ICN Research Group C. Gundogan
Internet-Draft T. Schmidt
Intended status: Experimental HAW Hamburg
Expires: September 6, 2018 M. Waehlisch
link-lab & FU Berlin
C. Scherb
C. Marxer
C. Tschudin
University of Basel
March 5, 2018

ICN Adaptation to LowPAN Networks (ICN LoWPAN)
draft-gundogan-icnrg-ccnlowpan-01

Abstract

In this document, a convergence layer for CCNx and NDN over IEEE 802.15.4 LowPan networks is defined. A new frame format is specified to adapt CCNx and NDN packets to the small MTU size of IEEE 802.15.4. For that, syntactic and semantic changes to the TLV-based header formats are described. To support compatibility with other LoWPAN technologies that may coexist on a wireless medium, the dispatching scheme provided by 6LoWPAN is extended to include new dispatch types for CCNx and NDN. Additionally, the link fragmentation component of the 6LoWPAN dispatching framework is applied to ICN chunks. Basic improvements in efficiency are advised by stateless compression schemes.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on September 6, 2018.

Copyright Notice

Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.


Table of Contents

1. Introduction

The Internet of Things (IoT) has been identified as a promising deployment area for Information Centric Networks (ICN), as infrastructureless access to content, resilient forwarding, and in-network data replication have shown noteable advantages over the traditional host-to-host approach on the Internet [NDN-EXP]. Recent studies [NDN-MAC] have shown that an appropriate mapping to link layer technologies has a large impact on the practical performance of an ICN. This will be even more relevant in the context of IoT communication where nodes often exchange messages via low-power wireless links under lossy conditions. In this memo, we address the base adaptation of data chunks to such link layers for the ICN flavors NDN [NDN] and CCNx.

The IEEE 802.15.4 [ieee802.15.4] link layer is used in low-power and lossy networks (see LLN in [RFC7228]), in which devices are typically battery-operated and constrained in resources. Characteristics of LLNs include an unreliable environment, low bandwidth transmissions, and increased latencies. IEEE 802.15.4 admits a maximum physical layer packet size of 127 octets. The maximum frame header size is 25 octets, which leaves 102 octets for the payload. IEEE 802.15.4 security features further reduce this payload length by up to 21 octets, yielding a net of 81 octets for CCNx or NDN packet headers, signatures and content.

6LoWPAN [RFC4944][RFC6282] is a convergence layer that provides frame formats, header compression and link fragmentation for IPv6 packets in IEEE 802.15.4 networks. The 6LoWPAN adaptation introduces a dispatching framework that prepends further information to 6LoWPAN packets, including a protocol identifier for IEEE 802.15.4 payload and meta information about link fragmentation.

Prevalent Type-Length-Value (TLV) based packet formats such as in CCNx and NDN are designed to be generic and extensible. This leads to header verbosity which is inappropriate in constrained environments of IEEE 802.15.4 links. This document presents ICN LoWPAN, a convergence layer for IEEE 802.15.4 motivated by 6LoWPAN that compresses packet headers of CCNx as well as NDN and allows for an increased payload size per packet. Additionally by reusing the dispatching framwork defined by 6LoWPAN, compatibility between coexisting wireless networks of competing technologies is enabled. This also allows to reuse the link fragmentation scheme specified by 6LoWPAN for ICN LoWPAN.

ICN LoWPAN utilizes a more space efficient representation of CCNx and NDN packet formats. This syntactic change is described for CCNx and NDN separately, as the header formats and TLV encodings differ largely. For further reductions, default header values suitable for constrained IoT networks are selected in order to elide corresponding TLVs.

In a typical IoT scenario (see Figure 1), embedded devices are interconnected via quasi-stationary infrastructure whith a border router (BR) interconnecting the constrained LoWPAN networks via some Gateway with the public Internet. In ICN based IoT networks, Interest and Data messages transparently travel through the BR up and down between a Gateway and the embedded devices within the constrained LoWPANs.

               |Gateway Services|
               -------------------------
                     |
                 ,--------,
                 |        |
                 |   BR   |
                 |        |
                 '--------'
                              LoWPAN
               O            O
                      O
             O                O   embedded
               O      O     O     devices
                O         O
                     

Figure 1: IoT Stub Network

2. Terminology

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]. The use of the term, "silently ignore" is not defined in RFC 2119. However, the term is used in this document and can be similarly construed.

This document uses the terminology of [RFC7476], [RFC7927], and [RFC7945] for ICN entities.

The following terms are used in the document and defined as follows:

ICN LoWPAN:
Information-Centric Networking over Low-power Wireless Personal Area Network
LLN
Low-Power and Lossy Network
CCNx:
Content-Centric Networking Architecture
NDN:
Named Data Networking

3. Overview of ICN LoWPAN

3.1. Link-Layer Convergence

ICN LoWPAN provides a convergence layer that maps ICN packets onto constrained link-layer technologies. This includes features such as link-layer fragmentation, protocol separation on the link-layer level, and link-layer address mappings. The stack traversal is visualized in Figure 2.

      Device 1                                         Device 2
,------------------,           Router            ,------------------,
|  Application   . |     __________________      | ,-> Application  |
|----------------|-|    |    NDN / CCNx    |     |-|----------------|
|  NDN / CCNx    | |    | ,--------------, |     | |    NDN / CCNx  |
|----------------|-|    |-|--------------|-|     |-|----------------|
|  ICN LoWPAN    | |    | |  ICN LoWPAN  | |     | |    ICN LoWPAN  |
|----------------|-|    |-|--------------|-|     |-|----------------|
|  Link-Layer    | |    | |  Link-Layer  | |     | |    Link-Layer  |
'----------------|-'    '-|--------------|-'     '-|----------------'
                 '--------'              '---------'
                    

Figure 2: ICN LoWPAN convergence layer for IEEE 802.15.4

Section 4 of this document defines the convergence layer for IEEE 802.15.4.

