OCO/MCO Basics
Session 1
Training and Development
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Agenda
Session 1
Session 2
Session 3
Session 4
Session 5
Analog and DS0 Transmission including DDS
Concepts
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Understand and explain the basics of analog transmission
Understand and explain the basics of analog technology
Identify analog circuits and equipment
Explain DDS data circuit configurations
Identify DDS network components
Session 1:
Analog and DS0 Transmission
Including DDS Concepts
Transmission of Voice Frequencies
Sound: An atmospheric disturbance or a stimulus whereby a sensation is produced in
the human ear. It is a wave motion produced by a vibrating body such as a bell, tuning
fork, human vocal cords or similar object.
Sine Wave: A simple harmonic that can be generated by a simple object like a tuning
fork. In electrical image, a harmonic is defined as an alternating voltage or current whose
frequency is some integral multiple of a fundamental frequency. For example, the third
harmonic of 20Hz is 60Hz and the fifth harmonic of 100Hz is 500Hz. If the source is a
mechanical motion like the human voice, the wave form is not a sine wave but a very
complex wave.
Voice Frequency Range
A vibrating mechanism giving a pure tone, a sine wave, is said to establish a tone of
low pitch if it is vibrating slowly and a high pitch if vibrating rapidly. The lowest pitch is
audible to the normal ear and lies somewhere in the octave between 16 and 32 vibrations
per second(Hz). The upper limit of audibility is somewhere between 16,000 and
32,000Hz. Audible sound is defined as vibrations of the atmosphere between 16 and
32,000Hz. In telephone transmission, sound frequencies which play the most important
part of rendering spoken words of ordinary conversation are in the frequency band of
frequencies form 200Hz to 3500Hz. Telephone transmission for local service is designed
for these criteria.
Attenuation and Gain
Attenuation, or transmission loss, is the energy loss in the transmission of any alternating
current signal from a sending device to a receiving device. The unit of measurement for
transmission loss, gain or relative level is the decibel or dB. The dB represents a fixed
percentage reduction or gain in power.
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•
Loss - Whenever the output of a circuit or device is less than the input, the circuit or
device is said to cause a loss in signal strength.
Gain - Whenever the output of a circuit or device is greater than the input, that circuit
or device is said to cause a gain in signal strength.
Loss Ratios
If the signal power entering a
system or device is 2 watts,
and leaving it is 1 watt, the
signal power has been
reduced by a ratio of ½ or
50%.
Two such devices connected
together would reduce the
power by a ratio of ¾ or 75%.
Loss Ratio’s (Con’t)
Suppose there are six devices connected in tandem and each has a different ration of loss.
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•
Each stage of the process has a input which is the output of the previous stage.
Using the value of 200 watts as an input, we can trace it’s level as it traverses each
device.
•
Each segment of a circuit will have a specific decibel loss, all of which are added
together to determine the output level.
Decibel
To grasp the literal meaning of decibel, the term can be broken in two parts.
Deci means one tenth and Bel (after Alexander Graham Bell) is used to express the
ratio of power.
A decibel is one tenth of a Bel. The mathematical definition of a decibel is as follows:
It is not necessary to understand the above formula in mathematical terms but you
need to have a feel for the relevant dB noise levels.
Decibel (Con’t)
The chart below shows the relationship between decibels and power ratios for
gains and losses.
This chart shows that
a circuit with a loss or
attenuation of 3 dB
has lost half it’s input
power. If the input
power were 3 watts,
the output power
would be 1.5 watts.
As shown, the correlation
between signal loss or
gain measured in dB is
not linear, as in a one-toone relationship or a
straight line.
What can be determined using the dB chart if an input signal of 4 watts suffers a 6
dB loss? An input signal of 4 watts sustaining a 6 dB loss will have ¼ of it’s signal
strength. The signal has lost ¾ of it’s original input power. he output will be 1 watt.
dB Relationship to Basic Telephone Circuit
In a basic telephone circuit, there is a steady DC current from the -48 volt battery through
one telephone circuit to ground. The magnitude of current flow is determined by the
resistance in the circuit. When we talk into the transmitter (at X time), the diaphragm
attached to the carbon chamber (variable resistor) varies the DC current in the circuit at
the frequencies of our voice. This results in a fluctuating DC signal superimposed on the
steady DC signal. This fluctuating DC does not change direction like the AC current does,
but it varies in magnitude much like AC current.
