Network Working Group T. Dreibholz Internet-Draft University of Duisburg-Essen Intended status: Experimental X. Zhou Expires: July 4, 2012 Hainan University January 01, 2012 Definition of a Delay Measurement Infrastructure and Delay-Sensitive Least-Used Policy for Reliable Server Pooling draft-dreibholz-rserpool-delay-09.txt Abstract This document contains the definition of a delay measurement infrastructure and a delay-sensitive Least-Used policy for Reliable Server Pooling. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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. 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Dreibholz & Zhou Expires July 4, 2012 [Page 1] Internet-Draft Delay-Sensitive Policy January 2012 This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. ENRP Server Considerations . . . . . . . . . . . . . . . . 5 3.3. Pool User Considerations . . . . . . . . . . . . . . . . . 5 3.4. Pool Member Selection Policy Parameter . . . . . . . . . . 5 4. Reference Implementation . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Dreibholz & Zhou Expires July 4, 2012 [Page 2] Internet-Draft Delay-Sensitive Policy January 2012 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 [RFC5356] 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 [KiVS2007]. 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 [RFC5354]. 1.3. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 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 [RFC4960] 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 [RFC6458]. 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. By using the option SCTP_DELAYED_SACK (see [RFC6458]), the maximum delay before acknowledging a packet can be set to 0ms (i.e. "acknowledge as soon as possible"). After that, the RTT Dreibholz & Zhou Expires July 4, 2012 [Page 3] Internet-Draft Delay-Sensitive Policy January 2012 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. 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. 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. Dreibholz & Zhou Expires July 4, 2012 [Page 4] Internet-Draft Delay-Sensitive Policy January 2012 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Load: Current load of the pool element. o Load DPF: The LoadDPF setting of the PE. Dreibholz & Zhou Expires July 4, 2012 [Page 5] Internet-Draft Delay-Sensitive Policy January 2012 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. 4. Reference Implementation The RSerPool reference implementation RSPLIB can be found at [RSerPoolPage]. 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 of course the option defined by this document. An introduction to this implementation is provided in [Dre2006]. 5. Security Considerations Security considerations for RSerPool systems are described by [RFC5355]. 6. IANA Considerations This document does not require additional IANA actions beyond those already identified in the ENRP and ASAP protocol specifications. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC5351] Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An Dreibholz & Zhou Expires July 4, 2012 [Page 6] Internet-Draft Delay-Sensitive Policy January 2012 Overview of Reliable Server Pooling Protocols", RFC 5351, September 2008. [RFC5352] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate Server Access Protocol (ASAP)", RFC 5352, September 2008. [RFC5353] Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A. Silverton, "Endpoint Handlespace Redundancy Protocol (ENRP)", RFC 5353, 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, September 2008. [RFC5355] Stillman, M., 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, September 2008. [RFC5356] Dreibholz, T. and M. Tuexen, "Reliable Server Pooling Policies", RFC 5356, September 2008. [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. Yasevich, "Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)", RFC 6458, December 2011. [I-D.dreibholz-rserpool-asap-hropt] Dreibholz, T., "Handle Resolution Option for ASAP", draft-dreibholz-rserpool-asap-hropt-09 (work in progress), July 2011. [I-D.dreibholz-rserpool-enrp-takeover] Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for the ENRP Handle Update Message", draft-dreibholz-rserpool-enrp-takeover-06 (work in progress), July 2011. 7.2. Informative References [Dre2006] Dreibholz, T., "Reliable Server Pooling - Evaluation, Optimization and Extension of a Novel IETF Architecture", March 2007. [KiVS2007] Dreibholz, T. and E. Rathgeb, "On Improving the Performance of Reliable Server Pooling Systems for Dreibholz & Zhou Expires July 4, 2012 [Page 7] Internet-Draft Delay-Sensitive Policy January 2012 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, February 2007. [RSerPoolPage] Dreibholz, T., "Thomas Dreibholz's RSerPool Page", 2011. 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@iem.uni-due.de URI: http://www.iem.uni-due.de/~dreibh/ Xing Zhou Hainan University, College of Information Science and Technology Renmin Avenue 58 570228 Haikou, Hainan China Phone: +86-898-66279141 Email: zhouxing@hainu.edu.cn Dreibholz & Zhou Expires July 4, 2012 [Page 8]