Internet DRAFT - draft-irtf-icnrg-icnlowpan
draft-irtf-icnrg-icnlowpan
ICN Research Group C. Gundogan
Internet-Draft TC. Schmidt
Intended status: Experimental HAW Hamburg
Expires: 31 March 2022 M. Waehlisch
link-lab & FU Berlin
C. Scherb
C. Marxer
C. Tschudin
University of Basel
27 September 2021
ICN Adaptation to LoWPAN Networks (ICN LoWPAN)
draft-irtf-icnrg-icnlowpan-11
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/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 31 March 2022.
Copyright Notice
Copyright (c) 2021 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/
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Please review these documents carefully, as they describe your rights
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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 . . . . . . . . . . . . . . . . . 9
4.2. Adaptation Layer Fragmentation . . . . . . . . . . . . . 10
5. Space-efficient Message Encoding for NDN . . . . . . . . . . 11
5.1. TLV Encoding . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Name TLV Compression . . . . . . . . . . . . . . . . . . 13
5.3. Interest Messages . . . . . . . . . . . . . . . . . . . . 13
5.3.1. Uncompressed Interest Messages . . . . . . . . . . . 13
5.3.2. Compressed Interest Messages . . . . . . . . . . . . 14
5.3.3. Dispatch Extension . . . . . . . . . . . . . . . . . 16
5.4. Data Messages . . . . . . . . . . . . . . . . . . . . . . 17
5.4.1. Uncompressed Data Messages . . . . . . . . . . . . . 17
5.4.2. Compressed Data Messages . . . . . . . . . . . . . . 17
5.4.3. Dispatch Extension . . . . . . . . . . . . . . . . . 19
6. Space-efficient Message Encoding for CCNx . . . . . . . . . . 20
6.1. TLV Encoding . . . . . . . . . . . . . . . . . . . . . . 20
6.2. Name TLV Compression . . . . . . . . . . . . . . . . . . 20
6.3. Interest Messages . . . . . . . . . . . . . . . . . . . . 20
6.3.1. Uncompressed Interest Messages . . . . . . . . . . . 20
6.3.2. Compressed Interest Messages . . . . . . . . . . . . 21
6.3.3. Dispatch Extension . . . . . . . . . . . . . . . . . 26
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6.4. Content Objects . . . . . . . . . . . . . . . . . . . . . 27
6.4.1. Uncompressed Content Objects . . . . . . . . . . . . 27
6.4.2. Compressed Content Objects . . . . . . . . . . . . . 27
6.4.3. Dispatch Extension . . . . . . . . . . . . . . . . . 30
7. Compressed Time Encoding . . . . . . . . . . . . . . . . . . 31
8. Stateful Header Compression . . . . . . . . . . . . . . . . . 32
8.1. LoWPAN-local State . . . . . . . . . . . . . . . . . . . 32
8.2. En-route State . . . . . . . . . . . . . . . . . . . . . 32
8.3. Integrating Stateful Header Compression . . . . . . . . . 34
9. ICN LoWPAN Constants and Variables . . . . . . . . . . . . . 35
10. Implementation Report and Guidance . . . . . . . . . . . . . 35
10.1. Preferred Configuration . . . . . . . . . . . . . . . . 35
10.2. Further Experimental Deployments . . . . . . . . . . . . 36
11. Security Considerations . . . . . . . . . . . . . . . . . . . 37
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
12.1. Reserving Space in the 6LoWPAN Dispatch Type Field
Registry . . . . . . . . . . . . . . . . . . . . . . . . 38
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
13.1. Normative References . . . . . . . . . . . . . . . . . . 38
13.2. Informative References . . . . . . . . . . . . . . . . . 39
Appendix A. Estimated Size Reduction . . . . . . . . . . . . . . 42
A.1. NDN . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
A.1.1. Interest . . . . . . . . . . . . . . . . . . . . . . 42
A.1.2. Data . . . . . . . . . . . . . . . . . . . . . . . . 43
A.2. CCNx . . . . . . . . . . . . . . . . . . . . . . . . . . 45
A.2.1. Interest . . . . . . . . . . . . . . . . . . . . . . 45
A.2.2. Content Object . . . . . . . . . . . . . . . . . . . 46
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 47
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
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
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LLNs include an unreliable environment, low 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 3 ...
