1 Telephony: Internal and External Chapter 6 Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4 th edition Not for distribution to students

2 Figure 6.1: Telephony Telephone Service is Expensive for Corporations LANs Use Traditional Telephone Building Wiring Telephone Technology is Basis for Much Wide Area Networking Telephone Regulation and Carriers Affect Wide Area Networking Desire for Converged Services: Integrated Management of Voice and Data Networks

3 Building Telephone Wiring Multi-floor Office Building

4 Figure 6.2: Internal PBX-Based Telephone Network 1. Equipment Room (Usually in Basement) 2. To Telcos 3. Entrance Facility 5. PBX Internal Telephone Switch 6. Wire Bundle (Many Pairs) 7. Vertical Riser Space 4. Termination Equipment

5 Figure 6.2: Internal PBX-Based Telephone Network 3. Telecommunications Closet on Floor 2. Wire Bundles 4. Cross-Connect Device 5. Horizontal Distribution 1.Vertical Distribution 4-Pair UTP Cords

6 Patch Panel 19” Equipment Rack Patch Panel Rack- Mounted Switches

7 Figure 6.2: Internal PBX-Based Telephone Network 1. Horizontal Distribution One 4-Pair UTP Cord 2. Final Distribution Along or Through Wall 3. Patch Cord

8 Figure 6.3: LAN Building Wiring 1. Equipment Room (Usually in Basement) 2. To WAN 3. Entrance Facility with Termination Equipment 5. Core Switch (Chassis) 6. Vertical Riser Space 4. Router

9 Figure 6.3: LAN Building Wiring 3. Telecommunications Closet on Floor 2. Optical Fiber One Pair per Floor 4. Workgroup Switch 5. Horizontal Distribution 1.Vertical Distribution

10 Workgroup Switch in Telecoms Closet Figure 6.3: LAN Building Wiring 1. Horizontal Distribution One 4-Pair UTP Cord Horizontal and Final Distribution are the Same as in Telephony

11 Building Cabling Management Structured Cabling Plans Testing Inexpensive just to test whether wires are connected properly More expensive to test for signal quality Documentation and Neatness Critical to avoid chaos in wiring

12 The Public Switched Telephone Network (PSTN)

13 Figure 6.4: Public Switched Telephone Network (PSTN) Customer Premises (Residential) Customer Premises (Business) Switching Office Central Office End Office Access Line Local Loop Single Twisted Pair Of Low Quality

14 Figure 6.4: Public Switched Telephone Network (PSTN) Switching Hierarchy Trunk Line Digital Class 4 Class 3 Class 5 End Office Class 5 End Office

15 Figure 6.5: Trunk Line Technologies Trunk LineSpeed North American Digital Hierarchy 56 kbps (DS0 Signaling)56 kbps (sometimes 64 kbps) T1 (DS1 Signaling)1.544 Mbps T3 (DS3 Signaling)44.7 Mbps CEPT Multiplexing Hierarchy 64 kbps E Mbps E334.4 Mbps Connect Pairs of Switches

16 Figure 6.5: Trunk Line Technologies Trunk LineSpeed SONET/SDH* OC3/STM1156 Mbps OC12/STM4622 Mbps OC48/STM162.5 Gbps OC192/STM6410 Gbps OC768/STM25640 Gbps Notes:SONET and SDH speeds are multiples of Mbps. OCx is the SONET designation. STMx is the SDH designation.

