Internet DRAFT - draft-mosko-icnrg-ccnxchunking
draft-mosko-icnrg-ccnxchunking
ICNRG M. Mosko
Internet-Draft PARC, Inc.
Intended status: Experimental June 1, 2016
Expires: December 3, 2016
CCNx Content Object Chunking
draft-mosko-icnrg-ccnxchunking-02
Abstract
This document specifies a chunking protocol for dividing a user
payload into CCNx Content Objects. This includes specification for
the naming convention to use for the chunked payload and a field
added to a Content Object to represent the last chunk of an object.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on December 3, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Chunking . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Cryptographic material . . . . . . . . . . . . . . . . . . 5
2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. TLV Types . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Name Types . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Chunk Number . . . . . . . . . . . . . . . . . . . . . 6
3.2. Protocol Information . . . . . . . . . . . . . . . . . . . 6
3.2.1. EndChunkNumber . . . . . . . . . . . . . . . . . . . . 7
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
CCNx Content Objects [CCNSemantics] are sized to amortize
cryptographic operations over user data while simultaneously staying
a reasonable size for transport over today's networks. This means a
Content Object is usually within common UDP or jumbo Ethernet size.
If a publisher has a larger amount of data to associate with a single
Name, the data should be chunked with this chunking protocol. This
protocol uses state in the Name and in an optional field within the
Content Object. A chunked object may also have an external metadata
content object that describes the original pre-chunked object.
CCNx uses two types of messages: Interests and Content Objects
[CCNSemantics]. An Interest carries the hierarchically structured
variable-length identifier (HSVLI), or Name, of a Content Object and
serves as a request for that object. If a network element sees
multiple Interests for the same name, it may aggregate those
Interests. A network element along the path of the Interest with a
matching Content Object may return that object, satisfying the
Interest. The Content Object follows the reverse path of the
Interest to the origin(s) of the Interest. A Content Object contains
the Name, the object's Payload, and the cryptographic information
used to bind the Name to the payload.
This specification adds a new segment to the Name TLV for conveying
the chunk number. It updates [CCNMessages]. It also provides
guidelines for the usage of the Key Locator in chunked objects.
Packets are represented as 32-bit wide words using ASCII art.
Because of the TLV encoding and optional fields or sizes, there is no
concise way to represent all possibilities. We use the convention
that ASCII art fields enclosed by vertical bars "|" represent exact
bit widths. Fields with a forward slash "/" are variable bitwidths,
which we typically pad out to word alignment for picture readability.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Chunking
Chunking, as used in this specification, means serializing user data
into one or more chunks, each encapsulated in a CCNx Content Object.
A chunk is a contiguous byte range within the user data. One segment
in the Name of that Content Object represents the chunk number. A
field in the Content Object - only mandatory in the final chunk -
represents the end of the stream. Chunks are denoted by a serial
counter, beginning at 0 and incrementing by 1 for each contiguous
chunk. The chunking ends at the final chunk. No valid user data
exists beyond the final chunk, and reading beyond the final chunk
MUST NOT return any user data.
Chunking MUST use a fixed block size, where only the final chunk MAY
use a smaller block size. This is required to allow a reader to seek
to a specific byte offset once it knows the block size. The
blocksize may be inferred from the size of the first chunk of user
data. The first chunk of user data may not be chunk 0.
Because of the requirement for a fixed block size, the inclusion of
certain cryptographic fields in the same content objects as user data
would throw off the ability to seek. Therefore, it is RECOMMENDED
that all required cryptographic data, such as public keys or key name
links, be included in the leading chunks before the first byte of
user data. User data SHOULD then run continuously and with the same
block size through the remainder of the content objects.
This draft introduces a new Name path segment TLV type, called the
ChunkNumber name segment. The ChunkNumber name segment is the serial
order of the chunks. It MUST begin at 0 and MUST be incremented by
1. The ChunkNumber name segment is appended to the base name of the
user data, and is usually the last name segment.
The new Content Object field is the EndChunkNumber. It MUST be
included in the Content Object which is the last chunk of user data,
but SHOULD be present at the earliest time it is known. The value of
the EndChunkNumber should be the network byte order value of the last
ChunkNumber. For example, if 3000 bytes of user data is split with a
1200 byte block size, there will be 3 chunks: 0, 1, and 2. The
EndChunkNumber is 2.
The EndChunkNumber may be updated in later Chunks to a larger value,
as long as it has not yet reached the end. The EndChunkNumber SHOULD
NOT decrease. If a publisher wishes to close a stream before
reaching the End Chunk, it should publish empty Content Objects to
fill out to the maximum EndChunkNumber ever published. These padding
chunks MUST contain the true EndChunkNumber.
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2.1. Cryptographic material
Chunk 0 SHOULD include the public key or key name link used to verify
the chunked data. It is RECOMMENDED to use the same key for the
whole set of chunked data. If a publisher uses multiple keys, then
the public key or key name link for all keys SHOULD be in the leading
chunks before any user data.
