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Network Working Group                                           A. Fessi
Internet-Draft                                   University of Tuebingen
Expires: December 27, 2006                                    C. Kappler
                                                                  C. Fan
                                                              Siemens AG
                                                             F. Dressler
                                                  University of Erlangen
                                                                A. Klenk
                                                 University of Tuebingen
                                                           June 25, 2006


                      Framework for Metering NSLP
               <draft-fessi-nsis-m-nslp-framework-03.txt>

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 27, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Monitoring, metering and accounting of packets are increasingly
   important functionalities that need to be provided in the Internet.



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   This document motivates and describes a framework for the path-
   coupled configuration of Metering Entities to record monitoring and
   measurement data and report it to a data collector.  Different
   scenarios are described where such a path-coupled configuration is
   useful.  Currently, the focus is on two scenarios: accounting and QoS
   measurement.

   Moreover, this document gathers requirements for a path-coupled
   configuration protocol of Metering Entities.  Finally, the
   applicability of the NSIS architecture for this purpose is discussed.
   The protocol itself is specified in a separate document
   [I-D.dressler-nsis-metering-nslp]


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4

   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  4

   4.  Scenarios  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Accounting . . . . . . . . . . . . . . . . . . . . . . . .  6
       4.1.1.  Scenario Description . . . . . . . . . . . . . . . . .  6
       4.1.2.  Required Configuration Parameters  . . . . . . . . . .  8
     4.2.  QoS Monitoring . . . . . . . . . . . . . . . . . . . . . . 10
       4.2.1.  Scenario Description . . . . . . . . . . . . . . . . . 10
       4.2.2.  Required Configuration Parameters  . . . . . . . . . . 13

   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 14
     5.1.  General requirements . . . . . . . . . . . . . . . . . . . 15
       5.1.1.  Extensibility  . . . . . . . . . . . . . . . . . . . . 15
       5.1.2.  Scalability  . . . . . . . . . . . . . . . . . . . . . 15
       5.1.3.  Security . . . . . . . . . . . . . . . . . . . . . . . 15
     5.2.  Distinguishing flows . . . . . . . . . . . . . . . . . . . 15
     5.3.  Aggregation of Metering Records  . . . . . . . . . . . . . 15
     5.4.  Transport of Metering Records  . . . . . . . . . . . . . . 16
     5.5.  Location of Metering Entities  . . . . . . . . . . . . . . 16
     5.6.  Location of the Collectors . . . . . . . . . . . . . . . . 16
     5.7.  Configuration protocol . . . . . . . . . . . . . . . . . . 16
       5.7.1.  Configuration of Metering Entities . . . . . . . . . . 16
       5.7.2.  Selection of Metering Entities . . . . . . . . . . . . 16
       5.7.3.  Metering Configuration State installation and
               removal  . . . . . . . . . . . . . . . . . . . . . . . 16
       5.7.4.  Initiation and maintenance of metering tasks . . . . . 17
       5.7.5.  Reaction to Route Changes  . . . . . . . . . . . . . . 17
       5.7.6.  Coordination of Metering Entities  . . . . . . . . . . 17



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       5.7.7.  Scoping of configuration . . . . . . . . . . . . . . . 17
       5.7.8.  Collection of information on available Metering
               Entities . . . . . . . . . . . . . . . . . . . . . . . 17
     5.8.  Metering across domains  . . . . . . . . . . . . . . . . . 18

   6.  Applicability of the NSIS Architecture . . . . . . . . . . . . 18

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     7.1.  Authorization Model  . . . . . . . . . . . . . . . . . . . 18
     7.2.  Inter-working between different domains  . . . . . . . . . 19
     7.3.  End User Privacy . . . . . . . . . . . . . . . . . . . . . 19
     7.4.  ISP Privacy  . . . . . . . . . . . . . . . . . . . . . . . 19
     7.5.  Forged Collector . . . . . . . . . . . . . . . . . . . . . 19
     7.6.  Denial-of-Service Attacks on the Collector . . . . . . . . 20
     7.7.  Denial-of-Service Attacks on Metering Entities . . . . . . 20
     7.8.  Verification of the Flow Specification . . . . . . . . . . 20

   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20

   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 21

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
   Intellectual Property and Copyright Statements . . . . . . . . . . 25


























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1.  Introduction

   Monitoring, metering and accounting of packets is an important
   functionality in many networks today.  Several working groups are
   working on mechanisms for collecting and reporting usage data, flow
   or packet information.  For example, the IPFIX (IP Flow Information
   Export) Working Group defines a protocol to collect and report flow
   information ([I-D.ietf-ipfix-protocol]).  The PSAMP (Packet SAMPling)
   Working Group focuses on reporting per packet information for further
   processing ([I-D.ietf-psamp-framework]).