+---+---+---+---+---
| 0 | P | M | C |
+---+---+---+---+---
Figure 4: Base dispatch format for ICN LoWPAN
P: Protocol 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.
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C: Compression 0: The message is uncompressed.
1: The message is compressed.
ICN LoWPAN frames with compressed CCNx and NDN messages (C=1) use the
extended dispatch format in Figure 5.
0 1 2 3 ... ...
+---+---+---+---+...+---+---+
| 0 | P | M | 1 | |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.
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.
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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.
+------...------+----...----+--------+------...-------+--------...
| IEEE 802.15.4 | Frag. 1st | Page | ICN LoWPAN | Payload /
+------...------+----...----+--------+------...-------+--------...
+------...------+----...----+--------...
| IEEE 802.15.4 | Frag. 2nd | Payload /
+------...------+----...----+--------...
.
.
.
+------...------+----...----+--------...
| IEEE 802.15.4 | Frag. Nth | Payload /
+------...------+----...----+--------...
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Figure 8: Fragmentation scheme
+------...------+--------+------...-------+--------...
| IEEE 802.15.4 | Page | ICN LoWPAN | Payload /
+------...------+--------+------...-------+--------...
Figure 9: Reassembled ICN LoWPAN frame
The 6LoWPAN Fragment Forwarding (6FF) [RFC8930] 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 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 encode type and length
fields using self-delimiting numeric values (SDNVs) [RFC6256]
commonly known from DTN protocols. Instead of using the first byte
as a marker for the number of following bytes, SDNVs use a single bit
to indicate subsequent bytes.
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+==========+==========================+==========================+
| Value | NDN TLV encoding | SDNV encoding |
+==========+==========================+==========================+
| 0 | 0x00 | 0x00 |
+----------+--------------------------+--------------------------+
| 127 | 0x7F | 0x7F |
+----------+--------------------------+--------------------------+
| 128 | 0x80 | 0x81 0x00 |
+----------+--------------------------+--------------------------+
| 253 | 0xFD 0x00 0xFD | 0x81 0x7D |
+----------+--------------------------+--------------------------+
| 2^14 - 1 | 0xFD 0x3F 0xFF | 0xFF 0x7F |
+----------+--------------------------+--------------------------+
| 2^14 | 0xFD 0x40 0x00 | 0x81 0x80 0x00 |
+----------+--------------------------+--------------------------+
| 2^16 | 0xFE 0x00 0x01 0x00 0x00 | 0x84 0x80 0x00 |
+----------+--------------------------+--------------------------+
| 2^21 - 1 | 0xFE 0x00 0x1F 0xFF 0xFF | 0xFF 0xFF 0x7F |
+----------+--------------------------+--------------------------+
| 2^21 | 0xFE 0x00 0x20 0x00 0x00 | 0x81 0x80 0x80 0x00 |
+----------+--------------------------+--------------------------+
| 2^28 - 1 | 0xFE 0x0F 0xFF 0xFF 0xFF | 0xFF 0xFF 0xFF 0x7F |
+----------+--------------------------+--------------------------+
| 2^28 | 0xFE 0x1F 0x00 0x00 0x00 | 0x81 0x80 0x80 0x80 0x00 |
+----------+--------------------------+--------------------------+
| 2^32 | 0xFF 0x00 0x00 0x00 0x01 | 0x90 0x80 0x80 0x80 0x00 |
| | 0x00 0x00 0x00 0x00 | |
+----------+--------------------------+--------------------------+
| 2^35 - 1 | 0xFF 0x00 0x00 0x00 0x07 | 0xFF 0xFF 0xFF 0xFF 0x7F |
| | 0xFF 0xFF 0xFF 0xFF | |
+----------+--------------------------+--------------------------+
| 2^35 | 0xFF 0x00 0x00 0x00 0x08 | 0x81 0x80 0x80 0x80 0x80 |
| | 0x00 0x00 0x00 0x00 | 0x00 |
+----------+--------------------------+--------------------------+
Table 1: NDN TLV encoding compared to SDNVs.
