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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-2 The Public Switched Telephone Network (PSTN) Carriers Telephony Television

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Elements of the Public Switched Telephone Network (PSTN) 1. Customer Premises Equipment 1. Customer Premises Equipment Customer premises Equipment (CPE) consists Of telephones, wires, And other infrastructure on the customer premises. It is owned by the customer.

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : Elements of the 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).

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Elements of the PSTN 3. Transport Core 3. Trunk Line 3. Switch The Transport Core connects end office switches and core switches. Trunk lines connect switches.

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Elements of the PSTN Telephone Company Switch

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-9 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 : 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 6-11 Circuits

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Circuit Switching

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : Dial-Up Circuits Versus Leased Line Circuits Dial-Up CircuitsLeased Line Circuits Is it a circuit with reserved capacity? Yes, by definition OperationDial-up. Separate circuit for each call Permanent circuit, always on Speed for Carrying Data Up to 33.6 kbps56 kbps to gigabit speeds Number of Simultaneous Voice Calls per Circuit OneSeveral due to multiplexing

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Time Division Multiplexing (TDM) in T1 Lines

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Time Division Multiplexing (TDM) in T1 Lines

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Time Division Multiplexing (TDM) in T1 Lines

© 2009 Pearson Education, Inc. Publishing as Prentice Hall TDM Multiplexer Example Show the contents of the five output frames for a synchronous TDM multiplexer that combines four sources sending the following characters. Note that the characters are sent in the same order that they are typed. The third source is silent. a. Source 1 message: HELLO b. Source 2 message: HI c. Source 3 message: d. Source 4 message: BYE

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Local Loop Technologies TechnologyUseStatus 1-Pair Voice-Grade UTP ResidencesAlready installed, so no installation cost 2-Pair Data-Grade UTP Businesses for high- speed access lines Must be pulled to the customer premises. (This is expensive) Optical FiberBusinesses for high- speed access lines 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 6-21 Analog versus Digital Transmission

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : Analog Telephone Transmission Speaking creates pressure waves, which hit the microphone in the handset. The microphone generates an analogous electrical signal. This is called an analog signal. Handset

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : 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 : 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 6-26 Cellular Telephony

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : Cellular Telephony Cellsites

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : Cellular Technology 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. New

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : 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 : 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 : Cellular Technology In handoff, a mobile phone moves from one cell to another cell. In roaming, a mobile phone is taken to a visited network. In handoff, a mobile phone moves from one cell to another cell. In roaming, a mobile phone is taken to a visited network.

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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-36 Voice over IP (VoIP)

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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. In voice over IP (VoIP), 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 : 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 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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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. 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.

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

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : VoIP 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 : 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. 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.

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : VoIP Signaling and Transport VoIP transport consists of a stream of VoIP packets. Each VoIP 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 : VoIP Codecs CodecTransmission Rate G kbps G kbps G.72248, 56, 64 kbps G , 32 kbps G , 6.4 kbps G.723.1A5.3, 6.3 kbps G.72616, 24, 32, 40 kbps G kbps G.729AB8 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 6-45 Wired “Last Mile” Services Telephone Modems ADSL Modem Service Cable Modem Service Fiber to the Home

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : “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 1960s, 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 : “Traditional” Technologies for the Last Mile Telephone Service and Cable TV –1950s 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 : “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 : “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 Telephone Modem Telephone Line Digital Computer Signal: Analog Telephone Signal:

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : “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 : Asymmetric Digital Subscriber Line (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 ADSL

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-52 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 : 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 : 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 : 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 : 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 : Cable Modem Service Cable modem service is provided by the cable television company, not by a telephone company Generally is faster than ADSL but also more expensive Cable Modem

© 2009 Pearson Education, Inc. Publishing as Prentice Hall : 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 : 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 6-60 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 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 6-61

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-62 Topics Covered

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-63 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 6-64 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 6-65 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 6-66 VoIP 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 6-67 Last Mile Services Wired Access –Telephone Modems –Asymmetric Digital Subscriber Line (ADSL) –Cable Modem Service –Fiber to the home

© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-68 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. Copyright © 2009 Pearson Education, Inc. Publishing as Prentice Hall