2The Public Switched Telephone Network (PSTN) The telephone network is officially the “Public Switched Telephone Network”.It is available to the public—that, is, anyone.It uses switches to link subscribers together.
36-1: Elements of the Public Switched Telephone Network (PSTN) Customer premisesEquipment (CPE) consistsOf telephones, wires,And other infrastructureon the customer premises.It is owned by the customer.Customer premises equipment, as the name suggests, is equipment on the customer’s site—residential homes and apartments and business buildings.This equipment is owned by the customer.[Actually, until the 1970s and 1980s, the telephone company owned the telephones and wires in homes and business buildings.]1. Customer PremisesEquipment1. Customer Premises Equipment
46-2: Customer Premises Equipment at a Business Site Most businesses have a PBX (private branch exchange).It acts like an internal switchboardBusinesses use 4-pair UTP for in-building telephone wiring.Have long used 4-pair UTP for telephony.Only recently was 4-pair UTP used for data.<Read the boxed text and point to the red-enclosed areas.>
56-1: Elements of the PSTN The Access System consists of the access line to the customer (called the local loop)and termination equipment at the end office (nearest telephone office switch).2.Access Line(Local Loop)2.Access Line(Local Loop)2. & 3. End OfficeSwitch (Class 5)<Read the boxed text and point to the red-enclosed area.>
66-1: Elements of the PSTN 3. Transport Core 3. Switch 3. Trunk Line <Read the boxed text and point to the red-enclosed area.>The Transport Core connects end officeswitches and core switches.Trunk lines connect switches.
76-1: Elements of the PSTN Telephone Company Switch Here is a picture of a telephone company switch.
86-1: Elements of the PSTN 4. Signaling System Transport is the actual transmission of voice.Signaling is the control of calling (setup, teardown, billing, etc.).SS7 in the United States, C7 in EuropeHere is a distinction that students tend to forget easily.<Read the text in the box.>
9Transport versus Signaling The carriage of voice during a conversationSignalingSupervisory communication to set up a connection, monitor connection quality, collect billing information, closing a connection, etc.<Read the slide.>A point of frequent confusion
106-3: Points of Presence (POPs) Local, long-distance, and internationalcarriers connect at POPs(points of presence)This permits their subscribersto call one another.<Read the boxed text and point to the red-enclosed area.>
11Circuits Data networks use packet switching to deliver messages. Telephone networks traditionally have used something simpler, called circuit switching.
136-5: Voice and Data Traffic <Read the text in the box.>Voice uses about 30% of capacity, on average.Data only uses about 5% of capacity, on average.Circuit switching is not too wasteful for voice,But it is very wasteful for data transmission.
146-6: Dial-Up Circuits versus Leased Line Circuits Is it a circuit with reserved capacity?YesOperationDial-up. Separate circuit for each call.Permanent circuit, always onSpeed for Carrying DataUp to 33.6 kbps56 kbps to gigabit speedsNumber of Voice CallsOneSeveral due to multiplexing<Read the text in the box.>
156- 7: Time Division Multiplexing (TDM) in T1 Lines <Read the red-enclosed text and then point to the red-enclosed areas.>
166- 7: Time Division Multiplexing (TDM) in T1 Lines <Read the red-enclosed text and then point to the red-enclosed areas.>
176- 7: Time Division Multiplexing (TDM) in T1 Lines <Read the red-enclosed text and then point to the red-enclosed areas.>
186- 7: Time Division Multiplexing (TDM) in T1 Lines CalculationEach conversation gets an 8-bit time slot in each frame.There are 8,000 frames per secondSo each conversation gets 64 kbps<Read the slide.>
19Analog and Digital Transmission In this book, we have been looking primarily at digital transmission, in which different states represent 1s and 0s.The PSTN was created to use a much older form of transmission called analog transmission.
206-9: Analog Telephone Transmission Speaking creates pressure waves, which hit the microphone.The microphone generates an analogous electrical signal.This is called an analog signal.<Read the text in the box.>
216-10: The PSTN: Mostly Digital with Analog Local Loops <Read the text in the box.>The PSTN today is almost entirely digital.This includes switches and trunk lines.It also includes digital leased access lines to businesses.
226-10: The PSTN: Mostly Digital with Analog Local Loops Only the residential telephone and the1-pair voice-grade UTP line going to residencesare analog today.Digital subscriber lines (which we will see later)Send digital signals over these 1-pair VG UTP lines.<Read the text in the box.>
236-11: Codec at the End Office Switch A codec at the end office switch translates between theanalog customer signals and digital signals in the PSTN coreADC is analog to digital conversion.DAC is digital to analog conversion.<Read the text in the box.>
246-12: Frequency Division Multiplexing (FDM) in Microwave Transmission BoxMicrowave providesPoint-to-pointTerrestrial Transmission<Read the red-enclosed text.>
256-14: Digital-to-Analog Conversion (DAC) BoxSo far, we have been looking at how analog-to-digital conversion works.In the other direction, the codec has to do digital-to-analog conversion.<Read the text in the box.>Signals arriving from the PSTN are digital.The DAC converts the 8 bits of each sample into a loudness level.Not smooth, but sounds smooth at 8,000 samples/second.
