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

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

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.

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)

6-1: 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.

6-1: Elements of the PSTN Telephone Company Switch

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

Transport Versus Signaling 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

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.

Circuits

6-4: Circuit Switching

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.

6-6: Dial-Up Circuits Versus 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

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

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

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

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

6-8: Local Loop Technologies Technology Use Status 1-Pair Voice-Grade UTP Residences Already 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 Fiber Note: Within buildings, corporate telephony uses 4-pair UTP

Analog versus Digital Transmission

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.

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).

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.

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.

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

For telephone transmission, a filter at the end office switch 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

More precisely, it cuts off all signal below about 300 Hz 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

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

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

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.

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

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.

Cellular Telephony

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

6-15: Cellular Telephony Cellsites

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.

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.

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.

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.

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.

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.

6-16: Handoff and Roaming in 802 6-16: Handoff and Roaming in 802.11 Wireless Networking and Cellular Telephony 802.11 WLANs Cellular Telephony Relationship Handoff 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) Mobile phone travels to a different city

Voice over IP (VoIP)

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.

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

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.

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.

6-18: VoIP Signaling and Transport Again, signaling is the transmission of supervisory messages. Transport is the actual transmission of voice.

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.

6-18: 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.

6-19: VoIP Codecs 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 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.723.1A 5.3, 6.3 kbps G.726 16, 24, 32, 40 kbps G.728 16 kbps G.729AB 8 kbps

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

6-20: “Traditional” Technologies for 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

6-20: “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

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

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: 1011001101010 Analog Telephone Signal: Telephone Modem Telephone Line

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

6-21: 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

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)

6-21: Asymmetric Digital Subscriber Line (ADSL) Unlike telephone modem services, ADSL provides simultaneous voice and data. The phone line is not tied up

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.

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

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

Cable Modem 6-22: 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

6-22: Cable Modem Service Optical fiber brings signals to and from the neighborhood. Thick coaxial cables carry signals in the neighborhood.

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.

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

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

Wireless Access Service Figure 6-23: Wireless Technologies for the Last Mile

6-23: Wireless for the Last Mile 3G Cellular Data Transmission 2G cellular service is for voice, texting, and photographs Can send data via a cellular modem, but only at 10 kbps 3G 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

6-23: Wireless for the Last Mile Cellular companies are using many 3G technologies Cellular companies will eventually introduce faster 4G service 100 Mbps or more Beginning to converge on Long-Term Evolution (LTE) Which is IP-based New

6-23: Wireless for the Last Mile WiMAX Metropolitan Area Networks Designed to compete with DSL, cable modem service, and 3G and 4G cellular service Designed to serve a metropolitan area Users can get service anywhere, not just at hotspots

6-23: Wireless for the Last Mile WiMAX Metropolitan Area Networks Promises to be faster than 3G 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

6-23: Wireless for the Last Mile WiMAX Metropolitan Area Networks Standards created by the WiMAX Forum WiMAX 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 WiMAX forum is initially developing profiles for the 2.3, 2.5, 3.5, and 5.8 GHz licensed bands WiMAX carriers want licensed bands for higher quality service

6-23: Wireless for the Last Mile WiMAX Metropolitan Area Networks Uses advanced technologies Scalable OFDM, MIMO, adaptive antennas systems (AAS) that do beam forming, and cellular organization for its base stations WiMAX technology provides high-quality service TDM gives each subscriber its fair share of the capacity

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

The Market Situation

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

6-24: The Market Situation The International Situation United States ranks 16th 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

Topics Covered

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)

PSTN Transmission Circuit Switching Analog and Digital Transmission 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

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

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

Last Mile Services Wired Access Wireless Access Telephone Modems Asymmetric Digital Subscriber Line (ADSL) Cable Modem Service Fiber to the home Wireless Access 3G and 4G Cellular Data Service WiMAX (based on 802.16 and 802.16e) Satellite service (expensive and so rare)

The Market Situation Triple Play International Situation 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

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