RTP port for sending media

Nadathur, Srivathsan G (Srivathsan) snadathur at LUCENT.COM
Thu Sep 14 15:23:52 EDT 2000

Thanks Paul.

I got confused by the following line from the H.245 section 7.3.2
However I think what is said in H.323 has more precedence over what is said
in H.245.

"mediaControlChannel indicates the media control channel in which the sender
of the openLogicalChannelAck will be listening for media control messages
for this session. This field is present only when a media control channel is


-----Original Message-----
From: Paul E. Jones [mailto:paulej at PACKETIZER.COM]
Sent: Thursday, September 14, 2000 2:52 PM
Subject: Re: RTP port for sending media

Srivathsan, 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"


----- 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
> 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
> as the "receive" address.  But then I questioned, "what about the fact
> the associated RTCP port (next odd port) is used for receiving RR
> 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
> 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
> assumptions can firewall vendors make, so we can run into trouble with
> 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
> 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
> Suppose I send an OLC proposing a channel to be opened and I provide my
> 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
> My understanding was that I was obligated to transmit media from port
> since I indicated that the RTCP port was 2501. Thanks,Paul
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