GSM Gateway¶
For: sites using mobile SIMs as their phone lines.
- A GSM gateway holds the SIM cards and presents each one to AstraDial as an ordinary line.
- Calls ring in the AstraDial app and are logged and recorded like any other line.
Values we will supply
Fields shown as <...> are issued by AstraDial. Credentials are sent separately, over a secure channel.
1. What gets connected¶
The gateway registers outbound to AstraDial, the same way a mobile phone registers to its network. Nothing is opened on your firewall and no public IP is needed.
2. What you need to provide¶
| Item | Requirement |
|---|---|
| GSM gateway | SIP-capable. One SIM = one call at a time, so pick the channel count to match. We have deployed Dinstar gateways and can recommend a model. |
| SIM cards | One per channel, on a plan with enough voice minutes. Data is not required. |
| Signal | Good signal, antennas clear of metal. Poor signal is the most common cause of bad audio. |
| Network | Wired ethernet on your LAN, with a reserved (static) IP so it does not change on reboot. |
| Power | A UPS is recommended. If the gateway is off, those lines are down. |
| Remote access | So we can configure and support it without a site visit. |
3. How the work goes¶
- SIMs in, gateway on the LAN. Antenna on every port that will hold a SIM, SIMs in, one Ethernet cable to your LAN switch.
- Give it a fixed IP that will not change on reboot, and tell us what it is.
- You give us access. Remote access to the gateway's admin page, so we can configure and support it without a site visit.
- We configure it. We point it at AstraDial, set the credentials, and map each SIM to a line — see What we set on the gateway.
- We confirm it is registered. The step that matters — see the warning below.
- Numbers. Each SIM's mobile number becomes a line you can route to a person, a team or a menu. See Add a number.
- We test with you. Details in Testing.
Registration is the whole game
The gateway has no fixed address — it registers outbound to AstraDial, like a mobile phone registering to its network.
If that registration drops, the gateway is invisible to us. Incoming calls have nowhere to go and outgoing calls cannot use it, however the routing is configured. It drops when the gateway is:
- powered off
- unplugged from the LAN
- given a different IP address
A previous deployment sat ready-to-go for weeks, everything else correct, waiting on exactly this.
4. What we set on the gateway¶
For your IT's information — we normally apply these ourselves.
| Setting | Value | Why |
|---|---|---|
| SIP server / registrar | supplied by AstraDial | Where the gateway registers |
| Registration | On, with the credentials we issue | See the warning above |
| Codec | alaw only | Matches the carrier side; other codecs cause negotiation failures |
| Check Net Status | No | See the warning below |
| Admin UI | HTTPS only | Plain http:// will never load |
Leave \"Check Net Status\" set to No
It sends a SIP probe every few seconds from an address that is not a real account.
Our intrusion protection counts those as failed attempts and blocks your site's entire public IP.
That takes down not just the gateway but every other device on that connection, remote access included.
We have had this happen. Enabling it after we hand over reproduces it.
Can't reach the admin page?
- Use
https://— plainhttp://will never load. - The certificate warning is expected, and safe to accept on your own LAN.
- Both Ethernet sockets are one bridged switch with a single IP, so either will do.
5. Important limits of GSM lines¶
These are properties of mobile networks, not of AstraDial. Read them before choosing this option.
| Limit | What it means | What to do |
|---|---|---|
| One SIM = one call at a time | An outgoing call makes that line unavailable for incoming calls. | Enough SIMs for your busiest moment, or keep one SIM for outbound. |
| Caller ID is the SIM's own number | Mobile networks do not allow it to be changed. | Need a landline number displayed? Use a SIP Trunk instead. |
| Signal quality is audio quality | A gateway in a metal cabinet or basement sounds poor however it is configured. | Test signal where you plan to mount it, before fixing it in place. |
| Do not share the line widely | A large team competes for one channel, and every call they make closes your published number. | Assign outgoing caller ID to the few who need it. |
| Use a business plan | Operators may treat a consumer SIM making constant business calls as commercial use. | A consumer SIM can be throttled or blocked without warning. |
6. Testing together¶
Have someone with a mobile phone ready. We run these with you:
- Incoming — call each SIM's number from a mobile. Each should ring in AstraDial, with clear audio both ways.
- Outgoing — place a call from AstraDial. Confirm it connects, audio is clear, and the SIM's number shows as the caller ID.
- Every channel — repeat for each SIM, not just the first. Weak signal or a bad SIM usually shows up on one channel only.
- Busy behaviour — with a call in progress, confirm what a second caller to that number hears, so it matches what you want.
7. Frequently asked questions¶
Can we add more SIMs later?
Yes. Fit the antenna, insert the SIM, and tell us the new number — we configure the extra port and raise the channel limit on our side. Nothing already working is disturbed.
How do we find out a SIM's own phone number?
The gateway cannot tell you: it knows the SIM's serial numbers, but the phone number is held by the mobile operator. Send an SMS from that port to your own mobile and read the sender, or use your operator's balance/number USSD code. We can do this during setup.
A port shows the SIM as unregistered. What do we check?
In order: reset that port from the gateway's admin page, then the antenna (fitted, finger-tight, away from metal), then whether the port is powered on, then reseat the SIM. Also confirm the SIM is active, has balance and is not PIN-locked.
The signal columns show 0%.
Those columns are usually call statistics, which stay at zero until calls have run. Signal strength is shown separately as a bar indicator.
Can the gateway be put on a VPN so you can support it remotely?
Not the gateway itself — on these devices a VPN takes over the whole network route, which badly degrades call quality and can break registration altogether. We put remote access on a separate small machine on the same LAN and leave the gateway's own path direct. We will agree the method with your IT.
What happens if the gateway loses power or its IP changes?
Those lines go down until it comes back and re-registers. Nothing is lost permanently, but calls will not arrive in the meantime — which is why we ask for a fixed IP and recommend a UPS.
Can calls be transferred from a GSM line?
Transfers work, but on a single-SIM line the transferred leg cannot use the same SIM — it is already occupied by the call being transferred. It goes out over your organisation's other line instead, so you need one.
Will these calls be recorded and logged like other calls?
Yes. Once the line is connected, GSM calls behave like any other line in AstraDial: call logs, recordings and reporting all work normally.
Can we use a GSM line as a backup for when our main line is busy?
Not automatically — there is no fallback between lines. What we can do is give the GSM line its own dialling prefix, so a user chooses it deliberately when they want it.
8. Before we schedule¶
- GSM gateway make, model and channel count
- How many SIMs, and on which operator
- The mobile numbers on those SIMs
- Where the gateway will be mounted, and signal strength there
- Remote access to the gateway
- A preferred low-traffic window for the changeover
AstraDial — IT and Ops · cats@astradial.com