Subject: [IPFIX] draft-ietf-ipfix-reducing-redundancy-04.txt: text clarification

From: Benoit Claise <[email-masked]>
Date: Wed, 11 Feb 2009 16:40:05 +0100

Dear all,

We received the following remark from Sven regarding 
http://www.ietf.org/internet-drafts/draft-ietf-ipfix-reducing-redundancy-04.txt

>     8.1.  Transport Protocol Choice
>
>       The proposed method is most effective using a reliable transport
>       protocol for the transfer of the Common Properties.  Therefore the
>       use of PR-SCTP with the reliable mode or TCP is recommended.
>       However, if the path from the Exporting Process to the Collecting
>       Process is not fully reliable, the SCTP or TCP retransmission might
>       reduce the benefits of this specification.  If the path from the
>       Exporting Process to the Collecting Process is full reliable,
>     the use
>       of UDP is less effective because the Common Properties have to
>     be re-
>       sent regularly.

    Do I understand that section correctly: If the path is reliable, you
    should use a reliable transport, and if the path is unreliable you
    should use unreliable UDP? Isn't that upside down? If the path is
    reliable, you can use UDP _without_ retransmission, no need for a
    reliable transport protocol then.

We proposed the following text, removing the confusing sentence.

NEW:

   The proposed method is most effective using a reliable transport
   protocol for the transfer of the Common Properties.  Therefore the
   use of PR-SCTP with the reliable mode or TCP is recommended.
   If the path from the Exporting Process to the Collecting Process is
   full reliable, the use of UDP is less effective because the Common
   Properties have to be re-sent regularly.

Any objections?
Pending on nobody objecting in a couple of work days,  this editorial 
disambiguation will be applied*//*.

Regards, Benoit.

---

From: Brian Trammell <[email-masked]>
Date: Wed, 11 Feb 2009 16:50:09 +0100

Hi Benoit, all,

Hm, that's still kind of confusing. First off, there's no "reliable  
mode" in PR-SCTP. SCTP is modeless, reliability is per-message. PR- 
SCTP can provide "fully reliable" transport. But this terminology  
seems to be overloaded:

"If the path from the Exporting Process to the Collecting Process is  
full reliable"

What does this mean, precisely? My assumption is that it means "if the  
link between the Exporting Process and the Collecting Process has low  
loss and reordering characteristics..." However, the guidance doesn't  
actually change depending on the loss characteristics of the lower  
layer: RR prefers reliable transport for Common Properties, full stop.  
I'd suggest (as usual...) removing any mention of UDP as recommended:

NEW:
The proposed method is most effective using a reliable transport  
protocol for the transfer of the Common Properties. Therefore the use  
of PR-SCTP with the full reliability or TCP is recommended for the  
transmission of IPFIX Messages containing Common Properties.

Cheers,

Brian

On Feb 11, 2009, at 4:40 PM, Benoit Claise wrote:

> Dear all,
>
> We received the following remark from Sven regarding http://www.ietf.org/internet-drafts/draft-ietf-ipfix-reducing-redundancy-04.txt
>>   Exporting Process to the Collecting Process is full reliable, the  
>> use
>>   of UDP is less effective because the Common Properties have to be  
>> re-
>>   sent regularly.
>
> Pending on nobody objecting in a couple of work days,  this  
> editorial disambiguation will be applied.
>
> Regards, Benoit.
> _______________________________________________
> IPFIX mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/ipfix

---

From: Benoit Claise <[email-masked]>
Date: Thu, 12 Feb 2009 09:38:11 +0100

Brian,

First of all, I would like to have Sven's feedback, as he was the one 
asking for this change.
Then, see inline.
> mode" in PR-SCTP. SCTP is modeless, reliability is per-message. 
> PR-SCTP can provide "fully reliable" transport. But this terminology 
> seems to be overloaded:
>
The recommendation doesn't change, agreed.
But the sentence is a warning/clarification against the use of UDP, even 
if the path is fully reliable.
So my preference is to keep this sentence (slightly modified, see 
below)... however, this is a minor point IMHO.
What are the others thinking?

NEW:
    The proposed method is most effective using a reliable transport 
protocol for the transfer
    of the Common Properties. Therefore the use of PR-SCTP with the full 
reliability or TCP
    is recommended for the transmission of IPFIX Messages containing 
Common Properties.
    If the path from the Exporting Process to the Collecting Process is 
fully reliable (i.e., no loss),
    the use of UDP is less effective because the Common Properties have 
to be re-sent regularly.

Regards, Benoit.
>>>   Exporting Process to the Collecting Process is full reliable, the use
>>>   of UDP is less effective because the Common Properties have to be re-
>>>   sent regularly.
>>
>> disambiguation will be applied.
>>
>> Regards, Benoit.

---

From: Brian Trammell <[email-masked]>
Date: Thu, 12 Feb 2009 10:14:08 +0100

Hi, Benoit,

Two minor points:

1. Change "...the use of PR-SCTP with the full reliability..." to  
"...the use of PR-SCTP with full reliability..." (no need for the  
article). Oops, sorry about that.

