Telecommunications Chapter 6 Updated January 2009 Raymond Panko s

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Telecommunications Chapter 6 Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications, 7 th edition May only be used by adopters of the book 6 -1 © 2009 Pearson Education, Inc. Publishing as Prentice Hall

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -3

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -4

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. & 3. End Office Switch (Class 5) © 2009 Pearson Education, Inc. Publishing as Prentice Hall 2. Access Line (Local Loop) 6 -5

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -6

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. ). SS 7 in the United States, C 7 in Europe © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -8

Transport Versus Signaling • 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. A frequent point of confusion © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -9

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -10

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -13

6 -6: Dial-Up Circuits Versus Leased Line Circuits Dial-Up Circuits Leased Line Circuits Is it a circuit with reserved capacity? Yes, by definition Operation Dial-up. Separate circuit for each call Permanent circuit, always on Speed for Carrying Data Up to 33. 6 kbps 56 kbps to gigabit speeds Number of Simultaneous Voice Calls per Circuit One Several due to multiplexing © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -14

6 - 7: Time Division Multiplexing (TDM) in T 1 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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -18

6 -8: Local Loop Technologies Technology 1 -Pair Voice-Grade UTP 2 -Pair Data-Grade UTP Use Residences Optical Fiber Businesses for highspeed access lines Status Already installed, so no installation cost Must be pulled to the customer premises. (This is expensive) Note: Within buildings, corporate telephony uses 4 -pair UTP © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -19

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -21

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). © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -22

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -23

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -24

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 k. Hz channels. Even when microwave is not used, this saves capacity © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -26

6 -13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM) Box 0 to 4 k. Hz 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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -27

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -28

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -29

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 = 0000 1 = 00000001 255=1111 This requires one octet of storage per sample. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -30

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -31

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -32

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -34

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -36

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -37

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -38

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -39

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -40

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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -41

6 -16: Handoff and Roaming in 802. 11 Wireless Networking and Cellular Telephony 802. 11 WLANs Relationship Cellular Telephony Handoff and roaming mean the same thing Handoff and roaming mean different things Handoffs (means Wireless host travels the same in between access points both) in an organization Mobile phone travels between cellsites in the same city Roaming (means Wireless host travels different things) between access points in an organization Mobile phone travels to a different city © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -42

6 -17: Voice over IP (Vo. IP) In voice over IP (Vo. IP), calls are digitized, packetized, and transported over an IP network: either an internal IP network or the Internet. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -44

6 -17: Voice over IP (Vo. IP) The user either has a PC with multimedia hardware and Vo. IP software or an IP telephone that can be plugged into an IP network via a wall jack. Either must have a codec © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -45

6 -17: Voice over IP (Vo. IP) A media gateway connects a Vo. IP network to the PSTN. This gives Vo. IP users access To PSTN users. The media gateway must translate between both signaling technology and transport technology. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -46

Vo. IP • Vo. IP means that a firm does not have to maintain two networks—an IP network for data and a circuitswitched voice network. – This should reduce costs considerably by only requiring the maintenance of a single network. • In addition, Vo. IP’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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -47

6 -18: Vo. IP Signaling and Transport Again, signaling is the transmission of supervisory messages. Transport is the actual transmission of voice. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -48

6 -18: Vo. IP Signaling and Transport The most popular SIGNALING protocol in Vo. IP 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. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -49

6 -18: Vo. IP Signaling and Transport Vo. IP transport consists of a stream of Vo. IP packets. Each Vo. IP packet contains a short amount codec-encoded voice. There is no time to wait for error correction, so UDP is used. The Real Time Protocol (RTP) header “fixes” weaknesses of UDP. First, the RTP has a sequence number to place packets in order. Second, RTP has a time stamp so that the voice steam can be played back at the correct time. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -50

6 -19: Vo. IP Codecs Codec Transmission Rate G. 711 64 kbps G. 721 32 kbps G. 722 48, 56, 64 kbps G. 722. 1 24, 32 kbps G. 723 5. 33, 6. 4 kbps G. 723. 1 A 5. 3, 6. 3 kbps G. 726 16, 24, 32, 40 kbps G. 728 16 kbps G. 729 AB 8 kbps The two phones must use the same codec to encode and decode voice. They must agree on one of several standard codec protocols through negotiation. Generally, more compression gives lower sound quality but lowers transmission cost © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -51

