network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Saturday, January 14, 2012

100th post... voice

how fitting for my hundredth post to launch a new beginning... voice
(notes after cioara)


Ground is tip, positive, one wire; battery is ring, negative, other wire
On hook is open circuit; off hook is closed completing 48vdc circuit

Loop start signaling commences at off hook provided by CO (48vdc)

Glare happens when phone is picked up as a call comes in

Digitizing voice means changing analog signals into numbers

TDM (time division multiplexing) allows for networks to carry multiple conversations over a single 4 wire pair (numbers sent are divided by time)

T1 24 separate 64kbps channels known as a digital signal 0 (DS0)

Signaling – 2 types

Channel associated signaling – transmitted using the same bw as voice
Common channel signaling – transmitted using separate, dedicated channel

Q.931 is the most popular signaling protocol, which is used by ISDN
Uh oh, isdn never goes away…

Just as in life, those who do not pay heed to history are doomed to repeat it; pstn and pbx should be looked at…

Benefits of VOIP
Cisco loves comparisons

reduced communications cost
reduced cabling cost
reduced cost of moving the phone from a to b
unification – email, voicemail, fax
open standards (wait, did I just say open standard and cisco in the same breath)

quantization is how an analog signal is converted to a number 0-255 or +127 and -127

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