VoIP Terms and acronyms
- BLF (Busy Lamp Field) A collection
of lights or indicators on a phone that indicate which lines are in use
on a PBX or Key System. Helps receptionists in routing incoming calls.
- DID (Direct Inward Dialing) - this is the service you need so people can call in from the PSTN
- SIP (Session Initiation Protocol)
- SAP (Session Announcement Protocol)
- SDP (Session Description Protocol)
a format for describing streaming media initialization parameters.
Intended for session announcement, session invitation, and parameter
negotiation. SDP does not deliver media itself but Does the negotiation
between end points for media type, format, and all associated
properties. This set of properties and parameters are called a session
profile. SDP started off as a component of SAP , but found other uses in
conjunction with Real-time Transport Protocol (RTP), Real-time
Streaming Protocol (RTSP), Session Initiation Protocol (SIP)
- RTP (Real-time Transport Protocol) See wikipedia
- Jingle - Googles Talks protocol
- PSTN (Public Switched Telephone Network) - standard phone system
- CNG (Comfort Noise Generation) (sometimes just CN) If the line is to quite, people think they have been hung up on - so a slight hiss is provided.
- VAD(Voice Activity Detection) If
nobody is speaking it is possible to either stop the flow of audio
packets, or change to a much lower rate of comfort noise packets. VAD is
usually a function within the endpoints of a VoIP path. VAD is not the
same as silence detection. Loud music is certainly not silence, but it
is also not voice, and a good VAD will declare "no voice present".
- Camp_on To stack a call onto a busy extension
(aka Call Waiting). The called party gets a signal to alert that there
is another call. If the called party hangs up, their phone will ring
with the stacked call.
- Silence suppression - Should really be called Silence data
suppression - (it does not suppress silence - that is comfort noise ).
When very quite - no need to pass data.
- POTS (Plain Old Telephone Service) What supplies your old land line
- FXO (Foreign Exchange Office) An
old term, 'Office' means equipment at the office - as in telephones.
Thus an interface that generates off-hook/on-hook indications (loop
closure/non-closure) at the other end of the wire where the Foreign
exchange station's (FXS) is. Analog telephone handsets, fax machines
etc. are FXO devices. FXO devices answer the call.
- FXS (Foreign Exchange Station) An
old term, 'Station' was the telephone companies station - what supplies
the loop voltage and current - Ring voltage etc.
- CPID (Calling Party IDntification)
as in 'caller ID' A 1200Baud Async Analog FSK data sent on the back end
of the first ringing signal ( thus in-band). (About 0.5VRMS)
- Disconnect-Supervision A signal from the FXS that the
call has ended. To test if you have this service: plug in a phone with a
lighted-keypad and watch to see if the keypad blinks off when the other
end hangs up. If it does, you have the disconnect supervision, which
would let your FXO (such as PBX) be able to detect hangup.
- Hookswitch Flash A short on switch pulse from a FXO - about 500ms
- Start methods
- Loop-start The FXS senses the closing of the loop - (by
sensing the current that starts flowing. Early system just used a
current sensitive relay) There are other start methods:
- Kewl-start extension of loop-start and fully compatable
with loop-start - mostlikely the setting you want. Adds Disconnect
supervision through the use of an Open Switching Interval (OSI). The FXS
signals the FXO
- Ground-start Adds
- Battery reversal is pretty much dead - most equipment is polarity neutral.
- Hangup notification Depends on the start method.
Generally, loopstart does not include hang-up notification unless
specifically done through forward-disconnect. Groundstart does include
This information may have errors; It is not permissible to be read by anyone who has ever met a lawyer.
Use is confined to Engineers with more than 370 course hours of electronic engineering for theoretical studies.
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