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34 Cards in this Set
- Front
- Back
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In analog wiring, what is the name for the ground or positive side? |
Tip
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In analog wiring, what is the name for the battery or negative side?
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Ring
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When a phone is taken off hook a circuit is completed. What kind of signaling is this?
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Loop start signaling.
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What is the typical problem with loop start signaling? Define the term.
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Glare. When you pick up the phone to make an outgoing call at the same time as a call comes in on the line.
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What type of signaling is typically used in a PBX?
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Ground start. Both tip and ring and temporarily grounded. Allows PBX to distinguish an an answering phone from an incoming line.
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What signal does a PBX send to the CO to receive dial tone?
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Ground start.
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What signal does a PBX send to the CO to receive an incoming call?
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Loop start.
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What are two problems with analog signaling?
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Signal degradation. Large number of wires.
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What are the two primary styles of signaling for digital circuits?
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CAS - Channel associated signaling;
CCS - Common channel signaling; |
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What is another name for CAS - Channel associated signaling?
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RBS - Robbed bit signaling.
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In CAS over T1, which bit is used for signaling?
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8th bit of every 6th sample.
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In CCS over T1, which time slot is used for signaling?
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24th time slot.
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In CCS over E1, which time slot is used for signaling?
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The 17th time slot.
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What is the most popular protocol for CCS signaling?
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Q.931, used for ISDN
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Describe 6 elements of the PSTN
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1. Analog Telephone
2. Local loop 3. CO Switch 4. Trunk Line 5. Private switch 6. Digital telephone |
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What is the common signaling protocol between telephony providers? What does it do?
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SS7 is an out-of-band (CSS-style) signaling method used to communicate call setup, routing, billing, and informational messages.
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What is the designation and format of the international numbering plan created by the ITU?
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E.164. Each number contains:
Country code National destination code Subscriber number |
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What is the Nyquist theorem?
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Sampling rate must be twice the highest frequency.
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What is the typical frequency range of a telephone channel?
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300-3,400 Hz
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The process of converting an analog wave into digital numeric values is know as...?
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Quantization. Perhaps also PAM
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Define PAM and PCM
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PAM = Pulse amplitude modulation. The process of sampling an analog waveform at timed intervals to obtain a digital measurement of the electrical signal.
PCM = Pulse coded modulation. The process of converting PAM values to binary equivalents for transmission over digital circuits. |
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What is a MOS?
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Mean Opinion Score - rating of the quality of a compression process
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What are the bandwidth requirements and MOS for common codes?
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G.711 - 64Kbps - 4.1
ILBC - 15.2 kbps - 4.1 G.729 - 8 kbps - 3.92 G.726 - 32 kbps - 3.85 G.729a - 8 kbps - 3.7 G.728 - 16 kbps - 3.61 |
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What are the two common codecs in the Cisco world?
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G.711 and G.729
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What are the two variants of G.729?
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G.729a sacrifices audio quality to achieve a more processor-efficient coding.
G.729b supports voice activity detection (VAD) to make voice transmissions more efficient. |
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What is the purpose and function of a DSP?
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Purpose: offload the processing for voice-related tasks from the processor of the router.
Function: sampling, coding, and compression; convert analog voice to packets. |
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What are the medium-complexity codecs?
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G.711, G.726, G.729a, G.729ab
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What are the high-complexity codecs?
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G.728, G.723, G.729, G.729b, iLBC
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Describe the two primary TCP/IP stack protocols for voice.
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RTP (Real-time Transport Protocol) runs on top of UDP, adding time stamps and sequence numbers.
RTCP (Real-time Transport Control Protocol) provides statistics - packet count, delay, loss, jitter. |
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Which UDP ports are used for an RTP audio stream?
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A random, even-numbered UDP port from 16,384 to 32767 for each one-way stream.
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Which UDP ports are used for an RTCP audio stream?
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The odd-numbered port immediately following the RTP port number.
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How often are RTCP packets sent?
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At least once every 5 seconds.
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Give three examples of supervisory signaling.
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On hook, off hook, ringing,
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Give three examples of informational signaling.
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Dial tone, busy, ringback
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