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Versions: 00 01                                                         
Internet Engineering Task Force                                   Z. Cao
Internet-Draft                                              China Mobile
Intended status: Informational                          October 15, 2012
Expires: April 18, 2013


  Synchronization Layer: an Implementation Method for Energy Efficient
                              Sensor Stack
                      draft-cao-lwig-syn-layer-00

Abstract

   This document analyzes the problem of energy efficient protocol
   implementation, and proposes an energy efficient design of mulitiple
   protocols by utilizing a common shim layer to synchronize the packet
   receipt and transimission on a single node.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 18, 2013.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Conventions used in this document . . . . . . . . . . . . . 3
   2.  Energy Consumption Analysis . . . . . . . . . . . . . . . . . . 3
   3.  Synchronization Layer Design  . . . . . . . . . . . . . . . . . 4
     3.1.  Synchronization Layer . . . . . . . . . . . . . . . . . . . 5
     3.2.  After Synchronization . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7





































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1.  Introduction

   This document analyzes the problem of energy efficient protocol
   implementation.  And inspired by the idea originally proposed in
   [ref.dunkel], proposes an energy efficient design of mulitiple
   protocols by utilizing a common shim layer to synchronize the packet
   receipt and transimission on a single node.

   The idea is straightforward.  Because different protocol cyclings
   result into the frequent and out-of-order wake-up of the radio, the
   energy consumption would be high.  By utilizing a shim layer between
   different applicaiton-layer protocols and the MAC/Link layer, the
   sending and receiving behavior of different protocols can be
   synchronized, which will wake up the radio at a low frequency and
   conserve energy consumption on the sensor.

1.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119]


2.  Energy Consumption Analysis

   Chipset normally provides different modes of operation that consume
   different levels of energy.  There are normally three modes of
   operation on a wireless chipset.

   Transmit mode:  The mode at a node when transmitting a packet.

   Receive mode:   The mode at a node when receiving a packet.

   Idle mode:   The mode generally used at a node with the node is
      neither transmitting nor receiving a packet.  This mode consumes
      power because the node has to listen to the wireless medium
      continuously in order to detect a packet that it should receive,
      so that the node can then switch into receive mode.

   Sleep mode:  Sleep mode has very low power consumption.  The network
      interface at a node in sleep mode can neither transmit nor receive
      packets; the network interface must be woken up to idle mode first
      by an explicit instruction from the node.

   Sleep mode is the most energy efficient mode.  Some transceivers
   provide different levels of sleeping mode.  For example, CC3530
   provides three of them, PM1, PM2 and PM3, according to its
   specificaiton.  PM3 is the most efficient mode of them.



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   Some research studies the energy efficiency of different operations
   on the sensor.  According to the investigation in [ref.icccn], the
   energy consumption of different operations are as follows.

   Operation
            /\
       Hum  |*
       Temp |**
       AES  |******
            |
     RX(10B)|***********************
            |
     TX(10B)|*******************************************************
            +-------------------------------------------------------->
                                                Energy Consumption (uJ)

   From this analysis we can clearly see that the most energy efficient
   way is to keep the sensor transciever sleep as much as possible.


3.  Synchronization Layer Design

   The key optimization direction is to reduce the frequency of radio
   wakeup.  But if there are multiple protocols running on a sensor
   node, the situation is unavoidable.  For example, as depicted in
   Figure 1 , there are three protocols running on a sensor node.  The
   three protocols have their different rate and phase of sending and/or
   receiving packets.  The figure shows an extreme case that their
   sending phases are totally un-overlapped.  In this case, the sensor
   radio stack should be active roughly 70% of time.  This makes the
   sensor stack not very energy efficient at all.

   The idea of handling this problem is to synchronize the transmission
   of different protocols.  We will introduce the synchronization layer
   and its impact in the following subsections.
















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          /|
   Prtl1   |       __             __
           |      |  |           |  |
           |______|  |___________|  |__________
   Prtl2   |          __              __
           |         |  |            |  |
           |_________|  |____________|  |_________
   Prtl3   |              __              __
           |             |  |            |  |
           |_____________|  |____________|  |_______
   Radio   |       _________       _________
           |      |         |     |         |
           |______|         |_____|         |__________
           |-------------------------------------------------->
                                                           Time

               Figure 1: Radio Wakeup for multiple protocols

3.1.  Synchronization Layer

   The synchronization layer is set between the application protocols
   and MAC/Phy layer.  The Syn-layer provides API to the upper layer
   protocols and has its own frequency of sending and receiving packets.

   After synchronization, the protocol's transceiving behavior has been
   adapted.  The synchronization layer keeps its own clock and will wake
   up the radio once the clock times up.
       +-------+           +-------+           +-------+
       | Prtl1 |           | Prtl2 |           | Prtl3 |
       +-------+           +-------+           +-------+
             \                 |                  /
              \_________       |       __________/
                        \      |      /
                  +-------------------------+
                  |         Syn Layer       |
                  +-------------------------+
                               ||
                  +-------------------------+
                  |      MAC/Phy Layer      |
                  +-------------------------+

                    Figure 2: The Synchronization Layer

   As envisioned, after synchronization, the protocol's realtime
   requirement will affected.  The protocol's behavior has been delayed
   until the Syn-layer's clock has been trigger.  To support the
   realtime communication requirement, we can utilize a design of the
   API between the application-layer protocol and the Syn-layer.  If the



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   protocol in consideration has specific realtime requirement, it can
   specify this requirement in the API call function.

         // protocol can specify the realtime requirment in the API call
         Pull (Key, Flag)


3.2.  After Synchronization

   After the synchronization layer is implemented and enabled, the
   packet transceiver is synchronized.  As shown in Figure 3, the radio
   wakeup rate is reduced to about 30%.


   Prtl1   |       __             __
           |      |  |           |  |
           |______|  |___________|  |__________
   Prtl2   |          __              __
           |         |  |            |  |
           |_________|  |____________|  |_________
   Prtl3   |              __              __
           |             |  |            |  |
           |_____________|  |____________|  |________
   Radio   |       _________       _________
           |      |         |     |         |
           |______|         |_____|         |__________
           |                 ____              ____
   Syn     |                |    |            |    |
           |________________|    |____________|    |_____
           |
           +-------------------------------------------------->
                                                           Time

               Figure 3: Radio Wakeup for multiple protocols


4.  IANA Considerations

   This document has no IANA requests.


5.  Security Considerations

   TBD.


6.  References




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6.1.  Normative References

   [ref.dunkel]
              Dunkels, A., "The Announcement Layer: Beacon Coordination
              for the Sensornet Stack. In Proceedings of EWSN 2011".

   [ref.icccn]
              Margi, C., "Impact of Operating Systems on Wireless Sensor
              Networks (Security) Applications and Testbeds, ICCCN
              2010".

6.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


Author's Address

   Zhen Cao
   China Mobile
   Xuanwumenxi Ave. No. 32
   Beijing,   100871
   China

   Phone: +86-10-52686688
   Email: zehn.cao@gmail.com, caozhen@chinamobile.com
























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