Subject: [Tsvwg] - Heart Beat interval

From: Kanand <[email-masked]>
Date: Mon, 08 May 2006 16:42:44 +0530

hi,
   As per RFC 2960 and present implementation of SCTP stack, HEARTBEAT 
interval is calculated  as mentioned in  
   section 8.3
              i,e  heartbeat interval = RTO + jittering of ± 50% of  
heartbeat interval
  
   As per  implementors  Guide in section 8.3,  hearbeat interval is 
calculated as follows,

    heartbeat interval = RTO + jttering of ± 50% of  RTO
    i,e  jttering of ± 50% of  RTO not  jttering of ± 50% of  HEARTBEAT

  do we need to implement  this calculation  in present stack according 
to implementor's guide?
  If so  what is the purpose of  doing this  change?.

regards
kalpana

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Mon, 8 May 2006 05:32:43 -0600

Kanand,

Kanand wrote:                                   (Mon, 08 May 2006 16:42:44)
>   do we need to implement  this calculation  in present stack according 

Yes, eventually.

>   If so  what is the purpose of  doing this  change?.

The jitter is to keep many hosts from sending at the same instant.  The
RFC 2960 calculation does not acheive that (±50% of a fixed, known value
is not a jitter at all).  The IG calculation, being ±50% of a variable
value that can vary widely from host to host, acheives the purpose.

--brian

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/

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From: devayya <[email-masked]>
Date: Mon, 08 May 2006 17:01:52 +0530

Brian,

But the HBInterval is re-calculated based on path RTO. So how can HB 
interval can be a fixed value? Please clarify.

thanks,
devayya

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Mon, 8 May 2006 06:33:19 -0600

devayya,

See rfc4460 section 2.10.1 "Description of the problem".

--brian

devayya wrote:                                                    (Mon, 08 May 2006 17:01:52)

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/

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From: Mark Butler <[email-masked]>
Date: Mon, 08 May 2006 10:35:55 -0600

>value that can vary widely from host to host, acheives the purpose.
The proper concept of "jitter" here is not to add one of two fixed 
values, but rather to add a random value that is within the specified 
range.  Given a suitable random number generator, the Implementor's 
Guide rule is much more stable and responsive - the previous formula can 
take an considerable amount of time to adapt to a decreasing RTO for 
example, not to mention produce negative results.

 - Mark B.