Internet DRAFT - draft-gundogan-icnrg-ccnlowpan
draft-gundogan-icnrg-ccnlowpan
ICN Research Group C. Gundogan
Internet-Draft T. Schmidt
Intended status: Experimental HAW Hamburg
Expires: January 17, 2019 M. Waehlisch
link-lab & FU Berlin
C. Scherb
C. Marxer
C. Tschudin
University of Basel
July 16, 2018
ICN Adaptation to LowPAN Networks (ICN LoWPAN)
draft-gundogan-icnrg-ccnlowpan-02
Abstract
In this document, a convergence layer for CCNx and NDN over IEEE
802.15.4 LoWPAN networks is defined. A new frame format is specified
to adapt CCNx and NDN packets to the small MTU size of IEEE 802.15.4.
For that, syntactic and semantic changes to the TLV-based header
formats are described. To support compatibility with other LoWPAN
technologies that may coexist on a wireless medium, the dispatching
scheme provided by 6LoWPAN is extended to include new dispatch types
for CCNx and NDN. Additionally, the link fragmentation component of
the 6LoWPAN dispatching framework is applied to ICN chunks. Basic
improvements in efficiency are advised by stateless and stateful
compression schemes.
Status of This Memo
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This Internet-Draft will expire on January 17, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
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to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of ICN LoWPAN . . . . . . . . . . . . . . . . . . . 5
3.1. Link-Layer Convergence . . . . . . . . . . . . . . . . . 5
3.2. Stateless Header Compression . . . . . . . . . . . . . . 5
3.3. Stateful Header Compression . . . . . . . . . . . . . . . 6
4. IEEE 802.15.4 Adaptation . . . . . . . . . . . . . . . . . . 8
4.1. LoWPAN Encapsulation . . . . . . . . . . . . . . . . . . 8
4.2. Link Fragmentation . . . . . . . . . . . . . . . . . . . 9
4.3. Integrating Stateful Header Compression . . . . . . . . . 10
5. ICN LoWPAN for NDN . . . . . . . . . . . . . . . . . . . . . 11
5.1. TLV Encoding . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Name TLV Compression . . . . . . . . . . . . . . . . . . 13
5.3. Interest Messages . . . . . . . . . . . . . . . . . . . . 14
5.4. Data Messages . . . . . . . . . . . . . . . . . . . . . . 16
6. ICN LoWPAN for CCNx . . . . . . . . . . . . . . . . . . . . . 18
6.1. TLV Encoding . . . . . . . . . . . . . . . . . . . . . . 18
6.2. Name TLV Compression . . . . . . . . . . . . . . . . . . 18
6.3. Interest Messages . . . . . . . . . . . . . . . . . . . . 18
6.4. Content Objects . . . . . . . . . . . . . . . . . . . . . 24
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8.1. Page Switch Dispatch Type . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Estimated Size Reduction . . . . . . . . . . . . . . 30
A.1. NDN . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.1.1. Interest . . . . . . . . . . . . . . . . . . . . . . 30
A.1.2. Data . . . . . . . . . . . . . . . . . . . . . . . . 31
A.2. CCNx . . . . . . . . . . . . . . . . . . . . . . . . . . 33
A.2.1. Interest . . . . . . . . . . . . . . . . . . . . . . 33
A.2.2. Data . . . . . . . . . . . . . . . . . . . . . . . . 34
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 35
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
The Internet of Things (IoT) has been identified as a promising
deployment area for Information Centric Networks (ICN), as
infrastructureless access to content, resilient forwarding, and in-
network data replication have shown noteable advantages over the
traditional host-to-host approach on the Internet [NDN-EXP]. Recent
studies [NDN-MAC] have shown that an appropriate mapping to link
layer technologies has a large impact on the practical performance of
an ICN. This will be even more relevant in the context of IoT
communication where nodes often exchange messages via low-power
wireless links under lossy conditions. In this memo, we address the
base adaptation of data chunks to such link layers for the ICN
flavors NDN [NDN] and CCNx.
The IEEE 802.15.4 [ieee802.15.4] link layer is used in low-power and
lossy networks (see "LLN" in [RFC7228]), in which devices are
typically battery-operated and constrained in resources.
Characteristics of LLNs include an unreliable environment, low
bandwidth transmissions, and increased latencies. IEEE 802.15.4
admits a maximum physical layer packet size of 127 octets. The
maximum frame header size is 25 octets, which leaves 102 octets for
the payload. IEEE 802.15.4 security features further reduce this
payload length by up to 21 octets, yielding a net of 81 octets for
CCNx or NDN packet headers, signatures and content.
6LoWPAN [RFC4944][RFC6282] is a convergence layer that provides frame
formats, header compression and link fragmentation for IPv6 packets
in IEEE 802.15.4 networks. The 6LoWPAN adaptation introduces a
dispatching framework that prepends further information to 6LoWPAN
packets, including a protocol identifier for IEEE 802.15.4 payload
and meta information about link fragmentation.
