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

RFC 4944 – IPv6 Header Compression 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

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

71st IETF Meeting - 6LoWPAN WG 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

LOWPAN_IPHC IPv6 Header Compression 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

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

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

LOWPAN_IPHC IID Derived from 802.15.4 Short Addresses RFC 4944 Includes PAN ID and 0xFFEE 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

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

LOWPAN_IPHC Multicast Address Compression For commonly-used, well-known multicast addresses Divide 16-bit compressed address into ranges Unicast: 0xxxxxxxxxxxxxxx Multicast: 101xxxxxxxxxxxxx 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 4 5 6 7 8 9 1 2 3 4 5 1 Scope Group ID 03/11/2008 71st IETF Meeting - 6LoWPAN WG

LOWPAN_NHC Next Header Compression 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

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

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

71st IETF Meeting - 6LoWPAN WG 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

71st IETF Meeting - 6LoWPAN WG Discussion Should 6lowpan-hc become a WG doc? 03/11/2008 71st IETF Meeting - 6LoWPAN WG

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 1 2 3 4 5 6 5 7 VTF HLIM SP DP C rsv uncompressed fields… 03/11/2008 71st IETF Meeting - 6LoWPAN WG