draft-ietf-core-block-01.txt   draft-ietf-core-block-02.txt 
CoRE Working Group Z. Shelby, Ed. CoRE Working Group Z. Shelby, Ed.
Internet-Draft Sensinode Internet-Draft Sensinode
Intended status: Standards Track C. Bormann Intended status: Standards Track C. Bormann
Expires: July 29, 2011 Universitaet Bremen TZI Expires: September 15, 2011 Universitaet Bremen TZI
January 25, 2011 March 14, 2011
Blockwise transfers in CoAP Blockwise transfers in CoAP
draft-ietf-core-block-01 draft-ietf-core-block-02
Abstract Abstract
CoAP is a RESTful transfer protocol for constrained nodes and CoAP is a RESTful transfer protocol for constrained nodes and
networks. CoAP is based on datagram transport, which limits the networks. CoAP is based on datagram transport, which limits the
maximum size of resource representations that can be transferred maximum size of resource representations that can be transferred
without too much fragmentation. The Block option provides a minimal without too much fragmentation. The Block option provides a minimal
way to transfer larger representations in a block-wise fashion. way to transfer larger representations in a block-wise fashion.
Status of this Memo Status of this Memo
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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 29, 2011. This Internet-Draft will expire on September 15, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 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
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Block-wise transfers . . . . . . . . . . . . . . . . . . . . . 5 2. Block-wise transfers . . . . . . . . . . . . . . . . . . . . . 5
2.1. The Block Option . . . . . . . . . . . . . . . . . . . . . 5 2.1. The Block Option . . . . . . . . . . . . . . . . . . . . . 5
2.2. Using the Block Option . . . . . . . . . . . . . . . . . . 7 2.2. Using the Block Option . . . . . . . . . . . . . . . . . . 7
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 3.1. HTTP Mapping Considerations . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
5.1. Mitigating Resource Exhaustion Attacks . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
5.2. Mitigating Amplification Attacks . . . . . . . . . . . . . 16 5.1. Mitigating Resource Exhaustion Attacks . . . . . . . . . . 18
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 5.2. Mitigating Amplification Attacks . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . . 18 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2. Informative References . . . . . . . . . . . . . . . . . . 18 7.1. Normative References . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 7.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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.
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(Note that, as an implementation convenience, the option value with (Note that, as an implementation convenience, the option value with
the last 4 bits masked out, shifted to the left by the value of SZX, the last 4 bits masked out, shifted to the left by the value of SZX,
gives the byte position of the block.) gives the byte position of the block.)
NUM: Block Number. The block number is a variable-size (4, 12, or NUM: Block Number. The block number is a variable-size (4, 12, or
20 bit) unsigned integer indicating the block number being 20 bit) unsigned integer indicating the block number being
requested or provided. Block number 0 indicates the first block requested or provided. Block number 0 indicates the first block
of a representation. of a representation.
M: More Flag. This flag indicates if this block is the last in a M: More Flag. This flag, if unset, indicates that this block is the
representation when set. When not set it indicates that there are last in a representation. When set it indicates that there are
one or more blocks available. When the block option is used to one or more additional blocks available. When the block option is
retrieve a specific block number the M bit MUST be sent as zero used in a request to retrieve a specific block number, the M bit
and ignored on reception. MUST be sent as zero and ignored on reception.
SZX: Block Size. The block size is a three-bit unsigned integer SZX: Block Size. The block size is a three-bit unsigned integer
indicating the size of a block to the power of two. Thus block indicating the size of a block to the power of two. Thus block
size = 2^(SZX + 4). As there are three bits available for SZX, size = 2^(SZX + 4). As there are three bits available for SZX,
the minimum block size is 2^(0+4) = 16 and the maximum is 2^(7+4) the minimum block size is 2^(0+4) = 16 and the maximum is 2^(7+4)
= 2048. = 2048.