   However, it is also necessary to configure and coordinate the
   entities performing the metering.  If one or more Metering Entities
   should meter a specific flow, then all potential candidates for this
   task are on the path followed by this particular flow.  They can be
   addressed by sending a configuration message along the path of the
   flow.  If more than one Metering Entity is required, all of them can
   potentially be configured and coordinated with a single message along
   the path.

   The Metering Entities can either collect statistics on these flows,
   perform packet sampling or apply some other special treatment for the
   packets, for example, examining the packet payload, or just report
   that this packet has passed this point.  The Metering Entities can be
   configured and can be coordinated to achieve a certain goal together,
   which can be, for example, accounting or QoS monitoring.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Furthermore, this document uses the terms "Metering Record",
   "Monitoring Probe", "Metering Entity", "Collector", as defined in
   [I-D.dressler-nsis-metering-nslp].


3.  Problem Statement

   There is a need in industry and the Internet research community to
   collect and export information on data flows.  We call such
   information Metering Records.  Metering Records are useful in
   mediation systems, accounting systems, and network management
   systems.  They facilitate services such as Internet research,
   measurement, accounting, billing, QoS monitoring, intrusion
   detection, and traffic profiling/engineering.  In recognition of the



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   need for such metering the IPFIX WG was founded.

   While the purpose for collecting Metering Records in each case is
   different, the basic architecture of such metering systems is usually
   identical, cf. Figure 1.  Metering data is collected by a Monitoring
   Probe.  The Metering Entity produces Metering Records from the
   metering data or additional data such as session information.  The
   Metering Entity transmits its Metering Records to a Collector.  The
   Collector correlates Metering Records relating to the same event from
   different Metering Entities.  There might be more than one Collector
   depending on the actual tasks.



                       +-----------------+
                       |    Collector    |
                       | +-------------+ |
                       | | Met. Record | |
                       | +-------------+ |
                       +-----------------+
                           ^ ^ ^ ^ ^
                       ***     *    ***
                    ***        *       ***
                 ***           *          ***
              ***              *              ***
       +-------------+    +-----------+    +-------------+
       |  Metering   |    |  Metering |    |  Metering   |
       |   Entity    |    |   Entity  |    |   Entity    |
   --->|             |--->|           |--->|             |
       |+----+ +----+|    |   +----+  |    |+----+ +----+|
       || MP | | MP ||    |   | MP |  |    || MP | | MP ||
       |+----+ +----+|    |   +----+  |    |+----+ +----+|
       +-------------+    +-----------+    +-------------+

       +----+                     --- = Data Flow
       | MP | = Monitoring
       +----+   Probe             *** = other Signaling
                                        Messages

   Figure 1: Schematic Metering Architecture

   In this context two problems need to be solved:
   o  Metering Records need to be transported from the Metering Entities
      to the Collector.  IPFIX is, for example, a suitable protocol for
      this task.
   o  The Metering Entities need to be configured and coordinated.  This
      document suggests path-coupled signaling for this purpose.




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   In a flexible environment, it must be possible to dynamically
   configure and coordinate Metering Entities rather than hardwiring
   them.  Configuration and coordination include, for example, which
   entities peform the metering for a particular flow, providing
   triggers to start or stop metering, distribution of identifiers for
   the Collector to correlate Metering Records, and so forth.  The IPFIX
   WG has identified the needs for such configurations but has defined
   the work currently as "out of the scope" [RFC3917].  The
   configuration can be performed, for example, using RADIUS ([RFC2138])
   or DIAMETER ([RFC3588]).  The PSAMP (Packet Sampling) WG is also
   currently developing a MIB module for configuring packet sampling
   ([I-D.ietf-psamp-mib]).  Nevertheless, all these alternatives allow
   only the configuration of single Metering Entities, and assume that
   the location of the Metering Entities to be configured is known in
   advance.  Dynamic discovery, configuration and coordination of
   distributed Metering Entities is not supported.

   Since the most appropriate Metering Entities for metering a specific
   flow are located along the path of the flow itself, a path-coupled
   signaling protocol for distributing the configuration information
   seems useful.


4.  Scenarios

   This section describes two different scenarios for the usage of path-
   coupled configuration of Metering Entities: accounting and QoS
   monitoring.

4.1.  Accounting

4.1.1.  Scenario Description

   Flexible usage-based charging is mainly a problem in 3G mobile
   telecommunication networks.  With the advent of IP in these networks
   and with 3GPP's All-IP perspective, there is also an increasing need
   for IP technology to provide such functionality.