The rationel for putting all cryptographic data up front is because
the protocol requires using a fixed block size for all user data to
enable seeking in the chunked stream.
2.2. Examples
Here are some examples of chunked Names using the Labeled Content
Identifier URI scheme in human readable form (ccnx:).
In this example, the content producer publishes a JPG that takes 4
Chunks. The EndChunkNumber is missing in the first content object
(Chunk 0), but is known and included when Chunk 1 is published. It
is omitted in Chunk 2, then appears in Chunk 3, where it is
mandatory.
ccnx:/Name=parc/Name=picture.jpg/Chunk=0 --
ccnx:/Name=parc/Name=picture.jpg/Chunk=1 EndChunkNumber=3
ccnx:/Name=parc/Name=picture.jpg/Chunk=2 --
ccnx:/Name=parc/Name=picture.jpg/Chunk=3 EndChunkNumber=3
In this example, the publisher is writing an audio stream that ends
before expected so the publisher fills empty Content Objects out to
the maximum ChunkNumber, stating the correct EndChunkNumber. Chunks
4, 5, and 6 do not contain any new user data.
ccnx:/Name=parc/Name=talk.wav/Chunk=0 --
ccnx:/Name=parc/Name=talk.wav/Chunk=1 EndChunkNumber=6
ccnx:/Name=parc/Name=talk.wav/Chunk=2 --
ccnx:/Name=parc/Name=talk.wav/Chunk=3 EndChunkNumber=3
ccnx:/Name=parc/Name=talk.wav/Chunk=4 EndChunkNumber=3
ccnx:/Name=parc/Name=talk.wav/Chunk=5 EndChunkNumber=3
ccnx:/Name=parc/Name=talk.wav/Chunk=6 EndChunkNumber=3
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3. TLV Types
This section specifies the TLV types used by CCNx chunking.
3.1. Name Types
CCNx chunking uses two new Name types: Chunk Number and Chunk
Metadata.
+--------+---------+-----------------+------------------------------+
| Type | Abbrev | Name | Description |
+--------+---------+-----------------+------------------------------+
| %x0010 | T_CHUNK | Chunk Number | The current Chunk Number, is |
| | | (Section 3.1.1) | an unsigned integer in |
| | | | network byte order without |
| | | | leading zeros. The value of |
| | | | zero is represented as the |
| | | | single byte %x00. |
+--------+---------+-----------------+------------------------------+
Table 1: Name Types
3.1.1. Chunk Number
The current chunk number, as an unsigned integer in network byte
order without leading zeros. The value of zero is represented as the
single byte %x00.
In ccnx: URI form, it is denoted as "Chunk".
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
+---------------+---------------+---------------+--------------+
| T_CHUNK | Length |
+---------------+---------------+---------------+--------------+
| variable length integer /
+---------------+---------------+
3.2. Protocol Information
CCNx chunking introduces one new TLV for use in a Content Object.
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+--------+------------+-----------------+---------------------------+
| Type | Abbrev | Name | Description |
+--------+------------+-----------------+---------------------------+
| %x000C | T_ENDCHUNK | EndChunkNumber | The last Chunk number, as |
| | | (Section 3.1.1) | an unsigned integer in |
| | | | network byte order |
| | | | without leading zeros. |
| | | | The value of zero is |
| | | | represented as the single |
| | | | byte %x00. |
+--------+------------+-----------------+---------------------------+
Table 2: Content Object Types
3.2.1. EndChunkNumber
The ending chunk number, as an unsigned integer in network byte order
without leading zeros. The value of zero is represented as the
single byte %x00.
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
+---------------+---------------+---------------+--------------+
| T_ENDCHUNK | Length |
+---------------+---------------+---------------+--------------+
| variable length integer /
+---------------+---------------+
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4. Acknowledgements
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5. IANA Considerations
The draft adds new types to the CCNx Name Segment Types registry and
the CCNx Content Object Types registry.
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6. Security Considerations
This draft does not put any requirements on how chunked data is
signed or validated.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[CCNMessages]
Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format (Internet draft)", 2016, <http://tools.ietf.org/
html/draft-irtf-icnrg-ccnxmessages-02>.
[CCNSemantics]
Mosko, M., Solis, I., and C. Wood, "CCNx Semantics
(Internet draft)", 2016, <http://tools.ietf.org/html/
draft-mosko-icnrg-ccnxsemantics-03>.
[CCNx] PARC, Inc., "CCNx Open Source", 2007,
<http://www.ccnx.org>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, DOI 10.17487/
RFC2616, June 1999,
<http://www.rfc-editor.org/info/rfc2616>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<http://www.rfc-editor.org/info/rfc3552>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
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Author's Address
Marc Mosko
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4405
Email: marc.mosko@parc.com
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