Firmware of your ER6020 is up to date?
On previous router, did you configure anything to make the telephone server work? You'd better confirm with the provider of telephone server.
Provide the topology.

hi,

on the previous server nothing was configure....
I update the firmware but then I was not able to enable or disable the SIP ALG function.

I show on a previous thread that H.323 should be also disable; I test it today and come back.

Thanks

problem still remains. with SIP ALG and H.323 ALG disable !

Topology

ISP => TL-ER6020 => Asterisk server on local LAN
=> Phones on local LAN

Connection problem between phones and asterisk !

Do you have to change any settings on Asterisk server after you use a new router?
The router's WAN is public or private? Maybe you have to open some ports for the server like UDP 5061 and 5060?

everything is private, nothing comes from public area... On the router, the port to open always refer to WAN, not to private LAN...
Don't know what to do...!

Contact TP-LINK to ask for the beta firmware which has solved the problem that SIP ALG doens't take effect. Hope it helps. Good luck.
http://ticket.tp-link.com/index.php?/Tickets/Submit

Mavis wrote

Contact TP-LINK to ask for the beta firmware which has solved the problem that SIP ALG doens't take effect. Hope it helps. Good luck.
http://ticket.tp-link.com/index.php?/Tickets/Submit

I think Mavis is on track. I too found the newest firmware prevented the ALG/SIP settings to be disabled. I downgraded to the previous firmware and that was resolved. I wish I had read Mavis' post before now. Had to go to a different router, but hope still to use the 6020 for voip.

The other SIP issue I experienced was that there appeared to be no way to provide QOS reserved bandwidth, so we were getting clipping. I think there might be a way to even do this. After some searching there is a bandwidth feature I hadn't noticed. If a group is created based on the mac addresses of all the phones this might allow the bandwidth to be allocated.

As I understand it the phones ring, but you cannot answer the calls,the phone keeps on ringing? Which Voip server are you using?

I have been bugging TP-LINK about needed firmware updates for both the TL-ER6120 and TL-ER6020. I like both of these routers, but problems like this (and others) are leading me to possibly look elsewhere.

Here is hoping there are some updates soon... and then consistent ones thereafter.