Simplified Message Desk Interface

Simplified Message Desk Interface (SMDI) is a protocol that defines the interface between a voice mail system and a phone system such as a PBX or Public Telephone Switch. 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.

Some of the more recent voicemail systems transmit the SMDI protocol over a network TCP/IP session rather than a serial interface.

The current requirements are provided in Telcordia Technologies Generic Requirements document GR-283-CORE^[1] (legacy document TR-NWT-000283). ^[2]

According to Telcordia GR-283-CORE, the Simplified Message Desk Interface (SMDI) is an analog interface between the local Stored Program Controlled Switching System (SPCS) and a Message Storage and Retrieval (MSR) System. Calls are distributed to the call answering points with normal call processing or using Multiline Hunt Group (MLHG) features. One or more MLHGs may be associated with the same set of SMDI data links. An identification scheme is assigned in the SPCS to uniquely identify each MLHG and each line in the MLHG, for which call information (e.g., calling number) is provided over the SMDI data link. This identification information is provided to the MSR System, with the call information, to help the MSR System correlate the call information with a call terminating to a particular line.

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, U equals Unknown)

<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)

Simplified Message Desk Interface

References

External links

See also