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Replacing a BT landline by VoIP

 
 
Graham.
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Posts: n/a
 
      02-27-2012
On Mon, 27 Feb 2012 20:40:55 +0000, Steve Slatcher
<(E-Mail Removed)> wrote:

>On 26/02/2012 22:02, Gordon Henderson wrote:
>
>> One way audio is almost always caused by NAT issues - look to disable the
>> SIP ALG in your router, or replace it with something that doesn't have
>> the issue or try using a STUN server in your ATA.

>
>Eh? Do general purpose routers have setting specifically for SIP?
>Cannot see such a thing in my Lynksys WRT54GS.
>
>If there are NAT issues, doesn't that simply mean my router is not
>working correctly? It does NAT all the time for my computer. Why is
>SIP to my ATA any different?


Netgear routers do, but note Gordon is suggesting *disable* it.

I think the whatever it is supposed to do is regarded as "broken" in
software terms.

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Graham.
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Steve Slatcher
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      02-27-2012
On 27/02/2012 21:12, Graham. wrote:
> On Mon, 27 Feb 2012 20:40:55 +0000, Steve Slatcher
> <(E-Mail Removed)> wrote:
>
>> On 26/02/2012 22:02, Gordon Henderson wrote:
>>
>>> One way audio is almost always caused by NAT issues - look to disable the
>>> SIP ALG in your router, or replace it with something that doesn't have
>>> the issue or try using a STUN server in your ATA.

>>
>> Eh? Do general purpose routers have setting specifically for SIP?
>> Cannot see such a thing in my Lynksys WRT54GS.
>>
>> If there are NAT issues, doesn't that simply mean my router is not
>> working correctly? It does NAT all the time for my computer. Why is
>> SIP to my ATA any different?

>
> Netgear routers do, but note Gordon is suggesting *disable* it.
>
> I think the whatever it is supposed to do is regarded as "broken" in
> software terms.


I did note that. Just curious...

--
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Gordon Henderson
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Posts: n/a
 
      02-27-2012
In article <(E-Mail Removed)>,
Steve Slatcher <(E-Mail Removed)> wrote:
>On 26/02/2012 22:02, Gordon Henderson wrote:
>
>> One way audio is almost always caused by NAT issues - look to disable the
>> SIP ALG in your router, or replace it with something that doesn't have
>> the issue or try using a STUN server in your ATA.

>
>Eh? Do general purpose routers have setting specifically for SIP?
>Cannot see such a thing in my Lynksys WRT54GS.


Some routers need a lower level interface to disable these features...

>If there are NAT issues, doesn't that simply mean my router is not
>working correctly? It does NAT all the time for my computer. Why is
>SIP to my ATA any different?



It's complex... And this is a somewhat simple explanation... VoIP via
SIP is 2 things - one part is a command channel and the other part is the
media channel. (audio) A bit like FTP. Or it might be if SIP didn't
encode the IP address of the unit *inside* it's commands to the other
end... So a SIP device on 192.168.3.4 will send that IP address to the
far-end... Which then tries to send a reply back to that IP address and
worse, tries to send the audio stream back to it. Which will fail unless
there is a VPN setup between the 2 endpoints...

Some routers have a SIP ALG - (Application Level Gateway) which tries
to do "deep packet inspection" on the SIP commands as they pass through
and substituting the proper external IP address in the packets as they
pass through, and un-doing it for the return. Unfortunately almost all
implementations I've seen are broken and just don't work.

SIP/VoIP works most of the time because the far-end can see the real
IP address and do it's own substitution of the internal IP addresses
and/or the user device (e.g. ATA, phone) is using a STUN server which
will tell the device it's external IP address so the device can put in
the real external IP address instead of it's private IP address.

There are devices and softwares that can run as part of the VoIP providers
network to assist in this packet mangling. (And there are alternatives
to STUN too)

The other hassle is working out the ports to use for the audio streams
and hoping that the device on the inside will start talking first so the
devices on the outside then have a path back to them after the router has
opened up the channel (and remembered it as part of its NAT processing)

One way audio is often caused by the far-end not having your correct
external IP address to send data back to, or the router simply blocking
it as it's coming in from a different IP address or port from the
outgoing stream.

If only the SIP people had thought about NAT, however...

But as we all know for the most-part it does work, but there are some
routers I've had issues with - BT homehubs, some netgears, Junipers...
Draytek 'v' series. And some routers just have issues with a device
keeping a NAT session open for a very long time - e.g. Drayteks.