Glossary of Decibel Reference Characters
DBM = decibels in reference to milliwatts
DBRN = decibels in reference to noise
DBRNC = decibels in reference to noise c-message weighting (voice 250-33—Hz)
DBM0 = decibels in reference to milliwatt from test level
DBRN0 = decibels in reference to noise from test level
What
did
you
learn?
Progress Check: Transmission
Progress Check: Feedback
Video
time
Inductance
Inductance
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•
•
Inductance is a physical property of a conductor (e.g. coil of wire) which opposes any
change in current flowing through the conductor.
Inductance is a measure of the electromotive force which will be generated as a result
of a given rate of change of current in the conductor. Current flowing through the
conductor produces a magnetic field.
When the current in a conductor increases or decreases, the strength and size of the
magnetic field around the conductor increases or decreases accordingly.
INDUCTANCE is the ability of a conductor to produce induced voltage when current
varies.
Once the current reaches its maximum value,
inductance is no longer present.
Inductance (Con’t)
Inductance – the effect of EMF or self-inductance – opposes any change in current
flow, whether it increases or decreases, by slowing down the rate at which the change
occurs.
• When the current (l) increases, inductance tries to hold it down.
• When the current (l) decreases, inductance tries to hold it up.
The basic unit of measure for inductance is the HENRY, abbreviated H. A smaller unit
MILLIHENRY, abbreviated mH, which equals 1/1000 of a HENRY.
If a current changing at a rate of ONE AMPERE PER SECOND causes an induced
voltage of ONE VOLT in a coil, we say that the coil has INDUCTANCE of ONE HENRY,
1H.
Inductance (Con’t)
Just like resisters, inductors may be connected in either series or parallel.
To solve for total inductance in a circuit, you use the same rules you learned for
resistance, namely:
• Inductance is additive in Series
• Inductance in parallel, total inductance is always less than the smallest inductor.
Inductance in Cable Pairs
Adding inductance to a cable pair at set intervals nullifies the effect of capacitance
within a cable pair and is called loading.
Inductors (load coils) can be selected and placed in the cable pairs at set intervals that
will nullify the capacitive effects of cables for voice frequencies.
The circuit and attenuation graph
at right would appear as below for
the 24 gauge cable loaded every
6000 ft.
What
did
you
learn?
Knowledge Check: Inductance
Knowledge Check: Feedback
Loading
Loading
Loading is a means of reducing transmission loss on a cable pair.
Loading consists of adding or splicing an inductor – a coil of wire wound on an iron
core – at regular intervals along the cable pair. It is critical that the spacing be uniform,
or else other transmission impairments will occur.
A code system is used to indicate the different loading schemes used. The loading
scheme codes show the cable gauge, spacing between load coils, and the coil
inductance value in Millihenries.
For example, loading designated 26H88 indicates:
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26 gauge cable
H spacing which is 6000 feet between coils
88 millihenries of inductance for each coil
Loop Transmission
At the time of service installation, all subscriber lines must be tested to ensure that they
meet minimum loop transmission standards. The standards include minimum
requirements for:
Loop Current
Circuit Loss
Circuit Noise
Power Influence
Loop Current provides “talk battery” and operates supervision and signaling equipment.
Sufficient loop current required for:
• Dial tone requests
• Touch-tone pad operation
• Tripping the ring when call is answered
• Providing talk battery for transmitter
Insufficient loop current:
• No dial tone
• Reaching wrong numbers
• Can’t be heard
• Bell rings but can’t be answered
When loop current falls below 23mA:
• Transmitter loses efficiency
• Customer must talk louder than normal
• Far end may complain of low volume while
near end may complain they can’t be heard
Loop current problems:
• Physical troubles on cable such as
short, ground, cross or open
• Conditions must be corrected before
other transmission tests are made.