3.2. Stateless Header Compression

ICN LoWPAN also defines a stateless header compression scheme with the main purpose of reducing header overhead of ICN packets. This is of particular importance for link-layers with small MTUs. The stateless compression does not require pre-configuration of global state.

The CCNx and NDN header formats are composed of Type-Length-Value (TLV) fields to encode header data. The advantage of TLVs is its native support of variable-sized data. The main disadvantage of TLVs is the verbosity that results from storing the type and length of the encoded data.

The stateless header compression scheme makes use of compact bit fields to indicate the presence of mandatory and optional TLVs in the uncompressed packet. The order of set bits in the bit fields corresponds to the order of each TLV in the packet. Further compression is achieved by specifying default values and reducing the codomain of certain header fields.

Figure 3 demonstrates the stateless header compression idea. In this example, the first type of the first TLV is removed and the corresponding bit in the bit field is set. The second TLV represents a fixed-length TLV (e.g. the Nonce TLV in NDN), so that the type and the length fields are removed. The third TLV represents a boolean TLV (e.g. the MustBeFresh selector in NDN) and is missing the type, length and the value field.

  +---+---+---+---+---+---+---+---+
  | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 |  Bit field
  +---+---+---+---+---+---+---+---+
    |       |                   |
 ,--'       '-----------,       '- boolean
 |                      |
+-------+--------------+-------------+
|  LEN  |     VALUE    |    VALUE    |
+-------+--------------+-------------+
                    

Figure 3: Compression using a compact bit field to encode context information.

4. IEEE 802.15.4 Adaptation

4.1. LoWPAN Encapsulation

The IEEE 802.15.4 frame header does not provide a protocol identifier for its payload. This causes problems of misinterpreting frames when several networks coexist on the same link layer. To mitigate errors, 6LoWPAN defines dispatches as encapsulation headers for IEEE 802.15.4 frames (see Section 5 of [RFC4944]). Multiple LoWPAN encapsulation headers can prepend the actual payload and each encapsulation header is identified by a dispatch type.

[RFC8025] further specifies dispatch pages to switch between different contexts. When a LoWPAN parser encounters a Page switch LoWPAN encapsulation header, then all following encapsulation headers are interpreted by using a dispatch table as specified by the Page switch header. Page 0 and page 1 are reserved for 6LoWPAN. This document defines dispatch types to identify the payload of CCNx or NDN messages under different compression schemes in Table 1 using page 2 (1111 0010 (0xF2)) to assure isolated code spaces.

ICN Dispatch Types for (un-)compressed CCNx and NDN
Bit Pattern Page Header Type
0000 0000 2 LOWPAN_CCNX_INT
001x xxxx 2 LOWPAN_CCNX_INT_HC
0100 0000 2 LOWPAN_CCNX_DATA
011x xxxx 2 LOWPAN_CCNX_DATA_HC
... 2 ...
1000 0000 2 LOWPAN_NDN_INT
101x xxxx 2 LOWPAN_NDN_INT_HC
1100 0000 2 LOWPAN_NDN_DATA
111x xxxx 2 LOWPAN_NDN_DATA_HC
... 2 ...

For backwards compatibility, [RFC8025] does not require a Page switch dispatch type for page 0. For page 2, a Page switch header is needed to indicate a context switch before parsing the dispatch type. As an example, to select page 2 and mark the payload as an uncompressed NDN Interest, the bit pattern reads: 1111 0010 1000 0000.

The encapsulation format for ICN LoWPAN identifying an NDN Interest message is exemplarily displayed in Figure 4.

+---------------+-------------+--------+----------------+-------+
| IEEE 802.15.4 | Dispatches  | Page 2 | LOWPAN_NDN_INT | Payl. /
+---------------+-------------+--------+----------------+-------+
                    

Figure 4: LoWPAN Encapsulation of NDN Interest with ICN LoWPAN

IEEE 802.15.4:
The IEEE 802.15.4 header.
Dispatches:
Optional additional dispatch types.
Page Switch 2:
This page identifier is set to 1111 0010.
LOWPAN_NDN_INT:
This code point is set to 1000 0000.
Payload:
The actual NDN Interest Message.

4.2. ICN LoWPAN Fragmentation

Section 5.3 of [RFC4944] defines a protocol independent fragmentation dispatch type, a fragmentation header for the first fragment and a separate fragmentation header for subsequent fragments. ICN LoWPAN adopts the fragmentation handling of [RFC4944].

The Fragmentation LoWPAN header can encapsulate other dispatch headers. The order of dispatch types is adopted from [RFC4944]. To use the ICN LoWPAN dispatch types (defined in Table 1), a page switch to page 2 MUST occure. Figure 5 shows the fragmentation scheme. The reassembled ICN LoWPAN frame does not contain any fragmentation headers and is depicted in Figure 6.

+---------------+-----------+--------+----------------+-------------+
| IEEE 802.15.4 | Frag. 1st | Page 2 | LOWPAN_NDN_INT | Payload ... /
+---------------+-----------+--------+----------------+-------------+

+---------------+-----------+-------------+
| IEEE 802.15.4 | Frag. 2nd | ... Payload /
+---------------+-----------+-------------+

                .
                .
                .

+---------------+-----------+-------------+
| IEEE 802.15.4 | Frag. Nth | ... Payload /
+---------------+-----------+-------------+
                  

Figure 5: Fragmentation scheme

+---------------+---------+-----------------+---------+
| IEEE 802.15.4 | Page 2  | LOWPAN_NDN_INT  | Payload /
+---------------+---------+-----------------+---------+
                  

Figure 6: Reassembled ICN LoWPAN frame

5. ICN LoWPAN Header Compression for NDN

5.1. TLV Encoding

The NDN packet format consists of TLV fields using the TLV encoding that is described in [NDN-TLV]. Type and length fields are of variable size, where numbers greater than 252 are encoded using multiple octets. Figure 7 shows the NDN TLV encoding scheme.

