Re: [6lo] Magnus Westerlund's Discuss on draft-ietf-6lo-deadline-time-04: (with DISCUSS and COMMENT)

"Lijo Thomas" <lijo@cdac.in> Wed, 05 June 2019 05:54 UTC

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From: "Lijo Thomas" <lijo@cdac.in>
To: "'Magnus Westerlund'" <magnus.westerlund@ericsson.com>, "'Charlie Perkins'" <charles.perkins@earthlink.net>, "'The IESG'" <iesg@ietf.org>
Cc: <6lo-chairs@ietf.org>, "'Samita Chakrabarti'" <samitac.ietf@gmail.com>, "'Shwetha Bhandari'" <shwethab@cisco.com>, <6lo@ietf.org>, <anand@ece.iisc.ernet.in>, "'satish anamalamudi'" <satishnaidu80@gmail.com>, <draft-ietf-6lo-deadline-time@ietf.org>
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Date: Wed, 5 Jun 2019 11:23:54 +0530
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Subject: Re: [6lo] Magnus Westerlund's Discuss on draft-ietf-6lo-deadline-time-04: (with DISCUSS and COMMENT)
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Hi Magnus,

Thanks for your detailed review and really appreciate your time taken for
the effort !!!!.

Please find our below response for the frame work query addressed by you.

One of the main use cases of the draft is the industrial automation and
control applications. The end point of such applications puts the deadline
information as per its delay requirements.
 
I agree that the underlying 6Lo network needs to ensure that the deadline is
met using its delay sensitive routing and scheduling mechanisms while
forwarding the packet along the path. The 6Lo network can support such a QoS
requirement through end-to-end provisioning of the required network
resources either centrally and/or in a distributed fashion .

In the case of a 6tisch network, one could think of setting up tracks
[draft-ietf-6tisch-architecture] along with delay aware Scheduling Function
implemented by the intermediate nodes. The deadline draft works well within
the context of the framework described in the draft-6tisch-architecture
draft. The 6tisch architecture draft defines tracks which could either be
set up by a centralised entity PCE or by setting up tracks in a distributed
fashion by reserving network resources that provide end-to-end delay
guarantees. Packets of application flows can be sent over these tracks and
scheduled based on their deadlines. The CAC can be exercised where
reservation fails for a new track setup.  There are situations like
asynchronous time critical emergency messages where track set up delay is
not acceptable.  In such cases, we can use distributed on-the-fly scheduling
using 6P protocol described in RFC 8480 that takes into consideration the
deadline information. 
 
There are several deadline based scheduling algorithms that have proposed in
the literature including the basic Earliest Deadline First (EDF). Based on
our deadline draft, we implemented this scheme over a 6tisch network running
on OpenWSN protocol stack and our draft implementation has been merged with
the OpenWSN environment for future downloads too.
 
We would be happy to add some additional text specifying that ** a network
monitoring entity with call admission policy is expected to be in place for
observation and consequently better results during real implementations**.

Hope this address your few concerns and based on your response we will
update the draft.

Happy to receive your further thoughts and valuable inputs.

Thanks & Regards,
Lijo Thomas 

-----Original Message-----
From: 6lo <6lo-bounces@ietf.org> On Behalf Of Magnus Westerlund
Sent: 03 June 2019 18:27
To: Charlie Perkins <charles.perkins@earthlink.net>et>; The IESG
<iesg@ietf.org>
Cc: draft-ietf-6lo-deadline-time@ietf.org; 6lo-chairs@ietf.org; Samita
Chakrabarti <samitac.ietf@gmail.com>om>; Shwetha Bhandari <shwethab@cisco.com>om>;
6lo@ietf.org
Subject: Re: [6lo] Magnus Westerlund's Discuss on
draft-ietf-6lo-deadline-time-04: (with DISCUSS and COMMENT)

Hi Charlie,

Please see for further comments inline.

On 2019-05-30 23:16, Charlie Perkins wrote:
> On 5/13/2019 6:41 AM, Magnus Westerlund via Datatracker wrote:
>> Magnus Westerlund has entered the following ballot position for
>> draft-ietf-6lo-deadline-time-04: Discuss
>>
>>
>>
>>
>> ---------------------------------------------------------------------
>> -
>> DISCUSS:
>> ---------------------------------------------------------------------
>> -
>>
>> The security consideration section have significant short comings as 
>> this mechanism enables multiple ways to attack both the packet and 
>> the system to my understanding. I would appreaciate your clarifications
on these matters.
>>
>> First of all by changing the dead-line so that it gets dropped 
>> because it is already late, alternatively move the deadline time out 
>> further in time (later), so that the forwarders may deliver it so 
>> late that the receiver considers it to late.
> Agreed that this vulnerability should be mentioned in the Security 
> Considerations.
>
>
>> Secondly, there is the question if extensive use of this header will 
>> cause overload or affect the scheduling of packet transmission affect 
>> other traffic negatively. There appear to exist potential for new 
>> ways of bad interflow interactions here.
> If other packet transmissions have to be pre-empted in order for the 
> deadline to be met for a particular packet, then indeed this could 
> affect other traffic.  It is also a matter of possible interest what 
> might happen if there were two packets in the transmission queue with 
> the same or different deadlines.  However, the processing in these 
> cases is a local matter at each intermediate point, and out of scope for
this
> draft.   Does this also belong to be mentioned in the Security 
> Considerations?

