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<DIV><SPAN class=190101317-14092000><FONT face=Arial color=#800000 size=2>I am
not sure it would help NAT devices. Couldn't a sender "fake" the RTP sender port
by inserting another value?</FONT></SPAN></DIV>
<DIV><SPAN class=190101317-14092000><FONT face=Arial color=#800000
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=190101317-14092000><FONT face=Arial color=#800000 size=2>More
commonly, I would believe that the port would typically be set to "0"?
</FONT></SPAN></DIV>
<DIV><SPAN class=190101317-14092000><FONT face=Arial color=#800000 size=2>RFC
768 (UDP) says:</FONT></SPAN></DIV>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV><SPAN class=190101317-14092000><FONT face=Courier size=2>Source Port is
an optional field, when meaningful, it indicates the port<BR>of the
sending process, and may be assumed to be the port to
which a<BR>reply should be addressed in the absence of any other
information. If<BR>not used, a value of zero is
inserted.</FONT><BR></SPAN></DIV></BLOCKQUOTE>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Paul E. Jones
[mailto:paulej@PACKETIZER.COM]<BR><B>Sent:</B> Tuesday, September 12, 2000 9:20
AM<BR><B>To:</B> ITU-SG16@MAILBAG.INTEL.COM<BR><B>Subject:</B> Re: RTP port for
sending media<BR><BR></DIV></FONT>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>Anatoli, et
al,</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"> </DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>I agree that it would be
very helpful for NAT devices or other equipment to be able to safely rely on
receiving media from the specified RTP port that is one lower than the RTCP port
advertised in the original OLC message. I thought that was the expected
behavior when using RTP/RTCP, but recent discussions with folks working on SIP
is that "no, that's not necessarily true." Apparently, it is believed that
a SIP device may send RTP from any port.</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial></FONT> </DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>So, if you have a line
like this in the INVITE message:</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>
m=</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>to indicate a
bi-directional media flow, the RTP address is interpreted only as the "receive"
address. But then I questioned, "what about the fact that the associated
RTCP port (next odd port) is used for receiving RR packets.. would that not
suggest that the RTP port for sending is also the same port specified in this
'm=' line?"</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"> </DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>The answer was
'no'. So this made me curious about H.323 implementations.</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"> </DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>Do we need to clarify
that the RTP port used to send data associated with the RTCP address in an OLC
is the next lower port (even) number, or do we have implementations out there
that send RTP traffic from and random port, irrespective of the RTCP port put in
the forwardLogicalChannelParameters of the OLC message? If the latter is
the case, I think we need to state this clearly, too.</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"> </DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>Thanks,</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"><FONT face=Arial>Paul</FONT></DIV>
<DIV dir=ltr style="MARGIN-RIGHT: 0px"> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=alevine@radvision.com href="mailto:alevine@radvision.com">Anatoli
Levine</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=paulej@packetizer.com
href="mailto:paulej@packetizer.com">Paul E. Jones</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Cc:</B> <A title=h323implementors@imtc.org
href="mailto:h323implementors@imtc.org">h323implementors@imtc.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, September 12, 2000 9:37
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: RTP port for sending
media</DIV>
<DIV><BR></DIV>Paul,
<P>when you are transmitting, you can probably can use any port, but the
problem is that usually it make sense to use the same RTP port for both
receive and transmit - in this case if you will use a random RTP port you will
violate the rules. Another dangerous thing is that we don 't know what
assumptions can firewall vendors make, so we can run into trouble with this
also ( if assumption will be made from the 2501 port number). I would suggest
that we will make it clear in the standard that two consequent port numbers
would be used for RTP/RTCP in any case.
<P>Anatoli
<P>"Paul E. Jones" wrote:
<BLOCKQUOTE TYPE="CITE">
<STYLE></STYLE>
<FONT face=Arial>Folks,</FONT> <FONT face=Arial>I have a question... I
thought this was clear, but perhaps it is not.</FONT> <FONT
face=Arial>Suppose I send an OLC proposing a channel to be opened and I
provide my RTCP port in the mediaControlChannel field. Say,
2501.</FONT> <FONT face=Arial>H.245 states in B.3.1:</FONT>
<BLOCKQUOTE style="MARGIN-RIGHT: 0px"><FONT size=-1>The mediaChannel
indicates a transportAddress to be used for the logical channel. When the
transport is unicast, mediaChannel is not present in the
OpenLogicalChannel forwardLogicalChannelParameters, but may be present in
the reverseLogicChannelParameters.</FONT></BLOCKQUOTE><FONT face=Arial>Is it
safe to assume, then, that I will send my media to you from the port 2500,
or am I at liberty to send my RTP data to you using any port I
choose?</FONT> <FONT face=Arial>My understanding was that I was
obligated to transmit media from port 2500, since I indicated that the RTCP
port was 2501.</FONT> <FONT face=Arial>Thanks,</FONT><FONT
face=Arial>Paul</FONT> </BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>