If the type or length number is less than 253, then that number is encoded into the actual type or length field (Figure 7 a). If the number is greater or equals 253 and fits into 2 octets, then the type or lengh field is set to 253 and the number is encoded in the next following 2 octets in network byte order, i.e., from the most significant byte (MSB) to the least significant byte (LSB) (Figure 7 b). If the number is greater than 2 octets and fits into 4 octets, then the type or length field is set to 254 and the number is encoded in the subsequent 4 octets in network byte order (Figure 7 c). For greater numbers, the type or length field is set to 255 and the number is encoded in the subsequent 8 octets in network byte order (Figure 7 d).

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
a) |     < 253     |
   +-+-+-+-+-+-+-+-+

    0                   1                   2
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
b) |      253      |      MSB             LSB      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      254      |      MSB                                      /
c) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      LSB      |
   +-+-+-+-+-+-+-+-+

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      255      |      MSB                                      /
   +-+-+-+-+-+-+-+-+                                               +
d) |                                                               /
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      LSB      |
   +-+-+-+-+-+-+-+-+
                  

Figure 7: NDN TLV encoding scheme

In this document, compressed NDN TLVs make use of a different TLV scheme that puts more emphasis on size reduction. Instead of using the first octet as a marker for the number of following octets, the compressed NDN TLV scheme uses a method to chain a variable number of octets together. If an octet equals 255 (0xFF), then the following octet will also be interpreted. The actual value of a chain equals the sum of all links.

If the type or length number is less than 255, then that number is encoded into the actual type or length field (Figure 8 a). If the type or length number (X) fits into 2 octets, then the first octet is set to 255 and the subsequent octet equals X mod 255 (Figure 8 b). Following this scheme, a variable-sized number (X) is encoded using multiple octets of 255 with a trailing octet containing X mod 255 (Figure 8 c).

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
a) |   < 255 (X)   | = X
   +-+-+-+-+-+-+-+-+

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
b) |      255      |   < 255 (X)   | = 255 + X
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0
    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+-+-+-.....-+-+-+-+-+-+-+-+-+-+-+
c) |      255      |      255      |   < 255 (X)   | = (N * 255) + X
   +-+-+-+-+-+-+-+-+-+-+-.....-+-+-+-+-+-+-+-+-+-+-+
                        (N - 1)
                  

Figure 8: Compressed NDN TLV encoding scheme

5.2. Interest

5.2.1. Uncompressed Interest

An uncompressed Interest message uses the LoWPAN dispatch LOWPAN_NDN_INT. The Interest message is handed to the NDN network stack without modifications.

5.2.2. Compression Base Header Format

The compression base header makes use of the dispatch type LOWPAN_NDN_INT_HC (Table 1).

By default, the Interest message is compressed with the following rule set: LOWPAN_NDN_INT_HC dispatch (Figure 9).

  1. The outermost Interest TLV is removed.
  2. The Type field of the Name TLV is removed.
  3. The Type and Length fields of the NonceTLV are removed.

Further compression rules are given in the

  0
  0   1   2   3   4   5   6   7
+---+---+---+---+---+---+---+---+
| 1 | 0 | 1 |NCO|SNC|SEL|GUI|EXT|
+---+---+---+---+---+---+---+---+
                       

Figure 9: Compression base header format for Interest

NCO: NameComponent TLVs
0:
The Name TLV is uncompressed and all NameComponent TLVs contain a type field.
1:
The first NameComponent TLV keeps the type field and all type fields of subsequent NameComponent TLVs are elided. When the Name TLV is decompressed, then the type field of the first NameComponent TLV is replicated to all other NameComponent TLVs.

SNC: Short NameComponent TLVs
0:
The length fields of NameComponent TLVs are encoded as described in Figure 8.
1:
All NameComponent TLVs are limited in size to 15 octets each and no 0 length NameComponent TLVs are present. The compressed length encoding for short NameComponent TLVs as described in Section 5.2.3 is used. Additionally, using this encoding, the outermost length field of the Name TLV is obsolete and removed.

SEL: Selector TLVs
0:
No Selector TLVs are present in the Interest message.
1:
Selector TLVs are present in the Interest message. An additional octet follows immediately this dispatch octet and handles Selector TLV compressions. See Section 5.2.4.

GUI: Guider TLVs
0:
No Guider TLVs are present in the Interest message.
1:
Guider TLVs are present in the Interest message. An additional octet follows immediately this dispatch octet and handles Guider TLV compressions. See Section 5.2.5.

EXT: Extension
0:
No extension octet follows.
1:
An extension octet follows immediately. Extension octets are used to extend the compression scheme, but are out of scope of this document.

5.2.3. Short NameComponent TLV Encoding

The short NameComponent TLV encoding encodes the length fields of two consecutive NameComponent TLVs into one octet, using 4 bits each. This process limits the length of a NameComponent TLV to 15 octets and is repeated until a length of 0 is encountered, which marks the end of the Name TLV. This encoding forbids 0 length NameComponent TLVs.


                Name: /HAW/Room/481/Humid/12

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 1|0 1 0 0|       H       |       A       |       W       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       R       |       o       |       o       |       m       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 1|0 1 0 1|       4       |       8       |       1       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       H       |       u       |       m       |       i       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       d       |0 0 1 0|0 0 0 0|       1       |       2       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       

Figure 10: Length field encoding for short NameComponent TLVs

5.2.4. Selectors Compression

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
| minSx | maxSx |  ppk  | excld |   ChildSel    | fresh | resvd |
+-------+-------+-------+-------+-------+-------+-------+-------+
                        

Figure 11: LOWPAN_NDN_INT_HC_SEL

minSX:
1 bit flag. If set, then MinSuffixComponents are present in the Interest message and the type field is removed.
maxSX:
1 bit flag. If set, then MaxSuffixComponents are present in the Interest message and the type field is removed.
ppk:
1 bit flag. If set, then a PublisherPublicKeyLocator is present in the Interest message and the type field is removed.
excld:
1 bit flag. If set, then an exclude selector is present in the Interest message and the type field is removed.
ChildSel: ChildSelector TLV
00:
The ChildSelector is absent and a value of 0 is assumed.
01:
The ChildSelector with value 0 was removed during the compression.
10:
The ChildSelector with value 1 was removed during the compression.

fresh:
1 bit flag. If set, then a MustBeFresh selector is present in the Interest message and the type and length fields are removed.
resvd:
1 bit reserved and MUST be set to 0.