6 -20: “Traditional” Technologies for the Last Mile • The Last Mile – The access line to your home – Traditionally, a 1 -pair VG UTP line from the telephone company – In the 1960 s, a few businesses started getting 2 -pair data -grade UTP and optical fiber – Given the cost of upgrading the 1 -pair VG UTP plant, 1 pair VG UTP seemed eternal © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -53

6 -20: “Traditional” Technologies for the Last Mile • Telephone Service and Cable TV – 1950 s brought cable television service • Used coaxial cable with a central wire and a coaxial conductive ring or mesh © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -54

6 -20: “Traditional” Technologies for the Last Mile • Telephone Service and Cable TV – A static situation emerged – Telephone companies controlled broadcast telephone service – Cable companies controlled television delivery service © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -55

6 -20: “Traditional” Technologies for Data Transmission in the Last Mile • Telephone modems – Convert digital computer signals to analog and send these over the telephone access line – They also convert incoming analog signals into digital signals for the computer Digital Computer Signal: 101101010 Telephone Modem Analog Telephone Signal: Telephone Line © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -56

6 -20: “Traditional” Technologies for the Last Mile • Telephone modems – Limited to 33. 6 kbps sending / 56 kbps receiving – Cannot use your telephone for calls while using the telephone modem © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -57

6 -21: Asymmetric Digital Subscriber Line (ADSL) ADSL Like telephone modems, ADSL also uses the existing 1 -pair voice-grade UTP line going to the home; but it offers higher speeds than telephone modems © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -58

Telephone Modems and ADSL • Both use the 1 -pair VG UTP line running to the subscriber’s home – Already installed, so no extra cost of running a new line • Telephone modems send analog signals – This is what the traditional telephone system expects • ADSL – Send digital signals for data (digital subscriber line) – Requires special equipment at the end office switch (DSLAM) © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -59

6 -21: Asymmetric Digital Subscriber Line (ADSL) Unlike telephone modem services, ADSL provides simultaneous voice and data. The phone line is not tied up © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -60

6 -21: Asymmetric Digital Subscriber Line (ADSL) Speed is asymmetric. Faster downstream (to home) speed than upstream (from the home) speed. This is ideal for World Wide Web downloads. Speeds are increasing rapidly in both directions. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -61

6 -21: Asymmetric Digital Subscriber Line (ADSL) Home user needs a splitter for each telephone outlet Connects a phone to the splitter voice port Connects an ADSL modem To the splitter data port © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -62

6 -21: Asymmetric Digital Subscriber Line (ADSL) End office switch needs a DSLAM (DSL access multiplexer) Connects voice calls to the PSTN Connects data calls to a data network © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -63

6 -22: Cable Modem Service Cable Modem Cable modem service is provided by the cable television company, not by a telephone company Generally is faster than ADSL but also more expensive © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -64

6 -22: Cable Modem Service Optical fiber brings signals to and from the neighborhood. Thick coaxial cables carry signals in the neighborhood. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -65

6 -22: Cable Modem Service Thin coaxial drop cables carry signals from the trunk cable to individual residences. Subscriber needs a cable modem to receive data service. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -66

ADSL Versus Cable Modem Service • Generally, cable modem service is somewhat faster and more expensive than ADSL service – However, price and performance ranges overlap – And performance is increasing rapidly • In cable modem service, all subscribers in a neighborhood must share the speed – However, cable modem speed to the neighborhood is very high, so cable modem subscribers usually still get higher-than-ADSL speeds – And other subscribers cannot read a subscriber’s transmissions, which are encrypted © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -67

Fiber to the Home • Some carriers are beginning to replace their 1 -pair voice grade UTP residential wiring with optical fiber • This is called fiber to the home or fiber to the premises • Download speeds of 100 Mbps or more • Substantially more expensive than DSL service © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -68

