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Versions: (draft-gundogan-icnrg-ccnlowpan) 00 01 02 03 04 05 06 07 08 09

ICN Research Group                                           C. Gundogan
Internet-Draft                                               TC. Schmidt
Intended status: Experimental                                HAW Hamburg
Expires: May 3, 2021                                        M. Waehlisch
                                                    link-lab & FU Berlin
                                                               C. Scherb
                                                               C. Marxer
                                                             C. Tschudin
                                                     University of Basel
                                                        October 30, 2020


             ICN Adaptation to LoWPAN Networks (ICN LoWPAN)
                     draft-irtf-icnrg-icnlowpan-09

Abstract

   This document defines a convergence layer for CCNx and NDN over IEEE
   802.15.4 LoWPAN networks.  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 fragmentation component of the
   6LoWPAN dispatching framework is applied to ICN chunks.  In its
   second part, the document defines stateless and stateful compression
   schemes to improve efficiency on constrained links.  Stateless
   compression reduces TLV expressions to static header fields for
   common use cases.  Stateful compression schemes elide state local to
   the LoWPAN and replace names in data packets by short local
   identifiers.

   This document is a product of the IRTF Information-Centric Networking
   Research Group (ICNRG).

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



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   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 May 3, 2021.

Copyright Notice

   Copyright (c) 2020 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Overview of ICN LoWPAN  . . . . . . . . . . . . . . . . . . .   6
     3.1.  Link-Layer Convergence  . . . . . . . . . . . . . . . . .   6
     3.2.  Stateless Header Compression  . . . . . . . . . . . . . .   6
     3.3.  Stateful Header Compression . . . . . . . . . . . . . . .   8
   4.  IEEE 802.15.4 Adaptation  . . . . . . . . . . . . . . . . . .   8
     4.1.  LoWPAN Encapsulation  . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Dispatch Extensions . . . . . . . . . . . . . . . . .  10
     4.2.  Adaptation Layer Fragmentation  . . . . . . . . . . . . .  10
   5.  Space-efficient Message Encoding for NDN  . . . . . . . . . .  11
     5.1.  TLV Encoding  . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Name TLV Compression  . . . . . . . . . . . . . . . . . .  12
     5.3.  Interest Messages . . . . . . . . . . . . . . . . . . . .  13
       5.3.1.  Uncompressed Interest Messages  . . . . . . . . . . .  13
       5.3.2.  Compressed Interest Messages  . . . . . . . . . . . .  13
       5.3.3.  Dispatch Extension  . . . . . . . . . . . . . . . . .  17
     5.4.  Data Messages . . . . . . . . . . . . . . . . . . . . . .  17
       5.4.1.  Uncompressed Data Messages  . . . . . . . . . . . . .  17
       5.4.2.  Compressed Data Messages  . . . . . . . . . . . . . .  18
       5.4.3.  Dispatch Extension  . . . . . . . . . . . . . . . . .  20
   6.  Space-efficient Message Encoding for CCNx . . . . . . . . . .  21
     6.1.  TLV Encoding  . . . . . . . . . . . . . . . . . . . . . .  21
     6.2.  Name TLV Compression  . . . . . . . . . . . . . . . . . .  21
     6.3.  Interest Messages . . . . . . . . . . . . . . . . . . . .  21
       6.3.1.  Uncompressed Interest Messages  . . . . . . . . . . .  21
       6.3.2.  Compressed Interest Messages  . . . . . . . . . . . .  22
       6.3.3.  Dispatch Extension  . . . . . . . . . . . . . . . . .  28
     6.4.  Content Objects . . . . . . . . . . . . . . . . . . . . .  28



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       6.4.1.  Uncompressed Content Objects  . . . . . . . . . . . .  28
       6.4.2.  Compressed Content Objects  . . . . . . . . . . . . .  29
       6.4.3.  Dispatch Extension  . . . . . . . . . . . . . . . . .  32
   7.  Compressed Time Encoding  . . . . . . . . . . . . . . . . . .  33
   8.  Stateful Header Compression . . . . . . . . . . . . . . . . .  34
     8.1.  LoWPAN-local State  . . . . . . . . . . . . . . . . . . .  34
     8.2.  En-route State  . . . . . . . . . . . . . . . . . . . . .  35
     8.3.  Integrating Stateful Header Compression . . . . . . . . .  37
   9.  ICN LoWPAN Constants and Variables  . . . . . . . . . . . . .  37
   10. Implementation Report and Guidance  . . . . . . . . . . . . .  37
     10.1.  Preferred Configuration  . . . . . . . . . . . . . . . .  37
     10.2.  Further Experimental Deployments . . . . . . . . . . . .  38
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  39
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  40
     12.1.  Reserving Space in the 6LoWPAN Dispatch Type Field
            Registry . . . . . . . . . . . . . . . . . . . . . . . .  40
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  40
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  40
     13.2.  Informative References . . . . . . . . . . . . . . . . .  41
   Appendix A.  Estimated Size Reduction . . . . . . . . . . . . . .  45
     A.1.  NDN . . . . . . . . . . . . . . . . . . . . . . . . . . .  45
       A.1.1.  Interest  . . . . . . . . . . . . . . . . . . . . . .  45
       A.1.2.  Data  . . . . . . . . . . . . . . . . . . . . . . . .  46
     A.2.  CCNx  . . . . . . . . . . . . . . . . . . . . . . . . . .  48
       A.2.1.  Interest  . . . . . . . . . . . . . . . . . . . . . .  48
       A.2.2.  Content Object  . . . . . . . . . . . . . . . . . . .  49
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  50
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

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 demonstrated notable advantages over the
   traditional host-to-host approach on the Internet [NDN-EXP1],
   [NDN-EXP2].  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 [RFC8569], [RFC8609].

   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



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   bandwidth transmissions, and increased latencies.  IEEE 802.15.4
   admits a maximum physical layer packet size of 127 bytes.  The
   maximum frame header size is 25 bytes, which leaves 102 bytes for the
   payload.  IEEE 802.15.4 security features further reduce this payload
   length by up to 21 bytes, yielding a net of 81 bytes for CCNx or NDN
   packet headers, signatures and content.

   6LoWPAN [RFC4944], [RFC6282] is a convergence layer that provides
   frame formats, header compression and adaptation layer 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 payload and
   meta information about 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.
   ICN LoWPAN compresses packet headers of CCNx as well as NDN and
   allows for an increased effective payload size per packet.
   Additionally, reusing the dispatching framework defined by 6LoWPAN
   enables compatibility between coexisting wireless deployments of
   competing network technologies.  This also allows to reuse the
   adaptation layer fragmentation scheme specified by 6LoWPAN for ICN
   LoWPAN.

   ICN LoWPAN defines 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
   notably.  For further reductions, default header values suitable for
   constrained IoT networks are selected in order to elide corresponding
   TLVs.  Experimental evaluations of the ICN LoWPAN header compression
   schemes in [ICNLOWPAN] illustrate a reduced message overhead, a
   shortened message airtime, and an overall decline in power
   consumption for typical Class 2 [RFC7228] devices compared to
   uncompressed ICN messages.

   In a typical IoT scenario (see (Figure 1)), embedded devices are
   interconnected via a quasi-stationary infrastructure using a border
   router (BR) that connects the constrained LoWPAN network by some
   Gateway with the public Internet.  In ICN based IoT networks, non-
   local Interest and Data messages transparently travel through the BR
   up and down between a Gateway and the embedded devices situated in
   the constrained LoWPAN.






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

                        Figure 1: IoT Stub Network

   The document has received fruitful reviews by members of the ICN
   community and the research group (see Acknowledgments) for a period
   of two years.  It is the consensus of ICNRG that this document should
   be published in the IRTF Stream of the RFC series.  This document
   does not constitute an IETF standard.

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 Architecture

   byte:         synonym for octet




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   nibble:       synonym for 4 bits

   time-value:   a time offset measured in seconds

   time-code:    an 8-bit encoded time-value

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 variably structured data.  The main disadvantage of
   TLVs is the verbosity that results from storing the type and length
   of the encoded data.





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   The stateless header compression scheme makes use of compact bit
   fields to indicate the presence of 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 range 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) for which the type,
   length and the value fields are elided.

