1. Panko’s Business Data Networks and Telecommunications, 6th edition Copyright 2007 Prentice-Hall May only be used by adopters of the book Telecommunications Chapter 6

2. 6-2 Telecommunications From Chapter 1: –Data communications –Telecommunications: Voice and Video Communications

3. Technical Elements of the Public Switched Telephone Network PSTN - CPE, Access, Transport, Signaling

4. 6-4 Figure 6-1: Elements of the Public Switched Telephone Network (PSTN) 1. Customer Premises Equipment 1. Customer Premises Equipment 房屋 經營場地

5. 6-5 Figure 6-2: Customer Premises Equipment PBX: Private Branch eXchange

6. 6-6 Figure 6-1: Elements of the Public Switched Telephone Network (PSTN) 2. & 3. End Office Switch (Class 5) 2. Access Line (Local Loop) 2. Access Line (Local Loop) 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).

7. 6-7 Figure 6-1: Elements of the Public Switched Telephone Network (PSTN) 3. Transport Core 3. Trunk Line 3. Switch The Transport Core connects end office switches and core switches. Trunk lines connect switches.

8. 6-8 Figure 6-1: Elements of the PSTN Telephone Company Switch

9. 6-9 Figure 6-1: Elements of the Public Switched Telephone Network (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 Europe

10. 6-10 Figure 6-3: Points of Presence (POPs) In the U.S., competing carriers connect at points of presence (POPs).

11. 6-11 Figure 6-4: Circuit Switching

12. 6-12 Figure 6-5: Voice and Data Traffic The reserved capacity of circuit switching is OK for voice, but not for bursty data transmission.

13. 6-13 Figure 6-6: Dial-Up Circuits Versus Leased Line Circuits Dial-Up CircuitsLeased Line Circuits OperationDial-Up. Separate circuit for each call. Permanent circuit, always on. Speed for Carrying Data Up to 56 kbps Residence can only Send up to 33.6 kbps 56 kbps to gigabit speeds Number of Voice Calls Multiplexed OneSeveral due to multiplexing There are two types of circuits between customer premises: ordinary dial-up circuits and leased line circuits.

14. 6-14 Figure 6-7: Local Loop Technologies TechnologyUseStatus 1-Pair Voice-Grade UTP Residences 住宅 Already installed 2-Pair Data-Grade UTP Businesses for Lowest-speed access lines Must be pulled to the customer premises (this is expensive) Optical FiberBusinesses for higher-speed access lines Must be pulled to the customer premises (this is expensive) Residential 1-pair voice-grade UTP is already installed. This makes it inexpensive to use Business 2-pair data-grade UTP and fiber for leased lines must be installed; this is expensive.

15. 6-15 Figure 6-8: Analog Telephone Transmission Analog signals rise and fall in intensity with the human voice. No resistance to errors as there is in digital transmission. Initially, the entire PSTN was analog.

16. 6-16 Figure 6-9: The PSTN: Mostly Digital with Analog Local Loops Today, everything is digital except for the local loop access line and residential telephones. The actual local loop line can carry either analog or digital signals, but the equipment at both ends is analog.

17. 6-17 Figure 6-10: Codec at the End Office Switch A codec at the end office translates between residential analog and PSTN digital signaling. ADC = analog to digital conversion DAC = digital to analog conversion

18. 6-18 Figure 6-11: Frequency Division Multiplexing (FDM) in Microwave Transmission Microwave uses radio transmission for PSTN trunk lines

19. 6-19 Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) At the end office, the voice signal is bandpass-filtered to limit its bandwidth to 4 KHz. This permits more calls to be multiplexed on trunk lines Filter at End Office Switch

20. 6-20 Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Actually, to provide a safety margin, the signal is filtered to between about 300 Hz and 3.4 kHz instead of from 0 Hz to 4 kHz.

21. 6-21 Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Nyquist found that signals must be sampled at twice their highest frequency. For a top frequency of 4 kHz, there must be 8,000 samples per second. Each sample is 1/8000 second.

