Network Working Group L. Braun
Internet-Draft C. Schmitt
Intended status: Standards Track TU Muenchen
Expires: March 22, 2012 B. Claise
Cisco Systems, Inc.
G. Carle
TU Muenchen
September 21, 2011
Compressed IPFIX for smart meters in constrained networks
<draft-braun-core-compressed-ipfix-03>
Abstract
This document specifies the Compressed IPFIX protocol that serves for
transmitting smart metering data in 6LoWPAN networks [RFC4944].
Compressed IPFIX is derived from IPFIX [RFC5101] and adopted to the
needs of constrained networks. This documents specifies how the
Compressed IPFIX Data and Template Records are transmitted in 6LoWPAN
networks and how Compressed IPFIX data can be converted into
uncompressed IPFIX data in a proxy device.
Status of this Memo
This Internet-Draft is submitted to IETF 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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 22, 2012.
Copyright Notice
Copyright (c) 2011 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
(http://trustee.ietf.org/license-info) in effect on the date of
Braun, et al. Compressed IPFIX [Page 1]
Internet-Draft Compressed IPFIX September 2011
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Document structure . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Hard- and Software constraints . . . . . . . . . . . . . . . . 7
3.1. Hardware constraints . . . . . . . . . . . . . . . . . . . 7
3.2. Energy constraints . . . . . . . . . . . . . . . . . . . . 8
3.3. Packet size constraints . . . . . . . . . . . . . . . . . 8
3.4. Transport protocol constraints . . . . . . . . . . . . . . 8
4. Application scenarios for Compressed IPFIX . . . . . . . . . . 9
5. Architecture for Compressed IPFIX . . . . . . . . . . . . . . 11
6. Compressed IPFIX Message Format . . . . . . . . . . . . . . . 13
6.1. Compressed IPFIX Message Header . . . . . . . . . . . . . 13
6.2. Compressed Set . . . . . . . . . . . . . . . . . . . . . . 15
6.3. Compressed Template Record Format . . . . . . . . . . . . 16
6.4. Field Specifier Format . . . . . . . . . . . . . . . . . . 17
6.5. Compressed Data Record Format . . . . . . . . . . . . . . 18
7. Compressed IPFIX Mediation . . . . . . . . . . . . . . . . . . 19
7.1. Expanding the Message header . . . . . . . . . . . . . . . 21
7.2. Translating the Set Headers . . . . . . . . . . . . . . . 22
7.3. Expanding the Template Record Header . . . . . . . . . . . 22
8. Template Management . . . . . . . . . . . . . . . . . . . . . 22
8.1. TCP / SCTP . . . . . . . . . . . . . . . . . . . . . . . . 23
8.2. UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9. Security considerations . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
11. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 23
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Braun, et al. Compressed IPFIX [Page 2]
Internet-Draft Compressed IPFIX September 2011
12.1. Norminative References . . . . . . . . . . . . . . . . . . 24
12.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
Braun, et al. Compressed IPFIX [Page 3]
Internet-Draft Compressed IPFIX September 2011
1. Introduction
Smart meters that form a constrained wireless network need an
application layer protocol that allows the efficient transmission of
metering data from the devices to some kind of central analysis
device. The meters used to build such networks are usually equipped
with low-cost and low-power hardware. This leads to constraints in
computational capacities, available memory and networking resources.
The devices are often battery powered and are expected to run for a
long time without having the possibility to re-charge themselves. In
order to save energy, smart meters often power off their wireless
networking device. Hence, they don't have a steady network
connection, but are only part of the wireless network as needed when
there is data that needs to be exported. A push protocol like
Compressed IPFIX, where data is transmitted autonomically from the
meters to one or more collectors, is suitable for reporting metering
data in such networks.
Compressed IPFIX is derived from IPFIX [RFC5101] and therefore
inherits most of its properties. One of these properties is the
separation of data and its data description by encoding the former in
Data Sets and the latter in Template Sets.
Transforming Compressed IPFIX to IPFIX as per [RFC5101] is very
simple and can be done on the border between the constrained network
and the more general network. The transformation between one form of
IPFIX data into another is known as IPFIX Mediation [RFC5982].
Hence, smart metering networks that are based on Compressed IPFIX can
be easily integrated into an existing IPFIX measurement
infrastructure.
1.1. Document structure
Section 2 introduces the used terminology in this draft. Afterwards,
hardware and software constraints in constrained networks, which will
motivate our modifications to the IPFIX protocol, are discussed in
Section 3. Section 4 describes the application scenarios and
Section 5 describes the architecture for Compressed IPFIX. Section 6
defines the Compressed IPFIX protocol itself and discusses the
differences between Compressed IPFIX and IPFIX. The Mediation
Process from Compressed IPFIX to IPFIX is described in Section 7.
Section 8 defines the process of Template Management on the Exporter
and the Collector. Section 9 and Section 10 discuss the security and
IANA considerations for Compressed IPFIX. Section 11 lists the open
issues that need to be addressed in further versions of this draft.
Braun, et al. Compressed IPFIX [Page 4]
Internet-Draft Compressed IPFIX September 2011
2. Terminology
The term smart meter is used to refer to constrained devices like
wireless senor nodes, motes or any other kind of small constraint
device that can be part of a network that is based on IEEE802.15.4
and 6LoWPAN [RFC4944].
