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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Dreibholz 3 Internet-Draft Simula Research Laboratory 4 Intended status: Experimental X. Zhou 5 Expires: January 3, 2013 Hainan University 6 July 2, 2012 8 Definition of a Delay Measurement Infrastructure and Delay-Sensitive 9 Least-Used Policy for Reliable Server Pooling 10 draft-dreibholz-rserpool-delay-10.txt 12 Abstract 14 This document contains the definition of a delay measurement 15 infrastructure and a delay-sensitive Least-Used policy for Reliable 16 Server Pooling. 18 Status of this Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on January 3, 2013. 35 Copyright Notice 37 Copyright (c) 2012 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 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 This document may contain material from IETF Documents or IETF 51 Contributions published or made publicly available before November 52 10, 2008. The person(s) controlling the copyright in some of this 53 material may not have granted the IETF Trust the right to allow 54 modifications of such material outside the IETF Standards Process. 55 Without obtaining an adequate license from the person(s) controlling 56 the copyright in such materials, this document may not be modified 57 outside the IETF Standards Process, and derivative works of it may 58 not be created outside the IETF Standards Process, except to format 59 it for publication as an RFC or to translate it into languages other 60 than English. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 66 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 67 1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Delay-Measurement Infrastructure . . . . . . . . . . . . . . . 3 69 2.1. Quantification of Distance . . . . . . . . . . . . . . . . 3 70 2.2. Distance Measurement Environment . . . . . . . . . . . . . 4 71 3. Distance-Sensitive Least-Used Policy . . . . . . . . . . . . . 4 72 3.1. Description . . . . . . . . . . . . . . . . . . . . . . . . 5 73 3.2. ENRP Server Considerations . . . . . . . . . . . . . . . . 5 74 3.3. Pool User Considerations . . . . . . . . . . . . . . . . . 5 75 3.4. Pool Member Selection Policy Parameter . . . . . . . . . . 5 76 4. Reference Implementation . . . . . . . . . . . . . . . . . . . 6 77 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 78 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 79 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 80 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 81 7.2. Informative References . . . . . . . . . . . . . . . . . . 7 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 84 1. Introduction 86 Reliable Server Pooling defines protocols for providing highly 87 available services. PEs of a pool may be distributed over a large 88 geographical area, in order to provide redundancy in case of 89 localized disasters. But the current pool policies defined in 90 [RFC5356] do not incorporate the fact of distances (i.e. delay) 91 between PU and PE. This leads to a low performance for delay- 92 sensitive applications. 94 1.1. Scope 96 This draft defines a delay measurement infrastructure for ENRP 97 servers to add delay information into the handlespace. Furthermore, 98 a delay-sensitive Least-Used policy is defined. Performance 99 evaluations can be found in [KiVS2007]. 101 1.2. Terminology 103 The terms are commonly identified in related work and can be found in 104 the Aggregate Server Access Protocol and Endpoint Handlespace 105 Redundancy Protocol Common Parameters document [RFC5354]. 107 1.3. Conventions 109 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 110 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 111 document are to be interpreted as described in [RFC2119]. 113 2. Delay-Measurement Infrastructure 115 This section describes the necessary delay measurement infrastructure 116 for the policy later defined in Section 3. It has to be provided as 117 part of the ENRP servers. 