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Checking references for intended status: Experimental ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 4960 (Obsoleted by RFC 9260) == Outdated reference: A later version (-32) exists of draft-ietf-tsvwg-sctpsocket-19 == Outdated reference: A later version (-34) exists of draft-dreibholz-rserpool-asap-hropt-04 == Outdated reference: A later version (-31) exists of draft-dreibholz-rserpool-enrp-takeover-01 Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Dreibholz 3 Internet-Draft University of Duisburg-Essen 4 Intended status: Experimental X. Zhou 5 Expires: January 6, 2010 Hainan University 6 July 5, 2009 8 Definition of a Delay Measurement Infrastructure and Delay-Sensitive 9 Least-Used Policy for Reliable Server Pooling 10 draft-dreibholz-rserpool-delay-04.txt 12 Status of this Memo 14 This Internet-Draft is submitted to IETF in full conformance with the 15 provisions of BCP 78 and BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on January 6, 2010. 35 Copyright Notice 37 Copyright (c) 2009 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents in effect on the date of 42 publication of this document (http://trustee.ietf.org/license-info). 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. 46 Abstract 48 This document contains the definition of a delay measurement 49 infrastructure and a delay-sensitive Least-Used policy for Reliable 50 Server Pooling. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Delay-Measurement Infrastructure . . . . . . . . . . . . . . . 3 59 2.1. Quantification of Distance . . . . . . . . . . . . . . . . 3 60 2.2. Distance Measurement Environment . . . . . . . . . . . . . 4 61 3. Distance-Sensitive Least-Used Policy . . . . . . . . . . . . . 4 62 3.1. Description . . . . . . . . . . . . . . . . . . . . . . . . 5 63 3.2. ENRP Server Considerations . . . . . . . . . . . . . . . . 5 64 3.3. Pool User Considerations . . . . . . . . . . . . . . . . . 5 65 3.4. Pool Member Selection Policy Parameter . . . . . . . . . . 5 66 4. Reference Implementation . . . . . . . . . . . . . . . . . . . 6 67 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 69 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 71 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 74 1. Introduction 76 Reliable Server Pooling defines protocols for providing highly 77 available services. PEs of a pool may be distributed over a large 78 geographical area, in order to provide redundancy in case of 79 localized disasters. But the current pool policies defined in 80 [RFC5356] do not incorporate the fact of distances (i.e. delay) 81 between PU and PE. This leads to a low performance for delay- 82 sensitive applications. 84 1.1. Scope 86 This draft defines a delay measurement infrastructure for ENRP 87 servers to add delay information into the handlespace. Furthermore, 88 a delay-sensitive Least-Used policy is defined. Performance 89 evaluations can be found in [KiVS2007]. 91 1.2. Terminology 93 The terms are commonly identified in related work and can be found in 94 the Aggregate Server Access Protocol and Endpoint Handlespace 95 Redundancy Protocol Common Parameters document [RFC5354]. 97 1.3. Conventions 99 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 100 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 101 document are to be interpreted as described in [RFC2119]. 103 2. Delay-Measurement Infrastructure 105 This section describes the necessary delay measurement infrastructure 106 for the policy later defined in Section 3. It has to be provided as 107 part of the ENRP servers. 109 2.1. Quantification of Distance 111 Measuring delay for SCTP associations is easy: the SCTP protocol 112 [RFC4960] already calculates a smoothed round-trip time (RTT) for the 113 primary path. This RTT only has to be queried via the standard SCTP 114 API as defined in [I-D.ietf-tsvwg-sctpsocket]. By default, the 115 calculated RTT has a small restriction: a SCTP endpoint waits up to 116 200ms before acknowledging a packet, in order to piggyback the 117 acknowledgement chunk with payload data. In this case, the RTT would 118 include this latency. Using the option SCTP_DELAYED_ACK_TIME (see 119 [I-D.ietf-tsvwg-sctpsocket]), the maximum delay before acknowledging 120 a packet can be set to 0ms (i.e. "acknowledge as soon as possible"). 