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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'I-D.ietf-dime-e2e-sec-req' is defined on line 1557, but no explicit reference was found in the text ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) == Outdated reference: draft-ietf-dime-e2e-sec-req has been published as RFC 7966 -- Obsolete informational reference (is this intentional?): RFC 4006 (Obsoleted by RFC 8506) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Diameter Maintenance and Extensions (DIME) J. Korhonen, Ed. 3 Internet-Draft Broadcom 4 Intended status: Standards Track S. Donovan, Ed. 5 Expires: February 7, 2016 B. Campbell 6 Oracle 7 L. Morand 8 Orange Labs 9 August 6, 2015 11 Diameter Overload Indication Conveyance 12 draft-ietf-dime-ovli-09.txt 14 Abstract 16 This specification defines a base solution for Diameter overload 17 control, referred to as Diameter Overload Indication Conveyance 18 (DOIC). 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on February 7, 2016. 37 Copyright Notice 39 Copyright (c) 2015 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3 56 3. Conventions Used in This Document . . . . . . . . . . . . . . 5 57 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5 58 4.1. Piggybacking . . . . . . . . . . . . . . . . . . . . . . 6 59 4.2. DOIC Capability Announcement . . . . . . . . . . . . . . 7 60 4.3. DOIC Overload Condition Reporting . . . . . . . . . . . . 9 61 4.4. DOIC Extensibility . . . . . . . . . . . . . . . . . . . 11 62 4.5. Simplified Example Architecture . . . . . . . . . . . . . 11 63 5. Solution Procedures . . . . . . . . . . . . . . . . . . . . . 12 64 5.1. Capability Announcement . . . . . . . . . . . . . . . . . 12 65 5.1.1. Reacting Node Behavior . . . . . . . . . . . . . . . 13 66 5.1.2. Reporting Node Behavior . . . . . . . . . . . . . . . 13 67 5.1.3. Agent Behavior . . . . . . . . . . . . . . . . . . . 14 68 5.2. Overload Report Processing . . . . . . . . . . . . . . . 15 69 5.2.1. Overload Control State . . . . . . . . . . . . . . . 15 70 5.2.2. Reacting Node Behavior . . . . . . . . . . . . . . . 19 71 5.2.3. Reporting Node Behavior . . . . . . . . . . . . . . . 20 72 5.3. Protocol Extensibility . . . . . . . . . . . . . . . . . 22 73 6. Loss Algorithm . . . . . . . . . . . . . . . . . . . . . . . 23 74 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 23 75 6.2. Reporting Node Behavior . . . . . . . . . . . . . . . . . 24 76 6.3. Reacting Node Behavior . . . . . . . . . . . . . . . . . 24 77 7. Attribute Value Pairs . . . . . . . . . . . . . . . . . . . . 25 78 7.1. OC-Supported-Features AVP . . . . . . . . . . . . . . . . 25 79 7.2. OC-Feature-Vector AVP . . . . . . . . . . . . . . . . . . 25 80 7.3. OC-OLR AVP . . . . . . . . . . . . . . . . . . . . . . . 26 81 7.4. OC-Sequence-Number AVP . . . . . . . . . . . . . . . . . 26 82 7.5. OC-Validity-Duration AVP . . . . . . . . . . . . . . . . 26 83 7.6. OC-Report-Type AVP . . . . . . . . . . . . . . . . . . . 27 84 7.7. OC-Reduction-Percentage AVP . . . . . . . . . . . . . . . 27 85 7.8. Attribute Value Pair flag rules . . . . . . . . . . . . . 27 86 8. Error Response Codes . . . . . . . . . . . . . . . . . . . . 28 87 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 88 9.1. AVP codes . . . . . . . . . . . . . . . . . . . . . . . . 29 89 9.2. New registries . . . . . . . . . . . . . . . . . . . . . 29 90 10. Security Considerations . . . . . . . . . . . . . . . . . . . 30 91 10.1. Potential Threat Modes . . . . . . . . . . . . . . . . . 30 92 10.2. Denial of Service Attacks . . . . . . . . . . . . . . . 31 93 10.3. Non-Compliant Nodes . . . . . . . . . . . . . . . . . . 32 94 10.4. End-to End-Security Issues . . . . . . . . . . . . . . . 32 95 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 33 96 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 97 12.1. Normative References . . . . . . . . . . . . . . . . . . 34 98 12.2. Informative References . . . . . . . . . . . . . . . . . 34 99 Appendix A. Issues left for future specifications . . . . . . . 35 100 A.1. Additional traffic abatement algorithms . . . . . . . . . 35 101 A.2. Agent Overload . . . . . . . . . . . . . . . . . . . . . 35 102 A.3. New Error Diagnostic AVP . . . . . . . . . . . . . . . . 35 103 Appendix B. Deployment Considerations . . . . . . . . . . . . . 35 104 Appendix C. Considerations for Applications Integrating the DOIC 105 Solution . . . . . . . . . . . . . . . . . . . . . . 36 106 C.1. Application Classification . . . . . . . . . . . . . . . 36 107 C.2. Application Type Overload Implications . . . . . . . . . 37 108 C.3. Request Transaction Classification . . . . . . . . . . . 38 109 C.4. Request Type Overload Implications . . . . . . . . . . . 39 110 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40 112 1. Introduction 114 This specification defines a base solution for Diameter overload 115 control, referred to as Diameter Overload Indication Conveyance 116 (DOIC), based on the requirements identified in [RFC7068]. 118 This specification addresses Diameter overload control between 119 Diameter nodes that support the DOIC solution. The solution, which 120 is designed to apply to existing and future Diameter applications, 121 requires no changes to the Diameter base protocol [RFC6733] and is 122 deployable in environments where some Diameter nodes do not implement 123 the Diameter overload control solution defined in this specification. 125 A new application specification can incorporate the overload control 126 mechanism specified in this document by making it mandatory to 127 implement for the application and referencing this specification 128 normatively. It is the responsibility of the Diameter application 129 designers to define how overload control mechanisms works on that 130 application. 132 Note that the overload control solution defined in this specification 133 does not address all the requirements listed in [RFC7068]. A number 134 of overload control related features are left for future 135 specifications. See Appendix A for a list of extensions that are 136 currently being considered. 138 2. Terminology and Abbreviations 140 Abatement 142 Reaction to receipt of an overload report resulting in a reduction 143 in traffic sent to the reporting node. Abatement actions include 144 diversion and throttling. 146 Abatement Algorithm 148 An extensible method requested by reporting nodes and used by 149 reacting nodes to reduce the amount of traffic sent during an 150 occurrence of overload control. 152 Diversion 154 An overload abatement treatment where the reacting node selects 155 alternate destinations or paths for requests. 157 Host-Routed Requests 159 Requests that a reacting node knows will be served by a particular 160 host, either due to the presence of a Destination-Host Attribute 161 Value Pair (AVP), or by some other local knowledge on the part of 162 the reacting node. 164 Overload Control State (OCS) 166 Internal state maintained by a reporting or reacting node 167 describing occurrences of overload control. 169 Overload Report (OLR) 171 Overload control information for a particular overload occurrence 172 sent by a reporting node. 174 Reacting Node 176 A Diameter node that acts upon an overload report. 178 Realm-Routed Requests 180 Requests that a reacting node does not know which host will 181 service the request. 183 Reporting Node 185 A Diameter node that generates an overload report. (This may or 186 may not be the overloaded node.) 188 Throttling 190 An abatement treatment that limits the number of requests sent by 191 the reacting node. Throttling can include a Diameter Client 192 choosing to not send requests, or a Diameter Agent or Server 193 rejecting requests with appropriate error responses. In both 194 cases the result of the throttling is a permanent rejection of the 195 transaction. 197 3. Conventions Used in This Document 199 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 200 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 201 document are to be interpreted as described in RFC 2119 [RFC2119]. 203 RFC 2119 [RFC2119] interpretation does not apply for the above listed 204 words when they are not used in all-caps format. 206 4. Solution Overview 208 The Diameter Overload Information Conveyance (DOIC) solution allows 209 Diameter nodes to request other Diameter nodes to perform overload 210 abatement actions, that is, actions to reduce the load offered to the 211 overloaded node or realm. 213 A Diameter node that supports DOIC is known as a "DOIC node". Any 214 Diameter node can act as a DOIC node, including Diameter Clients, 215 Diameter Servers, and Diameter Agents. DOIC nodes are further 216 divided into "Reporting Nodes" and "Reacting Nodes." A reporting 217 node requests overload abatement by sending Overload Reports (OLR). 219 A reacting node acts upon OLRs, and performs whatever actions are 220 needed to fulfill the abatement requests included in the OLRs. A 221 Reporting node may report overload on its own behalf, or on behalf of 222 other nodes. Likewise, a reacting node may perform overload 223 abatement on its own behalf, or on behalf of other nodes. 225 A Diameter node's role as a DOIC node is independent of its Diameter 226 role. For example, Diameter Agents may act as DOIC nodes, even 227 though they are not endpoints in the Diameter sense. Since Diameter 228 enables bi-directional applications, where Diameter Servers can send 229 requests towards Diameter Clients, a given Diameter node can 230 simultaneously act as both a reporting node and a reacting node. 232 Likewise, a Diameter Agent may act as a reacting node from the 233 perspective of upstream nodes, and a reporting node from the 234 perspective of downstream nodes. 236 DOIC nodes do not generate new messages to carry DOIC related 237 information. Rather, they "piggyback" DOIC information over existing 238 Diameter messages by inserting new AVPs into existing Diameter 239 requests and responses. Nodes indicate support for DOIC, and any 240 needed DOIC parameters, by inserting an OC-Supported-Features AVP 241 (Section 7.2) into existing requests and responses. Reporting nodes 242 send OLRs by inserting OC-OLR AVPs (Section 7.3). 