draft-ietf-core-block-07.txt		draft-ietf-core-block-08.txt
	CoRE Working Group C. Bormann		CoRE Working Group C. Bormann
	Internet-Draft Universitaet Bremen TZI		Internet-Draft Universitaet Bremen TZI
	Intended status: Standards Track Z. Shelby, Ed.		Intended status: Standards Track Z. Shelby, Ed.
	Expires: July 30, 2012 Sensinode		Expires: August 18, 2012 Sensinode
	January 27, 2012		February 15, 2012
	Blockwise transfers in CoAP		Blockwise transfers in CoAP
	draft-ietf-core-block-07		draft-ietf-core-block-08
	Abstract		Abstract
	CoAP is a RESTful transfer protocol for constrained nodes and		CoAP is a RESTful transfer protocol for constrained nodes and
	networks. Basic CoAP messages work well for the small payloads we		networks. Basic CoAP messages work well for the small payloads we
	expect from temperature sensors, light switches, and similar		expect from temperature sensors, light switches, and similar
	building-automation devices. Occasionally, however, applications		building-automation devices. Occasionally, however, applications
	will need to transfer larger payloads -- for instance, for firmware		will need to transfer larger payloads -- for instance, for firmware
	updates. With HTTP, TCP does the grunt work of slicing large		updates. With HTTP, TCP does the grunt work of slicing large
	payloads up into multiple packets and ensuring that they all arrive		payloads up into multiple packets and ensuring that they all arrive
	skipping to change at page 2, line 10		skipping to change at page 2, line 10
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on July 30, 2012.		This Internet-Draft will expire on August 18, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2012 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 3, line 12		skipping to change at page 3, line 12
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
	2. Block-wise transfers . . . . . . . . . . . . . . . . . . . . . 6		2. Block-wise transfers . . . . . . . . . . . . . . . . . . . . . 6
	2.1. The Block Options . . . . . . . . . . . . . . . . . . . . 6		2.1. The Block Options . . . . . . . . . . . . . . . . . . . . 6
	2.2. Using the Block Options . . . . . . . . . . . . . . . . . 10		2.2. Using the Block Options . . . . . . . . . . . . . . . . . 10
	3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13		3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	4. HTTP Mapping Considerations . . . . . . . . . . . . . . . . . 20		4. The Size Option . . . . . . . . . . . . . . . . . . . . . . . 20
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22		5. HTTP Mapping Considerations . . . . . . . . . . . . . . . . . 22
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 23		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
	6.1. Mitigating Resource Exhaustion Attacks . . . . . . . . . . 23		7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
	6.2. Mitigating Amplification Attacks . . . . . . . . . . . . . 24		7.1. Mitigating Resource Exhaustion Attacks . . . . . . . . . . 25
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25		7.2. Mitigating Amplification Attacks . . . . . . . . . . . . . 26
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26		8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 26		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
	8.2. Informative References . . . . . . . . . . . . . . . . . . 26		9.1. Normative References . . . . . . . . . . . . . . . . . . . 28
	Appendix A. Historical Note . . . . . . . . . . . . . . . . . . . 27		9.2. Informative References . . . . . . . . . . . . . . . . . . 28
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28		Appendix A. Historical Note . . . . . . . . . . . . . . . . . . . 29
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
	1. Introduction		1. Introduction
	The CoRE WG is tasked with standardizing an Application Protocol for		The CoRE WG is tasked with standardizing an Application Protocol for
	Constrained Networks/Nodes, CoAP. This protocol is intended to		Constrained Networks/Nodes, CoAP. This protocol is intended to
	provide RESTful [REST] services not unlike HTTP [RFC2616], while		provide RESTful [REST] services not unlike HTTP [RFC2616], while
	reducing the complexity of implementation as well as the size of		reducing the complexity of implementation as well as the size of
	packets exchanged in order to make these services useful in a highly		packets exchanged in order to make these services useful in a highly
	constrained network of themselves highly constrained nodes.		constrained network of themselves highly constrained nodes.