   When starting an application session, for example, a video streaming,
   usually there are several potential Metering Entities on the data
   path, for example, the application server, the WLAN access point, the
   ingress nodes of several transit networks or any router on the path
   with metering functionality.  These Metering Entities have different
   capabilities.  For example, routers along the path might be able to
   account packets and packets sizes while the WLAN access point is able
   to report the usage of the wireless link and whether the end host is
   roaming.  If content-based accounting is also required, the most
   appropriate Metering Entity to perform this task will be the



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   Application Server.

   An example of such a scenario is illustrated in Figure 2 where a data
   receiver expects data from a data sender via two routers Router 1 and
   Router 2.  The application server (i.e., data sender) may or may not
   (as in Figure 2) belong to the administrative domain.


                   +-------------------------+
   Data Receiver   | Router 1    Router 2    |       Data Sender
   +-----------+   |  +-----+     +-----+    |      +-----------+
   |           |<-----|     |<----|     |<----------|Application|
   |Application|   |  |+---+|     |+---+|    |      |   +---+   |
   |           |   |  ||ME ||<===>||ME ||<=========>|   |ME |   |
   +-----------+   |  |+---+|     |+---+|    |      |   +---+   |
                   |  +-----+     +-----+    |      +-----------+
                   |   Administrative Domain |
                   +-------------------------+
       +---+
       |ME | = Metering     === = Signaling    --- = Data Flow
       +---+   Entity             Messages

   Figure 2: Signaling to configure metering for accounting

   As a prerequisite to charging, one or more Metering Entities collect
   Metering Records independently for the same session.  Existing
   accounting concepts handle multiple Metering Entities by statically
   configuring them [3GPP.32.260],[3GPP.32.251].  Some of those Metering
   Entities always generate Metering Records, which will may be
   discarded later.  For example, in the case of a pure content charging
   scheme, only the Metering Entity at the Data Sender (Application
   Server) needs to perform metering.  All other Metering Entities do
   not need to perform any metering since their Metering Records will be
   discarded anyway.  Therefore, a flexible mechanism is required to
   distribute this information to the Metering Entities along the path
   and to find the appropriate Metering Entity on the path depending on
   the charging scheme.

   In the case where a mixed content and access charging should be
   applied, not only the content accessed but also the data volume is
   relevant for the metering process.  In this case, the Metering Entity
   at the Data Sender should be configured to account the content
   accessed, and one of the other Metering Entities along the path, for
   example, Router 1 or Router 2 must be configured to count bytes.

   Furthermore, Metering Records need to be correlated at the Collector
   in order to match them to the same session.  In current accounting
   concepts ([3GPP.32.260]), data correlation is performed by statically



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   configuring one of Metering Entities to generate a correlation ID,
   and by manually configuring a chain of Metering Entities to which
   this correlation ID is distributed.  This is very inflexible and
   leads to unnecessary overhead.

   Using a path-coupled configuration protocol, this correlation ID can
   be distributed at the configuration.

   When a handover occurs ([3GPP.32.252]) other Metering Entities become
   involved, for example the new WLAN access point.  Metering Records
   collected by the different Metering Entities needs to be correlated
   and aggregated.

   Furthermore, Metering Entities need to know to which Collector they
   must send their Metering Records.  This information can be also be
   distributed dynamically during the signaling for configuration.

4.1.2.  Required Configuration Parameters

   In a client/server environment the Application Server (for example, a
   video streaming server) acts as signaling initiator.  It sends a
   configuring request message towards the user terminal.  The Metering
   Entities along the path evaluate this message.

   Given that the user terminal can not be seen as a trusted network
   function, the signaling will travel until the last router before the
   user terminal which might be, for instance, a WLAN access point.
   This router acts as a signaling responder.

   The parameters that need to be configured with the configuration
   request message are the following:

   Correlation ID

      This parameter refers to an ID which is unique for each service.
      It will be used by the Collector to assign different accounting
      records to the same service.

   Flow Specification

      This parameter identifies the data flow(s) that need(s) to be
      accounted.  Here, the flow information from the NTLP can be used.
      However, several entries SHOULD be possible for this parameter to
      enable configuring the Metering Entities to perform accounting for
      several flows (for instance audio and video) using a single
      configuration message.





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   Metered Objects

      This parameter contains a list of the objects that need to be
      accounted for the considered data flow.

      *  Flow Properties: These are dynamic properties of the data
         stream to be metered:
         +  number of observed packets of the flow
         +  number of observed octets of the flow
         +  timestamp of first observation of a packet of the flow.
         +  timestamp of last observation of a packet of the flow.

      Note that in the timestamps, the absolute time might be required
      since the tariffs might depend on the time of the day.

