idnits 2.17.1 draft-ietf-soc-load-control-event-package-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 10, 2012) is 4482 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2141 (Obsoleted by RFC 8141) ** Obsolete normative reference: RFC 3023 (Obsoleted by RFC 7303) ** Obsolete normative reference: RFC 3265 (Obsoleted by RFC 6665) ** Obsolete normative reference: RFC 4288 (Obsoleted by RFC 6838) == Outdated reference: A later version (-15) exists of draft-ietf-soc-overload-control-06 -- Obsolete informational reference (is this intentional?): RFC 5246 (Obsoleted by RFC 8446) Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IETF SOC Working Group C. Shen 3 Internet-Draft AT&T 4 Intended status: Standards Track H. Schulzrinne 5 Expires: July 13, 2012 Columbia U. 6 A. Koike 7 NTT 8 January 10, 2012 10 A Session Initiation Protocol (SIP) Load Control Event Package 11 draft-ietf-soc-load-control-event-package-02.txt 13 Abstract 15 We define a load control event package for the Session Initiation 16 Protocol (SIP). It allows SIP servers to distribute load filters to 17 other SIP servers in the network. The load filters contain rules to 18 throttle calls based on their source or destination domain, telephone 19 number prefix or for a specific user. The mechanism helps to prevent 20 signaling overload and complements feedback-based SIP overload 21 control efforts. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on July 13, 2012. 40 Copyright Notice 42 Copyright (c) 2012 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5 59 3. Design Requirements . . . . . . . . . . . . . . . . . . . . . 6 60 4. SIP Load Filtering Overview . . . . . . . . . . . . . . . . . 6 61 4.1. Filter Format . . . . . . . . . . . . . . . . . . . . . . 6 62 4.2. Filter Computation . . . . . . . . . . . . . . . . . . . . 6 63 4.3. Filter Distribution . . . . . . . . . . . . . . . . . . . 7 64 4.4. Applicability in Different Network Environments . . . . . 10 65 5. Load Control Event Package . . . . . . . . . . . . . . . . . . 11 66 5.1. Event Package Name . . . . . . . . . . . . . . . . . . . . 11 67 5.2. Event Package Parameters . . . . . . . . . . . . . . . . . 11 68 5.3. SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 11 69 5.4. SUBSCRIBE Duration . . . . . . . . . . . . . . . . . . . . 11 70 5.5. NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 11 71 5.6. Notifier Processing of SUBSCRIBE Requests . . . . . . . . 12 72 5.7. Notifier Generation of NOTIFY Requests . . . . . . . . . . 12 73 5.8. Subscriber Processing of NOTIFY Requests . . . . . . . . . 12 74 5.9. Handling of Forked Requests . . . . . . . . . . . . . . . 13 75 5.10. Rate of Notifications . . . . . . . . . . . . . . . . . . 13 76 5.11. State Delta . . . . . . . . . . . . . . . . . . . . . . . 13 77 5.12. State Agents . . . . . . . . . . . . . . . . . . . . . . . 14 78 6. Load Control Document . . . . . . . . . . . . . . . . . . . . 14 79 6.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . . 14 80 6.2. Namespace . . . . . . . . . . . . . . . . . . . . . . . . 15 81 6.3. Conditions . . . . . . . . . . . . . . . . . . . . . . . . 15 82 6.3.1. Call Identity . . . . . . . . . . . . . . . . . . . . 15 83 6.3.2. Validity . . . . . . . . . . . . . . . . . . . . . . . 18 84 6.3.3. Method . . . . . . . . . . . . . . . . . . . . . . . . 18 85 6.4. Actions . . . . . . . . . . . . . . . . . . . . . . . . . 18 86 6.5. Complete Examples . . . . . . . . . . . . . . . . . . . . 19 87 7. XML Schema Definition for Load Control . . . . . . . . . . . . 21 88 8. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 22 89 8.1. Relationship with Load Filtering in PSTN . . . . . . . . . 22 90 8.2. Relationship with Other IETF SIP Load Control Efforts . . 23 91 9. Discussion of this specification meeting the requirements 92 of RFC5390 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 93 10. Security Considerations . . . . . . . . . . . . . . . . . . . 29 94 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 95 11.1. Load Control Event Package Registration . . . . . . . . . 29 96 11.2. application/load-control+xml MIME Registration . . . . . . 30 97 11.3. Load Control Schema Registration . . . . . . . . . . . . . 30 98 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 31 99 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 100 13.1. Normative References . . . . . . . . . . . . . . . . . . . 31 101 13.2. Informative References . . . . . . . . . . . . . . . . . . 32 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32 104 1. Introduction 106 Proper functioning of Session Initiation Protocol (SIP) [RFC3265] 107 signaling servers is critical in SIP-based communications networks. 