LEARNING OBJECTIVES
1. State four functions of a telephone set.
2. Label a block diagram of a telephone set.
3. Describe the electrical differences between pulse and tone dialing.
4. Describe the structure of the local telephone exchange.
5. Describe each of the BORSCHT functions.
6. Define “IDDD World Numbering Plan.”
7. Explain the differences between the telephone exchange classifications.
8. Describe the electrical characteristics of PAM, PDM, PCM, and DM.
9. Describe the advantage of companding.
10. State the companding technique used in the United States and Europe.
11. Analyze attenuation, delay, and line conditioning on a voice-channel.
12. Interpret attenuation/ delay charts for conditioned lines.
13. Prepare a brief definition of multiplexing and demultiplexing.
14. Describe the characteristics of SDM, FDM, TDM, and STDM techniques.
15. Describe the structure of the analog common carrier hierarchy.
16. Describe the structure of the digital common carrier hierarchy.
17. Explain the services offered through T1, T2, T3, and T4 connections.
18. Label a block diagram of the T1 frame format.
LEARNING OBJECTIVES (continued)
19. Prepare a brief definition of CSU/DSU.
20. State the advantages of superframes and extended superframes over
standard T1 frames.
21. Administer change controls by adding new telephone equipment.
22. Design the network by identifying the availability of local T1 access.
23. Describe the electrical characteristics of a T1 signal.
24. State two types of acceptable T1 connectors.
25. Ensure appropriate resources are available for implementing T-Carrier
access.
26. Describe the services available with a SONET connection.
27. Describe the frame format of a SONET STS1.
28. Define SONET terms such as virtual tributary, terminating multiplexer,
regenerator, and add/drop multiplexer.
29. While planning a customer’s job, study technology options, pro and con.
30. Identify the technical capabilities of T-Carrier, SONET, and
Multiplexing.
Figure 9-1: Frequency Response of Voice Channel
Figure 9-2: Producing Amplitude Modulation
Figure 9-3: AM Modulation Envelope
Figure 9-4: Frequency Modulation
Using Carson’s rule, bandwidth is
calculated by:
BW = 2(DFc + Fm)
where Fc is the deviation produced
by the modulating signal, and Fm is
the frequency of the modulating
signal.
The bandwidth of the FM signal is:
BW = 2(DFc + Fm)
BW = 2(1 kHz + 1 kHz)
BW = 2(2 kHz)
BW = 4 kHz
Figure 9-5: Phase Modulation
Figure 9-6: Equivalent Two-Conductor Cable Circuit
Table 9-1: Terminating Resistance Guide
For any length of RG-58 coaxial
cable, the characteristic impedance
can be approximated by:

Zo = L/C
This means the RG-58 cable will behave as
any circuit with a capacitor, and inductance,
and a 50-ohm load.
It will exhibit phase-shifts and time constants
as in any RCL circuit.
Zo = _________
73 x 10-9
295 x 10-12
Zo = 49.745 ohms
(a)
(b)
(c)
Figure 9-7: Effects Of Intersymbol Interference
on Data Signals
(a)
(b)
Figure 9-8: Evaluating the Eye Pattern with an
Oscilloscope for ISI Distortion
Figure 9-9: Equalizer Block Diagram
The following illustrates examples of
common logs:
104 = 10,000 = a log of 4
103 = 1,000 = a log of 3
102 = 100 = a log of 2
101 = 10 = a log of 1
100 = 1 = a log of 0
10–1 = .1 = a log of –1
10–2 = .01 = a log of –2
10–3 = .001 = a log of –3
10–4 = .0001 = a log of –4
Common logs are integrated with decibels in
the following formula:
dB = 10 log (Po/Pi)
where Po = Power out and Pi = Power in.
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
dB = 10 log (20
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
dB = 10 log (20
mW/10 mW)
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
dB = 10 log (20
mW/10 mW)
dB = 10 log (2)
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
dB = 10 log (20
mW/10 mW)
dB = 10 log (2)
dB = 10 (.3)
An amplifier has an input power of 10 mW
(milliwatts) and a power out of 20 mW.
Calculate the gain in decibels.
dB = 10 log (Po/Pi)
dB = 10 log (20
mW/10 mW)
dB = 10 log (2)
dB = 10 (.3)
dB = 3
The power received through a transmission
line is .25 mW. Using decibels, evaluate the
performance of the line if the power at the
transmitter is 1 mW.
dB = 10 log (Po/Pi)
The power received through a transmission
line is .25 mW. Using decibels, evaluate the
performance of the line if the power at the
transmitter is 1 mW.
dB = 10 log (Po/Pi)
dB = 10 log (.25 mW/1 mW)
The power received through a transmission
line is .25 mW. Using decibels, evaluate the
performance of the line if the power at the
transmitter is 1 mW.
