Telephone Service

PSTN The Public Switched Telephone Network Also Known as POTS Worldwide A call may cross many telephone company boundaries Also Known as POTS Plain old telephone service “Old” “Uninteresting”

PSTN Importance Corporate telephony spending is very high Amount of use makes it very important Deregulation is spurring price and product complexity Management is exploding in complexity Datacoms & telephony are managed together

The Traditional Telephone System Customer Premises Local Loop Switching Office End Office Trunk Lines

Customer Premises Your home or office You control service on your premises Beyond your premises, you need a telephone carrier

Local Loop Line between your premises and the first telephone company switching office Limits your transmission speed Usually a single twisted pair of copper wire Businesses may use higher-speed links “The Last Mile,” although often 2-4 miles Customer Premises Switching Office Local Loop

Switching Offices Connect Telephone Callers Can support many simultaneous connections Switching Office Local Loop Connection Customer Premises Customer Premises

Hierarchical Organization of Switches Classes (1-5) Class 3 Class 4 Class 4 Class 5 Class 5

Trunk Lines Connect switching offices All lines except local loop

Carriers in the United States Local Access and Transport Area (LATA) Intra-LATA Service Local Exchange Carrier (LEC) Competitive Access Providers (CAPs) Inter-LATA Service Inter-exchange Carriers (IXCs) International Common Carriers (ICCs)

Carriers in the United States POP Point of presence Located on LEC’s premises Connects all customers of the LEC, CAPs, IXCs, ICCs Allows new carriers to reach the total installed base, making competitive entry possible Gives customers access to everyone else

Carriers in Most Countries PTT Public Telephone and Telegraph (Authority) Traditional telephone monopoly carrier Government-owned Nationwide service Ministry of Telecommunication Government ministry that oversees, regulates the PTT

Regulation in the United States Nationally Federal Communications Commission (FCC) Sets interstate regulations, standards, prices Can set intrastate policies that affect the nation-wide system Within States Public Utilities Commissions (PUCs) Regulate most intrastate matters

Deregulation in the United States Relaxing rules that protect monopolies Fostering competition Competition should bring new services Competition should bring lower prices

Deregulation in the United States Ma Bell The Bell System AT&T Had national monopoly on long-distance service Owned LECs serving more than 80% of the U.S. Population

Deregulation in the United States Breaking Up Ma Bell (1983) Justice Department antitrust suit Results in agreement and Consent Decree AT&T keeps long-distance service, equipment manufacturing LECs divided among 7 Regional Bell Operating Companies (RBOCs)--”Baby Bells” Court-administered limits on AT&T & RBOCs

Deregulation in the United States Second Breakup of AT&T (1996) AT&T given freedom by courts to enter intra-LATA competition for transmission service AT&T moving increasingly into international competition for transmission services Problem: also sells equipment (switches, etc.) Sold equipment to firms with whom it was beginning to compete for transmission services Competitors would stop buying equipment once competition began

Deregulation in the United States Second Breakup of AT&T (1996) Voluntarily divided the company AT&T keeps transmission services Lucent manufactures telephone equipment NCR manufacturers computer equipment

Deregulation in the United States Telecommunications Act of 1996 Congressional Act Subjects intra-LATA service to open competition Before, many PUCs had limited local competition New competitors for service, including the local loop (dial tone service) New freedom in pricing Slowed by legal maneuvering

Deregulation Trends in the U.S. Customer Premises Most deregulated Once, you could not own modems or even telephones Deregulated in the 1970s Now fully deregulated: you can do what your like on your premises

Deregulation Trends in the U.S. Data networking services Called value added networks (VANs) Deregulated in 1970s Now wide open Inter-LATA service Deregulated in 1970s and 1980s Now, equal access: you get to choose your long-distance carrier Now wide-open

Deregulation Trends in the U.S. Intra-LATA Service Least deregulated Some prior deregulation Deregulation really began in earnest only with the Telecommunications Act of 1996

Deregulation in Other Countries Varies Considerably Few countries as deregulated as U.S. Prices generally higher than U.S. Services available in U.S. may not be available Customer premises usually deregulated most Basic voice telephone service usually deregulated least

Deregulation in Other Countries World Trade Organization (WTO) Agreement in 1997 on Telecommunications Services Agreement to open domestic (internal) competition Not total deregulation Not all countries sign Timetable for deregulation may be long Encouraging but not decisive

