the data.
TCP/IPand Connectivity:
TCP/IPis the communications protocol used by the Internet and all Internet devices.
TCP/IPprovides for breaking up digital messages into packets, routing them to theproper addresses, and then reassembling them into coherent messages.
TCP/IPuses a suite of protocols: TCP and IP.
Handlesthe movement of data between computers
Establishesa connection between the computers, sequences the transfer of packets, andacknowledges the packets sent
InternetProtocol (IP):
•Responsiblefor the delivery of packets
•Includesthe disassembling and reassembling of packets during transmission
Types of Signals: Analog andDigital
Analog signal
- Continuous waveform
- Passes through communications medium
- Used for voice communications
Digital signal
- Discrete waveform
- Transmits data coded into two discrete states as 1-bits and 0-bits
- Used for data communications
Modem
Translates computer’sdigital signals into analog and vice versa
PhysicalTransmission Media
Thedifferent kinds of physical transmission media used by the networks are:
- Twisted-pair wire
- Coaxial cable
- Fiber optics
- Optical Fiber
- Wireless Transmission
Twisted-pair wire
Twisted paircabling comes in two varieties: shielded and unshielded. Unshielded twistedpair (UTP) is the most popular and is generally the best option for schoolnetworks (See fig. 1).
Fig.1. Unshielded twisted pair
The qualityof UTP may vary from telephone-grade wire to extremely high-speed cable. Thecable has four pairs of wires inside the jacket. Each pair is twisted with adifferent number of twists per inch to help eliminate interference fromadjacent pairs and other electrical devices. The tighter the twisting, thehigher the supported transmission rate and the greater the cost per foot. TheEIA/TIA (Electronic Industry Association/ Telecommunication IndustryAssociation) has established standards of UTP and rated six categories of wire(additional categories are emerging).
Unshielded Twisted PairConnector
The standardconnector for unshielded twisted pair cabling is an RJ-45 connector. This is aplastic connector that looks like a large telephone-style connector (See fig.2). A slot allows the RJ-45 to be inserted only one way. RJ stands forRegistered Jack, implying that the connector follows a standard borrowed fromthe telephone industry. This standard designates which wire goes with each pininside the connector.
Although UTPcable is the least expensive cable, it may be susceptible to radio andelectrical frequency interference (it should not be too close to electricmotors, fluorescent lights, etc.). If you must place cable in environments withlots of potential interference, or if you must place cable in extremelysensitive environments that may be susceptible to the electrical current in theUTP, shielded twisted pair may be the solution. Shielded cables can also helpto extend the maximum distance of the cables.
Shieldedtwisted pair cable is available in three different configurations:
1. Each pair of wires is individuallyshielded with foil.
2. There is a foil or braid shield insidethe jacket covering all wires (as a group).
3. There is a shield around eachindividual pair, as well as around the entire group of wires (referred to asdouble shield twisted pair).
Coaxialcabling has a single copper conductor at its center. A plastic layer providesinsulation between the center conductor and a braided metal shield (See fig.3). The metal shield helps to block any outside interference from
Althoughcoaxial cabling is difficult to install, it is highly resistant to signalinterference. In addition, it can support greater cable lengths between networkdevices than twisted pair cable. The two types of coaxial
Thin coaxialcable is also referred to as thin net. 10Base2 refers to the specifications forthin coaxial cable carrying Ethernet signals. The 2 refers to the approximatemaximum segment length being 200 meters. In actual fact the maximum segmentlength is 185 meters. Thin coaxial cable has been popular in
Thickcoaxial cable is also referred to as thick net. 10Base5 refers to thespecifications for thick coaxial cable carrying Ethernet signals. The 5 refersto the maximum segment length being 500 meters. Thick coaxial cable has anextra protective plastic cover that helps keep moisture away from the centerconductor. This makes thick coaxial a great choice when running longer lengthsin a linear bus network. One disadvantage of thick coaxial is that it does
Coaxial Cable Connectors
The mostcommon type of connector used with coaxial cables is the Bayonne-Neill-Concelman(BNC) connector (See fig. 4). Different types of adapters are available for BNCconnectors, including a T-connector, barrel connector, and terminator.Connectors on the cable are the weakest points in any network. To help avoidproblems with your network, always use the BNC connectors that crimp, rather
Fiber opticcabling consists of a center glass core surrounded by several layers ofprotective materials (See fig. 5). It transmits light rather than electronicsignals eliminating the problem of electrical interference. This makes it idealfor certain environments that contain a large amount of electricalinterference. It has also made it the standard for connecting networks between
Fiber opticcable has the ability to transmit signals over much longer distances thancoaxial and twisted pair. It also has the capability to carry information atvastly greater speeds. This capacity broadens communication possibilities toinclude services such as video conferencing and interactive services. The costof fiber optic cabling is comparable to copper cabling; however, it is
The centercore of fiber cables is made from glass or plastic fibers (see fig 5). Aplastic coating then cushions the fiber center, and kevlar fibers help tostrengthen the cables and prevent breakage. The outer insulating jacket made ofTeflon or PVC.
