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Class 1TDC464 Voice Communications

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Class 1 Outline

• Overview of PSTN Components• Pre-Divestiture PSTN• Post-Divestiture PSTN• the NANP• Telecommunication Act of 1996• Signals in the time domain• Signals in the frequency domain• Signal Bandwidth• Filters and Channel Bandwidth• the decibel (dB)

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The Public Switch Telephone Network(PSTN)

Composed of the following major network elements:

lines

trunks

repeater

transmission equipment (e.g. repeaters, multiplexers, DCS)

switch switch

switch

switches

PBX

SS7 & IN

network signaling and control (e.g. SS7 and IN)

PCMODEM

station equipment (e.g. telephone sets, MODEMs, FAX machines, …)

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Mesh vs Hierarchical

Mesh Network: All switching offices at same level (e.g. Ethernet LAN) Each office exchange directly connected via a dedicated trunk group

to all others # of trunk groups = N(N-1)/2 N2 where N = # of COs

Hierarchical Network: each switching office “homed” in to a higher level office all routes are switched at the highest office fewer number of trunk groups, larger number of offices compared to

Mesh Networks

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Pre-Divestiture PSTNGeneral Characteristics:

Bell System implemented a hierarchical switching network, augmented with high capacity trunks (mesh network), to implement Direct Distance Dialing (DDD) in 1960’s.

five levels of switching (class 5 CO to Class 1 Primary)

traffic always routed through the lowest available level (1st choice route)

alternate routes utilized when 1st route encounters blocking

Independent phone companies (aka Independents) provided local phone service. In 1981, 23.5k non-Bell vs 20.8k Bell Class 5s.

Class 5Central Office

Class 5Central Office

Class 4Toll Office

Class 4Toll Office

Class 1Regional

Office

Class 3Primary

Class 2Sectional

Office

Class 2Sectional

Office

Class 3Primary

Bloomingdale Telephone Company, Inc. is a Michigan corporation established in 1955 for the purpose of providing telecommunications services and has been evolving ever since. Operating as a privately held stock corporation, it provides along with its subsidiary Bloomingdale Communications, Inc. a wide range of services throughout the southwest Michigan area. Each year the stockholders hold their annual meeting for the purpose of selecting the Board of Directors and conducting other business functions of the corporation. What makes our organization unique is the fact that our stockholders, directors, employees and customers all work toward our common goal of service to our subscribers.

In 1904, with very few customers, the Bloomingdale Telephone Company had its modest beginning. Today, it's a larger operation -- but still miniscule when compared to others. You can see just how much we've grown by seeing our Company History page. This independent company serves approximately 2,300 households and businesses in the village of Bloomingdale and parts of three Van Buren and Allegan county townships with service superior in quality to that supplied by many of the major telephone companies.

There is, however, one difference between us and the major telephone companies, and we take pride in that difference. Bloomingdale Telephone Company has a presence in West Michigan that ensures our customers will have quality, friendly, service. Our offices are here and so are we, so you'll never be greeted by a recording when you call us. At Bloomingdale Telephone Company, we have the technology and staff to provide our customers with the service quality they have come to expect and deserve.

Installed in May of 1995 was our Northern Telecom DMS-10 Rural and Global Switching System. This advanced equipment enables us to provide our customers with many of the custom calling features not available in

the surrounding communities.

Bloomingdale Telephone Company

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Post-Divestiture PSTN to 1996

• IEC’s (Inter-Exchange Carriers) (or IXC’s): long distance service providers• LEC’s (Local Exchange Carriers): local phone service provider. 100% of class 5 offices (End Office), 20% of class 4 offices (LATA

Tandem) given to LECs.

• LATAs divided into several Local Calling Areas (LCA)s. Intra LCA calls are local, inter LCA calls are” local toll” calls

• LEC’s must provide IXC’s equal access at Point of Presence (POP)

• LEC’s must use IXC’s to transport traffic across a LATA (Local Access Transport Area) boundary (LECs prohibited from offering long distance service)

POP POP

IXC network

End Office

LATA Tandem

LATA Tandem

End Office

End Office

End Office

End Office

LATA #1 LATA #2

IXC Trunk

Inter-Office Trunk

Subscriber Lines

PBX

PBX Trunk

• IXC’s switching networks has tended to “flatten” over time (less hierarchical)

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US LATA Map

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Equal Access to IXCs• Equal Access to IXCs was mandated by the MFJ to promote long

distance competition

– Feature Group A provides line access

• 1 + 800 + seven digital number + PIN + area code + seven digit number

• initially required for all IXC’s except AT&T (used 1 + dialing)

• Different levels of “Equal Access” provided based on switching technology’s ability to support Automatic Number Identification (ANI) for billing and database queries

– Feature Group B provides trunk access • PIC + 1 + area code + seven digital number• all IXCs assigned PIC codes• reduced total number of digits required to dial

– Feature Group D provides trunk access

• 1 + dialing (using prefered IXC)

• Feature B support to override preferred IXC

• used in the vast majority of POPs today

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Telecommunication Act of 1996

• Act Summary:

“To provide a pro-competitive, de-regulatory national policy framework designed to accelerate private sector development of advanced telecommunications and information technologies and services to all Americans”

• the Act ruled to:

remove entry barriers to allow local phone competition CLECs (Competitive LEC) vs ILECs (Incumbent LEC) allow LEC’s to provide long distance service (in their region) after

“opening up” their region to competition checklist defined as criteria for “opening up” region to competition allow LEC’s to manufacture telephone equipment deregulated Cable Television service (removed 1992 Cable Act

regulations) universal service ??