      Besides the metered objects above, the following objects may also
      need to be recorded and reported to the Collector:

      *  Application events: service invocation, insertion of
         advertisement and other application events.
      *  Mobility events: horizontal and vertical handovers.
      *  Bearer events: loss of bearer
      *  Access network type
      *  Report if the end host is roaming.
      *  Access network types: so the user can be charged differently
         depending on the current access technology
      *  Different identities for the end host: e.g.  Mobile Subsriber
         ISDN Number(MSISDN)
      *  IP address of gateways, meters and other network elements

   Reporting Interval

      In order to reduce the number of export messages sent to the
      Collector, it is advantageous not to send accounting data
      immediately but to wait until the message is filled with a certain
      amount of data.  This parameter indicates the maximum time to wait
      for more data until an exported data set is sent.  Long living
      flows are reported regularly in interval no longer than specified
      by this parameter.

   Flow Expiration Time

      If no packets are observed for the specified amount of time
      interval, the flow is considered as expired and it is reported.







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   Collector ID

      This parameter specifies where the accounting records need to be
      sent to.

   Reporting Protocol

      This parameter specifies which protocol to use to report the
      accounting data, for example, IPFIX, Diameter, Netflow5 or
      Netflow9.

   Selection of Metering Entities

      This parameter determines how the Metering Entities that should
      perform the accounting of the considered data flow are selected.
      For the accounting scenario, possible options for this parameter
      are:
      *  ANY: any Metering Entity on the path that is capable of
         performing accounting with the requested objects in the
         parameter "Metered Objects" should do it.  In the extreme case,
         this could be the signaling initiator itself.
      *  Enterprise-specific: Enterprises may wish to define their own
         methods to decide which Metering Entities should perform the
         metering.  In this case, the parameter "Selection of Metering
         Entities" needs to be combined with an enterprise-specific
         identifier.  (See also
         http://www.iana.org/assignments/enterprise-numbers)


4.2.  QoS Monitoring

4.2.1.  Scenario Description

   For a network user, it may be interesting at any time to check the
   QoS for a certain service.  The service of interest can be coarse
   grained, for example, the QoS parameters provided by the link to the
   edge router (access point) or fine grained, for example, the QoS
   provided to a UDP data stream received from a video server.  In any
   case, the first step of analysis that the user can perform is
   measuring the rates of sent and received traffic (including a
   consideration of re-transmissions).

   In such cases, local measurement is not sufficient.  A next step of
   analysis would be QoS measurement along the data path of the service
   of interest.  A measurement of packet bit rate, packet loss, jitter
   and other QoS parameters at several points of the data path could
   identify the cause of unsatisfactory QoS and locate where it is
   caused.



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   A similar, probably more important scenario is an ISP that detects
   that the QoS it provides to a customer does not match the service
   level agreement for this service.  Then a measurement at several
   locations along the data path of the service of interest would be
   desirable for identifying the cause and location of QoS degradation.

   Both cases described above (and a range of related cases) could be
   solved by massive deployment of metering technology, for example, by
   measuring all flows at all routers in the network.  Then, in case of
   a problem (or of a regular check) the information for a certain flow
   of interest can be retrieved from the huge amount of collected
   metering data.  This approach is oversized, scales badly, and the
   benefit gained is most likely not worth the investment and the
   operational costs.

   Configuring available Metering Entities on the data path appears to
   be a more appropriate approach.  In such a scenario, the requesting
   party would configure some or all available Metering Entities along
   the path of a service of interest in order to meter the particular
   service and report the metered data.

   Such configuration can be performed in a traditional way by
   individually, one by one, configuring all Metering Entities.  This
   requires knowledge about the path taken by the service of interest,
   knowledge about the available Metering Entities on this path and a
   communication with each of them using an agreed (preferably
   standardized) protocol.

   The approach suggested by this document simplifies this task.  By
   using path-coupled configuration of traffic measurement, a requesting
   party that is located on the path of interest does just need to send
   a single configuration request along the path in order to communicate
   with all available Metering Entities on this particular path.

   Since different measurements are required for different QoS
   parameters, the request sent along the path may vary.  This is
   illustrated by two example scenarios, one for packet loss metering
   and one for delay metering.