Prevalent Type-Length-Value (TLV) based packet formats such as in
CCNx and NDN are designed to be generic and extensible. This leads
to header verbosity which is inappropriate in constrained
environments of IEEE 802.15.4 links. This document presents ICN
LoWPAN, a convergence layer for IEEE 802.15.4 motivated by 6LoWPAN
that compresses packet headers of CCNx as well as NDN and allows for
an increased payload size per packet. Additionally by reusing the
dispatching framwork defined by 6LoWPAN, compatibility between
coexisting wireless networks of competing technologies is enabled.
This also allows to reuse the link fragmentation scheme specified by
6LoWPAN for ICN LoWPAN.
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ICN LoWPAN utilizes a more space efficient representation of CCNx and
NDN packet formats. This syntactic change is described for CCNx and
NDN separately, as the header formats and TLV encodings differ
largely. For further reductions, default header values suitable for
constrained IoT networks are selected in order to elide corresponding
TLVs.
In a typical IoT scenario (see Figure 1), embedded devices are
interconnected via quasi-stationary infrastructure whith a border
router (BR) interconnecting the constrained LoWPAN networks via some
Gateway with the public Internet. In ICN based IoT networks,
Interest and Data messages transparently travel through the BR up and
down between a Gateway and the embedded devices within the
constrained LoWPANs.
|Gateway Services|
-------------------------
|
,--------,
| |
| BR |
| |
'--------'
LoWPAN
O O
O
O O embedded
O O O devices
O O
Figure 1: IoT Stub Network
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The use of the term, "silently ignore" is not defined in RFC 2119.
However, the term is used in this document and can be similarly
construed.
This document uses the terminology of [RFC7476], [RFC7927], and
[RFC7945] for ICN entities.
The following terms are used in the document and defined as follows:
ICN LoWPAN: Information-Centric Networking over Low-power Wireless
Personal Area Network
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LLN Low-Power and Lossy Network
CCNx: Content-Centric Networking Architecture
NDN: Named Data Networking
3. Overview of ICN LoWPAN
3.1. Link-Layer Convergence
ICN LoWPAN provides a convergence layer that maps ICN packets onto
constrained link-layer technologies. This includes features such as
link-layer fragmentation, protocol separation on the link-layer
level, and link-layer address mappings. The stack traversal is
visualized in Figure 2.
Device 1 Device 2
,------------------, Router ,------------------,
| Application . | __________________ | ,-> Application |
|----------------|-| | NDN / CCNx | |-|----------------|
| NDN / CCNx | | | ,--------------, | | | NDN / CCNx |
|----------------|-| |-|--------------|-| |-|----------------|
| ICN LoWPAN | | | | ICN LoWPAN | | | | ICN LoWPAN |
|----------------|-| |-|--------------|-| |-|----------------|
| Link-Layer | | | | Link-Layer | | | | Link-Layer |
'----------------|-' '-|--------------|-' '-|----------------'
'--------' '---------'
Figure 2: ICN LoWPAN convergence layer for IEEE 802.15.4
Section 4 of this document defines the convergence layer for IEEE
802.15.4.
3.2. Stateless Header Compression
ICN LoWPAN also defines a stateless header compression scheme with
the main purpose of reducing header overhead of ICN packets. This is
of particular importance for link-layers with small MTUs. The
stateless compression does not require pre-configuration of global
state.
The CCNx and NDN header formats are composed of Type-Length-Value
(TLV) fields to encode header data. The advantage of TLVs is its
native support of variable-sized data. The main disadvantage of TLVs
is the verbosity that results from storing the type and length of the
encoded data.
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The stateless header compression scheme makes use of compact bit
fields to indicate the presence of mandatory and optional TLVs in the
uncompressed packet. The order of set bits in the bit fields
corresponds to the order of each TLV in the packet. Further
compression is achieved by specifying default values and reducing the
codomain of certain header fields.
Figure 3 demonstrates the stateless header compression idea. In this
example, the first type of the first TLV is removed and the
corresponding bit in the bit field is set. The second TLV represents
a fixed-length TLV (e.g. the Nonce TLV in NDN), so that the type and
the length fields are removed. The third TLV represents a boolean
TLV (e.g. the MustBeFresh selector in NDN) and is missing the type,
length and the value field.
+---+---+---+---+---+---+---+---+
| 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | Bit field
+---+---+---+---+---+---+---+---+
| | |
,--' '-----------, '- boolean
| |
+-------+--------------+-------------+
| LEN | VALUE | VALUE |
+-------+--------------+-------------+
Figure 3: Compression using a compact bit field to encode context
information.
3.3. Stateful Header Compression
ICN LoWPAN further employs 2 stateful compression schemes to enhance
size reductions. These mechanisms rely on shared contexts that are
either distributed and maintained in the whole LoWPAN, or are
generated on-demand for a particular Interest-data path.
3.3.1. LoWPAN-local State
A context identifier (CID) is a 1-octet wide number that refers to a
particular conceptual context between network devices and MAY be used
to replace frequently appearing information, like name prefixes,
suffixes, or meta information, such as Interest lifetime.