Most of the terms used in this draft are defined in [RFC5101]. All
these terms are written with their first letter being capitalized.
Most of the terms that are defined for IPFIX can be used to describe
Compressed IPFIX. The term "Compressed" is used in front of the
IPFIX term to distinguish between the IPFIX version and the
Compressed IPFIX version. This draft uses the term IPFIX to refer to
IPFIX as per RFC 5101 and the term Compressed IPFIX for the IPFIX
version defined in this draft.
The terms IPFIX Message, IPFIX Device, Set, Data Set, Template Set,
Data Record, Template Record, Collecting Process, Collector,
Exporting Process and Exporter are defined as in [RFC5101]. The term
IPFIX Mediator is defined in [RFC5982]. The terms Intermediate
Process, IPFIX Proxy, IPFIX Concentrator are defined in
[I-D.ietf-ipfix-mediators-framework].
All these terms above have been adapted from the IPFIX definitions.
As they keep a similar notion but in a different context of
constrained networks, the term "Compressed" now complements the
defined terms.
Compressed Exporting Process
The Compressed Exporting Process is a process that exports
Compressed Records.
Compressed Exporter
A Compressed Exporter is a smart metering device that contains at
least one Compressed Exporting Process.
Compressed Collecting Process
The Compressed Collecting Process is a process inside a device
that is able to receive and process Compressed Records.
Compressed IPFIX Collector
A Compressed Collector is a device that contains at least one
Compressed Collecting Process.
Braun, et al. Compressed IPFIX [Page 5]
Internet-Draft Compressed IPFIX September 2011
Compressed IPFIX Device
A Compressed IPFIX Device is a device that contains one or more
Compressed Collector or one or more Compressed Exporter.
Compressed IPFIX Smart Meter
A Compressed IPFIX Smart Meter is a device that contains the
functionality of an Compressed IPFIX device. It is usually
equipped with one or more sensors that meter a physical quantity,
like power consumption, temperature, or physical tempering with
the device. Every Compressed IPFIX Smart Meter MUST at least
contain an Compressed Exporting Process. It MAY contain a
Compressed Collecting Process in order to work as a Compressed
IPFIX Proxy or Concentrator.
Compressed IPFIX Message
The Compressed IPFIX Message is a message originated by an
Compressed IPFIX Exporter. It is composed of a Compressed Message
Header and one or more Compressed Sets. The Compressed IPFIX
Message Format is defined in Section 6.
Compressed Data Record
A Compressed Data Record equals a Data Record in [RFC5101]. The
term is used to distinguish between IPFIX and Compressed IPFIX
throughout the document.
Compressed Template Record
A Compressed Template Record is similar to a Template Record. The
Template Record Header is substituted with a Compressed Template
Record Header and is otherwise equal to a Template Record.
Section 6.3.
Compressed Set
The Compressed Set is a group of Compressed Data Records or
Compressed Template Records with a Compressed Set Header. Its
format is defined in Section 6.2.
Compressed Data Set
The Compressed Data Set is a Compressed Set that contains
Compressed Data Records. in Section 6.2.
Braun, et al. Compressed IPFIX [Page 6]
Internet-Draft Compressed IPFIX September 2011
Compressed Template Set
A Compressed Template Set is a Compressed Set that contains
Compressed Template Records.
Compressed Intermediate Process
A Compressed Intermediate Process is an Intermediate Process that
can handle Compressed IPFIX Messages.
Compressed IPFIX Proxy
A Compressed IPFIX Proxy is an IPFIX Proxy that can handle
Compressed IPFIX Messages.
Compressed IPFIX Concentrator
A Compressed IPFIX Concentrator is an IPFIX Concentrator that can
handle Compressed IPFIX Messages.
A Compressed IPFIX Transport Session is defined by the communication
between a Compressed Exporter (identified by an 6LowPAN-Address, the
Transport Protocol, and the Transport Port) and a Compressed
Collector (identified by the same properties).
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 [RFC2119].
3. Hard- and Software constraints
3.1. Hardware constraints
The target devices for Compressed IPFIX are usually equipped with
low-cost hardware and therefore face several constraints concerning
CPU and memory [Schmitt09]. For example, the IRIS mote from Crossbow
Technologies Inc. has a size of 58 x 32 x 7 mm (without a battery
pack) [Crossbow]. Thus, there is little space for micro controller,
flash memory (128 kb) and radio frequency transceiver, which are
located on the board.
Network protocols used on such hardware need to respect these
constraints. They must be simple to implement using little code and
little run time memory and should produce little overhead when
encoding the application payload.
Braun, et al. Compressed IPFIX [Page 7]
Internet-Draft Compressed IPFIX September 2011
3.2. Energy constraints
Smart meters that are battery powered have hard energy constraints
[Schmitt09]. By power supply of two 2 AA 2,800-mAh batteries this
means approximately 30,240J. If they run out of power, their battery
Has to be changed, which means physical manipulation to the device is
necessary. Using as little energy as possible for network
communication is therefore desired.