122 After that, the RTT approximately consists of the network latency 123 only. Then, using the RTT, the end-to-end delay between two 124 associated components is approximately 0.5*RTT. 126 In real networks, there may be negligible delay differences: for 127 example, the delay between a PU and PE #1 is 5ms and the latency 128 between the PU and PE #2 is 6ms. From the service user's 129 perspective, such minor delay differences may be ignored and are 130 furthermore unavoidable in Internet scenarios. Therefore, the 131 distance parameter between two components A and B is defined as 132 follows: 134 Distance = DistanceStep * round( (0.5*RTT) / DistanceStep ) 136 That is, the distance parameter is defined as the nearest integer 137 multiple of the constant DistanceStep for the measured delay (i.e. 138 0.5*RTT). 140 2.2. Distance Measurement Environment 142 In order to define a distance-aware policy, it is first necessary to 143 define a basic rule: PEs and PUs choose "nearby" ENRP servers. Since 144 the operation scope of RSerPool is restricted to a single 145 organization, this condition can be met easily by appropriately 146 locating ENRP servers. 148 o A Home ENRP server can measure the delay of the ASAP associations 149 to its PE. As part of its ENRP updates to other ENRP servers, it 150 can report this measured delay together with the PE information. 152 o A non-Home-ENRP server receiving such an update simply adds the 153 delay of the ENRP association with the Home ENRP server to the 154 PE's reported delay. 156 Now, each ENRP server can approximate the distance to every PE in the 157 operation scope using the equation in Section 2.1. 159 Note, that delay changes are propagated to all ENRP servers upon PE 160 re-registrations, i.e. the delay information (and the approximated 161 distance) dynamically adapts to the state of the network. 163 3. Distance-Sensitive Least-Used Policy 165 In this section, a distance-sensitive Least Used policy is defined, 166 based on the delay-measurement infrastructure introduced in 167 Section 2. 169 3.1. Description 171 The Least Used with Distance Penalty Factor (LU-DPF) policy uses load 172 information provided by the pool elements to select the lowest-loaded 173 pool elements within the pool. If there are multiple elements having 174 lowest load, the nearest PE should be chosen. 176 3.2. ENRP Server Considerations 178 The ENRP server SHOULD select at most the requested number of pool 179 elements. Their load values SHOULD be the lowest possible ones 180 within the pool and their distances also SHOULD be lowest. Each 181 element MUST NOT be reported more than once to the pool user. If 182 there is a choice of equal-loaded and equal-distanced pool elements, 183 round robin selection SHOULD be made among these elements. The 184 returned list of pool elements MUST be sorted by load value in 185 ascending order (1st key) and distance in ascending order (2nd key). 187 3.3. Pool User Considerations 189 The pool user should try to use the pool elements returned from the 190 list in the order returned by the ENRP server. A subsequent call for 191 handle resolution may result in the same list. Therefore, it is 192 RECOMMENDED for a pool user to request multiple entries in order to 193 have a sufficient amount of feasible backup entries available. 195 3.4. Pool Member Selection Policy Parameter 197 0 1 2 3 198 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 1 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | Parameter Type = 0x6 | Length = 0x14 | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Policy Type = 0x40000010 | 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | Load | 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | Load DPF | 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 | Distance | 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 o Load: Current load of the pool element. 213 o Load DPF: The LoadDPF setting of the PE. 215 o Distance: The approximated distance in milliseconds. 217 * Between PE and Home ENRP server: The distance SHOULD be set to 218 0. 