22. 6-22 Nyquist–Shannon sampling theorem “Exact reconstruction of a continuous-time baseband signal from its samples is possible if the signal is bandlimited and the sampling frequency is greater than twice the signal bandwidth.”baseband bandlimitedsampling frequency http://en.wikipedia.org/wiki/Nyquist%E2%80%93Sha nnon_sampling_theoremhttp://en.wikipedia.org/wiki/Nyquist%E2%80%93Sha nnon_sampling_theorem

23. 6-23 Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) In each sampling period, the intensity of the signal is measured. In pulse code modulation, the signal is measured as one of 256 intensity levels. One byte stores one sample.

24. 6-24 Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Pulse Code Modulation (PCM) produces 8,000 one-byte samples per second. This is 64 kbps of data. 8 bits/sample * 8000 samples/sec = 64,000 bps = 64 kbps

25. 6-25 ADC Recap First, Bandpass-Filter the Incoming Signal to 4 kHz –Really about 300 Hz to 3.4 kHz –To reduce transmission requirements The Codec then Uses PCM for the Conversion –Samples at twice the highest frequency (4 kHz so 8,000 samples/second) –Loudness is recorded with 8 bits per sample (to give 256 loudness levels) –Generates 64 kbps of traffic (8 bits/sample times 8,000 samples per second)

26. 6-26 Figure 6-13: Digital-to-Analog Conversion (DAC) Generated “Analog” to Customer (Sounds smooth because the sampling rate is very high) Arriving Digital Signal From the PSTN Core (8,000 Samples/Second) 00000100 00000011 00000111 DAC at End Office Switch One 8-Bit Sample One 8-Bit Sample

27. 6-27 Figure 6-14: Cellular Telephony In cellular technology, the region is divided into smaller cells. In each cell, a cellsite serves cellphones in the cell.

28. 6-28 Figure 6-14: Cellular Telephony Cellsites

29. 6-29 Figure 6-14: Cellular Telephony Channels can be reused in different cells. Channel reuse supports more customers. This is the reason for using cells. (Channel 47 is reused in cells A, D, and F)

30. 6-30 Figure 6-14: Cellular Telephony When a subscriber moves from one cell to another in a cellular system, this is called a handoff. When a subscriber moves from one city to another, this is roaming. (In WLANs, handoffs and roaming mean the same thing.)

31. 6-31 Figure 6-14: Cellular Telephony The Mobile Telephone Switching Office (MTSO) coordinates the cellsites and implements signaling and handoffs. The MTSO also connects cellphones to the PSTN (called the wireline network). MTSO

32. 6-32 Cellular Technologies GSM is the worldwide standard for cellular voice –Uses time division multiplexing (TDM) –Uses 200 kHz channels –Divides each second into many frame periods –Divides each frame into 8 slots –Gives same slot in each frame to a conversation Slot 1 Conversation A Slot 2 Conversation B Slot 8 Conversation H …… Slot 1 Conversation A Time Frame 1Frame 2

33. 6-33 Cellular Technologies Cannot use the same channel in adjacent cells –So can only reuse a channel about every 7 cells –For example, suppose there are 50 cells Channel can be reused 50 / 7 times This is 7 (not precise, so round things off) So each channel can support 7 simultaneous customers in these 7 cells

34. 6-34 Cellular Technologies Code Division Multiple Access (CDMA) –Also used in the United States –A form of spread spectrum transmission –1.25 MHz channels –Unlike traditional spread spectrum technology, multiple users can transmit simultaneously –Can support many users per channel Can use the same channel in adjacent cells –So can only reuse a channel in every cell

35. 6-35 Figure 6-15: Voice over IP (VoIP) VoIP carries telephone calls over LANs (for data link service) and the Internet With IP, there is no wasted capacity as there is with circuit switching. This reduces cost.