Loop Transmission (Con’t)
Circuit Loss is defined as the conductive loss on a loop from the C.O. to the terminating
Poinp of the circuit, i.e. a telephone set.
• Circuit loss (loss of power) is measured in decibels (dB)
• A decibel is a ratio of power output to power input the decibel milliwatt (dBm) is the
value used to measure the loss or gain of power in a telephone circuit
• Total end-to-end loss for a telephone connection should be -17dBm or less (loss is
for 2 subscribers connected through the CO, loss on each line should be no more
than 8.5dBm)
• Circuit losses are measured with a transmission loss test set
• Industry standard frequency used for transmission loss measurement is 1,000 Hz
The three electrical forces which affect circuit loss are:
Capacitance
Inductance
Resistance
Loop Transmission (Con’t)
Circuit Noise has been humorously described as “an oddity of nature with the ability
to travel further, last longer, and arrive in better condition than any type of telephone
signal”.
• Noise is measured in decibels referenced to noise (dBm)
• Noise measurements can be taken by dialing the silent (quiet) termination located in
every Central Office
• A reference point of -90dBm is used for noise measurements
Another important measuring unit is the dBrnC.
This unit expresses circuit noise readings that have been made in conjunction with a C
message filter.
• The C message filter takes the place of the telephone set which filters out some of the
noise on the telephone line.
• The process of C message filtering is often referred to as C message weighting.
Loop Transmission (Con’t)
The noise level categories and their impact on telephone service are:
0 to 15 dBmC
Noise is not noticed by people with normal hearing capabilities.
16 to 20 dBmC
Noise becomes audible, but is normally not disturbing.
21 to 30 dBmC
Noise is disturbing to the customer, considered marginal.
Over 30 dBmC
Noise makes it difficult for the customer to hear or to be heard.
Loop Transmission (Con’t)
Noise
Replacement of open wire, improved balancing in switching equipment, better loop aids,
subscriber line carrier, and fiber optic cable have all served to help alleviate the
incidence of noise and transmission impairments.
Noise can be defined as any unwanted disturbance in a communications system which
interferes with the normal transmission of information, i.e. voice and data. It is any signal
in a communications system other than the input signal. Power systems create noise in
the telephone systems.
90% of all telephone noise originates with the power systems. The secret to curing
telephone noise is in understanding how noise from power lines gets to the subscriber’s
ear.
Power Influence
There are magnetic fields around every power lead. The
magnetic field is always changing because the power is
AC (alternating current). The field can possibly be 400’ in
diameter. The magnetic lines do not stop at the ground.
These lines of force move unimpeded through all common
materials. Burying telephone cables does not shield them
from the effects of power lines.
One of the rules concerning magnetic field says
“Whenever there is relative motion between a
magnetic field and a conductor, there will be voltage
induced in the conductor.” Because the field around the
power lead is moving, and conductor within the field will
have a voltage induces in it, the value of which will depend
on:
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•
•
strength of the field
distance between the center of the field and
conductor
the length of the parallel relationship
Power Influence (Con’t)
If a telephone cable is placed in the magnetic field of a power lead, a voltage will be
induced in every conductor in the cable, including the sheath, which is also a conductor. It
is important to understand that the magnetic lines pass through the cable sheath and
induce voltages in the wires inside just as though the sheath were not there. The voltages
induced in conductors will become currents if a path exists from each end of the
conductor to ground. These currents then travel along the conductor to ground, back
through the ground to the far end of the conductor, forming a loop.
The amount of current that flows in these current loops depends on the impedance in the
loop.
Power Influence (Con’t)
Paths for induced currents on an open ended cable pair are shown below.
Note that the tip and ring
circuits are separate so far as
the noise currents are
concerned. Also note the tip
and ring currents flow in the
same direction along the
conductors at any given instant.
The term used to describe
these currents is POWER
INFLUENCE.
