Grandstream UCM6304A 4 FXO 4 FXS Audio PBX Service - Products

Frequently Asked Questions

My SIP trunks won’t register on the UCM6304A. What should I check first?

Start by confirming the trunk’s account credentials, SIP server address, and registration port are typed exactly as your provider gave you. Next, temporarily disable the PBX’s built-in firewall or any external firewall to rule out blocking, and make sure the UCM’s DNS server is reachable so it can resolve the provider’s domain. If the problem persists, a Toronto-based VoIP support provider can often diagnose registration failures remotely in a few minutes.

I connected an analog phone to an FXS port but there’s no dial tone. Why?

First, try a different phone and a different cable to rule out hardware faults. Then log into the UCM web interface, go to the analog port settings, and confirm the extension assigned to that FXS port is created and enabled. Sometimes a simple reboot of the PBX after making these changes forces the port to start providing voltage correctly.

Calls connect but we get no audio or only one-way audio. How can I fix this?

This is usually a NAT or RTP routing issue. Check that the UCM’s NAT settings match your network—enable ‘Use NAT’ if the PBX sits behind a router, and verify the external IP or STUN configuration. Also confirm your firewall permits the RTP port range (typically 10000-20000 UDP) both inbound and outbound.

The UCM6304A won’t power on at all after I plugged it in.

Make sure you’re using the power adapter that came with the unit and that it’s firmly seated in both the PBX and a known-working outlet. If possible, test the adapter with a voltmeter or try a different compatible DC adapter with the same voltage and polarity. No sign of life may indicate a faulty power brick, not necessarily the PBX itself.

My Grandstream IP phones aren’t pulling their configuration from the UCM. What could be wrong?

Verify the phones are on the same local network segment or VLAN as the PBX, and that DHCP option 66 is pointing to the UCM’s IP address, or check that multicast ‘Auto Discover’ is enabled on both the phones and the UCM. On the phone’s LCD, look for a provisioning status message; a timeout often means the phone can’t reach the PBX’s HTTPS provisioning port.

Remote workers can’t use the Wave app to join our UCM system.

First, ensure the UCM’s remote access service is turned on and that your office router forwards the required ports (typically 5060 UDP for SIP and a range for RTP, as well as the Wave service port). If the app connects but drops, enabling the built-in NAT traversal service on the UCM can help remote clients behind restrictive firewalls.

Can I hook up a traditional fax machine to this PBX?

Yes—connect the fax machine to an available FXS port and create a dedicated extension for it. For reliable faxing, disable ECM (Error Correction Mode) on the fax machine and, if your SIP trunk provider supports T.38, enable T.38 fax relay in the trunk settings rather than relying on in-band passthrough.

Does the UCM6304A work with Canadian SIP trunk providers like VoIP.ms or Telnyx?

Absolutely. It’s fully compatible with any standards-based SIP trunk carrier. You’ll configure the trunk with the provider’s specific server address, codec preferences, and registration method; many Canadian providers offer setup guides for Grandstream UCMs that walk through the exact fields.

How do I create a conference bridge that my team can dial into?

In the UCM’s web portal, set up a conference room under the ‘Call Features’ section—assign an extension number, optional password, and participant limit. Team members then dial that extension from any SIP phone or the Wave app to join. The system includes built-in audio conferencing, so no external bridge is needed.

I already have a PoE switch powering my phones. Can the UCM’s PoE ports cause a conflict?

It won’t damage anything, but you may want to avoid double-powering devices. If your LAN port connects from a PoE switch to the UCM’s network port, simply don’t connect a phone to the UCM’s PoE port while that phone is also connected to the switch. Alternatively, disable PoE on the specific UCM port in the PBX’s network settings to prevent confusion.

IP PBX

Grandstream UCM6304A 4 FXO 4 FXS Audio PBX

• The UCM6300 Audio series from Grandstream offers a powerful and scalable unified communication and collaboration solution for businesses. • This IP PBX platform unifies fundamental business communications needs, including voice, instant messaging, voice meetings, audio web meetings, data, analytics, mobility, facility access, intercoms, and more. Key Features: • Supports up to 1500 users • Built-in Instant Messaging (IM), Audio Conferencing & Web Meetings platform that supports access from computers, mobile devices, and SIP endpoints • Free Wave App for easy voice and instant messaging communications using desktops, web, and Android/iOS devices • API available for third-party integrations • Advanced security protection with secure boot, unique certificate, and random default password • Three Gigabit auto-sensing RJ45 network ports with integrated PoE+ and support NAT router • Automated NAT firewall traversal service facilitates secure remote connections • Enhanced reliability with support for Hot Standby High-Availability and local dual deployment Additional Information: • Weight: 2.89 lbs • Dimensions: 14.88 × 8.09 × 2.36 in • Brand: Grandstream • Number of Ports: 4 FXS, 4 FXO

About This Product

The UCM6304A suits a growing small-to-medium business that still depends on a handful of analog phone lines and legacy desk phones, yet wants to modernize with VoIP calling, mobile apps, and web-based conferencing. It’s a pragmatic bridge for offices that aren’t ready to rip out their copper lines but see value in unified communications—especially in older buildings around the GTA where Bell or Rogers analog lines remain common and reliable.

Because it includes four FXO ports for PSTN trunks and four FXS ports for analog devices, this appliance focuses on modest analog integration. It pairs naturally with Grandstream’s own IP phones and the Wave softphone app, creating a mixed environment where a receptionist can keep a traditional analog handset while mobile staff work entirely through their smartphones. The built-in NAT router and automated traversal help remote users connect without complex firewall configurations, though site-to-site VPNs or static IPs still boost stability.

Keep in mind the analog ports are a fixed quantity; if your business needs to connect more than four PSTN lines or more than four analog phones/fax machines, you’ll need additional gateways or a larger model. The 1500-user capacity far exceeds the analog trunk count, so this is best when most users are IP-based and the analog side covers only a few critical endpoints. It can be overkill for a micro-business with two or three people who only need a simple ATA and a softswitch, but it’s underpowered for a call centre that relies on dozens of copper lines or requires heavy inbound failover from multiple carriers.