	skipping to change at page 12, line 39		skipping to change at page 12, line 39
	In a blockwise transfer of a request payload (e.g., a PUT or POST)		In a blockwise transfer of a request payload (e.g., a PUT or POST)
	that is intended to be implemented in an atomic fashion at the		that is intended to be implemented in an atomic fashion at the
	server, the actual creation/replacement takes place at the time the		server, the actual creation/replacement takes place at the time the
	final block, i.e. a block with the M bit unset in the Block1 Option,		final block, i.e. a block with the M bit unset in the Block1 Option,
	is received. If not all previous blocks are available at the server		is received. If not all previous blocks are available at the server
	at this time, the transfer fails and error code 4.08 (Request Entity		at this time, the transfer fails and error code 4.08 (Request Entity
	Incomplete) MUST be returned. The error code 4.13 (Request Entity		Incomplete) MUST be returned. The error code 4.13 (Request Entity
	Too Large) can be returned at any time by a server that does not		Too Large) can be returned at any time by a server that does not
	currently have the resources to store blocks for a block-wise request		currently have the resources to store blocks for a block-wise request
	payload transfer that it would intend to implement in an atomic		payload transfer that it would intend to implement in an atomic
	fashion.		fashion. (Note that a 4.13 response to a request that does not
			employ Block1 is a hint for the client to try sending Block1, and a
			4.13 response with a smaller SZX in the Block1 than requested is a
			hint to try a smaller SZX.)
	If multiple concurrently proceeding block-wise request payload		If multiple concurrently proceeding block-wise request payload
	transfer (e.g., PUT or POST) operations are possible, the requester		transfer (e.g., PUT or POST) operations are possible, the requester
	SHOULD use the Token Option to clearly separate the different		SHOULD use the Token Option to clearly separate the different
	sequences. In this case, when reassembling the representation from		sequences. In this case, when reassembling the representation from
	the blocks being exchanged to enable atomic processing, the		the blocks being exchanged to enable atomic processing, the
	reassembler MUST compare any Token Options present (and, as usual,		reassembler MUST compare any Token Options present (and, as usual,
	taking an absent Token Option to default to the empty Token). If		taking an absent Token Option to default to the empty Token). If
	atomic processing is not desired, there is no need to process the		atomic processing is not desired, there is no need to process the
	Token Option (but it is still returned in the response as usual).		Token Option (but it is still returned in the response as usual).
	skipping to change at page 13, line 42		skipping to change at page 13, line 42
	| <------ ACK [MID=1235], 2.05 Content, 2/1/1/128 |		| <------ ACK [MID=1235], 2.05 Content, 2/1/1/128 |
	| |		| |
	| CON [MID=1236], GET, /status, 2/2/0/128 ------> |		| CON [MID=1236], GET, /status, 2/2/0/128 ------> |
	| |		| |
	| <------ ACK [MID=1236], 2.05 Content, 2/2/0/128 |		| <------ ACK [MID=1236], 2.05 Content, 2/2/0/128 |
	Figure 2: Simple blockwise GET		Figure 2: Simple blockwise GET
	In the second example (Figure 3), the client anticipates the		In the second example (Figure 3), the client anticipates the
	blockwise transfer (e.g., because of a size indication in the link-		blockwise transfer (e.g., because of a size indication in the link-
	format description) and sends a size proposal. All ACK messages		format description [I-D.ietf-core-link-format]) and sends a size
	except for the last carry 64 bytes of payload; the last one carries		proposal. All ACK messages except for the last carry 64 bytes of
	between 1 and 64 bytes.		payload; the last one carries between 1 and 64 bytes.
	CLIENT SERVER		CLIENT SERVER
	| |		| |
	| CON [MID=1234], GET, /status, 2/0/0/64 ------> |		| CON [MID=1234], GET, /status, 2/0/0/64 ------> |
	| |		| |
	| <------ ACK [MID=1234], 2.05 Content, 2/0/1/64 |		| <------ ACK [MID=1234], 2.05 Content, 2/0/1/64 |
	| |		| |
	| CON [MID=1235], GET, /status, 2/1/0/64 ------> |		| CON [MID=1235], GET, /status, 2/1/0/64 ------> |
	| |		| |
	| <------ ACK [MID=1235], 2.05 Content, 2/1/1/64 |		| <------ ACK [MID=1235], 2.05 Content, 2/1/1/64 |
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	| <------ CON [MID=4714], 2.01 Created, 37a, 2/2/1/128 |		| <------ CON [MID=4714], 2.01 Created, 37a, 2/2/1/128 |
	| |		| |
	| ACK [MID=4714], 0, 2/2/1/128 ------> |		| ACK [MID=4714], 0, 2/2/1/128 ------> |
	| |		| |
	| <------ CON [MID=4715], 2.01 Created, 37a, 2/3/0/128 |		| <------ CON [MID=4715], 2.01 Created, 37a, 2/3/0/128 |
	| |		| |
	| ACK [MID=4715], 0, 2/3/0/128 ------> |		| ACK [MID=4715], 0, 2/3/0/128 ------> |
	Figure 10: Atomic blockwise POST with separate blockwise response		Figure 10: Atomic blockwise POST with separate blockwise response
	4. HTTP Mapping Considerations		4. The Size Option
			In many cases when transferring a large resource representation block
			by block, it is advantageous to know the total size early in the
			process. Some indication may be available from the maximum size
			estimate attribute "sz" provided in a resource description
			[I-D.ietf-core-link-format]. However, the size may vary dynamically,
			so a more up-to-date indication may be useful.