Power influence may be further described as the environment for the telephone circuit.
Keep in mind that the PI currents are the result of the power lead induction and whatever
canceling may have taken place due to sheath current. PI can only be changed by cable
sheath bonding and grounding work or by changes in the power lead itself.
Power Influence (Con’t)
Sheath Continuity
A sheath is the protective outer covering of a cable. It is most commonly made of
polyethylene, or in some cases, lead. The cable shield within the cable sheath (usually
aluminum) is a low-resistance conductor. A typical value for sheath resistance is .5 ohm
per 1000 feet. Bonds across sheath openings are normally made with #6 AWG copper
wire. Sheath Grounds are also made with #6 AWG copper wire.
Bonds
A bond is the electrical connection of two or more pieces of telephone hardware or of
telephone hardware to hardware belonging to another utility. Bonding is done to maintain
a common electrical potential. Bonding telephone company hardware to power company
hardware or fixtures shall only be performed as specified in Verizon Company Practices.
Power Influence (Con’t)
Grounds
A ground is an electrical connection of telephone hardware to the earth or to a
conducting body which is at earth potential. Electrical connection to a low resistance
ground must be made to prevent the buildup of hazardous voltages to ground on
telephone equipment in the event of an electrical contact.
An effective ground can be a power system multi-grounded neutral, a metallic water
system (cold water pipe), or an extensive underground grounding system (grounding
grid).
The loop formed by the sheath and grounds has very low impedance if the cable sheath
is properly bonded. Sheath currents will be large because of low resistance. Values from
1 to 10 amps are expected.
Power Influence (Con’t)
Grounds (Con’t)
The current in a cable pair is small because these conductors are fine-gauge and have
relatively high resistive paths to ground through Central Office equipment.
Power Influence (Con’t)
Grounds (Con’t)
As stated earlier, whenever current flows in a conductor, a magnetic field is formed
around the conductor. The current flowing in the sheath causes a sizable magnetic field
and because the cable pair conductors are in this field, a voltage is induced in each of
these conductors.
The voltage caused by the sheath will tend to cancel each other. The result of this action
is that the net induced voltage on a cable conductor is the difference between the
voltages induced by the two fields.
Because the canceling magnetic field formed by the sheath is present only because of
sheath current, it should be apparent that anything which reduces sheath current will
reduce the canceling field.
Power Influence (Con’t)
A single open bond or missing ground can cause the sheath current to go to zero
and all cancelling action to stop.
Open bonds or missing grounds are a major cause of telephone noise.
Power Influence (Con’t)
Grounds (Con’t)
The same shielding effect takes place in any group of conductors paralleling a power
lead if one or more of the conductors are grounded on both ends. In aerial cable, open
bonds and even broken sheaths are commonly caused by wind, ice or improper
placement. Consequently, the only shielding in many aerial cables is caused by current
in the support strand.
It should also be recognized that the sheath does its work electrically and does not
shield the inner pairs from magnetic fields. The sheath would work just as well if it were
rolled onto a conductor and put in the center of the cable rather than on the outside.
In fact, one of the tests of sheath continuity is to select enough pairs to make a
conductor equivalent to the sheath and ground both ends of these pairs. If doing this
reduces the noise in the remaining pairs a great deal, it can be concluded that the
sheath is open.
Power Influence (Con’t)
Circuit Balance
How well we have done in our attempt to keep PI (Power Influence) currents equal on
T&R (Tip & Ring) is called Balance.
From a noise standpoint, balance is an expression of telephone circuit equality. It should
be recognized that the built-in circuit quality or balance is only part of the equation. The
balance problems seen in the field are usually physical trouble conditions. These
problems include unequal resistances in the T&R wires caused by:
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•
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Poor connections
Burned carbons
Depleted gas tube units
Bridge taps with one side open
Cable pairs with one side open beyond the customer
High resistance troubles
Power Influence (Con’t)
Balance can be described as the ability of the telephone circuit to ignore PI. The balance
of a telephone circuit measured in dB should be 60 or more. PI will usually be in the
Range if 60 to 80.
