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Network Working Group                                       T. Dreibholz
Internet-Draft                              University of Duisburg-Essen
Intended status: Experimental                                    X. Zhou
Expires: July 11, 2009                                 Hainan University
                                                         January 7, 2009


  Definition of a Delay Measurement Infrastructure and Delay-Sensitive
             Least-Used Policy for Reliable Server Pooling
                 draft-dreibholz-rserpool-delay-03.txt

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   This Internet-Draft will expire on July 11, 2009.

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Abstract

   This document contains the definition of a delay measurement
   infrastructure and a delay-sensitive Least-Used policy for Reliable
   Server Pooling.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Delay-Measurement Infrastructure  . . . . . . . . . . . . . . . 3
     2.1.  Quantification of Distance  . . . . . . . . . . . . . . . . 3
     2.2.  Distance Measurement Environment  . . . . . . . . . . . . . 4
   3.  Distance-Sensitive Least-Used Policy  . . . . . . . . . . . . . 4
     3.1.  Description . . . . . . . . . . . . . . . . . . . . . . . . 5
     3.2.  ENRP Server Considerations  . . . . . . . . . . . . . . . . 5
     3.3.  Pool User Considerations  . . . . . . . . . . . . . . . . . 5
     3.4.  Pool Member Selection Policy Parameter  . . . . . . . . . . 5
   4.  Reference Implementation  . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8























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1.  Introduction

   Reliable Server Pooling defines protocols for providing highly
   available services.  PEs of a pool may be distributed over a large
   geographical area, in order to provide redundancy in case of
   localized disasters.  But the current pool policies defined in
   [RFC5356] do not incorporate the fact of distances (i.e. delay)
   between PU and PE.  This leads to a low performance for delay-
   sensitive applications.

1.1.  Scope

   This draft defines a delay measurement infrastructure for ENRP
   servers to add delay information into the handlespace.  Furthermore,
   a delay-sensitive Least-Used policy is defined.  Performance
   evaluations can be found in [KiVS2007].

1.2.  Terminology

   The terms are commonly identified in related work and can be found in
   the Aggregate Server Access Protocol and Endpoint Handlespace
   Redundancy Protocol Common Parameters document [RFC5354].

1.3.  Conventions

   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].


2.  Delay-Measurement Infrastructure

   This section describes the necessary delay measurement infrastructure
   for the policy later defined in Section 3.  It has to be provided as
   part of the ENRP servers.

2.1.  Quantification of Distance

   Measuring delay for SCTP associations is easy: the SCTP protocol
   [RFC4960] already calculates a smoothed round-trip time (RTT) for the
   primary path.  This RTT only has to be queried via the standard SCTP
   API as defined in [I-D.ietf-tsvwg-sctpsocket].  By default, the
   calculated RTT has a small restriction: a SCTP endpoint waits up to
   200ms before acknowledging a packet, in order to piggyback the
   acknowledgement chunk with payload data.  In this case, the RTT would
   include this latency.  Using the option SCTP_DELAYED_ACK_TIME (see
   [I-D.ietf-tsvwg-sctpsocket]), the maximum delay before acknowledging
   a packet can be set to 0ms (i.e. "acknowledge as soon as possible").



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   After that, the RTT approximately consists of the network latency
   only.  Then, using the RTT, the end-to-end delay between two
   associated components is approximately 0.5*RTT.

   In real networks, there may be negligible delay differences: for
   example, the delay between a PU and PE #1 is 5ms and the latency
   between the PU and PE #2 is 6ms.  From the service user's
   perspective, such minor delay differences may be ignored and are
   furthermore unavoidable in Internet scenarios.  Therefore, the
   distance parameter between two components A and B is defined as
   follows:

   Distance = DistanceStep * round( (0.5*RTT) / DistanceStep )

   That is, the distance parameter is defined as the nearest integer
   multiple of the constant DistanceStep for the measured delay (i.e.
   0.5*RTT).

2.2.  Distance Measurement Environment

   In order to define a distance-aware policy, it is first necessary to
   define a basic rule: PEs and PUs choose "nearby" ENRP servers.  Since
   the operation scope of RSerPool is restricted to a single
   organization, this condition can be met easily by appropriately
   locating ENRP servers.

   o  A Home ENRP server can measure the delay of the ASAP associations
      to its PE.  As part of its ENRP updates to other ENRP servers, it
      can report this measured delay together with the PE information.

   o  A non-Home-ENRP server receiving such an update simply adds the
      delay of the ENRP association with the Home ENRP server to the
      PE's reported delay.

   Now, each ENRP server can approximate the distance to every PE in the
   operation scope using the equation in Section 2.1.

   Note, that delay changes are propagated to all ENRP servers upon PE
   re-registrations, i.e. the delay information (and the approximated
   distance) dynamically adapts to the state of the network.


3.  Distance-Sensitive Least-Used Policy

   In this section, a distance-sensitive Least Used policy is defined,
   based on the delay-measurement infrastructure introduced in
   Section 2.




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3.1.  Description

   The Least Used with Distance Penalty Factor (LU-DPF) policy uses load
   information provided by the pool elements to select the lowest-loaded
   pool elements within the pool.  If there are multiple elements having
   lowest load, the nearest PE should be chosen.