			The Size Option may be used for three purposes:
			o in a request, to ask the server to provide a size estimate in the
			response ("size request"). For this usage, the value MUST be set
			to 0.
			o in a response carrying a Block2 Option, to indicate the current
			estimate the server has of the total size of the resource
			representation.
			o in a request carrying a Block1 Option, to indicate the current
			estimate the client has of the total size of the resource
			representation.
			A size request can be easily distinguished from a size indication, as
			the third case is not useful for a GET or DELETE, and an actual size
			indication of 0 would either be overridden by the actual size of the
			payload for a PUT or POST or would not be useful.
			In the latter two cases ("size indication"), the value of the option
			is the current estimate, measured in bytes.
			The Size Option is "elective", i.e., a client MUST be prepared for
			the server to ignore the size estimate request. The Size Option MUST
			NOT occur more than once.
			+------+----------+------+--------+--------+---------+
			| Type | C/E | Name | Format | Length | Default |
			+------+----------+------+--------+--------+---------+
			| 18 | Elective | Size | uint | 0-4 B | (none) |
			+------+----------+------+--------+--------+---------+
			Implementation Notes:
			o As a quality of implementation consideration, blockwise transfers
			for which the total size considerably exceeds the size of one
			block are expected to include size indications, whenever those can
			be provided without undue effort (preferably with the first block
			exchanged). If the size estimate does not change, the indication
			does not need to be repeated for every block.
			o The end of a blockwise transfer is governed by the M bits in the
			Block Options, _not_ by exhausting the size estimates exchanged.
			o As usual for an option of type uint, the value 0 is best expressed
			as an empty option (0 bytes). There is no default value.
			5. HTTP Mapping Considerations
	In this subsection, we give some brief examples for the influence the		In this subsection, we give some brief examples for the influence the
	Block options might have on intermediaries that map between CoAP and		Block options might have on intermediaries that map between CoAP and
	HTTP.		HTTP.
	For mapping CoAP requests to HTTP, the intermediary may want to map		For mapping CoAP requests to HTTP, the intermediary may want to map
	the sequence of block-wise transfers into a single HTTP transfer.		the sequence of block-wise transfers into a single HTTP transfer.
	E.g., for a GET request, the intermediary could perform the HTTP		E.g., for a GET request, the intermediary could perform the HTTP
	request once the first block has been requested and could then		request once the first block has been requested and could then
	fulfill all further block requests out of its cache. A constrained		fulfill all further block requests out of its cache. A constrained
	skipping to change at page 22, line 5		skipping to change at page 24, line 5
	transmitting a request through that active TCP connection. The CoAP		transmitting a request through that active TCP connection. The CoAP
	4.08 response code indicates one or more missing blocks, which may be		4.08 response code indicates one or more missing blocks, which may be
	due to timeouts or resource constraints; as there is no connection		due to timeouts or resource constraints; as there is no connection
	state, there is no way to deliver such a response immediately;		state, there is no way to deliver such a response immediately;
	instead, it is delivered on the next block transfer. Still, HTTP 408		instead, it is delivered on the next block transfer. Still, HTTP 408
	is probably the best mapping back to HTTP, as the timeout is the most		is probably the best mapping back to HTTP, as the timeout is the most
	likely cause for a CoAP 4.08. Note that there is no way to		likely cause for a CoAP 4.08. Note that there is no way to
	distinguish a timeout from a missing block for a server without		distinguish a timeout from a missing block for a server without
	creating additional state, the need for which we want to avoid.)		creating additional state, the need for which we want to avoid.)