Table 1 compares the required bytes for encoding a few selected
values using the NDN TLV encoding and SDNVs. For values up to 127,
both methods require a single byte. Values in the range [128;252]
encode as one byte for the NDN TLV scheme, while SDNVs require two
bytes. Starting at value 253, SDNVs require a less or equal amount
of bytes compared to the NDN TLV encoding.
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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
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 10.
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 10: 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 0 and the P as well as the M flag to
0 (Figure 11). The Interest message is handed to the NDN network
stack without modifications.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
+---+---+---+---+---+---+---+---+
Figure 11: Dispatch format for uncompressed NDN Interest messages
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5.3.2. Compressed Interest Messages
The compressed Interest message uses the extended dispatch format
(Figure 5) and sets the C flag to 1, the P flag to 0 and the M flag
to 0. If an Interest message contains TLVs that are not 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 12. The
InterestLifetime is encoded as described in Section 7. On
decompression, this encoding may yield an Interestlifetime that
is smaller than the original value.
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 12.
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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 12: Compression of NDN LoWPAN Interest Message
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 13.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 0 | 1 |PFX|FRE|FWD|APM|DIG| RSV |CID|EXT|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 13: Dispatch format for compressed NDN Interest messages
PFX: CanBePrefix TLV 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
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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.
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.
5.3.3. Dispatch Extension
The EXT_0 byte follows the description in Section 4.1.1 and is
illustrated in Figure 14.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| NCS | RSV |EXT|
+---+---+---+---+---+---+---+---+
Figure 14: EXT_0 format
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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 flag to 0, the P flag to 0 and the M flag to 1 (Figure 15).
The Data message is handed to the NDN network stack without
modifications.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
+---+---+---+---+---+---+---+---+
Figure 15: Dispatch format for uncompressed NDN Data messages
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 M flags to 1. The P flag is
set to 0. 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.
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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 16.
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 16: Compression of NDN LoWPAN Data Message
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 17.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 0 | 1 | 1 |FBI|CON|KLO| RSV |CID|EXT|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 17: Dispatch format for compressed NDN Data messages
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.
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.
5.4.3. Dispatch Extension
The EXT_0 byte follows the description in Section 4.1.1 and is
illustrated in Figure 18.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| NCS | RSV |EXT|
+---+---+---+---+---+---+---+---+
Figure 18: 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. 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 M flag to 0. The P flag is
set to 1 (Figure 19). The Interest message is handed to the CCNx
network stack without modifications.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
+---+---+---+---+---+---+---+---+
Figure 19: 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 P flags to 1. The M flag is set to 0.
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 version is elided from the Fixed Header and assumed to be 1.
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 Interest message is visualized in
Figure 20.
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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 20: Compression of CCNx LoWPAN Interest Message
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 21.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 1 | 0 | 1 |FLG|PTY|HPL|FRS|PAY|ILT|MGH|KIR|CHR|VAL|CID|EXT|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 21: Dispatch format for compressed CCNx Interest messages
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
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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.
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.
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.
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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 ContentObject
HashRestriction 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 ContentObjectHashRestriction TLV is
omitted.
VAL: Optional ValidationAlgorithm and ValidationPayload TLVs 0: No
validation related TLVs are present in the Interest
message.
1: Val
idation 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.
CID: Context Identifier See Figure 5.
EXT: Extension 0: No extension byte follows.
1: Extension byte EXT_0 follows immediately. See
Section 6.3.3.
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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 22: Dispatch for Interset Validations
ValidationALg: Optional ValidationAlgorithm TLV 0000: An
uncompressed ValidationAlgorithm TLV is included.
0001: A T_CRC32C Va
lidationAlgorithm TLV is assumed, but no
ValidationAlgorithm TLV is included.
0010: A T_CRC32C Va
lidationAlgorithm 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.
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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: Th
e KeyId TLV is absent.
01: Th
e 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.