There aretwo common types of fiber cables -- single mode and multimode. Multimode cablehas a larger diameter; however, both cables provide high bandwidth at highspeeds. Single mode can provide more distance, but it is more expensive.
Ethernet Cable Summary
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Types of Networks
Wide Area Networks (WAN)
As the termimplies, a WANspans a large physical distance. The Internet is the largest WAN, spanning theEarth.
A WAN is ageographically-dispersed collection of LANs. A network device called a routerconnects LANs to a WAN. In IP networking, the router maintains both a LANaddress and a WAN address. A WAN differs from a LAN inseveral important ways. Most WANs (like the Internet) are not owned by any oneorganization but rather exist under collective or distributed ownership andmanagement. WANs tend to use technology like ATM,Frame Relayand X.25for connectivity over the longer distances.
• Cover a large geographic area.
• Telecommunication network
• Span large geographical distance
• Consist of variety of cable,satellite, and microwave technologies
• Switched lines, dedicated lines
Metropolitan area network (MAN)
A network is spanning a physical arealarger than a LAN but smaller than a WAN, such as a city. A MAN is typicallyowned and operated by a single entity such as a government body or largecorporation.
- Same city (10’s of kilometers)
- 800 Mb/s Gigabit Nectar
Campus Area Network (CAN)
A network is spanning multiple LANs butsmaller than a MAN, such as on a university or local business campus.
Local Area Networks (LAN)
ALANconnects network devices over a relatively short distance. A networked officebuilding, school, or home usually contains a single LAN, though sometimes onebuilding will contain a few small LANs (perhaps one per room), and occasionallya LAN will span a group of nearby buildings. In TCP/IP networking, a LANis often but not always implemented as a single IP subnet.
Inaddition to operating in a limited space, LANs are also typically owned,controlled, and managed by a single person or organization. They also tendto use certain connectivitytechnologies, primarily Ethernetand Token Ring.
Connectcomputers & other information processing devices within a limited physicalarea.
Telecommunicationnetwork require its’ own dedicated channels encompass a limited distance Transmithigh volumes of data, and other functions requiring high transmission speeds
Gateway,router, Network Operating System (NOS), peer-to-peer
Thegateway is a communications processor that can connect dissimilar networks by translatingfrom one set of protocols to another.
Connectedvia ordinary telephone wiring, coaxial cable, or wireless radio & infraredsystems
Virtual Private Networks (VPN)
Asecure network that uses the Internet as its main backbone network, but relieson firewalls and other security features
Avirtual private network based on the Internet Protocol provides a secureconnection between two points across the Internet, enabling privatecommunications to travel securely over the public infrastructure
Personal Area Networks (PAN)
- Connection of computer to peripherals or other computers
- Connect PDA and desktop computer
- Several connection methods:
- Blue tooth (radio frequency – up to 300 feet)
- IrDA (Infrared) (cheap)
- Wi-Fi: Wireless LAN 802.11b – wireless Ethernet (more reliable)
BroadbandNetwork Services and Technologies
Anumber of network services and technologies are available to companies thatneed high-speed transmission or access to the Internet.
Framerelay: Packages data into frames for high-speedtransmission over reliable circuits that require less error checking thanpacket switching
AsynchronousTransfer Mode (ATM):Parcels data into uniform 53-byte cells for high-speed transmission; cantransmit data, video, and audio over the same network
ATM (asynchronous transfer mode) is adedicated-connection switching technology that organizes digital data into 53-bytecellunits and transmits them over a physical medium using digital signaltechnology. Individually, a cell is processed asynchronously relative to otherrelated cells and is queued before being multiplexedover the transmission path.
BecauseATM is designed to be easily implemented by hardware (rather than software),faster processing and switchspeeds are possible. The prespecified bit rates are either 155.520 Mbpsor 622.080 Mbps. Speeds on ATM networks can reach 10 Gbps.Along with Synchronous Optical Network (SONET)and several other technologies, ATM is a key component of broadband ISDN (BISDN).
