3 Sep
2003
3 Sep
'03
1:14 p.m.
Thanks Jan,
I should have made myself a little bit clearer; I am using the RTC 1.2 API
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rt
c/real_time_communications_rtc_client_start_page.asp)
What I find the most interesting is -
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc
/traversal_of_upnp_enabled_nats.asp specifically the last sentence of the
third paragraph. Why I can't provide it my external IP address and port on
the NAT is annoying! I wonder if it would be possible to modify the REGISTER
message on the way to the SIP server and change the IP:Port to my external
NAT address mapping - or get NATHelper to do this for me.
Gary
-----Original Message-----
From: Jan Janak [mailto:jan@iptel.org]
Sent: 03 September 2003 10:34
To: Gary Brewer
Cc: serusers(a)lists.iptel.org
Subject: Re: [Serusers] NAT & RTPPRoxy
Hello, comments inline. All the NAT stuff is quite complicated and
whether it would work or not depends on many factors.
On 03-09 09:55, Gary Brewer wrote:
Hi,
I have come across a similar problem. I want to use the A/V facilities of
Windows Messenger if one or both of my clients are behind a NAT. I realise
that it seems to be impossible to get this to work if the NAT is
symmetric.
(See: RFC3489 "Applicability Statement")
That depends. It could work even with symmetric NAT if the client you
are using does support symmetric signalling and RTP (I am not sure Windows
Messenger is). That means the user agent must be ready to receive SIP
requests and responses on the same port which was used as the source port
for sending SIP messages. Also it must support symmetric RTP to make
media work.
Also the user agent must create REGISTERs containing public IP of the
NAT (can be determined using STUN, for example), or you would have to
use nathelper module on the server.
If only one of my clients is behind a NAT then it
would seem I would have
to
communicate my NATs external address and port mapping
to the non-NAT'd
client (possibly with the help of STUN) in my SIP Invite SDP message. I
Yes, but Windows Messenger doesn't support STUN.
would also have to setup UDP mappings for SIP,
RTP/RTCP Audio Video on my
NAT. Are my A/V port mappings also included in the Invite SDP message?
In case of symmetrict RTP, the client in the public internet will
ignore what it receives in SDP and will send media back to the same IP
and port from which it comes from the other side. That makes the
communication through a NAT possible, but the client behind the NAT
must send first media package (that packet will open a pinhole in the
NAT). Also both sides must support symmetrict RTP and the client
behind the NAT must signal that it is using this approach.
If the clients do not support symmetric signalling, then some kind of
"NAT configuration" would be necesarry.
For example, many user agents can be configured to use ports from a
specified port range only for RTP (let's say ports 10000-10100). You
can then configure your NAT box to forward all the ports from the
range back to your user agent.
If both clients are NAT'd then what is the
approach? I don't see how I
register with the SIP server using an external NAT address (my guess is
this
is what I would have to use if I wanted anyone on the
other side of the
NAT
to be able to see me). MSFT have seemed to got around
this problem by
recommended everyone to use uPnP enabled NATs, which will automatically
bind
to an external address on the NAT and, I assume, use
this when they
register
with the SIP server.
If both clients are behind NATs then you would probably have to use an
RTP proxy which will be placed in the public internet.
RTPProxy is here
https://demo.portaone.com/~sobomax/PortaSIP/ how does
RTPProxy help in the NAT situation, does it at all?
See the previous insertion. It could help in the case when both
clients are behind NATs and it could possibly help in some other cases
too.
Please correct me where I am wrong, I am still trying
to get my head
around
all of this! Has anyone successfully been able to get
any of the scenarios
above working (with AV)?
There is a couple of people who are running their clients behind NATs
on the mailing list, so I hope they could give you some advice.
Jan.
This email may contain material that is confidential and/or privileged. It
is for the sole use of the intended recipient. Any review, reliance or
distribution by others of the e-mail or its contents or forwarding without
express permission is strictly prohibited. No contractual undertakings are
accepted by virtue of transmission of this e-mail unless expressly stated
otherwise in the text of the e-mail itself. If you are not the intended
recipient, please contact the sender and delete all copies. Contact us
directly or via our website at www.rawcommunications.com.
3 Sep
3 Sep
1:32 p.m.
New subject: [Serusers] NAT & RTPPRoxy
On 03-09 11:14, Gary Brewer wrote:
Thanks Jan,
I should have made myself a little bit clearer; I am using the RTC 1.2 API
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rt
c/real_time_communications_rtc_client_start_page.asp)
I have no experience with that API, so you will have to experiment.
But if the webpages are correct and they really implemented everything
as they describe then it should work.
What I find the most interesting is -
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc
/traversal_of_upnp_enabled_nats.asp specifically the last sentence of the
third paragraph. Why I can't provide it my external IP address and port on
the NAT is annoying! I wonder if it would be possible to modify the REGISTER
message on the way to the SIP server and change the IP:Port to my external
NAT address mapping - or get NATHelper to do this for me.
Yes, the sentence is right, it says that the communication is not
possible without an Application Level Gateway.
