An SMS gateway is the system between your application and the mobile networks. It accepts messages from software — over an HTTP API or SMPP — works out which network each recipient is on, submits the message over a carrier connection, and collects the delivery receipt. Ontech BulkSMS is an SMS gateway with direct connections to MTN, Airtel and Zamtel in Zambia.
Why a gateway exists
A mobile network does not accept messages from arbitrary software. It accepts them from a connected party over an SMPP link, with agreed sender IDs and throughput, and it reports delivery back over the same link. Setting that up per network, keeping the sessions alive, handling receipts and routing is a full-time job, which is why applications use a gateway: one integration, one account, one place to see what was delivered.
What happens inside the gateway
- Ingress. A message arrives from the web console, the mobile app, the HTTP/JSON API or an SMPP bind, and is authenticated to an account.
- Validation. The number is normalised to international form and checked as Zambian; the account's blacklist is applied; the sender ID is checked against those approved for the account; the credit cost is calculated from the message length and encoding (160 GSM-7 characters or 70 Unicode characters per segment) and reserved.
- Queueing. The message is written to an outbox with a message ID and returned to the caller. Sends are paced per carrier connection so bursts from one account do not starve another.
- Routing. The recipient's number prefix decides the network — Zambian ranges are allocated to MTN, Airtel and Zamtel — and the message is submitted over that network's SMPP connection with the account's sender ID.
- Receipts. The network returns a delivery receipt when it has a final result. The gateway matches it to the message ID and stores the state, then makes it available in the dashboard, on the status endpoint, on the account's callback URL, and to any SMPP receiver bind.
- Inbound. Messages from handsets to the gateway's short code or long numbers are attributed to an account by keyword or reply window and delivered to its inbox or SMPP session.
A2P messaging and sender identity
A2P (application-to-person) is the class of traffic a gateway carries: messages from software to people. Unlike a text from a SIM, an A2P message can carry an alphanumeric sender ID — a company name of up to 11 characters — because the gateway submits it on the account's behalf over its carrier connection. That is also why sender IDs are approved: the gateway is responsible to the networks for what is sent under each name, so an authorization letter is required before a name is used.
Interfaces into the gateway
| Interface | Best for | Notes |
|---|---|---|
| Web console | Staff sending campaigns, uploads and scheduled messages | No integration needed; personalised preview and cost before sending |
| Android app | Field teams and small businesses | Quick sends, campaigns, contacts, mobile money top-ups |
| HTTP / JSON API | Applications sending event-driven messages | Simple requests; 60 per minute; batch via JSON |
| SMPP 3.4 | High-volume, low-latency systems (banks, platforms) | Persistent bind; receipts and inbound on the same session; per-credential TPS |
Delivery receipts
A gateway is only as useful as its reporting. Every message through Ontech BulkSMS has a delivery state — delivered, failed, rejected, queued, submitted — that comes from the network, not from the gateway's own guess. Final states can lag a send by minutes or longer when a handset is unreachable and the network is retrying. The delivery reports guide covers each state and how to collect them.
Gateway versus aggregator versus SMSC
- SMSC (Short Message Service Centre) is the network's own store-and-forward element. The gateway connects to it.
- Aggregator is a gateway operator that resells connectivity to many networks, often across countries. Ontech BulkSMS is an aggregator for the Zambian networks, with direct connections rather than onward routes through third parties.
- Gateway is the software and service that exposes those connections to applications through an API, SMPP and a console — with billing, sender IDs, reporting and inbound handling on top.
Security and accountability
- API keys are restricted to whitelisted IP addresses; SMPP binds are gated by the same whitelist.
- Every API request and every message is logged against the account with its outcome.
- Sender IDs are approved on documentation and only approved names can be used.
- Opt-out blacklists are enforced by the gateway on every send, whichever interface the message came in on.
- Ontech Solutions Limited is registered with Zambia's Data Protection Commission (DP000394); the Privacy notice describes how message data is handled.