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Network Working Group                                            S. Shah
Internet-Draft                                                P. Thubert
Intended status: Informational                             Cisco Systems
Expires: August 7, 2015                                February 03, 2015


      Differentiated Service Class Recommendations for LLN Traffic
           draft-svshah-tsvwg-lln-diffserv-recommendations-04

Abstract

   Differentiated services architecture is widely deployed in
   traditional networks.  There exist well defined recommendations for
   the use of appropriate differentiated service classes for different
   types of traffic (eg. audio, video) in these networks.  Per-Hop
   Behaviors are typically defined based on this recommendations.  With
   emerging Low-power and Lossy Networks (LLNs), it is important to have
   similar defined differentiated services recommendations for LLN
   traffic.  Defined recommendations are for LLN class of traffic
   exiting out of LLNs towards high-speed backbones, converged campus
   network and for the traffic in the reverse direction.

Status of this Memo

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   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
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   it for publication as an RFC or to translate it into languages other
   than English.


































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Application Types and Traffic Patterns . . . . . . . . . . . .  6
     3.1.  Alert signals  . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Control signals  . . . . . . . . . . . . . . . . . . . . .  7
       3.2.1.  Deterministic control signals  . . . . . . . . . . . .  7
     3.3.  Monitoring data  . . . . . . . . . . . . . . . . . . . . .  8
       3.3.1.  Video data . . . . . . . . . . . . . . . . . . . . . .  8
       3.3.2.  Query based data . . . . . . . . . . . . . . . . . . .  8
       3.3.3.  Periodic reporting/logging, Software downloads . . . .  8
     3.4.  Traffic Class Characteristics Table  . . . . . . . . . . . 10
   4.  Differentiated Service recommendations for LLN traffic . . . . 10
     4.1.  Alert signals  . . . . . . . . . . . . . . . . . . . . . . 10
     4.2.  Control signals  . . . . . . . . . . . . . . . . . . . . . 11
       4.2.1.  Deterministic Control Signals  . . . . . . . . . . . . 11
     4.3.  Monitoring Data  . . . . . . . . . . . . . . . . . . . . . 11
       4.3.1.  Video Data . . . . . . . . . . . . . . . . . . . . . . 11
       4.3.2.  Query based data . . . . . . . . . . . . . . . . . . . 11
       4.3.3.  Periodic reporting/logging, Software downloads . . . . 11
     4.4.  Summary of Differentiated Code-points and QoS
           Mechanics for them . . . . . . . . . . . . . . . . . . . . 12
   5.  Deployment Scenario  . . . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15




















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1.  Introduction

   With emerging LLN applications, it is anticipated that more and more
   LLNs will be federated by high-speed backbones, possibly supporting
   deterministic Ethernet service, and be further connected to some
   converged campus networks for less demanding usages such as
   supervisory control like traffic originated in a LLN, such as
   metering, command and control, may transit over a converged campus IP
   network.


                  ---+------------------------
                     |   Converged Campus Network
                     |
                  +-----+
                  |     | Gateway
                  |     |
                  +-----+
                     |
                     |      Backbone
               +--------------------+------------------+
               |                    |                  |
            +-----+             +-----+             +-----+
            |     | LLN border  |     | LLN border  |     | LLN border
       o    |     | router      |     | router      |     | router
            +-----+             +-----+             +-----+
       o                  o                   o                 o
           o    o   o         o   o  o   o         o  o   o o
           o o   o  o   o  o  o o   o  o  o   o   o   o  o  o  o o
          o  o o  o o    o   o   o  o  o  o       o  o  o o o
          o   o  M o  o  o     o  o    o  o  o    o  o   o  o   o
            o   o o       o        o  o         o        o o
                    o           o          o             o     o
                                           LLN
    o : stationary wireless field device, seldom acting as an LLN router



   In an example figure shown above, Per-Hop Behaviors (PHB) and Service
   Level Agreements (SLAs), for LLN traffic, require to be defined at
   the LLN Borders as well as Backbone and possibly in the Converged
   Campus network.

   In this document, we will first categorize different types of LLN
   traffic into service classes and then provide recommendations for
   Differentiated Service Code-Point(DSCP) for those service classes.
   Mechanisms to be used, like Traffic Conditioning and Active Queue
   Management, for differentiated services is well defined in RFC4594.