The Block option is used in one of three roles: The Block option is used in one of three roles:
o In the request for a GET, the Block option gives the block number o In the request for a GET, the Block option gives the block number
requested and suggests a block size (block number 0) or echoes the requested and suggests a block size (block number 0) or echoes the
block size of previous blocks received (block numbers other than block size of previous blocks received (block numbers other than
0). 0).
o In the response for a GET or in the request for a PUT or POST, the o In the response for a GET or in the request for a PUT or POST, the
Block option describes what block number is contained in the Block option describes what block number is contained in the
payload, and whether further blocks are required to complete the payload, and whether further blocks are required to complete the
transfer of that body (M bit). If the M bit is set, the size of transfer of that body (M bit). If the M bit is set, the size of
the payload body in bytes MUST indeed be the power of two given by the payload body in bytes MUST indeed be the power of two given by
the block size. All blocks for a REST transfer MUST use the same the block size. With certain exceptions given below, all blocks
block size, except for the last block (M bit not set). for a REST transfer MUST use the same block size, except for the
last block (M bit not set).
o In the response for a PUT or POST, the Block option indicates what o In the response for a PUT or POST, the Block option indicates what
block number is being acknowledged. In this case, the M bit is block number is being acknowledged. In this case, if the M bit is
set to indicate that this response does not carry the final set it indicates that this response does not carry the final
response to the request; this can occur when the M bit was set in response to the request; this can occur when the M bit was set in
the request and the server implements PUT/POST atomically (i.e., the request and the server implements PUT/POST atomically (i.e.,
acts only upon reception of the last block). acts only upon reception of the last block). Conversely, if the M
bit is unset, it indicates the block-wise request was enacted now,
and the response carries the final response to this request (and
to any previous ones with the M bit set in this sequence of block-
wise transfers). Finally, the block size given in such a Block
option indicates the largest block size preferred by the server
for transfers toward the resource that is the same or smaller than
the one used in the initial exchange; the client SHOULD use this
block size or a smaller one in all further PUT/POST requests in
the transfer sequence.
2.2. Using the Block Option 2.2. Using the Block Option
Using the Block option, a single REST operation can be split into Using the Block option, a single REST operation can be split into
multiple CoAP message exchanges. Each of these message exchanges multiple CoAP message exchanges. Each of these message exchanges
uses their own CoAP Message ID. uses their own CoAP Message ID.
When a GET is answered with a response carrying a Block option with When a GET is answered with a response carrying a Block option with
the M bit set, the requester may retrieve additional blocks of the the M bit set, the requester may retrieve additional blocks of the
resource representation by sending requests with a Block option resource representation by sending requests with a Block option
giving the block number desired. In such a Block option, the M bit giving the block number desired. In such a Block option, the M bit
MUST be sent as zero and ignored on reception. MUST be sent as zero and ignored on reception.
To influence the block size used in response to a GET request, the To influence the block size used in response to a GET request, the
requester uses the Block option, giving the desired size, a block requester uses the Block option, giving the desired size, a block
number of zero and an M bit of zero. A server SHOULD use the block number of zero and an M bit of zero. A server SHOULD use the block
size indicated or a smaller size. Any further block-wise requests size indicated or a smaller size. Any further block-wise requests
for blocks beyond the first one MUST indicate the same block size for blocks beyond the first one MUST indicate the same block size
that was used by the server in the response for the first one. that was used by the server in the response for the first request
that gave a desired size using a Block option.
If the Block option is used by the requester, all GET requests in a Once the Block option is used by the requester, all GET requests in a
single transfer MUST ultimately use the same size, except that there single transfer MUST ultimately use the same size, except that there
may not be enough content to fill the last block (the one returned may not be enough content to fill the last block (the one returned
with the M bit not set). The server SHOULD use the block size with the M bit not set). (Note that the client may start using the
indicated in the request option or a smaller size, but the requester Block option in a second request after a first request without a
MUST take note of the actual block size used in the response it Block option resulted in a Block option in the response.) The server
receives to its initial GET and proceed to use it in subsequent GETs; SHOULD use the block size indicated in the request option or a
the server behavior MUST ensure that this client behavior results in smaller size, but the requester MUST take note of the actual block
the same block size for all responses in a sequence (except for the size used in the response it receives to its initial GET and proceed
last one with the M bit not set). to use it in subsequent GETs; the server behavior MUST ensure that
this client behavior results in the same block size for all responses
in a sequence (except for the last one with the M bit not set, and
possibly the first one if the initial request did not contain a Block
option).
