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Network Working Group                                       T. Dreibholz
Internet-Draft                              University of Duisburg-Essen
Expires: August 6, 2006                                     Feb 02, 2006

   Applicability of Reliable Server Pooling for Real-Time Distributed

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document describes the applicability of the Reliable Server
   Pooling architecture to manage real-time distributed computing pools
   and access the resources of such pools.

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1.  Introduction

   Reliable Server Pooling defines protocols for providing highly
   available services.  The services are located in a pool of redundant
   servers and if a server fails, another server will take over.  The
   only requirement put on these servers belonging to the pool is that
   if state is maintained by the server, this state must be transferred
   to the other server taking over.

   The goal is to provide server-based redundancy.  Transport and
   network level redundancy are handled by the transport and network
   layer protocols.

   The application may choose to distribute its traffic over the servers
   of the pool conforming to a certain policy.

1.1  Scope

   The scope of this document is to explain the way of using Reliable
   Server Pooling mechanisms to manage and access pools of Distributed
   Computing resources.

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 ietf-rserpool-common-
   param [13]

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2.  Distributed Computing using RSerPool

2.1  Requirements

   o  Clients generate large computation jobs.  Jobs have to be
      processed by servers as soon as possible (real-time), i.e. unlike
      concepts like SETI@home [16], it is not possible to let clients
      fetch a job, process it later and may be some day upload the

   o  Jobs may be partitionable, i.e. they can be split up to smaller
      pieces which can be processed independently and the processing
      results can be concatenated to the processing result of the
      complete job.  Jobs have to be processed by servers.

   o  Servers may be unreliable; i.e. user computers may be temporarily
      added to the pool of computing resources and may be revoked when
      they are used again by their owners.  Furthermore, they may simply
      disappear because of broken network connections (modems, etc.) or
      power turned off.

   o  The processing power of servers in a pool of computing resources
      may be very heterogeneous, i.e. a few supercomputers and many low-
      end user PCs.

   o  It must be possible to manage large server pools, e.g. up to some
      hundreds or even thousands of servers.

   o  Due to the heterogeneousity of the processing resources within a
      pool, it must be possible to use appropriate server selection
      procedures to meaningfully utilize the available resources.

   o  It must be possible to dynamically add and remove servers.

   o  Servers may be unreliable, especially when the servers are
      represented by user PCs.  Failover mechanisms are required to
      continue an interrupted computation session.

2.1.1  Architecture

   o  An efficient implementation of the handlespace management
      structures allows pools to contain thousands of elements.
      Handlespace management structures have been proposed, implemented
      and analyzed in [7].

   o  RSerPool allows to specify server selection rules by pool member
      selection policies [14].  A set of adaptive and non-adaptive

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      policies is already defined.  To fulfill the requirements of new
      applications, it is also possible to define new policies.
      Research has already been made on the subject of load distribution
      efficiency of pool policies in Distributed Computing scenarios:
      see [5] for details.

   o  Dynamic addition and removal of PEs is a feature of RSerPool [11].

   o  The control/data channel concept [15] of RSerPool realizes a
      session layer.  That is, RSerPool already handles the main task of
      maintaining and monitoring connections between PUs and PEs; the
      only task of the application layer to provide full failover
      functionality is to realize an application-dependent failover
      procedure.  By the usage of client-based state synchronization [4]
      in the form of ASAP Cookies, a failover may be fully transparent
      to the PU while only a state restoration is necessary on the PE
      side.  A demo application [1] using the RSerPool session layer in
      a Distributed Computing application is described in [6].

2.1.2  Implementation

   A proof of concept implementation of a Distributed Computing
   application based on the RSerPool prototype rsplib can be found at
   [1].  This system provides a fractal graphics computation service;
   the failover procedure is handled by ASAP cookies.

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3.  Security considerations

   The protocols used in the Reliable Server Pooling architecture only
   try to increase the availability of the servers in the network.
   RSerPool protocols do not contain any protocol mechanisms which are
   directly related to user message authentication, integrity and
   confidentiality functions.  For such features, it depends on the
   IPSEC protocols or on Transport Layer Security (TLS) protocols for
   its own security and on the architecture and/or security features of
   its user protocols.

   The RSerPool architecture allows the use of different transport
   protocols for its application and control data exchange.  These
   transport protocols may have mechanisms for reducing the risk of
   blind denial-of-service attacks and/or masquerade attacks.  If such
   measures are required by the applications, then it is advised to
   check the SCTP applicability statement RFC3257 [9] for guidance on
   this issue.

4.  Normative References

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

   [2]   Dreibholz, T. and E. Rathgeb, "The Performance of Reliable
         Server Pooling Systems in Different Server Capacity Scenarios",
         Proceedings of the IEEE TENCON, November 2005.

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

   [4]   Dreibholz, T., "An efficient approach for state sharing in
         server pools", Proceedings of the 27th IEEE Local Computer
         Networks Conference, October 2002.

   [5]   Dreibholz, T., Rathgeb, E., and M. Tuexen, "Load Distribution
         Performance of the Reliable Server Pooling Framework",
         Proceedings of the 4th IEEE International Conference on
         Networking, April 2005.

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

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

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   [8]   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.

   [9]   Coene, L., "Stream Control Transmission Protocol Applicability
         Statement", RFC 3257, April 2002.

   [10]  Tuexen, M., Xie, Q., Stewart, R., Shore, M., Loughney, J., and
         A. Silverton, "Architecture for Reliable Server Pooling",
         draft-ietf-rserpool-arch-09 (work in progress), February 2005.

   [11]  Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
         Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-11
         (work in progress), February 2005.

   [12]  Xie, Q., Stewart, R., Stillman, M., and M. Tuexen, "Enpoint
         Handlespace Redundancy Protocol (ENRP)",
         draft-ietf-rserpool-enrp-11 (work in progress), February 2005.

   [13]  Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
         Server Access Protocol (ASAP) and Endpoint Name Resolution
         (ENRP) Parameters", draft-ietf-rserpool-common-param-08 (work
         in progress), February 2005.

   [14]  Tuexen, M. and T. Dreibholz, "Reliable Server Pooling
         Policies", draft-ietf-rserpool-policies-01 (work in progress),
         June 2005.

   [15]  Conrad, P. and P. Lei, "Services Provided By Reliable Server
         Pooling", draft-ietf-rserpool-service-01 (work in progress),
         June 2004.

   [16]  "SETI@home: Search for Extraterrestrial Intelligence at home",
         URL: http://setiathome.ssl.berkeley.edu.

   [17]  Bradner, S., "Intellectual Property Rights in IETF Technology",
         RFC 3668, February 2004.

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Author's Address

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

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

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