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Versions: 00 01 02 03

CoRE                                                            L. Braun
Internet-Draft                                                C. Schmitt
Intended status: Standards Track                             TU Muenchen
Expires: September 2, 2010                                     B. Claise
                                                     Cisco Systems, Inc.
                                                                G. Carle
                                                             TU Muenchen
                                                          March 01, 2010


       Compressed IPFIX for smart meters in constrained networks
                 <draft-braun-core-compressed-ipfix-00>

Abstract

   This document specifies the Compressed IPFIX protocol that serves for
   transmitting measurement data in 6LoWPAN networks [RFC4944].
   Compressed IPFIX is derived from IPFIX [RFC5101] and adopted to the
   needs of constrained networks.  This documents defines 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.

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), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 2, 2010.

Copyright Notice




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   Copyright (c) 2010 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
   publication of this document.  Please review these documents
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   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 BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Document structure . . . . . . . . . . . . . . . . . . . .  4

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5

   3.  Hard- and Software constraints . . . . . . . . . . . . . . . .  6
     3.1.  Hardware constraints . . . . . . . . . . . . . . . . . . .  6
     3.2.  Energy constraints . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Packet size constraints  . . . . . . . . . . . . . . . . .  7
     3.4.  Transport protocol constraints . . . . . . . . . . . . . .  7

   4.  Application scenarios for Compressed IPFIX . . . . . . . . . .  8
     4.1.  Architectures for Compressed IPFIX . . . . . . . . . . . .  9

   5.  Compressed IPFIX Message Format  . . . . . . . . . . . . . . . 11
     5.1.  Compressed IPFIX Message Header  . . . . . . . . . . . . . 12
     5.2.  Compressed Set . . . . . . . . . . . . . . . . . . . . . . 14
     5.3.  Compressed Template Record Format  . . . . . . . . . . . . 15
     5.4.  Field Specifier Format . . . . . . . . . . . . . . . . . . 16
     5.5.  Data Record Format . . . . . . . . . . . . . . . . . . . . 17

   6.  Compressed IPFIX Mediation . . . . . . . . . . . . . . . . . . 18
     6.1.  Expanding the Message header . . . . . . . . . . . . . . . 19
     6.2.  Expanding the Set headers  . . . . . . . . . . . . . . . . 20
     6.3.  Expanding the Template Record Header . . . . . . . . . . . 21

   7.  Template Management  . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  TCP / SCTP . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.2.  UDP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

   8.  Security considerations  . . . . . . . . . . . . . . . . . . . 22




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   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     10.1. Norminative References . . . . . . . . . . . . . . . . . . 22
     10.2. Informative References . . . . . . . . . . . . . . . . . . 23

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24












































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1.  Introduction

   Smart meters that form a constrained wireless network need an
   application protocol that allows the efficient transmission of
   metering data.  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
   network device.  Hence, they don't have a steady network connection,
   but are only part of the wireless network as needed when there is
   data to transmit.  A push protocol like Compressed IPFIX, where data
   is transmitted from the meters to one or more collectors only, 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 them 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 constrained network border.  The
   transformation between one form of IPFIX data into another is known
   as IPFIX Mediation [Kobayashi09].  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 for
   Compressed IPFIX and describes possible architectures for the
   Compressed IPFIX infrastructure.  Section 5 defines the Compressed
   IPFIX protocol itself and shows the differences between Compressed
   and IPFIX.  The Mediation process from Compressed IPFIX to IPFIX is
   described in Section 6.  Section 7 defines the process of Template
   Management on the Exporter and the Collector.  Section 8 and
   Section 9 discuss the security and IANA considerations for Compressed
   IPFIX.







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2.  Terminology

   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, if necessary.  This draft uses the
   expression IPFIX to refer to IPFIX as per RFC 5101 and the expression
   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, Collector and Exporter are defined as
   in [RFC5101].  The term IPFIX Mediator is defined in [Kobayashi09].

   Each of this terms has a correspondent term in Compressed IPFIX.  The
   objects behind these terms are also similar to the objects used for
   IPFIX.  The following list gives a brief overview on the changes to
   the IPFIX objects.  This brief overview is targeted for readers who
   are familiar with IPFIX.  A complete definition of these terms is
   given throughout this document.

   Compressed IPFIX Message

      The Compressed IPFIX Message is similar to an IPFIX Message with
      these exceptions: The Message Header is substituted with a
      Compressed Message Header and the Sets which are contained in the
      Compressed Messages are Compressed Sets.  The Compressed IPFIX
      Message Format is defined in Section 5.