      Uncompressed:

         Variable-length TLV      Fixed-length TLV      Boolean TLV
      ,-----------------------,-----------------------,-------------,
      +-------+-------+-------+-------+-------+-------+------+------+
      |  TYP  |  LEN  |  VAL  |  TYP  |  LEN  |  VAL  |  TYP | LEN  |
      +-------+-------+-------+-------+-------+-------+------+------+

      Compressed:

        +---+---+---+---+---+---+---+---+
        | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 |  Bit field
        +---+---+---+---+---+---+---+---+
          |       |                   |
       ,--'       '----,              '- Boolean Value
       |               |
      +-------+-------+-------+
      |  LEN  |  VAL  |  VAL  |
      +-------+-------+-------+
      '---------------'-------'
        Var-len Value  Fixed-len Value

     Figure 3: Compression using a compact bit field - bits encode the
                            inclusion of TLVs.

   Stateless TLV compression for NDN is defined in Section 5.  Section 6
   defines the stateless TLV compression for CCNx.

   The extensibility of this compression is described in Section 4.1.1
   and allows future documents to update the compression rules outlined
   in this manuscript.





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3.3.  Stateful Header Compression

   ICN LoWPAN further employs two orthogonal stateful compression
   schemes for packet size reductions which are defined in Section 8.
   These mechanisms rely on shared contexts that are either distributed
   and maintained in the entire LoWPAN, or are generated on-demand hop-
   wise on a particular Interest-data path.

   The shared context identification is defined in Section 8.1.  The
   hop-wise name compression "en-route" is specified in Section 8.2.

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 network layers coexist on the same link.  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 precede 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 uses page TBD1 ("1111 TBD1 (0xFTBD1)") for ICN LoWPAN.

   The base dispatch format (Figure 4) is used and extended by CCNx and
   NDN in Section 5 and Section 6.

                             0   1   2  ...
                           +---+---+-----------
                           | C | P | M |
                           +---+---+-----------

               Figure 4: Base dispatch format for ICN LoWPAN

   C: Compression

       0:          The message is compressed.

       1:          The message is uncompressed.

   P: Protocol




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       0:          The included protocol is NDN.

       1:          The included protocol is CCNx.

   M: Message Type

       0:          The payload contains an Interest message.

       1:          The payload contains a Data message.

   ICN LoWPAN frames with compressed CCNx and NDN messages (C=0) use the
   extended dispatch format in Figure 5.

                           0   1   2   3   4  ...
                         +---+---+---+---+---+---
                         | 0 | P | M |CID|EXT|
                         +---+---+---+---+---+---

       Figure 5: Extended dispatch format for compressed ICN LoWPAN

   CID: Context Identifier

       0:          No context identifiers are present.

       1:          Context identifier(s) are present (see Section 8.1).

   EXT: Extension

       0:          No extension bytes are present.

       1:          Extension byte(s) are present (see Section 4.1.1).

   The encapsulation format for ICN LoWPAN is displayed in Figure 6.

    +------...------+------...-----+--------+-------...-------+-----...
    | IEEE 802.15.4 | RFC4944 Disp.|  Page  | ICN LoWPAN Disp.| Payl. /
    +------...------+------...-----+--------+-------...-------+-----...

              Figure 6: LoWPAN Encapsulation with ICN-LoWPAN

   IEEE 802.15.4:  The IEEE 802.15.4 header.

   RFC4944 Disp.:  Optional additional dispatches defined in Section 5.1
                   of [RFC4944]

   Page:           Page Switch.  TBD1 for ICN LoWPAN.

   ICN LoWPAN:     Dispatches as defined in Section 5 and Section 6.



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   Payload:        The actual (un-)compressed CCNx or NDN message.

4.1.1.  Dispatch Extensions

   Extension bytes allow for the extensibility of the initial
   compression rule set.  The base format for an extension byte is
   depicted in Figure 7.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | - | - | - | - | - | - | - |EXT|
                     +---+---+---+---+---+---+---+---+

              Figure 7: Base format for dispatch extensions.

   EXT: Extension

       0:          No other extension byte follows.

       1:          A further extension byte follows.

   Extension bytes are numbered according to their order.  Future
   documents MUST follow the naming scheme "EXT_0, EXT_1, ...", when
   updating or referring to a specific dispatch extension byte.
   Amendments that require an exchange of configurational parameters
   between devices SHOULD use manifests to encode structured data in a
   well-defined format, as, e.g., outlined in [I-D.irtf-icnrg-flic].

4.2.  Adaptation Layer Fragmentation

   Small payload sizes in the LoWPAN require fragmentation for various
   network layers.  Therefore, 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 this fragmentation
   handling of [RFC4944].

   The Fragmentation LoWPAN header can encapsulate other dispatch
   headers.  The order of dispatch types is defined in Section 5 of
   [RFC4944].  Figure 8 shows the fragmentation scheme.  The reassembled
   ICN LoWPAN frame does not contain any fragmentation headers and is
   depicted in Figure 9.









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    +------...------+----...----+--------+------...-------+--------...
    | IEEE 802.15.4 | Frag. 1st |  Page  |   ICN LoWPAN   | Payload  /
    +------...------+----...----+--------+------...-------+--------...

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

                    .
                    .
                    .

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

                      Figure 8: Fragmentation scheme

          +------...------+--------+------...-------+--------...
          | IEEE 802.15.4 |  Page  |   ICN LoWPAN   | Payload  /
          +------...------+--------+------...-------+--------...

                  Figure 9: Reassembled ICN LoWPAN frame

   The 6LoWPAN Fragment Forwarding (6FF) [I-D.ietf-6lo-minimal-fragment]
   is an alternative approach that enables forwarding of fragments
   without reassembling packets on every intermediate hop.  By reusing
   the 6LoWPAN dispatching framework, 6FF integrates into ICN LoWPAN as
   seamless as the conventional hop-wise fragmentation.  Experimental
   evaluations [SFR-ICNLOWPAN], however, suggest that a more refined
   integration can increase the cache utilization of forwarders on a
   request path.

5.  Space-efficient Message Encoding for NDN

5.1.  TLV Encoding

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

   If the type or length number is less than "253", then that number is
   encoded into the actual type or length field.  If the number is
   greater or equals "253" and fits into 2 bytes, then the type or
   length field is set to "253" and the number is encoded in the next
   following 2 bytes in network byte order, i.e., from the most
   significant byte (MSB) to the least significant byte (LSB).  If the



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   number is greater than 2 bytes and fits into 4 bytes, then the type
   or length field is set to "254" and the number is encoded in the
   subsequent 4 bytes in network byte order.  For larger numbers, the
   type or length field is set to "255" and the number is encoded in the
   subsequent 8 bytes in network byte order.

   In this specification, compressed NDN TLVs make use of a different
   TLV encoding scheme that reduces size.  Instead of using the first
   byte as a marker for the number of following bytes, the compressed
   NDN TLV scheme uses a method to chain a variable number of bytes
   together.  If a byte equals "255 (0xFF)", then the following byte
   will also be interpreted.  The actual value of a chain equals the sum
   of all constituents.

   If the type or length number is less than "255", then that number is
   encoded into the actual type or length field (Figure 10 a).  If the
   type or length number (X) fits into 2 bytes, then the first byte is
   set to "255" and the subsequent byte equals "X mod 255" (Figure 10
   b).  Following this scheme, a variable-sized number (X) is encoded
   using multiple bytes of "255" with a trailing byte containing "X mod
   255" (Figure 10 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)

               Figure 10: Compressed NDN TLV encoding scheme

5.2.  Name TLV Compression

   This Name TLV compression encodes length fields of two consecutive
   NameComponent TLVs into one byte, using a nibble for each.  The most
   significant nibble indicates the length of an immediately following
   NameComponent TLV.  The least significant nibble denotes the length



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   of a subsequent NameComponent TLV.  A length of 0 marks the end of
   the compressed Name TLV.  The last length field of an encoded
   NameComponent is either 0x00 for a name with an even number of
   components, and 0xYF (Y > 0) if an odd number of components are
   present.  This process limits the length of a NameComponent TLV to 15
   bytes, but allows for an unlimited number of components.  An example
   for this encoding is presented in Figure 11.

                     Name: /HAW/Room/481/Humid/99

      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|       9       |       9       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 11: Name TLV compression for /HAW/Room/481/Humid/99

5.3.  Interest Messages

5.3.1.  Uncompressed Interest Messages

   An uncompressed Interest message uses the base dispatch format (see
   Figure 4) and sets the C flag to "1" and the P as well as the M flag
   to "0" (Figure 12).  The Interest message is handed to the NDN
   network stack without modifications.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
                     +---+---+---+---+---+---+---+---+

     Figure 12: Dispatch format for uncompressed NDN Interest messages

5.3.2.  Compressed Interest Messages

   The compressed Interest message uses the extended dispatch format
   (Figure 5) and sets the P flag to "0", the C flag to "0" and the M
   flag to "0".  If an Interest message contains TLVs that are not




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   mentioned in the following compression rules, then this message MUST
   be sent uncompressed.

