To set up an FQDN trunk on a Yeastar P-Series PBX, create the trunk the way your operator specifies (register or peer), put the operator’s domain name in Hostname/IP, set the same or operator-supplied value in Domain, choose the transport and port they give you, then configure Public IP (NAT) and forward the SIP and RTP ports. If the PBX can resolve the domain through DNS and NAT is right, the trunk comes up and audio flows both ways.
This guide is for IT administrators and integrators who manage Yeastar P-Series (appliance or software edition). Menu names follow Yeastar’s own administrator guide; check them against your firmware version.
Important in the UAE: the SIP trunk, numbers and lines come from the customer’s own licensed operator (du or e&). SNTECH installs and configures the phone system at the client’s UAE premises and does not provide trunks or calling services.
What an FQDN SIP trunk is, and why use a domain instead of an IP
An FQDN (fully qualified domain name) trunk points the PBX at a name such as sip.provider.example rather than a fixed IP address. The PBX looks the name up in DNS when it connects.
- Fewer outages after operator changes: if the operator moves or adds servers, the DNS record changes and your trunk follows.
- Cleaner SIP headers: some operators expect their domain in the From and To headers and reject calls that use a raw IP.
- Required by some services: certain operators only publish a domain, not an IP list.
Before you start: information to collect
| Item | Where it comes from | Notes |
|---|---|---|
| Trunk type (register or peer) | Operator | Register = username and password; peer = trusted by IP or domain |
| Hostname/IP (the FQDN) and port | Operator | Often port 5060 for UDP/TCP |
| Domain for SIP headers | Operator | If none is given, use the same value as Hostname/IP |
| Transport (UDP, TCP or TLS) | Operator | Must match the operator side exactly |
| Username, password, authentication name | Operator (register trunks) | Authentication name is often the account number |
| Public IP or your own PBX domain | Your internet line / DNS | Needed for NAT and for peer trunks |
| Allowed codecs | Operator | Commonly a-law (G.711A) in the UAE region; confirm with the operator |
Also check that the PBX has working DNS servers configured in its network settings. An FQDN trunk cannot come up if the PBX cannot resolve the operator’s domain.
Step-by-step Yeastar P-Series FQDN trunk setup
1. Create the trunk
- Go to the trunk settings in the web interface and add a new SIP trunk.
- Select the Trunk Type your operator gave you: Register Trunk or Peer Trunk.
- In Hostname/IP, enter the operator’s domain (FQDN), not an IP address, and set the Port they specified.
- In Domain, enter the domain the operator wants in the SIP URI. If they did not provide one, enter the same value as Hostname/IP.
- Set Transport to match the operator (UDP, TCP or TLS).
- For a register trunk, fill in Username, Password and Authentication Name. Use Enable Outbound Proxy only if the operator asks for it.
- For a peer trunk, check the From Host Part and To Host Part options so the headers carry the domain the operator expects.
2. Codecs, DTMF and caller ID
- Keep only the codecs the operator supports, in their preferred order. Fewer codecs means fewer negotiation surprises.
- Set DTMF to the operator’s mode (RFC4733 is the usual choice) so IVR menus and voicemail PINs work.
- Set how the PBX reads the DID from incoming calls, and the outbound caller ID, to match the numbers on your account.
Configure NAT and ports so audio works both ways
Most FQDN trunk problems are not the trunk at all: they are NAT. In Yeastar’s guide this is under System > Network > Public IP and Ports:
- Enable Public IP (NAT).
- Set NAT Type to your public IP, or to External Host with your own PBX domain if you have one.
- Add every internal subnet under Local Network Identification.
- Set NAT Mode as described in the guide so the PBX ignores private addresses inside SIP/SDP.
On the router or firewall, forward the SIP port and the RTP range to the PBX. Yeastar’s example uses SIP UDP 5060 and RTP 10000–12000; use the values shown on your own PBX.
Field note: FortiGate and SIP ALG
In UAE offices we often find a FortiGate in front of the PBX. Its SIP helper/ALG rewrites SIP packets and is a common cause of one-way audio, failed registrations and calls dropping after about 30 seconds. On FortiGate this is changed from the CLI (the VoIP ALG mode and the SIP session helper); follow Fortinet’s documentation for your FortiOS version, then reboot or clear sessions so the change takes effect.
Lock down the SIP port
Never leave port 5060 open to the whole internet. Allow SIP only from the operator’s published IP ranges, keep the PBX’s security features on, and use strong extension passwords. Exposed SIP ports attract automated scanning within hours.
Test the trunk: a 5-minute checklist
- Check the trunk status on the trunk list (a register trunk should show as registered).
- Make an outbound call to a mobile and confirm the caller ID shown.
- Call your DID from a mobile and confirm it reaches the right inbound route.
- Talk for over a minute in both directions: one-way audio or a drop at ~30 seconds points to NAT or SIP ALG.
- Press keys in an IVR to confirm DTMF works.
Common FQDN trunk errors and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| Trunk never registers | DNS not resolving, wrong port or transport | Check PBX DNS servers, then port and transport against the operator’s sheet |
| Registers, but calls are rejected | Wrong Domain or From header | Set Domain (and From Host Part on peer trunks) exactly as the operator requires |
| One-way or no audio | NAT or RTP ports | Enable Public IP (NAT), add local networks, forward RTP, disable SIP ALG |
| Calls drop after ~30 seconds | SIP ALG or NAT on the firewall | Disable SIP ALG; check the public address the PBX advertises |
| Trunk drops after operator maintenance | Old IP still in use | Make sure Hostname/IP holds the FQDN, not an IP |
Frequently asked questions
What is an FQDN trunk on Yeastar P-Series?
A SIP trunk where Hostname/IP contains your operator’s domain name instead of a fixed IP address, so the PBX follows DNS when servers change.
Should I use a register trunk or a peer trunk?
Use the type your operator specifies. Both accept a domain name in Hostname/IP.
What do I put in the Domain field?
The domain your operator wants in the SIP headers. If none is given, enter the same value as Hostname/IP.
Why do I get one-way audio?
Usually NAT: enable Public IP (NAT), add local networks, forward the RTP range and switch off SIP ALG.
Does SNTECH provide the SIP trunk?
No. The trunk and numbers come from your own licensed UAE operator (du or e&). We configure the PBX at your premises to use them.
Need help?
SNTECH has 8 years of hands-on experience with Yeastar, 3CX and Grandstream systems in the UAE. If your trunk will not register, audio is one-way, or you are moving to a new operator, we can configure and test it for you. See our Yeastar PBX service, IP PBX installation and networking and FortiGate support, or WhatsApp us on +971 56 669 8244.