The initial distribution and maintenance of shared context is out of
scope. Frames containing unknown or invalid CIDs are silently
discarded.
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3.3.2. 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 to
the original Name TLV, or they contain the original Name TLV as a
prefix. ICN LoWPAN reduces this duplication in responses by
replacing Name TLVs with 1-octet wide HopIDs. While an Interest is
forwarded, each hop generates an ephemeral HopID that is tied to a
PIT entry. Each HopID MUST be unique within the local PIT and only
exist 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 4).
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 4: 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
elided fully. Otherwise, the distinct 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 before forwarding
the reponse (Figure 5).
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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 | |
+--------+------++------+------+ +--------+------++------+------+
| ^ |
send | '----------------------, ,---' send
v match | v
,---, h_A ,---, h_B ,---,
| A | <------------------------ | B | <------------------------ | C |
'---' '---' '---'
Figure 5: Eliding Name TLVs using en-route state (data).
4. IEEE 802.15.4 Adaptation
4.1. LoWPAN Encapsulation
The IEEE 802.15.4 frame header does not provide a protocol identifier
for its payload. This causes problems of misinterpreting frames when
several networks coexist on the same link layer. To mitigate errors,
6LoWPAN defines dispatches as encapsulation headers for IEEE 802.15.4
frames (see Section 5 of [RFC4944]). Multiple LoWPAN encapsulation
headers can prepend the actual payload and each encapsulation header
is identified by a dispatch type.
[RFC8025] further specifies dispatch pages to switch between
different contexts. When a LoWPAN parser encounters a "Page switch"
LoWPAN encapsulation header, then all following encapsulation headers
are interpreted by using a dispatch table as specified by the "Page
switch" header. Page 0 and page 1 are reserved for 6LoWPAN. This
document uses page 2 ("1111 0010 (0xF2)") for NDN and page 3 ("1111
0011 (0xF3)") for CCNx.
The base dispatch format (Figure 6) is used and extended by CCNx and
NDN in Section 5 and Section 6.
0 1 2 ... 7
+---+---+-----------------------+
| C | M | |
+---+---+-----------------------+
Figure 6: Base dispatch format for NDN
C: Compression
0: The message is uncompressed.
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1: The message is compressed.
M: Message Type
0: The payload contains a Interest message.
1: The payload contains a Data message.
The encapsulation format for ICN LoWPAN identifying an NDN Interest
message is exemplarily displayed in Figure 7.
+---------------+------------+--------+----------------+-------+
| IEEE 802.15.4 | Dispatches | Page 2 | NDN Dispatches | Payl. /
+---------------+------------+--------+----------------+-------+
Figure 7: LoWPAN Encapsulation of NDN Interest with ICN LoWPAN
IEEE 802.15.4: The IEEE 802.15.4 header.
Dispatches: Optional additional dispatch types.
Page 2: Page Switch 2 (0xF2) for NDN.
NDN Dispatches: NDN dispatches as defined in Section 5.
Payload: The actual (un-)compressed NDN Interest.
4.2. Link Fragmentation
Section 5.3 of [RFC4944] defines a protocol independent fragmentation
dispatch type, a fragmentation header for the first fragment and a
separate fragmentation header for subsequent fragments. ICN LoWPAN
adopts the fragmentation handling of [RFC4944].
The Fragmentation LoWPAN header can encapsulate other dispatch
headers. The order of dispatch types is adopted from [RFC4944].
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 2 | 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 2 | ICN LoWPAN | Payload /
+---------------+--------+----------------+---------+
Figure 9: Reassembled ICN LoWPAN frame
4.3. Integrating Stateful Header Compression
4.3.1. LoWPAN-Local State
A CID is appended to the last ICN LoWPAN dispatch octet. Multiple
CIDs are chained together, whereas the most significant bit indicates
the presence of a subsequent CID (Figure 10).
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|1| CID | --> |1| CID | --> |0| CID |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 10: Multiple 1-octet wide context identifiers.
4.3.2. En-Route State
The HopID is included as the very first CID. To distinguish the
HopID from a typical LoWPAN-local CID, the 1st bit MUST be set
(Figure 11). This yields 64 distinct HopIDs. If this range (0..63)
is exhausted, the messages MUST be sent without en-route state
compression until new HopIDs are available.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| X | 1 | HopID |
+---+---+---+---+---+---+---+---+
Figure 11: Context Identifier as HopID.
5. ICN LoWPAN 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 octets. Figure 12 shows the NDN TLV encoding scheme.
If the type or length number is less than "253", then that number is
encoded into the actual type or length field (Figure 12 a). If the
number is greater or equals "253" and fits into 2 octets, then the
type or lengh field is set to "253" and the number is encoded in the
next following 2 octets in network byte order, i.e., from the most
significant byte (MSB) to the least significant byte (LSB) (Figure 12
b). If the number is greater than 2 octets and fits into 4 octets,
then the type or length field is set to "254" and the number is
encoded in the subsequent 4 octets in network byte order (Figure 12
c). For greater numbers, the type or length field is set to "255"
and the number is encoded in the subsequent 8 octets in network byte
order (Figure 12 d).