119 2.1. Quantification of Distance 121 Measuring delay for SCTP associations is easy: the SCTP protocol 122 [RFC4960] already calculates a smoothed round-trip time (RTT) for the 123 primary path. This RTT only has to be queried via the standard SCTP 124 API as defined in [RFC6458]. By default, the calculated RTT has a 125 small restriction: a SCTP endpoint waits up to 200ms before 126 acknowledging a packet, in order to piggyback the acknowledgement 127 chunk with payload data. In this case, the RTT would include this 128 latency. By using the option SCTP_DELAYED_SACK (see [RFC6458]), the 129 maximum delay before acknowledging a packet can be set to 0ms (i.e. 130 "acknowledge as soon as possible"). After that, the RTT 131 approximately consists of the network latency only. Then, using the 132 RTT, the end-to-end delay between two associated components is 133 approximately 0.5*RTT. 135 In real networks, there may be negligible delay differences: for 136 example, the delay between a PU and PE #1 is 5ms and the latency 137 between the PU and PE #2 is 6ms. From the service user's 138 perspective, such minor delay differences may be ignored and are 139 furthermore unavoidable in Internet scenarios. Therefore, the 140 distance parameter between two components A and B is defined as 141 follows: 143 Distance = DistanceStep * round( (0.5*RTT) / DistanceStep ) 145 That is, the distance parameter is defined as the nearest integer 146 multiple of the constant DistanceStep for the measured delay (i.e. 147 0.5*RTT). 149 2.2. Distance Measurement Environment 151 In order to define a distance-aware policy, it is first necessary to 152 define a basic rule: PEs and PUs choose "nearby" ENRP servers. Since 153 the operation scope of RSerPool is restricted to a single 154 organization, this condition can be met easily by appropriately 155 locating ENRP servers. 157 o A Home ENRP server can measure the delay of the ASAP associations 158 to its PE. As part of its ENRP updates to other ENRP servers, it 159 can report this measured delay together with the PE information. 161 o A non-Home-ENRP server receiving such an update simply adds the 162 delay of the ENRP association with the Home ENRP server to the 163 PE's reported delay. 165 Now, each ENRP server can approximate the distance to every PE in the 166 operation scope using the equation in Section 2.1. 168 Note, that delay changes are propagated to all ENRP servers upon PE 169 re-registrations, i.e. the delay information (and the approximated 170 distance) dynamically adapts to the state of the network. 172 3. Distance-Sensitive Least-Used Policy 174 In this section, a distance-sensitive Least Used policy is defined, 175 based on the delay-measurement infrastructure introduced in 176 Section 2. 178 3.1. Description 180 The Least Used with Distance Penalty Factor (LU-DPF) policy uses load 181 information provided by the pool elements to select the lowest-loaded 182 pool elements within the pool. If there are multiple elements having 183 lowest load, the nearest PE should be chosen. 185 3.2. ENRP Server Considerations 187 The ENRP server SHOULD select at most the requested number of pool 188 elements. Their load values SHOULD be the lowest possible ones 189 within the pool and their distances also SHOULD be lowest. Each 190 element MUST NOT be reported more than once to the pool user. If 191 there is a choice of equal-loaded and equal-distanced pool elements, 192 round robin selection SHOULD be made among these elements. The 193 returned list of pool elements MUST be sorted by load value in 194 ascending order (1st key) and distance in ascending order (2nd key). 196 3.3. Pool User Considerations 198 The pool user should try to use the pool elements returned from the 199 list in the order returned by the ENRP server. A subsequent call for 200 handle resolution may result in the same list. Therefore, it is 201 RECOMMENDED for a pool user to request multiple entries in order to 202 have a sufficient amount of feasible backup entries available. 204 3.4. Pool Member Selection Policy Parameter 206 0 1 2 3 207 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 1 208 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 | Parameter Type = 0x6 | Length = 0x14 | 210 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 211 | Policy Type = 0x40000010 | 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 | Load | 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Load DPF | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Distance | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 o Load: Current load of the pool element. 