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In-Region Competitive ChecklistUnder the Act an RBOC can offer in-region interLATA service within 90 days after FCC application demonstrating the following

(1) non-discriminatory interconnection; (2) unbundled network elements; (3) open access to RBOC poles, ducts, conduits and ROWs(4) unbundled local loops; (5) unbundled trunk side transport; (6) unbundled local switching; (7) nondiscriminatory access to 9-1-1, directory assistance data bases; (8) white pages listings for competitors' subscribers; (9) nondiscriminatory number assignment; (10) nondiscriminatory access to network databases; (11) interim number portability; (12) 1+ dialing parity;(13) reciprocal compensation (which may include "bill and keep")(14) resalable network functions (excluding universal services).

An RBOC must demonstrate that it has entered an interconnection agreement with an actual competitor offering service "predominantly over its own telephone exchange service facilities," The following companies do not qualify as actual competitors in this context: CAPs, LEC resellers, and cellular.

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CLECS and CAPS in Chicagoland

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Today’s Service Providers

Service Provider ILEC CLEC LEC(independent)

IXC

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North American Numbering Plan defines format for dialed numbers in US, Canada, Caribbean As of 1/95

prefix + 0/1 + NXX - NXX - XXXX

(N digits are 2-9, X digits are 0-9)

example: which of the following phone numbers are valid

1-188-346-9999 1-609-811-6673

1-404-168-5555 1-999-999-9999

1-419-111-7776101672312292110000

international calls are initiated by dialing 011, followed by country and city code (if any)

phone number shortage crisis – Why?

Primary IXC Carrier (PIC) code

101-XXXX (as of 7/98)

Station number

Exchange code (CO Prefix ID)411, 911, 555 reserved

Area code (geographic region)

Operator assistance (0=collect, calling card)

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Signals in the Time Domain - concepts & definitions -

continuous signal: intensity varies in a “smooth fashion overtime”

discrete signal: signal strength can change by only a fixed amount

analog signal: a continuous set of signal strengths

digital signal: a discrete signal (generally assume to consists of only two levels

periodic signal: s(t + T) = s(t) for all t

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Signals in the Time Domain

the sine wave signal: s(t) = A sin (2ft+)

frequency = f (Hz)

period = T = 1/f

peak-to-peak amplitude = 2x A

0-to-peak amplitude = A

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.500

0.06

0.13

0.19

0.25

0.31

0.38

0.44 0.5

0.56

0.63

0.69

0.75

0.81

0.88

0.94 1

Time (T)

Am

pli

tud

e

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Signals in the Time Domain

the square wave signal: s(t) = A for t <T+ -A for t >T+

frequency = f (Hz) = 1/T

duty cycle = /T

peak-to-peak amplitude = 2x A

0-to-peak amplitude = A

Time (T)

Am

plitu

de

A

-A

0 T

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Signals in the Frequency Domain- concepts & definitions -

Critical Concept:

It can be shown that any signal is composed of a summation of sinusoids of differing frequencies and amplitudes!

– The translation of a time domain signal, s(t), to a frequency domain signal, S(f), can be done using the following:

periodic signals: => Fourier Series

non-periodic signals: => Fourier Transform

example: square wave, s(t)

s(t) = A0 + A/n sin (2nft), n=1, 3, 5, 7, …

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Spectrum Plot of Square Wave

Spectrum Plot for the Square Wave:

s(t) = A0 + A/n sin (2nft), n=1, 3, 5, 7, …

Frequency (Hz)

Am

plitu

de

A

A/3

A/5A/7A/9

0 f 2f 3f 4f 5f 6f 7f 8f 9f

. . .

A0

dc offset

fundamental

harmonics

• The dc offset (A0) is the dc bias level of the waveform

• The fundamental is f = 1/T (n=1)• the harmonics are integer multiples of the fundamental (n x f; n=2,3,4,…)

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Square Wave “Construction”

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

00.

130.

250.

38 0.5

0.63

0.75

0.88

11.

131.

251.

38 1.5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

Fundamental + 1st Harmonic

-1.00

-0.50

0.00

0.50

1.00

00.

130.

250.

38 0.5

0.63

0.75

0.88

11.

131.

251.

38 1.5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

Fundamental + 1st, 3rd, & 5th Harmonics

-1.00

-0.50

0.00

0.50

1.00

0

0.13

0.25

0.38 0.

5

0.63

0.75

0.88

1

1.13

1.25

1.38 1.

5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

Fundamental + 1st, 3rd, 5th, & 7th Harmonics

-1.00

-0.50

0.00

0.50

1.00

0

0.13

0.25

0.38 0.