Block-wise transfers can be used to GET resources the representations Block-wise transfers can be used to GET resources the representations
of which are entirely static (not changing over time at all, such as of which are entirely static (not changing over time at all, such as
in a schema describing a device), or for dynamically changing in a schema describing a device), or for dynamically changing
resources. In the latter case, the Block option SHOULD be used in resources. In the latter case, the Block option SHOULD be used in
conjunction with the Etag option, to ensure that the blocks being conjunction with the ETag option, to ensure that the blocks being
reassembled are from the same version of the representation. When reassembled are from the same version of the representation. When
reassembling the representation from the blocks being exchanged, the reassembling the representation from the blocks being exchanged, the
reassembler MUST compare Etag options. If the Etag options do not reassembler MUST compare ETag options. If the ETag options do not
match in a GET transfer, the requester has the option of attempting match in a GET transfer, the requester has the option of attempting
to retrieve fresh values for the blocks it retrieved first. To to retrieve fresh values for the blocks it retrieved first. To
minimize the resulting inefficiency, the server MAY cache the current minimize the resulting inefficiency, the server MAY cache the current
value of a representation for an ongoing sequence of requests, but value of a representation for an ongoing sequence of requests, but
there is no requirement for the server to establish any state. The there is no requirement for the server to establish any state. The
client MAY facilitate identifying the sequence by using the Token client MAY facilitate identifying the sequence by using the Token
option with a non-default value. option with a non-default value.
In a PUT or POST transfer, the Block option refers to the body in the In a PUT or POST transfer, the Block option refers to the body in the
request, i.e., there is no way to perform a block-wise retrieval of request, i.e., there is no way to perform a block-wise retrieval of
the body of the response. Servers that do need to supply large the body of the response. Servers that do need to supply large
bodies in response to PUT/POST SHOULD therefore be employing bodies in response to PUT/POST SHOULD therefore be employing
mechanisms such as providing a location for a resource that can be mechanisms such as providing a location for a resource that can be
used in a GET to obtain that information. used in a GET to obtain that information.
In a PUT or POST transfer response, the block size given in the Block
option indicates the block size preference of the server for this
resource. Obviously, at this point the first block has already been
transferred without benefit of this knowledge. Still, the client
SHOULD heed the preference and use the block size preferred by the
server or a smaller one. Note that any reduction in the block size
may mean that the second request starts with a block number larger
than one, as the first request already transferred multiple blocks as
counted in the smaller size.
In a PUT or POST transfer that is intended to be implemented in an In a PUT or POST transfer that is intended to be implemented in an
atomic fashion at the server, the actual creation/replacement takes atomic fashion at the server, the actual creation/replacement takes
place at the time the final block, i.e. a block with the M bit unset, place at the time the final block, i.e. a block with the M bit unset,
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 PUT or currently have the resources to store blocks for a block-wise PUT or
POST transfer that it would intend to implement in an atomic fashion. POST transfer that it would intend to implement in an atomic fashion.
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| <------ ACK [MID=1239], 2.00 OK, 5/0/64 | | <------ ACK [MID=1239], 2.00 OK, 5/0/64 |
Figure 3: Blockwise GET with early negotiation Figure 3: Blockwise GET with early negotiation
In the third example (Figure 4), the client is surprised by the need In the third example (Figure 4), the client is surprised by the need
for a blockwise transfer, and unhappy with the size chosen for a blockwise transfer, and unhappy with the size chosen
unilaterally by the server. As it did not send a size proposal unilaterally by the server. As it did not send a size proposal
initially, the negotiation only influences the size from the second initially, the negotiation only influences the size from the second
message exchange. Since the client already obtained both the first message exchange. Since the client already obtained both the first
and second 64-byte block in the first 128-byte exchange, it goes on and second 64-byte block in the first 128-byte exchange, it goes on
requesting the third 64-byte block. None of this is understood by requesting the third 64-byte block ("2/0/64"). None of this is (or
the server, which simply responds to the requests as it best can. needs to be) understood by the server, which simply responds to the
requests as it best can.
