CCDA Chapter 8
Terms
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- What are the 3 steps for converting analog signal to PCM format?
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-filtering- filters over 4000 hz
-sampling- sample at 8000/sec
-digitizing-digitze the sample and put it into binary - PBXs and Switches- which one private and public?
- PBX is private and switches are public
- Local Loops
- -provide physical cabling between central office and home
- Phone Lines
- -communication between central office switch and home
- Station Lines
- -interconnect PBX and telephones
- Trunks
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Tie trunks -interconnect PBXs
CO trunks -central office trunks
PSTN switch trunks- interconnect central office switches - What are the 2 types of Basic Telephony Signaling
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-subscriber signaling- between PSTN switch and subscriber
-trunk signaling- between PSTN switches, between a PSTN switch and PBX, or between PBX switches - Name the 2 types of subscriber signaling.
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-loop start- residential, simplest
-ground start- modification of loop start, for PBX loops - Name the one type of trunk signaling.
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-E&M- recieve and transmit (between PBX)
-5 types of signaling
-separate paths for voice and signaling - CAS and CCS Signaling
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-channel associated signaling- signal for call setup in the same channel as a voice call
-exampples TI, DTMF dual tone multi frequency - CCS
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Commone channel signaling- separate channel for call setup
-E1, ISDN, DPNSS (Digital private networking signaling system)
-QSIG (Q signaling)
-SS7 (Signaling System 7) - Voice Coding and Compression
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-Pulse Code Modulation (PCM) used i traditional networks is wasteful
-uses 64 kpbs og bandwidth per call
-reduces amount of traffic
-hgher the compression the worst quality of voice,
-voice coding standard is CODE - Codec Mean Opinion Score (MOS)
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-compression used during Codec Rate
-offers certain quality of speech - What is voice communication a mix of?
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-contorl signaling
-voice conversation - What does voice control signaling require?
- -reliable transport provided by TCP/IP
- What does voice conversation transport based on?
- -connectionless UDP/IP
- What are some sources of fixed delay?
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-propogation delay
-sterlization delay
-processing delay - What are some sources of variable delay
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-queuing delay
-dejitter buffers
-variable packet sizes - What are some QoS mechanisms?
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-bandwidth reduction
-bandwidth reservation
-QoS classification
-Congestion management
-Congestion avoidance - What are some congestion management QoS Mechanisms?
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-IP RTP Priority- voice identified by RTP port #'s classified into PQ
-PQ- 4 buckets
-CQ- 16 buckets
-WQ- divides bandwidht across queues
-CBWFQ- divided bandwidh on defined weights and classes with no strict PQ avaliable
-LLQ- fair queuing with guarnteed bandwidth with strick prioirty queuing avaailable for voice traffic - On Net Calling
- -used to call private tie lines whenever possible
- Off Net Calling- when is it used?
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-when private lines are congested
-if called party is not reachable over the private network
-if user manually selects an off net extension - Grade of Service (GOS)
- probability of calling being blocked at the busiest hour
- Erlang
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used to calculate the GOS
-equals one full hour of conversation - Centum Call Seconds (CCS)
- Erlang/36
- One erlang equals;
- 3600 seconds of telephone seconds