244 A given OLR applies to the Diameter realm and application of the 245 Diameter message that carries it. If a reporting node supports more 246 than one realm and/or application, it reports independently for each 247 combination of realm and application. Similarly, the OC-Supported- 248 Features AVP applies to the realm and application of the enclosing 249 message. This implies that a node may support DOIC for one 250 application and/or realm, but not another, and may indicate different 251 DOIC parameters for each application and realm for which it supports 252 DOIC. 254 Reacting nodes perform overload abatement according to an agreed-upon 255 abatement algorithm. An abatement algorithm defines the meaning of 256 some of the parameters of an OLR and the procedures required for 257 overload abatement. An overload abatement algorithm separates 258 Diameter requests into two sets. The first set contains the requests 259 that are to undergo overload abatement treatment of either throttling 260 or diversion. The second set contains the requests that are to be 261 given normal routing treatment. This document specifies a single 262 must-support algorithm, namely the "loss" algorithm (Section 6). 263 Future specifications may introduce new algorithms. 265 Overload conditions may vary in scope. For example, a single 266 Diameter node may be overloaded, in which case reacting nodes may 267 attempt to send requests to other destinations. On the other hand, 268 an entire Diameter realm may be overloaded, in which case such 269 attempts would do harm. DOIC OLRs have a concept of "report type" 270 (Section 7.6), where the type defines such behaviors. Report types 271 are extensible. This document defines report types for overload of a 272 specific host, and for overload of an entire realm. 274 DOIC works through non supporting Diameter Agents that properly pass 275 unknown AVPs unchanged. 277 4.1. Piggybacking 279 There is no new Diameter application defined to carry overload 280 related AVPs. The overload control AVPs defined in this 281 specification have been designed to be piggybacked on top of existing 282 application messages. This is made possible by adding the optional 283 overload control AVPs OC-OLR and OC-Supported-Features into existing 284 commands. 286 Reacting nodes indicate support for DOIC by including the OC- 287 Supported-Features AVP in all request messages originated or relayed 288 by the reacting node. 290 Reporting nodes indicate support for DOIC by including the OC- 291 Supported-Features AVP in all answer messages originated or relayed 292 by the reporting node that are in response to a request that 293 contained the OC-Supported-Features AVP. Reporting nodes may include 294 overload reports using the OC-OLR AVP in answer messages. 296 Note that the overload control solution does not have fixed server 297 and client roles. The DOIC node role is determined based on the 298 message type: whether the message is a request (i.e., sent by a 299 "reacting node") or an answer (i.e., sent by a "reporting node"). 300 Therefore, in a typical "client-server" deployment, the Diameter 301 Client may report its overload condition to the Diameter Server for 302 any Diameter Server initiated message exchange. An example of such 303 is the Diameter Server requesting a re-authentication from a Diameter 304 Client. 306 4.2. DOIC Capability Announcement 308 The DOIC solution supports the ability for Diameter nodes to 309 determine if other nodes in the path of a request support the 310 solution. This capability is referred to as DOIC Capability 311 Announcement (DCA) and is separate from Diameter Capability Exchange. 313 The DCA mechanism uses the OC-Supported-Features AVPs to indicate the 314 Diameter overload features supported. 316 The first node in the path of a Diameter request that supports the 317 DOIC solution inserts the OC-Supported-Features AVP in the request 318 message. 320 The individual features supported by the DOIC nodes are indicated in 321 the OC-Feature-Vector AVP. Any semantics associated with the 322 features will be defined in extension specifications that introduce 323 the features. 325 Note: As discussed elsewhere in the document, agents in the path 326 of the request can modify the OC-Supported-Features AVP. 328 Note: The DOIC solution must support deployments where Diameter 329 Clients and/or Diameter Servers do not support the DOIC solution. 330 In this scenario, Diameter Agents that support the DOIC solution 331 may handle overload abatement for the non-supporting Diameter 332 nodes. In this case the DOIC agent will insert the OC-Supported- 333 Features AVP in requests that do not already contain one, telling 334 the reporting node that there is a DOIC node that will handle 335 overload abatement. For transactions where there was an OC- 336 Supporting-Features AVP in the request, the agent will insert the 337 OC-Supported-Features AVP in answers, telling the reacting node 338 that there is a reporting node. 340 The OC-Feature-Vector AVP will always contain an indication of 341 support for the loss overload abatement algorithm defined in this 342 specification (see Section 6). This ensures that a reporting node 343 always supports at least one of the advertized abatement algorithms 344 received in a request messages. 346 The reporting node inserts the OC-Supported-Features AVP in all 347 answer messages to requests that contained the OC-Supported-Features 348 AVP. The contents of the reporting node's OC-Supported-Features AVP 349 indicate the set of Diameter overload features supported by the 350 reporting node. This specification defines one exception - the 351 reporting node only includes an indication of support for one 352 overload abatement algorithm, independent of the number of overload 353 abatement algorithms actually supported by the reacting node. The 354 overload abatement algorithm indicated is the algorithm that the 355 reporting node intends to use should it enter an overload condition. 356 Reacting nodes can use the indicated overload abatement algorithm to 357 prepare for possible overload reports and must use the indicated 358 overload abatement algorithm if traffic reduction is actually 359 requested. 361 Note that the loss algorithm defined in this document is a 362 stateless abatement algorithm. As a result it does not require 363 any actions by reacting nodes prior to the receipt of an overload 364 report. Stateful abatement algorithms that base the abatement 365 logic on a history of request messages sent might require reacting 366 nodes to maintain state in advance of receiving an overload report 367 to ensure that the overload reports can be properly handled. 369 The DCA mechanism must also allow the scenario where the set of 370 features supported by the sender of a request and by agents in the 371 path of a request differ. In this case, the agent can update the OC- 372 Supported-Features AVP to reflect the mixture of the two sets of 373 supported features. 375 Note: The logic to determine if the content of the OC-Supported- 376 Features AVP should be changed is out-of-scope for this document, 377 as is the logic to determine the content of a modified OC- 378 Supported-Features AVP. These are left to implementation 379 decisions. Care must be taken not to introduce interoperability 380 issues for downstream or upstream DOIC nodes. As such, the agent 381 must act as a fully compliant reporting node to the downstream 382 reacting node and as a fully compliant reacting node to the 383 upstream reporting node. 385 4.3. DOIC Overload Condition Reporting 387 As with DOIC capability announcement, overload condition reporting 388 uses new AVPs (Section 7.3) to indicate an overload condition. 390 The OC-OLR AVP is referred to as an overload report. The OC-OLR AVP 391 includes the type of report, a sequence number, the length of time 392 that the report is valid and abatement algorithm specific AVPs. 394 Two types of overload reports are defined in this document: host 395 reports and realm reports. 397 A report of type "HOST_REPORT" is sent to indicate the overload of a 398 specific host, identified by the Origin-Host AVP of the message 399 containing the OLR, for the application-id indicated in the 400 transaction. When receiving an OLR of type "HOST_REPORT", a reacting 401 node applies overload abatement treatment to the host-routed requests 402 identified by the overload abatement algorithm (see definition in 403 Section 2) sent for this application to the overloaded host. 405 A report of type "REALM_REPORT" is sent to indicate the overload of a 406 realm for the application-id indicated in the transaction. The 407 overloaded realm is identified by the Destination-Realm AVP of the 408 message containing the OLR. When receiving an OLR of type 409 "REALM_REPORT", a reacting node applies overload abatement treatment 410 to realm-routed requests identified by the overload abatement 411 algorithm (see definition in Section 2) sent for this application to 412 the overloaded realm. 414 This document assumes that there is a single source for realm-reports 415 for a given realm, or that if multiple nodes can send realm reports, 416 that each such node has full knowledge of the overload state of the 417 entire realm. A reacting node cannot distinguish between receiving 418 realm-reports from a single node, or from multiple nodes. 420 Note: Known issues exist if multiple sources for overload reports 421 which apply to the same Diameter entity exist. Reacting nodes 422 have no way of determining the source and, as such, will treat 423 them as coming from a single source. Variance in sequence numbers 424 between the two sources can then cause incorrect overload 425 abatement treatment to be applied for indeterminate periods of 426 time. 428 Reporting nodes are responsible for determining the need for a 429 reduction of traffic. The method for making this determination is 430 implementation specific and depends on the type of overload report 431 being generated. A host-report might be generated by tracking use of 432 resources required by the host to handle transactions for the 433 Diameter application. A realm-report generally impacts the traffic 434 sent to multiple hosts and, as such, requires tracking the capacity 435 of all servers able to handle realm-routed requests for the 436 application and realm. 438 Once a reporting node determines the need for a reduction in traffic, 439 it uses the DOIC defined AVPs to report on the condition. These AVPs 440 are included in answer messages sent or relayed by the reporting 441 node. The reporting node indicates the overload abatement algorithm 442 that is to be used to handle the traffic reduction in the OC- 443 Supported-Features AVP. The OC-OLR AVP is used to communicate 444 information about the requested reduction. 446 Reacting nodes, upon receipt of an overload report, apply the 447 overload abatement algorithm to traffic impacted by the overload 448 report. The method used to determine the requests that are to 449 receive overload abatement treatment is dependent on the abatement 450 algorithm. The loss abatement algorithm is defined in this document 451 (Section 6). Other abatement algorithms can be defined in extensions 452 to the DOIC solution. 