IS605/606: Information Systems Instructor: Dr. Boris Jukic

Voice Telephony: Technology and Industry Overview

Telecommunication Industry: Carriers

Carriers– In the United States

U.S. is divided into regions called local access and transport areas (LATAs)

About 200 LATAs nationwide

LATA

Intra-LATA (Local/Toll)

Carriers– In the United States post 1996

Local exchange carriers (LECs) provide service within a LATA

Incumbent LEC (ILEC) is the traditional monopoly carrier in the LATA

Competitive LEC (CLEC) is a new competitor

LATA

LEC

ILEC CLEC

Inter-LATA (Long Distance)

LATA LATAIXC

Carriers– In the United States

Inter-exchange carriers (IXCs) provide service between LATAs

– LEC versus IXC distinction is used by data carriers as well as voice carriers.

POPs

– In the United StatesPoint of Presence (POP) is a place in a LATA

where all carriers interconnect to provide integrated service to all customers

LATAPOP

ILECCLEC IXC

IXC

IXCs carry traffic to POPs in other LATAs

Regulation of Land-Line Telephony

Regulation– Why regulation? Two Main Reasons:

An industry that supplies essential services where only one organization can operate efficiently in a given market is a "natural monopoly.“

Basic telephone service is considered a public utility whose efficient operation is in the public interest

– the monopolistic aspect of the basic telephone service industry is debatable– First steps to regulation were taken by the states in the early 1900s; now all 50

states plus D.C. have commissions that regulate intrastate telecommunications. – State regulatory agencies are generally known as public utility commissions or

public service commissions. – The Federal Communications Commission (FCC) was created by the

Communications Act of 1934. Independent agency charged with regulating interstate and international communications originating in the United States

Regulation of Land-Line Telephony

Common Carriers: carry signals between customer premises– Domestic Telephone Service provided by a single

telephone carrier within many countries: PTT – Public Telephone and Telegraph Authority

– Rights of Way: government permission to lay wire along roads, rails and in other public areas

– Tariffs are the published rates, regulations, and descriptions governing the provision of communication services.

Regulation and Carriers

International Service (Between Pairs of Countries)– Provided by international common carriers

(ICCs)– Allowed carriers, prices, and conditions of

service are settled through bilateral negotiation between each pair of countries

Country 1 Country 2ICC

Basic Telephony Infrastructure: Public Switched Telephone Network (PSTN)

GOLDMAN: DATACOMM FIG. 01-03

Modem

Local PCLocal loop

C.O.

P.O.P.

Remote PC

Modem

C.O.P.O.P.

Local loop

Inter-exchange circuit

Belongs to IXC (Inter-eXchange Carrier)

Belongs to LEC (Local-Exchange Carrier)

LATA - A

LATA - B

PSTN: Local Loop

CO

CO

CO

CO

Thousands of Central Offices (COs) that house telecom equipment.Some serve as “end offices” and some just as tandem offices.COs are connected using high-speed, redundant circuits (e.g., ATM over OC-48)

UTP, Coax, & Fiberare run into neighborhoodsto serve businesses and homes

“The Local Loop or Last Mile”

Reg. De-Reg.Terminating Equipment

“NID”

PSTN: Digital Trunks and Mostly Analog Local Loops

LocalLoop

(Analog)

ResidentialTelephone(Analog) Switch

(Digital)Switch(Digital)

Switch(Digital)

LocalLoop

(Digital)

PBX(Digital)Trunk Line

(Digital)

Circuit: End-to-End Connection Between Two Subscribers.Switches: Voice switches are Circuit-Switched.

Analog-to-Digital Conversion (ADC)

Sampling of the Voice Signal– Each second is divided into 8,000 sampling periods (Nyquist’s Law)– Each sampling period is 1/8,000 of a second– Voice intensity in each sampling period is recorded as fraction of a

maximum value (255). – The decimal value (210 in this example) is converted into an 8-bit

binary value, 11010010

Sample

1/8,000 sec Sampling Period

IntensityValue

210/255(1010010)

Transmission Rates

Transmission Rate for a telephone line– 8,000 samples/second * 8 bits/sample = 64

kbps– This is why telephone channels are 64 kbps

Mobile (Cellular) Telephony: Analog vs. Digital

Analog: broadcasts audio as a series of continuously changing, voltage levels representing the amplitude of the voice conversation.

– Each call is sent through a channel separated by 30 kHz: Frequency Division Multiple Access (FDMA)

• Digital: quantizes the voltage levels into a number of bins (typically 28 or 256 representing 8-bit encoding).

•bins are encoded as a binary number and sent as a series of ones and zeros. •Multiple conversations are possible over the same channel

Mobile (Cellular) Telephony: Digital Advantage

It economizes on bandwidth. – More digitized conversations per frequency band

Superior quality of voice transmission over long distances.

More difficult to decode. It can use lower average transmitter power. It enables smaller and less expensive individual

receivers and transmitters. It offers voice privacy.

Desirable Frequency Band for Wireless Providers: “Golden Zone”

At lower frequencies, there is little total bandwidth. At very high frequencies, propagation is poor. Mobile devices tend to work in the “golden zone”

from the high megahertz to the low gigahertz range. Frequencies in the golden zone are limited and in

high demand.– Very expensive to obtain– EU wide auctions for 3G spectrum yielded > $100

Billion

Generations of Cellular Service

Generation First 2nd 2.5G 3G

Technology Analog Digital Digital Digital

Data TransferRate

Data TransferIs Difficult

10 kbps*20 kbps to144 kbps

144 kbpsto 2 Mbps

*Sufficient for Short Message Service (SMS) and wireless Web accessusing the Wireless Access Protocol (WAP)

WorldStandardization(and therefore

roaming)

PoorGood(GSM)

Basedon 2G

(W-CDMA,CDMA-2000,

and othersystems

may compete)

U.S.Standardization

Good(AMPS)

Poor (GSM,CDMA, TDMA,

& CDPD)

Basedon 2G

?

3G Speeds (Throughput Rates)

ITU Speed Requirements for 3G– 2 Mbps for fixed devices– 384 kbps for walking people– 144 kbps for automotive users

Anything Less is 2.5 G– Some 2.5G vendors call themselves 3G but are

not

U.S. Cellular Telephony Usage Lag

The U.S. lags many other countries in cellular telephone use.– Europe and Asia-Pacific have higher rates of usage

The rest of the world also has very high usage rates when adjusted for per-capita income

– U.S. wired telephone charges are low, and in the case of local loop not based on usage

intensive usage of mobile telephony for local loop purposes is less attractive

– The lack of a dominant U.S. standard for 2nd generation cellular telephony

– Pricing schemes in U.S. discourages intensive use (receiver-based charging)

Recently, per-unit of usage prices have dropped significantly

– 3G deployment may change the perception of the “Lag” (stay tuned)