17 Figure 6.6: SONET/SDH Dual Rings SONET/SDH Ring Telephone Switch Telephone Switch Telephone Switch Telephone Switch Rings can be Wrapped if a Trunk line Is Broken (Ch. 5)

18 Figure 6.7: Circuit Switching 3. Circuit Switching: Circuit Reserved for Duration of Call 2. Across Multiple Access Lines, Switches, and Trunk Lines 1. Circuit End-to-End Connection Subscriber-Subscriber

19 Figure 6.7: Circuit Switching Dedicated Capacity Full capacity always available to pair of subscribers during their call Wasted if not used, and callers pay for whether use it or not Good for voice, in which there is almost always someone talking Expensive for data, which is bursty, having short transmissions mixed with long silences Time Data Burst

20 Figure 6.8: The PSTN: All-Analog Initially Original Telephone Network: All Analog Local Loop (Analog) Residential Telephone (Analog) Switch (Analog) Switch (Analog) Switch (Analog) Local Loop (Analog) Business Telephone (Analog) Trunk Line (Analog)

21 Figure 6.8: The PSTN: Mostly Digital with Analog Local Loops Local Loop (Analog) Residential Telephone (Analog) Switch (Digital) Switch (Digital) Switch (Digital) Local Loop (Digital) PBX (Digital) Trunk Line (Digital) Today’s Telephone Network: Predominantly Digital

22 Figure 6.9: Codec at the End Office Switch Subscriber Access Line is Analog Switch is Digital Codec Converts Between Them Codec Digital Internal Signal Digital Switch Local Loop Access Line End Office Analog Subscriber Signal ADC DAC

23 Figure 6.10: Sampling for Analog-to-Digital Conversion (ADC) Codec First Bandpass Filters the Voice Signal Cuts of all energy below about 300 Hz Cuts off all energy above about 3,400 Hz Bandpass-filtered signal of 300 Hz to 3.4 kHz Signal Energy Distribution for Human Speech O Hz300 Hz ~3,400 Hz 20 kHz Bypass Filter

24 Figure 6.10: Sampling for Analog-to- Digital Conversion (ADC) Codec Samples the Voice Signal Divides each second into 8,000 sampling periods Each sampling period is 1/8,000 of a second Sample 1/8,000 sec Sampling Period

25 Figure 6.10: Sampling for Analog-to- Digital Conversion (ADC) Codec Measure Signal Intensity Measures voice intensity in each sampling period as fraction of a maximum value (255). Here, it is 210/255. Converts decimal value 210 into an 8-bit binary value, Sample 1/8,000 sec Sampling Period Intensity Value 210/255 ( )

26 Figure 6.10: Sampling for Analog-to- Digital Conversion (ADC) Codec 8,000 samples/second * 8 bits/sample = 64 kbps This is why telephone channels are 64 kbps Designed for digitized voice Carrier often “steals” 8 kbps for supervisory signaling, so 56 kbps

27 Figure 6.11: Digital-to-Analog Conversion (DAC) Arriving Digital Signal From Telephone Switch (8,000 Samples/Second) Generated Analog Signal For Subscriber Line DAC 1/8000 Second (8 bits) Sounds smooth if there are enough samples per second

28 Question If you have an audio CD player, it contains a(n) _____. a. Analog-to-digital converter (ADC) b. Digital-to-analog converter (DAC) c. Both d. Neither

29 Cellular Telephony

30 Figure 6.12: Cellular Telephony B E H D I G L K F C M A J N P O PSTN Mobile Telephone Switching Office Cellsite 1. Divide Area Into Cells 2. Cellphone Communicates Via Cellsites, MTSO 3. To PSTN

31 Figure 6.12: Cellular Telephony B E H D I G L K F C M A J N P O 3. Reuse Channel 47 in D and F PSTN Cellsite 1. Reuse Channels in Non-Adjacent Cells 2. Use Channel 47 In Cell A

32 Figure 6.12: Cellular Telephony B E H D I G L K F C M A J N P O PSTN Cellsite 1. Use Channel 47 In A, D, and F 2. Reuse Channel 47 In What Other Cells?