2. This proposed change is much, much clearer. However, I'm still not  
convinced that
    (a) the recommendation against UDP is _really_ dependent on the  
loss characteristics of the lower layer; or that
    (b) on a second reading, this should really be a recommendation  
against UDP, but rather a caveat given that UDP has already been  
chosen (after all, if you're using UDP, you're doing NetFlow  
replacement, you've presumably already read Section 6.2 of RFC5153 and  
know all the caveats, and you're going to use UDP anyway). So I think  
the recommendation here would be clearer and more internally  
consistent if it restated the caveats in Section 4.2, instead:

So, I'd suggest:

NEW:

   The proposed method is most effective using a reliable transport  
protocol for the transfer
   of the Common Properties. Therefore the use of PR-SCTP with full  
reliability or TCP
   is recommended for the transmission of IPFIX Messages containing  
Common Properties.
   Note that this method loses some of its effectiveness if  UDP is  
used for the transmission
   of IPFIX Messages containing Common Properties, since the Common  
Properties MUST then,
   like Templates, be re-sent at regular intervals as in Section 4.2.

Cheers,

Brian

On Feb 12, 2009, at 9:38 AM, Benoit Claise wrote:

> Brian,
>
> First of all, I would like to have Sven's feedback, as he was the  
> one asking for this change.
> Then, see inline.
>> Hi Benoit, all,
>>
>> "If the path from the Exporting Process to the Collecting Process  
>> is full reliable"
>>
>> What does this mean, precisely? My assumption is that it means "if  
>> the link between the Exporting Process and the Collecting Process  
>> has low loss and reordering characteristics..." However, the  
>> guidance doesn't actually change depending on the loss  
>> characteristics of the lower layer: RR prefers reliable transport  
>> for Common Properties, full stop. I'd suggest (as usual...)  
>> removing any mention of UDP as recommended:
> But the sentence is a warning/clarification against the use of UDP,  
> even if the path is fully reliable.
>> use of PR-SCTP with the full reliability or TCP is recommended for  
>> the transmission of IPFIX Messages containing Common Properties.
> NEW:
>   of the Common Properties. Therefore the use of PR-SCTP with the  
> full reliability or TCP
>   If the path from the Exporting Process to the Collecting Process  
> is fully reliable (i.e., no loss),
>   the use of UDP is less effective because the Common Properties  
> have to be re-sent regularly.
>
>
> Regards, Benoit.
>>
>> Cheers,
>>
>> Brian
>>
>>> Do I understand that section correctly: If the path is reliable,  
>>> you should use a reliable transport, and if the path is unreliable  
>>> you should use unreliable UDP? Isn't that upside down? If the path  
>>> is reliable, you can use UDP _without_ retransmission, no need for  
>>> a reliable transport protocol then.

---

From: Benoit Claise <[email-masked]>
Date: Fri, 27 Feb 2009 14:28:38 +0100

Dear all,

While discussing further with Brian, the agreement is:

   The proposed method is most effective using a reliable transport 
protocol for the transfer
   of the Common Properties. Therefore the use of PR-SCTP with the full 
reliability or TCP
   is recommended for the transmission of IPFIX Messages containing 
Common Properties.
   Note that use of UDP is less efficient for the transmission of Common 
Properties, as
   they have to be re-sent regularly.

If someone objects, please quickly react.

Regards, Benoit.

>> the link between the Exporting Process and the Collecting Process has 
>> low loss and reordering characteristics..." However, the guidance 
>> doesn't actually change depending on the loss characteristics of the 
>> lower layer: RR prefers reliable transport for Common Properties, 
>> full stop. I'd suggest (as usual...) removing any mention of UDP as 
>> recommended:

---

From: Benoit Claise <[email-masked]>
Date: Fri, 27 Feb 2009 14:52:58 +0100

Dear all,

One quick objection received already for an editorial improvement: 
remove "the" twice
NEW:
  The proposed method is most effective using a reliable transport 
protocol for the transfer
  of Common Properties. Therefore the use of PR-SCTP with full 
reliability or TCP
     
^^^                                                                                  
^^^

Regards, Benoit.

>   Note that use of UDP is less efficient for the transmission of 
> Common Properties, as
>>> for Common Properties, full stop. I'd suggest (as usual...) removing 
>>> any mention of UDP as recommended:

---

From: Sven Anderson <[email-masked]>
Date: Fri, 27 Feb 2009 16:35:04 +0100

Dear all,

Am 27.02.2009 um 14:52 schrieb Benoit Claise:

> ^ 
> ^ 
> ^ 
>                                                                                   ^ 
> ^^

sorry for the long delay. I'm fine with this.

Sidenote: Is there a real life example for a reliable (no loss/ 
reordering) link layer? If so, it would be useful to have an IPFIX  
transport mode of using UDP _without_ retransmissions. In any other  
case: always discourage from using UDP. (Which makes the whole UDP/ 
retransmission scheme useless.)

Regards,

Sven

>>>> Hm, that's still kind of confusing. First off, there's no  
>>>> "reliable mode" in PR-SCTP. SCTP is modeless, reliability is per- 
>>>> message. PR-SCTP can provide "fully reliable" transport. But this  
>>>> terminology seems to be overloaded:
>>>>
>>>> What does this mean, precisely? My assumption is that it means  
>>>> "if the link between the Exporting Process and the Collecting  
>>>> Process has low loss and reordering characteristics..." However,  
>>>> the guidance doesn't actually change depending on the loss  
>>> But the sentence is a warning/clarification against the use of  
>>> UDP, even if the path is fully reliable.
>>>> use of PR-SCTP with the full reliability or TCP is recommended  
>>>> for the transmission of IPFIX Messages containing Common  
>>>> Properties.
>>> NEW:
>>>>> you should use a reliable transport, and if the path is  
>>>>> unreliable you should use unreliable UDP? Isn't that upside  
>>>>> down? If the path is reliable, you can use UDP _without_  
>>>>> retransmission, no need for a reliable transport protocol then.