A smart metering device can save a lot of energy, if it powers down
its radio frequency transceiver. Such devices do not have permanent
network connectivity but are only part of the network as needed. A
push protocol, where only one side is sending data, is suitable for
transmitting application data under such circumstances. As the
communication is unidirectional, a meter can completely power down
its radio frequency transceivers as long as it does not have any data
to sent. If the metering device is able to keep a few measurements
in memory, and if real time metering is not a requirement, the
Compressed Data Records can be pushed less frequently. Therefore,
saving some more energy on the radio frequency transceivers.
3.3. Packet size constraints
Compressed IPFIX is mainly targeted for the use in 6LoWPAN networks,
which are based on IEEE 802.15.4 [RFC4944]. However, the protocol
can also be used to transmit data in other networks. IEEE 802.15.4
defines a maximum frame size of 127 octets, which usually leaves 102
octets for user data. IPv6 on the other hand defines a minimum MTU
of 1280 octets. Hence, fragmentation has to be implemented in order
to transmit such large packets. While fragmentation allows the
transmission of large messages, its use is problematic in networks
with high packet loss because the complete message has to be
discarded if only a single fragment gets lost.
Compressed IPFIX enhances IPFIX by a header compression scheme, which
allows to reduce the overhead from header sizes significantly.
Additionally, the overall Compressed IPFIX Message size is reduced,
which reduces the need for fragmentation.
3.4. Transport protocol constraints
The IPFIX standard [RFC5101] defines several transport protocol
bindings for the transmission of IPFIX Messages. SCTP support is
REQUIRED for any IPFIX Device to achieve standard conformance
[RFC5101], and its use is highly recommended. However, sending IPFIX
over UDP and TCP MAY also be implemented.
This transport protocol recommendation is not suitable for Compressed
IPFIX. A header compression scheme that allows to compress an IPv6
Braun, et al. Compressed IPFIX [Page 8]
Internet-Draft Compressed IPFIX September 2011
header from 40 octets down to 2 octets is defined in 6LoWPAN. There
is a similar compression scheme for UDP, but there is no such
compression for TCP or SCTP headers. If header compression can be
employed, more space for application payload is available.
Using UDP on the transport layer for transmitting IPFIX Messages is
therefore highly recommended. Furthermore, TCP or SCTP are currently
not supported on some platforms, like on TinyOS [Harvan08]. Hence,
UDP may be the only option.
Every Compressed IPFIX Exporter and Collector MUST implement UDP
transport layer support for transmitting data in a constrained
network environment. It MAY also offer TCP or SCTP support.
However, using these protocols is NOT RECOMMENDED as their use will
consume more power and reduces the available size of application
payload compared to the use of UDP. If Compressed IPFIX is
transmitted over a non-constrained network, using SCTP as a transport
layer protocol is RECOMMENDED.
4. Application scenarios for Compressed IPFIX
Compressed IPFIX is derived from IPFIX [RFC5101] and is therefore a
unidirectional push protocol. This means all communication that
employs Compressed IPFIX is unidirectional from an Exporting Process
to a Collecting Process. Hence, Compressed IPFIX only fits for
application scenarios where meters transmit data to one or more
Collectors.
If Compressed IPFIX is used over UDP, as recommended, packet loss can
occur. Furthermore, if an initial Template Message gets lost, and is
therefore unknown to the Collector, all Data Sets that reference this
Template cannot be decoded. Hence, all these Messages are lost if
they are not cached by the Collector. It should be clear to an
application developer, that Compressed IPFIX can only be used over
UDP if these Compressed IPFIX Message losses are not a problem.
Compressed IPFIX over UDP is especially not a suitable protocol for
applications where sensor data trigger policy decisions or
configuration updates for which packet loss is not tolerable.
Applications that use smart sensors for accounting purposes for long
time measurements can benefit from the use of Compressed IPFIX. One
application for IPFIX can be long term monitoring of large physical
volumes. In [Tolle05], Tolle et al. built a system for monitoring a
"70-meter tall redwood tree, at a density interval of 5 minutes in
time and 2 meters in space". The sensor node infrastructure was
deployed to measure the air temperature, relative humidity and
Braun, et al. Compressed IPFIX [Page 9]
Internet-Draft Compressed IPFIX September 2011
photosynthetically active solar radiation over a long time period.
Deploying Compressed IPFIX in such scenarios seems to be a good fit.
The sensors of the IPFIX Smart Meter can be queried over several 5
minute time intervals and the query results can be aggregated into a
single Compressed IPFIX Message. As soon as enough query results are
stored in the Compressed IPFIX Message, e.g. if the Compressed IPFIX
Message size fills the available payload in a single IEEE 802.15.4
packet, the wireless transceiver can be activated and the Compressed
IPFIX Message can be exported to a Compressed IPFIX Collector.
Similar sensor networks have been built to monitor the habitat of
animals, e.g. in the "Great Duck Island Project" [GreatDuck],
[SMPC04]. The purpose of the sensor network was to monitor the birds
by deploying sensors in and around their burrows. The measured
sensor data was collected and stored in a database for offline
analysis and visualization. Again, the sensors can perform their
measurements periodically, aggregate the sensor data and export them
to a Compressed IPFIX Collector.