454 Two types of overload abatement treatment are defined, diversion and 455 throttling. Reacting nodes are responsible for determining which 456 treatment is appropriate for individual requests. 458 As the conditions that lead to the generation of the overload report 459 change the reporting node can send new overload reports requesting 460 greater reduction if the condition gets worse or less reduction if 461 the condition improves. The reporting node sends an overload report 462 with a duration of zero to indicate that the overload condition has 463 ended and abatement is no longer needed. 465 The reacting node also determines when the overload report expires 466 based on the OC-Validity-Duration AVP in the overload report and 467 stops applying the abatement algorithm when the report expires. 469 Note that erroneous overload reports can be used for DoS attacks. 470 This includes the ability to indicate that a significant reduction in 471 traffic, up to and including a request for no traffic, should be sent 472 to a reporting node. As such, care should be taken to verify the 473 sender of overload reports. 475 4.4. DOIC Extensibility 477 The DOIC solution is designed to be extensible. This extensibility 478 is based on existing Diameter based extensibility mechanisms, along 479 with the DOIC capability announcement mechanism. 481 There are multiple categories of extensions that are expected. This 482 includes the definition of new overload abatement algorithms, the 483 definition of new report types and the definition of new scopes of 484 messages impacted by an overload report. 486 A DOIC node communicates supported features by including them in the 487 OC-Feature-Vector AVP, as a sub-AVP of OC-Supported-Features. Any 488 non-backwards compatible DOIC extensions define new values for the 489 OC-Feature-Vector AVP. DOIC extensions also have the ability to add 490 new AVPs to the OC-Supported-Features AVP, if additional information 491 about the new feature is required. 493 Overload reports can also be extended by adding new sub-AVPs to the 494 OC-OLR AVP, allowing reporting nodes to communicate additional 495 information about handling an overload condition. 497 If necessary, new extensions can also define new AVPs that are not 498 part of the OC-Supported-Features and OC-OLR group AVPs. It is, 499 however, recommended that DOIC extensions use the OC-Supported- 500 Features AVP and OC-OLR AVP to carry all DOIC related AVPs. 502 4.5. Simplified Example Architecture 504 Figure 1 illustrates the simplified architecture for Diameter 505 overload information conveyance. 507 Realm X Same or other Realms 508 <--------------------------------------> <----------------------> 510 +--------+ : (optional) : 511 |Diameter| : : 512 |Server A|--+ .--. : +--------+ : .--. 513 +--------+ | _( `. : |Diameter| : _( `. +--------+ 514 +--( )--:-| Agent |-:--( )--|Diameter| 515 +--------+ | ( ` . ) ) : +--------+ : ( ` . ) ) | Client | 516 |Diameter|--+ `--(___.-' : : `--(___.-' +--------+ 517 |Server B| : : 518 +--------+ : : 520 End-to-end Overload Indication 521 1) <-----------------------------------------------> 522 Diameter Application Y 524 Overload Indication A Overload Indication A' 525 2) <----------------------> <----------------------> 526 Diameter Application Y Diameter Application Y 528 Figure 1: Simplified architecture choices for overload indication 529 delivery 531 In Figure 1, the Diameter overload indication can be conveyed (1) 532 end-to-end between servers and clients or (2) between servers and 533 Diameter agent inside the realm and then between the Diameter agent 534 and the clients. 536 5. Solution Procedures 538 This section outlines the normative behavior for the DOIC solution. 540 5.1. Capability Announcement 542 This section defines DOIC Capability Announcement (DCA) behavior. 544 Note: This specification assumes that changes in DOIC node 545 capabilities are relatively rare events that occur as a result of 546 administrative action. Reacting nodes ought to minimize changes 547 that force the reporting node to change the features being used, 548 especially during active overload conditions. But even if 549 reacting nodes avoid such changes, reporting nodes still have to 550 be prepared for them to occur. For example, differing 551 capabilities between multiple reacting nodes may still force a 552 reporting node to select different features on a per-transaction 553 basis. 555 5.1.1. Reacting Node Behavior 557 A reacting node MUST include the OC-Supported-Features AVP in all 558 requests. It MAY include the OC-Feature-Vector AVP, as a sub-avp of 559 OC-Supported-Features. If it does so, it MUST indicate support for 560 the "loss" algorithm. If the reacting node is configured to support 561 features (including other algorithms) in addition to the loss 562 algorithm, it MUST indicate such support in an OC-Feature-Vector AVP. 564 An OC-Supported-Features AVP in answer messages indicates there is a 565 reporting node for the transaction. The reacting node MAY take 566 action, for example creating state for some stateful abatement 567 algorithm, based on the features indicated in the OC-Feature-Vector 568 AVP. 570 Note: The loss abatement algorithm does not require stateful 571 behavior when there is no active overload report. 573 Reacting nodes need to be prepared for the reporting node to change 574 selected algorithms. This can happen at any time, including when the 575 reporting node has sent an active overload report. The reacting node 576 can minimize the potential for changes by modifying the advertised 577 abatement algorithms sent to an overloaded reporting node to the 578 currently selected algorithm and loss (or just loss if it is the 579 currently selected algorithm). This has the effect of limiting the 580 potential change in abatement algorithm from the currently selected 581 algorithm to loss, avoiding changes to more complex abatement 582 algorithms that require state to operate properly. 584 5.1.2. Reporting Node Behavior 586 Upon receipt of a request message, a reporting node determines if 587 there is a reacting node for the transaction based on the presence of 588 the OC-Supported-Features AVP in the request message. 590 If the request message contains an OC-Supported-Features AVP then a 591 reporting node MUST include the OC-Supported-Features AVP in the 592 answer message for that transaction. 594 Note: Capability announcement is done on a per transaction basis. 595 The reporting node cannot assume that the capabilities announced 596 by a reacting node will be the same between transactions. 598 A reporting node MUST NOT include the OC-Supported-Features AVP, OC- 599 OLR AVP or any other overload control AVPs defined in extension 600 drafts in response messages for transactions where the request 601 message does not include the OC-Supported-Features AVP. Lack of the 602 OC-Supported-Features AVP in the request message indicates that there 603 is no reacting node for the transaction. 605 A reporting node knows what overload control functionality is 606 supported by the reacting node based on the content or absence of the 607 OC-Feature-Vector AVP within the OC-Supported-Features AVP in the 608 request message. 610 A reporting node MUST A reporting node MUST select a single abatement 611 algorithm in the OC-Feature-Vector AVP. The abatement algorithm 612 selected MUST indicate the abatement algorithm the reporting node 613 wants the reacting node to use when the reporting node enters an 614 overload condition. 616 The abatement algorithm selected MUST be from the set of abatement 617 algorithms contained in the request message's OC-Feature-Vector AVP. 619 A reporting node that selects the loss algorithm may do so by 620 including the OC-Feature-Vector AVP with an explicit indication of 621 the loss algorithm, or it MAY omit OC-Feature-Vector. If it selects 622 a different algorithm, it MUST include the OC-Feature-Vector AVP with 623 an explicit indication of the selected algorithm. 625 The reporting node SHOULD indicate support for other DOIC features 626 defined in extension drafts that it supports and that apply to the 627 transaction. It does so using the OC-Feature-Vector AVP. 629 Note: Not all DOIC features will apply to all Diameter 630 applications or deployment scenarios. The features included in 631 the OC-Feature-Vector AVP are based on local reporting node 632 policy. 634 5.1.3. Agent Behavior 636 Diameter Agents that support DOIC can ensure that all messages 637 relayed by the agent contain the OC-Supported-Features AVP. 639 A Diameter Agent MAY take on reacting node behavior for Diameter 640 endpoints that do not support the DOIC solution. A Diameter Agent 641 detects that a Diameter endpoint does not support DOIC reacting node 642 behavior when there is no OC-Supported-Features AVP in a request 643 message. 645 For a Diameter Agent to be a reacting node for a non-supporting 646 Diameter endpoint, the Diameter Agent MUST include the OC-Supported- 647 Features AVP in request messages it relays that do not contain the 648 OC-Supported-Features AVP. 650 A Diameter Agent MAY take on reporting node behavior for Diameter 651 endpoints that do not support the DOIC solution. The Diameter Agent 652 MUST have visibility to all traffic destined for the non-supporting 653 host in order to become the reporting node for the Diameter endpoint. 654 A Diameter Agent detects that a Diameter endpoint does not support 655 DOIC reporting node behavior when there is no OC-Supported-Features 656 AVP in an answer message for a transaction that contained the OC- 657 Supported-Features AVP in the request message. 659 If a request already has the OC-Supported-Features AVP, a Diameter 660 agent MAY modify it to reflect the features appropriate for the 661 transaction. Otherwise, the agent relays the OC-Supported-Features 662 AVP without change. 664 For instance, if the agent supports a superset of the features 665 reported by the reacting node then the agent might choose, based 666 on local policy, to advertise that superset of features to the 667 reporting node. 669 If the Diameter Agent changes the OC-Supported-Features AVP in a 670 request message then it is likely it will also need to modify the OC- 671 Supported-Features AVP in the answer message for the transaction. A 672 Diameter Agent MAY modify the OC-Supported-Features AVP carried in 673 answer messages. 675 When making changes to the OC-Supported-Features or OC-OLR AVPs, the 676 Diameter Agent needs to ensure consistency in its behavior with both 677 upstream and downstream DOIC nodes. 679 5.2. Overload Report Processing 681 5.2.1. Overload Control State 683 Both reacting and reporting nodes maintain Overload Control State 684 (OCS) for active overload conditions. The following sections define 685 behavior associated with that OCS. 687 The contents of the OCS in the reporting node and in the reacting 688 node represent logical constructs. The actual internal physical 689 structure of the state included in the OCS is an implementation 690 decision. 