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              +-------------------------------------------------+
              |                                                 |
              |              Administrative Domain              |
              |                                                 |
              |  ingress     internal    internal     egress    |
              |   node        node 1      node 2       node     |
   +------+   | +-----+      +-----+      +-----+      +-----+  |
   | host |   | |     |<====>|     |<====>|     |<====>|     |  |
   |      |---->| ME  |----->| ME  |----->| ME  |----->|  ME |---->
   +------+   | +-----+      +-----+      +-----+      +-----+  |
              |                                                 |
              +-------------------------------------------------+

             +---+
             |ME | = Metering   === = Signaling    --- = Data Flow
             +---+   Entity           Messages

   Figure 3: Signaling to configure metering for QoS monitoring

   Figure 3 shows a data stream passing a domain.  Let's assume that at
   the ingress node a problem with the data stream is detected and that
   it wants to initiate traffic measurement for the data stream along
   the path it takes through the domain.  Then the ingress node sends a
   signaling message along the path in order to configure available
   Metering Entities.

   If packet loss in the domain is the target of this investigation,
   then all available Metering Entities on the path will be requested to
   participate in the measurement.  All will be requested to measure the
   number of packets observed for the data stream of interest and to
   report the results to either the requesting ingress node or to
   another Collector of traffic metering data.  Then the collected data
   can be analyzed in order to identify locations in the domain where
   packet loss occurs.  Note here, that the Metering Entities need to
   report their positions on the path to the Collector in order to
   enable correct evaluation of the Metering Records.

   In a similar way delay can be analyzed.  Different to loss metering,
   delay measurement requires per packet reporting from the Metering
   Entities.  For each observed packet belonging to the data stream of
   interest, the Metering entity needs to report a hash value of the
   packet header and a timestamp.  In order to reduce the number of
   reports, reporting can be restricted to a sampled set of packets.
   Sampling algorithms are defined in [I-D.ietf-psamp-framework].  If
   hash-based sampling is used, different Metering Entities along the
   path will sample the same set of packets and report the time-stamped
   hashvalues of these packet.  Then the Collector can correlate the
   Metering Records received from different Metering Entities and can



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   again analyze the sources of delay within the domain.

   Note here that, as above, the Metering Entities need to report their
   positions on the path to the Collector.

   Note also that the sampling algorithm plays a key role in the
   evaluation of the Metering Records.  For example, if probabilistic
   sampling is deployed, the Collector can not correlate Metering
   Records from different Metering Entitiy, since they will most
   probably contains information about unrelated packets.

   If less detailed metering is required, for example, if loss and delay
   only needs to be measured for the entire domain (and not hop by hop),
   then not all Metering Entities need to participate.  It is sufficient
   if just the ingress and the egress node perform metering.  Metering
   at internal nodes is not required.  Per-domain packet loss and per-
   domain delay can be derived from packet counters and time stamped
   packet hash values metered at ingress and egress nodes.

4.2.2.  Required Configuration Parameters

   Very similar to the accounting scenario in Section 4.1.2, the
   signaling initiator sends a configuration request message along the
   data path.  The parameters that need to be configured are the
   following:

   Correlation ID

      Similar to the accounting scenario, this is an ID that identifies
      this measurement.  It can be used by the Collector for identifying
      incoming reports that belong to the same measurement.

   Flow ID

      Same as for the accounting scenario

   Metered Objects

      The objects to be measured:
      1.  Flow Properties: same as for the accounting scenario.
      2.  Packet Properties:
          +  hash value
          +  number of octets
          +  time stamp







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   Packet Sampling Algorithm

      If packet properties need to be reported, this parameter specified
      which packet sampling to be used.

   Reporting Interval

      Same as for the accounting scenario

   Flow Expiration Time

      Same as for the accounting scenario

   Collector ID

      Same as for the accounting scenario

   Reporting Protocol

      Same as for the accounting scenario

   Selection of Metering Entities

      This parameter specifies the requirement for Metering Entities
      along the data path.  Among the required values for this parameter
      are
      *  first: only the first available Metering Entity on the path is
         requested to perform metering.  In the extreme case, this
         request is served by the signaling initiator itself.
      *  last: only the last available Metering Entity on the path is
         requested to perform metering.  In the extreme case, this
         request is served by the signaling responder.
      *  all: all available Metering Entities on the path are requested
         to perform metering.
      *  first and last: only the first and the last available Metering
         Entities on the path are requested to perform metering.



5.  Requirements

   This section describes the requirements for a path-coupled signaling
   for the configuration of Metering Entities.  We assume existing
   protocols or other means for transferring Metering Records from the
   Metering Entities to Collectors.






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5.1.  General requirements

5.1.1.  Extensibility

   The metering configuration protocol MUST support an extensible
   metering model.  Depending on the metering scenario, different
   information must be exchanged between the Metering Entities.

   The specification of the path-coupled metering configuration protocol
   SHOULD be extensible to future technologies.

   Moreover, the metering configuration protocol should bridge between
   different existing metering solutions, for example, those defined in
   3GPP.  The communication may be organized using proxies.

