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:MWI<0x20>XXXX!<EOT>
OP Operate Message Waiting Indicator (Turn On) <0x20> Space XXXX Extension Number <EOT> End of Transmission
OFF: 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, or port 7.
<CR><LF>MD0010007D<0x20>3500<0x20><CR><LF><^Y>