	5. IANA Considerations		6. IANA Considerations
	This draft adds the following option numbers to the CoAP Option		This draft adds the following option numbers to the CoAP Option
	Numbers registry of [I-D.ietf-core-coap]:		Numbers registry of [I-D.ietf-core-coap]:
	+--------+--------+-----------+		+--------+--------+-----------+
	| Number | Name | Reference |		| Number | Name | Reference |
	+--------+--------+-----------+		+--------+--------+-----------+
	| 17 | Block2 | [RFCXXXX] |		| 17 | Block2 | [RFCXXXX] |
	| | | |		| | | |
	| 19 | Block1 | [RFCXXXX] |		| 18 | Size | [RFCXXXX] |
			| | | |
			| 19 | Block1 | [RFCXXXX] |
	+--------+--------+-----------+		+--------+--------+-----------+
	Table 2: CoAP Option Numbers		Table 2: CoAP Option Numbers
	This draft adds the following response code to the CoAP Response		This draft adds the following response code to the CoAP Response
	Codes registry of [I-D.ietf-core-coap]:		Codes registry of [I-D.ietf-core-coap]:
	+------+--------------------------------+-----------+		+------+--------------------------------+-----------+
	| Code | Description | Reference |		| Code | Description | Reference |
	+------+--------------------------------+-----------+		+------+--------------------------------+-----------+
	| 136 | 4.08 Request Entity Incomplete | [RFCXXXX] |		| 136 | 4.08 Request Entity Incomplete | [RFCXXXX] |
	+------+--------------------------------+-----------+		+------+--------------------------------+-----------+
	Table 3: CoAP Response Codes		Table 3: CoAP Response Codes
	6. Security Considerations		7. Security Considerations
	Providing access to blocks within a resource may lead to surprising		Providing access to blocks within a resource may lead to surprising
	vulnerabilities. Where requests are not implemented atomically, an		vulnerabilities. Where requests are not implemented atomically, an
	attacker may be able to exploit a race condition or confuse a server		attacker may be able to exploit a race condition or confuse a server
	by inducing it to use a partially updated resource representation.		by inducing it to use a partially updated resource representation.
	Partial transfers may also make certain problematic data invisible to		Partial transfers may also make certain problematic data invisible to
	intrusion detection systems; it is RECOMMENDED that an intrusion		intrusion detection systems; it is RECOMMENDED that an intrusion
	detection system (IDS) that analyzes resource representations		detection system (IDS) that analyzes resource representations
	transferred by CoAP implement the Block options to gain access to		transferred by CoAP implement the Block options to gain access to
	entire resource representations. Still, approaches such as		entire resource representations. Still, approaches such as
	skipping to change at page 23, line 33		skipping to change at page 25, line 33
	Where access to a resource is only granted to clients making use of a		Where access to a resource is only granted to clients making use of a
	specific security association, all blocks of that resource MUST be		specific security association, all blocks of that resource MUST be
	subject to the same security checks; it MUST NOT be possible for		subject to the same security checks; it MUST NOT be possible for
	unprotected exchanges to influence blocks of an otherwise protected		unprotected exchanges to influence blocks of an otherwise protected
	resource. As a related consideration, where object security is		resource. As a related consideration, where object security is
	employed, PUT/POST should be implemented in the atomic fashion,		employed, PUT/POST should be implemented in the atomic fashion,
	unless the object security operation is performed on each access and		unless the object security operation is performed on each access and
	the creation of unusable resources can be tolerated.		the creation of unusable resources can be tolerated.
	6.1. Mitigating Resource Exhaustion Attacks		Misleading size indications may be used by an attacker to induce
			buffer overflows in poor implementations, for which the usual
			considerations apply.