   Compressed Data Set

      A Compressed Data Set is similar to an IPFIX Data Set. The Set
      Header is substituted with a Compressed Set Header.  The
      Compressed Set Header is defined in Section 5.2.

   Compressed Template Set

      A Compressed Template Set is a Template Set whose Set Header is
      replaced by a Compressed Set Header and whose Template Records are
      replaced by Compressed Template Records.

   Compressed Data Record

      A Compressed Data Record equals an IPFIX Data Record.






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   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.  The Compressed Template Record Format is defined
      in Section 5.3.

   Compressed IPFIX Mediator

      A Compressed IPFIX Mediator is an IPFIX Mediator that is able to
      receive and transform Compressed IPFIX Message and to export them
      using IPFIX or Compressed IPFIX as shown in Section 6.


   A Compressed IPFIX Transport Session is defined by the communication
   between an Exporter (identified by an 6LowPAN-Address, the Transport
   Protocol, and the Transport Port) and a 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, memory and energy resources [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.

3.2.  Energy constraints

   Smart meters that are battery powered have hard energy constraints.
   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.



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   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.

3.3.  Packet size constraints

   Compressed IPFIX is supposed to be used in 6LoWPAN networks, which
   are based on IEEE 802.15.4 [RFC4944].  IEEE 802.15.4 defines a
   maximum frame size of 127 octets, which usually leaves 102 octets for
   user data.  IPv6 defines a minimum MTU of 1280 octets.  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 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.
   However, sending IPFIX over UDP and TCP may also be implemented.
   SCTP is the recommended protocol.

   This transport protocol recommendation is not suitable for Compressed
   IPFIX. 6LoWPAN defines a compression scheme, which allows to compress
   an IPv6 header from 40 octets down to 2 octets.  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.  It MAY also offer TCP or SCTP support.
   However, using these protocols is NOT RECOMMENDED as their use will



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   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
   push protocol.  This means all communication that employs Compressed
   IPFIX is unidirectional.  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 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 where 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
   photosynthetically active solar radiation over a long time period.

   Deploying Compressed IPFIX in such scenarios seems to be a good fit.
   The sensors 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 a Message,
   e.g. if the Message size fills the available payload in a single IEEE
   802.15.4 packet, the wireless transceiver can be activated and the
   Message can be transmitted 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



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   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 smart meter decides for
       itself when to send its measurement data.
   2.  The property above allows a smart meter to turn off its wireless
       device in order to save energy, as it does not have to receive
       any data.
   3.  The application is allows to accumulate several measurements into
       a single packet.  Compressed IPFIX easily allows the aggregation
       of several measurements into a single Compressed IPFIX Message
       (or a single packet).  This aggregation can happen on the smart
       meter that aggregates several of its own measurements.  Or it can
       happen within a multi-hop wireless network where one smart meter
       aggregates several Compressed IPFIX Messages into a single
       Message before forwarding them.
   4.  The application MUST accept 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).

4.1.  Architectures for Compressed IPFIX

   Compressed IPFIX Devices can be deployed in different architectures,
   which are similar to the ones described in [RFC5470].  The
   architecture of these deployment possibilities are described in this
   section.  One possible architecture is described in figure Figure 1.








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                             +----------------+     +----------------+
                             |[*Application 1]| ... |[*Application n]|
                             +--------+-------+     +-------+--------+
                                      ^                     ^
                                      |                     |
                                      + = = = = -+- = = = = +
                                                 ^
                                                 |
 +------------------------+                  +-------+------------------+
 |         Sensor         | Compressed IPFIX |         Collector        |
 |[Exporting Process(es)] |----------------->| [Collecting Process(es)] |
 +------------------------+                  +--------------------------+


      Figure 1: Direct transmission between sensors and applications

   A smart meter queries its sensors, encodes the results into a
   Compressed IPFIX Message and sends that Message to one or more
   Collectors.  These Collectors run one or more applications which
   process the collected sensor data.  Such Collectors can be non-
   constrained devices at the constraint network border.

   A second architecture could employ aggregation on Compressed IPFIX
   Messages during their journey through the constrained network
   (Figure 2).  This aggregation can be performed by special aggregator
   nodes, which must have enough resources to perform the aggregation.


+------------------------+                   +-----------------------+
|         Sensor         | Compressed IPFIX  |    Aggregator         |
|[Exporting Process]     |------------------>| [Collecting Process]  |
+------------------------+        +--------->| [Exporting Process]   |
                                  |          +-----------------------+
+------------------------+        |                      |
|         Sensor         |        |      Compressed IPFIX|
|[Exporting Process]     |--------+                      |
+------------------------+                               v
                                             +-------+------------------+
                                             |      Collector(1)        |
                                             | [Collecting Process(es)] |
                                             +--------------------------+


                 Figure 2: Aggregation on Compressed IPFIX

   Several smart meters send their data to one aggregator 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



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   aggregated data can then be re-exported again to one or more
   Collectors.  The aggregator is then one form of a Compressed IPFIX
   Mediator.

