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. |
More than one SIM¶
A gateway with several SIMs connects to AstraDial as one line with several channels, one per SIM. Each SIM keeps its own number:
- Incoming: a call to any SIM's number arrives in AstraDial as that number. Each number can ring a different person, team or menu.
- Outgoing: choose which number a user calls out on. Their calls leave on that SIM, so the person you call sees that number.
- Everyone else keeps calling out on your main line, as before.
| SIM | Number | Rings | Calls out for |
|---|---|---|---|
| 1 | 98XXXXXX01 |
Reception | Front desk |
| 2 | 98XXXXXX02 |
Sales team | Sales staff |
| 3 | 98XXXXXX03 |
Support menu | Support lead |
Example layout. You decide the routing for each number.
Each SIM is still one call at a time
While one of your staff is on SIM 2, a caller to SIM 2's number gets busy. Give each SIM's outgoing number to only the few people who need it.
5a. Step by step: set up a SIM from scratch¶
Read this first: the story in one picture
Think of the gateway as a post office. Each SIM is a mailbox with a phone number on it. AstraDial is the sorting office that delivers calls to your staff.
Our job is to give every mailbox the right label, so calls go to and from the right box.
The 4 jobs¶
| Job | What it means | Where you do it | How often |
|---|---|---|---|
| Job 1 | Connect the gateway to AstraDial | AstraDial and gateway | Once, for a new gateway |
| Job 2 | Put a SIM in and find its number | Gateway | Every new SIM |
| Job 3 | Give the SIM its two labels | Gateway | Every new SIM |
| Job 4 | Tell AstraDial about the number | AstraDial | Every new SIM |
Already have a working gateway and just adding a SIM? Skip Job 1.
How to read the step tables:
| Column | Means |
|---|---|
| Where | The page you should be on |
| Do | What to click or type |
| You'll see | How you know it worked |
Values in <angle brackets> are yours to fill in. Your SIM number is always 10 digits, like 98XXXXXX02, with no +91, no 0 and no spaces.
You will need:
- The gateway on your network, and its admin page open (
https://+ its IP address) - An admin login to the AstraDial dashboard
- The SIM: active, with balance, not PIN-locked
- A mobile phone for testing
Job 1. Connect the gateway to AstraDial (once)¶
The gateway has to log in to AstraDial, like you log in to an app. AstraDial makes the login; the gateway types it in.
Step 1.1: make the line in AstraDial
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Trunks | Click Add Trunk | A form opens |
| Name | Type <your company>-gsm |
|
| Host | Leave empty | |
| Transport | Choose UDP | |
| Type | Choose Inbound | |
| Username | Type any label, e.g. <your company>_gsm |
|
| Password | Click Generate | A long password appears |
| Max Channels | Type how many SIMs you have | |
| Outbound prefix | Leave empty | |
| Click Save | Your line is in the list |
Why Inbound, when we want both directions?
"Inbound" only means the gateway logs in to us. One line carries calls both ways.
Step 1.2: get the login
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Trunks | On your line, click ⋯ → View credentials | A box with Server, Port, Transport, SIP User ID, Password |
| Keep this box open. You copy from it next. |
Use the SIP User ID, not the name you typed
The SIP User ID is the long one AstraDial made. The Username you typed in Step 1.1 is only a label. Using it gives "401 Unauthorized", which looks just like a wrong password.
Step 1.3: tell the gateway where AstraDial is
| Where | Do | You'll see |
|---|---|---|
| Gateway → Call Configuration → SIP Configuration | The SIP settings page | |
| SIP Server Address | Copy Server from the box | |
| SIP Server Port | Copy Port from the box | |
| Check Net Status | Choose No | |
| All Ports Register Used Same User ID | Choose Yes | |
| Click Save |
Check Net Status must be No
With Yes, the gateway knocks on our door every few seconds with a fake name. Our security thinks it is an attack and blocks your whole office internet address, gateway and all.
Step 1.4: type the login into the first port
| Where | Do | You'll see |
|---|---|---|
| Gateway → Call Configuration → Port Configuration | Use the port 0 row only | |
| SIP User ID | Copy SIP User ID from the box | |
| Authenticate ID | Copy SIP User ID again (same value) | |
| Authenticate Password | Copy Password from the box | Dots |
| Register to | Choose Sip Proxy | |
| To VOIP Hotline | Type the number of the SIM in port 0 (Job 2 shows how to find it) | |
| Click Save | ||
| Gateway → Tools → Restart | Restart the gateway | Wait about 2 minutes |
Paste, then check the end of the box
The SIP User ID is long and the box is short. After pasting, click into it and press End. The last digits must match the View credentials box.