On a telephone circuit, if the PI is 70 and the balance of noise is 60, the circuit noise
(noise across pair) will be 10. Both PI and circuit noise are measurable quantities while
circuit balance must be calculated.
The formula for circuit balance is balance equals PI minus circuit noise.
Balance (dB) = Power Influence – Circuit Noise
Power Influence (Con’t)
Circuit Balance (Con’t)
A repair technician can measure the PI and circuit noise, subtract one for the other and
arrive at a number which establishes whether a phone circuit is good or bad. For
example, take the case where PI is 100 and circuit noise is 40dB.
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The circuit balance is 60 (100 – 40 =60)
No physical telephone troubles
Problem is excessive PI
Bonding and grounding must be checked.
If the PI had been 60 and circuit noise had been 40, the circuit balance would be
20. This tells the technician there is a physical trouble, and that by improving the
balance to the required 60, circuit noise can be reduced to 0.
Power Influence: Review
The major source of external noise imposed on a telephone circuit comes from power
systems. Power influence (PI) produces circuit noise by causing unwanted current to flow
into the circuit.
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Noise or hum on the line that a customer hears is the only indication that there is
power influence in the circuit.
Power influence results from the magnetic field caused by a power system.
A magnetic field that can be as much as 500’ in diameter forms around power lines.
When a magnetic field cuts through a conductor like a telephone cable, it produces
a voltage on the conductor known as a magnetic coupling.
Voltage induced from the power system onto the telephone conductor is mostly
neutralized by using a process called shielding. This is accomplished by placing a
grounded cable shield along side the telephone conductor. This cable shield induces a
voltage of opposite polarity to that already induced from the power line. The two voltages
of opposing polarity cancel each other.
What
did
you
learn?
Knowledge Check: Noise
Match each of the following items
with their associated definitions.
Knowledge Check: Feedback
Transmission Impairments
Transmission Impairments
The purpose of an outside plant is to provide a physical path over which communication
signals can be transmitted. How well these signals are transmitted depends on the quality
of the transmission media over which they travel.
There are 7 types of transmission media used to provide transmission paths or channels:
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Open wire lines
Paired Cable
Coaxial Cable
Radio (terrestrial and satellite paths)
Waveguide/Fiber Optics
Microwave
Transmission Impairment (Con’t)
Paired Cable
• Paired cable consists of wood pulp or plastic insulated wires, 26 gauge to 19 gauge
in diameter.
• Paired cable contains copper wire.
• The wire is twisted in pairs with a 2-6 inch per 360 degree twist.
• The cable is stranded in binder groups or 25, 50 or 100 pairs, with a number of
different twist lengths for adjacent pairs in a binder group.
• Twisted pairs are used because of self-shielding.
• Twisting keeps both conductors in close proximity, and keeps the magnetic field
localized to the wire pair.
• Twisting minimizes cross-talk or coupling of energy from one circuit to another.
• Cables may have sheaths of plastic, aluminum, steel, lead or combination of 2 or
more sheaths.
• Cables may contain from 6 to 4,200 pairs.
Transmission Quality
The three standards used to judge the quality of a transmission system are volume or
amplitude, frequency distortion, and noise.
• Volume/Amplitude is the level of power available, usually at the receiving end
of the circuit.
• Frequency Distortion is an unrealistic sound which occurs when there is a
change in the relative magnitudes of the different components of a complex
wave such as the human voice.
• Noise is any signal other than the input signal in a communications system.
Introduction to Cable Trouble
Most cable troubles can be grouped according to trouble types and trouble causes.
The more knowledgeable you are of trouble types and causes, the better you will be able
to utilize the tools available to isolate and pinpoint cable faults. The first step in
developing good cable fault locating and repair techniques include a basic understanding
of the things that affect outside cable such as:
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•
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Capacitance
Resistance
Induction
Proper bonding and grounding
Cable Faults
Generally speaking, all cable faults can be placed into one of two categories –
metallic and non-metallic.
