[Lwip] draft-ietf-lwig-energy-efficient-00
Hannes Tschofenig <hannes.tschofenig@gmx.net> Thu, 03 July 2014 08:23 UTC
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Date: Thu, 03 Jul 2014 10:23:47 +0200
From: Hannes Tschofenig <hannes.tschofenig@gmx.net>
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Subject: [Lwip] draft-ietf-lwig-energy-efficient-00
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Hi all, I took a quick look at this document. Clearly this is an important topic but it is also challenging. When this topic was brought up at the IAB smart object workshop I was thinking about what guidelines I would offer and I came up with very few ideas. So, I was very interested to see what the authors have to say about this topic. A few aspects came to my mind when reading the document: a) The current discussion seems to focus on a single study only. I hope that's not true and the authors have done some studies themselves as well. It is also heavily focused on energy consumption of networking only. RAM costs energy. Computations cost energy. Even sleeping costs energy. For embedded hardware there is not just a binary sleep/awake mode but many intermediate steps. b) The comparison between different radio technologies would require far more details to be useful since there are many parameters that have an impact on the overall energy consumption. Selecting the right set of parameters also assumes that you understand the radio technique very well. c) This is mostly a non-IETF topic. The IETF does not design radio technologies, nor does it impact the hardware design or focus on implementations. I agree with the statement that it is good to know the behaviors of lower layers. What would, however, then be needed is a tutorial on various radio technologies since they are often written in a way that is very different from IETF specifications and somewhat hard to understand for IETF-minded folks. There is text in there in Section 3 about the different radios but it is too short to be understood by someone who does not yet already know the specific radio technology anyway. Why did you pick those three radios and not others? As an example, the text about Bluetooth Low Energy (which has been renamed to Bluetooth Smart) does not provide the reader much insight into the implications for the protocol design. Bluetooth Smart is different from Bluetooth and the specification defines an entire protocol stack. The required energy of a device depends on the function and on the parameter setting at each layer. Hence, it is a bit difficult to just focus on master / slave (terminology used for only one layer). It might also be worth pointing out that not all radio technologies used today are actually using IP. Bluetooth Smart is a good example that enjoys widespread deployment but there is almost no IP there since the wireless communication more or less replaces cables. d) The sections about routing protocols(Section 5), application layer (Section 6) and Cross Layer Optimization (Section 7) are currently a bit empty. It is also not clear whether you will be able to say too much there either. Summary Section The document provides a summary section explaining the goals of the document. That's good. Let me compare the goals outlined in the summary section with the rest of the document. a. All Internet protocols, which are in the scope of the IETF, are customers of the lower layers (PHY, MAC, and Duty-cycling). In order to get a better service, the designers of higher layers should know them better. --> The current document does not describe the different radio technologies in a sufficient level of detail so that protocol designers can take practical actions. Even if they know the radio technology better what conclusions should be drawn? Most likely the answer is that it depends what your product is going to do. You have some parameters you can use to fine-tune but there will always be tradeoffs. b. The IETF has developed multiple protocols for constrained networked devices. A lot of implicit energy efficient design principles have been used in these protocols. --> Do you think it is useful to provide a survey of the IETF IoT/smart object work? c. The power trace analysis of different protocol operations showed that for radio-duty-cycled networks broadcasts should be avoided. Saving unnecessary states maintenance is also an effective method to be energy-friendly. --> There are a few recommendations for protocol designers but they are all rather obvious: * don't use broadcast/multicast * don't communicate too often and communicate as little as possible * don't act as server (if you can) since listening costs money * sleep, sleep, sleep. What the document currently also does is to summarize one publication on energy consumption. Would it be useful to cover other publications as well? Ciao Hannes
- [Lwip] draft-ietf-lwig-energy-efficient-00 Hannes Tschofenig
- Re: [Lwip] draft-ietf-lwig-energy-efficient-00 Carles Gomez Montenegro