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IPv6 Header Compression for Global Addresses

IPv6 Header Compression for Global Addresses. Jonathan Hui David Culler. draft-hui-6lowpan-hc1g-00 – “Stateless IPv6 Header Compression for Globally Routable Packets in 6LoWPAN Subnetworks”. “IPv6 Communication over IEEE 802.15.4” ….

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IPv6 Header Compression for Global Addresses

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  1. IPv6 Header Compression for Global Addresses Jonathan Hui David Culler draft-hui-6lowpan-hc1g-00 – “Stateless IPv6 Header Compression for Globally Routable Packets in 6LoWPAN Subnetworks” 69th IETF Meeting - 6LoWPAN WG

  2. “IPv6 Communication over IEEE 802.15.4” … • 6LoWPAN supports IP communication using global (i.e., routable) IPv6 addresses • But it never compresses them! • HC1 compression only applies to the special link local prefix. • Shared by all nodes in the PAN • So if you use IP over 802.15.4 for what IP is typically used for (internetworking) you lose much of the virtue of 6LoWPAN. => Complement HC1 with HC1g stateless compression for a shared global prefix 69th IETF Meeting - 6LoWPAN WG

  3. Motivation • Why global addresses? • End-to-end communication in networks with heterogeneous links • without a stateful (possibly application specific) translation gateway • data collection point may be multiple IP hops away • End-to-end communication across different PANs • IP connects different subnetworks • ZigBee does not • LOWPAN_HC1 supports arbitrary addresses, but… • Only allows compression of the link-local (fe80::/64) prefix • Uncompressed addresses consume 32 bytes • 1/4th the 802.15.4 MTU before link and 6LoWPAN headers! • The Issue is compressing the origin / final IP addresses • Not the number of PAN hops between them 69th IETF Meeting - 6LoWPAN WG

  4. 802.15.4 802.3 hartcomm.org Collector/Controller Why Global Addresses? • Monitoring and Control Applications • Collector OR controller generally not a 802.15.4 device • Conventional device on conventional link 69th IETF Meeting - 6LoWPAN WG

  5. 802.15.4 802.3 Collector/Controller Translation Gateway Why Global Addresses? • Monitoring and Control Applications • Collector/controller often connected using other links • Link-local requires a stateful translation gateway • What about multiple 802.15.4 egress points? • Good for redundancy • But requires a translation gateway at each • How is state managed across them? 69th IETF Meeting - 6LoWPAN WG

  6. 802.15.4 802.3 Collector/Controller Why Global Addresses? • Route directly to the data collector • Possibly through different egress points 69th IETF Meeting - 6LoWPAN WG

  7. 802.15.4 802.15.4 802.15.4 Why Global Addresses? • Multiple PANs • May be different in PAN ID, channel, MAC, network-wide keys, etc. 69th IETF Meeting - 6LoWPAN WG

  8. 802.15.4 Why Global Addresses? • Assigned IP addresses within a PAN • IP addresses are useful for naming • If assigned IP address is used to name source or destination, no HC1 compression • Assigned prefix or assigned interface identifier 69th IETF Meeting - 6LoWPAN WG

  9. HC1g - In a Nutshell • Shared context of the PAN includes its prefix • Define compression for prefix other than link-local • PAN has a compressible global prefix (CGP) • Compression of Interface IDs derived from short addrs • Similar to LOWPAN_HC1 encoding • Compresses to 2 octets in best case • Allows arbitrary IPv6 addresses if needed • Same encoding octet • Uses lower-layer information when possible • Support for compressed well-known multicast addresses • Neighbor discovery, DHCPv6 • Uses 6LoWPAN short address encoding 69th IETF Meeting - 6LoWPAN WG

  10. HC1g Compliments HC1 • HC1 and HC1g identified by different dispatch values • HC1 is efficient for link-local communication • HC1g is efficient for off-link communication • Or on-link using non-default prefix Upper Layer Protocols Link-Local Communication Global Communication LOWPAN_HC1 LOWPAN_HC1g 6LoWPAN Mesh/Frag 802.15.4 69th IETF Meeting - 6LoWPAN WG

  11. LOWPAN_HC1g Addresses • PAN has a compressible global prefix (CGP) associated with it • Prefix is elided whenever it matches the CGP • Four HC1g address forms: • Full 128 bits for arbitrary IPv6 addresses • 64 bits: prefix derived from CGP, IID carried inline • 16 bits: prefix derived from CGP, 6LoWPAN encoded short inline • 0 bits: prefix derived from CGP, IID derived from lower layers (e.g. 802.15.4 src/dest or 6LoWPAN orig/final) Arbitrary Prefix Arbitrary IID Elided Arbitrary IID Elided SA Elided 69th IETF Meeting - 6LoWPAN WG

  12. HC1g Encoding • Source Compression • Destination Compression • Version, Traffic, Flow • Next Header • in-line, UCP, ICMP, TCP • L4 Compression • HC2 follows 1 2 3 5 6 7 0 4 SC DC V NH L4 69th IETF Meeting - 6LoWPAN WG

  13. LoWPAN HC1g 16-bit Addr • 16-bit short address follows 6LoWPAN encoding • Compression of IIDs derived from 802.15.4 short address • 802.15.4 short address when first bit is 0 • Upper 48-bits of IID is assumed to be zero • U/L bit is also zero, indicating local scope • Well-known multicast addresses • 16 bits starts with ’101’ • Allocates another range in 6LoWPAN short address encoding • Neither are supported in LOWPAN_HC1 69th IETF Meeting - 6LoWPAN WG

  14. Multicast Address Compression • For commonly-used, well-known multicast addresses • Use 6LoWPAN short address encoding • 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 • Only all-nodes and all-routers currently defined • Can be used in LOWPAN_HC1g or Mesh Addressing 128 bits FF Flags Scope Group ID 1 1 2 3 5 6 7 9 0 1 3 4 5 0 4 8 2 1 0 1 Scope Group ID 69th IETF Meeting - 6LoWPAN WG

  15. Other Differences • Changes made based on lessons learned from LOWPAN_HC1 implementations • Possible lack of octet alignment • Can consume several hundred bytes of code • Octet alignment broken in uncommon cases • Saves at most one octet in best case (when used with HC_UDP) • HC1g include 4-bit version field with Traffic Class and Flow Label • HC_UDP not possible when using IP extension headers • HC2 bit changed to specify layer 4 compression • Only UDP is currently valid, ICMP/TCP not yet defined 69th IETF Meeting - 6LoWPAN WG

  16. HC1g summary • Compression for prefixes other than link-local • PAN has a compressible global prefix (CGP) • Compression of Interface IDs derived from short addrs • Similar to LOWPAN_HC1 encoding, but for CGP • Compresses to 2 octets in best case • Allows arbitrary IPv6 addresses if needed • Same encoding octet, same HC2 • Uses lower-layer information when possible • Support for compressed well-known multicast addresses • Neighbor discovery, DHCPv6 • Uses 6LoWPAN short address encoding 69th IETF Meeting - 6LoWPAN WG

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