Telephone Service PSTN l The Public Switched Telephone
Telephone Service
PSTN l The Public Switched Telephone Network l l l Worldwide A call may cross many telephone company boundaries Also Known as POTS l l Plain old telephone service “Old” “Uninteresting” 2
PSTN l Importance l Corporate telephony spending is very high l Amount of use makes it very important l Deregulation is spurring price and product complexity l Management is exploding in complexity l Datacoms & telephony are managed together 3
The Traditional Telephone System l l l Customer Premises Local Loop Switching Office l l End Office Trunk Lines 4
Customer Premises l l Your home or office You control service on your premises l Beyond your premises, you need a telephone carrier 5
Local Loop l Line between your premises and the first telephone company switching office l l 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 Local Loop Customer Premises Switching Office 6
Switching Offices l Connect Telephone Callers l Can support many simultaneous connections Local Loop Switching Office Connection Customer Premises 7
Hierarchical Organization of Switches l Class 3 Classes (1 -5) Class 4 Class 5 8
Trunk Lines l l Connect switching offices All lines except local loop Trunk Line Local Loop Trunk Lines Local Loop 9
Carriers in the United States l l Local Access and Transport Area (LATA) Intra-LATA Service l l l Inter-LATA Service l l Local Exchange Carrier (LEC) Competitive Access Providers (CAPs) Inter-exchange Carriers (IXCs) International Common Carriers (ICCs) 10
Carriers in the United States l POP l Point of presence l Located on LEC’s premises l l l 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 11
Carriers in Most Countries l PTT l l l Public Telephone and Telegraph (Authority) Traditional telephone monopoly carrier Government-owned Nationwide service Ministry of Telecommunication l Government ministry that oversees, regulates the PTT 12
Regulation in the United States l Nationally l l Federal Communications Commission (FCC) Sets interstate regulations, standards, prices Can set intrastate policies that affect the nationwide system Within States l l Public Utilities Commissions (PUCs) Regulate most intrastate matters 13
Deregulation in the United States l Deregulation l l Relaxing rules that protect monopolies Fostering competition Competition should bring new services Competition should bring lower prices 14
Deregulation in the United States l Ma Bell l The Bell System l AT&T l Had national monopoly on long-distance service l Owned LECs serving more than 80% of the U. S. Population 15
Deregulation in the United States l Breaking Up Ma Bell (1983) l Justice Department antitrust suit l Results in agreement and Consent Decree l l l 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 16
Deregulation in the United States l Second Breakup of AT&T (1996) l l l 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 17
Deregulation in the United States l Second Breakup of AT&T (1996) l Voluntarily divided the company l AT&T keeps transmission services l Lucent manufactures telephone equipment l NCR manufacturers computer equipment 18
Deregulation in the United States l Telecommunications Act of 1996 l l 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) l New freedom in pricing l Slowed by legal maneuvering 19
Deregulation Trends in the U. S. l Customer Premises l l Most deregulated Once, you could not own modems or even telephones Deregulated in the 1970 s Now fully deregulated: you can do what your like on your premises 20
Deregulation Trends in the U. S l Data networking services l l Called value added networks (VANs) Deregulated in 1970 s Now wide open Inter-LATA service l l l Deregulated in 1970 s and 1980 s Now, equal access: you get to choose your long -distance carrier Now wide-open 21
Deregulation Trends in the U. S. l Intra-LATA Service l l l Least deregulated Some prior deregulation Deregulation really began in earnest only with the Telecommunications Act of 1996 22
International Service l Provided by international common carriers (ICCs) l Each pair of countries negotiates which ICCs may provide service l Each pair of countries negotiates settlement charges on calls l This bilateral negotiation often brings uneven pricing when you call nearby countries 23
Customer Premises Equipment l Private Branch Exchanges (PBXs) l l l Internal telephone network PBX is the switch Wiring to individual telephones Telephones themselves Lines to carriers for incoming, outgoing calls Carriers PBX Company Phones 24