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
a) | < 253 |
+-+-+-+-+-+-+-+-+
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
b) | 253 | MSB LSB |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 254 | MSB /
c) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSB |
+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 255 | MSB /
+-+-+-+-+-+-+-+-+ +
d) | /
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSB |
+-+-+-+-+-+-+-+-+
Figure 12: NDN TLV encoding scheme
In this document, compressed NDN TLVs make use of a different TLV
scheme that puts more emphasis on size reduction. Instead of using
the first octet as a marker for the number of following octets, the
compressed NDN TLV scheme uses a method to chain a variable number of
octets together. If an octet equals "255 (0xFF)", then the following
octet will also be interpreted. The actual value of a chain equals
the sum of all links.
If the type or length number is less than "255", then that number is
encoded into the actual type or length field (Figure 13 a). If the
type or length number (X) fits into 2 octets, then the first octet is
set to "255" and the subsequent octet equals "X mod 255" (Figure 13
b). Following this scheme, a variable-sized number (X) is encoded
using multiple octets of "255" with a trailing octet containing "X
mod 255" (Figure 13 c).
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0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
a) | < 255 (X) | = X
+-+-+-+-+-+-+-+-+
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
b) | 255 | < 255 (X) | = 255 + X
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-.....-+-+-+-+-+-+-+-+-+-+-+
c) | 255 | 255 | < 255 (X) | = (N * 255) + X
+-+-+-+-+-+-+-+-+-+-+-.....-+-+-+-+-+-+-+-+-+-+-+
(N - 1)
Figure 13: Compressed NDN TLV encoding scheme
5.2. Name TLV Compression
This Name TLV compression encodes length fields of two consecutive
NameComponent TLVs into one octet, using 4 bits each. This process
limits the length of a NameComponent TLV to 15 octets. A length of 0
marks the end of the compressed Name TLV.
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 14: Name TLV compression for /HAW/Room/481/Humid/99
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5.3. Interest Messages
5.3.1. Uncompressed Interest Messages
An uncompressed Interest message uses the base dispatch format (see
Figure 6) and sets the C as well as the M flag to "0" (Figure 15).
"resv" MUST be set to 0. The Interest message is handed to the NDN
network stack without modifications.
0 1 2 ... 7
+---+---+-----------------------+
| 0 | 0 | resv |
+---+---+-----------------------+
Figure 15: Dispatch format for uncompressed NDN Interest messages
5.3.2. Compressed Interest Messages
The compressed Interest message uses the base dispatch format and
sets the C flag to "1" and the M flag to "0". By default, the
Interest 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. Otherwise, the message MUST be sent
uncompressed.
3. The InterestLifetime TLV length is set to 2. Messages with
lifetimes that require more than 2 octets MUST be sent
uncompressed.
4. The Nonce TLV, InterestLifetime TLV and HopLimit TLV MUST be
moved to the end of the compressed Interest, keeping the order 1)
Nonce TLV, 2) InterestLifetime TLV and 3) HopLimit TLV.
5. The Type and Length fields of Nonce TLV, InterestLifetime TLV and
HopLimit TLV are elided. The presence of each TLV is deduced
from the remaining length to parse. The Nonce TLV has a fixed
length of 4, the InterestLifetime TLV has a fixed length of 2 and
the HopLimit TLV has a fixed length of 1. Any combination yields
a distinct value that matches the remaining length to parse.
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 16.
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0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 | 0 |DIG|PFX|FRE|FWD|PRM|CID|
+---+---+---+---+---+---+---+---+
Figure 16: Dispatch format for compressed NDN Interest messages
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.
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 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.
PRM: Parameters TLV
0: The uncompressed message does not include a
Parameters TLV.
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1: The uncompressed message does include a Parameters
TLV. The Type field is removed from the compressed
message.
CID: Context Identifiers
0: CID(s) are not appended to the dispatch octet.
1: CID(s) are appended to the dispatch octet.
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" and the M flag to "1" (Figure 17). "resv" MUST be
set to 0. The Data message is handed to the NDN network stack
without modifications.
0 1 2 ... 7
+---+---+-----------------------+
| 0 | 1 | resv |
+---+---+-----------------------+
Figure 17: Dispatch format for uncompressed NDN Data messages
5.4.2. Compressed Data Messages
The compressed Data message uses the base dispatch format and sets
the C flag as well as the M flag to "1". 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. Otherwise, the message MUST be sent
uncompressed.
3. The MetaInfo Type and Length fields are elided from the
compressed Data message.
4. If present, the FinalBlockId TLV is encoded according to
Section 5.2.
5. The ContentType TLV length is set to 1. Messages with
ContentTypes that require more than 1 octet MUST be sent
uncompressed.
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6. The FreshnessPeriod TLV length is set to 2. Messages with
FreshnessPeriods that require more than 2 octets MUST be sent
uncompressed.
7. The FreshnessPeriod TLV and ContntType TLV MUST be moved to the
end of the compressed Data, keeping the order 1) FreshnessPeriod
TLV and 2) ContentType TLV.
