RTP port for sending media

Paul E. Jones paulej at PACKETIZER.COM
Thu Sep 14 14:51:48 EDT 2000


Srivathsan,

6.2.8.2 states this:
``The initiating terminal shall send an openLogicalChannel message as
described in Recommendation H.245. If the logical channel is to carry a
media type using RTP (audio or video), the openLogicalChannel message shall
include the mediaControlChannel parameter containing the Transport Address
for the reverse RTCP channel.''

Note the part "shall include the mediaControlChannel parameter"

Paul

----- Original Message -----
From: "Nadathur, Srivathsan G (Srivathsan)" <snadathur at LUCENT.COM>
To: <ITU-SG16 at mailbag.cps.intel.com>
Sent: Thursday, September 14, 2000 12:56 PM
Subject: Re: RTP port for sending media


> Also, I remember H.245 spec implying that RTCP is not a mandatory
> requirement. Could someone clarify.
>
> Thanks
> Srivathsan.
>
> -----Original Message-----
> From: Paul E. Jones [mailto:paulej at packetizer.com]
> Sent: Tuesday, September 12, 2000 12:20 PM
> To: Anatoli Levine
> Cc: h323implementors at imtc.org; ITU-SG16 at mailbag.cps.intel.com
> Subject: Re: RTP port for sending media
>
>
> Anatoli, et al,
>
> 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.
>
> So, if you have a line like this in the INVITE message:
>     m=
> 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?"
>
> The answer was 'no'.  So this made me curious about H.323 implementations.
>
> 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.
>
> Thanks,
> Paul
>
>
> ----- Original Message -----
> From: Anatoli Levine <mailto:alevine at radvision.com>
> To: Paul E.  <mailto:paulej at packetizer.com> Jones
> Cc: h323implementors at imtc.org <mailto:h323implementors at imtc.org>
> Sent: Tuesday, September 12, 2000 9:37 AM
> Subject: Re: RTP port for sending media
>
> Paul,
>
> 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.
>
>
> Anatoli
>
>
> "Paul E. Jones" wrote:
>
>
> Folks, I have a question... I thought this was clear, but perhaps it is
not.
> Suppose I send an OLC proposing a channel to be opened and I provide my
RTCP
> port in the mediaControlChannel field.  Say, 2501. H.245 states in B.3.1:
>
> 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.
>
> 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?
> My understanding was that I was obligated to transmit media from port
2500,
> since I indicated that the RTCP port was 2501. Thanks,Paul
>
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