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H.323 VoIP Gateway Voice and Convergence Features
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Signaling Control and Voice Interoperability (Voice Features)
The ability to accommodate voice traffic using VoIP switches installed in data networks is
achieved by means of signaling controls and voice interoperability features. The VoIP signal-
ing control and voice interoperability functions includes telephony signaling and payload
packetization as described.
Telephony Signaling
Telephony signaling is used for signaling with telephone equipment, e.g., PBX, via the tele-
phony interface, as well as to control the communication signaling between the H.323 VoIP
gateway and the Customer Premises Equipment (CPE). It detects the presence of new calls,
collects dialed digit information (telephone number in some form or another) entered by the
caller to route a call via an AVNDS to its destination point, and is also used to detect the end
of calls (off hook).
Telephony signaling provides call progress supervision by generating supervisory and call
progress tones, as well as DTMF (Dual Tone Multi Frequency) tones for outbound calls. It
also provides DSP (Digital Signal Processor) interfacing control, and transfer of PCM-based
voice packets to and from the DSP subsystem or DIMM (DSP Interface Management Module).
It coordinates with the DSPs to select voice coders (codecs) at startup when a particular
vocoder is needed. When a call is received, telephony signaling is responsible for opening
channels and PCM data streams to the DSPs to process the voice data.
The signaling controls provided by the Telephony Signaling functions includes the following:
• Call Progress Tone and Tone Detection — detects individual in-band frequencies and
converts them into tones or other signaling events, e.g., answer or busy signals.
• Dialing Timers — used to time incoming signaling events, e.g., how long to wait for a
wink start, or how long to wait for another digit.
• E&M Signaling (Common, Wink Start, Immediate Start and Delay Start) — customizes
attribute settings or parameters to match CPE. (Available only on VSD-T1.)
• Foreign Exchange Station (FXS) Loop Start — customizes attribute settings or parame-
ters to match CPE.
• Foreign Exchange Office (FXO) Loop Start — customizes attribute settings or parame-
ters to match CPE.
• Caller ID — looks for Caller ID information, e.g., calling party telephone number
between first and second ring.
The telephony signaling configuration options for telephone signaling interfaces, e.g., ring
delay and cadence (ringing rhythm), are assigned to the physical ports on the daughtercard,
including the T1 and E1 line specifications. All options are defined at the channel level.
Parameters for telephony signaling and VoIP network preferences are pre-configured in text-
based configuration files referred to as
vsmboot.asc
files. The parameters are stored in the
boot files and subsequently assigned to a daughtercard and/or its components. For more
details on setting these parameters, see also Chapter 5, “VoIP Commands.”