108 The performance of SIP servers can be severely degraded when the 109 server is overloaded with excessive number of signaling requests. 110 Both legitimate and malicious traffic can overload SIP servers, 111 despite appropriate capacity planning. 113 There are three common examples of legitimate short-term increases in 114 call volumes. Viewer-voting TV shows or ticket giveaways may 115 generate millions of calls within a few minutes. Call volume may 116 also spike during special holidays such as New Year's Day and 117 Mother's Day. Finally, callers may want to reach friends and family 118 in natural disaster areas such as those affected by earthquakes. 119 When possible, only calls traversing overloaded servers should be 120 throttled under those conditions. 122 SIP load control mechanisms are needed to prevent congestion collapse 123 in these cases [RFC5390]. There are two types of load control 124 approaches. In the first approach, feedback control, SIP servers 125 provide load limits to upstream servers, to reduce the incoming rate 126 of all SIP requests [I-D.ietf-soc-overload-control]. These upstream 127 servers then drop or delay incoming SIP requests. Feedback control 128 is reactive and affects signaling messages that have already been 129 issued by user agent clients. They work well when SIP proxy servers 130 in the core networks (core proxy servers) or destination-specific SIP 131 proxy servers in the edge networks (edge proxy servers) are 132 overloaded. By their nature, they need to distribute rate, drop or 133 window information to all upstream SIP proxy servers and normally 134 affect all calls equally, regardless of destination. However, 135 feedback control is usually ineffective for overload of more general 136 purpose SIP edge proxy servers. For example, in the ticket giveaway 137 case, almost all calls to the hotline will fail at the core proxy 138 servers; if the edge proxy servers leading to the core proxy servers 139 are also overloaded, calls to other destinations will also be 140 rejected or dropped. 142 Here, we propose an additional, complementary mechanism, called load 143 filtering. Network operators create load filters that indicate that 144 calls to specific destinations or from specific sources should be 145 rate-limited or randomly dropped. These load filters are then 146 distributed to SIP servers and possibly user agents likely to 147 generate calls to the affected destinations or from the affected 148 sources. Load filtering works best if it prevents calls as close to 149 the user agent clients as possible. 151 Performing SIP load filtering requires three components: load filter 152 format, load filter computation method, and load filter distribution 153 mechanism. This specification addresses two of these three 154 components. The load filter format is defined in a SIP load control 155 event package, while the load filter distribution mechanism is built 156 upon the existing SIP event framework. The remaining component, load 157 filter computation method, depends heavily on the actual network 158 topology and service provider policies. Therefore it is out of scope 159 of this specification. 161 It is helpful to clarify two aspects regarding some terminology used 162 in this specification. Firstly, although the SIP load filtering 163 mechanism is motivated by the overload control problem, which is why 164 this specification refers extensively to other parallel SIP overload 165 control related efforts, the applicability of filtering extends 166 beyond the overload control purpose. For example, it can also be 167 used to implement quality of service or other service level agreement 168 commitments. Therefore, we use the term SIP "load control event 169 package", instead of a narrower term "overload control event 170 package". Secondly, since we are describing a specific control 171 mechanism based on filtering, the term "load control" in this 172 specification is used inter-changeably with the term "load filtering" 173 unless when associated with other explicit context. This 174 specification, however, does not preclude the load control document 175 defined here (Section 6) to be extended in the future for other forms 176 of control as appropriate. 178 The rest of this specification is structured as follows: we begin by 179 listing the design requirements for this work in Section 3. We then 180 give an overview of load filtering operation in Section 4. The load 181 control event package for filter distribution is detailed in 182 Section 5. The load filter format is defined in the two sections 183 that follow, with Section 6 introducing the XML document for load 184 control and Section 7 listing the associated schema. Section 8 185 relates this work to corresponding mechanisms in PSTN and other IETF 186 efforts addressing SIP load control. Section 9 evaluates whether 187 this specification meets the SIP overload control requirements set 188 forth by RFC5390 [RFC5390]. Finally, Section 10 presents security 189 considerations and Section 11 provides IANA considerations. 