33 Importance of Channel Reuse Channels are Scarce Only ~800 in First Generation Cellular Systems Only ~2,500 More for Second Generation Systems You Can Only Have an Average of 20 Customers per Channel Assumes each will use the system 5% of the time (generous) Only 16,000 to 50,000 customers without channel reuse

34 Importance of Channel Reuse Can Reuse Channel in Nonadjacent Cells In adjacent cells, signals will interfere To tell how roughly how many times you can reuse a channel on average Divide the number of cells by 7 Rough estimate but very useful 20 cells / 7 = 3 (Round off: It’s not exact) 100 cells / 7 = 14 You can multiply the possible number of subscribers by this factor

35 Importance of Channel Reuse Example 800 channels (First-generation system) 20 cells 3 (20/7) is the channel reuse factor 2,400 effective channels (800 x 3) 20 subscribers/channel maximum for good service 48,000 maximum subscribers (2,400 x 20)

36 Importance of Channel Reuse Example 2,000 channels 100 cells How many subscribers can you serve?

37 Compression Compression Multiplies Number of Possible Subscribers by About a Factor of 3 2,000 channels 100 cells How many subscribers can you serve?

38 Channel Reuse and CDMA Some cellular systems use CDMA We saw in Chapter 5 that CDMA is a form of spread spectrum transmission We saw in Chapter 5 that multiple stations can use CDMA channels simultaneously With CDMA, all channels can be used in all cells without fear of interference from adjacent cells This gives more subscribers for a given number of cells, but the gain over traditional cellular service is not linear New

39 Figure 6.12: Cellular Telephony B E H D I G L K F C M A J N P Handoff O PSTN Mobile Telephone Switching Office 1. Automatic Handoff Between Cellsites O to P as Phone Travels Between Cells

40 Handoffs versus Roaming Handoff Moving between cells within a single cellular system Cellular telephony wireless LANs Roaming Moving between systems Cellular telephony: use cellphone in another city

41 Figure 6.13: Generations of Cellular Service GenerationFirst2nd2.5G3G TechnologyAnalogDigital Data Transfer Rate Data Transfer Is Difficult 10 kbps* 20 kbps to 144 kbps to 2 Mbps Channels~800 ~ ,500 ~ ,500 ? Cells/ Channel Reuse Large/ Medium Small/ High Based on 2G ? *Sufficient for Short Message Service (SMS) and wireless Web access using the Wireless Access Protocol (WAP) or i-mode

42 3G Speeds ITU Speed Requirements for 3G 2 Mbps for fixed devices 384 kbps for walking people 144 kbps for automotive users Anything Less is 2.5 G Some 2.5G vendors call themselves 3G but are not New

43 Figure 6.13: Generations of Cellular Service GenerationFirst2nd2.5G3G World Standardization (and therefore roaming) Poor Good (GSM) Based on 2G ? (W-CDMA, CDMA-2000, and other systems may compete) U.S. Standardization Good (AMPS) Poor (GSM, CDMA, TDMA, & CDPD) Based on 2G ?

44 U.S. Cellular Telephony Lag The U.S. lags many other countries in cellular telephone use. U.S. wired telephone charges are low, making the price gap to get a cellular phone high The lack of a U.S. standard for 2 nd generation cellular telephones causes confusion and generally raises prices In the U.S., when someone calls a cellular number, the receiver pays. In the rest of the world, the caller pays New

45 Regulation and Carriers

46 Figure 6.14: Regulation and Deregulation Regulation Carriers: carry signals between customer premises Rights of Way: government permission to lay wire Monopoly: service was originally provided by a single telephone carrier Regulation: This monopoly carrier was regulated to prevent abuse of the monopoly Tariffs specify a service’s specific service parameters and pricing to prevent discrimination and guarantee service provision

47 Figure 6.14: Regulation and Deregulation Deregulation Deregulation: remove protections & restrictions To increase competition, lowering prices Varies by country Varies by service within countries Data, long-distance, and customer premises deregulation is high. Local voice service deregulation is low.