5.2.5. Guiders Compression

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|   InterestLifetime    |fwdhint|           Reserved            |
+-------+-------+-------+-------+-------+-------+-------+-------+
                        

Figure 12: LOWPAN_NDN_INT_HC_GUI

InterestLifetime TLV
000:
The InterestLifetime TLV is absent in the original packet and a default value of 4 seconds is assumed.
001:
The InterestLifetime TLV is present and the type field is removed. The length field is removed and assumed to be 1.
010:
The InterestLifetime TLV is present and the type field is removed. The length field is removed and assumed to be 2.
011:
The InterestLifetime TLV is present and the type field is removed. The length field is removed and assumed to be 4.
100:
The InterestLifetime TLV is present and the type field is removed. The length field is removed and assumed to be 8.
101:
The InterestLifetime TLV with value 4 seconds is present in the Interest message. It is removed on compression and inserted on decompression.
110:
Reserved.
111:
Reserved.

fwdhint:
1 bit flag. If set, then a ForwardingHint TLV is present in the Interest message and the type field is removed.

5.3. Data

5.3.1. Uncompressed Data

An uncompressed Data message uses the LoWPAN dispatch LOWPAN_NDN_DATA. The Data message is handed to the NDN network stack without modifications.

5.3.2. Compression Base Header Format

The compression base header makes use of the dispatch type LOWPAN_NDN_DATA_HC (Table 1).

By default, the Data message is compressed with the following rule set: LOWPAN_NDN_DATA_HC dispatch (Figure 13).

  1. The outermost Data TLV is removed.
  2. The Type field of the Name TLV is removed.
  3. The Type field of the MetaInfo TLV is removed.
  4. The Type field of the Content TLV is removed.
  5. The Type field of the SignatureInfo TLV is removed.
  6. The Type field of the SignatureValue TLV is removed.

Further compression rules are given in the

  0                                       1
  0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 1 | 0 | 1 |NCO|SNC|MET|EXT|     Reserved      |      SIG      |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
                       

Figure 13: Compression base header format for Data

NCO: NameComponent TLVs
See Section 5.2.2.
SNC: Short NameComponent TLVs
See Section 5.2.2.
MET: MetaInfo TLVs
0:
No MetaInfo TLVs are present in the Data message.
1:
MetaInfo TLVs are present in the Data message. An additional octet follows immediately that handles MetaInfo TLV compressions and is described in Section 5.3.3.

EXT: Extension
See Section 5.2.2.
SIG: Signature TLVs
0000:
The type fields of the SignatureInfo TLV, SignatureType TLV and SignatureValue TLV are removed.
0001:
The Signature represents a DigestSha256. The SignatureInfo and SignatureValue TLVs are absent. The 32 byte digest immediately follows the content.
0010:
The Signature represents a SignatureSha256WithRsa. The SignatureInfo TLV is absent and the SignatureValue TLV is present without a type field. A KeyLocator TLV without a type field follows immediately the content. The RSA signature immediately follows the SignatureValue TLV.
0011:
The Signature represents a SignatureSha256WithEcdsa. The SignatureInfo TLV is absent and the SignatureValue TLV is present without a type field. A KeyLocator TLV without a type field follows immediately the content. The ECDSA signature immediately follows the SignatureValue TLV.
0100:
The Signature represents a SignatureHmacWithSha256. The SignatureInfo and SignatureValue TLVs are absent. A KeyLocator TLV without a type field follows immediately the content. The 32 byte HMAC signature follows immediately the Keylocator TLV
0101:
Reserved.
0110:
Reserved.
0111:
Reserved.
1000:
Reserved.
1001:
Reserved.
1010:
Reserved.
1011:
Reserved.
1100:
Reserved.
1101:
Reserved.
1110:
Reserved.
1111:
Reserved.

5.3.3. MetaInfo Compression

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|         ctype         |      freshperiod      |   finalblid   |
+-------+-------+-------+-------+-------+-------+-------+-------+
                        

Figure 14: LOWPAN_NDN_DATA_HC_B

ctype: ContentType TLV
000:
The ContentType TLV is absent in the original Data message and the default value 0 is assumed.
001:
The ContentType TLV is present and the type field is removed. The length field is removed and assumed to be 1.
010:
The ContentType TLV is present and the type field is removed. The length field is removed and assumed to be 2.
011:
The ContentType TLV is present and the type field is removed. The length field is removed and assumed to be 4.
100:
The ContentType TLV is present and the type field is removed. The length field is removed and assumed to be 8.
101:
The ContentType TLV with value 0 is present in the Data message. It is removed on compression and inserted on decompression.
110:
Reserved.
111:
Reserved.

freshperiod: FreshnessPeriod TLV
000:
The FreshnessPeriod TLV is absent in the original Data message.
001:
The FreshnessPeriod TLV is present and the type field is removed. The length field is removed and assumed to be 1.
010:
The FreshnessPeriod TLV is present and the type field is removed. The length field is removed and assumed to be 2.
011:
The FreshnessPeriod TLV is present and the type field is removed. The length field is removed and assumed to be 4.
100:
The FreshnessPeriod TLV is present and the type field is removed. The length field is removed and assumed to be 8.
101:
Reserved.
110:
Reserved.
111:
Resedved.

finalblid: FinalBLockId TLV
00:
The FinalBlockId TLV is absent.
01:
The FinalBlockId TLV is absent, but a FinalBlockId TLV equal to the last NameComponent TLV of the Data message name is assumed.
10:
The FinalBlockId TLV is present and the type field is removed.
11:
Reserved.