191 2. Requirements Notation 193 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 194 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 195 document are to be interpreted as described in [RFC2119]. 197 3. Design Requirements 198 The SIP load filtering mechanism needs to satisfy the following 199 requirements: 201 o To simplify the solution, we focus on a method for controlling SIP 202 load, rather than a generic application-layer mechanism. 203 o The load filter needs to be distributed efficiently to possibly a 204 large subset of all SIP elements. 205 o The solution should re-use existing SIP protocol mechanisms to 206 reduce implementation and deployment complexity. 207 o For predictable overload situations, such as holidays and call-in 208 events, the load filter should specify during what time period it 209 is to be applied, so that the information can be distributed ahead 210 of time. 211 o For destination-specific overload situations, the load filter 212 needs to be able to describe the callee. 213 o To address accidental and intentional high-volume call generators, 214 the load filter should allow to specify the caller. 215 o Caller and callee need to be specified as both SIP URIs and 'Tel' 216 URIs[RFC3966]. 217 o For telephone numbers, it should be possible to specify prefixes 218 which allow control over limited regionally-focused overloads. 219 o The solution should draw upon experiences from related PSTN 220 mechanisms where applicable. 221 o The solution should be extensible to meet future needs. 223 4. SIP Load Filtering Overview 225 4.1. Filter Format 227 A load filter contains both conditions and actions. Filter 228 conditions include the identities of the targets to be controlled. 229 For example, there are two typical resource limits in a possible 230 overload situation, i.e., human destination limits (N number of call 231 takers) and proxy capacity limits. The control targets in these two 232 cases can be the specific callee numbers or the destination domains 233 corresponding to the overload. Filter conditions also indicate the 234 period of time during which the control should be activated, and the 235 specific message type to be controlled, e.g., the INVITE message of a 236 SIP session. Filter actions describe the desired control functions 237 such as limiting the request rate below a certain level. Detailed 238 formats of filter conditions and actions are defined in Section 6. 240 4.2. Filter Computation 242 Load filter computation needs to take into consideration information 243 such as the overload time, scope and network topology, as well as 244 service policies. It is also important to make sure that there is no 245 resource allocation loop, and that loads are allocated in a way which 246 both prevents overload and minimizes the likelihood of network 247 resource under-utilization. In some cases, in order to better 248 utilize system resources, it may be preferable to employ a dynamic 249 load computation algorithm which adapts to current network status, 250 rather than using a purely static mechanism. The load filter 251 computation algorithm is out of scope of this specification. 253 4.3. Filter Distribution 255 For load filter distribution, this specification defines the SIP 256 event package for load control, which is an "instantiation" of the 257 generic SIP events framework [RFC3265]. The SIP events framework 258 provides an existing method for SIP entities to subscribe to and 259 receive notifications when certain events have occurred. Such a 260 framework forms a scalable event distribution architecture that suits 261 our needs. This specification also defines the XML schema of a load 262 control document (Section 6), which is used to encode load filtering 263 rules. 265 In order for load filters to be properly distributed, each SIP proxy 266 server in the network is required to subscribe to the load control 267 event package from all its outgoing signaling neighbors, known as 268 notifiers (Section 5.6). Subscription is initiated and maintained 269 during normal server operation. Signaling neighbors are defined by 270 sending signaling messages. For instance, if A sends signaling 271 requests to B, B is an outgoing signaling neighbor of A. A needs to 272 subscribe to the load control event package of B in case B wants to 273 curb requests from A. On the other hand, if B also sends signaling 274 requests to A, then B also subscribes to A. Subscription of 275 neighboring SIP entities needs to be persistent so that they are in 276 place independently of any specific load filtering events. Key to 277 this is the fact that notification following initial subscription 278 includes an empty message body if no events are configured 279 (Section 5.7), and that the subscription needs to be refreshed 280 periodically to make it persistent, as described in Section 3.1.6 and 281 Section 3.1.4.2 of [RFC3265]. The notifier will send a notification 282 with its current control policy to its subscribers each time a new 283 subscription or a subscription refreshing is accepted (Section 5.7). 