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Compression Format for IPv6 Datagrams in 6LoWPAN Networks

Compression Format for IPv6 Datagrams in 6LoWPAN Networks. Jonathan Hui 6LoWPAN WG Meeting 71 st IETF Meeting Philadelphia, PA. RFC 4944 – IPv6 Header Compression. 0. 1. 2. 3. 4. 5. 6. 7. Most effective when communicating with link-local addresses

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Compression Format for IPv6 Datagrams in 6LoWPAN Networks

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  1. Compression Format for IPv6 Datagrams in 6LoWPAN Networks Jonathan Hui 6LoWPAN WG Meeting 71st IETF Meeting Philadelphia, PA 71st IETF Meeting - 6LoWPAN WG

  2. RFC 4944 – IPv6 Header Compression 0 1 2 3 4 5 6 7 • 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 SA DA TF NH HC2 uncompressed fields… 71st IETF Meeting - 6LoWPAN WG

  3. 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 71st IETF Meeting - 6LoWPAN WG

  4. 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 71st IETF Meeting - 6LoWPAN WG

  5. LOWPAN_IPHCIPv6 Header Compression • VTF: Version, Traffic Class, Flow Label • NH: Next Hop • HLIM: Hop Limit • SA: Source Address • DA: Destination Address • rsv: reserved • Payload Length always elided 0 1 2 3 4 5 6 7 VTF NH HLIM SA DA uncompressed fields… 71st IETF Meeting - 6LoWPAN WG

  6. LOWPAN_IPHCAddress Compression • 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 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 71st IETF Meeting - 6LoWPAN WG

  7. LOWPAN_IPHCObtaining 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? 71st IETF Meeting - 6LoWPAN WG

  8. LOWPAN_IPHCIID 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 71st IETF Meeting - 6LoWPAN WG

  9. LOWPAN_IPHCHop 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 71st IETF Meeting - 6LoWPAN WG

  10. LOWPAN_IPHCMulticast Address Compression • For commonly-used, well-known multicast addresses • Divide 16-bit compressed address into ranges • Unicast: 0xxxxxxxxxxxxxxx • Multicast: 100xxxxxxxxxxxxx • 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) 128 bits FF Flags Scope Group ID 1 2 3 5 6 7 9 0 1 3 4 5 0 4 8 2 1 0 0 Scope Group ID 71st IETF Meeting - 6LoWPAN WG

  11. LOWPAN_NHCNext Header Compression • 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 0 1 2 3 4 5 6 7 ID SP DP C rsv uncompressed fieds… 71st IETF Meeting - 6LoWPAN WG

  12. Unicast Examples • Link-Local, Mesh-Under (9 bytes) • Link-Local, Route-Over (4 bytes) • Routable, Mesh-Under (9 bytes) • Routable Addresses, Route-Over (9 bytes) 5 1 1 1 1 15.4 6LoWPAN Mesh Header Disp. IPHC NHC Ports 1 1 1 1 15.4 Disp. IPHC NHC Ports 5 1 1 1 1 15.4 6LoWPAN Mesh Header Disp. IPHC NHC Ports 1 1 1 2 2 1 1 15.4 Disp. IPHC HLIM Src Addr Dst Addr NHC Ports 71st IETF Meeting - 6LoWPAN WG

  13. Multicast Examples • Link-Local, Mesh-Under (11 bytes) • Link-Local, Route-Over (6 bytes) • Routable, Mesh-Under (11 bytes) • Routable Addresses, Route-Over (9 bytes) 5 1 1 1 1 1 1 15.4 6LoWPAN Mesh Header Disp. Bcast Disp. IPHC NHC Ports 15.4 Disp. IPHC Dst Addr NHC Ports 5 1 1 1 1 1 1 15.4 6LoWPAN Mesh Header Disp. Bcast Disp. IPHC NHC Ports 1 1 1 2 2 1 1 15.4 Disp. IPHC HLIM Src Addr Dst Addr NHC Ports 71st IETF Meeting - 6LoWPAN WG

  14. 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 71st IETF Meeting - 6LoWPAN WG

  15. Discussion • Should 6lowpan-hc become a WG doc? 71st IETF Meeting - 6LoWPAN WG

  16. 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 • Pro: Save an additional octet • Con: Additional code overhead 0 1 2 3 4 5 6 5 7 VTF HLIM 0 SP DP C rsv uncompressed fields… 71st IETF Meeting - 6LoWPAN WG

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