Step 1.5: check the login worked
| Where | Do | You'll see |
|---|---|---|
| Gateway → System Information → SIP Information | Look at the ports | Registered |
| AstraDial → Trunks | Look at your line | Registration: Reachable |
| Gateway → Call Configuration → Tel->IP Routing | Look at the list | A rule 63 default · Port Group-0 → SIP Server. It came with the gateway. Leave it. |
Not Registered? Check the Server, Port and the full SIP User ID first. If they're all right, turn off SIP ALG on your office router: it scrambles phone traffic.
Job 2. Put a SIM in and find its number¶
Step 2.1: put the SIM in
Turning the gateway off drops every SIM
While it is off, all your GSM numbers are down. Pick a quiet time and tell your team first.
| Where | Do | You'll see |
|---|---|---|
| Gateway → System Information | Find a port that says No SIM Card. Write its number down. | |
| At the gateway | Turn it off | Lights go out |
| At the gateway | Screw the antenna onto that port, finger-tight, away from metal | |
| At the gateway | Push the SIM into that port until it clicks | |
| At the gateway | Turn it on and wait 2 minutes | |
| Gateway → System Information → Mobile Information | Find your port's row | Mobile Registered + an operator name + signal bars |
Look at the signal bars
1 bar = calls may sound bad. Move the antenna (away from metal, nearer a window) before you carry on. Also check your old SIMs say Mobile Registered again after the restart.
Step 2.2: find the SIM's number
The gateway doesn't know the phone number, so we ask the mobile network.
| Where | Do | You'll see |
|---|---|---|
| Gateway → SMS and USSD → USSD | Tick your port's row | |
| USSD Request | Type your operator's "my number" code, e.g. *282# on Airtel |
|
| Click Send, then Auto Refresh | ||
| USSD Reply | Wait a few seconds | "Your Mobile no. is: 98XXXXXX02" |
No luck? Use SMS and USSD → Send SMS: send any text from that port to your own mobile. The number it comes from is the SIM's number.
Balance matters
A SIM with no balance still gets calls but can't make them. The same code often shows the balance.
Write it in your table:
| Port | SIM number | Rings who? | Who calls out on it? |
|---|---|---|---|
<port> |
<SIM number> |
<person / team / menu> |
<users> |
Job 3. Give the SIM its two labels (on the gateway)¶
Every SIM needs two labels. One is for calls going out, one for calls coming in.
| Label | Page on the gateway | The number goes in… | The port goes in… |
|---|---|---|---|
| A: outgoing | IP->Tel Routing | Source Prefix | Destination |
| B: incoming | Tel->IP Routing | Prefix to Add | Source |
The two pages look the same, but the boxes swap
On IP->Tel the number goes in Source Prefix. On Tel->IP it goes in Prefix to Add. Mixing them up is the most common mistake.
Step 3.1: Label A, outgoing (every SIM, port 0 too)
| Where | Do | You'll see |
|---|---|---|
| Gateway → Call Configuration → IP->Tel Routing | Click Add | A form |
| Index | Pick a number lower than 63. Easiest: the port number. | |
| Description | Type SIM<port>-<SIM number> (just a name tag) |
|
| Source | SIP Server | |
| Destination | Your port, e.g. port-2 | |
| Call Restriction | Allow Call | |
| Click Advanced Rules | More boxes appear | |
| Source Prefix | Type the SIM number | |
| Every other box | Leave empty | |
| Click Save | Your rule is in the list, and 63 default is still at the bottom |
Step 3.2: Label B, incoming (port 1 and above)
Port 0 already got its number in Step 1.4 (To VOIP Hotline). For every other port:
| Where | Do | You'll see |
|---|---|---|
| Gateway → Call Configuration → Tel->IP Routing | Click Add | A form |
| Index | Lower than 63, e.g. the port number | |
| Description | SIM<port>-<SIM number> |
|
| Source | Your port, e.g. port-2. Not Port Group-0! | |
| Destination | SIP Server | |
| Call Restriction | Allow Call | |
| Click Advanced Rules | More boxes appear | |
| Prefix to Add | Type the SIM number | |
| Source Prefix and every other box | Leave empty | |
| Click Save | Source column reads Port-2, and 63 default is still at the bottom |
Never choose Port Group-0 for Label B
Port Group-0 means all ports. The label would stick on every SIM, and your first number would stop working.
