1Telecommunications systems(Part 1)School of BusinessEastern Illinois University © Abdou Illia, Fall 2006(Week 11, Thursday 11/02/2006)2Learning Objectives Describe and compare types of connection to subnets and networks offered by telephone companies3Types of connection Standard telephone line 56K Leased line T-Carrier (T-1, T3) Integrated Services Digital Network (ISDN) Digital Subscriber Line (DSL)(Frame Relay)(Asynchronous Transfer Mode - ATM)24Standard telephone line Many home computer users use standard telephone lines and conventional modems to connect to networks. Dial-up connection (not always active) Speed limited by:– Bandwidth of standard telephone system (3.1 KHz)Shannon Equation:Maximum speed = Bandwidth * Log2(1 + Signal Power/Noise)~ 35 kbps5Modems StandardsName Receiving speed Sending speedV.92 56 kbps 48 kbpsV.90 56 kbps 33.6 kbpsV.34 33.6 kbps 33.6 kbpsModem standardsV.32 bis 14.4 kbps 14.4 kbps6Standard telephone line w/ Modem at each endPSTN (Digital)Client AServer A TelephoneTelephone33.6kbpsModemDigital SignalModulatedSignalModemNeed Modem at Each End* PSTN: Public Switched Telephone Network37Standard telephone line w/ Digital Access LinePSTN (Digital)Client BServerBTelephoneDigital Access Line56 kbpsModemFor 56 kbps Download SpeedServer Must Have a Digital Connection, Not a Modem8Standard telephone lineAlthough only 35 kbps can be sent through a typical 3.1 Khz telephone bandwidth, telephone system is digital internally with 56 kbps channels for individual telephone calls9Standard telephone line ADC limits transmission speed ADC needed because internal telephone system is digital410Standard telephone line Internet Service Provider (ISP) is not going through ADC So, ISP can make full use of telephone system’s 56 kbps11Standard telephone line When 56 kbps signal reaches the last telephone switch:– DAC translates the digital signal into an analog signal– DAC sends the analog signal to your telephone (therefore to modem)* DAC do not impose 3.1 kHz limitations. So modem can receive at 56 kbps12Standard telephone line (w. modem)Typical max speed33.6 Upstream56 kbps DownstreamCharacteristicsData or VoiceBothCost per month~$12.00Mode of connectionDial-up51356K Leased line Most businesses need permanent high-speed connection:– to the Internet– to other businesses– to remote databases A 56K Leased line is a possible solution 56K leased lines:– Are dedicated lines leased from telephone companies– Connect the Client to another party (Office, ISP, supplier, etc)– Are always active (No need for Dial)– Transfer data at 56,000 bps Cost depends on distance:– ~$100/mo for local connection (non long-distance)– ~$500/mo plus 1.00/mile for long-distance connection14Summary Questions1. When a standard telephone line is used to connect to a network: (a) What device limits the speed? (b) Where is this device located?(a) The analog-to-digital converter (ADC).(b) It is located at the telephone company’s switch at the end of your local loop access line. 2. (a) In using a V.90 modem for dial-up connection to the Internet, what is needed at the ISP end? (b) What does the telephone company need?(a) A digital access line to the telephone carrier (and some internal equipment).Note: The ISP does not have a V.90 modem. If it did, it could only transmit at 33.6 kbps.(b) The telephone company does not have to do anything differently.Note: the telephone company does not have to install ADCs. These are already there. You use ADCs and DACs every time you make a voice telephone call.15Summary Questions3. (a) How are 56K Leased lines and standard telephone lines different in terms of their operation? (b) How are they different in terms of speed and cost?(a) With standard telephone lines you need to dial a telephone number to connect. The connection is not permanent (active only during a call). With 56K Leased line, there is no need to dial a telephone number, and the connection is always active.(b) 56K Leased lines are faster and more expensive.616Elements of the Public Switched Telephone Network (PSTN)1. Customer Premises Equipment 1. Customer Premises Equipment17Elements of the Public Switched Telephone Network (PSTN), Continued2.Access Line(Local Loop)2.Access Line(Local Loop)The Access System consists ofthe access line to the customer(called the local loop)and termination equipment at the end office(nearest telephone office switch)18Elements of the Public Switched Telephone Network (PSTN), Continued3. Transport Core3. TrunkLine3.SwitchThe Transport Core is a subnet. It includesSwitches and Trunk lines that interconnect the
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