Hi.
Maybe you can change the ADSL mode of TD-8840T to ADSL2+, ADSL2, G.DMT or the others for a try.

Thanks for your support but the issue is not resolved. I noticed that the alignment values ​​(upload and download) are present so the problem is not sync but this router 8840T is unable to obtain the IP address, gateway, etc.. from the ISP. Why does this happen with the new router while connecting the old router the aligns right away and get the TCP / IP from the ISP?
cetalfio

cetalfio wrote

Thanks for your support but the issue is not resolved. I noticed that the alignment values ​​(upload and download) are present so the problem is not sync but this router 8840T is unable to obtain the IP address, gateway, etc.. from the ISP. Why does this happen with the new router while connecting the old router the aligns right away and get the TCP / IP from the ISP?
cetalfio

Hum, maybe it is the configuration problem on the new router.
Who is your Internet service provider? What is the connection type provided by your ISP? PPPoE or PPPoA or ??
Have you double checked your username, password, vpi,vci and connection type with your Internet service provider?

What are the log messages?

in the log of the device can not find any apparent problem, cetalfio

1/1/2000 0:0:1> Last errorlog repeat 1 Times
1/1/2000 0:0:1> SNMP TRAP 0: cold start
1/1/2000 0:0:1> main: init completed
1/1/2000 0:0:2> SNMP TRAP 3: link up
1/1/2000 0:0:2> No DNS server available
1/1/2000 0:0:2> Last errorlog repeat 10 Times
1/1/2000 0:0:2> adjTimeTask fail: no server available
1/1/2000 0:0:2> adjtime task pause 60 seconds
1/1/2000 0:0:2> No DNS server available
1/1/2000 0:0:2> Last errorlog repeat 10 Times
1/1/2000 0:0:2> adjTimeTask fail: no server available
1/1/2000 0:0:2> adjtime task pause 60 seconds
1/1/2000 0:0:2> No DNS server available
1/1/2000 0:0:2> Last errorlog repeat 10 Times
1/1/2000 0:0:2> adjTimeTask fail: no server available
1/1/2000 0:0:2> adjtime task pause 1 day
1/1/2000 0:0:28> MPOA Link Up
1/1/2000 0:0:36> ppp_ready: ch:804d01c8, iface:8044c620
1/1/2000 0:0:36> SNMP TRAP 3: link up
1/1/2000 0:0:36> Accept() fail
1/1/2000 0:0:36> Accept() fail

Try to set manually a DNS address of your ISP...

The problem is not in the resolution of domain names but the problem is that the router does not align properly with the ISP. I have asked the ISP support and they say they do not have problems on the line, I can not believe that the old router (blue firmware interface) works better than new. My question now is this: the hardware of the new 8840T is different from the old one maybe you should understand if the latter has some incompatibilities with the Italian ADSL lines.

I think I've found the problem, after the advice of Stella when the reboot went right I watched the modulation assigned by the DSLAM so I changed to Advanced Setup -> ADSL the Auto Sync-UP specifying only the type of modulation of my line eg. ADSL2+ so the router works fine. I believe that the Auto Sync-UP does not work well because of this annoying problem that is only an option of the router's default.