222 o Load DPF: The LoadDPF setting of the PE. 224 o Distance: The approximated distance in milliseconds. 226 * Between PE and Home ENRP server: The distance SHOULD be set to 227 0. 229 * Between Non-Home ENRP server and Home ENRP server: The delay 230 measured on the ASAP association between Home ENRP server and 231 PE. 233 * Between ENRP server and PU: The sums of the measured delays on 234 the ASAP association and the ENRP association to the Home ENRP 235 server. 237 4. Reference Implementation 239 The RSerPool reference implementation RSPLIB can be found at 240 [RSerPoolPage]. It supports the functionalities defined by 241 [RFC5351], [RFC5352], [RFC5353], [RFC5354] and [RFC5356] as well as 242 the options [I-D.dreibholz-rserpool-asap-hropt], 243 [I-D.dreibholz-rserpool-enrp-takeover] and of course the option 244 defined by this document. An introduction to this implementation is 245 provided in [Dre2006]. 247 5. Security Considerations 249 Security considerations for RSerPool systems are described by 250 [RFC5355]. 252 6. IANA Considerations 254 This document does not require additional IANA actions beyond those 255 already identified in the ENRP and ASAP protocol specifications. 257 7. References 259 7.1. Normative References 261 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 262 Requirement Levels", BCP 14, RFC 2119, March 1997. 264 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", 265 RFC 4960, September 2007. 267 [RFC5351] Lei, P., Ong, L., Tuexen, M., and T. Dreibholz, "An 268 Overview of Reliable Server Pooling Protocols", RFC 5351, 269 September 2008. 271 [RFC5352] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, 272 "Aggregate Server Access Protocol (ASAP)", RFC 5352, 273 September 2008. 275 [RFC5353] Xie, Q., Stewart, R., Stillman, M., Tuexen, M., and A. 276 Silverton, "Endpoint Handlespace Redundancy Protocol 277 (ENRP)", RFC 5353, September 2008. 279 [RFC5354] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, 280 "Aggregate Server Access Protocol (ASAP) and Endpoint 281 Handlespace Redundancy Protocol (ENRP) Parameters", 282 RFC 5354, September 2008. 284 [RFC5355] Stillman, M., Gopal, R., Guttman, E., Sengodan, S., and M. 285 Holdrege, "Threats Introduced by Reliable Server Pooling 286 (RSerPool) and Requirements for Security in Response to 287 Threats", RFC 5355, September 2008. 289 [RFC5356] Dreibholz, T. and M. Tuexen, "Reliable Server Pooling 290 Policies", RFC 5356, September 2008. 292 [RFC6458] Stewart, R., Tuexen, M., Poon, K., Lei, P., and V. 293 Yasevich, "Sockets API Extensions for the Stream Control 294 Transmission Protocol (SCTP)", RFC 6458, December 2011. 296 [I-D.dreibholz-rserpool-asap-hropt] 297 Dreibholz, T., "Handle Resolution Option for ASAP", 298 draft-dreibholz-rserpool-asap-hropt-10 (work in progress), 299 December 2011. 301 [I-D.dreibholz-rserpool-enrp-takeover] 302 Dreibholz, T. and X. Zhou, "Takeover Suggestion Flag for 303 the ENRP Handle Update Message", 304 draft-dreibholz-rserpool-enrp-takeover-07 (work in 305 progress), December 2011. 307 7.2. Informative References 309 [Dre2006] Dreibholz, T., "Reliable Server Pooling - Evaluation, 310 Optimization and Extension of a Novel IETF Architecture", 311 March 2007. 313 [KiVS2007] 314 Dreibholz, T. and E. Rathgeb, "On Improving the 315 Performance of Reliable Server Pooling Systems for 316 Distance-Sensitive Distributed Applications", Proceedings 317 of the 15. ITG/GI Fachtagung Kommunikation in Verteilten 318 Systemen (KiVS), Pages 39-50, ISBN 978-3-540-69962-0, 319 DOI 10.1007/978-3-540-69962-0_4, February 2007. 321 [RSerPoolPage] 322 Dreibholz, T., "Thomas Dreibholz's RSerPool Page", 2012. 324 Authors' Addresses 326 Thomas Dreibholz 327 Simula Research Laboratory, Network Systems Group 328 Martin Linges vei 17 329 1364 Fornebu, Oestlandet 330 Norway 332 Phone: +47-6782-8200 333 Fax: +47-6782-8201 334 Email: dreibh@simula.no 335 URI: http://www.iem.uni-due.de/~dreibh/ 337 Xing Zhou 338 Hainan University, College of Information Science and Technology 339 Renmin Avenue 58 340 570228 Haikou, Hainan 341 China 343 Phone: +86-898-66279141 344 Email: zhouxing@hainu.edu.cn