Other application scenarios for Compressed IPFIX could be
applications where sensor networks are used for long term structural
health monitoring in order to investigate long term weather
conditions on the structure of a building. For example, a smart
metering network has been built to monitor the structural health of
the Golden Gate Bridge [Kim07]. If a sensor network is deployed to
perform a long term measurement of the structural integrity,
Compressed IPFIX can be used to collect the sensor measurement data.
If an application developer wants to decide whether to use Compressed
IPFIX for transmitting data from smart meters, he must take the
following considerations into account:
1. The application must require a push protocol. It is not possible
to request data from a smart meter. The IPFIX Smart Meter
decides for itself when to send its metering data.
2. The property above allows a IPFIX Smart Meter to turn off its
wireless device in order to save energy, as it does not have to
receive any data.
3. If real-time is not required, the application might benefit from
accumulated several measurements into a single Compressed IPFIX
Message. Compressed IPFIX easily allows the aggregation of
several into a single Compressed IPFIX Message (or a single
packet). This aggregation can happen on the IPFIX Smart Meter
that aggregates several of its own measurements. Or it can
happen within a multi-hop wireless network where one IPFIX Proxy
aggregates several Compressed IPFIX Messages into a single
Compressed IPFIX Message before forwarding them.
Braun, et al. Compressed IPFIX [Page 10]
Internet-Draft Compressed IPFIX September 2011
4. The application must accept potential packet loss. Compressed
IPFIX only fits for applications where metering data is stored
for accounting purposes and not for applications where the sensor
data triggers configuration changes or policy decisions (except:
if Message loss is acceptable for some reason).
5. Architecture for Compressed IPFIX
The Compressed IPFIX architecture is similar to the IPFIX
architecture which is described in [RFC5470]. The most common
deployment of IPFIX Smart Meters is shown in Figure 1.
+----------------+ +----------------+
|[*Application 1]| ... |[*Application n]|
+--------+-------+ +-------+--------+
^ ^
| |
+ = = = = -+- = = = = +
^
|
+------------------------+ Compressed +--------+-------------------+
| Compressed IPFIX S.M. | IPFIX | Compressed IPFIX Collector |
| [Exporting Process] |----------->| [Collecting Process(es)] |
+------------------------+ +----------------------------+
Figure 1: Direct transmission between sensors and applications
An IPFIX Smart Meter (S.M.) queries its internal sensors to retrieve
the sensor data. It then encodes the results into a Compressed IPFIX
Message and exports this Compressed IPFIX Message to one or more
Compressed IPFIX Collectors. The Compressed IPFIX Collector runs one
or more applications that process the collected sensor data. The
Compressed IPFIX Collector can be deployed on non-constrained devices
at the constrained network border.
A second way to deploy IPFIX Smart Meter can employ aggregation on
Compressed IPFIX Messages during their journey through the
constrained network as shown in Figure 2. This aggregation can be
performed by special IPFIX Smart Meter that act as Compressed IPFIX
Concentrators. Such devices must have enough resources to perform
the aggregation.
Braun, et al. Compressed IPFIX [Page 11]
Internet-Draft Compressed IPFIX September 2011
+-------------------------+ +------------------------+
| Compressed IPFIX S.M. | Compressed IPFIX |Comp. IPFIX Concentrator|
| [Exporting Process] |----------------->| [Collecting Process] |
+-------------------------+ +-------->| [Exporting Process] |
| +------------------------+
+-------------------------+ | |
| Compressed IPFIX S.M. | | Compressed IPFIX|
| [Exporting Process] |--------+ |
+-------------------------+ v
+-------+------------------+
| Collector(1) |
| [Collecting Process(es)] |
+--------------------------+
Figure 2: Aggregation on Compressed IPFIX
IPFIX Smart Meters send their data to Compressed IPFIX Concentrator
which needs to have enough storage space to store the incoming data.
It may also aggregate the incoming data with its own measurement
data. The aggregated data can then be re-exported again to one or
more Collectors.
The last deployment, shown in Figure 3, employs another Compressed
IPFIX Mediation process.
+------------------------+ +------------------------+
| Compressed IPFIX S.M | Compressed IPFIX | Compressed IPFIX Proxy |
| [Exporting Process] |----------------->| [Collecting Process] |
+------------------------+ | [Exporting Process] |
+------------------------+
|
IPFIX |
|
v
+-------+------------------+
| IPFIX Collector(1) |
| [Collecting Process(es)] |
+--------------------------+
Figure 3: Aggregation on Compressed IPFIX
The IPFIX Smart Meters transmit their Compressed IPFIX Messages to
one node, e.g. the base station, which translates the Compressed
IPFIX Messages to IPFIX Messages. The IPFIX Messages can then be
exported into an existing IPFIX infrastructure. The Mediation
Braun, et al. Compressed IPFIX [Page 12]
Internet-Draft Compressed IPFIX September 2011
process from Compressed IPFIX to IPFIX is described in Section 7.
6. Compressed IPFIX Message Format
A Compressed IFPIX Message starts with a Compressed Message Header,
followed by one or more Compressed Sets. The Compressed Sets can be
any of the possible two types: Compressed Template Set and Compressed
Data Set. An Compressed IPFIX Message MUST only contain one type of
Compressed Set. The format of the Compressed IPFIX Message is shown
in Figure 4
+----------------------------------------------------+
| Compressed Message Header |
+----------------------------------------------------+
| Compressed Set |
+----------------------------------------------------+
| Compressed Set |
+----------------------------------------------------+
...