dB = 10 log (Po/Pi)
dB = 10 log (.25 mW/1 mW)
dB = 10 (–.6)
The power received through a transmission
line is .25 mW. Using decibels, evaluate the
performance of the line if the power at the
transmitter is 1 mW.
dB = 10 log (Po/Pi)
dB = 10 log (.25 mW/1 mW)
dB = 10 (–.6)
dB = –6
What is the value of the signal strength?
dB = 10 log (Po/Pi)
What is the value of the signal strength?
dB = 10 log (Po/Pi)
–6 dB = 10 log (x/1 mW)
What is the value of the signal strength?
dB = 10 log (Po/Pi)
–6 dB = 10 log (x/1 mW)
–.6 dB = log (x/1 mW)
What is the value of the signal strength?
dB = 10 log (Po/Pi)
–6 dB = 10 log (x/1 mW)
–.6 dB = log (x/1 mW)
.25 = x/1 mW
What is the value of the signal strength?
dB = 10 log (Po/Pi)
–6 dB = 10 log (x/1 mW)
–.6 dB = log (x/1 mW)
.25 = x/1 mW
.25 mW = x = Po
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
5 dB = 10 log (Po/6 mW)
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
5 dB = 10 log (Po/6 mW)
.5 dB = log (Po/6 mW)
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
5 dB = 10 log (Po/6 mW)
.5 dB = log (Po/6 mW)
Inverse log .5 = Po/6 mW
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
5 dB = 10 log (Po/6 mW)
.5 dB = log (Po/6 mW)
Inverse log .5 = Po/6 mW
3.16 = Po/6 mW
A power amplifier has 5-dB gain referenced
to 6 mW. What is the output power?
dB = 10 log (Po/Pi)
5 dB = 10 log (Po/6 mW)
.5 dB = log (Po/6 mW)
Inverse log .5 = Po/6 mW
3.16 = Po/6 mW
18.96 mW = Po
A data signal is permitted no more than 1 dB
of attenuation, or loss, from transmitter to
receiver. You measure the transmitter power
at 24.2 mW and the power received at 19.5
mW. Is this an acceptable amount of
attenuation?
dB = 10 log (Po/Pi)
A data signal is permitted no more than 1 dB
of attenuation, or loss, from transmitter to
receiver. You measure the transmitter power
at 24.2 mW and the power received at 19.5
mW. Is this an acceptable amount of
attenuation?
dB = 10 log (Po/Pi)
dB = 10 log (19.5 mW/24.2 mW)
A data signal is permitted no more than 1 dB
of attenuation, or loss, from transmitter to
receiver. You measure the transmitter power
at 24.2 mW and the power received at 19.5
mW. Is this an acceptable amount of
attenuation?
dB = 10 log (Po/Pi)
dB = 10 log (19.5 mW/24.2 mW)
dB = 10 log (.806)
A data signal is permitted no more than 1 dB
of attenuation, or loss, from transmitter to
receiver. You measure the transmitter power
at 24.2 mW and the power received at 19.5
mW. Is this an acceptable amount of
attenuation?
dB = 10 log (Po/Pi)
dB = 10 log (19.5 mW/24.2 mW)
dB = 10 log (.806)
dB = 10 (–.0936)
A data signal is permitted no more than 1 dB
of attenuation, or loss, from transmitter to
receiver. You measure the transmitter power
at 24.2 mW and the power received at 19.5
mW. Is this an acceptable amount of
attenuation?
dB = 10 log (Po/Pi)
dB = 10 log (19.5 mW/24.2 mW)
dB = 10 log (.806)
dB = 10 (–.0936)
dB = –.936
At a minimum, the telephone set:
1
Initiates use of the telephone system
when the handset is lifted.
Table 9-2: Typical SNRs of Communication
Channels
The signal-to-noise ratio is a measure of the
desired signal power to the noise signal power
at the same point in a circuit. It’s expressed
mathematically as:
SNR = Ps/Pn
where Ps = the power of the desired signal
and Pn = the power of the noise.
It’s often expressed in decibels as:
SNR = 10 log (Ps/Pn)
For example, if the SNR is to be determined
at the output of a transmitter, and the signal
level is determined to be 2 mW and the noise
is 500 mW, the SNR is:
SNR = 2 mW/.5 mW
SNR = 4
or, as a decibel:
SNR = 10 log (Ps/Pn)
SNR = 10 log (2 mW/.5 mW)
SNR = 10 log (4)
SNR = 10 (.602) dB
SNR = 6 dB
Noise factor is calculated as:
NF = 10 log ((Si/Ni)/(So/No))
where Si/Ni is the signal-to-noise ratio
at the input, and So/No is the signalto-noise ratio at the output.