   The last scenario, shown in Figure 3, employs another Compressed
   IPFIX Mediation process.


   +------------------------+                  +-----------------------+
   |         Sensors        | Compressed IPFIX |    IPFIX mediator     |
   |[Exporting Processes]   |----------------->| [Collecting Process]  |
   +------------------------+                  | [Exporting Process]   |
                                               +-----------------------+
                                                         |
                                                 IPFIX   |
                                                         |
                                                         v
                                            +-------+------------------+
                                            |      Collector(1)        |
                                            | [Collecting Process(es)] |
                                            +--------------------------+


                 Figure 3: Aggregation on Compressed IPFIX

   The smart meters transmit their Compressed IPFIX Messages to one
   node, e.g. the base station, which translates the Compressed IPFIX
   Messages to IPFIX.  The IPFIX Messages can then be exported into the
   existing IPFIX infrastructure.  The Mediation process from Compressed
   IPFIX to IPFIX is described in Section 6.

   Compressed IPFIX fits especially into those scenarios where sensors
   report their measurement data for accounting purposes and where
   packet loss is acceptable.


5.  Compressed IPFIX Message Format

   A Compressed IFPIX Message starts with a Message header, followed by
   one or more Sets.  The Sets can be any of the possible two types:
   Template Set and Data Set. An IPFIX Message MUST only contain one
   type of Set. The structure of the Compressed IPFIX message equals the
   structure of the IPFIX Messages with the following exceptions:
   1.  The Message header, the Set Header and the Template Header format
       use compression to reduce the header sizes.  This compression
       leads to the fact that only a subset of possible IPFIX Messages
       can be encoded in Compressed IPFIX message.  However, each
       Compressed IPFIX Message can be transformed into an IPFIX



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       Message.
   2.  There are no Option Sets in Compressed IPFIX.

   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

5.1.  Compressed IPFIX Message Header

   The Compressed IPFIX Message header is derived from the IPFIX Message
   header.  This is done by using compression on some of the header
   fields.  The original Message Header is shown in Figure 5.  Its
   length is 16 octets and every IPFIX Message has to be started with
   this header.



    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                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 5: IPFIX Message Header

   In order to reduce the header overhead from prepending a 16 octet
   message header, Compressed IPFIX introduces a Compressed IPFIX



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   Message Header that can reduce the header length to two octets.  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 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 6).

   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.

   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



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      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 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 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.

5.2.  Compressed Set

   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.









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   0                   1
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Set ID     |    Length     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 7: Compressed Set Header

   The two fields are defined as follows:

   Set ID

      The "Set ID" identifies the type of data that is transported in
      the Set. A Template Set is identified by Set ID 2.  This
      corresponds to the Set IDs that are used by IPFIX.  ID number 3
      MUST NOT be used.  All values from 4 to 127 are reserved for
      future use.  Values above 127 are used for Data Sets.

   Length

      The "Length" Field contains the total length of the set, including
      the Compressed Set Header.  This length MUST be set to the correct
      value.  It is necessary for an IPFIX Mediator as it only has to
      parse and expand the Set headers and needs the length information
      to proceed to the next Set header.

5.3.  Compressed Template Record Format

   The format of the Compressed Template Records is shown in Figure 8.
   It equals the format of IPFIX Template Records.  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 5.4 and is identical to the Field
   specifier definition in [RFC5101].


      +--------------------------------------------------+
      | Compressed Template Record Header                |
      +--------------------------------------------------+
      | Field Specifier                                  |
      +--------------------------------------------------+
      | Field Specifier                                  |
      +--------------------------------------------------+
       ...
      +--------------------------------------------------+
      | Field Specifier                                  |
      +--------------------------------------------------+



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                   Figure 8: Compressed Template Format

   The format of the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Temp ID(> 127) |  Field Count  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 9: Compressed Template Header


   Temp ID

      Each Template Record must have a unique Template ID between 128
      and 255.  The Template ID must be unique for the given Compressed
      Transport Session.

   Field Count

      The number of fields placed in the Template Record.

5.4.  Field Specifier Format

   The type and length of the transmitted data is encoded in Field
   Specifiers within Template Records.  The Field Specifier is shown in
   Figure 10 and is identical with the Field Specifier that was defined
   for IPFIX.