Gordon
 
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Steve Slatcher
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Posts: n/a
 
      02-27-2012
On 27/02/2012 22:06, Gordon Henderson wrote:
> In article<(E-Mail Removed)>,
> Steve Slatcher<(E-Mail Removed)> wrote:
>> On 26/02/2012 22:02, Gordon Henderson wrote:
>>
>>> One way audio is almost always caused by NAT issues - look to disable the
>>> SIP ALG in your router, or replace it with something that doesn't have
>>> the issue or try using a STUN server in your ATA.

>>
>> Eh? Do general purpose routers have setting specifically for SIP?
>> Cannot see such a thing in my Lynksys WRT54GS.

>
> Some routers need a lower level interface to disable these features...
>
>> If there are NAT issues, doesn't that simply mean my router is not
>> working correctly? It does NAT all the time for my computer. Why is
>> SIP to my ATA any different?

>
>
> It's complex... And this is a somewhat simple explanation... VoIP via
> SIP is 2 things - one part is a command channel and the other part is the
> media channel. (audio) A bit like FTP. Or it might be if SIP didn't
> encode the IP address of the unit *inside* it's commands to the other
> end... So a SIP device on 192.168.3.4 will send that IP address to the
> far-end... Which then tries to send a reply back to that IP address and
> worse, tries to send the audio stream back to it. Which will fail unless
> there is a VPN setup between the 2 endpoints...
>
> Some routers have a SIP ALG - (Application Level Gateway) which tries
> to do "deep packet inspection" on the SIP commands as they pass through
> and substituting the proper external IP address in the packets as they
> pass through, and un-doing it for the return. Unfortunately almost all
> implementations I've seen are broken and just don't work.
>
> SIP/VoIP works most of the time because the far-end can see the real
> IP address and do it's own substitution of the internal IP addresses
> and/or the user device (e.g. ATA, phone) is using a STUN server which
> will tell the device it's external IP address so the device can put in
> the real external IP address instead of it's private IP address.
>
> There are devices and softwares that can run as part of the VoIP providers
> network to assist in this packet mangling. (And there are alternatives
> to STUN too)
>
> The other hassle is working out the ports to use for the audio streams
> and hoping that the device on the inside will start talking first so the
> devices on the outside then have a path back to them after the router has
> opened up the channel (and remembered it as part of its NAT processing)
>
> One way audio is often caused by the far-end not having your correct
> external IP address to send data back to, or the router simply blocking
> it as it's coming in from a different IP address or port from the
> outgoing stream.
>
> If only the SIP people had thought about NAT, however...
>
> But as we all know for the most-part it does work, but there are some
> routers I've had issues with - BT homehubs, some netgears, Junipers...
> Draytek 'v' series. And some routers just have issues with a device
> keeping a NAT session open for a very long time - e.g. Drayteks.
>
> Gordon


Thank you for that clear explanation. Should the one-way audio get to
be a big problem (it isn't yet) I now know where to start looking.
After, a bit of googling, I think my first step would be to upgrade my
router firmware and hope those nice Cisco people have fixed any
responsible bugs!

--
www.winenous.co.uk
 
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Andrew Benham
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Posts: n/a
 
      02-28-2012
On Mon, 27 Feb 2012 22:06:04 +0000, Gordon Henderson wrote:

> In article <(E-Mail Removed)>, Steve Slatcher
> <(E-Mail Removed)> wrote:
>>On 26/02/2012 22:02, Gordon Henderson wrote:
>>
>>> One way audio is almost always caused by NAT issues - look to disable
>>> the SIP ALG in your router, or replace it with something that doesn't
>>> have the issue or try using a STUN server in your ATA.

>>
>>Eh? Do general purpose routers have setting specifically for SIP?
>>Cannot see such a thing in my Lynksys WRT54GS.

>
> Some routers need a lower level interface to disable these features...
>
>>If there are NAT issues, doesn't that simply mean my router is not
>>working correctly? It does NAT all the time for my computer. Why is
>>SIP to my ATA any different?

>
>
> It's complex... And this is a somewhat simple explanation... VoIP via
> SIP is 2 things - one part is a command channel and the other part is
> the media channel. (audio) A bit like FTP. Or it might be if SIP didn't
> encode the IP address of the unit *inside* it's commands to the other
> end... So a SIP device on 192.168.3.4 will send that IP address to the
> far-end... Which then tries to send a reply back to that IP address and
> worse, tries to send the audio stream back to it. Which will fail unless
> there is a VPN setup between the 2 endpoints...
>
> Some routers have a SIP ALG - (Application Level Gateway) which tries to
> do "deep packet inspection" on the SIP commands as they pass through and
> substituting the proper external IP address in the packets as they pass
> through, and un-doing it for the return. Unfortunately almost all
> implementations I've seen are broken and just don't work.
>
> SIP/VoIP works most of the time because the far-end can see the real IP
> address and do it's own substitution of the internal IP addresses and/or
> the user device (e.g. ATA, phone) is using a STUN server which will tell
> the device it's external IP address so the device can put in the real
> external IP address instead of it's private IP address.