Why not type the number in Port Configuration?
When all ports share one login (Step 1.3), the boxes for port 1 and above in Port Configuration are greyed out. That's normal, and Label B does the same job. Don't change Register to on those rows.
Check your two lists. With 4 SIMs they should look like this:
| IP->Tel (Label A) | Tel->IP (Label B) | ||
|---|---|---|---|
| Index · Destination | Source Prefix | Index · Source | Prefix to Add |
| 0 · port-0 | SIM 1 number | (port 0 uses To VOIP Hotline) | |
| 1 · port-1 | SIM 2 number | 1 · Port-1 | SIM 2 number |
| 2 · port-2 | SIM 3 number | 2 · Port-2 | SIM 3 number |
| 3 · port-3 | SIM 4 number | 3 · Port-3 | SIM 4 number |
| 63 · Port Group-0 | — | 63 · Port Group-0 | — |
Job 4. Tell AstraDial about the number¶
Step 4.1: add the number
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Phone Numbers | Click Add Custom Number (not "Buy a Number") | A form |
| Number | The SIM number | |
| Trunk | Your gateway line from Step 1.1 | |
| Description | A name, e.g. SIM 2 |
|
| Routing | Who it rings: a person, a team or a menu | |
| Click Save | The number shows as active |
Only your first number has a Default badge. The others don't need one.
Step 4.2: count the SIMs
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Trunks | On your line: ⋯ → Edit | |
| Max Channels | How many SIMs are in the gateway now | |
| Click Save | Channels shows the new number |
Step 4.3: choose who calls out on this SIM
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Users | Open a person → Edit | |
| Outbound Caller ID | Choose the SIM number | |
| Click Save |
Keep it to a few people per SIM: one SIM carries one call at a time. Anyone you don't change keeps calling out on your main line, as before.
Step 4.4: switch it all on
| Where | Do | You'll see |
|---|---|---|
| AstraDial → Settings → Asterisk Configuration | Click Deploy Config | Wait until it finishes |
| Click Reload Asterisk | A success message |
Both buttons, in that order
Deploy Config writes the changes. Reload Asterisk switches them on. Skip Reload and calls to the new number go nowhere. Reload does not cut calls in progress.
Test it¶
Before you test, set the person the number rings to Available, not on break. Otherwise it won't ring even when everything is right.
| Test | Do | Should happen |
|---|---|---|
| Incoming | From a mobile, call the SIM number | It rings who you chose in Step 4.1 |
| Outgoing | As a user from Step 4.3, call a mobile | The mobile shows that SIM's number |
| Old SIMs | Call your first number | Still rings, same as before |
| Two at once | Two users on different SIMs call out together | Both connect |
Something wrong?
| What happens | Most likely cause | Fix |
|---|---|---|
| Mobile hears ringing, nothing rings in AstraDial | Reload Asterisk skipped, or the person is on break | Step 4.4, set Available |
| Rings nowhere for one new number | Label B missing, or the number typed differently in Step 3.2 and Step 4.1 | Compare the digits |
| Mobile shows the wrong number | Label A missing, or the wrong port picked | Step 3.1 |
| Outgoing fails on one SIM only | No balance, or weak signal on that port | Recharge, move the antenna |
| Your first number stopped working | A Label B rule uses Port Group-0 | Change it to the single port |
| Gateway shows not Registered | Login typed wrong or cut off, or Check Net Status = Yes | Steps 1.3 and 1.4 |
Stuck? Send us a screenshot of the IP->Tel list, the Tel->IP list, and AstraDial's Phone Numbers page. Never send passwords.
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 map that port to its number on the gateway, add the number in AstraDial and raise the channel limit. Tell us where it should ring and who should call out on it. Nothing already working is disturbed, and no new line or account is needed.
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. Instead, choose per user: anyone whose outgoing number is a SIM's number calls out on that SIM, and everyone else stays on your main line.
Does each SIM keep its own number when calling out?
Yes. Mobile networks always show the SIM's own number, so we send each call out on the SIM that owns the number you chose. See More than one SIM.
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