Grandstream UCM6308A Audio Series IP PBX

The Grandstream UCM6308A is the largest of the UCM6300 audio-series PBXs: up to 1,500 SIP users and 200 concurrent calls, with eight FXS ports, eight FXO ports, nine audio conference rooms for up to 150 parties, and redundant 12V DC power input.

The redundant power input is the specification worth noticing at this size. Everything else on the list is a bigger number; that one is a different kind of feature. A PBX carrying 1,500 extensions is something a business genuinely cannot lose, and a second power feed removes the most common single cause of an outage — one failed power supply.

The A means audio only. The non-A UCM6308 adds video meeting hosting. Since organisations of this size almost always already run Teams, Zoom or Meet, the A is normally the right specification: same voice platform, no duplicate video stack to pay for and support.

Key features

• Up to 1,500 SIP users — extensions registered to the system
• 200 concurrent calls — the figure that actually sizes the platform
• 150 SRTP encrypted calls — note this is lower than the total call figure
• 8 FXO RJ11 ports — connect eight analogue telephone lines
• 8 FXS RJ11 ports — analogue phones, faxes and lifeline connections
• 9 audio conference rooms, up to 150 parties — meetings on your own system
• Redundant 12V DC power input — a second feed against power supply failure
• 1 Gigabit WAN and 1 Gigabit LAN port — separate the trunk side from the LAN
• Call recording, IVR, queues and voicemail — the full business feature set

Works with

• Grandstream UCM6304A — 1,000 users and 4 FXS / 4 FXO ports
• Grandstream UCM6302A — 500 users and 2 FXS / 2 FXO ports
• Grandstream HT881 — add eight more analogue lines separately
• Grandstream GRP2615 — a switchboard phone for reception
• PSU for UCM620x — spare or replacement adapter
• All IP PBX solutions

Frequently asked questions

What does redundant power actually protect against?

A failed power supply, which is the most common single cause of an unplanned outage on hardware like this. Two feeds mean one can fail without the phone system stopping. Put them on different circuits to get the benefit.

1,500 users or 200 calls — which is the real limit?

The 200 concurrent calls. Users are registrations; what sizes a PBX is how many people talk at once. Size against your busiest hour, not your headcount.

Why is the encrypted call figure lower?

Encryption costs processing. The platform handles 200 calls in total but 150 of them encrypted with SRTP. If you intend to encrypt everything, size against 150.

What does the A change?

It removes video meeting hosting. Voice, messaging, audio conferencing, recording, queues and IVR are unaffected.

Do I need all eight analogue ports?

Only if you have eight lines or eight analogue devices to keep. If it is really two lift lines and a fax, the UCM6304A or UCM6302A is the cheaper fit.

Should I plan for a second PBX?

At this size, seriously consider it. Redundant power protects one failure mode; a second system protects the rest. Ask us about high availability before you commit.

Specifying a phone system for a large site? Call 0333 242 1314 or email sales@clisecure.com and we will size it against your busiest hour and your resilience requirements.