Huawei 4G+ Router B535-235 TEL port giving callers echo on their end (Voxi network)


Novice Member
Can someone tell me why anyone on the other end of the call can hear themselves echo? It's like they're hearing everything coming through my end. I've plugged in a DECT phone via the RJ11 cable and it works (using voxi sim) but the echo makes it unusable. The internet works fine. I've just upgraded from a cat4 tenda 4g router with a tel rj11 port which had the same issue to this huawei B535-235 but the issue persists. I've also tried changing the DECT phone to a older BT wireless phone and that's the same as well an an even older ancient phone. I've also replaced the RJ11 to RJ11 cable with a brand name (rhino cables) to no avail. The only thing I haven't tried is changing the 4G sim to another network which I will be doing when a preloaded 3 SIM arrives next week.

I notice that there are VoIP settings for SIP VOIP providers but would this work behind carrier grade NAT? Does the cloud SIP VOIP providers have their own static IP associated with the packages they sell so you need not worry about CGNAT? As you can tell I don't know what I'm doing but I have a basic understanding of how networks work (I have a degree in computer networks and security) so if anyone could explain in detail why I'm having this problem with the echoing I'd really appreciate it.

EDIT - Since creating this post I have created a free sipgate account and allocated the settings to my router under the Advanced settings > VoIP > SIP server settings. However the account isn't active until I confirm my address in the event of using emergency services over VoIP so I must wait for the activation code to come in the post and hopefully once that's done, it'll allow me to register my DECT phones to be used through the sipgate VoIP service. I notice that in the advanced VoIP settings on the router, there is a toggle for enabling VoIP echo cancellation which I gather does not affect the phone plugged into the RJ11 socket until a VoIP provider is configured with it. I'm hoping this is all I need to do to resolve this problem.
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