Shim Header for CoAP Transfer over non-TCP/IP Networks
draft-ikpark-core-shim-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
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|---|---|---|---|
| Authors | Ilkyun Park , Seok-Kap Ko , Seung-Hun Oh , Byoung-Tak Lee | ||
| Last updated | 2013-07-15 | ||
| RFC stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-ikpark-core-shim-00
CoRE Working Group Ilkyun Park
Internet Draft Seok-Kap Ko
Intended status: Standard Track Seung-Hun Oh
Expires: January 14, 2014 Byung-Tak Lee
ETRI
July 14, 2013
Shim Header for CoAP Transfer over non-TCP/IP Networks
draft-ikpark-core-shim-00.txt
Abstract
This document defines shim header for the transfer of CoAP messages
over non-TCP/IP constrained networks. In this environment, IP and UDP
or TCP are not used, so that additional shim header as a container
for addresses of sender/receiver and the length of CoAP header and
its payload is required.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 14, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction ................................................ 4
2. Terminology ................................................. 5
3. Shim Header ................................................. 5
3.1. Header Format .......................................... 5
3.2. Identifying between CoAP Header and Shim Header ........ 7
3.3. Example ................................................ 7
4. Security Considerations ..................................... 8
5. IANA Considerations ......................................... 8
6. Acknowledgments ............................................. 9
7. References .................................................. 9
7.1. Normative References ................................... 9
7.2. Informative References ................................. 9
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1. Introduction
CoAP [CoAP] is a data transfer protocol over constrained nodes and
networks, e.g., 6LoWPAN. This protocol uses TCP/IP suit and some
other additional protocols designed for low-power and lossy networks
(LLN) like Routing Protocol for LLN (RPL) [RPL].
Nowadays many sensors are involved in variable area like industry,
security, environmental and etc., and many of them don't use TCP/IP
stack yet. They use various vender-specific transfer protocols. Also,
they contain diverse media like IEEE 802.15.4, RS485, CAN, and RS232
(or UART). In the case IEEE 802.15.4, there is a standard protocol
for the transmission of IPv6 packets [RFC4944], but many of nodes use
vender-specific protocols instead of it.
Hence, a CoAP proxy box is required to interconnect this vender-
specific non-TCP/IP network and LLN defined by IETF (e.g., 6LoWPAN).
CoAP is not required for vender-specific constrained nodes, because
the proxy can translate between vender-specific protocols and TCP/IP
as CoAP cross-proxy. But as a CoAP-to-CoAP proxy, the operation of
the proxy can be simplified, and the services are able to be
abstracted by CoAP overall networks, applying CoAP for both vender-
specific and LLN nodes are recommended.
But there are two restrictions on applying CoAP to vender-specific
nodes. The first is the lack of address. Peer-to-peer media like UART
and RS232 has no address to identify each node. RS485 has an integer
value as an identifier, but there is no standardized way to present
or carry this value over networks. IEEE 802.15.4 has Network Address
in their standard, but this address is allocated by Coordinator
dynamically. 64-bit extended address is too long and is sometimes not
used.
The second is that CoAP has not PDU size information in its header.
CoAP calculates the PDU size with the information from underlying
protocol like the payload size in IP header.
As a result, to apply CoAP to vender-specific networks and nodes, new
underlying protocol for CoAP must be defined to complement these two
restrictions. In this document, new Shim Header is specifies as a
underlying protocol for CoAP, and an example is added to explain this
shim header.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when they appear in ALL CAPS. These words may also appear
in this document in lower case as plain English words, absent their
normative meanings.
Shim Header
In front of a CoAP header, a slim header is inserted instead of
IP header and this contains addresses of CoAP sender and receiver
and the length of CoAP header and its payload.
Local ID
A local ID is an address of CoAP sender or receiver, and it is
uniqueness in a vender-specific non-TCP/IP constrained network.
This ID has a 16-bit length hexadecimal value, that is IEEE
802.15.4 Network Address compatible, and it can be extensible
later.
CoAP Proxy
A CoAP proxy in this document is a CoAP-to-CoAP proxy from [CoAP].
In additional, this CoAP proxy can read and insert a shim header
from/to the front of CoAP header.
Additional terminology for CoAP can be found in [CoAP].
3. Shim Header
3.1. Header Format
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+----+----+---------+
|Pre |Ver | Length |
+----+----+---------+
| CoAP Src Local ID |
+-------------------+
| CoAP Dst Local ID |
+-------------------+
Figure 1 Shim Header Format
Fig. 1 shows a basic format of shim header. Next is the explanation
of each field in the header.
* Pre: Preamble is a 4-bit field, and has a meaning of the start
of shim header. '0xa' is used currently.
