ISA SP100.11a Hybrid DLL Proposal by liuhongmei

VIEWS: 35 PAGES: 31

									  <May 2007>                                                      doc.: IEEE 802.15-15-07-0724-00-wng0

    Project: IEEE P802.15 Working Group for Wireless Personal Area Networks
                                   (WPANs)

Submission Title: [ISA SP100.11a Hybrid DLL Proposal]
Date Submitted: [14 May 2007]
Source: [Jay Werb] Company [Sensicast]
Address [Massachusetts, USA]
Voice:[Add telephone number], FAX: [Add FAX number], E-Mail:[jwerb07@sensicast.com]
Re: [Information for IEEE 802.15 as per WNG]
Abstract: [DLL proposal for ISA SP100.11a containing TDMA and CSMA properties]
Purpose: [Information as to how the ISA SP100.11a WG anticipates using IEEE 802.15.4]
Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for
discussion and is not binding on the contributing individual(s) or organization(s). The material in this
document is subject to change in form and content after further study. The contributor(s) reserve(s)
the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of
IEEE and may be made publicly available by P802.15.




  Submission                                     Slide 1                           <Jay Werb>, <Sensicast>
<May 2007>                  doc.: IEEE 802.15-15-07-0724-00-wng0




             Introduction




Submission        Slide 2                    <Jay Werb>, <Sensicast>
                                                                       2
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                   Flexibility and Options
• The ISA-SP100.11a DLL is designed to be flexible
   – Trade-offs are made by system designers
   – They know more about their applications than we do

   – Default settings will control the scope of validation & testing…
   – … but systems won’t be limited to those defaults
   – Default settings may be overridden by System Manager

• DLL supports a hierarchy of 5 device classes
   –   Backbone Routers (continuously powered)
   –   Dedicated Field Routers (continuously powered)
   –   Instruments with routing capability (battery powered)
   –   Instruments without routing capability (smaller batteries)
   –   Very low cost sensors (tiny batteries, CSMA only)
 Submission                          Slide 3                      <Jay Werb>, <Sensicast>
                                                                                            3
 <May 2007>                                                          doc.: IEEE 802.15-15-07-0724-00-wng0


         Overview of TDMA/CSMA Hybrid
Features added to a baseline TDMA structure

    – CSMA periods
          • Fast network discovery using control channels
          • Immediate next-hop propagation of unscheduled commands and alarms
          • Support low end CSMA-only field devices


    – Slot length is configurable to allow for
          •   Longer guard times (longer slots)
          •   Tighter implementations (shorter slots)
          •   Duocast (serial acknowledgement from two devices)
          •   CSMA at start of slot (prioritized access to shared slots)


    – Flexible options for hybrid centralized/decentralized
      operation
          • System Manager can delegate slot allocation to Routers
          • System Manager can allow Routers to create their own superframes & routes


 Submission                                        Slide 4                            <Jay Werb>, <Sensicast>
                                                                                                                4
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             Stack Structure




Submission         Slide 5                    <Jay Werb>, <Sensicast>
                                                                        5
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             Field Device Stack Diagram
                  “Current” Version




Submission               Slide 6                    <Jay Werb>, <Sensicast>
                                                                              6
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             Field Device Stack Diagram
               Recommended Changes




Submission               Slide 7                    <Jay Werb>, <Sensicast>
                                                                              7
 <May 2007>                                                           doc.: IEEE 802.15-15-07-0724-00-wng0


What’s in the Lower Data Link Layer (LDLL)?
 • Lower Data Link Layer (LDLL)
      – A continuous sequence of channel hopping slots
              •   One slot per hop for “TDMA”
              •   Slower hopping sequence (~10-25 slots per hop) for “CSMA”
              •   May be combined for “Hybrid TDMA/CSMA”

      – The LDLL is IEEE 802.15.4 as we wish it were
              •   Fewer “features”
              •   More flexibility



 • IEEE 802.15.4 MAC not discussed here
      – Treated as a pass-through to the PHY
              •   Designed to work with existing standard 15.4 MACs
                   – In silicon or otherwise “unchangeable”
      – LDLL security similar to IEEE 802.15.4, but not the same
              •   Slot number used for replay protection
              •   Not covered here

