SIP ALG SAGEMCOM 2704n

[#1]

https://community.plus.net/forum/index.php/topic,140064 may help but I suspect it is locked in the firmware
This may be the post you referred to in the opening post

[#2]

Hi,
Yes, I've seen this post but the solution appears to be relevant to a different modem/router?

[#3]

Quote

The provider has indicated that all I need to do is turn of SIP ALG and all will work fine

and he may well be right! but quite often a voip providers stock response is to disable any SIP ALG. I've never had one of the 2704n routers so I don't know much about them but I see JIm has posted the link I was about to suggest. There is an advanced settings url for the 2704 which MAY have the ability to disable the SIP ALG.
From what you say it does seem like multiple sip accounts on the single base unit, and I can see that is going to be a problem for all but a VERY good SIP ALG , most of which don't work anyway!

[#4]

Ahhh I see...  Yes, I've tried the expert user function but had no joy there - unless there is another area I'm missing!?

[#5]

Nope, that's it I'm afraid 
Going back to my original thoughts on local ports, I'm not sure it's applicable in your case since the base unit will automatically be using different ports for each account.
As a test though, you might try changing the 'local sip port in use' . On the N300 it's under Telephony->Advanced settings IIRC change it to something different to 5060 , that MIGHT defeat the SIP ALG if you're lucky

[#6]

My  Gigaset N300 settings appear to only offer the option of changing destination SIP ports (ie the port that the device sends to),  If that's the case then presumably the device uses different source ports for each profile.

[#7]

It's got to use different source ports for each profile, the network stack on the phone must allocate different ports automatically for each connection. I'm not at home at the mo so I can't check my C475IP ( forerunner to the N300 )  config but I was going on this gradwell config note here https://support.gradwell.com/entries/23145861-How-to-configure-the-Gigaset-range-of-IP-Phones regarding local ports ( see the Multple phones para )

[#8]

Does that Gradwell note not refer to multiple devices, rather than one device with multiple profiles?  I've found the local SIP port setting on my N300, and it's under Advanced VOIP Settings, for the device in general, not profile by profile.  The options are either a single fixed source port, or a range of ports.
However I think that if this was where the issue lies, I'd expect only one phone/profile to work, not three out of four.  It's not something silly like a concurrent call limit?

[#9]

Hi,
No, I've confirmed that I should have four phones at the same time able to make/receive calls...

[#10]

Quote

However I think that if this was where the issue lies, I'd expect only one phone/profile to work, not three out of four.

I'd tend to agree. I'm really clutching at straws here. My theory was that if the local port was defaulted to  say 5060 and the SIP ALG was using the local port rather than the remote port to decide on processing SIP packets, then, depending on how local ports are allocated for multiple connections, one of the phones could be affected.
The bottom line is that voip isn't designed to work behind NAT. Anything you do to make it work is a fiddle. If it works then fine, you're lucky , if it doesn't, then it's a right pain to sort... 

[#11]

Quote

I've found the local SIP port setting on my N300, and it's under Advanced VOIP Settings, for the device in general, not profile by profile.  The options are either a single fixed source port, or a range of ports.

I've just got home and checked my C475IP and it allows for a port range. See screendump attached. Hopefully the range of ports allows for a different listen port for each connection. Might be worth trying it at say 5070 - 5090 to force it away from anything that the SIP ALG may mess about with.

[#12]

That looks exactly the same as the equivalent page on my N300A so with any luck the N510 will be the same as well.  To me a key is that we have one handset and profile that consistently misbehaves, would it be worth swapping assignments between two handsets, just to see if the problem follows the profile or the handset?    Always remember there may be more than one fault.
As for NAT and ALG behaviour, people are right to be suspicious but most SIP providers are now pretty good at finding their way back to your system, typically by ignoring IP information in your SDP and instead sending to the address that your data appears to originate from on the basis that a normal stateful firewall will permit inbound packets that are effectively replies to your outbound.  One interesting test would be to call 0800 150 150 and see whether you hear ringback prior to the voice announcement.  I happen to know that the number uses inband audio to provide ringback, and it fools some SIP NAT traversal implementations because there's inbound audio before outbound - so there's no dynamic permission in the firewall for their RTP to use.  Theoretically that's the sort of thing that SIP inspection is supposed to fix up, but I'm not seen it do so.
I have a 2704N, but I don't specially want to put it in service here to test, and in any case I have only one SIP profile and it sounds like your symptoms are more related to multiple profiles and registrations.
Have you confirmed four concurrent calls are supported when you make outbound calls?  And when you have two calls in progress, the scenario where the fourth handset goes straight to missed calls, can you make an outbound call from that handset?

[#13]

True, most SIP providers cancope to a large extent with NAT and providing the NAT sessions on the router are kept open then it works.
Is it possible to look at the active NAT sessions on a 2704 ?
BTW I've just done some tests with my C475 using multiple SIP accounts and same local port is used for all connections. The firewall on my Draytek 2830 did show separate NAT sessions to the different SIP providers ip's though

[#14]

Quote from: MisterW

BTW I've just done some tests with my C475 using multiple SIP accounts and same local port is used for all connections.

That's interesting, in spite of you setting it to use random ports.  I'd expect to see separate NAT entries (strictly they're PAT) if the destinations were different.  Are your SIP accounts with the same provider?  I'm tempted to set up another SIP Gate account just to see how it behaves. 

[#15]

Sorry, maybe I wasn't clear about it above. There WERE separate NAT entries for the different SIP providers since the destination IP's are different but in both cases the local source port was 5079.  That will mean in knowsnotmuch's case, where the destinations are the same, there will only be 1 NAT entry.
@knowsnotmuch, Has the system worked reliably at all before OR is it just since the 2704 has been used that it's giving problems?