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CS4550: Computer Networks II public telecommunication networks “public” telecom networks US telco networks : history, business, politics US telco networks: basic structure cable TV networks wireless networks international telephone networks future (?) - fiber to the home?

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Cs4550 computer networks ii public telecommunication networks l.jpg

CS4550:Computer Networks IIpublic telecommunication networks

Public telecom networks l.jpg
“public” telecom networks

  • US telco networks : history, business, politics

  • US telco networks: basic structure

  • cable TV networks

  • wireless networks

  • international telephone networks

  • future (?) - fiber to the home?

Us telco networks history l.jpg
US telco networks : history

  • invention of telephone: ~1876

  • Alex. G. Bell, Elisha Gray, P. Reis

  • original telephone patents: 1876,77

  • spread of telephone companies: 1893-4 to 1901

  • establishment of AT&T, its tactics, monopoly in 3 areas

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US telco networks : history

  • hush-a-phone, pres. address, etc.

  • antitrust lawsuits : 1921, 1956, 1984

  • divestiture of 1984

  • other LD companies, Baby Bells, etc.

  • after 1984

  • 1996: second divestiture and TC Act

  • recent events

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US telco networks : business

  • generally very profitable, because

    - telephone service universal (in US)

    - local service companies often enjoy monopolies

    - ATT enjoyed 3 monopolies (<1984), protected by gov’t many years

    - ATT subsidized local service by overcharging on long distance (<84)

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US telco networks : politics

  • often have had major influence on telecommunications industry

    - companies are very large, have many customers (voters)

    - telecom. essential to modern economy

    - control of communications is power (political, economic)

    - at times gov’t has protected monopolies; at times, divested them

    - antitrust laws

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US telco nets : structure < 1984

  • ATT enjoyed monopolies in 3 areas:

    - local telco service

    - long distance

    - network equipment

  • telco network divided into 5-level hierarchy

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US telco nets : local loops

  • local loop; “end office” or central office; star topology; app. 19K in US


twisted pair


to l.d. switch

end office



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PBX : private branch exchange

  • a privately owned telephone switch; enables companies, etc. to have own private local phone network

  • several generations; most recent are digital, capable of data and voice

  • connect to public telco through a “trunk,” or higher capacity line

  • centrex - similar service, but owned and maintained by the telco

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telco switch - generic design






network interface





digital/analog devices

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US telco nets : structure < 1984

regional switch (10)

ATT l.d. structure < 84

-simple hierarchy, augmented

by tandem lines

-easy design, but not most efficient

use of resources

end office (19000)

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US telco nets : structure < 1984

  • AT&T was major telco in US, largest in world (approximations below)

    -70% of local telephones in US

    - 99% of l.d. traffic

    - 99% telecom equipment

    - 1,000,000 employees

    - total revenue was 2% of annual GNP of US

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US telco nets : structure < 1984

  • AT&T before 1984

    • 22 BOCs (Bell Operating Companies)

      --> local telephone service

    • Western Electric

      --> equipment

    • Long lines department

      --> long distance service

    • Bell Telephone laboratories

      --> research lab “national resource”

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AT&T : divestiture

  • background : 1956 consent decree

  • 1974 : US DOJ brought suit against ATT for violation of antitrust law. Charged that ATT “denied benefits of free and competitive market to purchasers of telecommunications equipment and service”

  • settlement negotiated after years of negotiations and softball

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AT&T divestiture, results

  • 22 BOCs separated, grouped into 7 RBOCs

  • RBOCs to provide “equal access”

  • RBOCs may sell but NOT manufacture CPE

  • ATT retained WE, long lines, part of Bell labs

  • Bell labs split between ATT and RBOCs (Bellcore)

  • 161 LATAs defined

  • ATT released from 1956 decree

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LATA local access transport area

  • defines boundaries local telcos cannot cross; so 3 types of calls

    • local (truly local) - no charge ; Monterey to Monterey

    • local access : toll charge to local company (Monterey to Salinas)

    • long distance : must use a long distance company (Monterey - San Jose)

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AT&T since 1984

  • l.d. share has decreased from 95%+ to ~60% or less, still quite profitable

  • employees --> ~300,000 (until 96)

  • ventured into computers - failed twice (ATT PC, NCR purchase)

  • bought out Craig McCaw’s cellular company --> cellular network

  • gone to all digital network

  • 2nd divestiture, 1996 (--> 180,000)

  • has agreement to merge with TCI

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telecom since 1984

  • AT&T doing well, but only 1 of several major companies

  • Sprint, MCI major competitors after 84

  • Worldcom-MCI merger produced major telecom power

  • Lucent Tech. --> another power

  • telecom in other countries have moved towards competition, freedom

  • technology moved forward faster than ever before

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telco companies today, US

  • ATT, Sprint, MCI-Worldcom ; GTE

  • original 7 RBOCs :

    Pacific Telesis; Nynex; Ameritech;

    US West ; Southwestern Bell (now SBC); Bell Atlantic; Bell South.

  • mergers have reduced these

    • SBC bought Pacific Telesis, and pending Ameritech

    • Nynex and Bell Atlantic merged

    • GTE may merge with Bell Atlantic

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some current and future trends

  • all networks converging towards data networking (Internet)

  • i.e., voice, TV cable and internet become 1 network

  • TCI-ATT merger pending

  • Sprint-Cisco agreement on data network

  • will have higher bandwidth available to home & throughout

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TV cable networks

  • designed for TV broadcast to homes

  • uses coaxial cable : 1 TV channel has 6 MHz, or 1500 voice channels; 1 cable can carry hundreds of channel

  • to carry voice/data, switching equipment needs to be modified.

  • TV networks can provide competition for voice, and higher speed internet access

  • ATT-TCI merger: ATT hopes to use TV cable for voice and data to penetrate home.

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TV cable -- long distance combo

ATT long distance network

TV cable network

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cellular nets : wireless phones

  • central station, and base stations

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cellular nets : wireless phones

  • base stations communicate through radio signals with end users

  • competition for local phone and limited data. Has difficulties inherent in wireless media - inference, capacity, handoffs between cells; but these are being addressed.

  • security also more difficult

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satellite networks : iridium, etc.

  • iridium project : Motorola and others; already has 80-90 satellites in orbit

  • other competing

  • will probably be expensive, but a world-wide network for voice data

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internet telephony

  • already here... will get better

  • quality less than conventional, but as speed improves, this will too

  • many parts of world have poor phone penetration; this may be the way to bring service, and break nationalistic monopolies (e.g., Telmex) and US telco monopolies

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international telco summary

  • US most advanced, but western Europe, Japan, Taiwan, Hong Kong, Singapore, others close

  • much of world - India, China, Indonesia, Mexico/Latin America - far behind; some still have monopolies (e.g. Telmex)

  • some leading internat’l companies:

    Erricson, Deutche Telecom, British Telecom, Cable and Wireless, Hong Kong Telecom, NTT

    Lucent Tech., MCI-Worldcom, Sprint-Cisco, ATT, GTE , SWB

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future : fiber to the home?

  • high capacity of fiber has drastically altered world of telecom

  • breakup of ATT 1984 has also drastically improved progress

  • fiber to the home?

    some predict this, may happen; but in whatever form, we can expect higher capacity internet and telephone access... possibly through TV cable... and continued progress in communications