Deregulation in Other Countries Europe 1998 European Community Has been breaking down many national monopolies As of January 1998, high degree of domestic telecommunication competition is mandated

International Service Provided by international common carriers (ICCs) Each pair of countries negotiates which ICCs may provide service Each pair of countries negotiates settlement charges on calls This bilateral negotiation often brings uneven pricing when you call nearby countries

Customer Premises Equipment Private Branch Exchanges (PBXs) Internal telephone network PBX is the switch Wiring to individual telephones Telephones themselves Lines to carriers for incoming, outgoing calls Company Phones Carriers PBX

Building Telephone Wiring In the Basement Line from carrier Termination Equipment protects carrier line PBX Wiring bundle (many pairs) out of PBX PBX Wiring Bundle Termination Equipment

Building Telephone Wiring Between Floors Vertical riser spaces Vertical Riser Spaces

Building Telephone Wiring Wiring Closets Break up bundle Sub-bundle goes to next floor Other wires are for distribution on floor Wiring Closet

Building Telephone Wiring Horizontal Distribution on Floors Run wires through false ceilings, conduits Drop down to faceplate phone jacks Single Line Wiring Bundle Wallplate

Telephone Wiring and LAN Wiring LAN Wiring Based on Building Wiring Cat5 UTP wiring bundles 8-wire bundles 100 meter limitation Sufficient to get from wiring closet to station Vertical Distribution Distance limitations sufficient to reach internetting device in basement

PBX Networks PBXs at different sites work together Connected by leased lines You can dial any telephone in the firm Leased Line

PBX User Services Speed Dialing Last Number Redial Dial a number using a 1- or 2-digit code Last Number Redial Easy redial of last number called Display of Called Number Display shows the number you dialed Allows you to check for dialing errors

PBX User Services Camp On You dial another number You get a busy signal You hit the camp on button You hang up When the called party hangs up, your phone rings You pick it up Called party’s phone rings

PBX User Services Call Waiting Hold ANI Conferencing You are on the phone Hold Place someone on hold ANI Automatic Number Identification Displays number of calling extension when your phone rings Conferencing 3-party calling

PBX User Services Call Transfer Call Forwarding Voice Mail You will be away from you desk Calls go automatically to a phone near you Call Forwarding Someone calls you Voice Mail Can leave messages

PBX Attendant Services Operator Assistance In-house operators to handle problems Automatic Call Distribution Call comes in from outside Automatically goes to correct extension Message Center Leave message with operator for anyone in the building

PBX Attendant Services Paging Broadcasts call for person over loudspeakers Nighttime Call Handling Special functions for nighttime calls E.g., transfer control to guard station Change Requests Automated adding, dropping, changing of numbers once information is typed in

PBX Management Services Automatic Route Selection For outgoing calls Automatically selects the lowest-cost line Call Restriction Prevent certain numbers from calling out, making long-distance calls, etc. Call Detail Reporting Reports with detailed charges go to departments

Voice Response Customer calls in Gets a recording that gives them a menu of choices Caller hits button on phone to select a menu choice Not voice recognition! Reduces operator time Can upset customers Can also be used in product support

Carrier Services and Pricing Tariffs Filed by carriers, approved by authority Lets customer know the details of the service to be provided Lets customer know exactly what price they should pay Provides recourse in disputes Deregulation is generating many untariffed services for faster response to competition

Local Calling Within local area Flat rate pricing Message unit pricing Fixed payment per month No charge per call Message unit pricing Charged message units for each call in local area Depends on distance and duration Penalizes Internet access, other resource hogs

Toll Calls Long-distance calls International calls Inter-LATA or Intra-LATA Priced per minute Price based on distance International calls Prices depend primarily on country called Prices depend less on distance than on country called Price may be lower calling from one country than from the other in the pair

Toll Calls Direct Distance Dialing Most common method Collect Calls Called party pays if accepts calls Pays more than direct dial rate 800/888 Numbers Area codes are with 800 or 888 Pays less than direct dial rates to support customers 900 Numbers Caller pays Called company can charge for user service

Toll Calls WATS Universal Availability Wide Area Telephone Service Company can call out from site, to phones throughout the WATS service area Pay less than direct dial rates Universal Availability Personal telephone number for person Will reach you wherever you are physically Some day given at birth?

