Network Working Group T. Dreibholz Internet-Draft University of Duisburg-Essen Intended status: Standards Track X. Zhou Expires: July 13, 2008 Hainan University January 10, 2008 Definition of a Delay Measurement Infrastructure and Delay-Sensitive Least-Used Policy for Reliable Server Pooling draft-dreibholz-rserpool-delay-01.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 July 13, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Dreibholz & Zhou Expires July 13, 2008 [Page 1] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 2] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 3] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 4] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 5] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 6] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 7] Internet-Draft Delay-Sensitive Policy January 2008 4. Reference Implementation The reference implementation based on the RSerPool prototype implementation rsplib can be found at [10]. Dreibholz & Zhou Expires July 13, 2008 [Page 8] Internet-Draft Delay-Sensitive Policy January 2008 5. Security Considerations This document does not identify security requirements beyond those already documented in the ENRP and ASAP protocol specifications. Dreibholz & Zhou Expires July 13, 2008 [Page 9] Internet-Draft Delay-Sensitive Policy January 2008 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 July 13, 2008 [Page 10] Internet-Draft Delay-Sensitive Policy January 2008 7. References 7.1. Normative References [1] Tuexen, M., "Architecture for Reliable Server Pooling", draft-ietf-rserpool-arch-10 (work in progress), July 2005. [2] Stewart, R., "Aggregate Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-13 (work in progress), February 2006. [3] Stewart, R., "Endpoint Handlespace Redundancy Protocol (ENRP)", draft-ietf-rserpool-enrp-13 (work in progress), February 2006. [4] Stewart, R., "Aggregate Server Access Protocol (ASAP) and Endpoint Handlespace Redundancy Protocol (ENRP) Parameters", draft-ietf-rserpool-common-param-10 (work in progress), February 2006. [5] Tuexen, M. and T. Dreibholz, "Reliable Server Pooling Policies", draft-ietf-rserpool-policies-02 (work in progress), February 2006. [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 July 13, 2008 [Page 11] Internet-Draft Delay-Sensitive Policy January 2008 [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 July 13, 2008 [Page 12] Internet-Draft Delay-Sensitive Policy January 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@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 July 13, 2008 [Page 13] Internet-Draft Delay-Sensitive Policy January 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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