5.1.2.  Scalability

   A Metering Entity needs to keep state and perform metering actions
   for each accepted metering task.  Handling high numbers of metering
   tasks need to be provided by the Metering Entity implementation and
   is not subject of a signaling protocol.  However, the protocol design
   should provide scalability for state keeping and refresh for a large
   number of concurrent metering tasks.

5.1.3.  Security

   Security requirement of the path-coupled metering configuration
   protocol are discussed in Section 7

5.2.  Distinguishing flows

   A primary capability of the metering function is the identification
   of data packets belonging to different applications or users.  The
   configuration of the Metering Entities should take this parameter
   into account.  During the data flow life-time, statistics describing
   the properties of this data flow are gathered and exported to a
   Collector.  The metering configuration should be flexible to allow
   the description of multiple services and associated flows.

   Flows belonging to one application: the metering configuration should
   allow the aggregation of Metering Records for streams belonging to a
   particular application, for example, a multimedia transmission with
   associated data transfers (web pages).

5.3.  Aggregation of Metering Records

   The metering configuration SHOULD allow the aggregation of Metering
   Records belonging to the same measurement or to the same applications



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   to reduce the data exported to the Collector.

5.4.  Transport of Metering Records

   The protocol for configuring Metering Entities MUST be independent of
   the protocol used for transferring Metering Records.  One possible
   protocol is IPFIX [I-D.ietf-ipfix-protocol].  The IPFIX information
   model ([I-D.ietf-ipfix-info]) is very flexible for extensions and,
   therefore, adequate for this application.

5.5.  Location of Metering Entities

   The Metering Entities are located on the data path, i.e., on the path
   of the data that should be metered.  It is an open issue how the
   initiator and receiver of the metering configuration signaling are
   determined.

   Metering Entities can be located anywhere along the data path, for
   example, only in a subset of the path, or only at start and end point
   etc.

5.6.  Location of the Collectors

   The Metering Records need to be transferred to one or eventually
   several Collectors.  The process of discovering which Collector is
   interested in which Metering Records is out of scope.  It is assumed
   that the signaling initiator learns the location of the Collectors by
   different means.

5.7.  Configuration protocol

5.7.1.  Configuration of Metering Entities

   The protocol MUST be able to configure Metering Entities, for
   example, to control which information needs to be collected and which
   entities are allocated which task.

   Protocol messages need to be interpreted only by Metering Entities.

5.7.2.  Selection of Metering Entities

   The protocol MUST provide functionality to select Metering Entities
   that become part of a metering process by specifying, for example,
   their type, position or total number.

5.7.3.  Metering Configuration State installation and removal

   The protocol MUST be able to install metering state and also to



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   remove it.  Furthermore, metering state MUST be soft state in order
   to cope with rerouting and device failure.

5.7.4.  Initiation and maintenance of metering tasks

   The protocol MUST be able to transport a trigger to start and stop
   the collection of metering data, a correlation identifier that allows
   the Collector to correlate Metering Records received from different
   Metering Entities, and a trigger to send off Metering Records to the
   Collector.

5.7.5.  Reaction to Route Changes

   The protocol MUST be able to react to rerouting of the packets that
   are to be metered.  Rerouting may imply including new Metering
   Entities and removing others.

   This requirement is important especially for the accounting scenario:
   if routes change unnoticed the user will use the service for free.

5.7.6.  Coordination of Metering Entities

   The protocol MUST be able to configure and coordinate several
   Metering Entities along the signaling path to gather and report
   Metering Records belonging to the same session/measurement.

5.7.7.  Scoping of configuration

   The protocol MUST be able to scope messages.  For example, the scope
   could be the domain of an operator.  Another important type of scope
   is up to a particular type of Metering Entity.  An example is a scope
   that terminates a signaling message at the access router in order to
   hide monitoring or charging configuration data from the user (and
   also save resources on the air interface).

   Another example is scoping the signaling, for example, at the
   responsible UMTS GGSN because it is known that Metering Entities
   beyond the GGSN are of no interest for this particular metering
   configuration.

5.7.8.  Collection of information on available Metering Entities

   The protocol MAY support the collection of information on Metering
   Entities and their capabilities without actually installing any
   state.






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5.8.  Metering across domains

   Metering configuration SHOULD be possible across administrative
   domains.  There are challenging security aspects in this goal.  (See
   also Section 7)


6.  Applicability of the NSIS Architecture

   According to the NSIS framework [RFC4080], the NSIS protocol suite
   can support various signaling applications that need to install or
   manipulate state in NSIS-aware network nodes (NEs) along the path of
   a data flow.  The NSLP messages do not need to run all the way
   between the data flow endpoints.  Rather, the NSIS initiating NE and
   the NSIS receiving NE can be located anywhere along the data path.

