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Telecommunications Chapter 6 Updated January 2009

Telecommunications Chapter 6 Updated January 2009. Raymond Panko’s Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book. The Public Switched Telephone Network (PSTN). Carriers Telephony Television.

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Telecommunications Chapter 6 Updated January 2009

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  1. TelecommunicationsChapter 6Updated January 2009 Raymond Panko’sBusiness Data Networks and Telecommunications, 7th editionMay only be used by adopters of the book

  2. The Public Switched Telephone Network (PSTN) Carriers Telephony Television

  3. 6-1: Elements of the Public Switched Telephone Network (PSTN) Customer premises Equipment (CPE) consists Of telephones, wires, And other infrastructure on the customer premises. It is owned by the customer. 1. Customer Premises Equipment 1. Customer Premises Equipment

  4. 6-2: Customer Premises Equipment at a Business Site Most businesses have a PBX (private branch exchange). It acts like an internal switchboard Businesses use 4-pair UTP for in-building telephone wiring. Have long used 4-pair UTP for telephony. Only recently was this 4-pair UTP used for data.

  5. 6-1: 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 Office Switch (Class 5)

  6. 6-1: Elements of the PSTN 3. Transport Core 3. Switch 3. Trunk Line The Transport Core connects end office switches and core switches. Trunk lines connect switches.

  7. 6-1: Elements of the PSTN • Telephone Company Switch

  8. 6-1: 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 Europe

  9. Transport Versus Signaling A frequent point of confusion • Transport • The carriage of voice during a conversation • Signaling • Supervisory communication to set up a connection, monitor connection quality, collect billing information, closing a connection, etc.

  10. 6-3: Points of Presence (POPs) Local, long-distance, and international carriers connect at POPs (points of presence) This permits their subscribers to call one another.

  11. Circuits

  12. 6-4: Circuit Switching

  13. 6-5: Voice and Data Traffic 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.

  14. 6-6: Dial-Up Circuits Versus Leased Line Circuits

  15. 6- 7: Time Division Multiplexing (TDM) in T1 Lines

  16. 6- 7: Time Division Multiplexing (TDM) in T1 Lines

  17. 6- 7: Time Division Multiplexing (TDM) in T1 Lines

  18. 6- 7: Time Division Multiplexing (TDM) in T1 Lines • Calculation • Each conversation gets an 8-bit time slot in each frame • There are 8,000 frames per second • So each conversation gets 64 kbps

  19. 6-8: Local Loop Technologies Note: Within buildings, corporate telephony uses 4-pair UTP

  20. Analog versus Digital Transmission

  21. 6-9: Analog Telephone Transmission Handset Speaking creates pressure waves, which hit the microphone in the handset. The microphone generates an analogous electrical signal. This is called an analog signal.

  22. 6-10: The PSTN: Mostly Digital with Analog Local Loops The PSTN today is almost entirely digital. This includes switches (3) and trunk lines (4). It also includes digital leased access lines to businesses (5).

  23. 6-10: The PSTN: Mostly Digital with Analog Local Loops Only the residential telephone (1) and the 1-pair voice-grade UTP line going to residences (2) are analog today. Digital subscriber lines (which we will see later) Send digital signals over these 1-pair VG UTP lines.

  24. 6-11: Codec at the End Office Switch A codec at the end office switch translates between the analog customer signals and digital signals in the PSTN core ADC is analog to digital conversion. DAC is digital to analog conversion.

  25. 6-12: Frequency Division Multiplexing (FDM) in Microwave Transmission Box Microwave provides Point-to-point Terrestrial Transmission

  26. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box For telephone transmission, a filter at the end office switch Bandpass filters the voice to fit into 4 kHz channels. Even when microwave is not used, this saves capacity

  27. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box 0 to 4 kHz More precisely, it cuts off all signal below about 300 Hz and above about 3,400 Hz This gives “guard bands” below 300 Hz And from 3,400 Hz to 4 Hz Voice still sounds good because most energy is 30 Hz to 3,400 Hz

  28. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box The signal is Sampled 8,000 Times per second. So each sample Is 1/8000 second

  29. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box In each sampling period, only the amplitude of the signal Is sampled

  30. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box The filter can distinguish 256 loudness levels. Each loudness level is represented as a binary number between 0 and 255. 0 = 00000000 1 = 00000001 255=11111111 This requires one octet of storage per sample.

  31. 6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box This sampling method, which is called pulse code modulation (PCM), produces 8 bits per sample. Times 8,000 samples per second – this means 64 kbps per conversation

  32. 6-14: Digital-to-Analog Conversion (DAC) 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.

  33. Cellular Telephony

  34. 6-15: Cellular Technology Customer has a mobile phone. A city is divided into small geographic regions called cells. Each cell has a cellsite with an antenna and equipment to serve mobile phones in the cell

  35. 6-15: Cellular Telephony • Cellsites

  36. 6-15: Cellular Technology A mobile telephone switching office (MTSO) coordinates activity among the cellsites. The MTSO also connects mobile customers with wired PSTN customers via a POP.

  37. 6-15: Cellular Technology New Cellsites 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.

  38. 6-15: Cellular Technology Channels can be reused in different cells. This permits more customers to be served. Serving more customers through channel reuse Is the whole reason for cellular service.

  39. 6-15: Cellular Technology GSM cellular technology cannot use the same channel in adjacent cells. CDMA can use the same channel in adjacent cells, providing more channel reuse and so more customers.

  40. 6-15: 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 between the cellsite in Cell O and the cellsite in Cell P.

  41. 6-15: Cellular Technology In handoff, a mobile phone moves from one cell to another cell in the same city. In roaming, a mobile phone is taken to a different city.

  42. 6-16: Handoff and Roaming in 802.11 Wireless Networking and Cellular Telephony

  43. Voice over IP (VoIP)

  44. 6-17: Voice over IP (VoIP) In voice over IP (VoIP), calls are digitized, packetized, and transported over an IP network: either an internal IP network or the Internet.

  45. 6-17: Voice over IP (VoIP) The user either has a PC with multimedia hardware and VoIP software or an IP telephone that can be plugged into an IP network via a wall jack. Either must have a codec

  46. 6-17: Voice over IP (VoIP) A media gateway connects a VoIP network to the PSTN. This gives VoIP users access To PSTN users. The media gateway must translate between both signaling technology and transport technology.

  47. VoIP • VoIP 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.

  48. 6-18: VoIP Signaling and Transport The most popular SIGNALING protocol in VoIP is SIP.This figure shows how a sender initiates a connection using SIP. The initiator sends a SIP INVITE message to its SIP proxy server. The initiator’s SIP proxy server passes the INVITE to the receivers’ server. The receiver’s SIP proxy server passes the INVITE to the receiver. If the receiver accepts the INVITE, the conversation begins.

  49. 6-19: VoIP Codecs The two phones must use the same codec to encode anddecode voice. They must agree on one of several standard codec protocols through negotiation. Generally, more compression gives lower sound quality but lowers transmission cost

  50. Wired “Last Mile” Services Telephone Modems ADSL Modem Service Cable Modem Service Fiber to the Home

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