692 5.2.1.1. Overload Control State for Reacting Nodes 694 A reacting node maintains the following OCS per supported Diameter 695 application: 697 o A host-type OCS entry for each Destination-Host to which it sends 698 host-type requests and 700 o A realm-type OCS entry for each Destination-Realm to which it 701 sends realm-type requests. 703 A host-type OCS entry is identified by the pair of application-id and 704 the node's DiameterIdentity. 706 A realm-type OCS entry is identified by the pair of application-id 707 and realm. 709 The host-type and realm-type OCS entries include the following 710 information (the actual information stored is an implementation 711 decision): 713 o Sequence number (as received in OC-OLR) 715 o Time of expiry (derived from OC-Validity-Duration AVP received in 716 the OC-OLR AVP and time of reception of the message carrying OC- 717 OLR AVP) 719 o Selected Abatement Algorithm (as received in the OC-Supported- 720 Features AVP) 722 o Abatement Algorithm specific input data (as received in the OC-OLR 723 AVP, for example, OC-Reduction-Percentage for the Loss abatement 724 algorithm) 726 5.2.1.2. Overload Control State for Reporting Nodes 728 A reporting node maintains OCS entries per supported Diameter 729 application, per supported (and eventually selected) Abatement 730 Algorithm and per report-type. 732 An OCS entry is identified by the tuple of Application-Id, Report- 733 Type and Abatement Algorithm and includes the following information 734 (the actual information stored is an implementation decision): 736 o Sequence number 738 o Validity Duration 739 o Expiration Time 741 o Algorithm specific input data (for example, the Reduction 742 Percentage for the Loss Abatement Algorithm) 744 5.2.1.3. Reacting Node Maintenance of Overload Control State 746 When a reacting node receives an OC-OLR AVP, it MUST determine if it 747 is for an existing or new overload condition. 749 Note: For the remainder of this section the term OLR refers to the 750 combination of the contents of the received OC-OLR AVP and the 751 abatement algorithm indicated in the received OC-Supported- 752 Features AVP. 754 When receiving an answer message with multiple OLRs of different 755 supported report types, a reacting node MUST process each received 756 OLR. 758 The OLR is for an existing overload condition if a reacting node has 759 an OCS that matches the received OLR. 761 For a host-report this means it matches the application-id and the 762 host's DiameterIdentity in an existing host OCS entry. 764 For a realm-report this means it matches the application-id and the 765 realm in an existing realm OCS entry. 767 If the OLR is for an existing overload condition then a reacting node 768 MUST determine if the OLR is a retransmission or an update to the 769 existing OLR. 771 If the sequence number for the received OLR is greater than the 772 sequence number stored in the matching OCS entry then a reacting node 773 MUST update the matching OCS entry. 775 If the sequence number for the received OLR is less than or equal to 776 the sequence number in the matching OCS entry then a reacting node 777 MUST silently ignore the received OLR. The matching OCS MUST NOT be 778 updated in this case. 780 If the reacting node determines that the sequence number has rolled 781 over then the reacting node MUST update the matching OCS entry. This 782 can be determined by recognizing that the number has changed from 783 something close to the maximum value in the OC-Sequence-Number AVP to 784 something close to the minimum value in the OC-Sequence-Number AVP. 786 If the received OLR is for a new overload condition then a reacting 787 node MUST generate a new OCS entry for the overload condition. 789 For a host-report this means a reacting node creates on OCS entry 790 with the application-id in the received message and DiameterIdentity 791 of the Origin-Host in the received message. 793 Note: This solution assumes that the Origin-Host AVP in the answer 794 message included by the reporting node is not changed along the 795 path to the reacting node. 797 For a realm-report this means a reacting node creates on OCS entry 798 with the application-id in the received message and realm of the 799 Origin-Realm in the received message. 801 If the received OLR contains a validity duration of zero ("0") then a 802 reacting node MUST update the OCS entry as being expired. 804 Note: It is not necessarily appropriate to delete the OCS entry, 805 as there is recommended behavior that the reacting node slowly 806 returns to full traffic when ending an overload abatement period. 808 The reacting node does not delete an OCS when receiving an answer 809 message that does not contain an OC-OLR AVP (i.e., absence of OLR 810 means "no change"). 812 5.2.1.4. Reporting Node Maintenance of Overload Control State 814 A reporting node SHOULD create a new OCS entry when entering an 815 overload condition. 817 Note: If a reporting node knows through absence of the OC- 818 Supported-Features AVP in received messages that there are no 819 reacting nodes supporting DOIC then the reporting node can choose 820 to not create OCS entries. 822 When generating a new OCS entry the sequence number SHOULD be set to 823 zero ("0"). 825 When generating sequence numbers for new overload conditions, the new 826 sequence number MUST be greater than any sequence number in an active 827 (unexpired) overload report for the same application and report-type 828 previously sent by the reporting node. This property MUST hold over 829 a reboot of the reporting node. 831 Note: One way of addressing this over a reboot of a reporting node 832 is to use a time stamp for the first overload condition that 833 occurs after the report and to start using sequences beginning 834 with zero for subsequent overload conditions. 836 A reporting node MUST update an OCS entry when it needs to adjust the 837 validity duration of the overload condition at reacting nodes. 839 For instance, if a reporting node wishes to instruct reacting 840 nodes to continue overload abatement for a longer period of time 841 than originally communicated. This also applies if the reporting 842 node wishes to shorten the period of time that overload abatement 843 is to continue. 845 A reporting node MUST update an OCS entry when it wishes to adjust 846 any abatement algorithm specific parameters, including, for example, 847 the reduction percentage used for the Loss abatement algorithm. 849 For instance, if a reporting node wishes to change the reduction 850 percentage either higher, if the overload condition has worsened, 851 or lower, if the overload condition has improved, then the 852 reporting node would update the appropriate OCS entry. 854 A reporting node MUST increment the sequence number associated with 855 the OCS entry anytime the contents of the OCS entry are changed. 856 This will result in a new sequence number being sent to reacting 857 nodes, instructing reacting nodes to process the OC-OLR AVP. 859 A reporting node SHOULD update an OCS entry with a validity duration 860 of zero ("0") when the overload condition ends. 862 Note: If a reporting node knows that the OCS entries in the 863 reacting nodes are near expiration then the reporting node might 864 decide not to send an OLR with a validity duration of zero. 866 A reporting node MUST keep an OCS entry with a validity duration of 867 zero ("0") for a period of time long enough to ensure that any non- 868 expired reacting node's OCS entry created as a result of the overload 869 condition in the reporting node is deleted. 871 5.2.2. Reacting Node Behavior 873 When a reacting node sends a request it MUST determine if that 874 request matches an active OCS. 876 If the request matches an active OCS then the reacting node MUST use 877 the overload abatement algorithm indicated in the OCS to determine if 878 the request is to receive overload abatement treatment. 880 For the Loss abatement algorithm defined in this specification, see 881 Section 6 for the overload abatement algorithm logic applied. 883 If the overload abatement algorithm selects the request for overload 884 abatement treatment then the reacting node MUST apply overload 885 abatement treatment on the request. The abatement treatment applied 886 depends on the context of the request. 888 If diversion abatement treatment is possible (i.e., a different path 889 for the request can be selected where the overloaded node is not part 890 of the different path), then the reacting node SHOULD apply diversion 891 abatement treatment to the request. The reacting node MUST apply 892 throttling abatement treatment to requests identified for abatement 893 treatment when diversion treatment is not possible or was not 894 applied. 896 Note: This only addresses the case where there are two defined 897 abatement treatments, diversion and throttling. Any extension 898 that defines a new abatement treatment must also define the 899 interaction of the new abatement treatment with existing 900 treatments. 902 If the overload abatement treatment results in throttling of the 903 request and if the reacting node is an agent then the agent MUST send 904 an appropriate error as defined in Section 8. 906 Diameter endpoints that throttle requests need to do so according to 907 the rules of the client application. Those rules will vary by 908 application, and are beyond the scope of this document. 910 In the case that the OCS entry indicated no traffic was to be sent to 911 the overloaded entity and the validity duration expires then overload 912 abatement associated with the overload report MUST be ended in a 913 controlled fashion. 915 5.2.3. Reporting Node Behavior 917 If there is an active OCS entry then a reporting node SHOULD include 918 the OC-OLR AVP in all answers to requests that contain the OC- 919 Supported-Features AVP and that match the active OCS entry. 921 Note: A request matches if the application-id in the request 922 matches the application-id in any active OCS entry and if the 923 report-type in the OCS entry matches a report-type supported by 924 the reporting node as indicated in the OC-Supported-Features AVP. 926 The contents of the OC-OLR AVP depend on the selected algorithm. 928 A reporting node MAY choose to not resend an overload report to a 929 reacting node if it can guarantee that this overload report is 930 already active in the reacting node. 932 Note: In some cases (e.g., when there are one or more agents in 933 the path between reporting and reacting nodes, or when overload 934 reports are discarded by reacting nodes) a reporting node may not 935 be able to guarantee that the reacting node has received the 936 report. 