   This specification assumes that a HopLimit TLV is part of the
   original Interest message.  If such HopLimit TLV is not present, it
   will be inserted with a default value of DEFAULT_NDN_HOPLIMIT prior
   to the compression.

   In the default use case, the Interest message is compressed with the
   following minimal rule set:

   1.  The "Type" field of the outermost MessageType TLV is removed.

   2.  The Name TLV is compressed according to Section 5.2.  For this,
       all NameComponents are expected to be of type
       GenericNameComponent with a length greater than 0.  An
       ImplicitSha256DigestComponent or ParametersSha256DigestComponent
       MAY appear at the end of the name.  In any other case, the
       message MUST be sent uncompressed.

   3.  The Nonce TLV and InterestLifetime TLV are moved to the end of
       the compressed Interest as illustrated in Figure 13.  The
       InterestLifetime is encoded as described in Section 7.  If a
       lifetime is not a valid time-value, then the lifetime is rounded
       up to the nearest valid time-value as specified in Section 7.

   4.  The Type and Length fields of Nonce TLV, HopLimit TLV and
       InterestLifetime TLV are elided.  The Nonce value has a length of
       4 bytes and the HopLimit value has a length of 1 byte.  The
       compressed InterestLifetime (Section 7) has a length of 1 byte.
       The presence of a Nonce and InterestLifetime TLV is deduced from
       the remaining length to parse.  A remaining length of "1"
       indicates the presence of an InerestLifetime, a length of "4"
       indicates the presence of a nonce, and a length of "5" indicates
       the presence of both TLVs.

   The compressed NDN LoWPAN Interest message is visualized in
   Figure 13.













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        T = Type, L = Length, V = Value
        Lc = Compressed Length, Vc = Compressed Value
        : = optional field, | = mandatory field

        +---------+---------+                 +---------+
        |  Msg T  |  Msg L  |                 |  Msg Lc |
        +---------+---------+---------+       +---------+
        | Name T  | Name L  | Name V  |       | Name Vc |
        +---------+---------+---------+       +---------+---------+
        : CBPfx T : CBPfx L :                 : FWDH Lc : FWDH Vc :
        +---------+---------+                 +---------+---------+
        : MBFr T  : MBFr L  :                 |  HPL V  |
        +---------+---------+---------+  ==>  +---------+---------+
        : FWDH T  : FWDH L  : FWDH V  :       :  APM Lc : APM Vc  :
        +---------+---------+---------+       +---------+---------+
        : NONCE T : NONCE L : NONCE V :       : NONCE V :
        +---------+---------+---------+       +---------+
        :  ILT T  :  ILT L  :  ILT V  :       :  ILT Vc :
        +---------+---------+---------+       +---------+
        :  HPL T  :  HPL L  :  HPL V  :
        +---------+---------+---------+
        :  APM T  :  APM L  :  APM V  :
        +---------+---------+---------+

           Figure 13: Compression of NDN LoWPAN Interest Message

   Further TLV compression is indicated by the ICN LoWPAN dispatch in
   Figure 14.

       0                                       1
       0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     | 0 | 0 | 0 |CID|EXT|PFX|FRE|FWD|APM|DIG|          RSV          |
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

      Figure 14: Dispatch format for compressed NDN Interest messages

   CID: Context Identifier  See Figure 5.

   EXT: Extension

       0:      No extension byte follows.

       1:      Extension byte "EXT_0" follows immediately.  See
               Section 5.3.3.

   PFX: CanBePrefix TLV




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       0:          The uncompressed message does not include a
                   CanBePrefix TLV.

       1:          The uncompressed message does include a CanBePrefix
                   TLV and is removed from the compressed message.

   FRE: MustBeFresh TLV

       0:          The uncompressed message does not include a
                   MustBeFresh TLV.

       1:          The uncompressed message does include a MustBeFresh
                   TLV and is removed from the compressed message.

   FWD: ForwardingHint TLV

       0:          The uncompressed message does not include a
                   ForwardingHint TLV.

       1:          The uncompressed message does include a
                   ForwardingHint TLV.  The Type field is removed from
                   the compressed message.  Further, all link delegation
                   types and link preference types are removed.  All
                   included names are compressed according to
                   Section 5.2.  If any name is not compressible, the
                   message MUST be sent uncompressed.

   APM: ApplicationParameters TLV

       0:          The uncompressed message does not include an
                   ApplicationParameters TLV.

       1:          The uncompressed message does include an
                   ApplicationParameters TLV.  The Type field is removed
                   from the compressed message.

   DIG: ImplicitSha256DigestComponent TLV

       0:          The name does not include an
                   ImplicitSha256DigestComponent as the last TLV.

       1:          The name does include an
                   ImplicitSha256DigestComponent as the last TLV.  The
                   Type and Length fields are omitted.

   RSV: Reserved  Must be set to 0.





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5.3.3.  Dispatch Extension

   The "EXT_0" byte follows the description in Section 4.1.1 and is
   illustrated in Figure 15.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     |  NCS  |        RSV        |EXT|
                     +---+---+---+---+---+---+---+---+

                          Figure 15: EXT_0 format

   NCS: Name Compression Strategy

       00:         Names are compressed with the default name
                   compression strategy (see Section 5.2).

       01:         Reserved.

       10:         Reserved.

       11:         Reserved.

   RSV: Reserved  Must be set to 0.

   EXT: Extension

       0:      No extension byte follows.

       1:      A further extension byte follows immediately.

5.4.  Data Messages

5.4.1.  Uncompressed Data Messages

   An uncompressed Data message uses the base dispatch format and sets
   the C as well as the M flag to "1" and the P flag to "0" (Figure 16).
   The Data message is handed to the NDN network stack without
   modifications.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
                     +---+---+---+---+---+---+---+---+

       Figure 16: Dispatch format for uncompressed NDN Data messages





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5.4.2.  Compressed Data Messages

   The compressed Data message uses the extended dispatch format
   (Figure 5) and sets the C as well as the P flag to "0".  The M flag
   is set to "1".  If a Data message contains TLVs that are not
   mentioned in the following compression rules, then this message MUST
   be sent uncompressed.

   By default, the Data message is compressed with the following base
   rule set:

   1.  The "Type" field of the outermost MessageType TLV is removed.

   2.  The Name TLV is compressed according to Section 5.2.  For this,
       all NameComponents are expected to be of type
       GenericNameComponent and to have a length greater than 0.  In any
       other case, the message MUST be sent uncompressed.

   3.  The MetaInfo TLV Type and Length fields are elided from the
       compressed Data message.

   4.  The FreshnessPeriod TLV MUST be moved to the end of the
       compressed Data message.  Type and Length fields are elided and
       the value is encoded as described in Section 7 as a 1-byte time-
       code.  If the freshness period is not a valid time-value, then
       the message MUST be sent uncompressed in order to preserve the
       security envelope of the Data message.  The presence of a
       FreshnessPeriod TLV is deduced from the remaining one byte length
       to parse.

   5.  The Type fields of the SignatureInfo TLV, SignatureType TLV and
       SignatureValue TLV are removed.

   The compressed NDN LoWPAN Data message is visualized in Figure 17.

















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        T = Type, L = Length, V = Value
        Lc = Compressed Length, Vc = Compressed Value
        : = optional field, | = mandatory field

        +---------+---------+                 +---------+
        |  Msg T  |  Msg L  |                 |  Msg Lc |
        +---------+---------+---------+       +---------+
        | Name T  | Name L  | Name V  |       | Name Vc |
        +---------+---------+---------+       +---------+---------+
        : Meta T  : Meta L  :                 : CTyp Lc : CType V :
        +---------+---------+---------+       +---------+---------+
        : CTyp T  : CTyp L  : CTyp V  :       : FBID V  :
        +---------+---------+---------+  ==>  +---------+---------+
        : FrPr T  : FrPr L  : FrPr V  :       : CONT Lc : CONT V  :
        +---------+---------+---------+       +---------+---------+
        : FBID T  : FBID L  : FBID V  :       |  Sig Lc |
        +---------+---------+---------+       +---------+---------+
        : CONT T  : CONT L  : CONT V  :       | SInf Lc | SInf Vc |
        +---------+---------+---------+       +---------+---------+
        |  Sig T  |  Sig L  |                 | SVal Lc | SVal Vc |
        +---------+---------+---------+       +---------+---------+
        | SInf T  | SInf L  | SInf V  |       : FrPr Vc :
        +---------+---------+---------+       +---------+
        | SVal T  | SVal L  | SVal V  |
        +---------+---------+---------+

             Figure 17: Compression of NDN LoWPAN Data Message

   Further TLV compression is indicated by the ICN LoWPAN dispatch in
   Figure 18.