8. The Type and Length fields of ContentType TLV and FreshnessPeriod
TLV are elided. The presence of each TLV is deduced from the
remaining length to parse. The FreshnessPeriod TLV has a fixed
length of 2 and the ContentType TLV has a fixed length of 1. Any
combination yields a distinct value that matches the remaining
length to parse.
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 18.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| 1 | 1 |DIG|FBI|CON| SIG |CID|
+---+---+---+---+---+---+---+---+
Figure 18: Dispatch format for compressed NDN Data messages
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.
FBI: FinalBlockId TLV
0: The uncompressed message does not include a
FinalBlockId TLV.
1: The uncompressed message does include a FinalBlockId.
CON: Content TLV
0: The uncompressed message does not include a Content
TLV.
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1: The uncompressed message does include a Content TLV.
The Type field is removed from the compressed
message.
SIG: Signature TLV
00: The Type fields of the SignatureInfo TLV,
SignatureType TLV and SignatureValue TLV are removed.
01: Reserved.
10: Reserved.
11: Reserved.
CID: Context Identifiers
0: CID(s) are not appended to the dispatch octet.
1: CID(s) are appended to the dispatch octet.
6. ICN LoWPAN for CCNx
6.1. TLV Encoding
The CCNx TLV encoding is described in [I-D.irtf-icnrg-ccnxmessages].
Type and Length fields are of fixed length of 2 octets each.
In this document, the TLV encoding is changed to the more space
efficient encoding described in Section 5.1. Type and Length fields
MUST be encoded as in Figure 13.
6.2. Name TLV Compression
Name TLVs are compressed using the same approach outlined in
Section 5.2.
6.3. Interest Messages
6.3.1. Uncompressed Interest Messages
An uncompressed Interest message uses the base dispatch format (see
Figure 6) and sets the C as well as the M flag to "0" (Figure 19).
"resv" MUST be set to 0. The Interest message is handed to the CCNx
network stack without modifications.
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0 1 2 ... 7
+---+---+-----------------------+
| 0 | 0 | resv |
+---+---+-----------------------+
Figure 19: Dispatch format for uncompressed CCNx Interest messages
6.3.2. Compressed Interest Messages
The compressed Interest message uses the base dispatch format and
sets the C flag to "1" and the M flag to "0". By default, the
Interest message is compressed with the following base rule set:
1. The Type and Length fields of the CCNx Message TLV are elided and
are obtained from the Fixed Header on decompression.
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 20.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 1 | 0 |FLG|HBH|PTY|HPL|FRS|MSG|PAY|VAL|EXT| RESVD |CID|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 20: 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 is carried in-line.
HBH: Optional Hop-By-Hop Header TLVs
0: No Hop-By-Hop Header TLVs are present in the Interest
message. Also, the HeaderLength field in the fixed
header is elided from the Interest message and assumed to
be "8".
1: Hop-By-Hop Header TLVs are present in the Interest
message. An additional octet follows immediately that
handles Hop-By-Hop Header TLV compressions and is
described in Section 6.3.3.
PTY: PacketType field in the fixed header
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0: The PacketType field is elided and assumed to be
"PT_INTEREST"
1: The PacketType field is elided and assumed to be
"PT_RETURN"
HPL: HopLimit field in the fixed header
0: The HopLimit field is carried in-line
1: The HopLimit field is elided and assumed to be "1"
FRS: Reserved field in the fixed header
0: The Reserved field is carried in-line
1: The Reserved field is elided and assumed to be "0"
MSG: Optional Interest Message TLVs
0: No Interest Message TLVs are present in the Interest
message.
1: Interest Message TLVs are present in the Interest
message. An additional octet follows immediately that
handles Interest Message TLV compressions and is
described in Section 6.3.4.
PAY: Optional Payload TLV
0: The Payload TLV is absent.
1: The Payload TLV is present and the type field is elided.
VAL: Optional ValidationAlgorithm and ValidationPayload TLVs
0: No validation related TLVs are present in the Interest
message.
1: Validation related TLVs are present in the Interest
message. An additional octet follows immediately that
handles validation related TLV compressions and is
described in Section 6.3.5.
EXT: Extension
0: No extension octet follows.
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1: An extension octet follows immediately. Extension octets
are used to extend the compression scheme, but are out of
scope of this document.
CID: Context Identifiers
0: CID(s) are not appended to the last dispatch octet.
1: CID(s) are appended to the last dispatch octet.
6.3.3. Hop-By-Hop Header TLVs Compression
Hop-By-Hop Header TLVs are unordered. For an Interest message, two
optional Hop-By-Hop Header TLVs are defined in
[I-D.irtf-icnrg-ccnxmessages], but several more can be defined in
higher level specifications. For better compression, an ordering of
Hop-By-Hop TLVs is enforced as follows:
1. Interest Lifetime TLV
2. Message Hash TLV
With this ordering in place, Type fields are elided from the Interest
Lifetime TLV and the Message Hash TLV.
Note: If the original Interest message includes Hop-By-Hop Header
TLVs with a different ordering, then they remain uncompressed.