220 * Between Non-Home ENRP server and Home ENRP server: The delay 221 measured on the ASAP association between Home ENRP server and 222 PE. 224 * Between ENRP server and PU: The sums of the measured delays on 225 the ASAP association and the ENRP association to the Home ENRP 226 server. 228 4. Reference Implementation 230 The RSerPool reference implementation RSPLIB can be found at 231 [RSerPoolPage]. It supports the functionalities defined by 232 [RFC5351], [RFC5352], [RFC5353], [RFC5354] and [RFC5356] as well as 233 the options [I-D.dreibholz-rserpool-asap-hropt], 234 [I-D.dreibholz-rserpool-enrp-takeover] and of course the option 235 defined by this document. An introduction to this implementation is 236 provided in [Dre2006]. 238 5. Security Considerations 240 Security considerations for RSerPool systems are described by 241 [RFC5355]. 243 6. IANA Considerations 245 This document does not require additional IANA actions beyond those 246 already identified in the ENRP and ASAP protocol specifications. 248 7. References 250 7.1. Normative References 252 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 253 Requirement Levels", BCP 14, RFC 2119, March 1997. 255 [RFC5351] Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An 256 Overview of Reliable Server Pooling Protocols", RFC 5351, 257 September 2008. 259 [RFC5352] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, 260 "Aggregate Server Access Protocol (ASAP)", RFC 5352, 261 September 2008. 263 [RFC5353] Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A. 264 Silverton, "Endpoint Handlespace Redundancy Protocol 265 (ENRP)", RFC 5353, September 2008. 267 [RFC5354] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, 268 "Aggregate Server Access Protocol (ASAP) and Endpoint 269 Handlespace Redundancy Protocol (ENRP) Parameters", 270 RFC 5354, September 2008. 272 [RFC5355] Stillman, M., Gopal, R., Guttman, E., Sengodan, S., and M. 273 Holdrege, "Threats Introduced by Reliable Server Pooling 274 (RSerPool) and Requirements for Security in Response to 275 Threats", RFC 5355, September 2008. 277 [RFC5356] Dreibholz, T. and M. Tuexen, "Reliable Server Pooling 278 Policies", RFC 5356, September 2008. 280 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", 281 RFC 4960, September 2007. 283 7.2. Informative References 285 [I-D.ietf-tsvwg-sctpsocket] 286 Stewart, R., Poon, K., Tuexen, M., Yasevich, V., and P. 287 Lei, "Sockets API Extensions for Stream Control 288 Transmission Protocol (SCTP)", 289 draft-ietf-tsvwg-sctpsocket-19 (work in progress), 290 February 2009. 292 [KiVS2007] 293 Dreibholz, T. and E. Rathgeb, "On Improving the 294 Performance of Reliable Server Pooling Systems for 295 Distance-Sensitive Distributed Applications", 296 Proceedings of the 15. ITG/GI Fachtagung Kommunikation in 297 Verteilten Systemen, February 2007. 299 [Dre2006] Dreibholz, T., "Reliable Server Pooling -- Evaluation, 300 Optimization and Extension of a Novel IETF Architecture", 301 Ph.D. Thesis University of Duisburg-Essen, Faculty of 302 Economics, Institute for Computer Science and Business 303 Information Systems, URL: http:// 304 duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/ 305 Derivate-16326/Dre2006-final.pdf, March 2007. 307 [RSerPoolPage] 308 Dreibholz, T., "Thomas Dreibholz's RSerPool Page", 309 URL: http://tdrwww.iem.uni-due.de.de/dreibholz/rserpool/. 311 [I-D.dreibholz-rserpool-asap-hropt] 312 Dreibholz, T., "Handle Resolution Option for ASAP", 313 draft-dreibholz-rserpool-asap-hropt-04 (work in progress), 314 January 2009. 316 [I-D.dreibholz-rserpool-enrp-takeover] 317 Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for 318 the ENRP Handle Update Message", 319 draft-dreibholz-rserpool-enrp-takeover-01 (work in 320 progress), January 2009. 322 Authors' Addresses 324 Thomas Dreibholz 325 University of Duisburg-Essen, Institute for Experimental Mathematics 326 Ellernstrasse 29 327 45326 Essen, Nordrhein-Westfalen 328 Germany 330 Phone: +49-201-1837637 331 Fax: +49-201-1837673 332 Email: dreibh@iem.uni-due.de 333 URI: http://www.iem.uni-due.de/~dreibh/ 335 Xing Zhou 336 Hainan University, College of Information Science and Technology 337 Renmin Avenue 58 338 570228 Haikou, Hainan 339 China 341 Phone: +86-898-66279141 342 Email: zhouxing@hainu.edu.cn