TAPI, How it connects to modem and phone line

Question

TAPI, How it connects to modem and phone line

Ed Bitzer 6

My question is about TAPI and how it connects through my modem to my telephone line but fear I am in the wrong place – if so please push me in the right direction.

Very old guy retired guy that still writes an occasional visual basic utility or modifies old utilities written years ago. Was brought up with Com ports and wrote an early dialer utility by providing the necessary variables to the SerialPort Control finishing with sending the ATCT string. A search here for “TAPI” had one hit this year about using and the response was to use an API. I just modified my old visual basic coded dialer using the COM port with the Lib “TAPI32.dll’s function tapiRequestMakeCall. This took a single line to send the phone number and works fine. But I do not understand how TAPI connects via what ports. Any help here?

Ed

Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2021-11-22T07:04:09.513+00:00

Have you seen the diagram?
Anonymous

2021-12-08T05:59:05.667+00:00

@Ed Bitzer Any updates about your issue? Does JunjieZhu 's reply make sense? If he helps you solve your issue, you could accept his reply as answer.

2 answers

Your answer

Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2021-11-22T07:04:09.513+00:00

Have you seen the diagram?
Anonymous

2021-12-08T05:59:05.667+00:00

@Ed Bitzer Any updates about your issue? Does JunjieZhu 's reply make sense? If he helps you solve your issue, you could accept his reply as answer.

Answer 1

Hello,
Welcome to Microsoft Q&A!

How TAPI works and connects to the device is explained in the documentation of Microsoft Telephony Programming Model. The process and schematic diagram are shown below.

An application loads the TAPI DLL into its process space and uses TAPI to communicate needs.
TAPI establishes an RPC link communications with the TAPI Server.
In addition, TAPI 3.x creates an MSP object and communicates with it using a defined set of commands, the Media Service Provider Interface (MSPI).
When an application calls a TAPI operation, the TAPI dynamic-link library validates and marshals the parameters, then forwards the information to TAPISRV.
TAPISRV tracks communications resources available to the local machine and interfaces with the Telephony Service Providers (TSPs) using the Telephony Service Provider Interface (TSPI).
Communications between a TSP and an MSP take place using a virtual connection that passes through the TAPI DLL and TAPISRV.
The TSP/MSP pair supplies information on device state and capabilities and implements the specific commands required for a desired response.

Thank you.

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Answer 2

Ed Bitzer 6

Sorry I am slow in responding. My fundamentals are weak and I spent several hours this morning reading to better understand the very thorough response by JunjieZhu.

The fundamentals may never be achieved at this age but I believe clarification on the link between the Telephone Service Provider (TSP) and Device would help. May I assume the Device in the schematic diagram is my modem, a USB 56K External Dial Up Fax Data Modem and the line connecting to the TSP is the port? If so can I identify that process name and port? I am comfortable with Device Manager and several SysInternals utilities that monitor ports.

Ed

Junjie Zhu - MSFT 21,746

Yes, the Device in the schematic diagram is your modem, and you can use the LineGetID function to get the modem identifier. Here's an example for your reference.

VARSTRING* vs;  
LONG lrc;  
DWORD dwSize;  
vs = (VARSTRING*)calloc(1, sizeof(VARSTRING));  
vs->dwTotalSize = sizeof(VARSTRING);  
do {  
        lrc = ::lineGetID(m_hLine, 0, NULL, LINECALLSELECT_LINE, vs, "comm/datamodem");  
        if (lrc) { free(vs); return lrc; }  
        if (vs->dwTotalSize < vs->dwNeededSize)  
        {  
              dwSize = vs->dwNeededSize;  
              free(vs);  
              vs = (VARSTRING*)calloc(1, dwSize);  
              vs->dwTotalSize = dwSize;  
              continue;  
         } /* end if (need more space) */  
         break; /* success */  
} while (TRUE);

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TAPI, How it connects to modem and phone line

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