ATMalso stands for automated teller machine, a machine that bank customers use tomake transactions without a human teller.
IntegratedServices Digital Network (ISDN):Dial-up network access standard that can integrate voice, data, and videoservices.
A rather dated communicationtechnology standard for simultaneous high speed basebandtransmission of voice and data(including videoand fax) over ordinary(twisted pair)coppertelephonelines.In most of the world it has been overtaken by datacompression technologies such as ADSL.It is available in two main configurations: (1) Basic rate interface(BRI) configuration, comes with three digitalchannelscomprising of two 64 Kbps bearer(B)channels and one 16 Kbps data (D) channel that providescontrol and signaling for the B channels.A merchant,for example, could run credit cardauthorization on the D channel, use one B channel for voice, and the other forfax; or combine two B channels for 128 Kbps connectionto the internetwithout needing a modem; (2) Primaryrate interface (PRI) configuration, comes with 23 B channels and one D channel.The newer broadbandversion(B-ISDN) supportstransmission ratesof up to 1.5 Mbps but requires fiber-optic cables.
DigitalSubscriber Line (DSL):Series of technologies for high-capacity transmission over copper wire.
Stands for "Digital SubscriberLine." It is medium for transferring data over regular phone lines and canbe used to connect to the Internet. However, like a cable modem, a DSL circuitis much faster than a regular phone connection, even though the wires it usesare copper like a typical phone line.
An asymmetric DSL (ADSL)connection allows download speeds of up to about 1.5 megabits (not megabytes)per second, and upload speeds of 128 kilobits per second. That is why it iscalled ADSL and not just DSL (because of the asymmetric speeds). There is alsoa "Symmetric Digital Subscriber Line" (SDSL) which is similar toADSL, but allows data transfer speeds of 384 Kilobits per second in bothdirections. Theoretically, this type of connection allows download speeds of upto 9 megabits per second and upload speeds of up to 640 kilobits per second.The difficult part in establishing an DSL circuit is that it must be configuredto connect two specific locations, unlike a regular phone line or cable modem.DSL is often seen as the new, better alternative to the older ISDN standard.
An asymmetric DSL (ADSL)connection allows download speeds of up to about 1.5 megabits (not megabytes)per second, and upload speeds of 128 kilobits per second. That is why it iscalled ADSL and not just DSL (because of the asymmetric speeds). There is alsoa "Symmetric Digital Subscriber Line" (SDSL) which is similar toADSL, but allows data transfer speeds of 384 Kilobits per second in bothdirections. Theoretically, this type of connection allows download speeds of upto 9 megabits per second and upload speeds of up to 640 kilobits per second.The difficult part in establishing an DSL circuit is that it must be configuredto connect two specific locations, unlike a regular phone line or cable modem.DSL is often seen as the new, better alternative to the older ISDN standard.
Cable modem: Service for high-speed transmissionof data over cable TV lines that are shared by many users
A cable modem is a device that enablesyou to hook up your PC to a local cable TVline and receive data at about 1.5 Mbps.This data rate far exceeds that of the prevalent 28.8 and 56 Kbps telephonemodems and the up to 128 Kbps of Integrated Services Digital Network (ISDN)and is about the data rate available to subscribers of Digital Subscriber Line(DSL)telephone service. A cable modem can be added to or integrated with a set-top boxthat provides your TV set with channels for Internet access. In most cases,cable modems are furnished as part of the cable access service and are notpurchased directly and installed by the subscriber.
Acable modem has two connections: one to the cable wall outlet and the other toa PC or to a set-top box for a TV set. Although a cable modem does modulationbetween analogand digitalsignals, it is a much more complex device than a telephone modem.It can be an external device or it can be integrated within a computer orset-top box. Typically, the cable modem attaches to a standard 10BASE-TEthernetcardin the computer.
Allof the cable modems attached to a cable TV company coaxial cableline communicate with a Cable Modem Termination System (CMTS) at the localcable TV company office. All cable modems can receive from and send signalsonly to the CMTS, but not to other cable modems on the line. Some services havethe upstream signals returned by telephone rather than cable, in which case thecable modem is known as a telco-return cable modem.
Theactual bandwidthfor Internet service over a cable TV line is up to 27 Mbps on the download pathto the subscriber with about 2.5 Mbps of bandwidth for interactive responses inthe other direction. However, since the local provider may not be connected tothe Internet on a line faster than a T-carriersystem at 1.5 Mpbs, a more likely data rate will be close to 1.5Mpbs.
Leadingcompanies using cable TV to bring the Internet to homes and businesses are@Home and Time-Warner.
