DTR-RI control signal simulation

Going off your last question, I'm gonna assume your interest remains centered on homework related to dial-up modems. Now, please bear with me here, this is gonna be off the toppa my head, so I have no idea where its gonna go as I start typing.

DTR is an acronym for "Data Terminal Ready", in modem terms, DSR is an acronym for "Data Set Ready" (as contrasted to an alternate computer-referenced meaning of "Dynamic Source Routing", a networking term). In simplest terms, a "Data Terminal" essentially would be a device configuration for the receipt of data, a "Data Set" a configuration for the transmission of data. DTR and DSR are included within the RS-232 protocol, which originally was established to provide a framework for communication between teletypewriters (TTY) and the modems through which teletypewriter communication was effected.
The RS-232 Protocol essentially defined and standardized the pin allocation and function of devices and the cables which connected those devices. As the RS-232 standard was well established (as ammended in the late '60s to the RS-232-C Protocol), it became the defacto norm for serial communication among electronic data-handling devices - computers.

Naturally, peripherals, such as printers, modems, faxes, scanners, and external drives, adhered to the standard, with the 9-pin DB-9 (originally - though no longer - typically serial - 1 "channel", "half-duplex", allowing for one-way communication at a time, data send and receive functions alternated serially, hence, "Serial" -sorta like a walkie-talkie) and 25-pin DB-25 (typically parallel - 2 "channels", "full-duplex", allowing for simultaneous send-and-receieve of data, send on 1 "channel", receive on the other, more or less side-by-side, hence "Parallel" - more like a telephone). Technologic advances over the years eventually resulted in a a configuration of the formerly one-way-at-a-time serial, "half-duplex" connection to achieve 2-way, "full-duplex" communication, though nominally at a slower data transfer rate than a parallel connection.

The sole function of TTY/RS-232 technology was the input (generally manual, via a keyboard much like that of a typewriter), transmission (generally over commercial telephone circuits, though closed, private networks existed) and display (generally impact-printed via key-and-ribbon onto paper) of text strings over distance. Following WWII, CRT-based electronic terminals increasingly began to accompany, and eventually, through the 1970s, replace, TTY devices.

Since the RS-232 standard was there, it was natural these CRT-based terminals employed it; they were deployed in conjunction with or in lieu of TTY terminals. With the advent of the personal computer, the autonomous-but-network-capable keyboard/monitor/CPU configuration has all but totally replaced TTY terminals except in a very few, narrowly-focused, limited-scope applications. The RS-232 standard pretty much was the cornerstone of the physical architecture of the modern computer and its associated peripherals, internal and external - its input/output devices, control devices, data storage devices, display devices and communications devices - it developed more or less into how all things computer went together.

Anyhow, I ramble - back to DTR-RI Control Signal Simulation

""RI", in modem terms, refers to "Ring Indicator", an electrical control signal which represents an incoming call, causing a telephone or modem annunciator to sound and/or triggering the signalled device (phone or modem) to "answer" the call and begin receiving data. Under the RS-232-C protocol, the Ring Indicator signal's voltage is applied through pin/line/socket #22 in DB-25 configuration, pin/line/socket #9 in DB-9 configuration. A Data Terminal Ready Ring Indicator Control Signal Simulation would amount to a test function which would cause the triggering of the answer (receive data) response of the DTR-configured device without an actual incoming call.

Well - here we are. Is this anywhere close to where you wanted to wind up?

I do admire your love for detail hehe, thanks for all the background, I also believe it has to do with the RI being asserted the moment the DTR is sent to the modem, although I'm not entirely sure if it's that or if it's that the DTR is only asserted once the DCE asserts the ring indicator so the DTE knows someone is on the other side. I assume DTR is always on though so the latter wouldn't be a likely scenario. At either rate I know there is a RI-DTR simulation, a modem called the Omnimode 96 used it, thing is it's very very difficult finding any concrete information on the matter.

So you believe it must be that the DTE asserts DTR, and the modem immediately responds with RI so that the data transmission will begin without need for handshaking? like an unreliable transmission that wants to save time by assuming the network connection is there and the modems are synchronised and ready to stream data?

Yeah, that pretty close to describes my view of it, in that context anyhow. There's still gonna be a handshake/synchronization cycle, though, before data starts streaming, as I recall. The Ring Indicator signal more or less "wakes" the modem, so it can execute the handshake and synchronization functions.

I hafta admit to some "cultural bias" ... my relevant experience was more-or-less from the "Just get the damned thing fixed yesterday" point of view, if you gather my meaning. Been lotsa years since I've "been there, done that", though - pretty hazy recollection of details, and I sure don't have any of the old manuals. A quick websearch indicates some may be available online, mostly in .pdf format. I recognized some titles, but didn't pursue it any further.

Here's a website you might find usefull: ModemHelp-dot-Org. I was a little surprised to see they're still around - they seem to be a fairly busy website, too - a bigger surprise. Lotsa handy links, and plenty of on-site info to chew through, if you're interested.