36. 6-36 Figure 6-15: Voice over IP (VoIP) Stations can be special IP telephones with IP functionality Or a PC with multimedia hardware and VoIP software IP phones need a codec to convert voice analog signals from the microphone into digital IP signals

37. 6-37 Figure 6-15: Voice over IP (VoIP) A media gateway connects a VoIP network to the PSTN Handles transport and signaling differences

38. 6-38 Figure 6-16: Speech Codes CodecTransmission Rate G.711 64 kbps (pulse code modulation) G.721 32 kbps (adaptive PCM) G.722 46, 56, or 64 kbps G.722.1 24, 32 kbps G.723.1A 5.3, 6.3 kbps There are several codec standards. They differ in transmission rate, sound quality, and latency. Both sides must use the same codec standard.

39. 6-39 Figure 6-17: VoIP Protocols Transport is the transmission of voice (carries codec data). Signaling is call supervision.

40. 6-40 Figure 6-17: VoIP Protocols VoIP transport packets use UDP at the transport layer. (There is no time for retransmissions to repair errors.) The receiver puts in fill sounds for lost packets.

41. 6-41 Figure 6-17: VoIP Protocols The UDP header is followed by a Real Time Protocol (RTP) header, which contains a sequence number and timing information. Receiver uses timing information to smooth out sound playback.

42. 6-42 Figure 6-17: VoIP Protocols Signaling is call supervision. The H.323 signaling standard came first. SIP is simpler and is beginning to dominate SIP: Session Initiation Protocol

43. 6-43 Video over IP The Other VoIP –It’s not just voice over IP –Video Telephones –Video Conferencing Multiparty Sometimes room-to-room –Video Downloads on Demand

44. 6-44 Figure 6-18: Residential Internet Access Services Telephone Modems Asymmetric Digital Subscriber Line (ADSL) Cable Modem Service 3G Cellular Data Service WiMAX (802.16d and 802.16e) Broadband over Power Lines Fiber to the Home (FTTH)

45. 6-45 Figure 6-19: Telephone Modem Connection to an ISP Telephone modems convert digital computer signals to analog telephone signals.

46. 6-46 Figure 6-19: Telephone Modem Connection to an ISP ISP does not have a modem. It has a digital leased line so can send at 56 kbps. (There is no bandpass filtering on digital leased lines.)

47. 6-47 Figure 6-19: Telephone Modem Connection to an ISP Dial-up circuits connect the client with the ISP. 56 kbps downstream, 33.6 kbps upstream 33.6 kbps

48. 6-48 Telephone Modem Limitations Very low transmission speeds –Long delays in downloading webpages Subscriber cannot simultaneously use the telephone line for voice calls Still used by 30% to 40% of Internet users.

49. 6-49 Figure 6-20: Amplitude Modulation Modems modulate signals— convert binary (digital) computer data into an analog signal to travel over the PSTN.

50. 6-50 Figure 6-20: Amplitude Modulation In amplitude modulation, there are two amplitude (loudness levels)— one for 1 and one for 0 1011 is loud-soft-loud-loud

51. 6-51 Figure 6-21: Asymmetric Digital Subscriber Line (ADSL) ADSL uses the existing residential local loop technology. Inexpensive because there is no need to pull new wires, but 1-pair voice-grade UTP is not great for data.

52. 6-52 Figure 6-21: Asymmetric Digital Subscriber Line (ADSL) Subscriber needs an ADSL modem. Also needs a splitter for each telephone wall outlet. Telephone carrier needs a digital subscriber line access multiplexer (DSLAM) to separate the two signals.

53. 6-53 Figure 6-21: Asymmetric Digital Subscriber Line (ADSL) Unlike telephone modems, ADSL service provides simultaneous voice and data transmission. Downstream Data Up to 3 Mbps

54. 6-54 Figure 6-21: Asymmetric Digital Subscriber Line (ADSL) Downstream Data Up to 3 Mbps Speed is asymmetric Faster downstream than upstream Ideal for Web access Acceptable for e-mail

55. 6-55 Figure 6-22: Cable Modem Service Cable modem service brings high-speed optical fiber lines to the neighborhood.

56. 6-56 Figure 6-22: Cable Modem Service In the neighborhood, thick coaxial cable brings service to households. This bandwidth is shared by everyone in the neighborhood. A thin coax line goes to each home’s cable modem.