284 The same subscription dialog can also be used to convey policies for 285 multiple different load filtering events in a set of rules 286 (Section 6.1). 288 +-----------+ +-----------+ +-----------+ +-----------+ 289 | | | | | | | | 290 | EPa1 | | EPa2 | | EPa3 | | EPa4 | 291 | | | | | | | | 292 +-----------+ +-----------+ +-----------+ +-----------+ 293 \ / \ / 294 \ / \ / 295 \ / \ / 296 +-----------+ +-----------+ 297 | | | | 298 | CPa1 |------------------| CPa2 | 299 | | | | 300 +-----------+ +-----------+ 301 | | 302 Service | | 303 Provider A | | 304 | | 305 ================================================================= 306 | | 307 Service | | 308 Provider B | | 309 | | 310 +-----------+ +-----------+ 311 | | | | 312 | CPb1 |------------------| CPb2 | 313 | | | | 314 +-----------+ +-----------+ 315 / \ / \ 316 / \ / \ 317 / \ / \ 318 +-----------+ +-----------+ +-----------+ +-----------+ 319 | | | | | | | | 320 | EPb1 | | EPb2 | | EPb3 | | EPb4 | 321 | | | | | | | | 322 +-----------+ +-----------+ +-----------+ +-----------+ 324 Figure 1: Example Network Scenario Using SIP Load Control Event 325 Package Mechanism 327 We use the example architecture shown in Figure 1 to illustrate load 328 filter distribution based on the SIP load control event package. 329 This scenario consists of two networks belonging to Service Provider 330 A and Service Provider B, respectively. Each provider's network is 331 made up of two SIP core proxy servers and four SIP edge proxy 332 servers. The core proxy servers and edge proxy servers of Service 333 Provider A are denoted as CPa1 to CPa2 and EPa1 to EPa4; the core 334 proxy servers and edge proxy servers of Service Provider B are 335 denoted as CPb1 to CPb2 and EPb1 to EPb4. At the initialization 336 stage, the proxy servers first identify all their outgoing signaling 337 neighbors and subscribe to them. The neighbor identification process 338 can be performed by service providers through direct provisioning, or 339 by the proxy servers themselves via progressively learning from the 340 singling messages sent and received. Assuming all signaling 341 relationship in Figure 1 is bi-directional, after this initialization 342 stage, each proxy server will be subscribed to all its neighbors. 343 That is, EPa1 subscribes to CPa1; CPa1 subscribes to EPa1, EPa2, CPa2 344 and CPb1, so on and so forth. The following cases then show two 345 examples of how load filter distribution in this network works. 347 Case I: EPa1 serves a TV program hotline and decides to limit the 348 total number of incoming calls to the hotline to prevent an overload. 349 To do so, EPa1 sends a notification to CPa1 with the specific hotline 350 number, time of activation and total acceptable call rate. Depending 351 on the filter computation algorithm, CPa1 may allocate the received 352 total acceptable rate among its neighbors, namely, EPa2, CPa2, and 353 CPb1, and notify them about the resulting allocation along with the 354 hotline number and the activation time. CPa2 and CPb1 may perform 355 further allocation among their own neighbors and notify the 356 corresponding proxy servers. This process continues until all edge 357 proxy servers in the network have been informed about the event and 358 have proper load filter configured. 360 Case II: an earthquake affects the region covered by CPb2, EPb3 and 361 EPb4. All the three proxy servers are overloaded. The rescue team 362 determines that outbound calls are more valuable than inbound calls 363 in this specific situation. Therefore, EPb3 and EPb4 are configured 364 with filters to accept more outbound calls than inbound calls. CPb2 365 may be configured the same way or receive dynamically computed 366 filters from EPb3 and EPb4. Depending on the filter computation 367 algorithm, CPb2 may also send out notifications to its outside 368 neighbors, namely CPb1 and CPa2, specifying a limit on the acceptable 369 rate of inbound calls to CPb2's responsible domain. CPb1 and CPa2 370 may subsequently notify their neighbors about limiting the calls to 371 CPb2's area. The same process could continue until all edge proxy 372 servers are notified and have filters configured. 