Subject: [AVT] RTP Testing Strategies - transmission interval

From: "Craciun Diana Madalina-STFD002" <[email-masked]>
Date: Tue, 3 Mar 2009 09:18:07 -0000

Hi,
 
Text extracted from RFC 3158 - "RTP Testing Strategies":
 
      o  the minimum interval is never less than 2 seconds or more than
2.5 seconds;        
      o  the maximum interval is never more than 7 seconds or less than
5.5 seconds;
      o  the average interval is between 4.5 and 5.5 seconds; 
      o  the number of intervals between x and x+500ms is less than the
number of intervals between x+500ms and x+1s, for any x.
 
I do not understand why the average interval is between 4.5 and 5.5
seconds. According to RFC 3550, if the bandwidth is configured to be
large, the minimum interval is selected: T=5s. After that the interval
is set to a number uniformly distributed between 0.5*T and 1.5*T, so
[2.5, 7.5]. The resulting interval is then divided by e -3/2 that gives
an interval [2.05, 6.15]. For this interval the average should be
somewhere around 4 not between 4.5 and 5.5.
 
Regards,
Diana Craciun

---

From: Magnus Westerlund <[email-masked]>
Date: Tue, 03 Mar 2009 10:42:04 +0100

Craciun Diana Madalina-STFD002 skrev:
> Hi,
>  
> Text extracted from RFC 3158 - “RTP Testing Strategies”:
>  

You forget about the reconsideration algorithm. Every time your timer
expires you create a new random number and only sends the RTCP packet if
the new number indicate a time no later then the current delay since
last RTCP packet. Thus you  bias the average towards higher numbers.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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