Simplified Message Desk Interface
Simplified Message Desk Interface (SMDI) is a protocol that defines the interface between a phone system and a voice mail system. It was developed by Bell Labs. It is used to provide the voice mail system the information it needs to process the call. Each time a call is sent to the voice mail a message is sent using SMDI over a serial interface that identifies the line, the type of call and Calling/Called party numbers. The SMDI protocol also specifies a method for turning Message Waiting Indication (MWI) on and off on individual telephone lines.
Message Format
<CR><LF>MDXXXLLLLT<0x20>YYYY<0x20><CR><LF><^Y>
<CR> Carriage Return
<LF> Line Feed
MDXXX Message Desk. This is a 3 digit field (usually 001)
LLLL Logical Terminal Number (0001 - 4096)
T Reason Code (D equals Direct Call, A equals All Calls Forwarded, B equals Busy Call)
<0x20> Space
YYYY Calling Party Number
<CR> Carriage Return
<LF> Line Feed
<^Y> End
MWI Format
OP Operate Message Waiting Indicator (Turn On)
OP:MWI<0x20>XXXX!<EOT>
<0x20> Space
XXXX Extension Number
<EOT> End of Transmission
RMV:MWI<0x20>XXXX!<EOT>
RMV Operate Message Waiting Indicator (Turn Off)
<0x20> Space
XXXX Extension Number
<EOT> End of Transmission
Example
This is an example of a direct call from extension 3500. It was presented to the voice messaging system on LTN 0007 (port 7)
<CR><LF>MD0010007D<0x20>3500<0x20><CR><LF><^Y>