Chapter 1-2 Flashcards
An analog circuit is composed of a pair of wires.
One wire is the ground _________
The other wire is the battery ___________
These two wires power the analog phone
(positive) - tip
(negative) - ring
Phone is lifted off hook - phone connects the two wires - electrical signal (\_\_\_ DC voltage) to flow from the phone company central office (CO) into the phone
Loop start signaling
48V
The phone is picked up at the same
time as a call comes in but before the
phone has a chance to ring.
Glare
a _________telephone has buttons for outside lines that are
pushed to directly access an outside line. Usually there is an
“intercom” button as well. Phones are answered by pushing
the button that the call comes in on, then lifting the handset.
key system
Analog voice signals converted to Digital
Requires _______ resources
Digital Signal Processing (DSP)
Uses __________ to carry multiple conversations
Eg. T1 carries up to ____ separate _____ channels
TDM (Time Division Multiplexing)
24
64Kbps
Inband signaling (robs bits of information to carry signaling)
CAS – Channel Associated Signaling
Out of band signaling (uses a channel to carry
signaling information)
T1 lines use the __th time slot for signaling and E1lines
use the __th time slot.
CCS – Common Channel Signaling
24
17
Designed for larger, corporate environments
Use ground start signaling
Grounding of the wires tells the phone company to send a dial-tone
on the line
Reduces Glare since a dial-tone is not received until the phone
company receives a ground signal
Private Branch eXchange:
- supervisory signaling
- informational signaling
- address signaling
(on hook, off hook, ringing)
(dial tone, busy, ringback, and others)
(dual-tone multifrequency (DTMF) and Pulse)
_____ signaling sends the signaling in the same
communications channel as the voice.
_____ signaling sends the signaling in a separate
communications channel from the voice.
In-band
Out-of-band
Connects to the PSTN
and converts audio
into electrical signals.
Analog telephone:
The link between the customer premises and the telecommunications service provider.
Local loop:
Provides services to the devices on the local loop.
CO switch:
Provides a connection between switches.
Trunk:
Allows a business to operate a “miniature
PSTN” inside its company.
Private switch (PBX):
: Typically connects to a PBX system.
Digital telephone:
_______ is an international numbering plan for public
telephony systems:
A valid number contains the following components:
Country code
National destination code
Subscriber number
Each number can be up to __ digits long.
E.164
15
converting the analog wave into digital, numeric values
Quantization
The average human ear is able to hear frequencies from
20–
20,000 Hz
Human speech uses frequencies from
Telephone channels transmit frequencies from
200–9,000 Hz.
300–3,400 Hz
Sampling at twice the highest audio frequency used in the audio
can accurately reconstruct audio streams
To reproduce frequencies from ____ Hz sampling would be
taken at twice ___, or ____
Sample “____ byte” of information ______ times per second.
8000Hz * 8bits = 64,000bits of information per second.
Nyquist Theorem:
300–4,000
4000Hz
8000Hz
one
8000
Uncompressed μ-law used in North America and Japan When the high order bit is a zero a-law (used everywhere else). Used when the high order bit is a one
G.711
Applies Compression
Reduces bandwidth to 8 kbps
Two variants _______________
a less processing, b adds VAD*
- VAD: Voice Activity Detection
- MOS: Mean Opinion Score
G.729
G.729a and G.729b
The protocols of voice
Real-time Transport Protocol (RTP)
Real-time Transport Control Protocol (RTCP)
RTP adds time stamps and sequence numbers
RTP streams are one way
two-way conversation requires dual RTP streams
RTP Based on UDP
RTCP’s primary purpose is statistics, for example:
Packet count
Packet delay
Packet loss
Jitter (delay variations
RTCP uses the __________ port following the RTP port
odd-numbered