6. ICN LoWPAN Header Compression for CCNx

6.1. TLV Encoding

The CCNx TLV encoding is described in [I-D.irtf-icnrg-ccnxmessages]. Type and length fields are of fixed length of 2 octets each.

In this document, the TLV encoding is changed to the more space efficient encoding described in Section 5.1. Type and length fields MUST be encoded as in Figure 8.

6.2. Interest

6.2.1. Uncompressed Interest

An uncompressed Interest message uses the LoWPAN dispatch LOWPAN_CCNX_INT. The Interest message is handed to the CCNx network stack without modifications.

6.2.2. Compression Base Header Format

The compression base header makes use of the dispatch type LOWPAN_CCNX_INT_HC (Table 1).

By default, the Interest message is compressed with the following rule set: LOWPAN_CCNX_INT_HC dispatch (Figure 15).

  1. The type and length fields of the CCNx Message TLV are elided and are obtained from the Fixed Header on decompression.

Further compression rules are given in the

  0                                       1
  0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 |NSG|SNS|FLG|HBH|PTY|HPL|FRS|MSG|PAY|VAL|EXT| RESVD |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
           

Figure 15: Compression base header format for Interest

NSG: NameSegment TLVs
See Section 5.2.2.
SNS: Short NameSegment TLVs
See Section 5.2.2.
FLG: Flags field in the Fixed Header
0:
The Flags field equals 0 and is removed from the Interest message.
1:
The Flags field is carried in-line.

HBH: Optional Hop-By-Hop Header TLVs
0:
No Hop-By-Hop Header TLVs are present in the Interest message. Also, the HeaderLength field in the fixed header is elided from the Interest message and assumed to be 8.
1:
Hop-By-Hop Header TLVs are present in the Interest message. An additional octet follows immediately that handles Hop-By-Hop Header TLV compressions and is described in Section 6.2.3.

PTY: PacketType field in the fixed header
0:
The PacketType field is elided and assumed to be PT_INTEREST
1:
The PacketType field is elided and assumed to be PT_RETURN

HPL: HopLimit field in the fixed header
0:
The HopLimit field is carried in-line
1:
The HopLimit field is elided and assumed to be 1

FRS: Reserved field in the fixed header
0:
The Reserved field is carried in-line
1:
The Reserved field is elided and assumed to be 0

MSG: Optional Interest Message TLVs
0:
No Interest Message TLVs are present in the Interest message.
1:
Interest Message TLVs are present in the Interest message. An additional octet follows immediately that handles Interest Message TLV compressions and is described in Section 6.2.4.

PAY: Optional Payload TLV
0:
The Payload TLV is absent.
1:
The Payload TLV is present and the type field is elided.

VAL: Optional ValidationAlgorithm and ValidationPayload TLVs
0:
No validation related TLVs are present in the Interest message.
1:
Validation related TLVs are present in the Interest message. An additional octet follows immediately that handles validation related TLV compressions and is described in Section 6.2.5.

EXT: Extension
0:
No extension octet follows.
1:
An extension octet follows immediately. Extension octets are used to extend the compression scheme, but are out of scope of this document.

6.2.3. Hop-By-Hop Header TLVs Compression

Hop-By-Hop Header TLVs are unordered. For an Interest message, two optional Hop-By-Hop Header TLVs are defined in [I-D.irtf-icnrg-ccnxmessages], but several more can be defined in higher level specifications. For better compression, an ordering of Hop-By-Hop TLVs is enforced as follows: LOWPAN_CCNX_INT_HC_HBH so that type fields are elided from the Interest Lifetime TLV and the Message Hash TLV.

  1. Interest Lifetime TLV
  2. Message Hash TLV

This ordering is encoded into

Note: If the original Interest message includes Hop-By-Hop Header TLVs with a different ordering, then they remain uncompressed.

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|  IntLifetime  |    MsgHash    |           Reserved            |
+-------+-------+-------+-------+-------+-------+-------+-------+
          

Figure 16: LOWPAN_CCNX_INT_HC_HBH

IntLifetime: InterstLifetime Hop-By-Hop Header TLV
00:
The Interest Lifetime TLV is absent.
01:
The Interest Lifetime TLV is present and the type field is removed.
10:
The Interest Lifetime TLV is absent and a default value of 0 seconds is assumed.
11:
The Interest Lifetime TLV is absent and a default value of 10 minutes is assumed.

MsgHash: Message Hash Hop-By-Hop Header TLV
00:
The Message Hash TLV is absent.
01:
The Message Hash TLV is present and uncompressed.
10:
A T_SHA-256 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 32 octets. The outer Message Hash TLV is omitted.
11:
A T_SHA-512 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 64 octets. The outer Message Hash TLV is omitted.

6.2.4. Interest Message TLVs Compression

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|  KeyIDRestr   |   CObHRestr   |           Reserved            |
+-------+-------+-------+-------+-------+-------+-------+-------+
          

Figure 17: LOWPAN_CCNX_INT_HC_MSG

KeyIDRestr: Optional KeyIdRestriction TLV within a CCNx Message TLV
00:
The KeyIdRestriction TLV is absent.
01:
The KeyIdRestriction TLV is present and uncompressed.
10:
A T_SHA-256 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 32 octets. The outer KeyIdRestriction TLV is omitted.
11:
A T_SHA-512 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 64 octets. The outer KeyIdRestriction TLV is omitted.

CObHRestr: Optional ContentObjectHashRestriction TLV within a CCNx Message TLV
00:
The ContentObjectHashRestriction TLV is absent.
01:
The ContentObjectHashRestriction TLV is present and uncompressed.
10:
A T_SHA-256 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 32 octets. The outer ContentObjectHashRestriction TLV is omitted.
11:
A T_SHA-512 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 64 octets. The outer ContentObjectHashRestriction TLV is omitted.