Inaddition to the faster data rate, an advantage of cable over telephone Internetaccess is that it is a continuous connection.
Tlines: Dedicatedlines for high-speed secure data transmission and Internet connection.
THE INTERNET
Technically,the Internet is a global information system defined by three characteristics:
•Anetwork composed of computers and other devices that are logically linkedtogether by a unique address space based on the Internet Protocol
•Anetwork where network devices are able to support communications using TCP/IPor other compatible protocols
•Anetwork that provides high-level services layered on a communication andnetwork infrastructure
InternetAddressing, Architecture, and Governance
TheDomain Name System:
Everydevice connected to the Internet has a unique 32-bit numeric IP address.
•ADomain Name System (DNS) converts IP addresses to English-like domain names.
•Thedomain name is the name that corresponds to the unique 32-bit numeric IPaddress for each computer connected to the Internet.
•DNSservers maintain a database containing IP addresses mapped to theircorresponding domain names.
•Toaccess a computer on the Internet, users need only specify its domain name.
Internet Network Architecture
InternetNetwork Architecture is by definition a meta-network, a constantly changingcollection of thousands of individual networks intercommunicating with a commonprotocol.
TheInternet's architecture is described in its name, a short from of the compoundword "inter-networking". This architecture is based in the veryspecification of the standard TCP/IPprotocol, designed to connect any two networks which may be very different ininternal hardware, software, and technical design. Once two networks areinterconnected, communication with TCP/IP is enabled end-to-end,so that any node on the Internet has the near magical ability to communicatewith any other no matter where they are. This openness of design has enabledthe Internet architecture to grow to a global scale.
InternetGovernance:
Internetgovernance is the development and application by governments, the privatesector and civil society, in their respective roles, of shared principles,norms, rules, decision-making procedures, and programmers that shape theevolution and use of the Internet.
Thisworking definition was taken up in the Tunis Agenda for the InformationSociety, one of the two outcome documents of the second phase of the WorldSummit on the Information Society (WSIS) in 2005.
Organizationsdealing with Internet Governance
Thereis a range of organizations dealing with various aspects of Internet Governancerelated issues.
No one “owns” the Internet; however,worldwide Internet policies are established by the following organizations:
•Internet Architecture Board (IAB)
•Internet Corporation for AssignedNames and Numbers (ICANN)
•Internet Network Information Center(InterNIC)
•Internet Engineering Steering Group(IESG)
•Internet Engineering Task Force(IETF)
•Internet Society (ISOC)
•World Wide Web Consortium (W3C)
Major Internet Services
•E-mail: Person-to-person messaging;document sharing
•Usenet newsgroups: Discussion groupson electronic bulletin boards
•LISTSERVs: Discussion groups usinge-mail mailing list servers
•Chatting and instant messaging:Interactive conversations
•Telnet: Logging on to one computersystem and doing work on another
•FTP: Transferring files from computerto computer
•World Wide Web: Retrieving,formatting, and displaying information (including text, audio, graphics, andvideo) using hypertext links
The Internet and Business Value
TheWorld Wide Web:
•Hypertext
•Web servers
•Searching for information on the Web
Searching and Finding Information onthe Internet
•The Internet lowers search costs
•Search engines
•Intelligent agents and shopping bots
•Broadcast and push technology
•The semantic Web
Hypertext:
Hypertext is text displayed on a computer orother electronic device with references (hyperlinks) to other text that thereader can immediately access, usually by a mouse click or key press sequence.Apart from running text, hypertext may contain tables, images and otherpresentational devices. Hypertext is the underlying concept defining thestructure of the World Wide Web, making it an easy-to-use and flexible formatto share information over the Internet
Web server:
A Web server is a computerprogram that delivers (serves) content, such as Web pages, using the HypertextTransfer Protocol (HTTP), over the World Wide Web. The term Web server can alsorefer to the computer or virtual machine running the program. In largecommercial deployments, a server computer running a Web server can berack-mounted in a server rack or cabinet with other servers to operate a Webfarm.
Web search engine:
A web search engine is designedto search for information on the World Wide Web. The search results are usuallypresented in a list of results and are commonly called hits. Theinformation may consist of web pages, images, information and other types offiles. Some search engines also mine data available in databases or opendirectories. Unlike Web directories, which are maintained by human editors,search engines operate algorithmically or are a mixture of algorithmic andhuman input.
