PowerPoint Presentation - 6LoWPAN Interoperability

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					        Compression Format for IPv6
      Datagrams in 6LoWPAN Networks


                  Jonathan Hui

               6LoWPAN WG Meeting
                 71st IETF Meeting
                  Philadelphia, PA



03/11/2008     71st IETF Meeting - 6LoWPAN WG   1
RFC 4944 – IPv6 Header Compression
     0        1     2        3   4      5        6     7

         SA             DA       TF         NH       HC2          uncompressed fields…

• Most effective when communicating with link-local
  addresses
      – Prefix: must be carried in-line when not link-local
              • Route-over, ROLL
              • Communicating with devices outside PAN
      – Suffix: must be 64 bits when carried in-line
              • No provision to shorten it even when IID is derived from short
                802.15.4 address.
      – Multicast: must carry all 128 bits in-line
              • Even for commonly used multicast addresses (e.g. link-local all
                nodes, IPv6 ND, etc.)
      – Hop-limit always carried in-line
03/11/2008                       71st IETF Meeting - 6LoWPAN WG                          2
RFC 4944 – Next Header Compression

• Defined for UDP header
      – No way to elide Checksum
             • End-to-end integrity checks may be provided by other end-to-
               end mechanisms (e.g. security).
      – No support for future compression of arbitrary next
        headers
             • UDP, TCP, or ICMPv6 only




03/11/2008                   71st IETF Meeting - 6LoWPAN WG               3
                  Proposed 6LoWPAN HC

• Generalize LOWPAN_HC1/HC2
      – Broader range of communication paradigms
             • Mesh-under, route-over, communication with external
               devices, multicast
      – Framework for compression of arbitrary next headers
             • UDP compression initially defined within this framework
      – IPv6 Hop Limit and UDP Checksum compression
      – Carry forward design concepts
             • Minimize state
             • Rely on shared context



03/11/2008                   71st IETF Meeting - 6LoWPAN WG              4
                          LOWPAN_IPHC
                     IPv6 Header Compression
     0       1   2    3    4        5     6        7

    VTF NH       HLIM          SA             DA            uncompressed fields…


•   VTF: Version, Traffic Class, Flow Label
•   NH: Next Hop
•   HLIM: Hop Limit
•   SA: Source Address
•   DA: Destination Address
•   rsv: reserved
•   Payload Length always elided

03/11/2008                 71st IETF Meeting - 6LoWPAN WG                          5
                            LOWPAN_IPHC
                            Address Compression

             00: 128 bits            Full 128-bit Address In-Line

             01: 64 bits        CP Implicit              64-bit Suffix In-Line

             10: 16 bits        CP Implicit                     0’s        SA

             11: 0 bits         CP Implicit              From Lower Layers

• Common Prefix (CP)
      – Implicit when prefix is elided
      – Link-local (LL) or Common Routable Prefix (CRP)
             • Identified by different 6LoWPAN Dispatch values
• SA derived from IEEE 802.15.4 Short Address
• Elided suffix derived from lower-layers

03/11/2008                     71st IETF Meeting - 6LoWPAN WG                    6
                      LOWPAN_IPHC
             Obtaining the Common Routable Prefix
• Assumption
      – 6LoWPAN network operate under a single administrative domain


• Single-homed
      – CRP is trivial (the only prefix assigned to the PAN).
      – Renumbering inconsistencies caught with pseudo-header
        checksum


• Multi-homed
      – Need to specify a protocol and think through the operational
        details
      – Can we go without for now?


03/11/2008                 71st IETF Meeting - 6LoWPAN WG              7
                       LOWPAN_IPHC
        IID Derived from 802.15.4 Short Addresses
• RFC 4944
      – Includes PAN ID and 0xFFFE
      – Is there a need to assign the same prefix to >1 PAN?


• Instead, prefix Short Address with zeros
      – u/l-bit is zero, indicating local scope
      – Could also be some fixed bit-pattern, other than 0’s.