      – Just about “everything else” is different … and handled by
        the UDLL
 Submission                                        Slide 8                             <Jay Werb>, <Sensicast>
     <May 2007>                                         doc.: IEEE 802.15-15-07-0724-00-wng0

                  Role of LDLL & UDLL Examples
                       LDLL                          UDLL & DLL Manager

Topology               Immediate neighborhood        “Mesh” (DLL subnet)

Time Synch             Device level                  DLL subnet level
                       Time synch mechanics          Manage time propagation messages
Building block         Channel hopping slots         Superframes
                                                     (Cyclic collections of slots)
Discovery              Sends and receives packets    Discovers and evaluates neighbors

Slot management        Follow a hop sequence         Manage thousands of slots cyclically

Diversity              Handled in by UDLL            Frequency, time, spatial diversity

Route Management       Measure the quality of        Accumulate & report statistics
                       specific links                and manage the network topology
                                                     based on link quality information
Security               Similar to 802.15.4 role      Interface with Security Manager

     Submission                            Slide 9                       <Jay Werb>, <Sensicast>
                                                                                                   9
<May 2007>               doc.: IEEE 802.15-15-07-0724-00-wng0




             Lower
              DLL




Submission    Slide 10                    <Jay Werb>, <Sensicast>
                                                                    10
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             DLL Structure




Submission        Slide 11                    <Jay Werb>, <Sensicast>
                                                                        11
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             TDMA, CSMA, and Hybrid




Submission             Slide 12                    <Jay Werb>, <Sensicast>
  <May 2007>                                                             doc.: IEEE 802.15-15-07-0724-00-wng0

                              Types of Superframes
• TDMA only
   – Channel-hopping slots of equal length


• CSMA only
   – Collect ~10-25 slots on same channel
   – Each collection treated as a single CSMA
     period
   – Slow channel hopping

• Hybrid TDMA/CSMA
   – TDMA slots followed by CSMA period
        •      This TDMA/CSMA ordering is not written in stone
               See Case Study (next slide)


   – TDMA and CSMA have independent channel
     hopping patterns
        •      TDMA follows an underlying sequence of one hop per slot
        •      CSMA follows a slower sequence
  Submission                                         Slide 13                             <Jay Werb>, <Sensicast>
<May 2007>                    doc.: IEEE 802.15-15-07-0724-00-wng0


             A Case Study
    WNSIA-Style Operational Superframe




Submission         Slide 14                    <Jay Werb>, <Sensicast>
                                                                         14
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             Channel Hopping Sequences




Submission              Slide 15                    <Jay Werb>, <Sensicast>
                                                                              15
<May 2007>                                           doc.: IEEE 802.15-15-07-0724-00-wng0


               Channel Hopping Sequence
             Implementing a WiFi Coexistence
                        Strategy




                  Slot-to-slot channel choices can be made to avoid
               consecutive channel usage within a single Wi-Fi channel

Submission                             Slide 16                       <Jay Werb>, <Sensicast>
                                                                                                16
<May 2007>Example: “Hop sequence 5”
                                doc.: IEEE 802.15-             15-07-0724-00-wng0


  Interlaced with 14 other identical but offset
                   sequences




             Slots within a set of coordinated hop sequences
Submission                      Slide 17                   <Jay Werb>, <Sensicast>
                                                                                     17
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                 Hop pattern
     Optimized for retry in CSMA channel




             Avoid the channels “around” the CSMA channel for
               better frequency diversity during CSMA retries


Submission                        Slide 18                       <Jay Werb>, <Sensicast>
                                                                                           18
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               Upper DLL
             TDMA Baseline




Submission        Slide 19                    <Jay Werb>, <Sensicast>
                                                                        19
<May 2007>                      doc.: IEEE 802.15-15-07-0724-00-wng0


      Typical TDMA as viewed by a single
                      router
              ~2 slots/second used




Submission           Slide 20                    <Jay Werb>, <Sensicast>
                                                                           20
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                  Example:
     8 Nodes sharing a TDMA superframe




