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@packetizer.com] Sent: Tuesday, September 12, 2000 12:20 PM To: Anatoli Levine Cc: h323implementors@imtc.org; ITU-SG16@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@radvision.com To: Paul E. mailto:paulej@packetizer.com Jones Cc: h323implementors@imtc.org mailto:h323implementors@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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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@LUCENT.COM To: ITU-SG16@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@packetizer.com] Sent: Tuesday, September 12, 2000 12:20 PM To: Anatoli Levine Cc: h323implementors@imtc.org; ITU-SG16@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@radvision.com To: Paul E. mailto:paulej@packetizer.com Jones Cc: h323implementors@imtc.org mailto:h323implementors@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
For help on this mail list, send "HELP ITU-SG16" in a message to listserv@mailbag.intel.com
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participants (2)
-
Nadathur, Srivathsan G (Srivathsan) -
Paul E. Jones