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   This document does not focus to re-call them again here but the
   document will call out any specific mechanism that requires
   particular consideration.

   This document focuses on Diffserv recommendations for LLN class of
   traffic in managed IP networks outside of LLNs, that is for the
   traffic from LLN towards LLN Border, Backbone, Campus Network as well
   as for the traffic in the reverse direction.  It does not focus on
   Diffserv architecture or any other QoS recommendations within the
   LLNs itself.  Given constraints of LLNs and their unique
   requirements, it is expected of a focus within a separate efforts.
   Though nodes inside LLNs MAY use code-points recommended here.

   In Section 3 we categorize different types of traffic from Different
   LLNs.  Section 4 recommends differentiated services, including DSCPs
   and QoS mechanics, for categorized classes of traffic.  Section 5
   evaluates one of the deployment scenario.

1.1.  Definitions

    DSCP: Differentiated Service Code Point. It is a 6-bits value in the
          TOS and Traffic Class field of the IPv4 and IPv6 header
          respectively. This 6-bits numerical value defines standard set
          of behavior to be performed by Differentiated Services capable
          hops.

    Diffserv
    Class: Diffser Class in this document is used to refer to DSCP code-
           point(s) and associated Per-hop Behaviors for it.

    LLN: Low-power and lossy Network. Network constructed with sensors,
         actuators, routers that are low-power and with higher loss/
         success transmission ratio, due to transmission medium and
         nature of dynamics of changing topology, compare to wired and
         other traditional networks.

    SLA: Service Level Agreement. It is a collection of Traffic
         classification rules and set of services associated with each
         Traffic Class. Traffic classification may be defined based
         on just DSCP code-points or additionally (or otherwise)
         based on some other packet attributes.



2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this



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   document are to be interpreted as described in RFC2119.


3.  Application Types and Traffic Patterns

      Different types of traffic can be collapsed into following network
      service classes.

      - Alert signals
      - Control signals
      - Monitoring data
        - Video data
        - Query-based response data
        - Periodic reporting/logging, Software downloads

3.1.  Alert signals

   Alerts/alarms reporting fall in this category where such signal is
   triggered in a rare un-usual circumstances.  An alert may be
   triggered for an example when environmental hazard level goes beyond
   certain threshold.  Such alerts require to be reported with in the
   human tolerable time.  Note that certain critical alert reporting in
   certain automation systems may be reported via very closely and
   tightly managed method that is not implemented within LLNs, due to
   the nature of transmission media of LLNs and due to the stringent
   latency requirement for those alerts.  Such types of signals are not
   considered here since they are not within the scope of LLN or any
   other IP networks.

Examples :
    - Environmental hazard level goes beyond certain threshold
    - Measured blood pressure exceeds the threshold or a person falls to
      the ground
    - Instructional triggers like start/stop traffic lights during
      certain critical event

Traffic Pattern:

   Typically size of such packets is very small. any specific device of
   LLN is expected to trigger only handful of packets (may be only 1
   packet).  That too only during an event which is not a common
   occurrence.

   In an affected vicinity, only a designated device or each affected
   devices may send alerts.  In certain type of sensor networks, it is
   predictable and expected to have only a designated device to trigger
   such an alert while in certain other types scale number of alert
   flows may be expected.



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   Latency required for such traffic is not stringent but is to be
   within human tolerable time bound.

3.2.  Control signals

   Besides alerts, LLNs also trigger and/or receive different types of
   control signals, to/from control applications outside of LLNs.  These
   control signals are important enough for the operation of sensors,
   actuators and underneath network.  Administrator controlling
   applications, outside of LLN network, may trigger a control signal in
   response to alerts/data received from LLN (in some cases control
   signal trigger may be automated without explicit human interaction in
   the loop) or administrator may trigger an explicit control signal for
   a specific function.