       0                                       1
       0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     | 0 | 0 | 1 |CID|EXT|FBI|CON|KLO|              RSV              |
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

        Figure 18: Dispatch format for compressed NDN Data messages

   CID: Context Identifier  See Figure 5.

   EXT: Extension

       0:      No extension byte follows.

       1:      Extension byte "EXT_0" follows immediately.  See
               Section 5.4.3.




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   FBI: FinalBlockId TLV

       0:          The uncompressed message does not include a
                   FinalBlockId TLV.

       1:          The uncompressed message does include a FinalBlockId
                   and it is encoded according to Section 5.2.  If the
                   FinalBlockId TLV is not compressible, then the
                   message MUST be sent uncompressed.

   CON: ContentType TLV

       0:          The uncompressed message does not include a
                   ContentType TLV.

       1:          The uncompressed message does include a ContentType
                   TLV.  The Type field is removed from the compressed
                   message.

   KLO: KeyLocator TLV

       0:          If the included SignatureType requires a KeyLocator
                   TLV, then the KeyLocator represents a name and is
                   compressed according to Section 5.2.  If the name is
                   not compressible, then the message MUST be sent
                   uncompressed.

       1:          If the included SignatureType requires a KeyLocator
                   TLV, then the KeyLocator represents a KeyDigest.  The
                   Type field of this KeyDigest is removed.

   RSV: Reserved  Must be set to 0.

5.4.3.  Dispatch Extension

   The "EXT_0" byte follows the description in Section 4.1.1 and is
   illustrated in Figure 19.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     |  NCS  |        RSV        |EXT|
                     +---+---+---+---+---+---+---+---+

                          Figure 19: EXT_0 format

   NCS: Name Compression Strategy





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       00:         Names are compressed with the default name
                   compression strategy (see Section 5.2).

       01:         Reserved.

       10:         Reserved.

       11:         Reserved.

   RSV: Reserved  Must be set to 0.

   EXT: Extension

       0:      No extension byte follows.

       1:      A further extension byte follows immediately.

6.  Space-efficient Message Encoding for CCNx

6.1.  TLV Encoding

   The generic CCNx TLV encoding is described in [RFC8609].  Type and
   Length fields attain the common fixed length of 2 bytes.

   The TLV encoding for CCNx LoWPAN is changed to the more space
   efficient encoding described in Section 5.1.  Hence NDN and CCNx use
   the same compressed format for writing TLVs.

6.2.  Name TLV Compression

   Name TLVs are compressed using the scheme already defined in
   Section 5.2 for NDN.  If a Name TLV contains T_IPID, T_APP, or
   organizational TLVs, then the name remains uncompressed.

6.3.  Interest Messages

6.3.1.  Uncompressed Interest Messages

   An uncompressed Interest message uses the base dispatch format (see
   Figure 4) and sets the C as well as the P flag to "1".  The M flag is
   set to "0" (Figure 20).  The Interest message is handed to the CCNx
   network stack without modifications.









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                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
                     +---+---+---+---+---+---+---+---+

    Figure 20: Dispatch format for uncompressed CCNx Interest messages

6.3.2.  Compressed Interest Messages

   The compressed Interest message uses the extended dispatch format
   (Figure 5) and sets the C and M flags to "0".  The P flag is set to
   "1".  If an Interest message contains TLVs that are not mentioned in
   the following compression rules, then this message MUST be sent
   uncompressed.

   In the default use case, the Interest message is compressed with the
   following minimal rule set:

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

   The compressed CCNx LoWPAN Interest message is visualized in
   Figure 21.




























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   T = Type, L = Length, V = Value
   Lc = Compressed Length, Vc = Compressed Value
   : = optional field, | = mandatory field

   +-----------------------------+           +-------------------------+
   |    Uncompr. Fixed Header    |           |   Compr. Fixed Header   |
   +-----------------------------+           +-------------------------+
   +---------+---------+---------+           +---------+
   : ILT T   : ILT L   : ILT V   :           : ILT Vc  :
   +---------+---------+---------+           +---------+
   : MSGH T  : MSGH L  : MSGH V  :           : MSGH Vc :
   +---------+---------+---------+           +---------+
   +---------+---------+                     +---------+
   | MSGT T  | MSGT L  |                     | Name Vc |
   +---------+---------+---------+           +---------+
   | Name T  | Name L  | Name V  |    ==>    : KIDR Vc :
   +---------+---------+---------+           +---------+
   : KIDR T  : KIDR L  : KIDR V  :           : OBHR Vc :
   +---------+---------+---------+           +---------+---------+
   : OBHR T  : OBHR L  : OBHR V  :           : PAYL Lc : PAYL V  :
   +---------+---------+---------+           +---------+---------+
   : PAYL T  : PAYL L  : PAYL V  :           : VALG Lc : VALG Vc :
   +---------+---------+---------+           +---------+---------+
   : VALG T  : VALG L  : VALG V  :           : VPAY Lc : VPAY V  :
   +---------+---------+---------+           +---------+---------+
   : VPAY T  : VPAY L  : VPAY V  :
   +---------+---------+---------+

          Figure 21: Compression of CCNx LoWPAN Interest Message

   Further TLV compression is indicated by the ICN LoWPAN dispatch in
   Figure 22.

       0                                       1
       0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     | 0 | 1 | 0 |CID|EXT|VER|FLG|PTY|HPL|FRS|PAY|ILT|MGH|KIR|CHR|VAL|
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

     Figure 22: Dispatch format for compressed CCNx Interest messages

   CID: Context Identifier  See Figure 5.

   EXT: Extension

       0:      No extension byte follows.





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       1:      Extension byte "EXT_0" follows immediately.  See
               Section 6.3.3.

   VER: CCNx protocol version in the fixed header

       0:      The Version field equals 1 and is removed from the fixed
               header.

       1:      The Version field appears in the fixed header.

   FLG: Flags field in the fixed header

       0:      The Flags field equals 0 and is removed from the Interest
               message.

       1:      The Flags field appears in the fixed header.

   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 appears in the fixed header.

       1:      The HopLimit field is elided and assumed to be "1".

   FRS: Reserved field in the fixed header

       0:      The Reserved field appears in the fixed header.

       1:      The Reserved field is elided and assumed to be "0".

   PAY: Optional Payload TLV

       0:      The Payload TLV is absent.

       1:      The Payload TLV is present and the type field is elided.

   ILT: Optional Hop-By-Hop InterestLifetime TLV

               See Section 6.3.2.1 for further details on the ordering
               of hop-by-hop TLVs.




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       0:      No InterestLifetime TLV is present in the Interest
               message.

       1:      An InterestLifetime TLV is present with a fixed length of
               1 byte and is encoded as described in Section 7.  The
               type and length fields are elided.  If a lifetime is not
               a valid time-value, then the lifetime is rounded up to
               the nearest valid time-value (see Section 7).

   MGH: Optional Hop-By-Hop MessageHash TLV

               See Section 6.3.2.1 for further details on the ordering
               of hop-by-hop TLVs.

               This TLV is expected to contain a T_SHA-256 TLV.  If
               another hash is contained, then the Interest MUST be sent
               uncompressed.

       0:      The MessageHash TLV is absent.

       1:      A T_SHA-256 TLV is present and the type as well as the
               length fields are removed.  The length field is assumed
               to represent 32 bytes.  The outer Message Hash TLV is
               omitted.

   KIR: Optional KeyIdRestriction TLV

               This TLV is expected to contain a T_SHA-256 TLV.  If
               another hash is contained, then the Interest MUST be sent
               uncompressed.

       0:      The KeyIdRestriction TLV is absent.

       1:      A T_SHA-256 TLV is present and the type as well as the
               length fields are removed.  The length field is assumed
               to represent 32 bytes.  The outer KeyIdRestriction TLV is
               omitted.

   CHR: Optional ContentObjectHashRestriction TLV

               This TLV is expected to contain a T_SHA-256 TLV.  If
               another hash is contained, then the Interest MUST be sent
               uncompressed.

       0:      The ContentObjectHashRestriction TLV is absent.