      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:






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   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.

5.5.  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.


      +--------------------------------------------------+
      | Field Value                                      |
      +--------------------------------------------------+
      | Field Value                                      |
      +--------------------------------------------------+
       ...
      +--------------------------------------------------+
      | Field Value                                      |
      +--------------------------------------------------+





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                       Figure 11: Data Record Format


6.  Compressed IPFIX Mediation

   There are two types of Compressed IPFIX mediation 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 +-----------------------+
   |         Sensors        |    6LoWPAN/UDP   |    IPFIX mediator     |
   |[Exporting Processes]   |----------------->| [Collecting Process]  |
   +------------------------+                  | [Exporting Process]   |
                                               +-----------------------+
                                                         |
                                      Compressed IPFIX   |
                                      IP/(UDP/SCTP|TCP)  |
                                                         v
                                            +-------+------------------+
                                            |      Collector(1)        |
                                            | [Collecting Process(es)] |
                                            +--------------------------+


    Figure 12: Transformation from compressed IPFIX over 6LowPAN/UDP to
                             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 7).

   The second type of mediation transforms Compressed IPFIX into IPFIX.
   This process MUST be combined with the transport protocol mediation
   as shown in Figure 13.












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   +------------------------+ Compressed IPFIX +-----------------------+
   |         Sensors        |    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 +-----------------------------+
|         Sensors        |    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 mediation process has to uncompress the IPFIX Message header, the
   Set Headers and the Template Record Header.  Afterwards, the new
   Message Length needs to be calculated and inserted into the Message
   header.

6.1.  Expanding the Message header

   The fields of the IPFIX Message Header that are shown in Figure 5 can
   be determined as follows:




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   Version

      This is always 0x000a.

   Length

      The IPFIX Message length can only be calculated after the complete
      message has been expanded.  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 original value MUST be used for the IPFIX
      Message.  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.

   Sequence Number

      If the "Sequence Number" is not compressed, the original value
      MUST be used for the IPFIX message.  If the number was compressed
      to one or two octets, the IPFIX Mediator MUST expand the
      Compressed Sequence Number into a four octet field.  If the
      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.


6.2.  Expanding the Set headers

   Both fields in the Compressed Set header are compressed and need to
   be expanded:







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   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 octets to match
      the additional size of the expanded Set Header.  For each Template
      Record that is contained in the Set, 2 more octets need to be
      added to the length.

6.3.  Expanding the Template Record Header

   Both fields in the Compressed Template Record Header are Compressed
   and therefore need expansion:

   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.


7.  Template Management

   The way Templates have to be managed depends on the transport
   protocol in use.  If TCP or SCTP is used, it can be ensured that
   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 Data Records that refer to this Template cannot be
   decoded.

7.1.  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
   standardized in [RFC5101] for IPFIX.




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7.2.  UDP

   Compressed IPFIX Templates MUST be sent by an Exporter before any
   Data that refers to the Template is transmitted.  Templates are not
   expected to change over time in Compressed IPFIX.  Hence, a Template
   that has been sent once MAY NOT be withdrawn and MUST NOT expire.  If
   a Sensor Node wants to use another Template it MUST use a new
   Template ID for this different Template.

   As UDP is used, reliable transport of Templates cannot be guaranteed
   and Templates can be lost and a Compressed Exporter MUST expect
   Template loss.  It MUST therefore re-send its template periodically.
   A Template MUST be re-send after a fixed number of N IPFIX Messages
   that contained Data Sets that referred to this Template.  The number
   N may be chosen by the application developer.


8.  Security considerations

   There are no security considerations defined in this draft (yet).
   There should be though ...


9.  IANA Considerations

   The Compressed IPFIX version number needs to be registered with IANA.
   The Set ID numbers used in this draft are already registered and
   their meaning is not changed.

   New assignments in either IPFIX Version Number or IPFIX Set ID
   assignments require a Standards Action [RFC2434], i.e., they are to
   be made via Standards Track RFCs approved by the IESG.


10.  References

10.1.  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.



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   [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.

   [Kobayashi09]
              Kobayashi, A. and B. Claise, "IPFIX Mediation: Problem
              Statement",
              draft-ietf-ipfix-mediators-problem-statement-07 ,
              December 2009.

   [Shelby09]
              Shelby, Z., Garrison Stuber, N., Sturek, D., Frank, B.,
              and R. Kelsey, "CoAP Feature Analysis",
              draft-shelby-6-lowapp-coap-00 , December 2009.

10.2.  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),



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              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.


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





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   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
































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