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 23.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| NCS | RSV |EXT|
+---+---+---+---+---+---+---+---+
Figure 23: 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 flag to 0, the P and M flags to 1
(Figure 24). The Content object is handed to the CCNx network stack
without modifications.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
+---+---+---+---+---+---+---+---+
Figure 24: 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 C, P, as well as the M flag to 1. 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:
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1. The version is elided from the Fixed Header and assumed to be 1.
2. The PacketType field is elided from the Fixed Header.
3. 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 25.
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 25: Compression of CCNx LoWPAN Data Message
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 26.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | 1 |FLG|FRS|PAY|RCT|MGH| PLTYP |EXP|VAL|RSV|CID|EXT|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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Figure 26: Dispatch format for compressed CCNx Content objects
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.
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
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tion 6.3.2.
RSV: Reserved Must be set to 0.
CID: Context Identifier See Figure 5.
EXT: Extension 0: No extension byte follows.
1: Extension byte EXT_0 follows immediately. See
Section 6.4.3.
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 27.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| NCS | RSV |EXT|
+---+---+---+---+---+---+---+---+
Figure 27: 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.
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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 8-bit compact time representation for
relative time values described in Section 5 of [RFC5497] with the
constant factor C set to C := 1/32.
Valid time offsets in CCNx and NDN reach from a few milliseconds
(e.g., lifetime of low-latency Interests) to several years (e.g.,
content freshness periods in caches). Therefore, this document adds
two modifications to the compression algorithm.
The first modification is the inclusion of a subnormal form
[IEEE.754.2019] for time-codes with exponent 0 to provide an
increased precision and a gradual underflow for the smallest numbers.
The formula is changed as follows (a := mantissa; b := exponent):
Subnormal (b == 0): (0 + a/8) * 2 * C
Normalized (b > 0): (1 + a/8) * 2^b * C (see [RFC5497])
This configuration allows for the following ranges:
* Minimum subnormal number: 0 seconds
* 2nd minimum subnormal number: ~0.007812 seconds
* Maximum subnormal number: ~0.054688 seconds
* Minimum normalized number: ~0.062500 seconds
* 2nd minimum normalized number: ~0.070312 seconds
* Maximum normalized number: ~3.99 years
The second modification only applies to uncompressible time offsets
that are outside any security envelope. An invalid time-value MUST
be set to the largest valid time-value that is smaller than the
invalid input value before compression.
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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 28: 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 28). If set the most significant bit
indicates the presence of another, subsequent ContextID byte (see
Figure 33).
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 29.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | HopID |
+---+---+---+---+---+---+---+---+
Figure 29: 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 30).
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 30: Setting compression state en-route (Interest).
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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 31).
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 31: 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.
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 32.
...-------+--------+-------...-------+--...-+-------...
/ ... | Page | ICN LoWPAN Disp.| CIDs | Payload /
...-------+--------+-------...-------+--...-+-------...
Figure 32: LoWPAN Encapsulation with ICN LoWPAN and CIDs
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Multiple CIDs are chained together, with the most significant bit
indicating the presence of a subsequent CID (Figure 33). 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 33: 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:
* Signed time offsets compress as per Section 7 without the need for
rounding.
* Contextual state (e.g., prefixes) is distributed, such that long
names can be elided from Interest and data messages.
* 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.
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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:
* 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.
* The fragmentation scheme (Section 4.2) inherited from 6LoWPAN
allows for a transparent, hop-wise reassembly of CCNx or NDN
packets. Fragment forwarding [RFC8930] with selective fragment
recovery [RFC8931] 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.
* 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
upcoming protocol features is necessary to identify other protocol
fields.
* 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.
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* 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.
* 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. Minimal fragment
forwarding [RFC8930] 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
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
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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 2
represents updates to the registry.
