Network Working Group                                       T. Dreibholz
Internet-Draft                                                 SimulaMet
Intended status: Informational                           J. Pulinthanath
Expires: September 14, 2021                 University of Duisburg-Essen
                                                          March 13, 2021

    Applicability of Reliable Server Pooling for SCTP-Based Endpoint


   This document describes a novel mobility concept based on a
   combination of SCTP with Dynamic Address Reconfiguration extension
   and Reliable Server Pooling (RSerPool).

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Existing Mobility Solutions . . . . . . . . . . . . . . . . .   2
     2.1.  Mobile IP and Mobile IPv6 . . . . . . . . . . . . . . . .   2
     2.2.  SCTP with Dynamic Address Reconfiguration . . . . . . . .   3
   3.  Solutions for Simultaneous Handovers  . . . . . . . . . . . .   3
     3.1.  SCTP with Add-IP and Mobile-IP  . . . . . . . . . . . . .   3
     3.2.  SCTP with Add-IP and RSerPool . . . . . . . . . . . . . .   4
   4.  Reference Implementation  . . . . . . . . . . . . . . . . . .   4
   5.  Testbed Platform  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   An increasing amount of Internet devices is getting mobile.
   Therefore, there is a growing demand for software solutions allowing
   for a seamless handover of communication sessions between multiple
   networks, e.g. to allow for a laptop or PDA to use a fast Ethernet
   connection when available, hand over to a WLAN when moving and hand
   over again to UMTS when the WLAN becomes unreachable - without
   interrupting the running communication sessions.

   Mobility handling is a deficiency of the common IP-based networks.
   Most of the available solutions are based on the network layer.  The
   disadvantage of such solutions is that fundamental changes in the
   network infrastructure are needed.  Therefore, we propose a new
   solution based on the upper layers to overcome these disadvantages.
   In this document, we present our mobility solution based on the SCTP
   protocol with Dynamic Address Reconfiguration extension and Reliable
   Server Pooling (RSerPool).

2.  Existing Mobility Solutions

2.1.  Mobile IP and Mobile IPv6

   In the concept of Mobile IP [RFC5944] every node must register to a
   Home-Agent (HA) in its own home network.  Then, the nodes are
   reachable under their home addresses managed by the HA.  When a node
   leaves its home network, it must also register at a Foreign Agent
   (FA) in the new network.  After that, a tunnel is established between
   the HA and the FA.  Any traffic to the mobile node is then tunnelled
   by its HA to the FA and forwarded by the FA to the node itself.

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   Clearly, the detour of all traffic via HA and FA is inefficient and
   results in an increased transmission delay.

   Mobile IPv6 [RFC6275] is an extension of Mobile IP.  In Mobile IPv6,
   the FA is not needed.  The packets will be tunnelled from the HA to
   the Gateway Router in the foreign network, which forwards the packets
   to the endpoint.  The inefficiency due to the detour of traffic as
   described for Mobile IP remains.

2.2.  SCTP with Dynamic Address Reconfiguration

   Using the SCTP protocol (see [RFC4960] together with its Dynamic
   Address Reconfiguration extension (Add-IP, see [RFC5061]), it is
   possible for a mobile endpoint to inform its peer on address changes.
   That is, when a moving mobile client gets in the vicinity of an
   additional radio station, it sends an "ASCONF Add Address Request" to
   tell its peer that it is now reachable under an additional network-
   layer address.  After that, the peer endpoint can use this additional
   address for a new SCTP path.  When the first radio station becomes
   unreachable, the node can send an "ASCONF Delete Address Request" to
   the peer endpoint.  After that, the peer removes the corresponding
   SCTP path to the unusable network-layer address.

   The following two cases for handovers are possible:

   o  Make-before-Break: An additional SCTP path can be used before the
      original path becomes unusable.  This case is trivial, since there
      is a continuous connectivity.

   o  Break-before-Make: The original SCTP path becomes unusable before
      a new SCTP path can be used.  For the case that only one endpoint
      performs a handover procedure at the same time, the mobile
      endpoint can always use Add-IP to communicate its new address to
      its peer endpoint.  However, when both endpoints perform a
      handover simultaneously, no endpoint is able to tell its
      corresponding peer the new address.

3.  Solutions for Simultaneous Handovers

3.1.  SCTP with Add-IP and Mobile-IP

   Using SCTP with Add-IP and Mobile IP/Mobile IPv6, the ASCONF messages
   will be sent to the home address of the peer node.  That is, even
   when both nodes are mobile, each endpoint is able to reach its peer
   endpoint using the corresponding home address.  However, this
   solution still requires the full Mobile IP/Mobile IPv6

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3.2.  SCTP with Add-IP and RSerPool

   Using RSerPool (see [RFC3237], [RFC5351], [RFC5352], [RFC5353],
   [RFC5354], [RFC5355], [RFC5356], at least one node registers as a
   Pool Element (PE) at an ENRP server under a Pool Handle (PH) known to
   both endpoints.  Upon handover, it is simply necessary for the PE
   endpoint to re-register, i.e. to update its registration with its new
   address.  The other endpoint can - in the role of a Pool User (PU) -
   ask an ENRP server for its peer node's new addresses.  After the new
   address is known, it is able to create a new SCTP path and continue
   the communication.