57. 6-57 Figure 6-22: Cable Modem Service Downstream speeds up to 5 Mbps. Upstream speeds up to about 1 Mbps.

58. 6-58 ADSL versus Cable Modem Service Do Not Over-Stress the Importance of Sharing –Cable modem service usually is still faster than ADSL service –DSLAM sharing can slow ADSL service too The Bottom Line Today: –Cable modem service usually is faster –ADSL service usually is cheaper ADSL offers more speed-price options Both are improving rapidly in terms of speed and (sometimes) price 過度強調

59. 6-59 Figure 6-23: Third-Generation (3G) Cellular Data Services Cellphone connects to computer via a cellphone modem or USB Traditional GSM and CDMA –Limited to only about 10 kbps –Far too slow for usability

60. 6-60 Figure 6-23: Third-Generation (3G) Cellular Data Services GSM FamilyCDMA Family 10 kbps (far too slow)Traditional GSM ( 1 slot/frame ) Traditional CDMA Telephone modem service speeds GPRS ( 3 slots / frame ) 1x DSL / cable modem service speeds EDGE ( 4 to 8 slots/frame ) 1x EV-DO Rev. A will triple EV-DO speed FutureWideband CDMA3X (uses three channels) EDGE: Enhanced Data rates for GSM Evolution EV-DO: Evolution-Data Optimized

61. 6-61 Figure 6-18: Residential Internet Access Services WiMax (802.16) –Wireless Internet access for metropolitan areas –Basic 802.16d standard: ADSL speeds to fixed locations Will use dish antennas Just reaching the market –802.16e will extend the service to mobile users Will use omnidirectional antennas

62. 6-62 Figure 6-18: Residential Internet Access Services Satellite Internet Access –Very expensive –Often needed to serve rural areas New

63. 6-63 Figure 6-18: Residential Internet Access Services Broadband over Power Lines –Broadband data from your electrical company –It already has transmission wires and access to residences and businesses –It modulates data signals over electrical power lines –It works, but has very limited availability –Especially promising for rural areas

64. 6-64 Figure 6-18: Residential Internet Access Services Fiber to the Home (FTTH) –Carrier runs fiber to the home –Provides speeds of tens of megabits per second for high- speed video, etc. Less if fiber only goes to the curb (FTTC) Or to the neighborhood (FTTN) –Much faster than other residential internet access services –Could dominate residential (and business) Internet access in the future 路邊

65. 6-65 Internet Access and VoIP Most Internet Access Providers are Planning to Provide VoIP Telephone Service –An alternative to the local telephone company service –Media gateways will interconnect with the PSTN –Should be less expensive that traditional phone service –Questions remain Voice quality and reliability 911 location discovery Regulation and taxation Laws that require wiretapping with warrants

66. Topics Covered

67. 6-67 Telecommunications Data Communications versus Telecommunications The PSTN’s Technical Elements –Customer premises equipment (PBX and 4-pair UTP) –Access system (local loop) –Transport core –Signaling (call setup and management) –POP to interconnect carriers

68. 6-68 PSTN Transmission Circuit Switching –Reserved capacity end-to-end –Acceptable for voice, but not for bursty data transmission –Dial-up and leased line circuits Analog and Digital Transmission –Analog signals on the local loop –ADC and DAC at the end office switch –ADC: bandpass filtering and sampling for 64 kbps –DAC: sample values are converted to sound levels

69. 6-69 Cellular Telephony Cells Allow Channel Reuse –Allows more customers to be served with a limited number of channels GSM: TDMA, most widely used technology for cellular telephony CDMA for greater channel reuse Handoffs and Roaming

70. 6-70 VoIP To allow voice to be carried over data networks Converge voice and data networks Phone needs a codec Transport: UDP header followed by and RTP header Signaling: H.323 and SIP Video over IP

71. 6-71 Residential Internet Access Services Telephone Modems Asymmetric Digital Subscriber Line (ADSL) Cable Modem Service 3G Cellular Data Service WiMAX (802.16 and 802.16e) Broadband Over Power Lines Fiber to the Home (FTTH)