5

0.63

0.75

0.88

1

1.13

1.25

1.38 1.

5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

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Square Wave “Construction”

Fundamental + 1st, 3rd, 5th, & 7th Harmonics

-1.00

-0.50

0.00

0.50

1.00

0

0.13

0.25

0.38 0.

5

0.63

0.75

0.88

1

1.13

1.25

1.38 1.

5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

fundamental + 1st, 3rd, 5th, 7th, & 9th Harmonics + dc offset (= 1)

0.00

0.50

1.00

1.50

2.00

0

0.13

0.25

0.38 0.

5

0.63

0.75

0.88

1

1.13

1.25

1.38 1.

5

1.63

1.75

1.88

2

Time (T)

Ampl

itude

• Waveform takes the form of a square wave as harmonics are added• the dc offset adjusts the centering of the waveform

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Signals in the Frequency Domain- key observations -

• periodic time varying signals are composed of a summation of discrete sinusoids (f0 + f1 + f2 +… + fn, n = integer)

• Non-periodic time varying signals are composed of a continuous range of harmonics (0 < f < )

• “Pure” digital signals are composed of an infinite number of harmonics

• Most of the digital signal’s energy content resides in the fundamental and first several harmonics

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Signal Bandwidth• Bandwidth (BW) is defined as a range of signal frequencies and has units of

Hz

– absolute BW: FMAX - FMIN

– relative BW (or just BW): range of “important” frequencies– example:

Source Flow (Hz) Fhigh(Hz) bandwidth (Hz)human voice (male) 100 8k ~8khuman voice (female) 150 10k ~10kViolin 180 15k ~15kAM radio station 50 8k ~8kFM radio station 50 16k ~16kNTSC video (TV station) ~4.2M

Real Life Signal Bandwidths

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Signal Bandwidth vs Bit Rate

• Students often (erroneously) interchange signal bit rate and bandwidth!

• As stated earlier, bandwidth is the range of sinusoids that composes a signal. It has the unit of Hertz (Hz).

• Bit rate refers to information rate that is often expressed in terms of Bits per Second (bps)

• Information represented in analog signal form is usually expressed in Hz

• Information represented in digital signal form is usually expressed in bps

• Relationship between signal bandwidth and bit rate is based on the encoding/decoding scheme:

– ex. local loop MODEM coding for PSTN

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Shannon – Hartley Law

The Shannon - Hartley Law relates the maximum theoretical channel capacity, C (in bps), as a function of channel bandwidth, B (in Hz).

C = B x log2 (1 + S/N)

where S/N is the “Signal-to-Noise ratio” of the channel

Question:

What is the maximum data rate that can be achieved on a typical “dial-up connection” ?

S/N = 45dB = 30,000 for a “good” PSTN local loop

C/B = 15 bps / Hz

With B = 3000Hz, C = 45kbps

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Filters

• A filter modifies a signal by removing some frequency components: Low Pass Filter (LPF[fcutoff])

eliminates all frequency components above fcutoff

channel bandwidth? examples?

High Pass Filter (HPF[fcutoff])

eliminates all frequency components below fcutoff

channel bandwidth? examples?

Band Pass Filter (BPF[f1, f2])

eliminates all frequency components outside of band defined by f1 and f2

channel bandwidth? examples?

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Filter Examples

BPF[250,550]

Output from BPF[250,550]

-1.00

-0.50

0.00

0.50

1.00

Time (T)

Ampl

itude

Frequency (Hz)

0 100 300 500 700 900

Frequency (Hz)

0 100 300 500 700 900

Time (T)

0 1/2 1 1.5 2

2

1

Square wave (A=1, dc offset =1)

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Filter Example

LPF[350]

Frequency (Hz)

0 100 300 500 700 900

Output form LPF[350Hz]

0.000.501.001.502.00

Time (T)

Ampli

tude

Frequency (Hz)

0 100 300 500 700 900

Time (T)

0 1/2 1 1.5 2

2

1

Square wave (A=1, dc offset =1)

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Why Do We Care About Filters?

• every transmission media filters (usually low pass) the signal that is sent through it.

• the PSTN BPF [300Hz, 3300Hz] voice and data signals transmitted through it

TransmissionMedia

Distance betweenrepeaters

operatingfrequency range

open wire 40km up to 160kHztwisted pair 3-6.5km up to 1MHzcoaxial 3-65km up to 100’s MHzmicrowave 30-50km 3.7-4.2GHzfiber 4-30km up to 10’s GHz

• media examples

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The decibel (dB)

the decibel (dB):

a logarithmic unit that expresses the relative relationship (e.g. ratio) between two powers (or voltages)

dB = 10log10[POUT/ PIN] for power

dB = 10log10[VOUT2/ VIN

2] for voltage

the decibel mW (dBm):

dBm is used as an absolute power measurement for signals relative to 1 mW

dBm = 10log10[POUT], POUT is in mW

the decibel pW (dBrn):

dBrn is used as an absolute power measurement for signals relative to 1 pW

dBrn = 10log10[POUT] = dBm + 90, POUT is in pW