+----------------------------------------------------+
| Compressed Set |
+----------------------------------------------------+
Figure 4: Compressed IPFIX Message Format
6.1. Compressed IPFIX Message Header
The Compressed IPFIX Message Header is derived from the IPFIX Message
Header, with some optimization using field compression. The IPFIX
Message Header from [RFC5101] is shown in Figure 5.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Export Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Observation ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Braun, et al. Compressed IPFIX [Page 13]
Internet-Draft Compressed IPFIX September 2011
Figure 5: IPFIX Message Header
The length of the IPFIX Message Header is 16 octets and every IPFIX
Message has to be started with it. The Compressed IPFIX Message
Header needs to be smaller due to the packet size constraints
discussed in Section 3.3. Compressed IPFIX introduces a Compressed
IPFIX Message Header that has a smaller size. The Compressed header
consists of a fixed part of two octets and a variable length
"Remaining Header" as shown in Figure 6.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version|ETC|SNC| Length |
|Number | | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remaining Header |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Format of the Compressed IPFIX Message header
The first part has a fixed length of two octets and consists of the
"Version Field" (4 bit), the "Export Time Compression" (ETC) field (2
bit), the "Sequence Number Compression" (SNC) field (2 bit) and the
"Length" field (8 bit). The second part (the "Remaining Header") has
a variable length. Its length is defined by the ETC and SNC fields
in the fixed header.
The fixed header has a length of two octets which equals the length
of the version field of the IPFIX Message Header. Hence, Compressed
IPFIX Messages can be read and identified by an IPFIX Collector.
This is important for building an IPFIX Mediator by extending an
IPFIX Collector (Section 7).
The fixed header fields are defined as follows:
Version number
The Compressed IPFIX version field MUST have the most significant
bit set to one and the other bits set to zero. The remaining bits
of the version field are reserved for future versions of
Compressed IPFIX. Note that IPFIX has the version 0x000a, hence
an IPFIX Collector can distinguish between IPFIX and Compressed
IPFIX by checking the first bit of the version field.
Braun, et al. Compressed IPFIX [Page 14]
Internet-Draft Compressed IPFIX September 2011
ETC
The ETC field defines the compression level of the "Export Time"
field of the IPFIX Messages Header. Its value defines the length
as follows. A bit sequence of "00" denotes that the "Export Time"
field is omitted. A sequence of "01" denotes that the "Export
Time" field has a size of one octet. A sequence of "10" denotes
that the "Export Time" field has a size of two octets. Finally, a
sequence of "11" denotes that the "Export Time" field has the
original length of four octets.
SNC
The SNC field defines the compression level of the "Sequence
Number" field of the IPFIX Messages Header. Its value defines the
length as follows. A bit sequence of "00" denotes that the
"Sequence Number" field is omitted. A sequence of "01" denotes
that the "Sequence Number" field has a size of one octet. A
sequence of "10" denotes that the "Sequence Number" field has a
size of two octets. Finally, a sequence of "11" denotes that the
"Sequence Number" field has the original length of four octets.
Length
The length field has a fixed length of one octet. Compressed
IPFIX Messages therefore have a maximum length of 255 octets.
An application SHOULD never send a Compressed IPFIX that is bigger
than 102 octets to avoid fragmentation. If the "Export Time" field
is not omitted, it is placed directly behind the length field. If
the Export Time field has a size of four octets, it MUST contain the
time in seconds since 0000 UTC Jan 1, 1970, at which the Compressed
IPFIX Message Header leaves the Exporter. This complies with the
"Export Time" field in IPFIX.
Afterwards, the "Sequence Number" field is attached (if not omitted).
If the field has a length of four bytes, it must contain the number
of records sent since the start of the Exporter module 2^32 at the
end of this Compressed IPFIX Message. If the field is Compressed to
one or two bytes, it must contain the number of IPFIX messages sent
by the Exporter since its start modulo 2^8 or 2^16.
6.2. Compressed Set
A Compressed Set is a set of Compressed Template or Compressed Data
Records. Depending on the Compressed Record type, the Compressed Set
can either be a Compressed Template Set or a Compressed Data Set.
Every Compressed Set is started with an Compressed Set Header and is
Braun, et al. Compressed IPFIX [Page 15]
Internet-Draft Compressed IPFIX September 2011
followed by one or more Compressed Records.
The IPFIX Set Header consists of an two octet "Set ID" field and a
two octet "Length" field. These two fields are compressed to one
octet each for the Compressed Set Header. The format of the
Compressed Set Header is shown in Figure 7.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Comp. Set ID | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Compressed Set Header
The two fields are defined as follows:
Compressed Set ID
The "Compressed Set ID" (Comp. Set ID) identifies the type of
data that is transported in the Compressed Set. A Compressed
Template Set is identified by Compressed Set ID 2. This
corresponds to the Set IDs that are used by Sets in IPFIX.
Compressed Set ID number 3 MUST NOT be used. All values from 4 to
127 are reserved for future use. Values above 127 are used for
Compressed Data Sets.