 Examples:
     - auto [demand] response (e.g. manage peak load, service
                                   disconnect, start/stop street lights)
     - manual remote service disconnect, remote demand reset

     - open-loop regulatory control
     - non-critical close-loop regulatory control
     - critical closed-loop control signals
     - trigger to start Video surveillance


 Traffic Pattern:

   Variable size packets but typically size of such packets is small.
   Certain control signals may be regular and so with number of devices
   in a particular LLN, it is predictable on average, how many such
   signals to expect.  However, certain other control signals are
   irregular or on-demand.

   Typically most of the open-loop, that requires manual interaction,
   signals are tolerant to latency above 1 second.  Certain close-loop
   control signals require low jitter and low latency, latency in the
   order of 100s of ms.

3.2.1.  Deterministic control signals

   Some of the LLN applications, like Industrial automation, have class
   of control signals that require very strict time scheduled service.
   This traffic is very sensitive to jitter.  Applications may be able
   to handle a loss of packet or two but are very sensitive to jitter
   and any delivery outside of the deterministic time schedule can have
   expensive effects on the Network.  Critical closed-loop control
   signals example falls in this category.



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   Deterministic control signals are very sensitive to jitter.  Scope of
   such traffic is contained to LL Network and to the IP backbone
   connecting to two or more such networks.  This traffic is not
   expected to be transmitted over Campus, WAN and Internet.

3.3.  Monitoring data

   Reaction to control signals may initiate flow of data-traffic in
   either direction.  Sensors/Actuators in LLNs may also trigger
   periodic data (eg. monitoring, reporting data).  All different types
   of data may be categorized in following classes.

3.3.1.  Video data

   A very common example of this type of monitoring data is Video
   surveillance or Video feed, triggered thru control signals.  This
   Video feed is typically from LLN towards an application outside of
   LLN.

   Traffic Pattern:

   Video frame size is expected to be big with a flow of variable rate.

3.3.2.  Query based data

   Application at the controller, outside the LLN, or user explicitly
   may launch query for the data.  For example, query for an urban
   environmental data, query for health report etc.  Since this data is
   query based data, it is important to report data with reasonable
   latency though not stringent.  In addition, some periodic logging
   data also may require timely reporting and so may expect same type of
   service (eg. at-home health reporting).

   Traffic Pattern:

   Size of packets can vary from small to big.  While rate may be
   predictable in some cases, in most of the cases traffic rate for such
   data is variable.  The traffic is bursty in the nature.

3.3.3.  Periodic reporting/logging, Software downloads

   Many sensors/actuator in different LLNs report data periodically.
   With some exceptions, as mentioned above for healthcare monitoring
   logs, most of such data do not have any latency requirement and can
   be forwarded either thru lower priority assured forwarding or with
   service of store and forward or even best effort.

   Sensors/actuators may require software/firmware upgrades where



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   software/ firmware may be downloaded on demand bases.  These upgrades
   and so downloads do not have stringent requirement of timely delivery
   to the accuracy of seconds.  This data also can be forwarded thru
   lower priority assured forwarding.

   Traffic Pattern:

   Periodic reporting/logging typically can be predicated as constant
   rate.  Data may be bursty in the nature.  Software download data also
   may be bursty in nature.  Such traffic is tolerant to jitter and
   latency.








































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3.4.  Traffic Class Characteristics Table

    -------------------------------------------------------------------
   |Traffic Class  |                              |    Tolerance to    |
   |    Name       |  Traffic Characteristics     | Loss |Delay |Jitter|
   |===============+==============================+======+======+======|
   |   Alerts/     |Packet size = small           | Low  |Low   |  N/A |
   |   alarms      |Rate = typically 1-few packets|      |      |      |
   |               |Short lived flow              |      |      |      |
   |               |Burst = none to some-what     |      |      |      |
   |---------------+------------------------------+------+------+------|
   |   Control     |Packet size = variable,       | Yes  |Low   |  Yes |
   |   Signals     |              typically small |      |      |      |
   |               |Rate = few packets            |      |      |      |
   |               |Short lived flow              |      |      |      |
   |               |Burst = none to some-what     |      |      |      |
   |---------------+------------------------------+------+------+------|
   | Deterministic |Packet size = variable,       | Low  |Very  | Very |
   |   Control     |              typically small |      |Low   |  Low |
   |   Signals     |Rate = few packets            |      |      |      |
   |               |Short lived flow              |      |      |      |
   |               |Burst = none to some-what     |      |      |      |
   |---------------+------------------------------+------+------+------|
   |     Video     |Packet size = big             | Low  |Low - |  Low |
   |Monitoring/feed|Rate = variable               |      |Medium|      |
   |               |Long lived flow               |      |      |      |
   |               |Burst = non-bursty            |      |      |      |
   |---------------+------------------------------+------+------+------|
   |  Query-based  |Packet size = variable        | Low  |Medium|  Yes |
   |      Data     |Rate = variable               |      |      |      |
   |               |Short lived elastic flow      |      |      |      |
   |               |Burst = bursty                |      |      |      |
   |---------------+------------------------------+------+------+------|
   |   Periodic    |variable packet size, rate    | Yes  |Medium|  Yes |
   |Reporting/log, |bursty                        |      |- High|      |
   |  Software     |                              |      |      |      |
   |   downloads   |                              |      |      |      |
    -------------------------------------------------------------------