       1:      A T_SHA-256 TLV is present and the type as well as the
               length fields are removed.  The length field is assumed



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               to represent 32 bytes.  The outer
               ContentObjectHashRestriction TLV is omitted.

   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 byte follows immediately that
               handles validation related TLV compressions and is
               described in Section 6.3.2.2.

6.3.2.1.  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 [RFC8609], but several
   more can be defined in higher level specifications.  For the
   compression specified in the previous section, the Hop-By-Hop TLVs
   are ordered as follows:

   1.  Interest Lifetime TLV

   2.  Message Hash TLV

   Note: Other Hop-By-Hop Header TLVs than those two remain uncompressed
   in the encoded message and they appear in the same order as in the
   original message, but after the Interest Lifetime TLV and Message
   Hash TLV.

6.3.2.2.  Validation

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

               Figure 23: Dispatch for Interset Validations

   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.






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       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 included.  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 bytes.  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 bytes.  The outer KeyId TLV is
               omitted.



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   RSV: Reserved  Must be set to 0.

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

6.3.3.  Dispatch Extension

   The "EXT_0" byte follows the description in Section 4.1.1 and is
   illustrated in Figure 24.

                     0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     |  NCS  |        RSV        |EXT|
                     +---+---+---+---+---+---+---+---+

                          Figure 24: EXT_0 format

   NCS: Name Compression Strategy

       00:         Names are compressed with the default name
                   compression strategy (see Section 5.2).

       01:         Reserved.

       10:         Reserved.

       11:         Reserved.

   RSV: Reserved  Must be set to 0.

   EXT: Extension

       0:      No extension byte follows.

       1:      A further extension byte follows immediately.

6.4.  Content Objects

6.4.1.  Uncompressed Content Objects

   An uncompressed Content object uses the base dispatch format (see
   Figure 4) and sets the C, P and M flags to "1" (Figure 25).  The
   Content object is handed to the CCNx network stack without
   modifications.







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                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
                     +---+---+---+---+---+---+---+---+

     Figure 25: Dispatch format for uncompressed CCNx Content objects

6.4.2.  Compressed Content Objects

   The compressed Content object uses the extended dispatch format
   (Figure 5) and sets the P as well as the M flag to "1".  The C flag
   is set to "0".  If a Content object contains TLVs that are not
   mentioned in the following compression rules, then this message MUST
   be sent uncompressed.

   By default, the Content object is compressed with the following base
   rule set:

   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.

   The compressed CCNx LoWPAN Data message is visualized in Figure 26.



























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   T = Type, L = Length, V = Value
   Lc = Compressed Length, Vc = Compressed Value
   : = optional field, | = mandatory field

   +-----------------------------+           +-------------------------+
   |    Uncompr. Fixed Header    |           |   Compr. Fixed Header   |
   +-----------------------------+           +-------------------------+
   +---------+---------+---------+           +---------+
   : RCT T   : RCT L   : RCT V   :           : RCT Vc  :
   +---------+---------+------.--+           +---------+
   : MSGH T  : MSGH L  : MSGH V  :           : MSGH Vc :
   +---------+---------+---------+           +---------+
   +---------+---------+                     +---------+
   | MSGT T  | MSGT L  |                     | Name Vc |
   +---------+---------+---------+           +---------+
   | Name T  | Name L  | Name V  |    ==>    : EXPT Vc :
   +---------+---------+---------+           +---------+---------+
   : PTYP T  : PTYP L  : PTYP V  :           : PAYL Lc : PAYL V  :
   +---------+---------+---------+           +---------+---------+
   : EXPT T  : EXPT L  : EXPT V  :           : VALG Lc : VALG Vc :
   +---------+---------+---------+           +---------+---------+
   : PAYL T  : PAYL L  : PAYL V  :           : VPAY Lc : VPAY V  :
   +---------+---------+---------+           +---------+---------+
   : VALG T  : VALG L  : VALG V  :
   +---------+---------+---------+
   : VPAY T  : VPAY L  : VPAY V  :
   +---------+---------+---------+

            Figure 26: Compression of CCNx LoWPAN Data Message

   Further TLV compression is indicated by the ICN LoWPAN dispatch in
   Figure 27.

       0                                       1
       0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     | 0 | 1 | 1 |CID|EXT|VER|FLG|FRS|PAY|RCT|MGH| PLTYP |EXP|VAL|RSV|
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

      Figure 27: Dispatch format for compressed CCNx Content objects

   CID: Context Identifier  See Figure 5.

   EXT: Extension

       0:      No extension byte follows.





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       1:      Extension byte "EXT_0" follows immediately.  See
               Section 6.4.3.

   VER: CCNx protocol version in the fixed header

       0:      The Version field equals 1 and is removed from the fixed
               header.

       1:      The Version field appears in the fixed header.

   FLG: Flags field in the fixed header  See Section 6.3.2.

   FRS: Reserved field in the fixed header  See Section 6.3.2.

   PAY: Optional Payload TLV  See Section 6.3.2.

   RCT: Optional Hop-By-Hop RecommendedCacheTime 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.

   MGH: Optional Hop-By-Hop MessageHash TLV

               See Section 6.4.2.1 for further details on the ordering
               of hop-by-hop TLVs.

               This TLV is expected to contain a T_SHA-256 TLV.  If
               another hash is contained, then the Content Object MUST
               be sent uncompressed.

       0:      The MessageHash TLV is absent.

       1:      A T_SHA-256 TLV is present and the type as well as the
               length fields are removed.  The length field is assumed
               to represent 32 bytes.  The outer Message Hash TLV is
               omitted.



       PLTYP: Optional PayloadType TLV

           00:     The PayloadType TLV is absent.

           01:     The PayloadType TLV is absent and T_PAYLOADTYPE_DATA
                   is assumed.




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           10:     The PayloadType TLV is absent and T_PAYLOADTYPE_KEY
                   is assumed.

           11:     The PayloadType TLV is present and uncompressed.

   EXP: Optional ExpiryTime TLV

       0:      The ExpiryTime TLV is absent.

       1:      The ExpiryTime TLV is present and the type as well as the
               length fields are elided.

   VAL: Optional ValidationAlgorithm and ValidationPayload TLVs  See Sec
       tion 6.3.2.

   RSV: Reserved  Must be set to 0.

6.4.2.1.  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 [RFC8609], but
   several more can be defined in higher level specifications.  For the
   compression specified in the previous section, the Hop-By-Hop TLVs
   are ordered as follows:

   1.  Recommended Cache Time TLV

   2.  Message Hash TLV

   Note: Other Hop-By-Hop Header TLVs than those two remain uncompressed
   in the encoded message and they appear in the same order as in the
   original message, but after the Recommended Cache Time TLV and
   Message Hash TLV.

6.4.3.  Dispatch Extension

   The "EXT_0" byte follows the description in Section 4.1.1 and is
   illustrated in Figure 28.

                     0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     |  NCS  |        RSV        |EXT|
                     +---+---+---+---+---+---+---+---+

                          Figure 28: EXT_0 format

   NCS: Name Compression Strategy




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       00:         Names are compressed with the default name
                   compression strategy (see Section 5.2).

       01:         Reserved.

       10:         Reserved.

       11:         Reserved.

   RSV: Reserved  Must be set to 0.

   EXT: Extension

       0:      No extension byte follows.

       1:      A further extension byte follows immediately.

7.  Compressed Time Encoding

   This document adopts the compact time representation
   [I-D.gundogan-icnrg-ccnx-timetlv] for relative time values.  Exponent
   and mantissa values are encoded in a 1-byte wide representation as
   depicted in Figure 29.  The exponent occupies the most significant
   bits, while the mantissa uses the least significant bits.

                           0   1   2   3   4   5   6   7
                         +---+---+---+---+---+---+---+---+
                         |     exponent      | mantissa  |
                         +---+---+---+---+---+---+---+---+

       Figure 29: A time-code with exponent and mantissa to encode a
                  logarithmic range time representation.

   The mantissa size is set to 3 bits, the exponent size to 5 bits, and
   a bias of -5 is applied.  This allows for a time representation that
   ranges from tens of milliseconds with high precision to days with low
   precision.  The base unit for time values are seconds.  A time-value
   is calculated using the following formula, where (e) represents the
   exponent, (m) the mantissa, (m_max = 8) the maximum mantissa value,
   and (b) the bias.

   Subnormal (e == 0):  (0 + m/m_max) * 2^(1+b)

   Normalized (e > 0):  (1 + m/m_max) * 2^(e+b)

   The subnormal form provides a gradual underflow from the smallest
   normalized number towards zero.




