Issue ringing multiple phones at once



I have 5 DP720 handsets hanging off a DP750 base unit, each with their own SIP account and corresponding outgoing line setting for outgoing calls (only 1 line assigned per handset) and each sip account set to HS1, HS2, etc for incoming calls.

On incoming calls our Asterisk 13.8 server attempts to ring all 5 handsets at once using the Dial application.

For some reason, it only rings a random selection of 3 out of the 5 DP720 handsets at once (should ring all 5). The random selection of 3 varies each time and the other two just don’t ring.

I also get SIP retransmission timeouts when this happens.

I suspect this is a hardware limitation of the DP750 base unit, even though it can supposedly support 5 simultaneous calls.

All handsets were reset to factory defaults and the issue persists. They are running the latest firmware

two out of the 5 handsets are running a different hardware revision (1.6A instead of 1.8A for the other 3 handsets).

Can anyone shed light on this?

Is there a way to allocate an incoming call to just two of the handsets for one SIP account? I suspect reducing the number of SIP accounts to 3 might work around this also.


DP750 support ring 5 handset at the same time without issue.
Could you please confirm your settings at -> DECT -> Handset Account Settings, if you have assigned the account HS Mode to parallel mode?
Then please confirm DECT -> Handset Line Settings, if you have assigned the parallel account to all 5 handsets.
If you want still get incoming call when one of your handset is in call, please enable “Enable Call Waiting in Parallel Mode” at Profile x -> Call Settings


Hello, Shawn: I did setup per your recommendation but still does not ring 2 handsets the package captured showed me that error 486? Could you please follow up?

Looking forward to hearing from you
Thank you


Hi, I am experiencing this issue on DP750 firmware version Just to be clear, each handset has a unique SIP account. The SIP PBX (3CX in our case) sends calls to multiple numbers simultaneously as all of the extensions are in a ring group. When this happens, if the call originates from outside the DP750, then three of the phones ring at random. If the call originates from a phone on the same DP750, then only two phones ring (again, random different phones each time). This suggests that although the DP750 may be able to support five simultaneous calls, can it only support three when they are all in the ringing state? I can confirm that the error code for the extension that doesn’t ring is 486.


I am not sure what the complaint is. A ringing state is not a call as no one has yet to answer. Only when answered is there a session (call) established. Also, what may ring might depend on the settings you have for the extension as well as the 3CX ring group. Do you have accept multiple calls enabled at the extension level (forwarding rules) in 3CX and is the following in the parameters -

set to 1?
Finally, do you have enough line appearance in the handset such that it can handle more than one call at a time?

486 is not an error, but an indication of busy.


if you want 5 handset ring at the same time, you need use the DP75x Parallel Account Mode, what you are using is the Ring Group on PBX. A Ring Group has “Random” (ring all accounts randomly), “Parallel” (ring all accounts at the same time), “Linear”(ring accounts in the group 1 by 1, start from last answered accounts), or “Circular”(ring accounts in the group 1 by 1, always start from the 1st account). you need check your Ring Group type settings on the 3CX.

In your case, if you use a DP720 call the ring group number, it will randomly call the numbers in the group, other 2 DP720 wiil ring, and for itself, it will never ring and received 486 is the expected and correct behavior. You can try use any DP720 to dial it’s own number, you will get line busy 486.

The DP75x also implemented some feature similar to the PBX Ring Group, on DP75x, you just register a single account, and set it as “Parallel” mode, or “Circular”, or “Linear”, and assign it to all 5 handsets, the DP75x base station will handle the call route, it will either ring 5 DP720 simultaneous, or 1 by 1.

Here is an example, set the account to parallel mode:

Assign it to all handsets:

When it receives call from outside, it will ring all 5 handsets simultaneous, but any one answered that call will stop the ring on others.

you can enable the call waiting on Parallel, so when some HS is in call, the others can still ring.