4.  Differentiated Service recommendations for LLN traffic

4.1.  Alert signals

   Alerts/alarms signaling service requires transmission of few packets
   with low delay, tolerable to human.  This requirement is very similar
   to signaling traffic in the traditional networks.  Alert signals MAY
   use Diffserv code-point CS5.



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4.2.  Control signals

   As described in earlier section, control signals over IP are divided
   in two categories.  Control signals that require deterministic
   forwarding service, and control signals that require relatively low
   delay.  Service requirement for later class of control signals is
   very similar to service for signaling traffic in the traditional
   networks.  Recommendation for this class of control signals is to use
   Diffserv code-point CS5.

4.2.1.  Deterministic Control Signals

   PHB for this class of traffic is defined as forwarding of a packet at
   determined/scheduled time providing no jitter service.

   Recommended DSCP code-point for this class of traffic is EF.  Since
   this class of traffic is not expected to co-exist with voice like
   traffic, that implements EF code-point as used in traditional Campus
   and WAN networks, the same code-point is re-used here for the purpose
   of deterministic control signals.  However, a note to be made for
   defined PHB for this code-point as deterministic forwarding behavior
   as defined in this document.

   Scheduling MUST pre-empt service of any other class of traffic during
   the scheduled time for this class of traffic.

4.3.  Monitoring Data

4.3.1.  Video Data

   RFC4594 has well documented recommendations for different types of
   Video traffic.  If there is any Video traffic from/to LLNs to/from
   outside of LLNs, they should use same recommended dscp from RFC4594.
   For example, surveillance video feed is recommended to use dscp CS3.

4.3.2.  Query based data

   Low latency data, like query based report and non-critical signals,
   is recommended to use AF2 assured forwarding service.  Also, certain
   periodic reporting/logging data that are critical to be reported with
   regular interval with relatively low jitter is recommended to use
   AF2x service.

4.3.3.  Periodic reporting/logging, Software downloads

   Non-critical periodic reporting/logging and rest all other data MAY
   use AF1x or BE service class.




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4.4.  Summary of Differentiated Code-points and QoS Mechanics for them

    - Alert Signals                          CS5

    - Control Signaling                      CS5

    - Deterministic Control Signals           EF

    - Video broadcast/feed                   CS3

    - Query-based data                       AF2x

    - Assured monitoring data                AF1x
      high throughput

    - Best Effort monitoring data            BE
      Reporting (periodic reporting.certain types of periodic monitoring
                 MAY require assured forwarding)
     ------------------------------------------------------------------
    |  Service      | DSCP | Conditioning at   |   PHB   | Queuing| AQM|
    |   Class       |      |    DS Edge        |  Used   |        |    |
    |===============+======+===================+=========+========+====|
    | Deterministic |  EF  |                   |         |Time    | No |
    |control signals|      |Police using sr+bs |         |Schedule|    |
    |---------------+------+-------------------+---------+--------+----|
    |Alert  signals/|      |                   |         |        |    |
    |Control signals| CS5  |Police using sr+bs | RFC2474 |  Rate  | No |
    |---------------+------+-------------------+---------+--------+----|
    |   Video feed  | CS3  |Police using sr+bs | RFC2474 |  Rate  | No |
    |---------------+------+-------------------+---------+--------+----|
    |    Query-     | AF21 | Using single-rate,|         |        | Yes|
    |    based      | AF22 |three-color marker | RFC2597 |  Rate  | per|
    |    Data       | AF23 | (such as RFC 2697)|         |        |DSCP|
    |---------------+------+-------------------+---------+--------+----|
    |  Periodic     | AF11 |  Using two-rate,  |         |        | Yes|
    |  Reporting/   | AF12 |three-color marker | RFC2597 |  Rate  | per|
    |    logging    | AF13 | (such as RFC 2698)|         |        |DSCP|
     ------------------------------------------------------------------
    *  "sr+bs" represents a policing mechanism that provides single rate
       with burst size control [RFC4594]


