IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Paging Dispatch
updates
- rfc-4944 — Transmission of IPv6 Packets over IEEE 802.15.4 Networks
Extracted elements (15)
The paging mechanism is designed to maintain backward compatibility with RFC 4944 by treating all existing dispatch values as belonging to Page 0, which is the implicit default context requiring no explicit signaling.
The specification allocates a new Dispatch Bit Pattern (11 11xxxx) for Paging Dispatch rather than extending the existing Escape Dispatch, because multiple new headers may appear in a single frame and the one-octet overhead per Escape Dispatch occurrence would be prohibitive.
Because LOWPAN_IPHC values are defined identically in Page 0 and Page 1, and because NALP is only valid at the first octet, there is no need to restore the Page 0 context after switching to Page 1 in practice.
The NALP Dispatch Bit Pattern is only defined for the first octet in the packet (RFC 4944). Switching back to Page 0 for NALP inside a 6LoWPAN packet does not make sense, so the Page 0 Paging Dispatch (11 110000) may not actually occur in packets adhering to current 6LoWPAN specifications.
Fragment Headers as defined in RFC 4944 MUST always be placed in the packet before the first Page 1 Paging Dispatch, if any, for the same reason as Mesh Headers (Layer 2 information processed first).
If a 6LoWPAN packet requires a Mesh Header, the Mesh Header MUST always be placed in the packet before the first Page 1 Paging Dispatch, if any, because Mesh Headers represent Layer 2 information processed before Layer 3.
Page 0 is the default parsing context and corresponds to all Dispatch byte values defined in RFC 4944. It does not need to be signaled explicitly at the beginning of a 6LoWPAN packet, ensuring backward compatibility.
Page 1 reuses the LOWPAN_IPHC Dispatch bit values (01 100000–01 111111) defined in RFC 6282 with the same meaning, so no context switch from Page 1 back to Page 0 is required to decode RFC 6282-compressed packets.
Pages 1 through 14 are available for assignment to new protocols. Page 15 is reserved for Experimental Use per RFC 5226. Page 0 retains all RFC 4944 dispatch values.
The Paging Dispatch is a 1-byte dispatch value with bit pattern 11 11xxxx, where the lower 4 bits (xxxx) encode the Page Number (0–15). It signals a context switch to the named page in the 6LoWPAN parser.
IANA allocated 16 values (11 110000–11 111111) for 'Page switch' Dispatch types from the existing 'Dispatch Type Field' registry created by RFC 4944, representing Page Numbers 0–15.
The 'Dispatch Type Field' registry (RFC 4944, updated by RFC 6282) is extended with a new 'Page' column. Preexisting entries are assigned to Page 0; LOWPAN_IPHC values (01 1xxxxx) are associated with both Page 0 and Page 1; Page 15 values (except page-switch space) are reserved for Experimental Use. Future assignments require 'Specification Required' policy.
The security considerations of RFC 4944 and RFC 6282 apply. This document introduces no new security considerations beyond those already established for 6LoWPAN.
A Page N parsing context becomes active when the Page N Paging Dispatch is parsed, and remains active until another Paging Dispatch is encountered. The initial state is Page 0 (default).
The Paging Dispatch byte is encoded as 8 bits: bits 0–3 are '1111' and bits 4–7 carry the Page Number (0–15). Values 11 110000 through 11 111111 are allocated for page switching.