   The problem of path-coupled signaling to configure Metering Entities
   seems to be well suited to be solved with an NSIS signaling
   application, the Metering NSLP.  The Metering NSLP can run on top of
   the NTLP similarly to the QoS NSLP [I-D.ietf-nsis-qos-nslp] and the
   NAT/Firewall NSLP [I-D.ietf-nsis-nslp-natfw]

   The Metering NSLP needs to be able to install, modify and remove
   metering configuration related state.  Furthermore, signaling for
   metering configuration needs the flexibility provided by NSIS to
   start and end on arbitrary Metering Entities.  Any Metering Entity on
   the data path is able to initiate metering configuration signaling.
   The selection of signaling initiator and receiver depends on the
   configuration and on the specific application environment.

   Finally, a Metering NSLP, similar to QoS NSLP, would be independent
   of the actual configuration information it carries.  Hence, it can be
   used for any metering application.


7.  Security Considerations

   The process of configuring Metering Entities to start and stop
   metering and to transmit collected Metering Records to a third party
   introduces several security challenges.  The following security
   issues need to be considered for the design of the Metering NSLP.

7.1.  Authorization Model

   It MUST be assured that configuration messages for starting,
   refreshing and stopping a metering configuration are correctly
   authorized before the configuration is executed.  Bogus configuration
   messages can be used for different kind of attacks.  For example, in



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   the accounting scenario if a malicious user is able to stop metering
   of requested services then fraud is possible.  Also, it MUST NOT
   possible to configure Metering Entities in such a way that other
   users are charged for the usage of a service which they have not
   used.

7.2.  Inter-working between different domains

   Inter-working between multiple domains causes authorization problems.
   If the scope of the configuration signaling should go beyond the
   borders of a single domain, the ISPs need to be authorized to perform
   metering configuration across other domains and to collect metering
   and monitoring data.  A high degree of trust is required to allow
   other domains to configure Metering Entities and to collect the
   metering data of particular users.

   The above considerations raise the main question whether the Metering
   NSLP can be used outside a single administrative domain.  Ideally, it
   should have a broader applicability but security, privacy and other
   operational concerns may limit its applicability for multiple domain
   traversal (and also end-to-end signaling).

7.3.  End User Privacy

   The collection of metering data about individual flows is a privacy
   sensitive task.  ISPs which intend to deploy the Metering NSLP may
   need to clarify the legal terms for collecting and processing the
   Metering Records.

7.4.  ISP Privacy

   This issue is relevant only for the case that the signaling for
   metering configuration operates across several domains and Metering
   Records might be delivered to a Collector belonging to a foreign
   administrative domain.  In this case, the Metering Records may reveal
   sensitive topology information of the ISP network.

7.5.  Forged Collector

   It MUST be assured that the Collector that is specified in a
   configuration message is eligible to receive the Metering Records.
   Otherwise several kind of attacks are possible.
   o  As already mentioned in Section 7.3 and Section 7.4 if the
      Metering Records are received by a bogus Collector, this will
      reveal customer and/or ISP sensitive information
   o  In the accounting scenario the customer could cause the resource
      usage data to be sent to a bogus Collector and therefore would be
      able to use the services for free.



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7.6.  Denial-of-Service Attacks on the Collector

   In any application scenario for the Metering NSLP, it MUST be assured
   that the Collector is supposed to receive the Metering Records.
   Otherwise, a DoS attack (via amplification) would be possible if data
   can be sent to an arbitrary IP address.  The adversary needs to send
   a single metering NSLP message in order to flood a victim with
   potentially a huge amount of data over a certain, or perhaps
   uncertain, period of time.

7.7.  Denial-of-Service Attacks on Metering Entities

   Metering Entities can be subject to DoS attacks if a large number of
   Metering Data have to be collected or large per-flow states are
   created.

7.8.  Verification of the Flow Specification

   The flow specification within a metering configuration message
   (which, as mentioned above, may or may not be equal to the Message
   Routing Information from the NTLP) needs to be verified for
   integrity.  In particular, it MUST be assured that an end host may be
   able to trigger the collection of metering data by itself about a
   flow that it created (this depends also on the application scenario)
   but not for other flows that belong to other users.  However, if
   there is a signaling proxy that initiates the signaling on behalf of
   other users, different authorization policies need to be deployed.


8.  Contributors

   This document is the result of the effort of a Metering NSLP team.
   In addition to the individuals listed in the author list, the team
   includes also Juergen Quittek and Hannes Tschofenig.

