Definition of a Delay Measurement Infrastructure and Delay-Sensitive Least-Used Policy for Reliable Server Pooling
draft-dreibholz-rserpool-delay-38

Network Working Group                                       T. Dreibholz
Internet-Draft                                                 SimulaMet
Intended status: Standards Track                                 X. Zhou
Expires: 20 March 2027                                 Hainan University
                                                       16 September 2026

  Definition of a Delay Measurement Infrastructure and Delay-Sensitive
             Least-Used Policy for Reliable Server Pooling
                   draft-dreibholz-rserpool-delay-38

Abstract

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     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 . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  ENRP Server Considerations  . . . . . . . . . . . . . . .   4
     3.3.  Pool User Considerations  . . . . . . . . . . . . . . . .   5
     3.4.  Pool Member Selection Policy Parameter  . . . . . . . . .   5
   4.  Reference Implementation  . . . . . . . . . . . . . . . . . .   5
   5.  Testbed Platform  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 [8] do
   not incorporate distance (i.e., delay) between PU and PE.  This leads
   to 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 [14].

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 [7].

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1.3.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [1] [2] when, and only when, they appear in all capitals, as shown
   here.

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 [3]
   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 [9].  By default, the calculated RTT has a small
   restriction: an SCTP endpoint waits up to 200 ms before acknowledging
   a packet, in order to piggyback the acknowledgement chunk with
   payload data.  In this case, the RTT would include this latency.  By
   using the option SCTP_DELAYED_SACK (see [9]), the maximum delay
   before acknowledging a packet can be set to 0 ms (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 5 ms and the latency
   between the PU and PE #2 is 6 ms.  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).

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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.

   *  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.

   *  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.

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
   the 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 the lowest
   possible ones.  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).

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

   *  Load: Current load of the pool element.

   *  Load DPF: The LoadDPF setting of the PE.

   *  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 [17].
   It supports the functionalities defined by [4], [5], [6], [7] and [8]
   as well as the options [10], [11] and the option defined in this
   document.  An introduction to this implementation is provided in
   [13].

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5.  Testbed Platform

   A large-scale and realistic Internet testbed platform with support
   for the multi-homing feature of the underlying SCTP protocol is
   NorNet.  A description of NorNet is provided in [16] and [15].
   Further information can be found on the project website [18].

6.  Security Considerations

   Security considerations for RSerPool systems are described in [12].

7.  IANA Considerations

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

8.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [2]        Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [3]        Stewart, R., Tüxen, M., and K. Nielsen, "Stream Control
              Transmission Protocol", RFC 9260, DOI 10.17487/RFC9260,
              June 2022, <https://www.rfc-editor.org/info/rfc9260>.

   [4]        Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An
              Overview of Reliable Server Pooling Protocols", RFC 5351,
              DOI 10.17487/RFC5351, September 2008,
              <https://www.rfc-editor.org/info/rfc5351>.

   [5]        Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
              "Aggregate Server Access Protocol (ASAP)", RFC 5352,
              DOI 10.17487/RFC5352, September 2008,
              <https://www.rfc-editor.org/info/rfc5352>.

   [6]        Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A.
              Silverton, "Endpoint Handlespace Redundancy Protocol
              (ENRP)", RFC 5353, DOI 10.17487/RFC5353, September 2008,
              <https://www.rfc-editor.org/info/rfc5353>.

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   [7]        Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
              "Aggregate Server Access Protocol (ASAP) and Endpoint
              Handlespace Redundancy Protocol (ENRP) Parameters",
              RFC 5354, DOI 10.17487/RFC5354, September 2008,
              <https://www.rfc-editor.org/info/rfc5354>.

   [8]        Dreibholz, T. and M. Tuexen, "Reliable Server Pooling
              Policies", RFC 5356, DOI 10.17487/RFC5356, September 2008,
              <https://www.rfc-editor.org/info/rfc5356>.

   [9]        Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
              Yasevich, "Sockets API Extensions for the Stream Control
              Transmission Protocol (SCTP)", RFC 6458,
              DOI 10.17487/RFC6458, December 2011,
              <https://www.rfc-editor.org/info/rfc6458>.

   [10]       Dreibholz, T., "Handle Resolution Option for ASAP", Work
              in Progress, Internet-Draft, draft-dreibholz-rserpool-
              asap-hropt-38, 15 March 2026,
              <https://datatracker.ietf.org/doc/html/draft-dreibholz-
              rserpool-asap-hropt-38>.

   [11]       Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for
              the ENRP Handle Update Message", Work in Progress,
              Internet-Draft, draft-dreibholz-rserpool-enrp-takeover-35,
              15 March 2026, <https://datatracker.ietf.org/doc/html/
              draft-dreibholz-rserpool-enrp-takeover-35>.

9.  Informative References

   [12]       Stillman, M., Ed., 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, DOI 10.17487/RFC5355,
              September 2008, <https://www.rfc-editor.org/info/rfc5355>.

   [13]       Dreibholz, T., "Reliable Server Pooling – Evaluation,
              Optimization and Extension of a Novel IETF Architecture",
              7 March 2007,
              <https://www.nntb.no/~dreibh/rserpool/Dre2006.pdf>.

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   [14]       Dreibholz, T. and E. P. 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 (KiVS) Pages 39–50, ISBN 978-3-540-69962-0,
              DOI 10.1007/978-3-540-69962-0_4, 28 February 2007,
              <https://web.archive.org/web/20260420112909/
              https://www.wiwi.uni-due.de/fileadmin/fileupload/I-
              TDR/ReliableServer/Publications/KiVS2007.pdf>.

   [15]       Dreibholz, T. and E. G. Gran, "Design and Implementation
              of the NorNet Core Research Testbed for Multi-Homed
              Systems", Proceedings of the 3rd International Workshop on
              Protocols and Applications with Multi-Homing
              Support (PAMS) Pages 1094–1100, ISBN 978-0-7695-4952-1,
              DOI 10.1109/WAINA.2013.71, 27 March 2013, <https://web-
              backend.simula.no/sites/default/files/publications/
              threfereedinproceedingsreference.2012-12-20.7643198512.pdf>.

   [16]       Gran, E. G., Dreibholz, T., and A. Kvalbein, "NorNet Core
              – A Multi-Homed Research Testbed", Computer Networks,
              Special Issue on Future Internet Testbeds Volume 61, Pages
              75–87, ISSN 1389-1286, DOI 10.1016/j.bjp.2013.12.035, 14
              March 2014, <https://web-
              backend.simula.no/sites/default/files/publications/
              Simula.simula.2236.pdf>.

   [17]       Dreibholz, T., "Thomas Dreibholz's RSerPool Page", 16
              September 2026, <https://www.nntb.no/~dreibh/rserpool/>.

   [18]       Dreibholz, T., "NorNet – A Real-World, Large-Scale Multi-
              Homing Testbed", 16 September 2026,
              <https://www.nntb.no/>.

Authors' Addresses

   Thomas Dreibholz
   Simula Metropolitan Centre for Digital Engineering
   Stensberggata 27
   0170 Oslo
   Norway
   Email: dreibh@simula.no
   URI:   https://www.simula.no/people/dreibh

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

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   570228 Haikou
   Hainan,
   China
   Phone: +86-898-66279141
   Email: zhouxing@hainanu.edu.cn

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