Subject: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

From: Ash Kat <[email-masked]>
Date: Wed, 4 Jun 2008 15:13:38 +0530 (IST)

Hello All,
 
SCTP RFC 4690 has mentioned a parameter HB.Max.Burst.
As per RFC 4960 section 4.5 :
   The number of HEARTBEATS sent at each RTO SHOULD be limited by the
   HB.Max.Burst parameter.
 
During the Path verification when an RTO expires, SCTP will re-send the Heartbeat to that address.
Please clarify me, how HB.Max.Burst parameter will control the number of Heartbeat sent to that address.
Shouldn't the number of Heartbeat send to a particular address at any time will always be 1? 
If Yes, then why HB.Max.Burst is required?
If No, then please make me understand that how this parameter is used.
 
Thanks & Regards,
Ashwani Kathuria

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From: "Ashish Gupta" <[email-masked]>
Date: Wed, 4 Jun 2008 15:39:00 +0530

Hi Ashwani,

When RTO expires for an address, your path probing module will get
chance to send HEARTBEATS to other UNCONFIREMD addresses as well (NOT
only to the address for which RTO has expired) limited by HB.Max.Burst
parameter.

Hope this helps.

Regards,

-Ashish

________________________________

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Ash Kat
Sent: Wednesday, June 04, 2008 3:14 PM
To: [email-masked]; [email-masked]
Subject: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Hello All,

During the Path verification when an RTO expires, SCTP will re-send the
Heartbeat to that address.

Please clarify me, how HB.Max.Burst parameter will control the number of
Heartbeat sent to that address.

Shouldn't the number of Heartbeat send to a particular address at any
time will always be 1? 

Thanks & Regards,

Ashwani Kathuria

________________________________

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---

From: Ash Kat <[email-masked]>
Date: Wed, 4 Jun 2008 17:16:12 +0530 (IST)

Hello Ashish,
 
Thanks for your prompt response.
The purpose of HB.Max.Burst is still not clear to me.
Let us take an example scenario. 
 
Suppose the peer to IUT has 2 interfaces IP-X and IP-Y RTO for IP-X is 1 sec. and for IP-Y is 2 sec.
HB.Max.Burst at IUT set to 2.
 
The IUT has sent the HBeat to IP-X & IP-Y and started the Retransmission-timer separately for IP-X (1 sec) and I-Y (2 sec)..
 
Both IP-X and IP-Y are not responding.
 
After 1 sec.
RTO expired for IP-X. 
As the HB.Max.Burst in 2, so IUT will send the HBeat to both, IP-X and IP-Y, on the expiry of RTO for IP-X alone.
 
Why SCTP needs to send the Heartbeat to IP-Y even if I have already sent an Heartbeat to IP-Y for which Retransmission timer is already running?
Here, the retransmission timer for IP-Y will take 1 more second to expire.
 
Also, if IUT sends the Heartbeat to IP-Y on the RTO expiry of IP-X then will it restart the RTO timer for IP-Y?
 
Please clarify as I am not able to understand the benefit of making HB.Max.Burst > 1.
 
Thanks & Regards,
Ashwani Kathuria
----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <[email-masked]>; [email-masked]; [email-masked]
Sent: Wednesday, 4 June, 2008 3:39:00 PM
Subject: RE: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Hi Ashwani,
 
When RTO expires for an address, your path probing module will get chance to send HEARTBEATS to other UNCONFIREMD addresses as well (NOT only to the address for which RTO has expired) limited by HB.Max.Burst parameter.
 
Hope this helps.
 
Regards,
-Ashish

From:[email-masked] [mailto:[email-masked]] On Behalf Of Ash Kat
Sent: Wednesday, June 04, 2008 3:14 PM
To: [email-masked]; [email-masked]
Subject: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter
 
Hello All,
 
SCTP RFC 4690 has mentioned a parameter HB.Max.Burst.
As per RFC 4960 section 4..5 :
   The number of HEARTBEATS sent at each RTO SHOULD be limited by the
   HB.Max.Burst parameter.

Thanks & Regards,
Ashwani Kathuria

Bring your gang together. Do your thing. Find your favourite Yahoo! Group.