Electronic Switching Services Switches are Computers Can provide services beyond switching through software Can provide PBX-like user services to carrier customers ISDN standardizes these services and allow them to work worldwide. (Integrated Services Digital Network)

Electronic Switching Services Automatic Number Identification (ANI) You see the number of the person calling you Lets you screen calls Lets companies route caller to personal service representative automatically Concerns about privacy Can be blocked, so that receiver will not see your number Receiver can refuse calls from blocked ANI

Cellular Telephones Original Mobile Telephones One transmitter/receiver Limited number of channels For good service can support about 20 subscribers per channel Transmitter/ Receiver Mobile Phone

Cellular Telephones Divide Region into Cells One cellsite per cell Channels can be reused in non-adjacent cells Yes Uses Channel 232 No Can Reuse Ch. 232? No No Yes Yes No No Channel 232 Used in 4 cells No

Cellular Telephones Reuse Reuse Rule (Rough) Without reuse, only 20 users per channel for good service If reused 4 times, 80 subscribers per channel Reuse Rule (Rough) Reuse factor = Number of cells / 7 If 20 cells, reuse factor is about 3

Handoffs When you move to another cell You are transferred automatically to that cell’s cellsite

Roaming Take your cellphone to another city Use it there to send and receive Not always possible technically May be limited procedurally because of high rates of cellular fraud in some areas Don’t confuse this with handoff, which takes place within a cellular system between cells

Control Mobile Telephone Switching Office Controls cellsites, handoffs, etc. Calls go to/from MTSO Connects to POP at LEC to link to traditional telephone (wireline) carriers POP at LEC MTSO

Placing a Call Enter number, hit send Cellphone broadcasts request Several cellsites receive, send to MTSO MTSO assigns cellphone to cellsite with loudest signal MTSO sends message to cellphone, telling it what incoming, outgoing channels to use

Receiving a Call MTSO has each cellsite broadcast cellphone’s ID number Cellphone transmits a response Responses from cellsites go to MTSO MTSO selects loudest cellsite MTSO sends message to cellphone, giving channels and telling the cellphone to ring

First Generation Cellular Analog Operation Limits services and signal quality How Many Subscribers can it support? Large Cells (20-40 per city) 20 cells, and frequency reuse is about 3 (20/7) 832 channels, and with frequency reuse, 2,496 available channels 20 users per available channel, then only about 50,000 subscribers per system Engineering tricks can extend, but only somewhat

First Generation Cellular United States AMPS standard Elsewhere Many incompatible standards Use different radio bands Limits multinational roaming

Second Generation Cellular What it is Digital instead of analog for better service Still uses large cells Still has about the same number of channels In the United States Retrofitting existing analog systems with some digital channels CDPD (Cellular Digital Packet Data) is the most common technology Not widely used Elsewhere in the World Standardizing almost completely on GSM - General System for Mobile (communication)

Third-Generation Cellular Personal Communication Service (PCS) Or Personal Communication Network (PCN) Smaller cells More frequency reuse More channels About 2,500 Digital, like 2nd generation 3rd generation companies usually offer more services at a price similar to that of 1st generation instead of dropping prices

Third-Generation Cellular Most of World Standardized on DCS Technology Based on GSM U.S. FCC did not specify a standard! Different carriers use different technologies Many have standardized on DCS Your cellphone may not work with another carrier Limits roaming

Potential System Capacity Category 1st Gen 3nd Gen Cells/City 30 100? Channel reuse ~4 ~14 Channels 800 2,500 Effective channels 3,200 35,000 Subscribers 60,000 700,000 This analysis is inexact but illustrative

U.S. PCS Standards Coordinated by the TIA TR-45 Committee 3 standards selected DCS (Digital Communications Service) Based on GSM Time division multiplexing 2-3 times as many simultaneous calls as first generation in the same bandwidth

Personal Service Telephones On the road Personal cellphone acts like 3d generation cellphone At home Cellphone acts like cordless telephone No cellular charges when you use it At work Wireless PBXs treat it like a business phone No cellular charges

Traditional Communications Satellites In geosynchronous orbit Appear to be stationary Far from the ground (22,300 miles) Need much power to send/receive Need dish antennas to concentrate signals Must point dish at the satellite Impractical for portable telephony

LEO Satellites Low Earth Orbit Satellites Only 100 to 200 miles above the earth Need far less power to reach than 22,300 mile geosynchronous satellites Can get by with omnidirectional antenna Can use phone of reasonable size, cost Access anywhere Omnidirectional Antenna

LEO Satellites Satellites circle the earth every 90 minutes Handoffs between satellites serving you Like cellular, except you are (relatively) stationary and the transmitter/receiver moves