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5.1 Guidelines for Inband Integration
Installation Manual 153
Following are the minimum current and voltages that the PBX must supply:
DTMF Signalling
For system users to access VPS services and features, they must be able to send DTMF signals from
their telephones to the VPS port. As a general rule, most SLTs can send DTMF signals; however,
many proprietary telephones cannot. Some PBXs need to be programmed to make proprietary
telephones use DTMF signalling.
Message Waiting Notification on an SLT
When the Message-Waiting-Lamp-On code is dialled by the VPS, either the lamp on the
corresponding extension should light or the extension should receive a stutter dial tone. The VPS
functions best when the extension number of the mailbox subscriber follows the Light-On or Light-Off
code. On some PBXs, however, the extension number is dialled first, followed by a hookswitch flash
and then the On code. This presents a problem if the extension is answered before the VPS sends
the hook-switch flash.
If the PBX does not provide Message Waiting Notification on an SLT, the VPS can only notify
mailbox owners by dialling a beeper number or user-assigned extension.
This process slows down VPS performance as it dials the beeper or extension number and waits to
confirm notification. The beeper or user-assigned extension notification is meant to be used for
necessity, usually for mailbox owners who are often out of the office (e.g., sales people or field
representatives). The only other option, without Message Waiting Notification is for mailbox owners
to periodically call the VPS to check for messages.
Screened Transfer from an SLT
The PBX must provide a screened transfer from an SLT for the VPS to function properly.
A screened transfer:
1. Puts the caller on hold, usually with a hookswitch flash.
2. Dials the extension.
Minimum Loop Current 20 mA
Minimum Line Voltage 7 V DC
Minimum Ringing Voltage 40 V AC
TEST: Call an SLT extension from the telephone in question. When the call
is answered, see if the person receiving the call hears DTMF tones when
numbers are dialled.
TEST: See if dialling the On code from an SLT can turn on an extension's
message waiting indicator.