Subject: [AVT] draft-ietf-avt-app-rtp-keepalive-01

From: "Alfred E. Heggestad" <[email-masked]>
Date: Tue, 18 Dec 2007 11:04:51 +0100

Hi

I have some comments on draft-ietf-avt-app-rtp-keepalive-01. I found
the document very useful, many thanks for writing this!

Section 4.8 describes the RTP Packet with unknown payload type. It should
be added some text describing how the RTP header fields should be handled.
For example marker bit, sequence number, timestamp. My guess is that the
sequence number is incremented by one for each packet sent. What about
timestamp? Should it be incremented for each packet sent? Since we are
sending 0 bytes of payload, which value should it be increment by.

NITS:

6.  Additional considerations

    The agent SHOULD only send RTP keepalive when it does not send
    regular RTP paquets.
                ^^^^^^^

-> typo: should be "packets"

7.  Security Considerations

    The keepalive packets are sent on the same path as regular RTP media
    packets.  In addition, they do not convey any valuable information.
    So the mechanism described here doest not imply new security issues.
                                    ^^^^^

-> typo: should be "does"

/alfred

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: "SOLLAUD Aurelien RD-TECH-LAN" <[email-masked]>
Date: Tue, 18 Dec 2007 12:10:56 +0100

Hi

Thank you for the feedback.

You are right there is a lack of details in section 4.8.
The keepalive packet is sent within the same RTP session as the actual media, so yes, the sequence number will be incremented by one for each packet.
For the timestamp, it seems good to fill the field with the same value a media packet would have at this time.
The marker bit is not significant for the keepalive packets, so it should be set to zero.

We'll add more text in a next revision. We'll also fix the typos, thanks.

Regards,
Aurelien 

-----Message d'origine-----
De : Alfred E. Heggestad [mailto:[email-masked]] 
Envoyé : mardi 18 décembre 2007 11:05
À : MARJOU Xavier RD-CORE-LAN; SOLLAUD Aurelien RD-TECH-LAN; [email-masked]
Objet : draft-ietf-avt-app-rtp-keepalive-01

Hi

I have some comments on draft-ietf-avt-app-rtp-keepalive-01. I found the document very useful, many thanks for writing this!

Section 4.8 describes the RTP Packet with unknown payload type. It should be added some text describing how the RTP header fields should be handled.
For example marker bit, sequence number, timestamp. My guess is that the sequence number is incremented by one for each packet sent. What about timestamp? Should it be incremented for each packet sent? Since we are sending 0 bytes of payload, which value should it be increment by.

NITS:

/alfred

---

From: Colin Perkins <[email-masked]>
Date: Sun, 30 Dec 2007 11:24:31 +0000

Aurelien,

I'm very happy to see some concrete recommendations in this version  
of the draft, however I'm concerned that the final recommendation (to  
use RTP packets with unknown payload type as a keep alive mechanism)  
leads implementers in an undesirable direction.

The desired solution to keep alive the session is to send RTCP  
packets multiplexed on the RTP port. This is desirable because it  
reduces the number of ports used, and also because the keep alive  
packets provide some useful functionality, in addition to keeping  
middlebox bindings open. The issue, as your draft points out, is  
moving implementations to use multiplexed RTCP, since it must be  
signalled. To encourage this, I suggest the draft recommends  
implementations "SHOULD use multiplexed RTP and RTCP" as the main  
keep alive mechanism, explaining why its desirable to do so, but then  
recommends the use of RTP packets with unknown payload type number as  
a fallback if multiplexed RTCP cannot be negotiated.

Cheers,
Colin

On 18 Dec 2007, at 11:10, SOLLAUD Aurelien RD-TECH-LAN wrote:
> The keepalive packet is sent within the same RTP session as the  
> actual media, so yes, the sequence number will be incremented by  
> one for each packet.
> For the timestamp, it seems good to fill the field with the same  
> value a media packet would have at this time.
> I have some comments on draft-ietf-avt-app-rtp-keepalive-01. I  
> found the document very useful, many thanks for writing this!
>
>
> Section 4.8 describes the RTP Packet with unknown payload type. It  
> should be added some text describing how the RTP header fields  
> should be handled.
> For example marker bit, sequence number, timestamp. My guess is  
> that the sequence number is incremented by one for each packet  
> sent. What about timestamp? Should it be incremented for each  
> packet sent? Since we are sending 0 bytes of payload, which value  
> should it be increment by.
>
>
>
> NITS:
>

-- 
Colin Perkins
http://csperkins.org/