Re: [6tisch] Time to Live

Hello Lijo:

Like Thomas, I’d love to understand what your case and solution approach is. Is asynchronous OAM like the openWSN application enough for you? Or else are you looking for per packet information to as to monitor and maybe influence the forwarding and delivery?

In the latter case, your work may be related to other efforts, and if your experimentation is successful then why not consider a more general applicability?

All in all I have this feeling that time-aware forwarding is on the way, in which exact shape and form is left TBD:

-        DetNet is discussing validating the end-to-end latency of individual packets to make sure that the delivery was within bounds. Is that similar to your need?

-        I’ve participated to work where the QoS of the packet was estimated at each hop depending on whether the packet was early or late vs. a predefined schedule. This makes things much simpler but slightly less deterministic than a tight scheduling.

-        There’s also OAM work that uses HbH headers to monitor the packets as they flow along the network (IOW, in band as opposed to asynchronous OAM packets)

My understanding is that you want HbH behavior.

-        If you are doing a mesh, you can probable hack a mesh header.

-        But if you are considering a larger applicability (I hope so!) then you probably want to hack at L3.

You can find tons of ideas of what can be done at L3 in various environments in https://tools.ietf.org/html/draft-dt-detnet-dp-alt-03, which is pending adoption call.

But if you narrow down to 6TiSCH, then you probably want to design you own option in the HbH header and incode it in a 6LoRH similar to the RPL RPI. You may use ASN to start with, but when going standard you’ll have to abstract that a little bit, even if the data in the packet is unchanged.

Very keen to hear more!

Pascal

From: 6tisch [mailto:6tisch-bounces@ietf.org] On Behalf Of Thomas Watteyne
Sent: jeudi 25 août 2016 08:28
To: Lijo Thomas <lijo@cdac.in>
Cc: 6tisch@ietf.org
Subject: Re: [6tisch] Time to Live - ASN in a packet

Lijo,

It looks like you are describing two things: the TTL (or hop limit in IPv6 parlance) which decrements by one by each router, and some timestamp which can be used to measure end -to-end latency. I'm assuming the latter.

I'm also assuming you are doing this as part of an experiment, to look at the end-to-end/hop-by-hop latency. In that context, you probably aren't looking for standardizing that (or even standards-compliance during your experiment), but more at an implementation technique to keep that information.

Of course, the answer depends entirely on the information we are missing. But assuming you are playing with the OpenWSN implementation, there is already an application called rrt which sends the ASN as application payload at the source, and records the ASN when the DAGroot has received that. You can then substract one by the other and do some stats. Please ask further questions to the OpenWSN community [1] as such technical discussion on a particular implementation doesn't belong on the 6TiSCH WG ML.

If you are using the commercial SmartMesh IP solution by Linear Tech [2], good news, all of that is already built in. The manager (~DAGroot) keeps track of timing and can send you average latencies for each of your nodes. If you're interested, you can look at these numbers "live" on deployments in Argentina [3,4] or California [5]. As you might imagine, latency/throughput/lifetime trade-off for one another, so there is a handy "performance estimator" tool you can use [6,7]. For further question on this topic, please use www.dustcloud.org<http://www.dustcloud.org>.

Finally, looking at lowering latency in 6TiSCH has been an important research topic in the last year or so. Look for example at the "Low-Latency Scheduling Function" [8] work which lowers the per-hop latency to 10's of ms withing the 6TiSCH framework.

Thomas

[1] www.openwsn.org<http://www.openwsn.org>
[2] www.linear.com/dust<http://www.linear.com/dust>
[3] http://www.savethepeaches.com/
[4] PEACH: Predicting Frost Events in Peach Orchards Using IoT Technology. Thomas Watteyne, Ana Laura Diedrichs, Keoma Brun-Laguna, Javier Emilio Chaar, Diego Dujovne, Juan Carlos Taffernaberry, Gustavo Mercado. EAI Endorsed Transactions on the Internet of Things, to appear in 2016.
[5] http://www.snowhow.io/
[6] http://www.linear.com/docs/42452
[7] Industrial IEEE802.15.4e Networks: Performance and Trade-offs. Thomas Watteyne, Joy Weiss, Lance Doherty, Jonathan Simon. IEEE International Conference on Communications (IEEE ICC), Internet of Things Symposium, London, UK, 8-12 June 2015.
[8] LLSF: Low Latency Scheduling Function for 6TiSCH Networks. Tengfei Chang, Thomas Watteyne, Qin Wang, Xavier Vilajosana. IEEE International Conference on Distributed Computing in Sensor Systems (DCOSS), Washington, DC, USA, 26-28 May 2016.

On Thu, Aug 25, 2016 at 7:57 AM, Lijo Thomas <lijo@cdac.in<mailto:lijo@cdac.in>> wrote:
Hi all,

We are working on problem which needs the Time to Live (TTL) information in terms of ASN  to be included as part of the Packet.

We require the intermediate nodes to update TTL at each hop.

How this information can be passed in a 6tisch framework.

Suggestions are welcome..

Thanks & Regards
Lijo Thomas

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--
_______________________________________

Thomas Watteyne, PhD
Research Scientist & Innovator, Inria
Sr Networking Design Eng, Linear Tech
Founder & co-lead, UC Berkeley OpenWSN
Co-chair, IETF 6TiSCH

www.thomaswatteyne.com<http://www.thomaswatteyne.com>
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