Application Level Gateway is something that can configure your NAT box
so the media traffic gets through. In the simplest form it could be a
couple of rules in your NAT that allow traffic from a specified port
range (as described in my previous email), it can be also an
application that monitors all the SIP traffic and opens the pinholes
accordingly, or it can be a separate application that is told to open
a pinhole using some other protocol -- like FCP, see
http://iptel.org/fcp.
Ad REGISTER, yes, nathelper can do this for you on the server.
Jan.
1:39 p.m.
New subject: [Serusers] NAT & RTPPRoxy
BTW, the webpage says that you can find out the IP and ports used by
yourself if the NAT doesn't support UPnP and make the API to use it.
BTW2: I am aware of one IP phone that supports UPnP:
http://www.act-tel.com.tw
Those guys had UPnP testbed at the last SIPIt.
Jan.
On 03-09 11:14, Gary Brewer wrote:
Thanks Jan,
I should have made myself a little bit clearer; I am using the RTC 1.2 API
(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rt
c/real_time_communications_rtc_client_start_page.asp)
What I find the most interesting is -
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc
/traversal_of_upnp_enabled_nats.asp specifically the last sentence of the
third paragraph. Why I can't provide it my external IP address and port on
the NAT is annoying! I wonder if it would be possible to modify the REGISTER
message on the way to the SIP server and change the IP:Port to my external
NAT address mapping - or get NATHelper to do this for me.
Gary
-----Original Message-----
From: Jan Janak [mailto:jan@iptel.org]
Sent: 03 September 2003 10:34
To: Gary Brewer
Cc: serusers(a)lists.iptel.org
Subject: Re: [Serusers] NAT & RTPPRoxy
Hello, comments inline. All the NAT stuff is quite complicated and
whether it would work or not depends on many factors.
On 03-09 09:55, Gary Brewer wrote:
Hi,
I have come across a similar problem. I want to use the A/V facilities of
Windows Messenger if one or both of my clients are behind a NAT. I realise
that it seems to be impossible to get this to work if the NAT is
symmetric.
(See: RFC3489 "Applicability
Statement")
That depends. It could work even with symmetric NAT if the client you
are using does support symmetric signalling and RTP (I am not sure Windows
Messenger is). That means the user agent must be ready to receive SIP
requests and responses on the same port which was used as the source port
for sending SIP messages. Also it must support symmetric RTP to make
media work.
Also the user agent must create REGISTERs containing public IP of the
NAT (can be determined using STUN, for example), or you would have to
use nathelper module on the server.
If only one of my clients is behind a NAT then it
would seem I would have
to
communicate my NATs external address and port
mapping to the non-NAT'd
client (possibly with the help of STUN) in my SIP Invite SDP message. I
Yes, but Windows Messenger doesn't support STUN.
would also have to setup UDP mappings for SIP,
RTP/RTCP Audio Video on my
NAT. Are my A/V port mappings also included in the Invite SDP message?
In case of symmetrict RTP, the client in the public internet will
ignore what it receives in SDP and will send media back to the same IP
and port from which it comes from the other side. That makes the
communication through a NAT possible, but the client behind the NAT
must send first media package (that packet will open a pinhole in the
NAT). Also both sides must support symmetrict RTP and the client
behind the NAT must signal that it is using this approach.
If the clients do not support symmetric signalling, then some kind of
"NAT configuration" would be necesarry.
For example, many user agents can be configured to use ports from a
specified port range only for RTP (let's say ports 10000-10100). You
can then configure your NAT box to forward all the ports from the
range back to your user agent.
If both clients are NAT'd then what is the
approach? I don't see how I
register with the SIP server using an external NAT address (my guess is
this
is what I would have to use if I wanted anyone on
the other side of the
NAT
to be able to see me). MSFT have seemed to got
around this problem by
recommended everyone to use uPnP enabled NATs, which will automatically
bind
to an external address on the NAT and, I assume,
use this when they
register
with the SIP server.
If both clients are behind NATs then you would probably have to use an
RTP proxy which will be placed in the public internet.
RTPProxy is here
https://demo.portaone.com/~sobomax/PortaSIP/ how does
RTPProxy help in the NAT situation, does it at all?
See the previous insertion. It could help in the case when both
clients are behind NATs and it could possibly help in some other cases
too.
Please correct me where I am wrong, I am still
trying to get my head
around
all of this! Has anyone successfully been able to
get any of the scenarios
above working (with AV)?
There is a couple of people who are running their clients behind NATs
on the mailing list, so I hope they could give you some advice.
Jan.
This email may contain material that is confidential and/or privileged. It
is for the sole use of the intended recipient. Any review, reliance or
distribution by others of the e-mail or its contents or forwarding without
express permission is strictly prohibited. No contractual undertakings are
accepted by virtue of transmission of this e-mail unless expressly stated
otherwise in the text of the e-mail itself. If you are not the intended
recipient, please contact the sender and delete all copies. Contact us
directly or via our website at www.rawcommunications.com.
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Jan Janak