      Meet people who discuss and share your passions. Go to http://in.promos.yahoo.com/groups/bestofyahoo/

---

From: "Ashish Gupta" <[email-masked]>
Date: Wed, 4 Jun 2008 17:29:33 +0530

Ashwani,

It's a max value. So, in the example scenario, it is not required to
send HEARTBEAT to IP-Y, on IP-X RTO expiry.

If the peer has got large number of addresses, then this parameter is
used to control the number of HEARTBEAT sent for probing as one would
not like to flood the network with too many heartbeats. You can think of
a scenario with 6 addresses and the value of HB.Max.Burst as 2. Every
time your path probing module get chance, it will send two HEARTBEATS to
probe the UNCONFIRMED addresses.

Regards,

-Ashish 

From: Ash Kat [mailto:[email-masked]] 
Sent: Wednesday, June 04, 2008 5:16 PM
To: Ashish Gupta; [email-masked]; [email-masked]
Subject: Re: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Hello Ashish,

Suppose the peer to IUT has 2 interfaces IP-X and IP-Y 

RTO for IP-X is 1 sec. and for IP-Y is 2 sec..

The IUT has sent the HBeat to IP-X & IP-Y and started the
Retransmission-timer separately for IP-X (1 sec) and I-Y (2 sec).

After 1 sec.

RTO expired for IP-X. 

As the HB.Max.Burst in 2, so IUT will send the HBeat to both, IP-X and
IP-Y, on the expiry of RTO for IP-X alone.

Why SCTP needs to send the Heartbeat to IP-Y even if I have already sent
an Heartbeat to IP-Y for which Retransmission timer is already running?

Here, the retransmission timer for IP-Y will take 1 more second to
expire.

Also, if IUT sends the Heartbeat to IP-Y on the RTO expiry of IP-X then
will it restart the RTO timer for IP-Y?

Please clarify as I am not able to understand the benefit of making
HB.Max.Burst > 1.

Thanks & Regards,

Ashwani Kathuria

----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <[email-masked]>; [email-masked];
[email-masked]

Hi Ashwani,

Hope this helps.

Regards,

-Ashish

Hello All,

Thanks & Regards,

Ashwani Kathuria

---

From: Ash Kat <[email-masked]>
Date: Wed, 4 Jun 2008 18:09:59 +0530 (IST)

Ashish,
 
You have mentioned the 2 points:
 
1. HB.Max.Burst is a max value and the number of heartbeat sent should be less then or equal to this number.
On what basis the SCTP will decide whether the number of heartbeats sent is less then HB.Max.Burst or should it send number of Heartbeats equal to the number of HB.Max.Burst?
It means RFC 4960 is not clear about the usage of HB.Max.Burst.
2. This parameter will prevent network from flooding with too many heartbeats to network, in case peer has large number of addresses.
I do not think so, because keeping this parameter > 1 will create even more traffic. As after the RTO expiry of an address, the SCTP will send Heartbeat to even those addresses for which heartbeat was already been sent.
If this happens, then we have 2 Heartbeats on network for an UNCONFIRMED address for which Retransmission timer has still not expired.
 
One more question, is SCTP re-starting the RTO of those addresses for which RTO has not expired but a heartbeat is sent to them only because some other address' RTO has expired?
according to example mentioned in previous mail, will SCTP of IUT will re-start the RTO for IP-Y when the RTO of IP-X expires, even if RTO for IP-Y is still running?
 
Thanks & Regards
Ashwani Kathuria
IMO the value of HB..Max.Burst can be equal to one only.(as also recommended by the RFC 4960)
Keeping it greater then 1 would not control the flooding of Heartbeats on network but will make it worse.
 
If this is not the case then there should be some other way to implement this parameter which is still not clear to us.
----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <[email-masked]>; [email-masked]
Sent: Wednesday, 4 June, 2008 5:29:33 PM
Subject: RE: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Ashwani,
 
It’s a max value. So, in the example scenario, it is not required to send HEARTBEAT to IP-Y, on IP-X RTO expiry.
 
If the peer has got large number of addresses, then this parameter is used to control the number of HEARTBEAT sent for probing as one would not like to flood the network with too many heartbeats. You can think of a scenario with 6 addresses and the value of HB.Max.Burst as 2. Every time your path probing module get chance, it will send two HEARTBEATS to probe the UNCONFIRMED addresses.
 