CLIENT SERVER CLIENT SERVER
| | | |
| CON [MID=1234], GET, /status ------> | | CON [MID=1234], GET, /status ------> |
| | | |
| <------ ACK [MID=1234], 2.00 OK, 0/1/128 | | <------ ACK [MID=1234], 2.00 OK, 0/1/128 |
| | | |
| CON [MID=1235], GET, /status, 2/0/64 ------> | | CON [MID=1235], GET, /status, 2/0/64 ------> |
| | | |
| <------ ACK [MID=1235], 2.00 OK, 2/1/64 | | <------ ACK [MID=1235], 2.00 OK, 2/1/64 |
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responses to the requests that have a more bit in the request block responses to the requests that have a more bit in the request block
option are provisional; only the final response tells the client that option are provisional; only the final response tells the client that
the PUT succeeded. the PUT succeeded.
CLIENT SERVER CLIENT SERVER
| | | |
| CON [MID=1234], PUT, /options, v17, 0/1/128 ------> | | CON [MID=1234], PUT, /options, v17, 0/1/128 ------> |
| | | |
| <------ ACK [MID=1234], 2.04 Changed, 0/1/128 | | <------ ACK [MID=1234], 2.04 Changed, 0/1/128 |
| | | |
| CON [MID=1235], PUT, /options, v17, 1/1/12 ------> | | CON [MID=1235], PUT, /options, v17, 1/1/128 ------> |
| | | |
| <------ ACK [MID=1235], 2.04 Changed, 1/1/128 | | <------ ACK [MID=1235], 2.04 Changed, 1/1/128 |
| | | |
| CON [MID=1236], PUT, /options, v17, 2/0/128 ------> | | CON [MID=1236], PUT, /options, v17, 2/0/128 ------> |
| | | |
| <------ ACK [MID=1236], 2.04 Changed, 2/0/128 | | <------ ACK [MID=1236], 2.04 Changed, 2/0/128 |
Figure 7: Simple atomic blockwise PUT Figure 7: Simple atomic blockwise PUT
A stateless server that simply builds/updates the resource in place A stateless server that simply builds/updates the resource in place
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present during the run of the message exchange sequence does not lead present during the run of the message exchange sequence does not lead
to problems, e.g. because the resource being created or changed is to problems, e.g. because the resource being created or changed is
not yet or not currently in use. not yet or not currently in use.
CLIENT SERVER CLIENT SERVER
| | | |
| CON [MID=1234], PUT, /options, v17, 0/1/128 ------> | | CON [MID=1234], PUT, /options, v17, 0/1/128 ------> |
| | | |
| <------ ACK [MID=1234], 2.04 Changed, 0/0/128 | | <------ ACK [MID=1234], 2.04 Changed, 0/0/128 |
| | | |
| CON [MID=1235], PUT, /options, v17, 1/1/12 ------> | | CON [MID=1235], PUT, /options, v17, 1/1/128 ------> |
| | | |
| <------ ACK [MID=1235], 2.04 Changed, 1/0/128 | | <------ ACK [MID=1235], 2.04 Changed, 1/0/128 |
| | | |
| CON [MID=1236], PUT, /options, v17, 2/0/128 ------> | | CON [MID=1236], PUT, /options, v17, 2/0/128 ------> |
| | | |
| <------ ACK [MID=1236], 2.04 Changed, 2/0/128 | | <------ ACK [MID=1236], 2.04 Changed, 2/0/128 |
Figure 8: Simple stateless blockwise PUT Figure 8: Simple stateless blockwise PUT
Finally, a server receiving a blockwise PUT or POST may want to
indicate a smaller block size preference (Figure 9). In this case,
the client SHOULD continue with a smaller block size; if it does, it
MUST adjust the block number to properly count in that smaller size.