938 A reporting node MUST NOT send overload reports of a type that has 939 not been advertised as supported by the reacting node. 941 Note: A reacting node implicitly advertises support for the host 942 and realm report types by including the OC-Supported-Features AVP 943 in the request. Support for other report types will be explicitly 944 indicated by new feature bits in the OC-Feature-Vector AVP. 946 A reporting node SHOULD explicitly indicate the end of an overload 947 occurrence by sending a new OLR with OC-Validity-Duration set to a 948 value of zero ("0"). The reporting node SHOULD ensure that all 949 reacting nodes receive the updated overload report. 951 A reporting node MAY rely on the OC-Validity-Duration AVP values for 952 the implicit overload control state cleanup on the reacting node. 954 Note: All OLRs sent have an expiration time calculated by adding 955 the validity-duration contained in the OLR to the time the message 956 was sent. Transit time for the OLR can be safely ignored. The 957 reporting node can ensure that all reacting nodes have received 958 the OLR by continuing to send it in answer messages until the 959 expiration time for all OLRs sent for that overload condition have 960 expired. 962 When a reporting node sends an OLR, it effectively delegates any 963 necessary throttling to downstream nodes. If the reporting node also 964 locally throttles the same set of messages, the overall number of 965 throttled requests may be higher than intended. Therefore, before 966 applying local message throttling, a reporting node needs to check if 967 these messages match existing OCS entries, indicating that these 968 messages have survived throttling applied by downstream nodes that 969 have received the related OLR. 971 However, even if the set of messages match existing OCS entries, the 972 reporting node can still apply other abatement methods such as 973 diversion. The reporting node might also need to throttle requests 974 for reasons other than overload. For example, an agent or server 975 might have a configured rate limit for each client, and throttle 976 requests that exceed that limit, even if such requests had already 977 been candidates for throttling by downstream nodes. The reporting 978 node also has the option to send new OLRs requesting greater 979 reductions in traffic, reducing the need for local throttling. 981 A reporting node SHOULD decrease requested overload abatement 982 treatment in a controlled fashion to avoid oscillations in traffic. 984 For example, it might wait some period of time after overload ends 985 before terminating the OLR, or it might send a series of OLRs 986 indicating progressively less overload severity. 988 5.3. Protocol Extensibility 990 The DOIC solution can be extended. Types of potential extensions 991 include new traffic abatement algorithms, new report types or other 992 new functionality. 994 When defining a new extension that requires new normative behavior, 995 the specification must define a new feature for the OC-Feature- 996 Vector. This feature bit is used to communicate support for the new 997 feature. 999 The extension may define new AVPs for use in DOIC Capability 1000 Announcement and for use in DOIC Overload reporting. These new AVPs 1001 SHOULD be defined to be extensions to the OC-Supported-Features or 1002 OC-OLR AVPs defined in this document. 1004 [RFC6733] defined Grouped AVP extension mechanisms apply. This 1005 allows, for example, defining a new feature that is mandatory to be 1006 understood even when piggybacked on an existing application. 1008 When defining new report type values, the corresponding specification 1009 must define the semantics of the new report types and how they affect 1010 the OC-OLR AVP handling. 1012 The OC-Supported-Feature and OC-OLR AVPs can be expanded with 1013 optional sub-AVPs only if a legacy DOIC implementation can safely 1014 ignore them without breaking backward compatibility for the given OC- 1015 Report-Type AVP value. Any new sub-AVPs must not require that the 1016 M-bit be set. 1018 Documents that introduce new report types must describe any 1019 limitations on their use across non-supporting agents. 1021 As with any Diameter specification, RFC6733 requires all new AVPs to 1022 be registered with IANA. See Section 9 for the required procedures. 1024 New features (feature bits in the OC-Feature-Vector AVP) and report 1025 types (in the OC-Report-Type AVP) MUST be registered with IANA. 1027 6. Loss Algorithm 1029 This section documents the Diameter overload loss abatement 1030 algorithm. 1032 6.1. Overview 1034 The DOIC specification supports the ability for multiple overload 1035 abatement algorithms to be specified. The abatement algorithm used 1036 for any instance of overload is determined by the Diameter Overload 1037 Capability Announcement process documented in Section 5.1. 1039 The loss algorithm described in this section is the default algorithm 1040 that must be supported by all Diameter nodes that support DOIC. 1042 The loss algorithm is designed to be a straightforward and stateless 1043 overload abatement algorithm. It is used by reporting nodes to 1044 request a percentage reduction in the amount of traffic sent. The 1045 traffic impacted by the requested reduction depends on the type of 1046 overload report. 1048 Reporting nodes request the stateless reduction of the number of 1049 requests by an indicated percentage. This percentage reduction is in 1050 comparison to the number of messages the node otherwise would send, 1051 regardless of how many requests the node might have sent in the past. 1053 From a conceptual level, the logic at the reacting node could be 1054 outlined as follows. 1056 1. An overload report is received and the associated OCS is either 1057 saved or updated (if required) by the reacting node. 1059 2. A new Diameter request is generated by the application running on 1060 the reacting node. 1062 3. The reacting node determines that an active overload report 1063 applies to the request, as indicated by the corresponding OCS 1064 entry. 1066 4. The reacting node determines if overload abatement treatment 1067 should be applied to the request. One approach that could be 1068 taken for each request is to select a uniformly selected random 1069 number between 1 and 100. If the random number is less than or 1070 equal to the indicated reduction percentage then the request is 1071 given abatement treatment, otherwise the request is given normal 1072 routing treatment. 1074 6.2. Reporting Node Behavior 1076 The method a reporting node uses to determine the amount of traffic 1077 reduction required to address an overload condition is an 1078 implementation decision. 1080 When a reporting node that has selected the loss abatement algorithm 1081 determines the need to request a reduction in traffic, it includes an 1082 OC-OLR AVP in answer messages as described in Section 5.2.3. 1084 When sending the OC-OLR AVP, the reporting node MUST indicate a 1085 percentage reduction in the OC-Reduction-Percentage AVP. 1087 The reporting node MAY change the reduction percentage in subsequent 1088 overload reports. When doing so the reporting node must conform to 1089 overload report handing specified in Section 5.2.3. 1091 6.3. Reacting Node Behavior 1093 The method a reacting node uses to determine which request messages 1094 are given abatement treatment is an implementation decision. 1096 When receiving an OC-OLR in an answer message where the algorithm 1097 indicated in the OC-Supported-Features AVP is the loss algorithm, the 1098 reacting node MUST apply abatement treatment to the requested 1099 percentage of request messages sent. 1101 Note: The loss algorithm is a stateless algorithm. As a result, 1102 the reacting node does not guarantee that there will be an 1103 absolute reduction in traffic sent. Rather, it guarantees that 1104 the requested percentage of new requests will be given abatement 1105 treatment. 1107 If reacting node comes out of the 100 percent traffic reduction, 1108 meaning it has received an OLR indicating that no traffic should be 1109 sent, as a result of the overload report timing out the reacting node 1110 sending the traffic SHOULD be conservative and, for example, first 1111 send "probe" messages to learn the overload condition of the 1112 overloaded node before converging to any traffic amount/rate decided 1113 by the sender. Similar concerns apply in all cases when the overload 1114 report times out unless the previous overload report stated 0 percent 1115 reduction. 1117 The goal of this behavior is to reduce the probability of overload 1118 condition thrashing where an immediate transition from 100% 1119 reduction to 0% reduction results in the reporting node moving 1120 quickly back into an overload condition. 1122 7. Attribute Value Pairs 1124 This section describes the encoding and semantics of the Diameter 1125 Overload Indication Attribute Value Pairs (AVPs) defined in this 1126 document. 1128 Refer to section 4 of [RFC6733] for more information on AVPs and AVP 1129 data types. 1131 7.1. OC-Supported-Features AVP 1133 The OC-Supported-Features AVP (AVP code TBD1) is of type Grouped and 1134 serves two purposes. First, it announces a node's support for the 1135 DOIC solution in general. Second, it contains the description of the 1136 supported DOIC features of the sending node. The OC-Supported- 1137 Features AVP MUST be included in every Diameter request message a 1138 DOIC supporting node sends. 1140 OC-Supported-Features ::= < AVP Header: TBD1 > 1141 [ OC-Feature-Vector ] 1142 * [ AVP ] 1144 7.2. OC-Feature-Vector AVP 1146 The OC-Feature-Vector AVP (AVP code TBD2) is of type Unsigned64 and 1147 contains a 64 bit flags field of announced capabilities of a DOIC 1148 node. The value of zero (0) is reserved. 1150 The OC-Feature-Vector sub-AVP is used to announce the DOIC features 1151 supported by the DOIC node, in the form of a flag-bits field in which 1152 each bit announces one feature or capability supported by the node. 1153 The absence of the OC-Feature-Vector AVP in request messages 1154 indicates that only the default traffic abatement algorithm described 1155 in this specification is supported. The absence of the OC- Feature- 1156 Vector AVP in answer messages indicates that the default traffic 1157 abatement algorithm described in this specification is selected 1158 (while other traffic abatement algorithms may be supported), and no 1159 features other than abatement algorithms are supported. 