Submission          Slide 21                    <Jay Werb>, <Sensicast>
                                                                          21
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              Upper DLL
             CSMA Baseline




Submission        Slide 22                    <Jay Werb>, <Sensicast>
                                                                        22
 <May 2007>                                            doc.: IEEE 802.15-15-07-0724-00-wng0


                                    CSMA
• CSMA is fully supported by SP100.11a
         • Typically combined with TDMA (next section)
         • Typically hosted by “continuously powered” routers
            – If you have power available, you might as well provide some level of
              services when you are not committed to other communications
         • Battery-powered routers may briefly enable CSMA on startup
            – Facilitate network formation


• CSMA provides key advantages
         • Fast neighbor discovery
         • Immediate transmission of unscheduled commands and alarms
         • Support low-end field devices (tiny batteries, CSMA only)



• Similar to 802.15.4 CSMA-CA with enhancements
         • Channel hopping
         • Retry involves channel and link diversity
 Submission                             Slide 23                        <Jay Werb>, <Sensicast>
                                                                                                  23
<May 2007>                         doc.: IEEE 802.15-15-07-0724-00-wng0


             Example of CSMA Operation




Submission              Slide 24                    <Jay Werb>, <Sensicast>
                                                                              24
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                         8 Routers
             With interlaced CSMA Hopping
                        Sequences




Submission               Slide 25                    <Jay Werb>, <Sensicast>
                                                                               25
<May 2007>                    doc.: IEEE 802.15-15-07-0724-00-wng0




                Upper DLL
             TDMA/CSMA Hybrid




Submission         Slide 26                    <Jay Werb>, <Sensicast>
                                                                         26
 <May 2007>                                                           doc.: IEEE 802.15-15-07-0724-00-wng0


                          TDMA/CSMA Hybrid
• TDMA/CSMA Hybrid is a fully-supported mode of operation
    –   Scheduled messages in TDMA slots
    –   Retries and unscheduled messages in CSMA periods
    –   CSMA periods used for subnet discovery
    –   Intended for continuously powered routers
         •    Since they have the power, they might as well run their receivers whenever possible
         •    Battery powered routers may briefly enable CSMA during network formation



• TDMA slots provide
    – Predictable performance
    – Managed bandwidth
    – Reduced contention for CSMA bandwidth

• CSMA periods enable
    – Fast network discovery using control channels (next slide)
    – Immediate transmission of unscheduled commands and alarms
    – Support for low-end CSMA-only field devices
 Submission                                         Slide 27                             <Jay Werb>, <Sensicast>
                                                                                                                   27
<May 2007>                          doc.: IEEE 802.15-15-07-0724-00-wng0


                 TDMA/CSMA Hybrid
             with 3 CSMA Control Channels




Submission               Slide 28                    <Jay Werb>, <Sensicast>
                                                                               28
<May 2007>                       doc.: IEEE 802.15-15-07-0724-00-wng0




                 DLL Manager
             Decentralized Operation




Submission            Slide 29                    <Jay Werb>, <Sensicast>
                                                                            29
   <May 2007>                                         doc.: IEEE 802.15-15-07-0724-00-wng0

 Centralized and decentralized Slot allocation
• Flexible range of centralized/decentralized options
   Centralized: Network Brain allocates and manages all slots in the network
   Decentralized: Network Brain authorizes Routers to create and manage superframes
   Hybrid: Network Brain may delegate slot allocation to capable Routers


   Resource-limited routers need not support decentralized options



• Delegated slot allocation: The basics
   –   Superframes created by Network Brain
   –   Blocks of slots within superframes are delegated to routers
   –   Router autonomously allocates delegated slots to its neighbors
   –   Mechanics of delegation is standardized
   –   Router’s use of slots is opportunity for “value add”


   Submission                            Slide 30                      <Jay Werb>, <Sensicast>
                                                                                                 30
<May 2007>                                doc.: IEEE 802.15-15-07-0724-00-wng0

  Example of delegated slot allocation 8 routers
             sharing a superframe




                       Different routers have different slots allocated to them
                                   which they manage on their own
Submission             Slide 31                               <Jay Werb>, <Sensicast>
                                                                                        31

								
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