Regards,
-Ashish 

From:Ash Kat [mailto:[email-masked]] 
Sent: Wednesday, June 04, 2008 5:16 PM
To: Ashish Gupta; [email-masked]; [email-masked]
Subject: Re: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter
 
Hello Ashish,

 

The IUT has sent the HBeat to IP-X & IP-Y and started the Retransmission-timer separately for IP-X (1 sec) and I-Y (2 sec).

After 1 sec.
RTO expired for IP-X. 

 
 
Thanks & Regards,
Ashwani Kathuria
 
----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <ashwani_groups@yahoo..com>; [email-masked]; [email-masked]
Sent: Wednesday, 4 June, 2008 3:39:00 PM
Subject: RE: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter
Hi Ashwani,

Hope this helps.
 
Regards,
-Ashish

 
Hello All,

 
Thanks & Regards,
Ashwani Kathuria

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---

From: "Ashish Gupta" <[email-masked]>
Date: Wed, 4 Jun 2008 18:20:25 +0530

Please see my comments inline.

Regards,

-Ashish

From: Ash Kat [mailto:[email-masked]] 
Sent: Wednesday, June 04, 2008 6:10 PM
To: Ashish Gupta; [email-masked]
Subject: Re: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Ashish,

1.. HB.Max.Burst is a max value and the number of heartbeat sent should
be less then or equal to this number.

On what basis the SCTP will decide whether the number of heartbeats sent
is less then HB.Max.Burst or should it send number of Heartbeats equal
to the number of HB.Max.Burst?

[Ashish] See, it is the number of HEARTBEATs sent during one execution
of your path probing module. It does not count HEARTBEATs sent in
earlier execution.

2. This parameter will prevent network from flooding with too many
heartbeats to network, in case peer has large number of addresses.

I do not think so, because keeping this parameter > 1 will create even
more traffic. As after the RTO expiry of an address, the SCTP will send
Heartbeat to even those addresses for which heartbeat was already been
sent.

If this happens, then we have 2 Heartbeats on network for an UNCONFIRMED
address for which Retransmission timer has still not expired.

One more question, is SCTP re-starting the RTO of those addresses for
which RTO has not expired but a heartbeat is sent to them only because
some other address' RTO has expired?

according to example mentioned in previous mail, will SCTP of IUT will
re-start the RTO for IP-Y when the RTO of IP-X expires, even if RTO for
IP-Y is still running?

[Ashish] You got me wrong. HEARTBEAT to IP-Y won't be sent again if it's
RTO is still running. That's what I said, it is a max value, if RTO is
till running for IP-Y, on RTO expiry for IP-X, heartbeat will be sent to
IP-X ONLY.

IMO the value of HB.Max.Burst can be equal to one only.(as also
recommended by the RFC 4960)

Keeping it greater then 1 would not control the flooding of Heartbeats
on network but will make it worse.

If this is not the case then there should be some other way to implement
this parameter which is still not clear to us.

Thanks & Regards

Ashwani Kathuria

----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <[email-masked]>; [email-masked]
Sent: Wednesday, 4 June, 2008 5:29:33 PM
Subject: RE: [Sigtran] [SCTP] clarification about HB.Max.Burst parameter

Ashwani,

Regards,

-Ashish 

Hello Ashish,

After 1 sec.

RTO expired for IP-X. 

Thanks & Regards,

Ashwani Kathuria

----- Original Message ----
From: Ashish Gupta <[email-masked]>
To: Ash Kat <[email-masked]>; [email-masked];
[email-masked]

Hi Ashwani,

When RTO expires for an address, your path probing module will get
chance to send HEARTBEATS to other UNCONFIREMD addresses as well (NOT
only to the address for which RTO has expired) limited by HB..Max.Burst
parameter.

Hope this helps.

Regards,

-Ashish

Hello All,

SCTP RFC 4690 has mentioned a parameter HB..Max.Burst.

Thanks & Regards,

Ashwani Kathuria

Send free SMS to your Friends on Mobile from your Yahoo! Messenger.
Download Now! http://messenger.yahoo.com/download.php