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   This configuration allows for the following ranges:

   o  Minimum subnormal number: 0 seconds

   o  Maximum subnormal number: ~0.054688 seconds

   o  Minimum normalized number: ~0.062500 seconds

   o  Maximum normalized number: ~3.987284 years

   Valid time-values are positive numbers, including 0.  An invalid
   time-value (t, in seconds) MUST be rounded down to the nearest valid
   time-value using this algorithm, where (e) represents the number of
   bits for the exponent, (m) the number of bits for the mantissa, and
   (m_max = 8) the maximum mantissa value.  The bias (b) is set to -5 as
   before.

   o  e := floor( log2( t/(2^-b) ))

   o  m := floor( 8 * (t / 2^(e+b) - 1 ))

8.  Stateful Header Compression

   Stateful header compression in ICN LoWPAN enables packet size
   reductions in two ways.  First, common information that is shared
   throughout the local LoWPAN may be memorized in context state at all
   nodes and omitted from communication.  Second, redundancy in a single
   Interest-data exchange may be removed from ICN stateful forwarding on
   a hop-by-hop bases and memorized in en-route state tables.

8.1.  LoWPAN-local State

   A context identifier (CID) is a byte that refers to a particular
   conceptual context between network devices and MAY be used to replace
   frequently appearing information, such as name prefixes, suffixes, or
   meta information, such as Interest lifetime.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | X |         ContextID         |
                     +---+---+---+---+---+---+---+---+

                      Figure 30: Context Identifier.

   The 7-bit ContextID is a locally-scoped unique identifier that
   represents contextual state shared between sender and receiver of the
   corresponding frame (see Figure 30).  If set the most significant bit




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   indicates the presence of another, subsequent ContextID byte (see
   Figure 35).

   Context state shared between senders and receivers is removed from
   the compressed packet prior to sending, and reinserted after
   reception prior to passing to the upper stack.

   The actual information in a context and how it is encoded are out of
   scope of this document.  The initial distribution and maintenance of
   shared context is out of scope of this document.  Frames containing
   unknown or invalid CIDs MUST be silently discarded.

8.2.  En-route State

   In CCNx and NDN, Name TLVs are included in Interest messages, and
   they return in data messages.  Returning Name TLVs either equal the
   original Name TLV, or they contain the original Name TLV as a prefix.
   ICN LoWPAN reduces this redundancy in responses by replacing Name
   TLVs with single bytes that represent link-local HopIDs.  HopIDs are
   carried as Context Identifiers (see Section 8.1) of link-local scope
   as shown in Figure 31.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | X |          HopID            |
                     +---+---+---+---+---+---+---+---+

                  Figure 31: Context Identifier as HopID.

   A HopID is valid if not all ID bits are set to zero and invalid
   otherwise.  This yields 127 distinct HopIDs.  If this range (1...127)
   is exhausted, the messages MUST be sent without en-route state
   compression until new HopIDs are available.  An ICN LoWPAN node that
   forwards without replacing the name by a HopID (without en-route
   compression) MUST invalidate the HopID by setting all ID-bits to
   zero.

   While an Interest is traversing, a forwarder generates an ephemeral
   HopID that is tied to a PIT entry.  Each HopID MUST be unique within
   the local PIT and only exists during the lifetime of a PIT entry.  To
   maintain HopIDs, the local PIT is extended by two new columns: HIDi
   (inbound HopIDs) and HIDo (outbound HopIDs).

   HopIDs are included in Interests and stored on the next hop with the
   resulting PIT entry in the HIDi column.  The HopID is replaced with a
   newly generated local HopID before the Interest is forwarded.  This
   new HopID is stored in the HIDo column of the local PIT (see
   Figure 32).



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       PIT of B      PIT Extension          PIT of C      PIT Extension
   +--------+------++------+------+     +--------+------++------+------+
   | Prefix | Face || HIDi | HIDo |     | Prefix | Face || HIDi | HIDo |
   +========+======++======+======+     +========+======++======+======+
   |  /p0   | F_A  || h_A  | h_B  |     |  /p0   | F_A  || h_A  |      |
   +--------+------++------+------+     +--------+------++------+------+
                       ^       |                            ^
                 store |       '----------------------, ,---' store
                       |                 send         v |
   ,---,         /p0, h_A          ,---,         /p0, h_B          ,---,
   | A | ------------------------> | B | ------------------------> | C |
   '---'                           '---'                           '---'

         Figure 32: Setting compression state en-route (Interest).

   Responses include HopIDs that were obtained from Interests.  If the
   returning Name TLV equals the original Name TLV, then the name is
   entirely elided.  Otherwise, only the matching name prefix is elided
   and the distinct name suffix is included along with the HopID.  When
   a response is forwarded, the contained HopID is extracted and used to
   match against the correct PIT entry by performing a lookup on the
   HIDo column.  The HopID is then replaced with the corresponding HopID
   from the HIDi column prior to forwarding the response (Figure 33).

       PIT of B      PIT Extension          PIT of C      PIT Extension
   +--------+------++------+------+     +--------+------++------+------+
   | Prefix | Face || HIDi | HIDo |     | Prefix | Face || HIDi | HIDo |
   +========+======++======+======+     +========+======++======+======+
   |  /p0   | F_A  || h_A  | h_B  |     |  /p0   | F_A  || h_A  |      |
   +--------+------++------+------+     +--------+------++------+------+
                       |       ^                            |
                  send |       '----------------------, ,---' send
                       v                 match        | v
   ,---,              h_A          ,---,              h_B          ,---,
   | A | <------------------------ | B | <------------------------ | C |
   '---'                           '---'                           '---'

         Figure 33: Eliding Name TLVs using en-route state (data).

   It should be noted that each forwarder of an Interest in an ICN
   LoWPAN network can individually decide whether to participate in en-
   route compression or not.  However, an ICN LoWPAN node SHOULD use en-
   route compression whenever the stateful compression mechanism is
   activated.

   Note also that the extensions of the PIT data structure are required
   only at ICN LoWPAN nodes, while regular NDN/CCNx forwarders outside
   of an ICN LoWPAN domain do not need to implement these extensions.



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8.3.  Integrating Stateful Header Compression

   A CID appears whenever the CID flag is set (see Figure 5).  The CID
   is appended to the last ICN LoWPAN dispatch byte as shown in
   Figure 34.

          ...-------+--------+-------...-------+--...-+-------...
          /  ...    |  Page  | ICN LoWPAN Disp.| CIDs | Payload /
          ...-------+--------+-------...-------+--...-+-------...

         Figure 34: LoWPAN Encapsulation with ICN LoWPAN and CIDs

   Multiple CIDs are chained together, with the most significant bit
   indicating the presence of a subsequent CID (Figure 35).  This allows
   to use multiple shared contexts in compressed messages.

   The HopID is always included as the very first CID.

       +-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+
       |1| CID / HopID | --> |1|     CID     | --> |0|     CID     |
       +-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+     +-+-+-+-+-+-+-+-+

                Figure 35: Chaining of context identifiers.

9.  ICN LoWPAN Constants and Variables

   This is a summary of all ICN LoWPAN constants and variables.

   DEFAULT_NDN_HOPLIMIT:  255

10.  Implementation Report and Guidance

   The ICN LoWPAN scheme defined in this document has been implemented
   as an extension of the NDN/CCNx software stack [CCN-LITE] in its IoT
   version on RIOT [RIOT].  An experimental evaluation for NDN over ICN
   LOWPAN with varying configurations has been performed in [ICNLOWPAN].
   Energy profilings and processing time measurements indicate
   significant energy savings, while amortized costs for processing show
   no penalties.

10.1.  Preferred Configuration

   The header compression performance depends on certain aspects and
   configurations.  It works best for the following cases:

   o  Relative time values use a compressible encoding as per Section 7.





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   o  Contextual state (e.g., prefixes) is distributed, such that long
      names can be elided from Interest and data messages.

   o  Frequently used TLV type numbers for CCNx and NDN stay in the
      lower range (< 255).

   Name components are of GenericNameComponent type and are limited to a
   length of 15 bytes to enable compression for all messages.