			7.1. Mitigating Resource Exhaustion Attacks
	Certain blockwise requests may induce the server to create state,		Certain blockwise requests may induce the server to create state,
	e.g. to create a snapshot for the blockwise GET of a fast-changing		e.g. to create a snapshot for the blockwise GET of a fast-changing
	resource to enable consistent access to the same version of a		resource to enable consistent access to the same version of a
	resource for all blocks, or to create temporary resource		resource for all blocks, or to create temporary resource
	representations that are collected until pressed into service by a		representations that are collected until pressed into service by a
	final PUT or POST with the more bit unset. All mechanisms that		final PUT or POST with the more bit unset. All mechanisms that
	induce a server to create state that cannot simply be cleaned up		induce a server to create state that cannot simply be cleaned up
	create opportunities for denial-of-service attacks. Servers SHOULD		create opportunities for denial-of-service attacks. Servers SHOULD
	avoid being subject to resource exhaustion based on state created by		avoid being subject to resource exhaustion based on state created by
	skipping to change at page 24, line 13		skipping to change at page 26, line 17
	fragmentation, adaptation layer fragmentation), e.g. because there is		fragmentation, adaptation layer fragmentation), e.g. because there is
	application layer semantics that can be used for mitigation or		application layer semantics that can be used for mitigation or
	because lower layers provide security associations that can prevent		because lower layers provide security associations that can prevent
	attacks. However, it is less common to apply timeouts and keepalive		attacks. However, it is less common to apply timeouts and keepalive
	mechanisms at the application layer than at lower layers. Servers		mechanisms at the application layer than at lower layers. Servers
	MAY want to clean up accumulated state by timing it out (cf. response		MAY want to clean up accumulated state by timing it out (cf. response
	code 4.08), and clients SHOULD be prepared to run blockwise transfers		code 4.08), and clients SHOULD be prepared to run blockwise transfers
	in an expedient way to minimize the likelihood of running into such a		in an expedient way to minimize the likelihood of running into such a
	timeout.		timeout.
	6.2. Mitigating Amplification Attacks		7.2. Mitigating Amplification Attacks
	[I-D.ietf-core-coap] discusses the susceptibility of CoAP end-points		[I-D.ietf-core-coap] discusses the susceptibility of CoAP end-points
	for use in amplification attacks.		for use in amplification attacks.
	A CoAP server can reduce the amount of amplification it provides to		A CoAP server can reduce the amount of amplification it provides to
	an attacker by offering large resource representations only in		an attacker by offering large resource representations only in
	relatively small blocks. With this, e.g., for a 1000 byte resource,		relatively small blocks. With this, e.g., for a 1000 byte resource,
	a 10-byte request might result in an 80-byte response (with a 64-byte		a 10-byte request might result in an 80-byte response (with a 64-byte
	block) instead of a 1016-byte response, considerably reducing the		block) instead of a 1016-byte response, considerably reducing the
	amplification provided.		amplification provided.
	7. Acknowledgements		8. Acknowledgements
	Much of the content of this draft is the result of discussions with		Much of the content of this draft is the result of discussions with
	the [I-D.ietf-core-coap] authors, and via many CoRE WG discussions.		the [I-D.ietf-core-coap] authors, and via many CoRE WG discussions.
	Tokens were suggested by Gilman Tolle and refined by Klaus Hartke.		Tokens were suggested by Gilman Tolle and refined by Klaus Hartke.
	Charles Palmer provided extensive editorial comments to a previous		Charles Palmer provided extensive editorial comments to a previous
	version of this draft, some of which the authors hope to have covered		version of this draft, some of which the authors hope to have covered
	in this version. Esko Dijk reviewed a more recent version, leading		in this version. Esko Dijk reviewed a more recent version, leading
	to a number of further editorial improvements.		to a number of further editorial improvements.
	8. References		Kepeng Li, Linyi Tian, and Barry Leiba wrote up an early version of
			the Size Option, which has informed this draft.
	8.1. Normative References		9. References
			9.1. Normative References
	[I-D.ietf-core-coap]		[I-D.ietf-core-coap]
	Shelby, Z., Hartke, K., Bormann, C., and B. Frank,		Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
	"Constrained Application Protocol (CoAP)",		"Constrained Application Protocol (CoAP)",
	draft-ietf-core-coap-08 (work in progress), October 2011.		draft-ietf-core-coap-08 (work in progress), October 2011.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext		Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
	Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.		Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
	8.2. Informative References		9.2. Informative References
			[I-D.ietf-core-link-format]
			Shelby, Z., "CoRE Link Format",
			draft-ietf-core-link-format-11 (work in progress),
			January 2012.
	[REST] Fielding, R., "Architectural Styles and the Design of		[REST] Fielding, R., "Architectural Styles and the Design of
	Network-based Software Architectures", 2000.		Network-based Software Architectures", 2000.
	[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6		[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
	over Low-Power Wireless Personal Area Networks (6LoWPANs):		over Low-Power Wireless Personal Area Networks (6LoWPANs):
	Overview, Assumptions, Problem Statement, and Goals",		Overview, Assumptions, Problem Statement, and Goals",
	RFC 4919, August 2007.		RFC 4919, August 2007.
	Appendix A. Historical Note		Appendix A. Historical Note
End of changes. 17 change blocks.
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