1161 The following capabilities are defined in this document: 1163 OLR_DEFAULT_ALGO (0x0000000000000001) 1164 When this flag is set by the a DOIC reacting node it means that 1165 the default traffic abatement (loss) algorithm is supported. When 1166 this flag is set by a DOIC reporting node it means that the loss 1167 algorithm will be used for requested overload abatement. 1169 7.3. OC-OLR AVP 1171 The OC-OLR AVP (AVP code TBD3) is of type Grouped and contains the 1172 information necessary to convey an overload report on an overload 1173 condition at the reporting node. The application the OC-OLR AVP 1174 applies to is the same as the Application-Id found in the Diameter 1175 message header. The host or realm the OC-OLR AVP concerns is 1176 determined from the Origin-Host AVP and/or Origin-Realm AVP found in 1177 the encapsulating Diameter command. The OC-OLR AVP is intended to be 1178 sent only by a reporting node. 1180 OC-OLR ::= < AVP Header: TBD2 > 1181 < OC-Sequence-Number > 1182 < OC-Report-Type > 1183 [ OC-Reduction-Percentage ] 1184 [ OC-Validity-Duration ] 1185 * [ AVP ] 1187 7.4. OC-Sequence-Number AVP 1189 The OC-Sequence-Number AVP (AVP code TBD4) is of type Unsigned64. 1190 Its usage in the context of overload control is described in 1191 Section 5.2. 1193 From the functionality point of view, the OC-Sequence-Number AVP is 1194 used as a non-volatile increasing counter for a sequence of overload 1195 reports between two DOIC nodes for the same overload occurrence. 1196 Sequence numbers are treated in a uni-directional manner, i.e., two 1197 sequence numbers on each direction between two DOIC nodes are not 1198 related or correlated. 1200 7.5. OC-Validity-Duration AVP 1202 The OC-Validity-Duration AVP (AVP code TBD5) is of type Unsigned32 1203 and indicates in seconds the validity time of the overload report. 1204 The number of seconds is measured after reception of the first OC-OLR 1205 AVP with a given value of OC-Sequence-Number AVP. The default value 1206 for the OC-Validity-Duration AVP is 30 seconds. When the OC- 1207 Validity-Duration AVP is not present in the OC-OLR AVP, the default 1208 value applies. The maximum value for the OC-Validity-Duration AVP is 1209 86,400 seconds (24 hours). If the value received in the OC-Validity- 1210 Duration is greater than the maximum value then the default value 1211 applies. 1213 7.6. OC-Report-Type AVP 1215 The OC-Report-Type AVP (AVP code TBD6) is of type Enumerated. The 1216 value of the AVP describes what the overload report concerns. The 1217 following values are initially defined: 1219 HOST_REPORT 0 The overload report is for a host. Overload abatement 1220 treatment applies to host-routed requests. 1222 REALM_REPORT 1 The overload report is for a realm. Overload 1223 abatement treatment applies to realm-routed requests. 1225 7.7. OC-Reduction-Percentage AVP 1227 The OC-Reduction-Percentage AVP (AVP code TBD7) is of type Unsigned32 1228 and describes the percentage of the traffic that the sender is 1229 requested to reduce, compared to what it otherwise would send. The 1230 OC-Reduction-Percentage AVP applies to the default (loss) algorithm 1231 specified in this specification. However, the AVP can be reused for 1232 future abatement algorithms, if its semantics fit into the new 1233 algorithm. 1235 The value of the Reduction-Percentage AVP is between zero (0) and one 1236 hundred (100). Values greater than 100 are ignored. The value of 1237 100 means that all traffic is to be throttled, i.e., the reporting 1238 node is under a severe load and ceases to process any new messages. 1239 The value of 0 means that the reporting node is in a stable state and 1240 has no need for the reacting node to apply any traffic abatement. 1242 7.8. Attribute Value Pair flag rules 1243 +---------+ 1244 |AVP flag | 1245 |rules | 1246 +----+----+ 1247 AVP Section | |MUST| 1248 Attribute Name Code Defined Value Type |MUST| NOT| 1249 +--------------------------------------------------+----+----+ 1250 |OC-Supported-Features TBD1 7.1 Grouped | | V | 1251 +--------------------------------------------------+----+----+ 1252 |OC-Feature-Vector TBD2 7.2 Unsigned64 | | V | 1253 +--------------------------------------------------+----+----+ 1254 |OC-OLR TBD3 7.3 Grouped | | V | 1255 +--------------------------------------------------+----+----+ 1256 |OC-Sequence-Number TBD4 7.4 Unsigned64 | | V | 1257 +--------------------------------------------------+----+----+ 1258 |OC-Validity-Duration TBD5 7.5 Unsigned32 | | V | 1259 +--------------------------------------------------+----+----+ 1260 |OC-Report-Type TBD6 7.6 Enumerated | | V | 1261 +--------------------------------------------------+----+----+ 1262 |OC-Reduction | | | 1263 | -Percentage TBD7 7.7 Unsigned32 | | V | 1264 +--------------------------------------------------+----+----+ 1266 As described in the Diameter base protocol [RFC6733], the M-bit usage 1267 for a given AVP in a given command may be defined by the application. 1269 8. Error Response Codes 1271 When a DOIC node rejects a Diameter request due to overload, the DOIC 1272 node MUST select an appropriate error response code. This 1273 determination is made based on the probability of the request 1274 succeeding if retried on a different path. 1276 Note: This only applies for DOIC nodes that are not the originator 1277 of the request. 1279 A reporting node rejecting a Diameter request due to an overload 1280 condition SHOULD send a DIAMETER_TOO_BUSY error response, if it can 1281 assume that the same request may succeed on a different path. 1283 If a reporting node knows or assumes that the same request will not 1284 succeed on a different path, DIAMETER_UNABLE_TO_COMPLY error response 1285 SHOULD be used. Retrying would consume valuable resources during an 1286 occurrence of overload. 1288 For instance, if the request arrived at the reporting node without 1289 a Destination-Host AVP then the reporting node might determine 1290 that there is an alternative Diameter node that could successfully 1291 process the request and that retrying the transaction would not 1292 negatively impact the reporting node. DIAMETER_TOO_BUSY would be 1293 sent in this case. 1295 If the request arrived at the reporting node with a Destination- 1296 Host AVP populated with its own Diameter identity then the 1297 reporting node can assume that retrying the request would result 1298 in it coming to the same reporting node. 1299 DIAMETER_UNABLE_TO_COMPLY would be sent in this case. 1301 A second example is when an agent that supports the DOIC solution 1302 is performing the role of a reacting node for a non-supporting 1303 client. Requests that are rejected as a result of DOIC throttling 1304 by the agent in this scenario would generally be rejected with a 1305 DIAMETER_UNABLE_TO_COMPLY response code. 1307 9. IANA Considerations 1309 9.1. AVP codes 1311 New AVPs defined by this specification are listed in Section 7. All 1312 AVP codes are allocated from the 'Authentication, Authorization, and 1313 Accounting (AAA) Parameters' AVP Codes registry. 1315 9.2. New registries 1317 Two new registries are needed under the 'Authentication, 1318 Authorization, and Accounting (AAA) Parameters' registry. 1320 A new "Overload Control Feature Vector" registry is required. The 1321 registry must contain the following: 1323 Feature Vector Value Name 1325 Feature Vector Value 1327 Specification - the specification that defines the new value. 1329 See Section 7.2 for the initial Feature Vector Value in the registry. 1330 This specification is the specification defining the value. New 1331 values can be added into the registry using the Specification 1332 Required policy. [RFC5226]. 1334 A new "Overload Report Type" registry is required. The registry must 1335 contain the following: 1337 Report Type Value Name 1338 Report Type Value 1340 Specification - the specification that defines the new value. 1342 See Section 7.6 for the initial assignment in the registry. New 1343 types can be added using the Specification Required policy [RFC5226]. 1345 10. Security Considerations 1347 DOIC gives Diameter nodes the ability to request that downstream 1348 nodes send fewer Diameter requests. Nodes do this by exchanging 1349 overload reports that directly effect this reduction. This exchange 1350 is potentially subject to multiple methods of attack, and has the 1351 potential to be used as a Denial-of-Service (DoS) attack vector. For 1352 instance, a series of injected realm OLRs with a requested reduction 1353 percentage of 100% could be used to completely eliminate any traffic 1354 from being sent to that realm. 1356 Overload reports may contain information about the topology and 1357 current status of a Diameter network. This information is 1358 potentially sensitive. Network operators may wish to control 1359 disclosure of overload reports to unauthorized parties to avoid its 1360 use for competitive intelligence or to target attacks. 1362 Diameter does not include features to provide end-to-end 1363 authentication, integrity protection, or confidentiality. This may 1364 cause complications when sending overload reports between non- 1365 adjacent nodes. 1367 10.1. Potential Threat Modes 1369 The Diameter protocol involves transactions in the form of requests 1370 and answers exchanged between clients and servers. These clients and 1371 servers may be peers, that is, they may share a direct transport 1372 (e.g., TCP or SCTP) connection, or the messages may traverse one or 1373 more intermediaries, known as Diameter Agents. Diameter nodes use 1374 TLS, DTLS, or IPsec to authenticate peers, and to provide 1375 confidentiality and integrity protection of traffic between peers. 1376 Nodes can make authorization decisions based on the peer identities 1377 authenticated at the transport layer. 1379 When agents are involved, this presents an effectively transitive 1380 trust model. That is, a Diameter client or server can authorize an 1381 agent for certain actions, but it must trust that agent to make 1382 appropriate authorization decisions about its peers, and so on. 1383 Since confidentiality and integrity protection occurs at the 1384 transport layer, agents can read, and perhaps modify, any part of a 1385 Diameter message, including an overload report. 1387 There are several ways an attacker might attempt to exploit the 1388 overload control mechanism. An unauthorized third party might inject 1389 an overload report into the network. If this third party is upstream 1390 of an agent, and that agent fails to apply proper authorization 1391 policies, downstream nodes may mistakenly trust the report. This 1392 attack is at least partially mitigated by the assumption that nodes 1393 include overload reports in Diameter answers but not in requests. 1394 This requires an attacker to have knowledge of the original request 1395 in order to construct an answer. Such an answer would also need to 1396 arrive at a Diameter node via a protected transport connection. 