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
NF = 10 log ((22 mW/1 mW)/(18.5 mW/2.25 mW))
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
NF = 10 log ((22 mW/1 mW)/(18.5 mW/2.25 mW))
NF = 10 log (22/8.22)
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
NF = 10 log ((22 mW/1 mW)/(18.5 mW/2.25 mW))
NF = 10 log (22/8.22)
NF = 10 log (2.676)
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
NF = 10 log ((22 mW/1 mW)/(18.5 mW/2.25 mW))
NF = 10 log (22/8.22)
NF = 10 log (2.676)
NF = 10 (.427) dB
For example, the NF of a transmission line is to
be calculated. The signal level at the transmitter
is 22 mW and the noise level is 1 mW. At the
receiver, the signal level has dropped to 18.5 mW
and the noise increased to 2.25 mW.
NF = 10 log ((Si/Ni)/(So/No))
NF = 10 log ((22 mW/1 mW)/(18.5 mW/2.25 mW))
NF = 10 log (22/8.22)
NF = 10 log (2.676)
NF = 10 (.427) dB
NF = 4.27 dB
(a)
(b)
(c)
Figure 9-10: Noise and Distortion Contribute to
Data Errors
At a minimum, the telephone set:
1
Initiates use of the telephone system
when the handset is lifted.
At a minimum, the telephone set: (continued)
2
Receives a dial tone indicating the
system is ready to be used.
At a minimum, the telephone set: (continued)
3
Transmits the number to be
called to the telephone system.
At a minimum, the telephone set: (continued)
4
Supervises the status of the set
by indicating to a caller if the
set is in use (busy), or available
to receive a call (ring).
At a minimum, the telephone set: (continued)
5
Acknowledges an incoming call
by ringing.
At a minimum, the telephone set: (continued)
6
Performs the duties of a transducer by
converting audio signals into electrical
signals, and electrical signals into
audio signals.
At a minimum, the telephone set: (continued)
7
Compensates for varying power levels
supplied to it.
At a minimum, the telephone set: (continued)
8
Provides an indication to the telephone
system that a call is finished when the
caller hangs up.
Figure 9-11: The Telephone Set
TIP
When working on telephone lines in
the premises, if unable to disconnect
the phone service, take the phone off
the hook to avoid electrical shock by
reducing the continuous voltage.
(a)
(b)
Figure 9-12: Pulse Dialing 3-4-7
The total time required to pulse dial the three
numbers is:
(3 x 100) + 500 + (4 x 100) + 500 + (7 x 100)
= 300 + 500 + 400 + 500 + 700
= 2,400 ms
Figure 9-13: DTMF Keypad
Figure 9-14: Central Office Exchange Loop
Figure 9-15: Structure of the Central Office
(a)
Figure 9-16:
Overvoltage
Protection
(b)
Figure 9-17: Central Office Supervisory Signals
Figure 9-18: Two-Wire to Four-Wire Hybrid
Figure 9-19: IDDD World Numbering System
Figure 9-20: Telephone Exchange Classification
Figure 9-21: Possible Long Distance Routings
Figure 9-22: Interconnection of Central Office
Exchanges
(a)
(b)
Figure 9-23: Pulse Amplitude Modulation
(a)
(b)
(c)
Figure 9-24:
Pulse Duration
Modulation
(a)
(b)
(c)
Figure 9-25:
Pulse Code
Modulation
Figure 9-26: The m-Law Companding Code
Figure 9-27(a): Delta Modulation Transmitter
Block Diagram
Figure 9-27(b): Delta Modulation Transmitter
Waveforms
Figure 9-28: Interconnection of Central Office
Exchanges
The signal strength ratio is expressed as the
logarithmic function of the ratio:
dB = 10 log P1/P2
where P1 = signal power and P2 = the 1mW
reference.
For example, a signal delivers 50 mW of
power at a specified frequency to a load.
The power gain is found by:
dBm = 10 log P1/1 mW
dBm = 10 log 50 mW/1 mW
dBm = 17
For example: a signal delivering .5 mW to
a load has a loss of:
dBm = 10 log .5 mW/1 mW
dBm = –3
Figure 9-29: Voice-Channel Attenuation Response
Curve
Figure 9-30: Voice-Channel Delays
(a)
Figure 9-31:
3002 Leased
Line
(b)
(a) C1
(b) C2
Figure 9-32:
C1, C2, and C3
Conditioned Lines
(c) C4
Figure 9-32(a): C1 Conditioned Line (continued)
Figure 9-32(b): C2 Conditioned Line (continued)
Figure 9-32(c): C3 Conditioned Line (continued)
LAB 25 OBJECTIVE
Measuring Data Throughput of the Local
Subscriber Loop
Use an Internet download speed
measurement site to evaluate the
current condition of your local
loop.
Figure 9-33: MSN Connection Speed Test Results
Table 9-3: Speed Test
LAB 25 QUESTIONS
1
Summarize the results of the download
test in Table 9-3.