6.2.5. Validation

0       1       2       3       4       5       6       7       8
+-------+-------+-------+-------+-------+-------+-------+-------+
|         ValidationAlg         |     KeyID     |   Reserved    |
+-------+-------+-------+-------+-------+-------+-------+-------+
                        

Figure 18: LOWPAN_CCNX_INT_HC_VAL

ValidationALg: Optional ValidationAlgorithm TLV
0000:
An uncompressed ValidationAlgorithm TLV is included.
0001:
A T_CRC32C ValidationAlgorithm TLV is assumed, but no ValidationAlgorithm TLV is included.
0010:
A T_CRC32C ValidationAlgorithm TLV is assumed, but no ValidationAlgorithm TLV is included. Additionally, a Sigtime TLV is inlined without a type and a length field.
0011:
A T_HMAC-SHA256 ValidationAlgorithm TLV is assumed, but no ValidationAlgorithm TLV is included.
0100:
A T_HMAC-SHA256 ValidationAlgorithm TLV is assumed, but no ValidationAlgorithm TLV is inclued. Additionally, a Sigtime TLV is inlined without a type and a length field.
0101:
Reserved.
0110:
Reserved.
0111:
Reserved.
1000:
Reserved.
1001:
Reserved.
1010:
Reserved.
1011:
Reserved.
1100:
Reserved.
1101:
Reserved.
1110:
Reserved.
1111:
Reserved.

KeyID: Optional KeyID TLV within the ValidationAlgorithm TLV
00:
The KeyId TLV is absent.
01:
The KeyId TLV is present and uncompressed.
10:
A T_SHA-256 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 32 octets. The outer KeyId TLV is omitted.
11:
A T_SHA-512 TLV is present and the type field as well as the length fields are removed. The length field is assumed to represent 64 octets. The outer KeyId TLV is omitted.

The ValidationPayload TLV is present if the ValidationAlgorithm TLV is present. The type field is omitted.

6.3. Content Object

6.3.1. Uncompressed Content Object

An uncompressed Content Object message uses the LoWPAN dispatch LOWPAN_CCNX_DATA. The Content Object message is handed to the CCNx network stack without modifications.

6.3.2. Compression Base Header Format

The compression base header makes use of the dispatch type LOWPAN_CCNX_DATA_HC (Table 1).

By default, the Content Object message is compressed with the following rule set: LOWPAN_CCNX_DATA_HC dispatch (Figure 19).

  1. The PacketType field is elided from the Fixed Header.
  2. The type and length fields of the CCNx Message TLV are elided and are obtained from the Fixed Header on decompression.

Further compression rules are given in the

  0                                       1
  0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 |NSG|SNS|FLG|HBH|FRS|MSG|PAY|VAL|EXT|     RESVD     |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
           

Figure 19: Compression base header format for Content Object

NSG: NameSegment TLVs
See Section 5.2.2.
SNS: Short NameSegment TLVs
See Section 5.2.2.
FLG: Flags field in the fixed header
See Section 6.2.2.
HBH: Optional Hop-By-Hop Header TLVs
0:
No Hop-By-Hop Header TLVs are present in the Content Object message. Also, the HeaderLength field in the fixed header is elided from the Content Object message and assumed to be 8.
1:
Hop-By-Hop Header TLVs are present in the Content Object message. An additional octet follows immediately that handles Hop-By-Hop Header TLV compressions and is described in Section 6.3.3.

FRS: Reserved field in the Fixed Header
See Section 6.2.2.
MSG: Optional Content Object Message TLVs
0:
No Content Object Message TLVs are present in the Content Object message.
1:
Content Object Message TLVs are present in the Content Object message. An additional octet follows immediately that handles Content Object Message TLV compressions and is described in Section 6.3.4.

PAY: Optional Payload TLV
See Section 6.2.2.
VAL: Optional ValidationAlgorithm and ValidationPayload TLVs
See Section 6.2.2.
EXT: Extension
See Section 6.2.2.

6.3.3. Hop-By-Hop Header TLVs Compression

Hop-By-Hop Header TLVs are unordered. For a Content Object message, two optional Hop-By-Hop Header TLVs are defined in [I-D.irtf-icnrg-ccnxmessages], but several more can be defined in higher level specifications. For better compression, an ordering of Hop-By-Hop TLVs is enforced as follows: LOWPAN_CCNX_DATA_HC_HBH so that type fields are elided from the Recommended Cache Time TLV and the Message Hash TLV.

  1. Recommended Cache Time TLV
  2. Message Hash TLV

This ordering is encoded into

Note: If the original Content Object message includes Hop-By-Hop Header TLVs with a different ordering, then they remain uncompressed.

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|  RCT  |    MsgHash    |               Reserved                |
+-------+-------+-------+-------+-------+-------+-------+-------+
          

Figure 20: LOWPAN_CCNX_DATA_HC_HBH

RCT: Recommended Cache Time Hop-By-Hop Header TLV
0:
The Recommended Cache Time TLV is absent.
1:
The Recommended Cache Time TLV is present and the type as well as the length fields are elided.

MsgHash: Message Hash Hop-By-Hop Header TLV
See Section 6.2.3.

6.3.4. Content Object Message TLVs Compression

    0       1       2       3       4       5       6       7
+-------+-------+-------+-------+-------+-------+-------+-------+
|  PayloadType  |ExpTime|               Reserved                |
+-------+-------+-------+-------+-------+-------+-------+-------+
          

Figure 21: LOWPAN_CCNX_DATA_HC_MSG

PayloadType: Optional PayloadType TLV within a CCNx Message TLV
00:
The PayloadType TLV is absent and T_PAYLOADTYPE_DATA is assumed.
01:
The PayloadType TLV is absent and T_PAYLOADTYPE_KEY is assumed.
10:
The PayloadType TLV is absent and T_PAYLOADTYPE_LINK is assumed.
11:
The PayloadType TLV is present and uncompressed.

ExpTime: Optional ExpiryTime TLV within a CCNx Message TLV
0:
The ExpiryTime TLV is absent.
1:
The ExpiryTime TLV is present and the type as well as the length fields are elided.