                                    0’s            SA




03/11/2008                 71st IETF Meeting - 6LoWPAN WG       8
                      LOWPAN_IPHC
                    Hop Limit Compression
• 1 bit to indicate compression
• 1 bit to indicate 63 (egress) or 1 (ingress)

• Most useful for mesh-under
      – All nodes connected via a single IP hop


• Not as useful for route-over
      – Forwarding nodes have to expand anyway




03/11/2008                71st IETF Meeting - 6LoWPAN WG   9
                               LOWPAN_IPHC
                   Multicast Address Compression
• For commonly-used, well-known multicast addresses
      – Divide 16-bit compressed address into ranges
             • Unicast: 0xxxxxxxxxxxxxxx
             • Multicast: 100xxxxxxxxxxxxx

                                                128 bits
FF Flags         Scope                                           Group ID
                   0   1   2   3    4   5   6   7   8   9    0    1   2   3   4   5
                   1 0 0           Scope                    Group ID

• Prefix (8-bits): Compressed to 3-bit range
• Flags (4-bits): Assumed to be zero
      – permanent, not derived from prefix, doesn’t embed RP
• Scope (4-bits): Carried in-line
• Group ID (112-bits): Mapped to 9-bits
      – Currently defined: All Nodes (1) and All Routers (2)
03/11/2008                          71st IETF Meeting - 6LoWPAN WG                    10
                            LOWPAN_NHC
                       Next Header Compression
     0       1    2     3    4      5         6    7

    ID       SP   DP    C               rsv                   uncompressed fieds…

• IPHC NH indicates next header compression
      – IPv6 Next Header elided, derived from first bits in NHC
      – Encoding gives shorter bit-patterns to frequently used next headers

•   ID: 0 for UDP, 1 for other
•   SP: Source Port
•   DP: Destination Port
•   C: Checksum
•   Length always elided

• Checksum MUST NOT be elided when no other end-to-end integrity
  cover the pseudo-header, UDP header, and UDP payload
03/11/2008                   71st IETF Meeting - 6LoWPAN WG                         11
                      Unicast Examples
• Link-Local, Mesh-Under (9 bytes)
                            5                              1       1    1     1
    15.4           6LoWPAN Mesh Header                Disp. IPHC       NHC   Ports


• Link-Local, Route-Over (4 bytes)
               1      1     1        1
    15.4     Disp. IPHC   NHC     Ports


• Routable, Mesh-Under (9 bytes)
                            5                              1       1    1     1
    15.4           6LoWPAN Mesh Header                Disp. IPHC       NHC   Ports


• Routable Addresses, Route-Over (9 bytes)
               1      1     1             2                    2        1      1
    15.4     Disp. IPHC HLIM         Src Addr              Dst Addr    NHC   Ports

03/11/2008                71st IETF Meeting - 6LoWPAN WG                             12
                         Multicast Examples
   • Link-Local, Mesh-Under (11 bytes)
                         5                        1        1      1      1      1     1
15.4            6LoWPAN Mesh Header            Disp. Bcast Disp. IPHC          NHC   Ports


   • Link-Local, Route-Over (6 bytes)
15.4 Disp.       IPHC    Dst Addr       NHC    Ports


   • Routable, Mesh-Under (11 bytes)
                         5                        1        1      1      1      1     1
15.4            6LoWPAN Mesh Header            Disp. Bcast Disp. IPHC          NHC   Ports


   • Routable Addresses, Route-Over (9 bytes)
        1          1    1           2                  2          1     1
15.4 Disp.       IPHC HLIM     Src Addr           Dst Addr       NHC   Ports

   03/11/2008                   71st IETF Meeting - 6LoWPAN WG                       13
                  6LoWPAN HC Summary

• Generalize LOWPAN_HC1/HC2
      – Broader range of communication paradigms
             • Mesh-under, route-over, communication with external
               devices, multicast
      – Framework for compression of arbitrary next headers
             • UDP compression initially defined within this framework
      – IPv6 Hop Limit and UDP Checksum compression
      – Carry forward design concepts
             • Minimize state
             • Rely on shared context



03/11/2008                   71st IETF Meeting - 6LoWPAN WG              14
              Discussion

• Should 6lowpan-hc become a WG doc?




03/11/2008   71st IETF Meeting - 6LoWPAN WG   15
                 Combining IPHC and NHC
                 (From Discussion with Pascal Thubert)

• Another dispatch for combining LOWPAN_IPHC/NHC?
      – Fully elided Source and Destination addresses and Hop Limit
      – Next header compression

     0       1    2   3    4      5       6
                                          5         7

  VTF HLIM        0   SP   DP     C           rsv           uncompressed fields…



• Pro: Save an additional octet
• Con: Additional code overhead




03/11/2008                 71st IETF Meeting - 6LoWPAN WG                          16

				
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