0 1 2 3 4 5 6 7
+-------+-------+-------+-------+-------+-------+-------+-------+
| IntLifetime | MsgHash | Reserved |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 21: Dispatch for HBH Compression
IntLifetime: InterstLifetime Hop-By-Hop Header TLV
00: The Interest Lifetime TLV is absent.
01: The Interest Lifetime TLV is present and the type field
is removed.
10: The Interest Lifetime TLV is absent and a default value
of 0 seconds is assumed.
11: The Interest Lifetime TLV is absent and a default value
of 10 minutes is assumed.
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MsgHash: Message Hash Hop-By-Hop Header TLV
00: The Message Hash TLV is absent.
01: The Message Hash TLV is present and uncompressed.
10: A T_SHA-256 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 32 octets. The outer Message Hash
TLV is omitted.
11: A T_SHA-512 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 64 octets. The outer Message Hash
TLV is omitted.
6.3.4. Interest Message TLVs Compression
0 1 2 3 4 5 6 7
+-------+-------+-------+-------+-------+-------+-------+-------+
| KeyIDRestr | CObHRestr | Reserved |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 22: Dispatch for Interest Messages
KeyIDRestr: Optional KeyIdRestriction TLV within a CCNx Message TLV
00: The KeyIdRestriction TLV is absent.
01: The KeyIdRestriction TLV is present and uncompressed.
10: A T_SHA-256 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 32 octets. The outer
KeyIdRestriction TLV is omitted.
11: A T_SHA-512 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 64 octets. The outer
KeyIdRestriction TLV is omitted.
CObHRestr: Optional ContentObjectHashRestriction TLV within a CCNx
Message TLV
00: The ContentObjectHashRestriction TLV is absent.
01: The ContentObjectHashRestriction TLV is present and
uncompressed.
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10: A T_SHA-256 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 32 octets. The outer
ContentObjectHashRestriction TLV is omitted.
11: A T_SHA-512 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 64 octets. The outer
ContentObjectHashRestriction TLV is omitted.
6.3.5. Validation
0 1 2 3 4 5 6 7 8
+-------+-------+-------+-------+-------+-------+-------+-------+
| ValidationAlg | KeyID | Reserved |
+-------+-------+-------+-------+-------+-------+-------+-------+
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.
0010: A T_CRC32C ValidationAlgorithm TLV is assumed, but no
ValidationAlgorithm TLV is included. Additionally, a
Sigtime TLV is inlined without a type and a length field.
0011: A T_HMAC-SHA256 ValidationAlgorithm TLV is assumed, but
no ValidationAlgorithm TLV is included.
0100: A T_HMAC-SHA256 ValidationAlgorithm TLV is assumed, but
no ValidationAlgorithm TLV is inclued. Additionally, a
Sigtime TLV is inlined without a type and a length field.
0101: Reserved.
0110: Reserved.
0111: Reserved.
1000: Reserved.
1001: Reserved.
1010: Reserved.
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1011: Reserved.
1100: Reserved.
1101: Reserved.
1110: Reserved.
1111: Reserved.
KeyID: Optional KeyID TLV within the ValidationAlgorithm TLV
00: The KeyId TLV is absent.
01: The KeyId TLV is present and uncompressed.
10: A T_SHA-256 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 32 octets. The outer KeyId TLV is
omitted.
11: A T_SHA-512 TLV is present and the type field as well as
the length fields are removed. The length field is
assumed to represent 64 octets. The outer KeyId TLV is
omitted.
The ValidationPayload TLV is present if the ValidationAlgorithm TLV
is present. The type field is omitted.
6.4. Content Objects
6.4.1. Uncompressed Content Objects
An uncompressed Content object uses the base dispatch format (see
Figure 6) and sets the C flag to "0" and the M flag to "1"
(Figure 24). "resv" MUST be set to 0. The Content object is handed
to the CCNx network stack without modifications.
0 1 2 ... 7
+---+---+-----------------------+
| 0 | 1 | resv |
+---+---+-----------------------+
Figure 24: Dispatch format for uncompressed CCNx Content objects
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6.4.2. Compressed Content Objects
The compressed Content object uses the base dispatch format and sets
the C flag as well as the M flag to "1". 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.
Further TLV compression is indicated by the ICN LoWPAN dispatch in
Figure 25.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 1 | 1 |FLG|HBH|FRS|MSG|PAY|VAL|EXT| RESVD |CID|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 25: Dispatch format for compressed CCNx Content objects
FLG: Flags field in the fixed header See Section 6.3.2.
HBH: Optional Hop-By-Hop Header TLVs
0: No Hop-By-Hop Header TLVs are present in the Content
Object message. Also, the HeaderLength field in the
fixed header is elided from the Content Object message
and assumed to be "8".
1: Hop-By-Hop Header TLVs are present in the Content Object
message. An additional octet follows immediately that
handles Hop-By-Hop Header TLV compressions and is
described in Section 6.4.3.
FRS: Reserved field in the Fixed Header See Section 6.3.2.