3.2.  ENRP Server Considerations

   The ENRP server SHOULD select at most the requested number of pool
   elements.  Their load values SHOULD be the lowest possible ones
   within the pool and their distances also SHOULD be lowest.  Each
   element MUST NOT be reported more than once to the pool user.  If
   there is a choice of equal-loaded and equal-distanced pool elements,
   round robin selection SHOULD be made among these elements.  The
   returned list of pool elements MUST be sorted by load value in
   ascending order (1st key) and distance in ascending order (2nd key).

3.3.  Pool User Considerations

   The pool user should try to use the pool elements returned from the
   list in the order returned by the ENRP server.  A subsequent call for
   handle resolution may result in the same list.  Therefore, it is
   RECOMMENDED for a pool user to request multiple entries in order to
   have a sufficient amount of feasible backup entries available.

3.4.  Pool Member Selection Policy Parameter


   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Parameter Type = 0x6     |         Length = 0x14          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Policy Type = 0x40000010                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Load                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Load DPF                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Distance                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Load: Current load of the pool element.

   o  Load DPF: The LoadDPF setting of the PE.





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   o  Distance: The approximated distance in milliseconds.

      *  Between PE and Home ENRP server: The distance SHOULD be set to
         0.

      *  Between Non-Home ENRP server and Home ENRP server: The delay
         measured on the ASAP association between Home ENRP server and
         PE.

      *  Between ENRP server and PU: The sums of the measured delays on
         the ASAP association and the ENRP association to the Home ENRP
         server.


4.  Reference Implementation

   The RSerPool reference implementation RSPLIB can be found at
   [RSerPoolPage].  It supports the functionalities defined by
   [RFC5351], [RFC5352], [RFC5353], [RFC5354] and [RFC5356] as well as
   the options [I-D.dreibholz-rserpool-asap-hropt],
   [I-D.dreibholz-rserpool-enrp-takeover] and of course the option
   defined by this document.  An introduction to this implementation is
   provided in [Dre2006].


5.  Security Considerations

   Security considerations for RSerPool systems are described by
   [RFC5355].


6.  IANA Considerations

   This document does not require additional IANA actions beyond those
   already identified in the ENRP and ASAP protocol specifications.


7.  References

7.1.  Normative References

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

   [RFC5351]  Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An
              Overview of Reliable Server Pooling Protocols", RFC 5351,
              September 2008.




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   [RFC5352]  Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
              "Aggregate Server Access Protocol (ASAP)", RFC 5352,
              September 2008.

   [RFC5353]  Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A.
              Silverton, "Endpoint Handlespace Redundancy Protocol
              (ENRP)", RFC 5353, September 2008.

   [RFC5354]  Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
              "Aggregate Server Access Protocol (ASAP) and Endpoint
              Handlespace Redundancy Protocol (ENRP) Parameters",
              RFC 5354, September 2008.

   [RFC5355]  Stillman, M., Gopal, R., Guttman, E., Sengodan, S., and M.
              Holdrege, "Threats Introduced by Reliable Server Pooling
              (RSerPool) and Requirements for Security in Response to
              Threats", RFC 5355, September 2008.

   [RFC5356]  Dreibholz, T. and M. Tuexen, "Reliable Server Pooling
              Policies", RFC 5356, September 2008.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

7.2.  Informative References

   [I-D.ietf-tsvwg-sctpsocket]
              Stewart, R., Poon, K., Tuexen, M., Yasevich, V., and P.
              Lei, "Sockets API Extensions for Stream Control
              Transmission Protocol (SCTP)",
              draft-ietf-tsvwg-sctpsocket-18 (work in progress),
              November 2008.

   [KiVS2007]
              Dreibholz, T. and E. Rathgeb, "On Improving the
              Performance of Reliable Server Pooling Systems for
              Distance-Sensitive Distributed Applications",
              Proceedings of the 15. ITG/GI Fachtagung Kommunikation in
              Verteilten Systemen, February 2007.

   [Dre2006]  Dreibholz, T., "Reliable Server Pooling -- Evaluation,
              Optimization and Extension of a Novel IETF Architecture",
              Ph.D. Thesis University of Duisburg-Essen, Faculty of
              Economics, Institute for Computer Science and Business
              Information Systems, URL: http://
              duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/
              Derivate-16326/Dre2006-final.pdf, March 2007.




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   [RSerPoolPage]
              Dreibholz, T., "Thomas Dreibholz's RSerPool Page",
              URL: http://tdrwww.iem.uni-due.de.de/dreibholz/rserpool/.

   [I-D.dreibholz-rserpool-asap-hropt]
              Dreibholz, T., "Handle Resolution Option for ASAP",
              draft-dreibholz-rserpool-asap-hropt-03 (work in progress),
              October 2008.

   [I-D.dreibholz-rserpool-enrp-takeover]
              Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for
              the ENRP Handle Update Message",
              draft-dreibholz-rserpool-enrp-takeover-00 (work in
              progress), December 2008.


Authors' Addresses

   Thomas Dreibholz
   University of Duisburg-Essen, Institute for Experimental Mathematics
   Ellernstrasse 29
   45326 Essen, Nordrhein-Westfalen
   Germany

   Phone: +49-201-1837637
   Fax:   +49-201-1837673
   Email: dreibh@iem.uni-due.de
   URI:   http://www.iem.uni-due.de/~dreibh/


   Xing Zhou
   Hainan University, College of Information Science and Technology
   Renmin Avenue 58
   570228 Haikou, Hainan
   China

   Phone: +86-898-66279141
   Email: zhouxing@hainu.edu.cn













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