26Cellular Telephony Nearly everyone today has a cellular telephone. In this section, we will look at how your mobile phone works.
276-15: Cellular Technology Customer has a mobile phone.A city is divided into smallgeographic regions called cells.Each cell has a cellsitewith an antenna and equipmentto serve mobile phones in the cell<Read the text in the box.>
286-15: Cellular Telephony Cellsites Here are some pictures of cellular telephone towers.The antennas are the rectangular metal boxes.They are not as strongly directional as dish antennas, but they are still strongly direction.
296-15: Cellular Technology A mobile telephone switching office (MTSO)coordinates activity among the cellsites.The MTSO also connects mobile customerswith wired PSTN customers via a POP.<Read the text in the box.>
306-15: Cellular Technology NewCellsites connect to the MTSO using a landline or a point-to-point radio system called microwave.Here is a microwave dish.It is covered with cloth, which does not interfere with radio transmission.Here is something that was not in the book.Obviously, cellsites need to connect to the MTSO.<Read the text>
316-15: Cellular Technology Channels can be reused in different cells.This permits more customers to be served.Serving more customers through channel reuseIs the whole reason for cellular service.<Read the text in the box.>
326-15: Cellular Technology GSM cellular technology cannot use thesame channel in adjacent cellsCDMA can use the same channel in adjacentcells, providing more channel reuseand so more customers.<Read the text in the box.>
336-15: Cellular Technology When a mobile phone travels between cells,it is handed off to the cellsite in the new cell.In this figure, there is handoff betweenthe cellsite in Cell O and the cellsite in Cell P.<Read the text in the box.>
346-15: Cellular Technology In handoff, a mobile moves from one cellto another cell in the same city.In roaming, a mobile is taken to a different city.<Read the text in the box.>
356-16: Handoff and Roaming in 802 6-16: Handoff and Roaming in Wireless Networking and Cellular TelephonyWLANsCellular TelephonyRelationshipHandoff and roaming mean the same thingHandoff and roaming mean different thingsHandoffs (means the same in both)Wireless host travels between access points in an organizationMobile phone travels between cellsites in the same cellular systemRoaming (means different things)Mobile phone travels to a different cellular systemWe have seen handoffs and roaming in both wireless LANs and cellular telephony.Sadly, these two terms are not used consistently in the two contexts.<Read the text in the table.>
36Voice over IP (VoIP)You may use Skype or some other program to talk over the Internet at low cost or even no cost.This is called voice over IP, because you are using an IP network, namely the Internet.Companies also use VoIP, both within their buildings and outside their buildings.They do not always use the Internet for transmission.
376-17: Voice over IP (VoIP) In voice over IP (VoIP), calls are transported over an IP network:either an internal IP network or the Internet.<Read the text in the boxes.>In VoIP, sound is digitized and sent in packets.
386-17: Voice over IP (VoIP) The user either has a PC with multimedia hardwareand VoIP softwareorAn IP telephone that can beplugged into an IP networkvia a wall jack.<Read the text in the box.>
396-17: Voice over IP (VoIP) A media gateway connects a VoIP network to the PSTN.This gives VoIP users accessTo PSTN users.The media gateway must translatebetween both signaling technologyand transport technology.<Read the text in the box.>
40VoIPVoIP means that a firm does not have to maintain two networks—an IP network for data and a circuit- switched voice network.This should reduce costs considerably by only requiring the maintenance of a single network.In addition, VoIP’s packet switching should be more efficient than the PSTN’s circuit switching.But companies have concerns about sound quality and the high availability expected of telephone service.<Read the text.>
41Wired “Last Mile” Services Telephone ModemsADSL Modem ServiceCable Modem ServiceYou need to get to the Internet from your home or apartment.Businesses need to get to the Internet from their sites.We will begin looking at three traditional ways to connect to the Internet.All of them used wired transmission.
426-20: “Traditional” Technologies for the Last Mile The access line to your homeTraditionally, a 1-pair VG UTP line from the telephone companyIn the 1960s, a few businesses started getting 2-pair data-grade UTP and optical fiberGiven the cost of upgrading the 1-pair VG UTP plant, it seemed eternal<Read the text.>
436-20: “Traditional” Technologies for the Last Mile Telephone Service and Cable TV1950s brought cable televisionUsed coaxial cable with a central wire and a coaxial conductive ring or meshThick coax trunk lines past homesThin coax drop lines to homes<Read the text.>
446-20: “Traditional” Technologies for the Last Mile Telephone Service and Cable TVTelevision services soon went beyond delivering over- the-air signalsA static situation emergedTelephone companies controlled telephone serviceCable companies controlled television delivery service<Read the text.>
456-20: “Traditional” Technologies for the Last Mile Telephone modemsConvert digital computer signals to analog and send these over the telephone access lineThey also convert incoming analog signals into digital signals for the computerDigitalComputerSignal:AnalogTelephoneSignal:TelephoneModem<Read the text.>Telephone Line
466-20: “Traditional” Technologies for the Last Mile Telephone modemsLimited to 33.6 kbps sending / 56 kbps receivingCannot use your telephone for calls while using the telephone modem<Read the text.>
476-21: Asymmetric Digital Subscriber Line (ADSL) <Read the text in the box.>Like telephone modems,ADSL also uses the existing 1-pair voice-gradeUTP line going to the home;But it offers higher speeds than telephone modems.