7. Security Considerations

TODO

8. IANA Considerations

8.1. Page Switch Dispatch Type

This document makes use of Page 2 from the existing paging dispatches in [RFC8025].

9. References

9.1. Normative References

[ieee802.15.4] IEEE Computer Society, "IEEE Std. 802.15.4-2015", April 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J. and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011.

9.2. Informative References

[CCN-LITE] "CCN-lite: A lightweight CCNx and NDN implementation"
[I-D.irtf-icnrg-ccnxmessages] Mosko, M., Solis, I. and C. Wood, "CCNx Messages in TLV Format", Internet-Draft draft-irtf-icnrg-ccnxmessages-06, October 2017.
[I-D.irtf-icnrg-ccnxsemantics] Mosko, M., Solis, I. and C. Wood, "CCNx Semantics", Internet-Draft draft-irtf-icnrg-ccnxsemantics-06, October 2017.
[NDN] Jacobson, V., Smetters, D., Thornton, J. and M. Plass, "Networking Named Content", 5th Int. Conf. on emerging Networking Experiments and Technologies (ACM CoNEXT), 2009.
[NDN-EXP] Baccelli, E., Mehlis, C., Hahm, O., Schmidt, TC. and M. Waehlisch, "Information Centric Networking in the IoT: Experiments with NDN in the Wild", Proc. of 1st ACM Conf. on Information-Centric Networking (ICN-2014) ACM DL, pp. 77-86, September 2014.
[NDN-MAC] Kietzmann, P., Gundogan, C., Schmidt, TC., Hahm, O. and M. Waehlisch, "The Need for a Name to MAC Address Mapping in NDN: Towards Quantifying the Resource Gain", Proc. of 4th ACM Conf. on Information-Centric Networking (ICN-2017) ACM DL, pp. 36-42, September 2017.
[NDN-TLV] "NDN Packet Format Specification"
[RFC7228] Bormann, C., Ersue, M. and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014.
[RFC7476] Pentikousis, K., Ohlman, B., Corujo, D., Boggia, G., Tyson, G., Davies, E., Molinaro, A. and S. Eum, "Information-Centric Networking: Baseline Scenarios", RFC 7476, DOI 10.17487/RFC7476, March 2015.
[RFC7927] Kutscher, D., Eum, S., Pentikousis, K., Psaras, I., Corujo, D., Saucez, D., Schmidt, T. and M. Waehlisch, "Information-Centric Networking (ICN) Research Challenges", RFC 7927, DOI 10.17487/RFC7927, July 2016.
[RFC7945] Pentikousis, K., Ohlman, B., Davies, E., Spirou, S. and G. Boggia, "Information-Centric Networking: Evaluation and Security Considerations", RFC 7945, DOI 10.17487/RFC7945, September 2016.
[RFC8025] Thubert, P. and R. Cragie, "IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Paging Dispatch", RFC 8025, DOI 10.17487/RFC8025, November 2016.

Appendix A. Estimated Size Reduction

In the following a theoretical evaluation is given to estimate the gains of ICN LoWPAN compared to uncompressed CCNx and NDN messages.

We assume that n is the number of name components, comps_n denotes the sum of n name component lengths. We also assume that the length of each name component is lower than 16 bytes. The length of the content is given by clen. The lengths of TLV components is specific to the CCNx or NDN encoding and outlined below.

A.1. NDN

The NDN TLV encoding has variable-sized TLV fields. For simplicity, the 1 octet form of each TLV component is assumed. A typical TLV component therefore is of size 2 (type field + length field) + the actual value.

A.1.1. Interest

Figure 22 depicts the size requirements for a basic, uncompressed NDN Interest containing a MustBeFresh selector, a ChildSelector with value 1 (rightmost child) and an InterestLifetime guider set to 4 seconds. Numbers below represent the amount of octets.

------------------------------------,
Interest                = 2         |
  ---------------------,            |
  Name                 |  2 +       |
    NameComponents      = 2n +      |
                       |  comps_n   |
  ---------------------'            |
  ---------------------,             = 21 + 2n + comps_n
  Selectors            |            |
    MustBeFresh         = 7         |
    ChildSelector      |            |
  ---------------------'            |
  Nonce                 = 6         |
  InterestLifetime      = 4         |
------------------------------------'
                        

Figure 22: Estimated size of an uncompressed NDN Interest

Figure 23 depicts the size requirements after compression.

------------------------------------,
Dispatch Page Switch    = 1         |
LOWPAN_NDN_INT_HC       = 1         |
LOWPAN_NDN_INT_HC_SEL   = 1         |
LOWPAN_NDN_INT_HC_GUI   = 1         |
-----------------------,             = 9 + n/2 + comps_n
Name                   |  1 +       |
  NameComponents        = n/2 +     |
                       |  comps_n   |
-----------------------'            |
Nonce                   = 4         |
------------------------------------'
                        

Figure 23: Estimated size of a compressed NDN Interest

The NDN Interest message is compressed with the LOWPAN_NDN_INT_HC strategy using the two additional octets LOWPAN_NDN_INT_HC_SEL and LOWPAN_NDN_INT_HC_GUI. The MustBeFresh and Child selectors are omitted. The type and length fields of the Nonce TLV are elided.

The size difference is:
12 + 1.5n octets.

For the name /DE/HH/HAW/BT7, the total size gain is 18 octets, which is 46% of the uncompressed packet.

A.1.2. Data

Figure 24 depicts the size requirements for a basic, uncompressed NDN Data containing a FreshnessPeriod as MetaInfo. A FreshnessPeriod of 10 minutes is assumed and the value is given as 600,000 milliseconds. The value is thereby encoded using 4 octets. An HMACWithSha256 is assumed as signature. The key locator is assumed to contain a Name TLV of length klen.

