cs4550 computer networks ii public telecommunication networks l.
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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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public telecom 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?
us telco networks history
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
us telco networks history4
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
us telco networks business
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)

us telco networks politics
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

us telco nets structure 1984
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
us telco nets local loops
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



pbx private branch exchange
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
telco switch generic design
telco switch - generic design






network interface





digital/analog devices

us telco nets structure 198411
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)

us telco nets structure 198412
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

us telco nets structure 198413
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”

at t divestiture
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
at t divestiture results
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
lata local access transport area
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)
at t since 1984
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
telecom since 1984
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
telco companies today us
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
some current and future trends
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
tv cable networks
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.
tv cable long distance combo
TV cable -- long distance combo

ATT long distance network

TV cable network

cellular nets wireless phones
cellular nets : wireless phones
  • central station, and base stations
cellular nets wireless phones24
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
satellite networks iridium etc
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
internet telephony
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
international telco summary
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

future fiber to the home
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