MSG: Optional Content Object Message TLVs
0: No Content Object Message TLVs are present in the Content
Object message.
1: Content Object Message TLVs are present in the Content
Object message. An additional octet follows immediately
that handles Content Object Message TLV compressions and
is described in Section 6.4.4.
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PAY: Optional Payload TLV See Section 6.3.2.
VAL: Optional ValidationAlgorithm and ValidationPayload TLVs See Sec
tion 6.3.2.
EXT: Extension See Section 6.3.2.
CID: Context Identifiers
0: CID(s) are not appended to the last dispatch octet.
1: CID(s) are appended to the last dispatch octet.
6.4.3. Hop-By-Hop Header TLVs Compression
Hop-By-Hop Header TLVs are unordered. For a Content Object message,
two optional Hop-By-Hop Header TLVs are defined in
[I-D.irtf-icnrg-ccnxmessages], but several more can be defined in
higher level specifications. For better compression, an ordering of
Hop-By-Hop TLVs is enforced as follows:
1. Recommended Cache Time TLV
2. Message Hash TLV
With this ordering in place, Type fields are elided from the
Recommended Cache Time TLV and Message Hash TLV.
Note: If the original Content Object message includes Hop-By-Hop
Header TLVs with a different ordering, then they remain uncompressed.
0 1 2 3 4 5 6 7
+-------+-------+-------+-------+-------+-------+-------+-------+
| RCT | MsgHash | Reserved |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 26: Dispatch for HBH Compression
RCT: Recommended Cache Time Hop-By-Hop Header TLV
0: The Recommended Cache Time TLV is absent.
1: The Recommended Cache Time TLV is present and the type as
well as the length fields are elided.
MsgHash: Message Hash Hop-By-Hop Header TLV See Section 6.3.3.
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6.4.4. Content Object Message TLVs Compression
0 1 2 3 4 5 6 7
+-------+-------+-------+-------+-------+-------+-------+-------+
| PayloadType |ExpTime| Reserved |
+-------+-------+-------+-------+-------+-------+-------+-------+
Figure 27: Dispatch for Message TLVs
PayloadType: Optional PayloadType TLV within a CCNx Message TLV
00: The PayloadType TLV is absent and T_PAYLOADTYPE_DATA is
assumed.
01: The PayloadType TLV is absent and T_PAYLOADTYPE_KEY is
assumed.
10: The PayloadType TLV is absent and T_PAYLOADTYPE_LINK is
assumed.
11: The PayloadType TLV is present and uncompressed.
ExpTime: Optional ExpiryTime TLV within a CCNx Message TLV
0: The ExpiryTime TLV is absent.
1: The ExpiryTime TLV is present and the type as well as the
length fields are elided.
7. Security Considerations
TODO
8. IANA Considerations
8.1. Page Switch Dispatch Type
This document makes use of "Page 2" from the existing paging
dispatches in [RFC8025].
9. References
9.1. Normative References
[ieee802.15.4]
IEEE Computer Society, "IEEE Std. 802.15.4-2015", April
2016, <https://standards.ieee.org/findstds/
standard/802.15.4-2015.html>.
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[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>.
[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>.
9.2. Informative References
[CCN-LITE]
"CCN-lite: A lightweight CCNx and NDN implementation",
<http://ccn-lite.net/>.
[I-D.irtf-icnrg-ccnxmessages]
Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format", draft-irtf-icnrg-ccnxmessages-08 (work in
progress), July 2018.
[I-D.irtf-icnrg-ccnxsemantics]
Mosko, M., Solis, I., and C. Wood, "CCNx Semantics",
draft-irtf-icnrg-ccnxsemantics-09 (work in progress), June
2018.
[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-EXP] Baccelli, E., Mehlis, C., Hahm, O., Schmidt, TC., and M.
Waehlisch, "Information Centric Networking in the IoT:
Experiments with NDN in the Wild", Proc. of 1st ACM Conf.
on Information-Centric Networking (ICN-2014) ACM DL, pp.
77-86, September 2014,
<http://dx.doi.org/10.1145/2660129.2660144>.
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[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",
<http://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>.
[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>.
[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>.
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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 octet form of each TLV component is assumed. A typical TLV
component therefore is of size 2 (type field + length field) + the
actual value.
A.1.1. Interest
Figure 28 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 octets.
------------------------------------,
Interest TLV = 2 |
---------------------, |
Name | 2 + |
NameComponents = 2n + |
| comps_n |
---------------------' = 21 + 2n + comps_n
CanBePrefix = 2 |
MustBeFresh = 2 |
Nonce = 6 |
InterestLifetime = 4 |
HopLimit = 3 |
------------------------------------'
Figure 28: Estimated size of an uncompressed NDN Interest
Figure 29 depicts the size requirements after compression.
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------------------------------------,
Dispatch Page Switch = 1 |
NDN Interset Dispatch = 1 |
Interest TLV = 1 |
-----------------------, |
Name | = 9 + n/2 + comps_n
NameComponents = n/2 + |
| comps_n |
-----------------------' |
Nonce = 4 |
InterestLifetime = 2 |
------------------------------------'
Figure 29: Estimated size of a compressed NDN Interest
The size difference is:
12 + 1.5n octets.