6 -23: Wireless for the Last Mile • 3 G Cellular Data Transmission – 2 G cellular service is for voice, texting, and photographs • Can send data via a cellular modem, but only at 10 kbps – 3 G cellular was created to send data faster • Most current services offer low DSL speeds at higher prices • 2 Mbps to 3 Mbps speeds are arriving but will be even more expensive • Consumer usage is dominating with downloading music, videos, and games © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -70

6 -23: Wireless for the Last Mile • Cellular companies are using many 3 G technologies • Cellular companies will eventually introduce faster 4 G service – 100 Mbps or more New – Beginning to converge on Long-Term Evolution (LTE) – Which is IP-based © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -71

6 -23: Wireless for the Last Mile • Wi. MAX Metropolitan Area Networks – Designed to compete with DSL, cable modem service, and 3 G and 4 G cellular service – Designed to serve a metropolitan area – Users can get service anywhere, not just at hotspots © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -72

6 -23: Wireless for the Last Mile • Wi. MAX Metropolitan Area Networks – Promises to be faster than 3 G service at lower cost • Beginning with 1 to 4 Mbps and will be faster • Mobile subscribers with omnidirectional antennas will receive speeds at the lower end • Fixed subscribers in homes will have directional antennas and speeds will be at the higher end © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -73

6 -23: Wireless for the Last Mile • Wi. MAX Metropolitan Area Networks – Standards created by the Wi. MAX Forum – Wi. MAX depends on the IEEE 802. 16 standard but goes beyond it – A single MAC-layer standard for all service bands between 2 GHz to 11 GHz • Wi. MAX forum is initially developing profiles for the 2. 3, 2. 5, 3. 5, and 5. 8 GHz licensed bands • Wi. MAX carriers want licensed bands for higher quality service © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -74

6 -23: Wireless for the Last Mile • Wi. MAX Metropolitan Area Networks – Uses advanced technologies • Scalable OFDM, MIMO, adaptive antennas systems (AAS) that do beam forming, and cellular organization for its base stations – Wi. MAX technology provides high-quality service • TDM gives each subscriber its fair share of the capacity © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -75

6 -23: Wireless for the Last Mile • Satellite Access Service – Very expensive because of long transmission distance to satellites • Hundreds to thousands of miles from the user site • One-way transmission, which is used in television delivery, is not too expensive • Two-way data transmission is complex and therefore expensive © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -76

6 -24: The Market Situation • The Triple Play – The goal of access carriers • Telephony companies • Cable television companies • Wireless access companies – Provide telephony, data, and video in a package – Video is the hardest • People want multiple incoming TV signals • They also want HDTV © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -78

6 -24: The Market Situation • The International Situation – United States ranks 16 th internationally in broadband speed and availability – Korea 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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -79

Telecommunications • Access Lines – For residences, 1 -pair voice-grade UTP • DSL uses existing residential access lines to carry data by changing the electronics at each end (DSL modem in the home and DSLAM at the end office switch) • DSL is cheap because 1 -p VG UTP is already in place – For businesses, • 2 -pair data-grade UTP for speeds up to a few Mbps • Optical fiber for faster speeds • Usually must be pulled into place, so expensive – Coming: fiber to the home (FTTH) © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -81

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 © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -82

Cellular Telephony • Cells Allow Channel Reuse – Channel reuse allows more customers to be served with a limited number of channels • GSM: most widely used technology for cellular telephony • CDMA for greater channel reuse • Handoffs and Roaming © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -83

Vo. IP • To allow voice to be carried over data networks • Converge voice and data networks • Phone or user’s computer contains a codec • Transport: UDP header followed by RTP header • Signaling: H. 323 and SIP © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -84

Last Mile Services • Wired Access – Telephone Modems – Asymmetric Digital Subscriber Line (ADSL) – Cable Modem Service – Fiber to the home • Wireless Access – 3 G and 4 G Cellular Data Service – Wi. MAX (based on 802. 16 and 802. 16 e) – Satellite service (expensive and so rare) © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -85

The Market Situation • Triple Play – Traditional telephone companies, cable companies, and even wireless companies want to provide voice, data, and television • International Situation – U. S. is not a leader in broadband data service or cellular telephone service © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -86

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America. Copyright © 2009 Pearson Education, Inc. Publishing as Prentice Hall 6 -87