Cable Trouble (Con’t)
Metallic Faults
A metallic fault is a metal to metal condition in which a portion of a cable conductor (tip,
ring., or both) comes in contact with a portion of another conductor. The conductor(s)
should be in contact with the metallic shield (sheath) of the cable.
There are 3 types of metallic faults:
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•
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Shorts
Grounds
Crosses
An Ohmmeter, which measures resistance, is used to test for metallic faults:
• Shorts, grounds, and crosses are resistive type faults.
• Electric current diverts to and follows path of least resistance. When a conductor
comes into contact with something that offers a high degree of resistance, very little
of the current will be diverted and transmission may not be adversely affected.
• If that same conductor comes into contact with something offering a low degree of
resistance, more current will be diverted, causing either a partial or complete
disruption of service.
Cable Trouble (Con’t)
Shorts
A short occurs when 2 wires of the same cable pair come into contact with each other.
The contact can be direct or through a resistive path. This can happen anywhere in the
loop, i.e. in the Central Office, a cable, a terminal, the drop wire , the network interface
device (NID), or in the customer’s inside wiring or equipment.
Symptoms:
• Reduced signal level
• Noisy circuit
Probable Causes:
• Cable damage
• Moisture
• Lightning Damage
• Abrasion of Service Wire
• Terminal Deterioration
• Insect or Rodent Damage
• Corrosion
• Water in Cable
Cable Trouble (Con’t)
Ground
A ground occurs when one or both conductors of a cable pair come into contact with a
path to ground. The path could be the cable shield, a metal closure, a buried pedestal,
support strand, a water pipe, etc.
Symptoms:
• Reduction in signal level
• Possibly no dial tone
• A noisy customer line
Probable Causes:
• Grounded carbon in a protector
• Moisture
• Cable or wire damage
• Lightning damage
• Terminal deterioration
• Insect or rodent damage
• Water in the cable
Cable Trouble (Con’t)
Crosses
A cross occurs when the Tip and Ring of one pair comes into contact with the Tip or Ring
or another pair. The contact can be direct or through a resistive path.
Symptoms:
• Capacitance unbalance between conductors and ground
• Reduction in signal level
• No dial tone
• Foreign Battery
• Noisy circuit cross talk
Probable Causes:
• Moisture
• Cable Damage
• Lightning Damage
• Terminal Deterioration
• Insect or Rodent Damage
• Water in cable
Cable Trouble (Con’t)
Non-Metallic Faults
There are 3 types of non-metallic faults They are in the category of capacitive faults:
• Opens
• Splits
• Unbalances (Inductive)
Opens:
An open occurs whenever there is a break in either one or both conductors of a cable
pair. The insulation does not have to be broken, only the conductor(s). Open conditions
also occur when either one or both conductors have not been terminated, or have
broken away from their binding posts.
Symptoms:
• No dial tone
• An unbalance between the conductors and ground
• Noise on the cable pair
Cable Trouble (Con’t)
Probable Causes for Opens:
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Corrosion
A bad splice connection
Lightning damage
Cable or wire damage
Rodent damage
Terminal deterioration
Cable Trouble (Con’t)
Splits
A split is a trouble condition normally resulting from human error. The split occurs when
the tip or ring side or one pair is connected to the tip or ring of another pair. This usually
occurs when the pairs are being spliced.
Symptoms:
• Capacitance Unbalance
• Noise
• Cross-talk
• No dial tone
• Splicing error
Unbalance (Inductive/Capacitive)
Induced current is a form of electrical energy induced in a cable pair by the flowing in
other cable pairs and from external sources such as an overhead power line. Induced
current can cause the circuit to become noisy. In a well-balanced circuit, noise, for the
most part, will be negligible or non-existent. In an unbalance circuit, the effects of the
electrical energy will be apparent.
Fault Diagrams
Fault Diagrams (Con’t)
What
did
you
learn?