1397 Therefore, implementations MUST validate that an answer containing an 1398 overload report is a properly constructed response to a pending 1399 request prior to acting on the overload report, and that the answer 1400 was received via an appropriate transport connection. 1402 A similar attack involves a compromised but otherwise authorized node 1403 that sends an inappropriate overload report. For example, a server 1404 for the realm "example.com" might send an overload report indicating 1405 that a competitor's realm "example.net" is overloaded. If other 1406 nodes act on the report, they may falsely believe that "example.net" 1407 is overloaded, effectively reducing that realm's capacity. 1408 Therefore, it's critical that nodes validate that an overload report 1409 received from a peer actually falls within that peer's responsibility 1410 before acting on the report or forwarding the report to other peers. 1411 For example, an overload report from a peer that applies to a realm 1412 not handled by that peer is suspect. This may require out-of-band, 1413 non Diameter agreements and/or mechanisms. 1415 This attack is partially mitigated by the fact that the 1416 application, as well as host and realm, for a given OLR is 1417 determined implicitly by respective AVPs in the enclosing answer. 1418 If a reporting node modifies any of those AVPs, the enclosing 1419 transaction will also be affected. 1421 10.2. Denial of Service Attacks 1423 Diameter overload reports, especially realm-reports, can cause a node 1424 to cease sending some or all Diameter requests for an extended 1425 period. This makes them a tempting vector for DoS attacks. 1426 Furthermore, since Diameter is almost always used in support of other 1427 protocols, a DoS attack on Diameter is likely to impact those 1428 protocols as well. In the worst case, where the Diameter application 1429 is being used for access control into an IP network, a coordinated 1430 DOS attack could result in the blockage of all traffic into that 1431 network. Therefore, Diameter nodes MUST NOT honor or forward OLRs 1432 received from peers that are not trusted to send them. 1434 An attacker might use the information in an OLR to assist in DoS 1435 attacks. For example, an attacker could use information about 1436 current overload conditions to time an attack for maximum effect, or 1437 use subsequent overload reports as a feedback mechanism to learn the 1438 results of a previous or ongoing attack. Operators need the ability 1439 to ensure that OLRs are not leaked to untrusted parties. 1441 10.3. Non-Compliant Nodes 1443 In the absence of an overload control mechanism, Diameter nodes need 1444 to implement strategies to protect themselves from floods of 1445 requests, and to make sure that a disproportionate load from one 1446 source does not prevent other sources from receiving service. For 1447 example, a Diameter server might throttle a certain percentage of 1448 requests from sources that exceed certain limits. Overload control 1449 can be thought of as an optimization for such strategies, where 1450 downstream nodes never send the excess requests in the first place. 1451 However, the presence of an overload control mechanism does not 1452 remove the need for these other protection strategies. 1454 When a Diameter node sends an overload report, it cannot assume that 1455 all nodes will comply, even if they indicate support for DOIC. A 1456 non-compliant node might continue to send requests with no reduction 1457 in load. Such non-compliance could be done accidentally, or 1458 maliciously to gain an unfair advantage over compliant nodes. 1459 Requirement 28 [RFC7068] indicates that the overload control solution 1460 cannot assume that all Diameter nodes in a network are trusted. It 1461 also requires that malicious nodes not be allowed to take advantage 1462 of the overload control mechanism to get more than their fair share 1463 of service. 1465 10.4. End-to End-Security Issues 1467 The lack of end-to-end integrity features makes it difficult to 1468 establish trust in overload reports received from non-adjacent nodes. 1469 Any agents in the message path may insert or modify overload reports. 1470 Nodes must trust that their adjacent peers perform proper checks on 1471 overload reports from their peers, and so on, creating a transitive- 1472 trust requirement extending for potentially long chains of nodes. 1473 Network operators must determine if this transitive trust requirement 1474 is acceptable for their deployments. Nodes supporting Diameter 1475 overload control MUST give operators the ability to select which 1476 peers are trusted to deliver overload reports, and whether they are 1477 trusted to forward overload reports from non-adjacent nodes. DOIC 1478 nodes MUST strip DOIC AVPs from messages received from peers that are 1479 not trusted for DOIC purposes. 1481 The lack of end-to-end confidentiality protection means that any 1482 Diameter agent in the path of an overload report can view the 1483 contents of that report. In addition to the requirement to select 1484 which peers are trusted to send overload reports, operators MUST be 1485 able to select which peers are authorized to receive reports. A node 1486 MUST NOT send an overload report to a peer not authorized to receive 1487 it. Furthermore, an agent MUST remove any overload reports that 1488 might have been inserted by other nodes before forwarding a Diameter 1489 message to a peer that is not authorized to receive overload reports. 1491 A DOIC node cannot always automatically detect that a peer also 1492 supports DOIC. For example, a node might have a peer that is a 1493 non-supporting agent. If nodes on the other side of that agent 1494 send OC-Supported-Features AVPs, the agent is likely to forward 1495 them as unknown AVPs. Messages received across the non-supporting 1496 agent may be indistinguishable from messages received across a 1497 DOIC supporting agent, giving the false impression that the non- 1498 supporting agent actually supports DOIC. This complicates the 1499 transitive-trust nature of DOIC. Operators need to be careful to 1500 avoid situations where a non-supporting agent is mistakenly 1501 trusted to enforce DOIC related authorization policies. 1503 It is expected that work on end-to-end Diameter security might make 1504 it easier to establish trust in non-adjacent nodes for overload 1505 control purposes. Readers should be reminded, however, that the 1506 overload control mechanism allows Diameter agents to modify AVPs in, 1507 or insert additional AVPs into, existing messages that are originated 1508 by other nodes. If end-to-end security is enabled, there is a risk 1509 that such modification could violate integrity protection. The 1510 details of using any future Diameter end-to-end security mechanism 1511 with overload control will require careful consideration, and are 1512 beyond the scope of this document. 1514 11. Contributors 1516 The following people contributed substantial ideas, feedback, and 1517 discussion to this document: 1519 o Eric McMurry 1521 o Hannes Tschofenig 1523 o Ulrich Wiehe 1525 o Jean-Jacques Trottin 1527 o Maria Cruz Bartolome 1528 o Martin Dolly 1530 o Nirav Salot 1532 o Susan Shishufeng 1534 12. References 1536 12.1. Normative References 1538 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1539 Requirement Levels", BCP 14, RFC 2119, 1540 DOI 10.17487/RFC2119, March 1997, 1541 . 1543 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1544 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1545 DOI 10.17487/RFC5226, May 2008, 1546 . 1548 [RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn, 1549 Ed., "Diameter Base Protocol", RFC 6733, 1550 DOI 10.17487/RFC6733, October 2012, 1551 . 1553 12.2. Informative References 1555 [Cx] 3GPP, , "ETSI TS 129 229 V11.4.0", August 2013. 1557 [I-D.ietf-dime-e2e-sec-req] 1558 Tschofenig, H., Korhonen, J., Zorn, G., and K. Pillay, 1559 "Diameter AVP Level Security: Scenarios and Requirements", 1560 draft-ietf-dime-e2e-sec-req-01 (work in progress), October 1561 2013. 1563 [PCC] 3GPP, , "ETSI TS 123 203 V11.12.0", December 2013. 1565 [RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J. 1566 Loughney, "Diameter Credit-Control Application", RFC 4006, 1567 DOI 10.17487/RFC4006, August 2005, 1568 . 1570 [RFC7068] McMurry, E. and B. Campbell, "Diameter Overload Control 1571 Requirements", RFC 7068, DOI 10.17487/RFC7068, November 1572 2013, . 1574 [S13] 3GPP, , "ETSI TS 129 272 V11.9.0", December 2012. 1576 Appendix A. Issues left for future specifications 1578 The base solution for the overload control does not cover all 1579 possible use cases. A number of solution aspects were intentionally 1580 left for future specification and protocol work. The following sub- 1581 sections define some of the potential extensions to the DOIC 1582 solution. 1584 A.1. Additional traffic abatement algorithms 1586 This specification describes only means for a simple loss based 1587 algorithm. Future algorithms can be added using the designed 1588 solution extension mechanism. The new algorithms need to be 1589 registered with IANA. See Sections 7.1 and 9 for the required IANA 1590 steps. 1592 A.2. Agent Overload 1594 This specification focuses on Diameter endpoint (server or client) 1595 overload. A separate extension will be required to outline the 1596 handling of the case of agent overload. 1598 A.3. New Error Diagnostic AVP 1600 This specification indicates the use of existing error messages when 1601 nodes reject requests due to overload. There is an expectation that 1602 additional error codes or AVPs will be defined in a separate 1603 specification to indicate that overload was the reason for the 1604 rejection of the message. 1606 Appendix B. Deployment Considerations 1608 Non-Supporting Agents 1610 Due to the way that realm-routed requests are handled in Diameter 1611 networks with the server selection for the request done by an 1612 agent, network operators should enable DOIC at agents that perform 1613 server selection first. 1615 Topology Hiding Interactions 1617 There exist proxies that implement what is referred to as Topology 1618 Hiding. This can include cases where the agent modifies the 1619 Origin-Host in answer messages. The behavior of the DOIC solution 1620 is not well understood when this happens. As such, the DOIC 1621 solution does not address this scenario. 1623 Inter Realm/Administrative Domain Considerations 1624 There are likely to be special considerations for handling DOIC 1625 signaling across administrative boundaries. This includes 1626 considerations for whether or not information included in the DOIC 1627 signaling should be sent across those boundaries. In addition 1628 consideration should be taken as to whether or not a reacting node 1629 in one realm can be trusted to implement the requested overload 1630 abatement handling for overload reports received from a separately 1631 administered realm. 