For the name "/DE/HH/HAW/BT7", the total size gain is 18 octets,
which is 46% of the uncompressed packet.
A.1.2. Data
Figure 30 depicts the size requirements for a basic, uncompressed NDN
Data containing a FreshnessPeriod as MetaInfo. A FreshnessPeriod of
1 minute is assumed. The value is thereby encoded using 2 octets.
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 30: Estimated size of an uncompressed NDN Data
Figure 31 depicts the size requirements for the compressed version of
the above Data packet.
------------------------------------,
Dispatch Page Switch = 1 |
NDN Data Dispatch = 1 |
-----------------------, |
Name | = 38 + n/2 + comps_n +
NameComponents = n/2 + | clen + klen
| comps_n |
-----------------------' |
Content = 1 + clen |
KeyLocator = 1 + klen |
DigestSha256 = 32 |
FreshnessPeriod = 2 |
------------------------------------'
Figure 31: Estimated size of a compressed NDN Data
The size difference is:
15 + 1.5n octets.
For the name "/DE/HH/HAW/BT7", the total size gain is 21 octets.
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A.2. CCNx
The CCNx TLV encoding defines a 2-octet encoding for type and length
fields, summing up to 4 octets in total without a value.
A.2.1. Interest
Figure 32 depicts the size requirements for a basic, uncompressed
CCNx Interest. No Hop-By-Hop TLVs are included and the protocol
version as well as the reserved field are assumed to be 0. A
KeyIdRestriction TLV with T_SHA-256 is included to limit the
responses to Content Objects containing the specific key.
------------------------------------,
Fixed Header = 8 |
Message = 4 |
---------------------, |
Name | 4 + = 56 + 4n + comps_n
NameSegments = 4n + |
| comps_n |
---------------------' |
KeyIdRestriction = 40 |
------------------------------------'
Figure 32: Estimated size of an uncompressed CCNx Interest
Figure 33 depicts the size requirements after compression.
------------------------------------,
Dispatch Page Switch = 1 |
CCNx Interest Dispatch = 3 |
Fixed Header = 3 |
-----------------------, |
Name | = 39 + n/2 + comps_n
NameSegments = n/2 + |
| comps_n |
-----------------------' |
T_SHA-256 = 32 |
------------------------------------'
Figure 33: Estimated size of a compressed CCNx Interest
The size difference is:
17 + 3.5n octets.
For the name "/DE/HH/HAW/BT7", the total size gain is 31 octets,
which is 38% of the uncompressed packet.
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A.2.2. Data
Figure 34 depicts the size requirements for a basic, uncompressed
CCNx Data containing an ExpiryTime Message TLV, an HMAC_SHA-256
signature, the signature time and a hash of the shared secret key.
------------------------------------,
Fixed Header = 8 |
Message = 4 |
---------------------, |
Name | 4 + |
NameSegments = 4n + |
| comps_n |
---------------------' |
ExpiryTime = 12 = 124 + 4n + comps_n + clen
Payload = 4 + clen |
---------------------, |
ValidationAlgorithm | |
T_HMAC-256 = 56 |
KeyId | |
SignatureTime | |
---------------------' |
ValidationPayload = 36 |
------------------------------------'
Figure 34: Estimated size of an uncompressed CCNx Data Object
Figure 35 depicts the size requirements for a basic, compressed CCNx
Data.
------------------------------------,
Dispatch Page Switch = 1 |
CCNx Content Dispatch = 4 |
Fixed Header = 2 |
-----------------------, |
Name | |
NameSegments = n/2 + |
| comps_n = 91 + n/2 + comps_n + clen
-----------------------' |
ExpiryTime = 8 |
Payload = 1 + clen |
T_HMAC-SHA256 = 32 |
SignatureTime = 8 |
ValidationPayload = 34 |
------------------------------------'
Figure 35: Estimated size of a compressed CCNx Data Object
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The size difference is:
33 + 3.5n octets.
For the name "/DE/HH/HAW/BT7", the total size gain is 47 octets.
Acknowledgments
Authors' Addresses
Cenk Gundogan
HAW Hamburg
Berliner Tor 7
Hamburg D-20099
Germany
Phone: +4940428758067
EMail: cenk.guendogan@haw-hamburg.de
URI: http://inet.haw-hamburg.de/members/cenk-gundogan
Thomas C. Schmidt
HAW Hamburg
Berliner Tor 7
Hamburg D-20099
Germany
EMail: t.schmidt@haw-hamburg.de
URI: http://inet.haw-hamburg.de/members/schmidt
Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
Berlin D-10318
Germany
EMail: mw@link-lab.net
URI: http://www.inf.fu-berlin.de/~waehl
Christopher Scherb
University of Basel
Spiegelgasse 1
Basel CH-4051
Switzerland
EMail: christopher.scherb@unibas.ch
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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
Gundogan, et al. Expires January 17, 2019 [Page 36]
