Cannot receive calls for a while after restarting modem

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Cannot receive calls for a while after restarting modem

Postby torontovoipnewuserx » 11/23/2020

I set up FreePhoneLine in an ATA box.

It works fine except during a small time period immediately after a modem restart, meaning if I restart my modem, then I cannot receive incoming calls, until the next registration from the ATA box.

Is it due to the fact that the new public (WAN) IP address of my modem, after the restart, will only be sent to the registration server in the next ATA box registration action, instead of being immediately sent to the registration server when the modem restarts?
torontovoipnewuserx
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Re: Cannot receive calls for a while after restarting modem

Postby Liptonbrisk » 11/23/2020

torontovoipnewuserx wrote:It works fine except during a small time period immediately after a modem restart, meaning if I restart my modem, then I cannot receive incoming calls, until the next registration from the ATA box.


That's normal. When you reboot your modem, if you're on DSL, there's a good chance your WAN IP has changed (SIP signalling based on new IP can’t occur as you suggested), and new associations in your router need to occur. You'll have effectively lost registration even if your ATA's status (or FPL's website) doesn't reflect that immediately due to the long 3600 registration period.

With cable internet, if your IP hasn't changed and provided the ATA didn't make a registration attempt while internet access was down, chances are the ATA doesn't need to make another registration attempt to continue working for incoming calls, in particular if UDP timeouts have been set properly in the router. However, with X_ProxyServerRedundancy configured in an Obihai ATA, it's almost impossible for internet access to re-establish before the ATA's status for FPL changes to "Register Failed: No Response From Server" anyway, especially if a Hitron gateway is being used.

With Obihai ATAs, you'll eventually see "Register Failed: No Response From Server" (Status-->System Status-->FPL Service Status) if internet access isn't established before the ATA makes a registration attempt.

With an Obihai ATA, after a failed registration, you'll need to wait for the duration defined by RegisterRetryInterval (ITSP Profile FPL-->SIP) before another registration attempt is made.
According to Freephoneline, that setting should be 120 seconds: https://support.freephoneline.ca/hc/en- ... redentials.
"Failed Registration Re-Try Interval: 120 seconds"

It's okay to increase RegisterRetryInterval above 120s when using Freephoneline, but it's not a good idea to lower RegisterRetryInterval below 120s.

https://community.freepbx.org/t/trunk-s ... ca/22479/8
"As May 2013, our servers will rate limit REGISTER requests to a maximum of 10 requests per 5 minutes. Each authentication round usually consumes 2 requests (digest auth), so it is a fair number given our guidelines. Also, it does not affect INVITES (which are also authenticated)…"

If too many registration attempts are made within that 5 minute interval you will be temporarily IP banned by the specific proxy server you were attempting to register with.


Note that only one registration per FPL account is allowed at any time. When there are multiple devices/softphones using the same account, only the most recent registration is valid. The previous device will lose registration, and, consequently, incoming calls will not work on it. This is especially important to consider if someone else is using your SIP credentials (username and password) that are found after logging in at https://www.freephoneline.ca/showSipSettings or if you're trying to register your FPL account with a smartphone SIP app or with another device. Registration is required for incoming calls. It is not required for outgoing calls. A more significant concern, though, is that multiple registration attempts can lead to temporary IP bans. The more devices being used can make the temporary ban happen more quickly. Note that each time you reboot or restart your ATA or SIP app, it's attempting to register with Freephoneline again. Multiple registration attempts within a short period can result in temporary IP ban. Each time you reboot your ATA it's attempting to register with FPL's proxy server.

So, the 3600 seconds registration interval and the 120s failed retry timers are important with FPL to help avoid temporary IP bans.

If the ATA doesn't indicate registration has failed, then you will be waiting for the next registration interval before another registration attempt is made.



Also, thanks to Mango, many of us now understand that in order for ATAs to remain registered and working properly with a VoIP SIP provider like Freephoneline, in particular after power failures, the following conditions must be met:

UDP Unreplied Timeout (in your router) < NAT Keep-alive Interval (in your ATA; for Obihai ATAs this is X_KeepAliveExpires; for Grandstream, the setting is SIP OPTIONS Keep Alive Interval) < UDP Assured Timeout (in your router) < SIP Registration Failure Retry Wait Time (or RegisterRetryInterval in Obihai ATAs)

“<“ means less than.

When a modem leases a new IP address, a problem can arise where prior associations using the old IP address are maintained in the router. When the ATA attempts to communicate using the old IP address, the response is unreplied, and then if the UDP Unreplied timeout is greater than the Keep Alive Interval (and UDP Unreplied timeout is often set to 30 by default in consumer routers) a problem arises where the corrupted connection persists. If UDP Unreplied timeout is, for example, 17, and the NAT Keep Alive Interval is 20, then the corrupted connection will timeout or close. A new connection will be created, and everything will work fine.

Another problem can occur when the Keep-Alive interval is greater than UDP Assured Timeout (often 180 by default in consumer routers): the NAT hole will close due to the ATA not communicating frequently enough with the SIP server. In turn, incoming calls may, intermittently, not reach the ATA. Again, X_Keepalives expires is supposed to be 20 with FPL.

(the above settings are making reference to those in Obihai ATAs)

Getting access to both UDP Unreplied Timeout and UDP Assured Timeout settings in consumer routers may be difficult, if not impossible. Asuswrt-Merlin (I would avoid any model below/less powerful than an RT-AC68U), third party firmware for Asus routers, does offer easy access to these two settings, which are found under General–>Tools-->Other settings. My understanding is that third party Tomato firmware has these two settings as well. So if your router supports Tomato firmware, that may be another option. Note that I will not be held accountable any damage resulting from failed firmware updates. Apparently, Mikrotik routers also allow users to change both Assured and Unreplied UDP timeout settings as well: https://forums.redflagdeals.com/recomme ... #p28056619.

Router firmware that allows users to adjust Assured and Unreplied UDP timeouts include

Asuswrt-Merlin
Ubiquiti
Mikrotik
pfSense
Tomato
DD-WRT


The keep alive interval for FPL is 20. The SIP Registration Failure Retry Wait Time is 120. I use 15 for UDP Unreplied Timeout and 115 for UDP Assured Timeout.
Please do not send me emails; I do not work for nor represent Freephoneline or Fongo. Post questions on the forums so that others may learn from responses or assist you. Thank you. If you have an issue with your account or have a billing issue, submit a ticket here: https://support.fongo.com/hc/en-us/requests/new. Visit http://status.fongo.com/ to check FPL/Fongo service status. Freephoneline setup guides can be found at viewforum.php?f=15.
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