science

Simplified Message Desk Interface

Simplified Message Desk Interface is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Simplified Message Desk Interface rather than just read about it. In short: 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.

Key takeaways

Simplified Message Desk Interface belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Simplified Message Desk Interface to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Simplified Message Desk Interface from memory before moving on to harder problems.

Reference excerpt

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 with the information it needs to process the call. Each time a call is sent to the voice mail system, a message is sent using SMDI over a serial interface that identifies the line, the type of call, and the calling/called party numbers. The SMDI protocol also specifies a method for turning the message-waiting indicator (MWI) on and off on individual telephones. Some of the more recent voicemail systems transmit the SMDI protocol over a network TCP session rather than a serial interface. The current requirements are provided in the Telcordia Technologies Generic Requirements document GR-283-CORE (legacy document TR-NWT-000283).

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 the 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 identify each MLHG uniquely 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, along with the call information, to help the MSR system correlate the call information with a call terminating on a particular line.

Message format <CR><LF>MDXXXLLLLTYYYYYYY<0x20>ZZZZZZZ<0x20><CR><LF><^Y> Meaning of the individual segments:

<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 for direct call, A for all calls forwarded, B for busy forwarding, U for unknown) <0x20> - space YYYYYYY - called party number (maybe not present, such as for direct calls) ZZZZZZZ - calling party number (CPN) (maybe not present if unavailable) <CR> - carriage return <LF> - line feed <^Y> - end marker, Ctrl-Y, ASCII "EM" Each of the numbers is a common fixed length for each link, such as 5 (extensions), 7 (US PSTN numbers without area code), or 10 (US PSTN numbers) digits, zero-padded on the left where necessary, and terminated with <0x20>. A typical use of the called party number is to select which voicemail greeting to play for the call.

MWI format OP:MWI<0x20>XXXX!<EOT> Meaning of the individual segments:

OP - Operate message-waiting indicator (turn on) <0x20> - space XXXX - extension number <EOT> - end-of-transmission character RMV:MWI<0x20>XXXX!<EOT>

RMV - remove 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). This would be someone calling from their extension to pick up their voicemail and thus would likely ask for sign-on credentials, such as a PIN. <CR><LF>MD0010007D<0x20>3500<0x20><CR><LF><^Y>

See also Session Initiation Protocol Analog Display Services Interface

References

External links Cisco Call Manager Use of SMDI Asterisk, an example open source PBX that supports SMDI A Simplified Message Desk Interface (SMDI) Primer from Dialogic

Worked examples

Example 1 — a first encounter with Simplified Message Desk Interface

Start with the simplest possible case. Write down what Simplified Message Desk Interface claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Simplified Message Desk Interface before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Simplified Message Desk Interface ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Simplified Message Desk Interface

In research: Simplified Message Desk Interface appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Simplified Message Desk Interface in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Simplified Message Desk Interface is common in secondary-school and first-year university syllabi. It links to neighbouring topics Telephony, Voicemail, so understanding it makes those chapters shorter.
In everyday life: Look for Simplified Message Desk Interface outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Simplified Message Desk Interface in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Simplified Message Desk Interface means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Simplified Message Desk Interface out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Simplified Message Desk Interface in simple terms?

Why does Simplified Message Desk Interface matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Simplified Message Desk Interface?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Simplified Message Desk Interface.