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Telephony concepts
November 2004
Avaya Modular Messaging Concepts and
Planning Guide
8-9
bearer channels (voice), one signaling channel (data), and one framing
channel. Each time slot carries 64 KBps of data.
Digital Set
Emulation
Digital Set Emulation is a digital protocol developed by switch
manufacturers to connect digital telephones to their switches. Using
Digital Set Emulation, Avaya Modular Messaging can emulate digital
telephone sets. These telephone sets can provide all the features that a
voicemail system requires to integrate with a switch. For example, they
can support the receipt of calling and called party identity and can have
message waiting indicators and programmable keys.
Analog telephony
interface
With analog signaling, sound is represented by varying current rather than
digital signals. Telephony signaling, such as on-hook or off-hook, is
conveyed by completing and disconnecting the circuit. The MAS dials
outbound calls using DTMF tones. All other call progress states, such as
dialtone, ring-back, and busy, are conveyed using standard tones.
To initiate a three-way call, Avaya Modular Messaging issues a
flash-hook (also known as a “switch hook flash”). On receipt of the
flash-hook, the switch normally gives a second dialtone, allowing Avaya
Modular Messaging to place an enquiry call. The MAS can then dial
another number and transfer the call (by hanging up). Depending on the
switch type, the switch reconnects Avaya Modular Messaging to the caller
if the inquiry call clears or fails.
Analog with DTMF call-progress signaling
Using standard tones, such as ring-back and busy, to convey call progress
can be imprecise and slow. For example, when an MAS dials an outbound
call and detects when the call is answered, it must to go off-hook, wait for
a dialtone, and then dial the number. At this point, it detects one of the
following standard tones: ring-back, busy, speech, or silence. It can take
some time to detect the standard tone, particularly if detection is inferred
by the absence of other tones. However, when using DTMF tones the
MAS can quickly and accurately detect call progress.