Intranets:
An intranet is a private networkthat is contained within an enterprise.It may consist of many interlinked local area networks and also use leasedlines in the wide areanetwork. Typically, an intranet includes connections through one ormore gatewaycomputers to the outside Internet. The main purpose of an intranet is to sharecompany information and computing resources among employees. An intranet canalso be used to facilitate working in groups and for teleconferences.
Anintranet uses TCP/IP,HTTP,and other Internet protocols and in general looks like a private version of theInternet. With tunneling,companies can send private messages through the public network, using thepublic network with special encryption/decryption and other security safeguardsto connect one part of their intranet to another.
Extranets:
Anextranet is a private network that uses Internet technology and the publictelecommunication system to securely share part of a business's information oroperations with suppliers, vendors, partners, customers, or other businesses.An extranet can be viewed as part of a company's intranetthat is extended to users outside the company. It has also been described as a"state of mind" in which the Internet is perceived as a way to dobusiness with other companies as well as to sell products to customers.
Anextranet requires security and privacy. These can include firewallserver management, the issuance and use of digitalcertificates or similar means of user authentication, encryptionof messages, and the use of virtual private networks (VPNs)that tunnel through the public network.
Companiescan use an extranet to:
- Exchange large volumes of data using Electronic Data Interchange (EDI)
- Share product catalogs exclusively with wholesalers or those "in the trade"
- Collaborate with other companies on joint development efforts
- Jointly develop and use training programs with other companies
- Provide or access services provided by one company to a group of other companies, such as an online banking application managed by one company on behalf of affiliated banks
- Share news of common interest exclusively with partner companies
E-mail:
Electronic mail, most commonly abbreviated emailor e-mail, is a method of exchanging digital messages. E-mail systemsare based on a store-and-forward model in which e-mail server computer systemsaccept, forward, deliver and store messages on behalf of users, who only needto connect to the e-mail infrastructure, typically an e-mail server, with anetwork-enabled device for the duration of message submission or retrieval.Originally, e-mail was always transmitted directly from one user's device toanother's; nowadays this is rarely the case.
Chat:
Online chat can refer to any kind ofcommunication over the Internet, but is primarily meant to refer to directone-on-one chat or text-based group chat (formally also known as synchronousconferencing), using tools such as instant messengers, Internet Relay Chat,talkers and possibly MUDs. The expression online chat comes from theword chat which means "informal conversation.
IMs(Instant Messages):
Instant messaging, or IM in Internet slang, consists of sendingreal time messages to another Internet user. Instant messaging is comparable tochatting in your own private chat room, with only thosepeople you choose to invite. You can create a list to keep track of welcomeguests and alert you when one of them sends you a message.
VPN:
A virtual private network (VPN)is a computer network that is layered on top of an underlying computer network.The private nature of a VPN means that the data travelling over the VPN is notgenerally visible to, or is encapsulated from, the underlying network traffic.Similarly, the traffic within the VPN appears to the underlying network as justanother traffic stream to be passed. A VPN connection can be envisioned as a"pipe within a pipe", with the outer pipe being the underlyingnetwork connection.
Theterm VPN can be used to describe many different network configurations andprotocols. As such, it can become complex when trying to generalize about thecharacteristics of a VPN. Some of the more common uses of VPNs are describedbelow, along with more detail about the various classification schemes and VPNmodels.
Groupware: Provides capabilities for supportingenterprise-wide communication and collaborative work
Team-ware: Enables companies to implementcollaboration applications easily that can be accessed using Web browsersoftware
Electronic conferencingtools: Provides avirtual conference table where participants can view and modify documents andslides or share their thoughts and comments using chat, audio, or video
Internettelephony: Enablecompanies to use Internet technology for telephone voice transmission over theInternet or private networks
Voiceover IP (VoIP) technology:Uses the Internet Protocol (IP) to deliver voice information in digital formusing packet switching
Unifiedmessaging systems:Combine voice mail, e-mail, and faxes so they can all be obtained from onesystem
Optical fiber (or "fiberoptic") refers to the medium and the technology associated with thetransmission of information as light pulses along a glass or plastic strand orfiber. Optical fiber carries much more information than conventional copperwire and is in general not subject to electromagnetic interference and the needto retransmit signals. Most telephone company long-distance lines are now madeof optical fiber. Transmission over an optical fiber cable requires repeatersat distance intervals. The glass fiber requires more protection within an outercable than copper. For these reasons and because the installation of any newcabling is labor-intensive, few communities have installed optical fiber cablesfrom the phone company's branch office to local customers (known as localloops). A type of fiber known as singlemode fiber is used for longer distances; multimodefiber is used for shorter distances.
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