Discussion:
SIP ALG. What exactly is it?
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Otto Pylot
2014-02-16 22:21:09 UTC
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I know it stands for Session Initiated Protocol Applications Layer
Gateway, but what exactly does it do and how does it interfere? This is
in relationship to a question someone asked me about Vonage VoIP and
AT&T's VoIP service.
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Deja Moo: I've seen this bullshit before. Please respond to: ***@invalid.net
replacing invalid with sonic.
Kevin McMurtrie
2014-02-17 08:28:52 UTC
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Post by Otto Pylot
I know it stands for Session Initiated Protocol Applications Layer
Gateway, but what exactly does it do and how does it interfere? This is
in relationship to a question someone asked me about Vonage VoIP and
AT&T's VoIP service.
It's just a protocol for networked phone calls. It has a little bit of
resemblance to HTTP.

Interfere? It doesn't, but some ISPs will block VOIP if they sell phone
service and there's no competition around.
o***@gmail.com
2014-02-17 19:31:52 UTC
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Post by Kevin McMurtrie
Post by Otto Pylot
I know it stands for Session Initiated Protocol Applications Layer
Gateway, but what exactly does it do and how does it interfere? This is
in relationship to a question someone asked me about Vonage VoIP and
AT&T's VoIP service.
It's just a protocol for networked phone calls. It has a little bit of
resemblance to HTTP.
Interfere? It doesn't, but some ISPs will block VOIP if they sell phone
service and there's no competition around.
By interfere I meant with AT&T's VoIP service. I have a poster in the MicroCell forum (AT&T's femtocell brand of VoIP service) who was having issues with his MicroCell and it turns out that he also has Vonage, which, after a little digging seems to use the SIP ALG protocol and once he removed that, the MicroCell worked just fine. I'm just wondering what is it about that protocol that would inhibit the MicroCell from reaching the AT&T servers.
Roy
2014-02-17 20:15:09 UTC
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Post by o***@gmail.com
Post by Kevin McMurtrie
Post by Otto Pylot
I know it stands for Session Initiated Protocol Applications
Layer
Gateway, but what exactly does it do and how does it interfere? This is
in relationship to a question someone asked me about Vonage VoIP and
AT&T's VoIP service.
It's just a protocol for networked phone calls. It has a little bit of
resemblance to HTTP.
Interfere? It doesn't, but some ISPs will block VOIP if they sell phone
service and there's no competition around.
By interfere I meant with AT&T's VoIP service. I have a poster in the
MicroCell forum (AT&T's femtocell brand of VoIP service) who was
having issues with his MicroCell and it turns out that he also has
Vonage, which, after a little digging seems to use the SIP ALG
protocol and once he removed that, the MicroCell worked just fine.
I'm just wondering what is it about that protocol that would inhibit
the MicroCell from reaching the AT&T servers.
SIP uses UDP and is locked into certain ports. The protocol also has
difficulties with NAT.

Older routers can have problems where you have two SIP devices on the
LAN side. Newer routers don't seem to have the same problems.

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