Length
The "Length" Field contains the total length of the Compressed
Set, including the Compressed Set Header.
6.3. Compressed Template Record Format
The format of the Compressed Template Records is shown in Figure 8.
The Compressed Template Record starts with an Compressed Template
Record Header and is followed by one or more Field Specifiers. The
Field Specifier format is defined as in Section 6.4 and is identical
to the Field Specifier definition in [RFC5101].
Braun, et al. Compressed IPFIX [Page 16]
Internet-Draft Compressed IPFIX September 2011
+--------------------------------------------------+
| Compressed Template Record Header |
+--------------------------------------------------+
| Field Specifier |
+--------------------------------------------------+
| Field Specifier |
+--------------------------------------------------+
...
+--------------------------------------------------+
| Field Specifier |
+--------------------------------------------------+
Figure 8: Compressed Template Format
The format of the Compressed Template Record Header is shown in
Figure 9.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Comp. Temp ID | Field Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Compressed Template Header
Compressed Template ID
Each Compressed Template Record must have a unique Compressed
Template ID (Comp. Temp ID) between 128 and 255. The Compressed
Template ID must be unique for the given Compressed Transport
Session.
Field Count
The number of fields placed in the Compressed Template Record.
6.4. Field Specifier Format
The type and length of the transmitted data is encoded in Field
Specifiers within Compressed Template Records. The Field Specifier
is shown in Figure 10 and is identical with the Field Specifier that
was defined for IPFIX [RFC5101]. The following text has been copied
from [RFC5101] for completeness.
Braun, et al. Compressed IPFIX [Page 17]
Internet-Draft Compressed IPFIX September 2011
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| Information Element ident. | Field Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Enterprise Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Compressed Template Header
Where:
E
Enterprise bit. This is the first bit of the Field Specifier. If
this bit is zero, the Information Element Identifier identifies an
IETF-specified Information Element, and the four-octet Enterprise
Number field MUST NOT be present. If this bit is one, the
Information Element Identifier identifies an enterprise-specific
Information Element, and the Enterprise Number field MUST be
present.
Information Element Identifier
A numeric value that represents the type of Information Element.
Field Length
The length of the corresponding encoded Information Element, in
octets. Refer to [RFC5102]. The value 65535 is illegal as there
are no variable size encoded elements as they are defined in
IPFIX.
Enterprise Number
IANA [IANA] enterprise number of the authority defining the
Information Element identifier in this Template Record.
Vendors can easily define their own data model by registering a
Enterprise ID with IANA. Using their own Enterprise ID, they can use
any ID in the way they want them to use.
6.5. Compressed Data Record Format
The Data Records are sent in Compressed Data Sets. The format of the
Data Records is shown in Figure 11 and matches the Data Record format
from IPFIX.
Braun, et al. Compressed IPFIX [Page 18]
Internet-Draft Compressed IPFIX September 2011
+--------------------------------------------------+
| Field Value |
+--------------------------------------------------+
| Field Value |
+--------------------------------------------------+
...
+--------------------------------------------------+
| Field Value |
+--------------------------------------------------+
Figure 11: Data Record Format
7. Compressed IPFIX Mediation
There are two types of Compressed IPFIX Intermediate Processes. The
first one can occur on the transition between a constraint 6LoWPAN
and the non-constrained network. This mediation changes the network
and transport protocol from 6LowPAN/UDP to IP/(SCTP|TCP|UDP) and is
shown in Figure 12.
+-----------------------+Compressed IPFIX+-------------------------+
|Compressed IPFIX S.M. | 6LoWPAN/UDP |Compressed IPFIX mediator|
| [Exporting Process] |--------------->| [Collecting Process] |
+-----------------------+ | [Exporting Process] |
+-------------------------+
|
Compressed IPFIX |
IP/(UDP/SCTP|TCP) |
v
+-------+------------------+
| Collector(1) |
| [Collecting Process(es)] |
+--------------------------+
Figure 12: Translation from Compressed IPFIX over 6LowPAN/UDP to
Compressed IPFIX over IP/(SCTP|TCP|UDP)
The mediator removes the Compressed IPFIX Messages from the 6LowPAN/
UDP packets and wraps them into the new network and transport
protocols. Templates MUST be managed the same way as in the
constraint environment after the translation to IP/(SCTP|UDP|TCP)
(see Section 8).
The second type of mediation transforms Compressed IPFIX into IPFIX.
Braun, et al. Compressed IPFIX [Page 19]
Internet-Draft Compressed IPFIX September 2011
This process MUST be combined with the transport protocol mediation
as shown in Figure 13.
+------------------------+ Compressed IPFIX+-----------------------+
| Compressed IPFIX S.M. | 6LoWPAN/UDP | IPFIX mediator |
|[Exporting Processes] |---------------->| [Collecting Process] |
+------------------------+ | [Exporting Process] |
+-----------------------+
|
IPFIX |
IP/(UDP/SCTP|TCP) |
v
+-------+------------------+
| Collector(1) |
| [Collecting Process(es)] |
+--------------------------+
Figure 13: Transformation from Compressed IPFIX to IPFIX
This mediation can also be performed by an IPFIX Collector before
parsing the IPFIX message as shown in Figure 14. There is no need
for a Compressed IPFIX parser if such a mediation process can be
employed in front of an already existing IPFIX collector.