CLIENT SERVER
| |
| CON [MID=1234], PUT, /options, v17, 0/1/128 ------> |
| |
| <------ ACK [MID=1234], 2.04 Changed, 0/1/32 |
| |
| CON [MID=1235], PUT, /options, v17, 4/1/32 ------> |
| |
| <------ ACK [MID=1235], 2.04 Changed, 4/1/32 |
| |
| CON [MID=1236], PUT, /options, v17, 5/1/32 ------> |
| |
| <------ ACK [MID=1235], 2.04 Changed, 5/1/32 |
| |
| CON [MID=1237], PUT, /options, v17, 6/0/32 ------> |
| |
| <------ ACK [MID=1236], 2.04 Changed, 6/0/32 |
Figure 9: Simple atomic blockwise PUT with negotiation
3.1. HTTP Mapping Considerations
In this subsection, we give some brief examples for the influence the
Block Option might have on intermediaries that map between CoAP and
HTTP.
For mapping CoAP requests to HTTP, the intermediary may want to map
the block-wise transfer into a single HTTP transfer. E.g., for a GET
request, the intermediary could perform the HTTP request once the
first block has been requested and could then fulfill all further
block requests out of its cache. A constrained implementation may
not be able to cache the entire object and may use a combination of
TCP flow control and (in particular if timeouts occur) HTTP range
requests to obtain the information necessary for the next block
transfer at the right time.
For PUT or POST requests, there is more variation in how HTTP servers
might implement ranges. Some WebDAV servers do, but in general the
CoAP-to-HTTP intermediary will have to try sending the payload of all
the blocks of a block-wise transfer within one HTTP request. If
enough buffering is available, this request can be started when the
last CoAP block is received. A constrained implementation may want
to relieve its buffering by already starting to send the HTTP request
at the time the first CoAP block is received; any HTTP 408 status
code that indicates that the HTTP server became impatient with the
resulting transfer can then be mapped into a CoAP 4.08 response code
(similarly, 413 maps to 4.13).
For mapping HTTP to CoAP, the intermediary may want to map a single
HTTP transfer into a block-wise transfer. If the HTTP client is too
slow delivering a request body on a PUT or POST, the CoAP server
might time out and return a 4.08 response code, which in turn maps
well to an HTTP 408 status code (again, 4.13 maps to 413). HTTP
range requests received on the HTTP side may be served out of a cache
and/or mapped to GET requests that request a sequence of blocks
overlapping the range.
4. IANA Considerations 4. IANA Considerations
This draft adds the following option number to the CoAP Option This draft adds the following option number 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 |
+--------+-------+-------------+ +--------+-------+-----------+
| 13 | Block | Section 2.1 | | 13 | Block | [RFCXXXX] |
+--------+-------+-------------+ +--------+-------+-----------+
Table 1: CoAP Option Numbers Table 1: 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 | Section 2.1 | | 136 | 4.08 Request Entity Incomplete | [RFCXXXX] |
+------+--------------------------------+-------------+ +------+--------------------------------+-----------+
Table 2: CoAP Response Codes Table 2: CoAP Response Codes
5. Security Considerations 5. 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
skipping to change at page 18, line 10 skipping to change at page 21, line 10
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.
7. References 7. References
7.1. Normative References 7.1. Normative References
[I-D.ietf-core-coap] [I-D.ietf-core-coap]
Shelby, Z., Frank, B., and D. Sturek, "Constrained Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
Application Protocol (CoAP)", draft-ietf-core-coap-03 "Constrained Application Protocol (CoAP)",
(work in progress), October 2010. draft-ietf-core-coap-05 (work in progress), March 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.
7.2. Informative References 7.2. Informative References
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