Ground start signalling is preferable on trunk links, due to it's ability to prevent 'glare' - seizure of the phone linesimultaneously by the end station and CO switch/PBX.
Ground start provides current detection at both ends of the line.
CO switch - interconnect local-loop, trunks to CO's/PBX's
PBX - private switch, typically digital, propriatory
Key system - less scalable, 'shared' trunk
DTMF/Pulse dialing - methods for sending digits
On-hook - AC current sent for ringing tone, open circuit
Off-hook - DC current (-48v), closed circuit
Key Points - Chapter 2
Cisco fax relay - prestandard Cisco prop.
T.38 - Standards based, supports servers using T.38
T.39 - Standards based, supports email/scanning of faxes
Fax-Passthru - g711 call, susceptable to packet loss
CCS - common channel for all signalling e.g. Q.931, QSIG, DPNSS, SS7
Compression - PCM, 8000 samples/sec a/u-law e.g. g711
Compression - ADPCM, looks at difference (current/next sample)
Compression - CELP, voice prediction and synthesis (g729)
Anlog/Digi conversion: Sample, Quantisise, encode, compress
Echo - acoustic, audio feedback from MIC
Echo - eletrical, electrical impodence mis-match
No comments:
Post a Comment