------------------------------------,
Data                    = 2         |
  ---------------------,            |
  Name                 |  2 +       |
    NameComponents      = 2n +      |
                       |  comps_n   |
  ---------------------'            |
  ---------------------,            |
  MetaInfo             |            |
    FreshnessPeriod     = 8          = 55 + 2n + comps_n +
                       |            |  clen + klen
  ---------------------'            |
  Content               = 2 + clen  |
  ---------------------,            |
  SignatureInfo        |            |
    SignatureType      |            |
      KeyLocator        = 41 + klen |
  SignatureValue       |            |
    DigestSha256       |            |
  ---------------------'            |
------------------------------------'
                        

Figure 24: Estimated size of an uncompressed NDN Data

Figure 25 depicts the size requirements for the compressed version of the above Data packet.

------------------------------------,
Dispatch Page Switch    = 1         |
LOWPAN_NDN_DATA_HC      = 2         |
LOWPAN_NDN_DATA_HC_MET  = 1         |
-----------------------,            |
Name                   |  1 +        = 43 + n/2 + comps_n +
  NameComponents        = n/2 +     |  clen + klen
                       |  comps_n   |
-----------------------'            |
FreshnessPeriod         = 4         |
Content                 = 1 + clen  |
KeyLocator              = 1 + klen  |
DigestSha256            = 32        |
------------------------------------'
                        

Figure 25: Estimated size of a compressed NDN Data

The size difference is:
12 + 1.5n octets.

For the name /DE/HH/HAW/BT7, the total size gain is 18 octets.

A.2. CCNx

The CCNx TLV encoding defines a 2-octet encoding for type and length fields, summing up to 4 octets in total without a value.

A.2.1. Interest

Figure 26 depicts the size requirements for a basic, uncompressed CCNx Interest. No Hop-By-Hop TLVs are included and the protocol version as well as the reserved field are assumed to be 0. A KeyIdRestriction TLV with T_SHA-256 is included to limit the responses to Content Objects containing the specific key.

------------------------------------,
Fixed Header            = 8         |
Message                 = 4         |
  ---------------------,            |
  Name                 |  4 +        = 56 + 4n + comps_n
    NameSegments        = 4n +      |
                       |  comps_n   |
  ---------------------'            |
  KeyIdRestriction      = 40        |
------------------------------------'
                        

Figure 26: Estimated size of an uncompressed CCNx Interest

Figure 27 depicts the size requirements after compression.

------------------------------------,
Dispatch Page Switch    = 1         |
LOWPAN_CCNX_INT_HC      = 2         |
LOWPAN_CCNX_INT_HC_MSG  = 1         |
Fixed Header            = 3         |
-----------------------,             = 40 + n/2 + comps_n
Name                   |  1 +       |
  NameSegments          = n/2 +     |
                       |  comps_n   |
-----------------------'            |
T_SHA-256               = 32        |
------------------------------------'
                        

Figure 27: Estimated size of a compressed CCNx Interest

The size difference is:
16 + 3.5n octets.

For the name /DE/HH/HAW/BT7, the total size gain is 30 octets, which is 36% of the uncompressed packet.

A.2.2. Data

Figure 28 depicts the size requirements for a basic, uncompressed CCNx Data containing an ExpiryTime Message TLV, an HMAC_SHA-256 signature, the signature time and a hash of the shared secret key.

------------------------------------,
Fixed Header            = 8         |
Message                 = 4         |
  ---------------------,            |
  Name                 |  4 +       |
    NameSegments        = 4n +      |
                       |  comps_n   |
  ---------------------'            |
  ExpiryTime            = 12         = 124 + 4n + comps_n + clen
  Payload               = 4 + clen  |
  ---------------------,            |
  ValidationAlgorithm  |            |
    T_HMAC-256          = 56        |
      KeyId            |            |
    SignatureTime      |            |
  ---------------------'            |
  ValidationPayload     = 36        |
------------------------------------'
                        

Figure 28: Estimated size of an uncompressed CCNx Data Object

Figure 29 depicts the size requirements for a basic, compressed CCNx Data.

------------------------------------,
Dispatch Page Switch    = 1         |
LOWPAN_CCNX_DATA_HC     = 2         |
LOWPAN_CCNX_DATA_HC_MSG = 1         |
LOWPAN_CCNX_DATA_HC_VAL = 1         |
Fixed Header            = 2         |
-----------------------,            |
Name                   |  1 +        = 92 + n/2 + comps_n + clen
  NameSegments          = n/2 +     |
                       |  comps_n   |
-----------------------'            |
ExpiryTime              = 8         |
Payload                 = 1 + clen  |
T_HMAC-SHA256           = 32        |
SignatureTime           = 8         |
ValidationPayload       = 34        |
------------------------------------'
                        

Figure 29: Estimated size of a compressed CCNx Data Object

The size difference is:
32 + 3.5n octets.

For the name /DE/HH/HAW/BT7, the total size gain is 46 octets.

Acknowledgments

Authors' Addresses

Cenk Gundogan HAW Hamburg Berliner Tor 7 Hamburg, D-20099 Germany Phone: +4940428758067 EMail: cenk.guendogan@haw-hamburg.de URI: http://inet.haw-hamburg.de/members/cenk-gundogan
Thomas C. Schmidt HAW Hamburg Berliner Tor 7 Hamburg, D-20099 Germany EMail: t.schmidt@haw-hamburg.de URI: http://inet.haw-hamburg.de/members/schmidt
Matthias Waehlisch link-lab & FU Berlin Hoenower Str. 35 Berlin, D-10318 Germany EMail: mw@link-lab.net URI: http://www.inf.fu-berlin.de/~waehl
Christopher Scherb University of Basel Spiegelgasse 1 Basel, CH-4051 Switzerland EMail: christopher.scherb@unibas.ch
Claudio Marxer University of Basel Spiegelgasse 1 Basel, CH-4051 Switzerland EMail: claudio.marxer@unibas.ch
Christian Tschudin University of Basel Spiegelgasse 1 Basel, CH-4051 Switzerland EMail: christian.tschudin@unibas.ch