Subject: [AVT] Lack of clarity in RFC 3550 on packet loss

From: Rajesh Kumar <[email-masked]>
Date: Fri, 03 Jun 2005 13:07:19 -0700

Steve,

RFC 3550 does not explicitly say that the "fraction lost" and the 
"cumulative number of packets lost" fields in RTCP sender reports and 
receiver reports refer to packet losses after the effects of RFC 2198 
redundancy and RFC 2733 FEC have been taken into account. However, this 
is a reasonable assumption to make, and is in sync with RFC 3611, which 
does make such an assertion.

Is this what the intent of RFC 3550 was?

Thanks,

Rajesh

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

---

From: Colin Perkins <[email-masked]>
Date: Fri, 3 Jun 2005 23:53:23 +0100

Rajesh,

On 3 Jun 2005, at 21:07, Rajesh Kumar wrote:
> "cumulative number of packets lost" fields in RTCP sender reports  
> and receiver reports refer to packet losses after the effects of  
> RFC 2198 redundancy and RFC 2733 FEC have been taken into account.  
> However, this is a reasonable assumption to make, and is in sync  
> with RFC 3611, which does make such an assertion.
>

No, that is exactly the opposite of the intent of RFC 3550.

The "fraction lost" and "cumulative number of packets lost" fields in  
RTCP SR and RR reports always refer to the number of packets lost on  
the wire.  The use of RFC 2198 redundancy or RFC 3722 FEC changes the  
amount of payload data received, but does not affect the pattern of  
packet loss on the network, and hence doesn't affect the packet loss  
statistics reported by RTCP (indeed, reporting loss after the effects  
of RFC 2198 or RFC 2733 would break applications that use RTCP RR  
packets to control the amount of redundancy they add).

Colin

---

From: Rajesh Kumar <[email-masked]>
Date: Fri, 03 Jun 2005 17:11:29 -0700

Colin,
Thanks for the clarification.

RFC 3611 (RTCP-XR) defines a loss rate, which it says is after taking 
redundancy and FEC into account. It also defined a discard rate. It says 
nothing about whether this discard rate is after taking redundancy and 
FEC into account, but should we assume that this is so? I would think so 
- in order for RTCP-XR to be consistent with itself in this regard, even 
if it is not consistent with RTCP.

Thanks,

Rajesh

Colin Perkins wrote:

>> and receiver reports refer to packet losses after the effects of  RFC 
>> 2198 redundancy and RFC 2733 FEC have been taken into account.

---

From: Colin Perkins <[email-masked]>
Date: Sat, 4 Jun 2005 11:07:12 +0100

Rajesh,

On 4 Jun 2005, at 01:11, Rajesh Kumar wrote:
> RFC 3611 (RTCP-XR) defines a loss rate, which it says is after  
> taking redundancy and FEC into account. It also defined a discard  
> rate. It says nothing about whether this discard rate is after  
> taking redundancy and FEC into account, but should we assume that  
> this is so?

I'll let the authors clarify.

> I would think so - in order for RTCP-XR to be consistent with  
> itself in this regard, even if it is not consistent with RTCP.

Note that the RTCP XR report is intentionally different from RTCP RR  
in this respect, since the need for both types of metric was realised.

Colin

---

From: "Alan Clark" <[email-masked]>
Date: Thu, 9 Jun 2005 09:40:21 -0400

Rajesh

The discard rate and loss rate are both determined after redundancy and FEC

Regards

Alan

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of
> Colin Perkins
> Sent: Saturday, June 04, 2005 6:07 AM
> To: [email-masked]
> Cc: [email-masked]; [email-masked]
> Subject: Re: [AVT] Lack of clarity in RFC 3550 on packet loss
> 
> 
> Rajesh,
>