Knowledge Check: Transmission Impairments
Knowledge Check (Con’t): Transmission Impairments
Knowledge Check: Feedback
Knowledge Check: Feedback
DDS Concepts
DDS Network Objectives
Digital transmission provides a highly reliable means of transporting data through our
network. The bandwidth used in a DS0 is 64kbps. Bandwidth available for DDS services
are:
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2.4 kbps
4.8 kbps
9.6 kbps
56 kbps
64kbps
19.2 and 38.4 kbps seldom used
Two non-loaded copper pairs were required to pass a traditional DDS signal. The
maximum resistance of the pairs is 4200 ohms on each pair. Today, we convert the
customers 4 wire DDS circuit into a 2W IDSL DDS circuit. The pair is qualified for this
service by sending 40 kHz. The loss must be 40 dbm or less. When the loss exceeds 40
dbm, we use a Total Reach 2 wire DDS circuit. The pair is qualified for this service by
sending 13.3 kHz. The loss must be 50 dbm or less. The 2W IDSL & Total Reach DDS
circuits will use the RJ48S jack that is built into the digital mounting as the point of
demarcation.
DDS Network Objectives (Con’t)
By using only digital transmission techniques, the DDS network can provide a high
degree of quality and availability.
• Quality = percentage of error free seconds
• Availability = percentage of time the customer can use the channel
• Reduce unavailable time = reduce the number of individual outages that exceed 2
hours.
Note: DDS is now a system of networks separately administered by individual operating
companies and interLATA carriers. Actual objectives vary from company to company. It is
not possible to specify DDS quality and availability with specific numbers. Transmission
Delay is another characteristic of the DDS network. Although delay is not closely
controlled, the DDS network does not use satellite connections partly because of the long
round-trip delay that occurs. Such delay is unacceptable for current widely used protocols
or applications requiring retransmission of error blocks of data.
DDS supports synchronous, end-to-end digital data communications. The four basic
rates of DDS are 2.4, 4.8, 9.6 and 56 kbps. The 3 lower speeds are called sub-rates.
Terminal equipment connected to a DDS channel derives timing from the network via the
received DDS Bit stream. DDS supports 2-point circuits, providing full duplex
transmission. DDS also supports multi-point circuits.
DDS Architecture Examples
Shown above, the DTE CSU-DSU connects to 2 non-loaded cable pairs (a 4W loop) in the “A” end CO.
They are terminated on the frame (not shown) and connect to an OCU in a D4 bank. Then, they interface
with a DCS machine via a DS1. At the “Z” end CO, the circuit exits the DCS via a DS1 and connects to a
DSODP in a Litespan 2000, transported from the Co over Fiber to an RT Litespan OCU. From there, it
travels on a 4W loop to the customer premise, terminated in the CSU-DSU Data Termination Equipment.
DDS Architecture Examples (Con’t)
Shown above, the DDS signal leaving the CSU-DSU at the “A” end is 4W. It connects to a Total Reach
OCU-R where it is converted to IDSL. -130vDC is applied and the 2W circuit travels 36K’ over a single
pair of non-loaded 19Ga copper wire. In the CO, it connects to a DDSDP in a D4 channel bank. The DS1
signal then connects to a DCS and gets transported to the “Z” end CO. Then it connects to a D4 bank
DSODP. That signal then connects to a DSODDP in a SLC5 at the CO. It connects to the SLC5 RT
DDSDP. -130vDC is applied to a single cable pair leaving the RT to power the OCU-R at the customer
site. The OCU-R converts the signal from 2W to 4W DDS and hands off to the customer as a 4W DDS.
DDS Architecture Examples (Con’t)
It’s important to note that DDS circuits have at least two ends (refer to your notes on
bridged circuits), typically called “A” and “Z”. Any combination of architecture might be
used at either end.
All copper from the “A” customer premise to the “A” CO, fiber through a DCS,
multiplexers, pair gain systems or any combination of these may be used.
A circuit could be IDSL on one side and 4W DDS through regenerators at the other. The
route, equipment used and transport method are determined by the circuit provisioning
center and are turned into work documents.
The word document is the roadmap of the circuit.
Questions?
Training and Development