Building Telephone Wiring l In the Basement l l Line from carrier Termination Equipment protects carrier line PBX Wiring bundle (many pairs) out of PBX Wiring Bundle Termination Equipment 25
Building Telephone Wiring l Between Floors l Vertical riser spaces Vertical Riser Spaces 26
Building Telephone Wiring l Wiring Closets l l l Break up bundle Sub-bundle goes to next floor Other wires are for distribution on floor Wiring Closet 27
Building Telephone Wiring l Horizontal Distribution on Floors l Run wires through false ceilings, conduits l Drop down to faceplate phone jacks Single Line Wiring Bundle Wallplate 28
Telephone Wiring and LAN Wiring l l LAN Wiring Based on Building Wiring Cat 5 UTP wiring bundles l l 100 meter limitation l l 8 -wire bundles Sufficient to get from wiring closet to station Vertical Distribution l Distance limitations sufficient to reach internetting device in basement 29
Cellular Telephones l Original Mobile Telephones l l l One transmitter/receiver Limited number of channels For good service can support about 20 subscribers per channel Mobile Phone Transmitter/ Receiver 30
Cellular Telephones l Divide Region into Cells l l One cellsite per cell Channels can be reused in non-adjacent cells Uses Channel 232 Used in 4 cells Yes Can Reuse Ch. 232? No No No Yes No No No 31
Cellular Telephones l Reuse l l l Without reuse, only 20 users per channel for good service If reused 4 times, 80 subscribers per channel Reuse Rule (Rough) l l Reuse factor = Number of cells / 7 If 20 cells, reuse factor is about 3 32
Handoffs l When you move to another cell l You are transferred automatically to that cell’s cellsite 33
Roaming l Take your cellphone to another city l Use it there to send and receive l Not always possible technically l l 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 34
Control l Mobile Telephone Switching Office l l l 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 35
Placing a Call l l Enter number, hit send Cellphone broadcasts request Several cellsites receive, send to MTSO assigns cellphone to cellsite with loudest signal MTSO sends message to cellphone, telling it what incoming, outgoing channels to use 36
Receiving a Call l l MTSO has each cellsite broadcast cellphone’s ID number Cellphone transmits a response Responses from cellsites go to MTSO selects loudest cellsite MTSO sends message to cellphone, giving channels and telling the cellphone to ring 37
First Generation Cellular l Analog Operation l l Limits services and signal quality How Many Subscribers can it support? l l l 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 38
First Generation Cellular l United States l l AMPS standard Elsewhere l l l Many incompatible standards Use different radio bands Limits multinational roaming 39
Second Generation Cellular l What it is l l In the United States l l Digital instead of analog for better service Still uses large cells Still has about the same number of channels 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 l Standardizing almost completely on GSM - General System for Mobile (communication) 40
Third-Generation Cellular l Personal Communication Service (PCS) l l Smaller cells l l More frequency reuse More channels l l Or Personal Communication Network (PCN) About 2, 500 Digital, like 2 nd generation l 3 rd generation companies usually offer more services at a price similar to that of 1 st generation instead of dropping prices 41
Third-Generation Cellular l Most of World l l l Standardized on DCS Technology Based on GSM U. S. l l l 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 42
Wide Area Wireless Networks (next class meeting) l Review of l l l multiplexing spread spectrum cellular generations Comparison of Wi-Fi and cellular New generation: 4 G Wi. MAX and LTE l l Wi-Fi and cellular convergence mobile computing growth 43
Traditional Communications Satellites l In geosynchronous orbit l l l 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 44
LEO Satellites l Low Earth Orbit Satellites l l l 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 45
LEO Satellites l Satellites circle the earth every 90 minutes l l Handoffs between satellites serving you Like cellular, except you are (relatively) stationary and the transmitter/receiver moves 46
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