Telephone Circuit Flashcards
is the only facility required by all voice-band circuits, as it is the means by which the subscriber locations are connected to the local telephone company
Local Loop
the sole purpose of the local loop is to provide subscriber access to the ___
PTN - Public Telephone Network
7 Main Components that make up a traditional local loop
- Feeder Cable
- Serving Area Interface
- Distribution Cable
- Subscriber or Standard Network Interface
- Drop Wire
- Aerial
- Drop-wire cross-connect point
The largest cable used in a local loop, usually 3600 pair of copper wire placed underground or in a conduit.
Feeder cable
A cross-connect point used to distribute the larger feeder cable into smaller distribution cables.
Serving-area interface
A smaller version of a feeder cable containing less wire pairs
Distribution cable
The portion of the local loop that is strung in between poles.
Aerial
A device that serves as the demarcation point between the local telephone company responsibility and the subscriber responsibility for telephone service
Standard network interface
Final length of cable pair that terminates at the SNI
Drop wire
The location where individual cable pairs within a distribution cable are separated and extended to the subscriber’s location on a drop wire
Drop wire cross-connect points
Studies of attenuation on cable pairs have shown that substantial reduction in attenuation is achieved by increasing the inductance value of the cable
Loading Coils
decrease the attenuation, increase line impedance, and improve transmission levels for circuits longer than 18000 feet
Loading Coils
are unused sections of a cable that are connected in shunt to a working cable pair, such as a local loop
Bridge taps
Were used for party lines to connect more than one subscriber to the same local loop
Bridge taps
is comprised of 2 or more facilities, interconnected in tandem to provide a transmission path between a source and a destination
Telephone Circuit
Information or __
Message
Circuit used in telephone circuit
Message Channel
In telephone terminology, ___ denoted speech information
Message
Are unused frequency bands located between information signals
Guard Bands
Local loop is the primary cause of __ and ___
Attenuation and Phase Distortion
Transmission characteristics of a local subscriber loop: (4)
- wire diameter
- conductor spacing
- dielectric constant
- conductivity of the wire
The electrical characteristics of a cable (resistance, inductance, capacitance) are uniformly distributed along its length, referred to as
Distributed Parameters
Noise signals with equal interferring effects are assigned equal magnitude. To accomplish this effect, AT&T developed a weighting network called
C-message weighting
Assumes a perfect receiver, therefore its weighting curve corresponds to the frequency response of the human ear only
Psophometric Noise Weighting
dBm referenced to 0 TLP
dBm0
dB level of noise with respect to reference noise (-90 dBm)
dBrn
same to dBrn except dB value of noise is with respect to reference noise with C-message weighting
dBrnC0
noise readings taken with a filter that has a flat frequency response from 30 Hz to 3 kHz
dBrn 3kHz flat
dBrn 3 kHz flat readings are typically ____ db higher than dBrnc reading for equal noise power levels
1.5 dB
amount of noise in dBrnc corrected to 0 TLP
dBrnc0
Apply to dedicated private-line data circuits that utilize the private sector of the PTN
Transmission Parameters
Circuits with BW comparable to those of standard voice-grade telephone channels that do not utilize the PSTN
Private-line Data Circuits
Difference in circuit gain experienced at a particular frequency with respect to the circuit gain of a reference frequency
Attenuation Distortion
Process used to improve the basic telephone channel
line conditioning
is a relatively low-capacity switching machine where the subscriber are generally limited to stations within the same building or building complex
PBX or private branch exchange
pertains line impairments for w/c compensation can be made with filters and equalizers
C-type line conditioning
Neither reduces the noise on a circuit nor improves the SNR; Simply sets the minimum requirements for SNR and non-linear distortion
D-type line conditioning
originally coined to indicate the presence of unwanted speech sounds in a telephone receiver caused by conversations on another telephone circuit
Crosstalk
is a direct result of nonlinear amplification in analog communications system
Nonlinear Crosstalk
interference caused by inadequate control of the transfer characteristics or transmittance of networks
Transmittance Crosstalk
eletromagnetic coupling between 2 or more physically isolated transmission media
Coupling Crosstalk
2 types of coupling crosstalk
- near-end cosstalk (NEXT)
- far-end crosstalk (FEXT)
is a decrease in circuit gain of more than 12 dB lasting longer than 4ms
dropout