   Furthermore, the authors would like to thank Ralph Kuehne for his
   input on the description of the accounting scenario and Andreas
   Pashalidis for his comments.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [I-D.dressler-nsis-metering-nslp]



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              Dressler, F., "NSLP for Metering Configuration Signaling",
              draft-dressler-nsis-metering-nslp-03 (work in progress),
              October 2005.

   [I-D.ietf-nsis-ntlp]
              Schulzrinne, H. and R. Hancock, "GIST: General Internet
              Signaling Transport", draft-ietf-nsis-ntlp-09 (work in
              progress), February 2006.

   [I-D.ietf-ipfix-protocol]
              Claise, B., "IPFIX Protocol Specification",
              draft-ietf-ipfix-protocol-22 (work in progress),
              June 2006.

9.2.  Informative References

   [RFC2138]  Rigney, C., Rigney, C., Rubens, A., Simpson, W., and S.
              Willens, "Remote Authentication Dial In User Service
              (RADIUS)", RFC 2138, April 1997.

   [RFC3726]  Brunner, M., "Requirements for Signaling Protocols",
              RFC 3726, April 2004.

   [RFC3588]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
              Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC3917]  Quittek, J., Zseby, T., Claise, B., and S. Zander,
              "Requirements for IP Flow Information Export (IPFIX)",
              RFC 3917, October 2004.

   [RFC4080]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
              Bosch, "Next Steps in Signaling (NSIS): Framework",
              RFC 4080, June 2005.

   [I-D.ietf-ipfix-info]
              Quittek, J., "Information Model for IP Flow Information
              Export", draft-ietf-ipfix-info-12 (work in progress),
              June 2006.

   [I-D.ietf-nsis-qos-nslp]
              Manner, J., "NSLP for Quality-of-Service Signaling",
              draft-ietf-nsis-qos-nslp-10 (work in progress),
              March 2006.

   [I-D.ietf-nsis-nslp-natfw]
              Stiemerling, M., "NAT/Firewall NSIS Signaling Layer
              Protocol (NSLP)", draft-ietf-nsis-nslp-natfw-11 (work in
              progress), April 2006.



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   [I-D.ietf-psamp-framework]
              Duffield, N., "A Framework for Packet Selection and
              Reporting", draft-ietf-psamp-framework-10 (work in
              progress), January 2005.

   [I-D.ietf-psamp-mib]
              Dietz, T. and B. Claise, "Definitions of Managed Objects
              for Packet Sampling", draft-ietf-psamp-mib-06 (work in
              progress), June 2006.

   [3GPP.32.240]
              3GPP, "Telecommunication management; Charging management;
              Charging architecture and principles", 3GPP TS 32.240
              6.0.0.

   [3GPP.32.260]
              3GPP, "Telecommunication management; Charging management;
              Charging architecture and principles;  IP Multimedia
              Subsystem (IMS) charging", 3GPP TS 3GPP.32.260.

   [3GPP.32.251]
              3GPP, "Telecommunication management; Charging management;
              Packet Switched (PS) domain charging", 3GPP
              TS 3GPP.32.251.

   [3GPP.32.252]
              3GPP, "Telecommunication management; Charging management;
              Wireless Local Area Network (WLAN) charging", 3GPP
              TS 3GPP.32.252.






















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Authors' Addresses

   Ali Fessi
   University of Tuebingen
   Wilhelm-Schickard-Institute for Computer Science
   Auf der Morgenstelle 10C
   Tuebingen  72076
   Germany

   Phone: +49 7071 29-70534
   Email: fessi@informatik.uni-tuebingen.de
   URI:   http://net.informatik.uni-tuebingen.de/


   Cornelia Kappler
   Siemens AG
   Siemensdamm 62
   Berlin  13627
   Germany

   Phone: +49 30 386-32894
   Email: cornelia.kappler@siemens.com


   Changpeng Fan
   Siemens AG
   Siemensdamm 62
   Berlin  13627
   Germany

   Phone: +49 30 386-36361
   Email: changpeng.fan@siemens.com


   Falko Dressler
   University of Erlangen
   Department of Computer Science 7
   Martensstr. 3
   Erlangen  91058
   Germany

   Phone: +49 9131 85-27914
   Email: dressler@informatik.uni-erlangen.de
   URI:   http://www7.informatik.uni-erlangen.de/







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   Andreas Klenk
   University of Tuebingen
   Wilhelm-Schickard-Institute for Computer Science
   Auf der Morgenstelle 10C
   Tuebingen  72076
   Germany

   Phone: +49 7071 29-70535
   Email: klenk@informatik.uni-tuebingen.de
   URI:   http://net.informatik.uni-tuebingen.de/









































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