48Telephone Modems and ADSL Both use the 1-pair VG UTP line running to the subscriber’s homeAlready installed, so no extra cost of running a new lineTelephone modems send analog signalsThis is what the traditional telephone system expectsADSLSend digital signals for data (digital subscriber line)Requires special equipment at the end office switch (DSLAM)<Read the text.>
496-21: Asymmetric Digital Subscriber Line (ADSL) <Read the text in the box.>Unlike telephone modem services,ADSL provides simultaneous voice and data.The phone line is not tied up
506-21: Asymmetric Digital Subscriber Line (ADSL) Speed is asymmetric.Faster downstream (to home) speedthan upstream (from the home) speed.This is ideal for World Wide Web downloads.Speeds are increasing rapidly in both directions.<Read the text in the box.>
516-21: Asymmetric Digital Subscriber Line (ADSL) Home user needsa splitter for eachtelephone outlet.Connects a phoneto the splitter voice port.Connects anADSL modemTo the splitter data port<Read the text in the box.>
526-21: Asymmetric Digital Subscriber Line (ADSL) End office switchneeds a DSLAM(DSL access multiplexer)Connects voice callsto the PSTNConnects data callsto a data network<Read the text in the box.>
53Cable Modem 6-22: Cable Modem Service Cable modem service is provided by the cable television company,not by a telephone company.Generally is faster than ADSLbut also more expensive<Read the text in the box.>
546-22: Cable Modem Service Optical fiber brings signals to and from the neighborhood.Thick coaxial cables carry signals in the neighborhood.<Read the text in the box.>
556-22: Cable Modem Service Thin coaxial drop cables carry signals from the trunk cableto individual residences.Subscriber needs a cable modemto receive data service.<Read the text in the box.>
56ADSL versus Cable Modem Service Generally, cable modem service is somewhat faster and more expensive than ADSL serviceHowever, price and performance ranges overlapAnd performance is increasing rapidlyIn cable modem service, all subscribers in a neighborhood must share the speedHowever, cable modem speed to the neighborhood is very high, so cable modem subscribers usually still get higher-than-ADSL speedsAnd other subscribers cannot read a subscriber’s transmissions<Read the text.>
57Wireless Access Service Figure 6-23: Wireless Technologies for the Last MileWe have looked at wired access to the Internet.We will no look at wireless access technologies to get you to the Internet.
586-23: Wireless for the Last Mile 3G Cellular Data Transmission2G cellular service is for voice, texting, and photographsCan send data via a cellular modem, but only at 10 kbps3G cellular was created to send data fasterMost current services offer low DSL speeds at higher prices2 Mbps to 3 Mbps speeds are arriving but will be even more expensiveConsumer usage is dominating with downloading music, videos, and games<Read the text.>
596-23: Wireless for the Last Mile WiMAX Metropolitan Area NetworksDesigned to compete with DSL and cable modem serviceDesigned to serve a metropolitan areaUsers can get service anywhere, not just at hotspots.<Read the text.>
606-23: Wireless for the Last Mile WiMAX Metropolitan Area NetworksPromises to be faster than 3G service at lower costBeginning with 1 to 4 Mbps and will be fasterMobile subscribers with omnidirectional antennas will receive speeds at the lower endFixed subscribers in homes will have directional antennas and speeds will be at the higher end<Read the text.>
616-23: Wireless for the Last Mile Satellite Access ServiceVery expensive because of long transmission distance to satellitesHundreds to thousands of miles from the user siteOne-way transmission, which is used in television delivery, is not too expensiveTwo-way data transmission is complex and therefore expensive<Read the text.>
62The Market SituationHaving looked at technologies, we need to turn the situation in the marketplace for services.
636-24: The Market Situation The Triple PlayThe goal of access carriersTelephony companiesCable television companiesWireless access companiesProvide telephony, data, and video in a packageVideo is the hardestPeople want multiple incoming TV signalsThey also want HDTV<Read the text.>
646-24: The Market Situation Very High Speed Access Is ComingFiber to the home (FTTH)Speeds of up to 100 Mbps or moreThe backhaul issue: the entire network must be upgraded in capacity<Read the text.>
656-24: The Market Situation The International SituationUnited States ranks 16th internationally in broadband speed and availabilityKorea and Japan provide 50 Mbps speeds or faster at prices comparable to U.S. prices (for lower speeds)Leadership in speed brings leadership in applications.<Read the text.>