1633 Appendix C. Considerations for Applications Integrating the DOIC 1634 Solution 1636 This section outlines considerations to be taken into account when 1637 integrating the DOIC solution into Diameter applications. 1639 C.1. Application Classification 1641 The following is a classification of Diameter applications and 1642 request types. This discussion is meant to document factors that 1643 play into decisions made by the Diameter entity responsible for 1644 handling overload reports. 1646 Section 8.1 of [RFC6733] defines two state machines that imply two 1647 types of applications, session-less and session-based applications. 1648 The primary difference between these types of applications is the 1649 lifetime of Session-Ids. 1651 For session-based applications, the Session-Id is used to tie 1652 multiple requests into a single session. 1654 The Credit-Control application defined in [RFC4006] is an example of 1655 a Diameter session-based application. 1657 In session-less applications, the lifetime of the Session-Id is a 1658 single Diameter transaction, i.e., the session is implicitly 1659 terminated after a single Diameter transaction and a new Session-Id 1660 is generated for each Diameter request. 1662 For the purposes of this discussion, session-less applications are 1663 further divided into two types of applications: 1665 Stateless Applications: 1667 Requests within a stateless application have no relationship to 1668 each other. The 3GPP defined S13 application is an example of a 1669 stateless application [S13], where only a Diameter command is 1670 defined between a client and a server and no state is maintained 1671 between two consecutive transactions. 1673 Pseudo-Session Applications: 1675 Applications that do not rely on the Session-Id AVP for 1676 correlation of application messages related to the same session 1677 but use other session-related information in the Diameter requests 1678 for this purpose. The 3GPP defined Cx application [Cx] is an 1679 example of a pseudo-session application. 1681 The handling of overload reports must take the type of application 1682 into consideration, as discussed in Appendix C.2. 1684 C.2. Application Type Overload Implications 1686 This section discusses considerations for mitigating overload 1687 reported by a Diameter entity. This discussion focuses on the type 1688 of application. Appendix C.3 discusses considerations for handling 1689 various request types when the target server is known to be in an 1690 overloaded state. 1692 These discussions assume that the strategy for mitigating the 1693 reported overload is to reduce the overall workload sent to the 1694 overloaded entity. The concept of applying overload treatment to 1695 requests targeted for an overloaded Diameter entity is inherent to 1696 this discussion. The method used to reduce offered load is not 1697 specified here but could include routing requests to another Diameter 1698 entity known to be able to handle them, or it could mean rejecting 1699 certain requests. For a Diameter agent, rejecting requests will 1700 usually mean generating appropriate Diameter error responses. For a 1701 Diameter client, rejecting requests will depend upon the application. 1702 For example, it could mean giving an indication to the entity 1703 requesting the Diameter service that the network is busy and to try 1704 again later. 1706 Stateless Applications: 1708 By definition there is no relationship between individual requests 1709 in a stateless application. As a result, when a request is sent 1710 or relayed to an overloaded Diameter entity - either a Diameter 1711 Server or a Diameter Agent - the sending or relaying entity can 1712 choose to apply the overload treatment to any request targeted for 1713 the overloaded entity. 1715 Pseudo-Session Applications: 1717 For pseudo-session applications, there is an implied ordering of 1718 requests. As a result, decisions about which requests towards an 1719 overloaded entity to reject could take the command code of the 1720 request into consideration. This generally means that 1721 transactions later in the sequence of transactions should be given 1722 more favorable treatment than messages earlier in the sequence. 1723 This is because more work has already been done by the Diameter 1724 network for those transactions that occur later in the sequence. 1725 Rejecting them could result in increasing the load on the network 1726 as the transactions earlier in the sequence might also need to be 1727 repeated. 1729 Session-Based Applications: 1731 Overload handling for session-based applications must take into 1732 consideration the work load associated with setting up and 1733 maintaining a session. As such, the entity sending requests 1734 towards an overloaded Diameter entity for a session-based 1735 application might tend to reject new session requests prior to 1736 rejecting intra-session requests. In addition, session ending 1737 requests might be given a lower probability of being rejected as 1738 rejecting session ending requests could result in session status 1739 being out of sync between the Diameter clients and servers. 1740 Application designers that would decide to reject mid-session 1741 requests will need to consider whether the rejection invalidates 1742 the session and any resulting session cleanup procedures. 1744 C.3. Request Transaction Classification 1746 Independent Request: 1748 An independent request is not correlated to any other requests 1749 and, as such, the lifetime of the session-id is constrained to an 1750 individual transaction. 1752 Session-Initiating Request: 1754 A session-initiating request is the initial message that 1755 establishes a Diameter session. The ACR message defined in 1756 [RFC6733] is an example of a session-initiating request. 1758 Correlated Session-Initiating Request: 1760 There are cases when multiple session-initiated requests must be 1761 correlated and managed by the same Diameter server. It is notably 1762 the case in the 3GPP PCC architecture [PCC], where multiple 1763 apparently independent Diameter application sessions are actually 1764 correlated and must be handled by the same Diameter server. 1766 Intra-Session Request: 1768 An intra-session request is a request that uses the same Session- 1769 Id than the one used in a previous request. An intra-session 1770 request generally needs to be delivered to the server that handled 1771 the session creating request for the session. The STR message 1772 defined in [RFC6733] is an example of an intra-session request. 1774 Pseudo-Session Requests: 1776 Pseudo-session requests are independent requests and do not use 1777 the same Session-Id but are correlated by other session-related 1778 information contained in the request. There exists Diameter 1779 applications that define an expected ordering of transactions. 1780 This sequencing of independent transactions results in a pseudo 1781 session. The AIR, MAR and SAR requests in the 3GPP defined Cx 1782 [Cx] application are examples of pseudo-session requests. 1784 C.4. Request Type Overload Implications 1786 The request classes identified in Appendix C.3 have implications on 1787 decisions about which requests should be throttled first. The 1788 following list of request treatment regarding throttling is provided 1789 as guidelines for application designers when implementing the 1790 Diameter overload control mechanism described in this document. The 1791 exact behavior regarding throttling is a matter of local policy, 1792 unless specifically defined for the application. 1794 Independent Requests: 1796 Independent requests can generally be given equal treatment when 1797 making throttling decisions, unless otherwise indicated by 1798 application requirements or local policy. 1800 Session-Initiating Requests: 1802 Session-initiating requests often represent more work than 1803 independent or intra-session requests. Moreover, session- 1804 initiating requests are typically followed by other session- 1805 related requests. Since the main objective of the overload 1806 control is to reduce the total number of requests sent to the 1807 overloaded entity, throttling decisions might favor allowing 1808 intra-session requests over session-initiating requests. In the 1809 absence of local policies or application specific requirements to 1810 the contrary, Individual session-initiating requests can be given 1811 equal treatment when making throttling decisions. 1813 Correlated Session-Initiating Requests: 1815 A Request that results in a new binding, where the binding is used 1816 for routing of subsequent session-initiating requests to the same 1817 server, represents more work load than other requests. As such, 1818 these requests might be throttled more frequently than other 1819 request types. 1821 Pseudo-Session Requests: 1823 Throttling decisions for pseudo-session requests can take into 1824 consideration where individual requests fit into the overall 1825 sequence of requests within the pseudo session. Requests that are 1826 earlier in the sequence might be throttled more aggressively than 1827 requests that occur later in the sequence. 1829 Intra-Session Requests: 1831 There are two types of intra-sessions requests, requests that 1832 terminate a session and the remainder of intra-session requests. 1833 Implementers and operators may choose to throttle session- 1834 terminating requests less aggressively in order to gracefully 1835 terminate sessions, allow cleanup of the related resources (e.g., 1836 session state) and avoid the need for additional intra-session 1837 requests. Favoring session-termination requests may reduce the 1838 session management impact on the overloaded entity. The default 1839 handling of other intra-session requests might be to treat them 1840 equally when making throttling decisions. There might also be 1841 application level considerations whether some request types are 1842 favored over others. 1844 Authors' Addresses 1846 Jouni Korhonen (editor) 1847 Broadcom 1848 Porkkalankatu 24 1849 Helsinki FIN-00180 1850 Finland 1852 Email: jouni.nospam@gmail.com 1854 Steve Donovan (editor) 1855 Oracle 1856 7460 Warren Parkway 1857 Frisco, Texas 75034 1858 United States 1860 Email: srdonovan@usdonovans.com 1861 Ben Campbell 1862 Oracle 1863 7460 Warren Parkway 1864 Frisco, Texas 75034 1865 United States 1867 Email: ben@nostrum.com 1869 Lionel Morand 1870 Orange Labs 1871 38/40 rue du General Leclerc 1872 Issy-Les-Moulineaux Cedex 9 92794 1873 France 1875 Phone: +33145296257 1876 Email: lionel.morand@orange.com