+------------------------+ Compressed IPFIX +----------------------+
| Compressed IPFIX S.M. | 6LoWPAN/UDP | IPFIX Mediator |
| [Exporting Processes] |----------------->| [Collecting Process] |
+------------------------+ | [Exporting Process] |
| | |
| |IPFIX |
| | |
| v |
| Collector(1) |
| [Collecting Process] |
+----------------------+
Figure 14: Transformation from Compressed IPFIX to IPFIX
The Compressed Mediation Process has to translate the Compressed
IPFIX Message Header, the Compressed Set Headers and the Compressed
Template Record Header into their counterparts in IPFIX Afterwards,
the new IPFIX Message Length needs to be calculated and inserted into
the IPFIX Message header.
Braun, et al. Compressed IPFIX [Page 20]
Internet-Draft Compressed IPFIX September 2011
7.1. Expanding the Message header
The fields of the IPFIX Message Header that are shown in Figure 5 can
be determined as follows:
Version
This is always 0x000a.
Length
The IPFIX Message Length can only be calculated after the complete
Compressed IPFIX Message has been translated. The new length can
be calculated by adding the length of the IPFIX Message Header,
which is 16 octets, and the length of all Sets that are contained
in the IPFIX Message.
Export Time
If the "Export Time" in the Compressed IPFIX Message Header has a
length of 4 octets, the value from the Compressed Message Header
MUST be used for the IPFIX Message Header. If it was omitted, the
"Export Time" MUST be generated by the Mediator. If the IPFIX
Message is exported again, the "Export Time" field MUST contain
the time in seconds since 0000 UTC Jan 1, 1970, at which the IPFIX
Message leaves the Exporter. If the Message is passed to an IPFIX
Collector for decoding directly, the "Export Time" field is the
time in seconds since 0000 UTC Jan 1 1970 at which the Compressed
IPFIX Message has been received by the Compressed IPFIX Exporter.
Sequence Number
If the Compressed Sequence Number has a length of 4 octets, the
original value MUST be used for the IPFIX Message. If the
Compressed Sequence Number has a size of one or two octets, the
Compressed IPFIX Mediator MUST expand the Compressed Sequence
Number into a four octet field. If the Compressed Sequence Number
was omitted, the Mediator needs to calculate the Sequence Number
as per RFC 5101 [RFC5101].
Observation Domain ID
This is always 0 indicating to the IPFIX Collector, that the
Observation Domain ID is not relevant.
Braun, et al. Compressed IPFIX [Page 21]
Internet-Draft Compressed IPFIX September 2011
7.2. Translating the Set Headers
Both fields in the Compressed Set Header have a size of one octet and
need to be expanded:
Set ID
The field needs to be expanded from one octet to two octets. If
the Set ID is below 128, no recalculation needs to be performed.
This is because all IDs below 128 are reserved for special
messages and match the IDs used in IPFIX. The Compressed Set IDs
starting with 128 identify Data Sets. Therefore, every Compressed
Set ID above 127 needs to be incremented by 128 because IPFIX Data
Set IDs are located above 255.
Set Length
The field needs to be expanded from one octet to two octets. It
needs to be recalculated by adding a value of 2 octet to match the
additional size of the Set Header. For each Compressed Template
Record that is contained in the Compressed Set, 2 more octets need
to be added to the length.
7.3. Expanding the Template Record Header
Both fields in the Compressed Template Record Header have a length of
one octet and therefore need translation:
Template ID
The field needs to be expanded from one octet to two octets. The
Template ID needs to be increased by a value of 128.
Field Count
The field needs to be expanded from one octet to two octets.
8. Template Management
The way Compressed Templates have to be managed depends on the usd
transport protocol. If TCP or SCTP is used, it can be ensured that
Compressed Templates are delivered reliably. Template loss can occur
on UDP on the other hand. If a Template is lost on its way to the
Collector, all following Compressed Data Records that refer to this
Compressed Template cannot be decoded.
Braun, et al. Compressed IPFIX [Page 22]
Internet-Draft Compressed IPFIX September 2011
8.1. TCP / SCTP
If TCP or SCTP is an option and can be used for the transmission of
Compressed IPFIX, Template Management MUST be performed as defined in
[RFC5101] for IPFIX.
8.2. UDP
All specifications for Template management from [RFC5101] apply
unless specified otherwise in this document.
Compressed Templates MUST be sent by an Compressed Exporter before
any Compressed Data Set that refers to the Compressed Template is
transmitted. Compressed Templates are not expected to change over
time in Compressed IPFIX. Hence, a Compressed Template that has been
sent once MAY NOT be withdrawn and MUST NOT expire. If an IPFIX
Smart Meter wants to use another Compressed Template it MUST use a
new Compressed Template ID for the Compressed Template.
As UDP is used, reliable transport of Compressed Templates cannot be
guaranteed and Compressed Templates can be lost. A Compressed
Exporter MUST expect Compressed Template loss. It MUST therefore re-
send its Compressed Templates periodically. A Compressed Template
MUST be re-send after a fixed number of N Compressed IPFIX Messages
that contained Compressed Data Sets that referred to this Compressed
Template. The number N MUST be configured by the application
developer.
