1. 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

2. RFC 4944 – IPv6 Header Compression1 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 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

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

4. 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

5. LOWPAN_IPHC IPv6 Header Compression1 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

6. 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 Short Address
Elided suffix derived from lower-layers
03/11/2008
71st IETF Meeting - 6LoWPAN WG

7. 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

8. 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

9. 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

10. 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

11. LOWPAN_NHC Next Header Compression1 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

12. 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

13. 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

14. 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

15. 71st IETF Meeting - 6LoWPAN WG
Discussion
Should 6lowpan-hc become a WG doc?
03/11/2008
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 1 2 3 4 5 6 5 7
VTF
HLIM SP DP C
rsv
uncompressed fields…
03/11/2008
71st IETF Meeting - 6LoWPAN WG