374 In the above two cases, the network entity where load filtering 375 policy is first introduced is the SIP server to be protected. In 376 other cases, the network entry point of load filtering policy could 377 also be an entity that the protected SIP server is connected to. For 378 example, an operator may host an application server that performs 800 379 number translation services. The application server may itself be a 380 SIP proxy or a SIP Back-to-Back User Agent (B2BUA). If one of the 381 800 numbers hosted at the application server creates the overload 382 condition, the load filtering policies can be introduced from the 383 application server and then propogated to other SIP proxy servers in 384 the network. 386 Note that this specification does not define the provisioning 387 interface between the party who determines the load control policy 388 and the network entry point where the policy is introduced. One of 389 the options for the provisioning interface is the Extensible Markup 390 Language (XML) Configuration Access Protocol (XCAP) [RFC4825]. 392 4.4. Applicability in Different Network Environments 394 SIP load filtering is more effective when the filters can be pushed 395 to the proximity of signaling sources. But even if only part of the 396 signaling path towards the signaling source could be covered, use of 397 this mechanism can still be beneficial. In fact, due to possibly 398 sophisticated call routing and security concerns, trying to apply 399 automated load filter distribution in the entire inter-domain network 400 path could get extremely complicated and be unrealistic. 402 The scenarios where this mechanism could be most useful are 403 environments consisting of servers with secure and trust relationship 404 and with relatively straightforward routing configuration known to 405 the filter computation algorithm. These scenarios may include intra- 406 domain environments such as those inside a service provider or 407 enterprise domain; inter-domain environments such as where enterprise 408 connecting to a few service providers or between service providers 409 with manageable routing configurations. 411 Another important aspect that affects the applicability of SIP load 412 filtering is that all possible signaling source neighbors need to 413 participate and enforce the designated filter. Otherwise, a single 414 non-conforming neighbor could make the whole control efforts useless 415 by pumping in excessive traffic to overload the server. Therefore, 416 the SIP server that initiates the filter needs to take counter- 417 measures towards any non-conforming neighbors. A simple policy is to 418 reject excessive requests with 500 responses as if they were obeying 419 the rate. Considering the rejection costs, a more complicated but 420 fairer policy would be to allocate at the overloaded server the same 421 amount of processing to the combination of both normal processing and 422 rejection as the overloaded server would devote to processing 423 requests for a conforming upstream SIP server. These approaches work 424 as long as the total rejection cost does not overwhelm the entire 425 server resources. In addition, whatever the actual policy is, SIP 426 servers SHOULD honor the Resource-Priority Header (RPH) [RFC4412] 427 when processing messages. The RPH contents may indicate high 428 priority requests that should be preserved as much as possible, or 429 low priority requests that could be dropped during overload. SIP 430 request rejection and message prioritization at an overloaded server 431 are also discussed in Section 5.1 of [I-D.ietf-soc-overload-control] 432 and Section 12 of [RFC6357]. 434 5. Load Control Event Package 436 The SIP load filtering mechanism uses the SIP event package for load 437 control. This section defines details of the SIP event package for 438 load control according to [RFC3265]. 440 5.1. Event Package Name 442 The name of this event package is "load-control". This name is 443 carried in the Event and Allow-Events header, as specified in 444 [RFC3265]. 446 5.2. Event Package Parameters 448 No package specific event header field parameters are defined for 449 this event package. 451 5.3. SUBSCRIBE Bodies 453 The effectiveness of SIP load filtering relies on the scope of 454 distribution and installation of the control policies in the network. 455 Since wide distribution of control policies is desirable, subscribers 456 SHOULD try to subscribe to all those notifiers with which they have 457 regular signaling exchanges, although not all such notifiers may 458 permit such a subscription. 