LAB 25 QUESTIONS
2
Why should you choose a compressed file
when measuring modem data rates?
LAB 25 QUESTIONS
3
How close was your speed to the
theoretical maximum for a conditioned
line of 53.3 kbps?
Figure 9-34: Multiplexing Reduces Hardware
Figure 9-35: Space-Division Multiplexing
(a)
(b)
Figure 9-36: FDM Frame Formatting
Figure 9-37: FDM Analog Common-Carrier
Hierarchy
(a)
(b)
(c)
Figure 9-38: TDM Frame Format
Figure 9-39: T-Carrier Multiplexing Scheme
Figure 9-40: T1 Frame Format
Figure 9-41: Simplified STDM
Figure 9-42: STDM Frame Format
Consider the phrase:
THAT CAT
Another compression technique is the
dictionary method. The dictionary is
composed of the words contained in the
data to be transmitted.
For example:
THAT CAT ATE THAT RAT
may be filed alphabetically in the
dictionary.
THAT CAT ATE THAT RAT
Once all of the redundancies in the
phrase are deleted, the above phrase
would look like:
ATE, CAT, RAT, THAT
1
2
3
4
The numbers are encoded into a
3- or 4-bit format and transmitted
in the sequence shown.
4
2
1
4
3
(THAT) (CAT) (ATE) (THAT) (RAT)
Figure 9-43(a): FDM Common-Carrier Analog
Hierarchy
Figure 9-43(b): FDM Typical Modulation Method
Figure 9-44: T-Carrier Digital Hierarchy
Table 9-4: T-Carrier Digital Hierarchy
Figure 9-45: T-Simplified D4 Channel Bank
Table 9-5: Superframe Format
Each synchronization technique uses a specific
6-bit code that’s interleaved within the
superframe.
The bit codes are as follows:
Terminal: 101010
Superframe: 001110
Once the two codes are interleaved at bit
position 193 in each of the T1 frames,
they generate the following 12-bit code:
100011011100
Table 9-6:
Extended
Superframe
Format
The ESF contains 24, 12-channel T1 frames
(288 total channels). Bit 193 is multiplexed to
serve three distinct purposes:
1 The Fe bit provides frame synchronization at every
fourth frame using the bit pattern 001011. Fe serves
the same purpose as the S and T bits in the D4
format.
2 The Data Link (DL) bit carries line performance
information at every other frame.
3 The CRC-6 is a 6-bit cyclic redundancy check that
inspects all 4,632 bits of the frame for errors.
Table 9-7: DS1 Signal Characteristics
Table 9-8:
AT&T T1
Connector
Pinout
Table 9-9: ANSI T1 Connector Pinout
(a)
(b)
Figure 9-46: Word and Bit Interleaving
The four levels of service are:
1 The customer may change the location of
terminating equipment with carrier’s assistance.
2 The use of multiplexing to allow the customer to
connect up to 24 channels to switched or dial-up
services
3 The use of multiplexing to allow two T1 lines
that carry up to 22 channels on a single T1
connection
4 The customer controls all configurations. This
allows dynamic allocation of circuits—all
without assistance from the carrier.
Figure 9-47: Typical T1 Interconnection
SONET networks are tasked to provide the
following services:
Reduction in copper-based equipment costs
and increased reliability
Frame lengths of sufficient size to carry
management information about the link and
the pay-load carried in the frame
The establishment of accepted standards that
permit networks to be built that are vendor
independent
SONET networks are tasked to provide the
following services (continued) :
The ability to format lower speed frames such
as DS1, and multiplex these using a
synchronous structure
The creation of an architecture that promotes
future development at varying
transmission rates
Table 9-10: SONET Signaling Hierarchy
Figure 9-48:
SONET
Frame Format
Figure 9-49: SONET Terminating Multiplexer
There are three basic configurations used
with SONET:
1 Point-to-Point
2 Hub (Star)
3 Ring
Figure 9-50: SONET Configuration Topologies
REVIEW QUESTIONS
1
What are the components of the
local exchange loop?
REVIEW QUESTIONS
2
What characteristic of a telephone set
allows for full-duplex operations?
REVIEW QUESTIONS
3
What are the BORSCHT functions?
REVIEW QUESTIONS
4
State the voltages present on the line
when a telephone is on-hook and
off-hook.
REVIEW QUESTIONS
5
What is the purpose of companding a
PCM-encoded signal?
REVIEW QUESTIONS
6
What signal characteristics are
controlled through line conditioning?
REVIEW QUESTIONS
7
What is the data rate of a T1 channel?
REVIEW QUESTIONS
8
Describe the difference between
FDM and TDM.
REVIEW QUESTIONS
9
What is the data rate of an OC1
channel?
REVIEW QUESTIONS
10 How many PCM-encoded channels
comprise a T1 frame?