10.2.  Further Experimental Deployments

   An investigation of ICN LoWPAN in large-scale deployments with
   varying traffic patterns using larger samples of the different board
   types available remains as future work.  This document will be
   revised to progress it to the Standards Track, once sufficient
   operational experience has been acquired.  Experience reports are
   encouraged, particularly in the following areas:

   o  The name compression scheme (Section 5.2) is optimized for short
      name components of GenericNameComponent type.  An empirical study
      on name lengths in different deployments of selected use cases,
      such as smart home, smart city, and industrial IoT can provide
      meaningful reports on necessary name component types and lengths.
      A conclusive outcome helps to understand whether and how extension
      mechanisms are needed (Section 5.3.3).  As a preliminary analysis,
      [ICNLOWPAN] investigates the effectiveness of the proposed
      compression scheme with URLs obtained from the WWW.  Studies on
      CoAP [RFC7252] deployments can offer additional insights on naming
      schemes in the IoT.

   o  The fragmentation scheme (Section 4.2) inherited from 6LoWPAN
      allows for a transparent, hop-wise reassembly of CCNx or NDN
      packets.  Fragment forwarding [I-D.ietf-6lo-minimal-fragment] with
      selective fragment recovery [I-D.ietf-6lo-fragment-recovery] can
      improve the end-to-end latency and reliability, while it reduces
      buffer requirements on forwarders.  Initial evaluations
      ([SFR-ICNLOWPAN]) show that a naive integration of these upcoming
      fragmentation features into ICN LoWPAN renders the hop-wise
      content replication inoperative, since Interest and data messages
      are reassembled end-to-end.  More deployment experiences are
      necessary to gauge the feasibility of different fragmentation
      schemes in ICN LoWPAN.

   o  Context state (Section 8.1) holds information that is shared
      between a set of devices in a LoWPAN.  Fixed name prefixes and
      suffixes are good candidates to be distributed to all nodes in
      order to elide them from request and response messages.  More
      experience and a deeper inspection of currently available and



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      upcoming protocol features is necessary to identify other protocol
      fields.

   o  The distribution and synchronization of contextual state can
      potentially be adopted from Section 7.2 of [RFC6775], but requires
      further evaluations.  While 6LoWPAN uses the Neighbor Discovery
      protocol to disseminate state, CCNx and NDN deployments are
      missing out on a standard mechanism to bootstrap and manage
      configurations.

   o  The stateful en-route compression (Section 8.2) supports a limited
      number of 127 distinct HopIDs that can be simultaneously in use on
      a single node.  Complex deployment scenarios that make use of
      multiple, concurrent requests can provide a better insight on the
      number of open requests stored in the Pending Interest Table of
      memory-constrained devices.  This number can serve as an upper-
      bound and determines whether the HopID length needs to be resized
      to fit more HopIDs to the cost of additional header overhead.

   o  Multiple implementations that generate and deploy the compression
      options of this memo in different ways will also add to the
      experience and understanding of the benefits and limitations of
      the proposed schemes.  Different reports can help to illuminate on
      the complexity of implementing ICN LoWPAN for constrained devices,
      as well as on maintaining interoperability with other
      implementations.

11.  Security Considerations

   Main memory is typically a scarce resource of constrained networked
   devices.  Fragmentation as described in this memo preserves fragments
   and purges them only after a packet is reassembled, which requires a
   buffering of all fragments.  This scheme is able to handle fragments
   for distinctive packets simultaneously, which can lead to overflowing
   packet buffers that cannot hold all necessary fragments for packet
   reassembly.  Implementers are thus urged to make use of appropriate
   buffer replacement strategies for fragments.  The upcoming minimal
   fragment forwarding [I-D.ietf-6lo-minimal-fragment] can potentially
   prevent fragment buffer saturation in forwarders.

   The stateful header compression generates ephemeral HopIDs for
   incoming and outgoing Interests and consumes them on returning Data
   packets.  Forged Interests can deplete the number of available
   HopIDs, thus leading to a denial of compression service for
   subsequent content requests.

   To further alleviate the problems caused by forged fragments or
   Interest initiations, proper protective mechanisms for accessing the



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   link-layer should be deployed.  IEEE 802.15.4, e.g., provides
   capabilities to protect frames and restrict them to a point-to-point
   link, or a group of devices.

12.  IANA Considerations

12.1.  Reserving Space in the 6LoWPAN Dispatch Type Field Registry

   IANA has assigned dispatch values of the "6LoWPAN Dispatch Type
   Field" registry [RFC4944][RFC8025] with Page TBD1 for ICN LoWPAN.
   Table 1 represents updates to the registry.

    +-------------+------+-------------------------------------------+
    | Bit Pattern | Page | Header Type                               |
    +-------------+------+-------------------------------------------+
    |  00 000000  | TBD1 | Uncompressed NDN Interest messages        |
    |  00 100000  | TBD1 | Uncompressed NDN Data messages            |
    |  01 000000  | TBD1 | Uncompressed CCNx Interest messages       |
    |  01 100000  | TBD1 | Uncompressed CCNx Content Object messages |
    |  10 0xxxxx  | TBD1 | Compressed NDN Interest messages          |
    |  10 1xxxxx  | TBD1 | Compressed NDN Data messages              |
    |  11 0xxxxx  | TBD1 | Compressed CCNx Interest messages         |
    |  11 1xxxxx  | TBD1 | Compressed CCNx Content Object messages   |
    +-------------+------+-------------------------------------------+

         Table 1: Dispatch types for NDN and CCNx with page TBD1.

13.  References

13.1.  Normative References

   [ieee802.15.4]
              "IEEE Std. 802.15.4-2015", April 2016,
              <https://standards.ieee.org/findstds/
              standard/802.15.4-2015.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc4944>.






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   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <https://www.rfc-editor.org/info/rfc6282>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

13.2.  Informative References

   [CCN-LITE]
              "CCN-lite: A lightweight CCNx and NDN implementation",
              <http://ccn-lite.net/>.

   [I-D.gundogan-icnrg-ccnx-timetlv]
              Gundogan, C., Schmidt, TC., Oran, D., and M. Waehlisch,
              "An Alternative Delta Time encoding for CCNx using
              Interval Time from RFC5497", draft-gundogan-icnrg-ccnx-
              timetlv-00 (work in progress), November 2019.

   [I-D.ietf-6lo-fragment-recovery]
              Thubert, P., "6LoWPAN Selective Fragment Recovery", draft-
              ietf-6lo-fragment-recovery-21 (work in progress), March
              2020.

   [I-D.ietf-6lo-minimal-fragment]
              Watteyne, T., Thubert, P., and C. Bormann, "On Forwarding
              6LoWPAN Fragments over a Multihop IPv6 Network", draft-
              ietf-6lo-minimal-fragment-15 (work in progress), March
              2020.

   [I-D.irtf-icnrg-flic]
              Tschudin, C., Wood, C., Mosko, M., and D. Oran, "File-Like
              ICN Collections (FLIC)", draft-irtf-icnrg-flic-02 (work in
              progress), November 2019.

   [ICNLOWPAN]
              Gundogan, C., Kietzmann, P., Schmidt, TC., and M.
              Waehlisch, "ICNLoWPAN -- Named-Data Networking in Low
              Power IoT Networks", Proc. of 18th IFIP Networking
              Conference, May 2019,
              <https://doi.org/10.23919/IFIPNetworking.2019.8816850>.






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   [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, <https://doi.org/10.1145/1658939.1658941>.

   [NDN-EXP1]
              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,
              <http://dx.doi.org/10.1145/2660129.2660144>.

   [NDN-EXP2]
              Gundogan, C., Kietzmann, P., Lenders, M., Petersen, H.,
              Schmidt, TC., and M. Waehlisch, "NDN, CoAP, and MQTT: A
              Comparative Measurement Study in the IoT", Proc. of 5th
              ACM Conf. on Information-Centric Networking (ICN-2018) ACM
              DL, pp. 159-171, September 2018,
              <https://doi.org/10.1145/3267955.3267967>.

   [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,
              <https://doi.org/10.1145/3125719.3125737>.

   [NDN-PACKET-SPEC]
              "NDN Packet Format Specification",
              <https://named-data.net/doc/NDN-packet-spec/0.3/>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7476]  Pentikousis, K., Ed., 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,
              <https://www.rfc-editor.org/info/rfc7476>.




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   [RFC7927]  Kutscher, D., Ed., 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,
              <https://www.rfc-editor.org/info/rfc7927>.

   [RFC7945]  Pentikousis, K., Ed., Ohlman, B., Davies, E., Spirou, S.,
              and G. Boggia, "Information-Centric Networking: Evaluation
              and Security Considerations", RFC 7945,
              DOI 10.17487/RFC7945, September 2016,
              <https://www.rfc-editor.org/info/rfc7945>.

   [RFC8025]  Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
              RFC 8025, DOI 10.17487/RFC8025, November 2016,
              <https://www.rfc-editor.org/info/rfc8025>.