+=============+======+===========================================+
| Bit Pattern | Page | Header Type |
+=============+======+===========================================+
| 00 000000 | TBD1 | Uncompressed NDN Interest messages |
+-------------+------+-------------------------------------------+
| 00 01xxxx | TBD1 | Compressed NDN Interest messages |
+-------------+------+-------------------------------------------+
| 00 100000 | TBD1 | Uncompressed NDN Data messages |
+-------------+------+-------------------------------------------+
| 00 11xxxx | TBD1 | Compressed NDN Data messages |
+-------------+------+-------------------------------------------+
| 01 000000 | TBD1 | Uncompressed CCNx Interest messages |
+-------------+------+-------------------------------------------+
| 01 01xxxx | TBD1 | Compressed CCNx Interest messages |
+-------------+------+-------------------------------------------+
| 01 100000 | TBD1 | Uncompressed CCNx Content Object messages |
+-------------+------+-------------------------------------------+
| 01 11xxxx | TBD1 | Compressed CCNx Content Object messages |
+-------------+------+-------------------------------------------+
Table 2: Dispatch types for NDN and CCNx with page TBD1.
13. References
13.1. Normative References
[IEEE.754.2019]
Institute of Electrical and Electronics Engineers, C/MSC -
Microprocessor Standards Committee, "Standard for
Floating-Point Arithmetic", June 2019,
<https://standards.ieee.org/content/ieee-standards/en/
standard/754-2019.html>.
[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>.
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[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>.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497,
DOI 10.17487/RFC5497, March 2009,
<https://www.rfc-editor.org/info/rfc5497>.
[RFC6256] Eddy, W. and E. Davies, "Using Self-Delimiting Numeric
Values in Protocols", RFC 6256, DOI 10.17487/RFC6256, May
2011, <https://www.rfc-editor.org/info/rfc6256>.
[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.irtf-icnrg-flic]
Tschudin, C., Wood, C., Mosko, M., and D. Oran, "File-Like
ICN Collections (FLIC)", Work in Progress, Internet-Draft,
draft-irtf-icnrg-flic-02, 4 November 2019,
<http://www.ietf.org/internet-drafts/draft-irtf-icnrg-
flic-02.txt>.
[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>.
[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>.
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[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>.
[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>.
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[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>.
[RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On
Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6
Network", RFC 8930, DOI 10.17487/RFC8930, November 2020,
<https://www.rfc-editor.org/info/rfc8930>.
[RFC8931] Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal
Area Network (6LoWPAN) Selective Fragment Recovery",
RFC 8931, DOI 10.17487/RFC8931, November 2020,
<https://www.rfc-editor.org/info/rfc8931>.
[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>.
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[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>.
[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>.
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 34 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.
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------------------------------------,
Interest TLV = 2 |
---------------------, |
Name | 2 + |
NameComponents = 2n + |
| comps_n |
---------------------' = 21 + 2n + comps_n
CanBePrefix = 2 |
MustBeFresh = 2 |
Nonce = 6 |
InterestLifetime = 4 |
HopLimit = 3 |
------------------------------------'
Figure 34: Estimated size of an uncompressed NDN Interest
Figure 35 depicts the size requirements after compression.
------------------------------------,
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 35: 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 36 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 36: Estimated size of an uncompressed NDN Data
Figure 37 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 37: 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 38 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 38: Estimated size of an uncompressed CCNx Interest
Figure 39 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 39: 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 40 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 40: Estimated size of an uncompressed CCNx Content Object
Figure 41 depicts the size requirements for a basic, compressed CCNx
Data.
------------------------------------,
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 |
------------------------------------'
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Figure 41: 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 and Lars Eggert, 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
Cenk Gundogan
HAW Hamburg
Berliner Tor 7
D-20099 Hamburg
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
D-20099 Hamburg
Germany
Email: t.schmidt@haw-hamburg.de
URI: http://inet.haw-hamburg.de/members/schmidt
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Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
D-10318 Berlin
Germany
Email: mw@link-lab.net
URI: http://www.inf.fu-berlin.de/~waehl
Christopher Scherb
University of Basel
Spiegelgasse 1
CH-4051 Basel
Switzerland
Email: christopher.scherb@unibas.ch
Claudio Marxer
University of Basel
Spiegelgasse 1
CH-4051 Basel
Switzerland
Email: claudio.marxer@unibas.ch
Christian Tschudin
University of Basel
Spiegelgasse 1
CH-4051 Basel
Switzerland
Email: christian.tschudin@unibas.ch
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