5.  Deployment Scenario

   Industrial Automation, as described in [RFC5673] and [ISA100.11a],
   classifies different types of traffic in following six classes
   ranging in complexity from Class 5 to Class 0 where Class 0 is the
   most time sensitive class.



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    o  Safety

      *  Class 0: Emergency action - Always a critical function

    o  Control

      *  Class 1: Closed-loop regulatory control - Often a critical
         function

      *  Class 2: Closed-loop supervisory control - Usually a non-
         critical function

      *  Class 3: Open-loop control - Operator takes action and controls
         the actuator (human in the loop)

   o  Monitoring

      *  Class 4: Alerting - Short-term operational effect (for example,
         event-based maintenance)

      *  Class 5: Logging and downloading / uploading - No immediate
         operational consequence (e.g., history collection, sequence-of-
         events, preventive maintenance)

    It might not be appropriate to transport Class 0 traffic over a
    wireless network or a multihop network, unless tight mechanisms are
    put in place such as TDM and frequency hopping. Today this class of
    traffic is expected to use other tightly managed method outside of
    IP networks. Excluding class 0 traffic, following table maps Class 1
    thru Class 5 service classes to Diffserv code-point.

     -------------------------
    |  Service      | DSCP    |
    |   Class       |         |
    |===============+=========|
    |   Class 1     | EF      |
    +-------------------------+
    |   Class 2     | CS5     |
    +-------------------------+
    |   Class 3     | CS5     |
    +-------------------------+
    |   Class 4     | AF2x    |
    +-------------------------+
    |   class 5     | AF1x/BE |
    +-------------------------+






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6.  Security Considerations

   A typical trust model, as much is applicable in traditional networks,
   is applicable with LLN traffic as well.  At the border of the LLN, a
   trust model needs to be established for any traffic coming out of
   LLN.  Without appropriate trust model to accept/mark dscp code-point
   for LLN traffic, misbehaving flow may attack a specific Diffserv
   class disrupting expected service for other traffic from the same
   Diffserv class.  Trust models are typically established at the border
   router by employing rate-limiting and even marking down dscp code-
   point to Best Effort for non-trusted flows or dropping them as
   required.


7.  Acknowledgements

   Thanks to Fred Baker, James Polk for their valuable comments and
   suggestions.


8.  References

8.1.  Normative References

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

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              August 2006.

   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of
              Diffserv Service Classes", RFC 5127, February 2008.

   [RFC5548]  Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
              "Routing Requirements for Urban Low-Power and Lossy
              Networks", RFC 5548, May 2009.

   [RFC5673]  Pister, K., Thubert, P., Dwars, S., and T. Phinney,
              "Industrial Routing Requirements in Low-Power and Lossy
              Networks", RFC 5673, October 2009.

   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks",
              RFC 5826, April 2010.

   [RFC5867]  Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
              "Building Automation Routing Requirements in Low-Power and



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              Lossy Networks", RFC 5867, June 2010.

8.2.  Informative References

   [ISA100.11a]
              ISA, "ISA-100.11a-2011 - Wireless systems for industrial
              automation: Process control and related applications",
              May 2011.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              December 1998.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [RFC6272]  Baker, F. and D. Meyer, "Internet Protocols for the Smart
              Grid", RFC 6272, June 2011.


Authors' Addresses

   Shitanshu Shah
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Email: svshah@cisco.com


   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410
   FRANCE

   Email: pthubert@cisco.com









Shah & Thubert           Expires August 7, 2015                [Page 15]


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