Yes, I think so, as it points to a requirement to consider either admission
control or other solutions to keep the interaction on an acceptable level.


>
>
>>
>> ---------------------------------------------------------------------
>> -
>> COMMENT:
>> ---------------------------------------------------------------------
>> -
>>
>> Looking at this mechanism it appears to me as something that should 
>> fit into a frame work, but that is not explicitly given. The main 
>> reason I am raising that is that it appears to not care about a 
>> number of interesting and challenging questions for a mechanism like 
>> this. Questions that a particular framework can take care of, or 
>> which any user of this mechanism would need to consider in their 
>> deployment before they can determine if they can safely deploy it. It 
>> might be that some of the questions have answers and I missed. In 
>> that case please straighten me out. And if you have some additional 
>> document that provides more detailed usage which discuss any of these
issues I would appreciate a pointer.
> This mechanism is a simple kind of signaling that could fit into 
> various frameworks, and exploring that space would be pretty 
> interesting.  But it would represent a huge digression away from the 
> point of this draft, which all along was intended to offer a simple 
> mechanisms without getting involved with messy issues of policy.  If 
> there is something missing in the basic mechanism, then that should be 
> fixed.  But I don't see what is missing.  Some of the discussion below 
> is also relevant to this point.


So, there no specific first initial framework that this solution has been
developed to support? And you say you do not want to deal with policy, and
instead put that on the ones attempting to utilize it.
Considering the security issues, and the higher layer requirements that this
solution appears to create I think that is far from optimal. I really think
this document should have a section making the assumptions about its
expected deployments clear.

>
>
>> So quesitons that I got when reading this specification:
>>
>> 1. Are there any mechanism to provide feedback if the packets reach 
>> the receiver in time? If the sender sets the deadline shorter than 
>> the minimal one-way path delay, then all packets will be late. Will 
>> any feedback be provided that this is happening? In cases D=1 this 
>> appear to be a recipe for a black hole for the traffic. One can also 
>> end up in situation where a large fraction of the packet are late.
> This kind of signaling is far more appropriate at the application 
> level.  To fully characterize the expected distribution of latency 
> values is out of scope for the draft, and the information needed would 
> usually depend on the application.  Some applications don't care much 
> for dropped packets but don't want to handle packets coming in too 
> late.  For other applications, knowing the distribution would allow 
> for setting a deadline that would usually all reception of 85% of the 
> packets (or some percentage predetermined by the application).  It's 
> hard for me to see that as in scope for our draft.


Sure, but the document could make it clear that there exist a need to
monitor the actual performance to know if the application will work
successful

>
>
>
>> 2. Any mechanism that exist to determine what the expected latency 
>> are from sender to receiver?
> As above, I think this is most properly handled by the application
>
>
>> 3. Are there any type of admittance or policy approval to use this
mechanism?
> The policy details are out of scope for this draft.  However, it might 
> be worthwhile to mention that (similar to many QoS efforts) care must 
> be taken to avoid abuse.


Please do.

>
>
>> 4. What is the relationship between traffic with a dead-line and 
>> other traffic without a dead-line. Are traffic with a dead-line 
>> implicitly allowed to pre-empt other traffic or at least to delay it in
its queue?
>
> We don't specify that, and since it's a local matter at each node, a 
> mandate would be unenforceable.  However, if it is important, we could 
> design an advisory extension to the draft for this purpose.  The 
> problem is that the application should not necessarily need to be 
> involved with changing its behavior in response to (highly dynamic)
traffic conditions.

Ok, I can agree that there is difficult to be descriptive here. As long at
the potential impact is a discussed security issue I think this will be
considered addressed.

>
>> 5. As Barry noted, what are the protection against missuse?
>>
>> These are issue that a framework or architecture would consider, I 
>> note that 
>> https://datatracker.ietf.org/doc/draft-ietf-detnet-architecture/ 
>> include some discussion of these topics. Still DETNET architecture appear
more constrained when it comes to usage than what this mechanism through its
examples.
>
> I think it would be best to enlarge the discussion in the draft to 
> explain about the potential for abuse.  I don't see just how the 
> simple mechanism at the level of 6LoRH should be charged with the 
> responsibility for an entire framework, and I really hope that simple 
> mechanisms such as this one can be found to have value even without 
> specification of a much larger set of protections and repairs.


My questions where more coming from the aspect, how do you have been part of
developing this technical solution without having at least one framework
that addresses the raised issue? 

Thus, my preference that in the absence of a framework to point at, that the
assumptions on the hypothetical framework are documented.

Cheers

Magnus Westerlund 

----------------------------------------------------------------------
Network Architecture & Protocols, Ericsson Research
----------------------------------------------------------------------
Ericsson AB                 | Phone  +46 10 7148287
Torshamnsgatan 23           | Mobile +46 73 0949079
SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
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