9. Security considerations
The same security considerations as for the IPFIX Protocol [RFC5101]
apply.
10. IANA Considerations
The same IANA considerations as for the IPFIX Protocol [RFC5101]
apply.
11. Open Issues
1. Export Time field value if the field is compressed to one or two
bytes is unclear.
2. It is unclear how reserved IPFIX Set IDs above 127 can be
handled, if they are standardized some day
Braun, et al. Compressed IPFIX [Page 23]
Internet-Draft Compressed IPFIX September 2011
3. Translating the one or two byte long Sequence Number from
Compressed IPFIX to IPFIX has some pitfalls when packet loss
occurs.
4. Option Templates need to be defined (they are forbidden right
now)
5. Section on the Collector side (as in RFC 5101) is needed.
12. References
12.1. Norminative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
[RFC5101] Claise, B., "Specification of the IP Flow Information
Export (IPFIX) Protocol for the Exchange of IP Traffic
Flow Information", RFC 5101, January 2008.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, January 2008.
[RFC5470] Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
"Architecture for IP Flow Information Export", RFC 5470,
March 2009.
[RFC5982] Kobayashi, A. and B. Claise, "IP Flow Information Export
(IPFIX) Mediation: Problem Statement", RFC 5982,
August 2010.
[I-D.ietf-ipfix-mediators-framework]
Kobayashi, A., Claise, B., Muenz, G., and K. Ishibashi,
"IPFIX Mediation: Framework",
draft-ietf-ipfix-mediators-framework-09 (work in
progress), October 2010.
[I-D.shelby-core-coap]
Shelby, Z., Frank, B., and D. Sturek, "Constrained
Application Protocol (CoAP)", draft-shelby-core-coap-01
Braun, et al. Compressed IPFIX [Page 24]
Internet-Draft Compressed IPFIX September 2011
(work in progress), May 2010.
12.2. Informative References
[IANA] "IANA Private Enterprise Numbers registry
http://www.iana.org/assignments/enterprise-numbers.".
[Schmitt09]
Schmitt, C. and G. Carle, "Applications for Wireless
Sensor Networks", In Handbook of Research on P2P and Grid
Systems for Service-Oriented Computing: Models,
Methodologies and Applications, Antonopoulos N.;
Exarchakos G.; Li M.; Liotta A. (Eds.), Information
Science Publishing. , 2010.
[Tolle05] Tolle, G., Polastre, J., Szewczyk, R., Turner, N., Tu, K.,
Buonadonna, P., Burgess, S., Gay, D., Hong, W., Dawnson,
T., and D. Culler, "A macroscope in the redwoods", In the
Proceedings of the 3rd ACM Conference on Embedded
Networked Sensor Systems (Sensys 05), San Diego, ACM
Press , November 2005.
[Kim07] Kim, S., Pakzad, S., Culler, D., Demmel, J., Fenves, G.,
Glaser, S., and M. Turon, "Health Monitoring of Civil
Infrastructure Using Wireless Sensor Networks", In the
Proceedings of the 6th International Conference on
Information Processing in Sensor Networks (IPSN 2007),
Cambridge, MA, ACM Press, pp. 254-263 , April 2007.
[SMPC04] Szewczyk, R., Mainwaring, A., Polastre, J., and D. Culler,
"An analysis of a large scale habitat monitoring
application", The Proceedings of the Second ACM Conference
on Embedded Networked Sensor Systems (SenSys 04) ,
November 2004.
[GreatDuck]
Habitat Monitoring on Great Duck Island,
"http://www.greatduckisland.net", The Proceedings of the
Second ACM Conference on Embedded Networked Sensor Systems
(SenSys 04) , November 2004.
[Harvan08]
Harvan, M. and J. Schoenwaelder, "TinyOS Motes on the
Internet: IPv6 over 802.15.4 (6lowpan)", 2008.
[Crossbow]
Crossbow Technologies Inc., "http://www.xbow.com", 2010.
Braun, et al. Compressed IPFIX [Page 25]
Internet-Draft Compressed IPFIX September 2011
Authors' Addresses
Lothar Braun
Technische Universitaet Muenchen
Department of Informatics
Chair for Network Architectures and Services (I8)
Boltzmannstr. 3
Garching 85748
Germany
Email: braun@net.in.tum.de
URI: http://www.net.in.tum.de/~braun
Corinna Schmitt
Technische Universitaet Muenchen
Department of Informatics
Chair for Network Architectures and Services (I8)
Boltzmannstr. 3
Garching 85748
Germany
Email: schmitt@net.in.tum.de
URI: http://www.net.in.tum.de/~schmitt
Benoit Claise
Cisco Systems, Inc.
De Kleetlaan 6a b1
Diegem 1831
Belgium
Email: bclaise@cisco.com
Georg Carle
Technische Universitaet Muenchen
Department of Informatics
Chair for Network Architectures and Services (I8)
Boltzmannstr. 3
Garching 85748
Germany
Email: carle@net.in.tum.de
URI: http://www.net.in.tum.de/~carle
Braun, et al. Compressed IPFIX [Page 26]