48 Figure 6.15: Regulation and Carriers Carriers Public Telephone and Telegraph (PTT) authority is the traditional domestic monopoly carrier in most countries. Domestic transmission: within a country UK: British Telecoms Japan: NTT

49 Figure 6.15: Regulation and Carriers Carriers In the United States U.S. is divided into regions called local access and transport areas (LATAs) About 200 LATAs nationwide Small states have just one LATA Large states have 10 to 20 LATAs LATA

50 Figure 6.15: Regulation and Carriers Carriers In the United States Local exchange carriers (LECs) provide service within a LATA Incumbent LEC (ILEC) is the traditional monopoly carrier in the LATA Competitive LEC (CLEC) is a new competitor LATA LEC ILECCLEC

51 Figure 6.15: Regulation and Carriers LATA IXC Carriers In the United States Inter-exchange carriers (IXCs) provide service between LATAs LEC versus IXC distinction is used by data carriers as well as voice carriers

52 Mix and Match Quiz A. Geographical Region B. Carrier within a region C. Carrier Between Regions 1. IXC 2. LEC 3. LATA

53 Figure 6.15: Regulation and Carriers Carriers In the United States Point of Presence (POP) is a place in a LATA where all carriers interconnect to provide integrated service to all customers LATA POP ILEC CLECIXC

54 Figure 6.15: Regulation and Carriers International Service (Between Pairs of Countries) Provided by international common carriers (ICCs) Allowed carriers, prices, and conditions of service are settled through bilateral negotiation between each pair of countries Country 1Country 2 ICC

55 Carrier Quiz In what country do you find each of the following? 1. LATA 2. PTT 3. LEC 4. IXC 5. ICC

56 Figure 6.15: Carriers: Recap U.S. Intra-LATA LECs ILEC CLECs Inter-LATA IXCs Most of the World PTTs for domestic service ICCs

57 Converged Services TelephonyData

58 Figure 6.16: Converged Services Integrate Voice and Data Networks Often referred to as voice over IP (VoIP) and IP telephony Provide Voice and Data Over a Single Network Most firms now maintain two networks—one for voice, the other for data Using only a single network should reduce costs

59 Figure 6.16: Converged Services Save money compared to traditional telephony Reducing staff and economies of scale in purchasing technology New encoding standards encoding voice to less than 64 kbps so fewer bits need to be sent Packet switching to reduce transmission costs for bits sent

60 Figure 6.17: PBX-PBX IP Telephony Ordinary Telephone Ordinary Telephone Frame Relay, ATM, or the Internet IP Packet PBX with IP Telephony Module PBX with IP Telephony Module

61 Figure 6.16: Converged Services Implementation PBX-to-PBX connectivity is easy and saves money on long-distance calls LAN implementations are more difficult, less well- developed, and may not save money

62 Figure 6.16: Converged Services Will Cost Savings be Realized? Convergence justified by gap between high long- distance and international telephone charges and possible savings through IP telephony Falling traditional telephone prices are reducing the gap Packet transmission inefficiency is reducing the theoretical savings and therefore the gap Does the remaining gap justify convergence? Telephone Price VoIP Price Gap

63 Figure 6.16: Converged Services Other advantages Computer-telephony integration (CTI) Provide integrated voice and data applications E.g., when a customer calls, his or her information can be brought up on-screen

64 Figure 6.16: Converged Services Service Quality Availability (less than the PSTN’s %) Companies expect telephone service to be available all the time. Sound quality latency produces pauses Millisecond-to-millisecond inconstancy of latency produces jitter

65 Figure 6.18: Using a Single ISP for VoIP ISP 1 Backbone ISP 2 Site A Site B Site C No Congestion in Site A-C Communication Because All Traffic Passes through a Single ISP. It Avoids the Congested Internet Backbone. Congestion in Site A-B Communication Because of Passage Through Internet Backbone.

66 Voice/Data Cultural Concerns Data Networking Concerns Will all this voice traffic mean that my data cannot get through well? Telephony Concerns Will people get the same level of voice quality? Will they get secondary services (3-party calling, call waiting, etc.) New