[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Network Working Group                                       T. Dreibholz
Internet-Draft                              University of Duisburg-Essen
Intended status: Standards Track                                 X. Zhou
Expires: December 15, 2007                             Hainan University
                                                           June 13, 2007


  Definition of a Delay Measurement Infrastructure and Delay-Sensitive
             Least-Used Policy for Reliable Server Pooling
                 draft-dreibholz-rserpool-delay-00.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
   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
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 15, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).












Dreibholz & Zhou        Expires December 15, 2007               [Page 1]


Internet-Draft           Delay-Sensitive Policy                June 2007


Abstract

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














































Dreibholz & Zhou        Expires December 15, 2007               [Page 2]


Internet-Draft           Delay-Sensitive Policy                June 2007


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 [5] 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 [8].

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 [4].






























Dreibholz & Zhou        Expires December 15, 2007               [Page 3]


Internet-Draft           Delay-Sensitive Policy                June 2007


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 [6]
   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 [7].  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 [7]), the maximum delay before
   acknowledging a packet can be set to 0ms (i.e. "acknowledge as soon
   as possible").  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.





Dreibholz & Zhou        Expires December 15, 2007               [Page 4]


Internet-Draft           Delay-Sensitive Policy                June 2007


   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.









































Dreibholz & Zhou        Expires December 15, 2007               [Page 5]


Internet-Draft           Delay-Sensitive Policy                June 2007


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.

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



Dreibholz & Zhou        Expires December 15, 2007               [Page 6]


Internet-Draft           Delay-Sensitive Policy                June 2007


   o  Load: Current load of the pool element.

   o  Load DPF: The LoadDPF setting of the PE.

   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.



































Dreibholz & Zhou        Expires December 15, 2007               [Page 7]


Internet-Draft           Delay-Sensitive Policy                June 2007


4.  Reference Implementation

   The reference implementation based on the RSerPool prototype
   implementation rsplib can be found at [10].















































Dreibholz & Zhou        Expires December 15, 2007               [Page 8]


Internet-Draft           Delay-Sensitive Policy                June 2007


5.  Security Considerations

   This document does not identify security requirements beyond those
   already documented in the ENRP and ASAP protocol specifications.















































Dreibholz & Zhou        Expires December 15, 2007               [Page 9]


Internet-Draft           Delay-Sensitive Policy                June 2007


6.  IANA Considerations

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















































Dreibholz & Zhou        Expires December 15, 2007              [Page 10]


Internet-Draft           Delay-Sensitive Policy                June 2007


7.  References

7.1.  Normative References

   [1]   Tuexen, M., "Architecture for Reliable Server Pooling",
         draft-ietf-rserpool-arch-12 (work in progress), November 2006.

   [2]   Stewart, R., "Aggregate Server Access Protocol (ASAP)",
         draft-ietf-rserpool-asap-15 (work in progress), January 2007.

   [3]   Stewart, R., "Endpoint Handlespace Redundancy Protocol (ENRP)",
         draft-ietf-rserpool-enrp-15 (work in progress), January 2007.

   [4]   Stewart, R., "Aggregate Server Access Protocol (ASAP) and
         Endpoint Handlespace Redundancy  Protocol (ENRP) Parameters",
         draft-ietf-rserpool-common-param-11 (work in progress),
         October 2006.

   [5]   Tuexen, M. and T. Dreibholz, "Reliable Server Pooling
         Policies", draft-ietf-rserpool-policies-04 (work in progress),
         March 2007.

   [6]   Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
         H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V.
         Paxson, "Stream Control Transmission Protocol", RFC 2960,
         October 2000.

   [7]   Stewart, R., "Sockets API Extensions for Stream Control
         Transmission Protocol (SCTP)", draft-ietf-tsvwg-sctpsocket-14
         (work in progress), December 2006.

7.2.  Informative References

   [8]   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.

   [9]   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.

   [10]  Dreibholz, T., "Thomas Dreibholz's RSerPool Page",
         URL: http://tdrwww.exp-math.uni-essen.de/dreibholz/rserpool/.




Dreibholz & Zhou        Expires December 15, 2007              [Page 11]


Internet-Draft           Delay-Sensitive Policy                June 2007


   [11]  Dreibholz, T. and E. Rathgeb, "On the Performance of Reliable
         Server Pooling Systems", Proceedings of the 30th IEEE Local
         Computer Networks Conference, November 2005.

   [12]  Dreibholz, T. and E. Rathgeb, "Implementing the Reliable Server
         Pooling Framework", Proceedings of the 8th IEEE International
         Conference on Telecommunications, June 2005.

   [13]  Dreibholz, T., Zhou, X., and E. Rathgeb, "A Performance
         Evaluation of RSerPool Server Selection Policies in Varying
         Heterogeneous Capacity Scenarios", Proceedings of the 33rd IEEE
         EuroMirco Conference on Software Engineering and Advanced
         Applications, August 2007.

   [14]  Dreibholz, T. and E. Rathgeb, "An Application Demonstration of
         the Reliable Server Pooling Framework", Proceedings of the 24th
         IEEE Infocom, March 2005.


































Dreibholz & Zhou        Expires December 15, 2007              [Page 12]


Internet-Draft           Delay-Sensitive Policy                June 2007


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@exp-math.uni-essen.de
   URI:   http://www.exp-math.uni-essen.de/~dreibh/


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

   Phone: +86-898-66279141
   Email: xing.zhou@uni-due.de





























Dreibholz & Zhou        Expires December 15, 2007              [Page 13]


Internet-Draft           Delay-Sensitive Policy                June 2007


Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Dreibholz & Zhou        Expires December 15, 2007              [Page 14]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/