* Ver: Version is also a 4-bit field, currently the version
number is '1'.
* Length: is the length of CoAP header and its payload followed
by the shim header. This has a value between 1 and 255.
* CoAP Source Local ID, CoAP Destination Local ID: are the local
IDs of the sender and receiver of its CoAP message. Each
field has 16-bit field.
Fig. 2 shows the extended format of shim header. This format is used
when the length of CoAP header and its payload is larger than 255. If
the value of Length field is '0', this means its followed field is
the 16-bit extended length field, not CoAP source ID. This field can
have a range of value from 0 to 65535.
+----+----+---------+
|Pre |Ver | 0x00 |
+----+----+---------+
| Ext. Length |
+-------------------+
| CoAP Dst Local ID |
+-------------------+
| CoAP Dst Local ID |
+-------------------+
Figure 2 Shim Header Format with Extended Length
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3.2. Identifying between CoAP Header and Shim Header
According to the type of constrained nodes, Shim header can be
hardcoded, or not be involved in the CoAP node implementation. But at
the following cases, CoAP and shim header must be identified when a
packet receiver of a node meets a start point of some header.
* The CoAP receiver has multiple heterogeneous media, and are not
able to identify the received interface among them. And some
media use shim header on their interfaces and the others are
not.
* The CoAP receiver receives CoAP messages from two or more other
CoAP nodes.
As a result, the start point of shim header must be differentiated
from it of CoAP header. According to the CoAP draft, CoAP header
starts with version and message type, which has a range of values
from 0x04 to 0x07. But in the case of shim header, it starts with
preamble field, and its value is '0xa' to identify shim header
against COAP header.
3.3. Example
As shown in [CoAP], first example in Appendix A illustrates a basic
Confirmable CoAP request and response in piggy-backed manner. In this
section, we add shim header to this example. In this case, the client
and the server are connected via non-TCP/IP. The client can be a data
collector node or a proxy node. The server may be a temperature
sensor. In this example, we assume that the client has an ID of
0x0000, and the server has an ID of 0x0001.
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Client Server
(0x0000) (0x0001)
| |
| | Shim: Length=16, Src=0x0000, Dst=0x0001
+----->| Header: GET (T=CON, Code=0.01, MID=0x7d34)
| GET | Uri-Path: "temperature"
| |
| | Shim: Length=11, Src=0x0001, Dst=0x0000
|<-----+ Header: 2.05 Content (T=ACK, Code=2.05,
| | MID=0x7d34)
| 2.05 | Payload: "22.3 C"
| |
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xa | 1 | Length=16 | Source ID=0x0000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination ID=0x0001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 0 | 0 | GET=1 | MID=0x7d34 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11 | 11 | "temperature" (11 B) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xa | 1 | Length=11 | Source ID=0x0001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination ID=0x0000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 2 | 0 | 2.05=69 | MID=0x7d34 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1 1 1 1 1| "22.3 C" (6 B) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4. Security Considerations
(TBD)
5. IANA Considerations
(TBD)
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6. Acknowledgments
(TBD)
7. References
7.1. Normative References
[CoAP] Z. Shelby, K. Hartke, C. Bormann, "Constrained Application
Protocol (CoAP)", draft-ietf-core-coap-18, June 28, 2013.
[RFC6550] T. Winter, P. Thubert, A. Brandt, J. Hui, R. Kelsey, P.
Levis, K. Pister, R. Struik, JP. Vasseur, and R. Alexander,
"RPL: IPv6 Routing Protocol for Low-Power and Lossy
Networks", RFC 6550, March 2012.
[RFC4944] G. Montenegro, N. Kushalnagar, J. Hui, and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4 Networks",
RFC 4944, September 2007.
7.2. Informative References
[RFC2119] S. Brander, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[IEEE 802.15.4] IEEE Computer Society, "IEEE STd. 802.15.4-2003",
October 2003.
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Author's Addresses
Ilkyun Park
ETRI
1000-6 Oryong-dong, Buk-gu, Gwangju, 500-480,
Korea
Phone: +82-62-970-6651
Email: ikpark@etri.re.kr
Seok-Kap Ko
ETRI
1000-6 Oryong-dong, Buk-gu, Gwangju, 500-480,
Korea
Phone: +82-62-970-6677
Email: softgear@etri.re.kr
Seung-Hun Oh
ETRI
1000-6 Oryong-dong, Buk-gu, Gwangju, 500-480,
Korea
Phone: +82-62-970-6655
Email: osh93@etri.re.kr
Byung-Tak Lee
ETRI
1000-6 Oryong-dong, Buk-gu, Gwangju, 500-480,
Korea
Phone: +82-62-970-6624
Email: bytelee@etri.re.kr
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