Telecom n00b here, veteran software engineer. If there is another stackexchange that is more appropriate for this question, lmk.
I've built an interactive SMS based app in Nodejs that functions entirely via SMS with users. I'm currently using a single GSM modem connected to my test server via USB to send and receive SMS, but I understand there are throughput limitations with this model and it will not be scalable. It seems like, depending on the modem, signal strength and whether the message is sent via GPRS or basic SMS, you can expect 5-30 messages per minute. Messages containing emojis are required for this app, which I understand can change / complicate things as the message encoding changes.
I would like to understand how to send SMS directly from my own server without using a GSM modem or a third party gateway like Twilio, if it's possible.
I've read a bit about SMSCs, SMPP servers, 10dlc and short code provisioning, etc in the last weeks, but I'm still struggling to understand how this all comes together. I've been researching Kannel and Jasmin SMS and still don't really understand what they are for exactly. There is also SO much SEO optimized content from SMS gateways that it's difficult to find any actual neutral information.
Carrier specific email -> SMS gateways don't seem viable. I tested with these and encountered too many issues with deliverability, lag, messages arriving with incorrect replyTo addresses, black box spam filters etc.
Looking for wisdom from a a developer who is well versed in telecom infrastructure who can shine some light on this stuff. Basically I'm looking at companies like Twilio and thinking ... they are able to rapidly provision phone numbers and send messages at a rate of 100-6000 messages per minute. I want to know how this works exactly. I assume they're not using banks of GSM modems and possibly have some direct arrangement with mobile carriers. There are SO many of these companies that it can't be THAT complicated to arrange.
Is there a way that a small app developer can set up relationships with mobile carriers to send messages directly through the carriers? Or is there something that I'm missing about how to send SMS directly from a server to mobile phones without an intermediary like Twilio?
Banging my head against telecom architecture and trying to understand how a company like Twilio sends messages from servers to mobile phones.