Class 1

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• Class 1
• TDC464 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

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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 PSTN

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

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Bloomingdale Telephone Company

• 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.

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Post-Divestiture PSTN to 1996

• IECs (Inter-Exchange Carriers) (or IXCs) long
  distance service providers

• LECs (Local Exchange Carriers) local phone
  service provider. 100 of class 5 offices (End
  Office), 20 of class 4 offices (LATA Tandem)
  given to LECs.

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

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

• LECs must provide IXCs equal access at Point of
  Presence (POP)

• IXCs 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

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

• Feature Group A provides line access
• 1 800 seven digital number PIN area code
  seven digit number
• initially required for all IXCs except ATT
  (used 1 dialing)

• 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 LECs 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 LECs to manufacture telephone equipment
• deregulated Cable Television service (removed
  1992 Cable Act regulations)
• universal service ??

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In-Region Competitive Checklist
Under 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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Todays Service Providers
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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
• 1-419-111-7776 101672312292110000
• 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)
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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
(2?ft?) frequency f (Hz) period T
1/f peak-to-peak amplitude 2x A 0-to-peak
amplitude A
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Signals in the Time Domain
the square wave signal s(t) A for t ltT
? -A for t gtT ? frequency f (Hz)
1/T duty cycle ? /T peak-to-peak amplitude
2x A 0-to-peak amplitude A
A
Amplitude
Time (T)
0
?
T
-A
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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 gt Fourier Series
• non-periodic signals gt Fourier Transform
• example square wave, s(t)
• s(t) A0 A/n ? sin (2?nft), n1, 3, 5, 7,
  ?

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Spectrum Plot of Square Wave
Spectrum Plot for the Square Wave s(t) A0
A/n ? sin (2?nft), n1, 3, 5, 7, ?

• The dc offset (A0) is the dc bias level of the
  waveform
• The fundamental is f 1/T (n1)
• the harmonics are integer multiples of the
  fundamental (n x f n2,3,4,)

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Square Wave Construction
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Square Wave Construction

• 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 lt f lt ?)

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

• Most of the digital signals 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

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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 Questio
n 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 (LPFfcutoff)
• eliminates all frequency components above fcutoff
• channel bandwidth?
• examples?
• High Pass Filter (HPFfcutoff)
• eliminates all frequency components below fcutoff
• channel bandwidth?
• examples?
• Band Pass Filter (BPFf1, f2)
• eliminates all frequency components outside of
  band defined by f1 and f2
• channel bandwidth?
• examples?

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Filter Examples
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Filter Example
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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

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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
10log10POUT/ PIN for power dB
10log10VOUT2/ VIN2 for voltage the decibel
mW (dBm) dBm is used as an absolute power
measurement for signals relative to 1 mW dBm
10log10POUT, POUT is in mW the decibel pW
(dBrn) dBrn is used as an absolute power
measurement for signals relative to 1 pW dBrn
10log10POUT dBm 90, POUT is in pW