Or the SIP phone has a config option where you can enter the external IP
address manually (only useful if you have a static IP). My Grandstream
BT200 has this, so it doesn't need to talk to a STUN server to discover
its external address.

> There are devices and softwares that can run as part of the VoIP
> providers network to assist in this packet mangling. (And there are
> alternatives to STUN too)
>
> The other hassle is working out the ports to use for the audio streams
> and hoping that the device on the inside will start talking first so the
> devices on the outside then have a path back to them after the router
> has opened up the channel (and remembered it as part of its NAT
> processing)
>
> One way audio is often caused by the far-end not having your correct
> external IP address to send data back to, or the router simply blocking
> it as it's coming in from a different IP address or port from the
> outgoing stream.
>
> If only the SIP people had thought about NAT, however...


Then a lot of network engineers would be short of work

> But as we all know for the most-part it does work, but there are some
> routers I've had issues with - BT homehubs, some netgears, Junipers...
> Draytek 'v' series. And some routers just have issues with a device
> keeping a NAT session open for a very long time - e.g. Drayteks.
>
> Gordon


 
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David Woolley
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Posts: n/a
 
      02-28-2012
Gordon Henderson wrote:
> In article <fV45K0OBJxbE-pn2-KDvZKoRJuV2l@localhost>,
> Dave Saville <(E-Mail Removed)> wrote:
>> On Mon, 27 Feb 2012 10:36:36 UTC, Gordon Henderson
>> <(E-Mail Removed)> wrote:
>>
>>> In article <fV45K0OBJxbE-pn2-m9jj5kLeWd55@localhost>,
>>> Dave Saville <(E-Mail Removed)> wrote:
>>>> On Sun, 26 Feb 2012 22:02:52 UTC, Gordon Henderson
>>>> <(E-Mail Removed)> wrote:
>>>>
>>>> <snip>
>>>>> I seem to have missed a bit about one way audio, but please do not
>>>>> ever port-forward 5060 externally to an internal device unless you
>>>>> are 100% sure that you know what you are doing. Similarly don't use the
>>>>> DMZ facilities and don't put an ATA in-line with your router and
>>>>> cable modem.
>>>> Would you care to enlarge on that paragraph?
>>> I thought I had, but you
>>>
>>>> <snip>
>>> ed it.
>>>
>>> Briefly, criminals will hack into it and steal your VoIP minutes if
>>> it's exposed to the Internet and you don't take adequate precautions.

>> Gordon - I got that bit. What I don't understand is the quoted
>> paragraph. If you don't forward 5060 how is *anything* going to get
>> through to the ATA? And what do you mean about "in-line" with router?

>
> OK... If you have a device in the "inside" of your NAT router, then
> it can talk to devices on the outside - that's fairly OK, however
> if it hasn't established an existing connection to a device on the outside
> then nothing on the outside should be able to talk back into the device.


SIP, in standard form, is connectionless, and at the level at which you
would have to do this (a continuous sequence of successful re-REGISTERs)
is connectionless below the application layer. I don't believe there is
any real name for the sort of connection that exists with a chain of
re-REGISTERs. If you have static addresses, even that concept of a
connection doesn't exist.


>
> What's not good is allowing any device in the internet to talk into
> your ATA - that would be achieved by port forwarding, or using the DMZ



SIP was, of course, designed for a fully decentralized system, even
though nearly everyone operates it centralised and always uses the PSTN
as an intermediary. (Then again, so was SMTP.)
 
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Gordon Henderson
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Posts: n/a
 
      02-29-2012
In article <(E-Mail Removed)>,
Bob L <(E-Mail Removed)> wrote:
>On Mon, 27 Feb 2012 09:38:01 +0000 (UTC), "Dave Saville"
><(E-Mail Removed)> wrote:
>
>>On Sun, 26 Feb 2012 22:02:52 UTC, Gordon Henderson
>><(E-Mail Removed)> wrote:
>>
>><snip>
>>> I seem to have missed a bit about one way audio, but please do not
>>> ever port-forward 5060 externally to an internal device unless you
>>> are 100% sure that you know what you are doing. Similarly don't use the
>>> DMZ facilities and don't put an ATA in-line with your router and
>>> cable modem.

>
>Is there less of a problem if you use a different port(s), say 49494 ?


Sure - but unless the person trying to contct you knows what port you're
using then they won't be able to contact you...

You may also find that commercial suppliers simply won't entertain it.

Gordon
 
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