460 A SUBSCRIBE request for the SIP load control event package MAY 461 contain a body to filter the requested load control event 462 notification. For example, a subscriber may be interested in some 463 specific types of load control policy only. The details of the 464 subscription filter specification are not yet defined. 466 A SUBSCRIBE request sent without a body implies the default 467 subscription behavior as specified in Section 5.7. 469 5.4. SUBSCRIBE Duration 471 The default expiration time for a subscription to load control policy 472 is one hour. Since the desired expiration time may vary 473 significantly for subscriptions among SIP entities with different 474 signaling relationships, the subscribers and notifiers are 475 RECOMMENDED to explicitly negotiate appropriate subscription 476 durations when knowledge about the mutual signaling relationship is 477 available. 479 5.5. NOTIFY Bodies 481 The body of a NOTIFY request in this event package contains load 482 control policy. As specified in [RFC3265], the format of the NOTIFY 483 body MUST be in one of the formats defined in the Accept header field 484 of the SUBSCRIBE request or be the default format. The default data 485 format for the NOTIFY body of this event package is "application/ 486 load-control+xml" (defined in Section 6). This means that if no 487 Accept header field is specified to a SUBSCRIBE request, the NOTIFY 488 request will contain a body in the "application/load-control+xml" 489 format. If the Accept header field is present, it MUST include 490 "application/load-control+xml" and MAY include any other types. 492 5.6. Notifier Processing of SUBSCRIBE Requests 494 Notifier accepts a new subscription or updates an existing 495 subscription upon receiving a valid SUBSCRIBE request. 497 If the identity of the subscriber sending the SUBSCRIBE request is 498 not allowed to receive load control policy, the notifier MUST return 499 a 403 "Forbidden" response. 501 If none of MIME types specified in the Accept header of the SUBSCRIBE 502 is supported, the Notifier SHOULD return 406 "Not Acceptable" 503 response. 505 5.7. Notifier Generation of NOTIFY Requests 507 Following [RFC3265] specification, a notifier MUST send a NOTIFY with 508 its current load control policy to the subscriber upon successfully 509 accepting or refreshing a subscription. If no applicable restriction 510 is active when the subscription request is received, an empty message 511 body is attached to the NOTIFY request. This is often the case when 512 a subscription is initiated for the first time, e.g., when a SIP 513 entity is just introduced, because there may be no planned events 514 configured at that time. A notifier SHOULD generate NOTIFY requests 515 each time the load control policy changes, with the maximum 516 notification rate not exceeding values defined in Section 5.10. 518 5.8. Subscriber Processing of NOTIFY Requests 520 The way subscribers process NOTIFY requests depends on the contents 521 of the notifications. Typically, a load control notification 522 consists of rules that should be applied to requests matching certain 523 identities. A subscriber receiving the notification first installs 524 these rules and then filter incoming requests to enforce actions on 525 appropriate requests, for example, limiting the sending rate of call 526 requests destined for a specific SIP entity. 528 In the case when load control rules specify a future validity time, 529 it is possible that when the validity time comes, the subscription to 530 the specific notifier that conveyed the rules has expired. In this 531 case, it is RECOMMENDED that the subscriber re-activate its 532 subscription with the corresponding notifier. Regardless of whether 533 this re-activation of subscription is successful or not, when the 534 validity time is reached, the subscriber SHOULD enforce the 535 corresponding rules. 537 Upon receipt of a NOTIFY request with a Subscription-State header 538 field containing the value "terminated", the subscription status with 539 the particular notifier will be terminated. However, subscribers 540 SHOULD NOT change previously received load control policies from that 541 notifier because of this change in subscription status, unless it has 542 other specific reasons to do so. Modifications of existing load 543 control policies at the subscriber is performed after directly 544 receiving notifications containing updated load control policies. 546 The subscriber SHALL discard unknown bodies. If the NOTIFY request 547 contains several bodies, none of them being supported, it SHOULD 548 unsubscribe. A NOTIFY request that does not contain a body MUST be 549 ignored. 