Firmware for GSC3510/GSC3505 released as Beta



Dear Grandstream Customers,

Firmware for GSC3510/GSC3505 is now released as Beta. Here is the link to the release notes:

The firmware and release notes can be downloaded from:

Please contact us should you have any issues. Thank you for your support for Grandstream products.

Technical Support
Grandstream Networks, Inc.



No fix for the “Bad Gateway” bug yet?


Hi Frederick,

After disabling the setting “Only Accept SIP Requests from Known Servers”, are you able to register successfully on 3CX? The official 3CX template will be updated to include this change soon.



It happens with a Netsapiens platform too


The issue should be the combination of using STUN and having the setting “Only Accept SIP Requests from Known Servers” enabled, so it would happen regardless of platform. Could you try disabling the setting and let me know if that fixes it for you?




Hello! I realize that fmarcoux96t may have never replied to you, but I hope that you are able to shed further light on this issue even if it is a number of months later, as your questions led me to my only temporary solution so far.

I currently have a client with an environment of 40+ GSC3510’s distributed to multiple physical locations that have all begun experiencing this specific issue of “502, Bad Gateway, Unregistered” to their remote VoIP Server, configured in STUN Mode. Once encountered I began reviewing the forums at length and can provide the following information from an aggregation of two forum posts and this beta release post:

  • History: Issue began occurring somewhere between firmware and As that the current firmware version is and the last two downloads available are and for “previous firmwares”, this limits the ability to revert to previous functioning firmware.

  • Solution 1: During this firmware timeframe, the default TLS version changes from 1.0 to 1.1. A user proposed that this resolved the issue for them - myself and another forum member tested and were not able to replicate.

  • Solution 2: Another solution proposed was to change the provisioning link to use static IP address which resolved the issue for them - I tested and was not able to replicate.

  • Solution 3 (Current Fix): Not a confirmed solution, but a question from “you” asked about changing the “Only Accept SIP Requests From Known Servers” setting due to a combination with STUN. Using this I dug into the user manual and found the setting at "Account -> Account Settings / Account 1 Selection -> Advanced Settings Tab -> Security Settings Section -> “Only Accept SIP Requests from Known Servers”, which was checked in previous firmwares (back to and is checked now, but when unchecked, the SIP Speaker does resume registration immediately after setting application. HOWEVER, this setting/fix does NOT persist when the SIP Speaker is restarted.

If you could please advise on a permanent fix or on any further information, it will be greatly appreciated. Thank you and have a great day!


We had a ticket opened and the solutions never worked. Your fix is also not recommended for STUN FYI but I agree it’s a temporary fix.

For us, we simply stopped using those devices.


Thank you for responding! I agree that is not preferred for STUN, we have additional security measures but still. That is concerning to hear you never found a resolution. Hopefully we will hear more / hear in a future firmware.


Hi JustinC,

We are planning to release fw to fix this issue soon. I’ve already given it a test and was able to register via STUN and with the setting “Only Accept SIP Requests from Known Servers” enabled as before. If all goes well, it should be released as Beta in a week. Please give it a try then.



Thank you for the update so quickly! I was wondering if there is a specific action to gain beta access, or simply download the firmware from the beta thread.

I am new to Grandstream, but we are growing on the number of Grandstream devices we support so we will likely be interested in beta moving forward.


Nope, there isn’t anything you need to do on your end to get beta access, you can get the firmware from the beta thread once we post it.