   [RFC8569]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Semantics", RFC 8569,
              DOI 10.17487/RFC8569, July 2019,
              <https://www.rfc-editor.org/info/rfc8569>.

   [RFC8609]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Messages in TLV Format", RFC 8609,
              DOI 10.17487/RFC8609, July 2019,
              <https://www.rfc-editor.org/info/rfc8609>.

   [RIOT]     Baccelli, E., Gundogan, C., Hahm, O., Kietzmann, P.,
              Lenders, MS., Petersen, H., Schleiser, K., Schmidt, TC.,
              and M. Waehlisch, "RIOT: an Open Source Operating System
              for Low-end Embedded Devices in the IoT", IEEE Internet of
              Things Journal Vol. 5, No. 6, p. 4428-4440, December 2018,
              <https://doi.org/10.1109/JIOT.2018.2815038>.

   [SFR-ICNLOWPAN]
              Lenders, M., Gundogan, C., Schmidt, TC., and M. Waehlisch,
              "Connecting the Dots: Selective Fragment Recovery in
              ICNLoWPAN", Proc. of 7th ACM Conf. on Information-Centric
              Networking (ICN-2020) ACM DL, pp. 70-76, September 2020,
              <https://doi.org/10.1145/3405656.3418719>.

   [TLV-ENC-802.15.4]
              "CCN and NDN TLV encodings in 802.15.4 packets",
              <https://datatracker.ietf.org/meeting/interim-2015-icnrg-
              01/materials/slides-interim-2015-icnrg-1-2>.






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   [WIRE-FORMAT-CONSID]
              "CCN/NDN Protocol Wire Format and Functionality
              Considerations", <https://datatracker.ietf.org/meeting/
              interim-2015-icnrg-01/materials/slides-interim-2015-icnrg-
              1-8>.














































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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 byte 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 36 depicts the size requirements for a basic, uncompressed NDN
   Interest containing a CanBePrefix TLV, a MustBeFresh TLV, a
   InterestLifetime TLV set to 4 seconds and a HopLimit TLV set to 6.
   Numbers below represent the amount of bytes.

         ------------------------------------,
         Interest TLV            = 2         |
           ---------------------,            |
           Name                 |  2 +       |
             NameComponents      = 2n +      |
                                |  comps_n   |
           ---------------------'             = 21 + 2n + comps_n
           CanBePrefix           = 2         |
           MustBeFresh           = 2         |
           Nonce                 = 6         |
           InterestLifetime      = 4         |
           HopLimit              = 3         |
         ------------------------------------'

         Figure 36: Estimated size of an uncompressed NDN Interest

   Figure 37 depicts the size requirements after compression.









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         ------------------------------------,
         Dispatch Page Switch    = 1         |
         NDN Interset Dispatch   = 2         |
         Interest TLV            = 1         |
         -----------------------,            |
         Name                   |            |
           NameComponents        = n/2 +      = 10 + n/2 + comps_n
                                |  comps_n   |
         -----------------------'            |
         Nonce                   = 4         |
         HopLimit                = 1         |
         InterestLifetime        = 1         |
         ------------------------------------'

          Figure 37: Estimated size of a compressed NDN Interest

   The size difference is:
   11 + 1.5n bytes.

   For the name "/DE/HH/HAW/BT7", the total size gain is 17 bytes, which
   is 43% of the uncompressed packet.

A.1.2.  Data

   Figure 38 depicts the size requirements for a basic, uncompressed NDN
   Data containing a FreshnessPeriod as MetaInfo.  A FreshnessPeriod of
   1 minute is assumed and the value is encoded using 1 byte.  An
   HMACWithSha256 is assumed as signature.  The key locator is assumed
   to contain a Name TLV of length klen.






















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        ------------------------------------,
        Data TLV                = 2         |
          ---------------------,            |
          Name                 |  2 +       |
            NameComponents      = 2n +      |
                               |  comps_n   |
          ---------------------'            |
          ---------------------,            |
          MetaInfo             |            |
            FreshnessPeriod     = 6         |
                               |             = 53 + 2n + comps_n +
          ---------------------'            |  clen + klen
          Content               = 2 + clen  |
          ---------------------,            |
          SignatureInfo        |            |
            SignatureType      |            |
              KeyLocator        = 41 + klen |
          SignatureValue       |            |
            DigestSha256       |            |
          ---------------------'            |
        ------------------------------------'

           Figure 38: Estimated size of an uncompressed NDN Data

   Figure 39 depicts the size requirements for the compressed version of
   the above Data packet.

        ------------------------------------,
        Dispatch Page Switch    = 1         |
        NDN Data Dispatch       = 2         |
        -----------------------,            |
        Name                   |            |
          NameComponents        = n/2 +     |
                               |  comps_n    = 38 + n/2 + comps_n +
        -----------------------'            |  clen + klen
        Content                 = 1 + clen  |
        KeyLocator              = 1 + klen  |
        DigestSha256            = 32        |
        FreshnessPeriod         = 1         |
        ------------------------------------'

            Figure 39: Estimated size of a compressed NDN Data

   The size difference is:
   15 + 1.5n bytes.

   For the name "/DE/HH/HAW/BT7", the total size gain is 21 bytes.




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A.2.  CCNx

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

A.2.1.  Interest

   Figure 40 depicts the size requirements for a basic, uncompressed
   CCNx Interest.  No Hop-By-Hop TLVs are included, the protocol version
   is assumed to be 1 and the reserved field is 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 40: Estimated size of an uncompressed CCNx Interest

   Figure 41 depicts the size requirements after compression.

         ------------------------------------,
         Dispatch Page Switch    = 1         |
         CCNx Interest Dispatch  = 2         |
         Fixed Header            = 3         |
         -----------------------,            |
         Name                   |             = 38 + n/2 + comps_n
           NameSegments          = n/2 +     |
                                |  comps_n   |
         -----------------------'            |
         T_SHA-256               = 32        |
         ------------------------------------'

          Figure 41: Estimated size of a compressed CCNx Interest

   The size difference is:
   18 + 3.5n bytes.

   For the name "/DE/HH/HAW/BT7", the size is reduced by 53 bytes, which
   is 53% of the uncompressed packet.




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A.2.2.  Content Object

   Figure 42 depicts the size requirements for a basic, uncompressed
   CCNx Content Object containing an ExpiryTime Message TLV, an
   HMAC_SHA-256 signature, the signature time and a hash of the shared
   secret key.  In the fixed header, the protocol version is assumed to
   be 1 and the reserved field is assumed to be 0

     ------------------------------------,
     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 42: Estimated size of an uncompressed CCNx Content Object

   Figure 43 depicts the size requirements for a basic, compressed CCNx
   Data.




















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     ------------------------------------,
     Dispatch Page Switch    = 1         |
     CCNx Content Dispatch   = 3         |
     Fixed Header            = 2         |
     -----------------------,            |
     Name                   |            |
       NameSegments          = n/2 +     |
                            |  comps_n    = 89 + n/2 + comps_n + clen
     -----------------------'            |
     ExpiryTime              = 8         |
     Payload                 = 1 + clen  |
     T_HMAC-SHA256           = 32        |
     SignatureTime           = 8         |
     ValidationPayload       = 34        |
     ------------------------------------'

        Figure 43: Estimated size of a compressed CCNx Data Object

   The size difference is:
   35 + 3.5n bytes.

   For the name "/DE/HH/HAW/BT7", the size is reduced by 70 bytes, which
   is 40% of the uncompressed packet containing a 4-byte payload.

Acknowledgments

   This work was stimulated by fruitful discussions in the ICNRG
   research group and the communities of RIOT and CCNlite.  We would
   like to thank all active members for constructive thoughts and
   feedback.  In particular, the authors would like to thank (in
   alphabetical order) Peter Kietzmann, Dirk Kutscher, Martine Lenders,
   Colin Perkins, Junxiao Shi. The hop-wise stateful name compression
   was brought up in a discussion by Dave Oran, which is gratefully
   acknowledged.  Larger parts of this work are inspired by [RFC4944]
   and [RFC6282].  Special mentioning goes to Mark Mosko as well as G.Q.
   Wang and Ravi Ravindran as their previous work in [TLV-ENC-802.15.4]
   and [WIRE-FORMAT-CONSID] provided a good base for our discussions on
   stateless header compression mechanisms.  Many thanks also to Carsten
   Bormann, who contributed in-depth comments during the IRSG review.
   This work was supported in part by the German Federal Ministry of
   Research and Education within the projects I3 and RAPstore.

Authors' Addresses








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   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











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   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

































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