   The usage of RSerPool to provide support for mobile endpoints
   provides the following advantages:

   o  Simplicity: No Mobile IP/Mobile IPv6 infrastructure is needed.  In
      particular, it is not necessary that the providers of used
      networks (e.g. public WLAN access points, UMTS providers, etc.)
      provide any support for the mobility solution.

   o  Efficiency: No tunnelling of traffic is necessary.

   o  Applicability: All major SCTP implementations already support the
      Dynamic Address Reconfiguration extension.  It is only necessary
      to provide support for RSerPool, e.g. in the form of a userspace
      library, which is much easier to deploy than kernel extensions.

   o  Flexibility: RSerPool provides a complete session layer.  That is,
      providing applications on top of RSerPool makes the support for
      high availability simple.

   A more detailed description of our approach for endpoint mobility, as
   well as a performance analysis using a prototype implementation, can
   be found in our paper [LCN2003].

4.  Reference Implementation

   The RSerPool reference implementation RSPLIB can be found at
   [RSerPool-Website].  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
   [I-D.dreibholz-rserpool-delay].  An introduction to this
   implementation is provided in [Dre2006].

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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 [PAMS2013-NorNet],
   some further information can be found on the project website

6.  Security Considerations

   Security considerations for RSerPool systems are described by

7.  IANA Considerations

   This document introduces no additional considerations for IANA.

8.  References

8.1.  Normative References

              Dreibholz, T., "Handle Resolution Option for ASAP", draft-
              dreibholz-rserpool-asap-hropt-27 (work in progress),
              September 2020.

              Dreibholz, T. and X. Zhou, "Definition of a Delay
              Measurement Infrastructure and Delay-Sensitive Least-Used
              Policy for Reliable Server Pooling", draft-dreibholz-
              rserpool-delay-26 (work in progress), September 2020.

              Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for
              the ENRP Handle Update Message", draft-dreibholz-rserpool-
              enrp-takeover-24 (work in progress), September 2020.

   [RFC3237]  Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L.,
              Loughney, J., and M. Stillman, "Requirements for Reliable
              Server Pooling", RFC 3237, DOI 10.17487/RFC3237, January
              2002, <>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,

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   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061,
              DOI 10.17487/RFC5061, September 2007,

   [RFC5351]  Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An
              Overview of Reliable Server Pooling Protocols", RFC 5351,
              DOI 10.17487/RFC5351, September 2008,

   [RFC5352]  Stewart, R., Xie, Q., Stillman, M., and M. Tuexen,
              "Aggregate Server Access Protocol (ASAP)", RFC 5352,
              DOI 10.17487/RFC5352, September 2008,

   [RFC5353]  Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A.
              Silverton, "Endpoint Handlespace Redundancy Protocol
              (ENRP)", RFC 5353, DOI 10.17487/RFC5353, 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, DOI 10.17487/RFC5354, September 2008,

   [RFC5355]  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, <>.

   [RFC5356]  Dreibholz, T. and M. Tuexen, "Reliable Server Pooling
              Policies", RFC 5356, DOI 10.17487/RFC5356, September 2008,

   [RFC5944]  Perkins, C., Ed., "IP Mobility Support for IPv4, Revised",
              RFC 5944, DOI 10.17487/RFC5944, November 2010,

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <>.

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8.2.  Informative References

   [Dre2006]  Dreibholz, T., "Reliable Server Pooling - Evaluation,
              Optimization and Extension of a Novel IETF Architecture",
              March 2007, <https://duepublico.uni-duisburg-

   [LCN2003]  Dreibholz, T., Jungmaier, A., and M. Tuexen, "A New Scheme
              for IP-based Internet Mobility", Proceedings of the 28th
              IEEE Local Computer Networks Conference (LCN) Pages
              99-108, ISBN 0-7695-2037-5, DOI 10.1109/LCN.2003.1243117,
              October 2003, <https://www.wiwi.uni-

              Dreibholz, T., "NorNet - A Real-World, Large-Scale Multi-
              Homing Testbed", Online:, 2019,

              Dreibholz, T. and E. Gran, "Design and Implementation of
              the NorNet Core Research Testbed for Multi-Homed Systems",
              Proceedings of the 3nd 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, March 2013,

              Dreibholz, T., "Thomas Dreibholz's RSerPool Page",
              Online:, 2019,

Authors' Addresses

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   Thomas Dreibholz
   Simula Metropolitan Centre for Digital Engineering
   Pilestredet 52
   0167 Oslo, Oslo

   Phone: +47-6782-8200
   Fax:   +47-6782-8201

   Jobin Pulinthanath
   University of Duisburg-Essen, Institute for Experimental Mathematics
   Ellernstrasse 29
   45326 Essen, Nordrhein-Westfalen

   Phone: +49-201-1837637
   Fax:   +49-201-1837673

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