551 5.9. Handling of Forked Requests 553 Forking is not applicable when the load control event package is used 554 within a single-hop distance between neighboring SIP entities. If 555 the communication scope of the load control event package is among 556 multiple hops, forking is not expected to happen either because the 557 subscription request is addressed to a clearly defined SIP entity. 558 However, in the unlikely case when forking does happen, the load 559 control event package only allows the first potential dialog- 560 establishing message to create a dialog, as specified in Section 561 4.4.9 of [RFC3265]. 563 5.10. Rate of Notifications 565 Rate of notifications is likely not a concern for this event package 566 when it is used in a non-real-time mode for relatively static load 567 control policies. Nevertheless, if situation does arise that a 568 rather frequent load control policy update is needed, it is 569 RECOMMENDED that the notifier does not generate notifications at a 570 rate higher than once per-second in all cases, in order to avoid the 571 NOTIFY request itself overloading the system. 573 5.11. State Delta 575 It is likely that updates to specific load control events are made by 576 changing the control restriction parameter information only (e.g. 577 rate, percent), but not other rule elements, such as call-identity. 579 This will typically be because the utilisation of a resource subject 580 to overload depends upon dynamic unknowns such as holding time and 581 the relative distribution of offered loads over subscribing SIP 582 entities. The updates could originate manually or be determined 583 automatically by a dynamic filter computation algorithm 584 (Section 4.2). Another factor usually not known precisely or is 585 computed automatically is the validity duration of the load control 586 event. Therefore it would also be common for the validity to change 587 frequently. 589 This event package allows the use of state delta to accommodate 590 frequent updates of partial rule parameters. As in [RFC3265], a 591 version number that increases by exactly one is included in the 592 NOTIFY body for each NOTIFY transaction in a subscription. When the 593 subscriber receives a state delta, it associates the partial updates 594 to the particular rules by matching the appropriate rule id 595 (Section 6.5). If the subscriber receives a NOTIFY that has a 596 version number that is increased by more than one, it knows that it 597 has missed a state delta. The subscriber then keeps the version 598 number, ignores the NOTIFY request containing the state delta, and 599 re-sends a SUBSCRIBE to force a NOTIFY containing a complete state 600 snapshot. 602 5.12. State Agents 604 The load control policy can be directly generated by concerned SIP 605 entities distributed in the network. Alternatively, qualified state 606 agents external to the SIP entities MAY be defined to take charge of 607 determining load control policies. 609 6. Load Control Document 611 6.1. Format 613 A load control document is an XML document that inherits and enhances 614 the common policy document defined in [RFC4745]. A common policy 615 document contains a set of rules. Each rule consists of three parts: 616 conditions, actions and transformations. The conditions part is a 617 set of expressions containing attributes such as identity, domain, 618 and validity time information. Each expression evaluates to TRUE or 619 FALSE. Conditions are matched on "equality" or "greater than" style 620 comparison. There is no regular expression matching. Conditions are 621 evaluated on receipt of an initial SIP request for a dialog or 622 standalone transaction. If a request matches all conditions in a 623 rule set, the action part and the transformation part are consulted 624 to determine the "permission" on how to handle the request. Each 625 action or transformation specifies a positive grant to the policy 626 server to perform the resulting actions. Well-defined mechanism are 627 available for combining actions and transformations obtained from 628 more than one sources. 630 6.2. Namespace 632 The namespace URI for elements defined by this specification is a 633 Uniform Resource Namespace (URN) ([RFC2141]), using the namespace 634 identifier 'ietf' defined by [RFC2648] and extended by [RFC3688]. 635 The URN is as follows: 637 urn:ietf:params:xml:ns:load-control 639 6.3. Conditions 641 [RFC4745] defines three condition elements: , and 642 . In this specification, we re-define an element for 643 identity and reuse the element. The element is 644 not used. 646 6.3.1. Call Identity 648 Since the problem space of this specification is different from that 649 of [RFC4745], the [RFC4745] element is not sufficient for 650 use with load control. First, load control may be applied to 651 different identities contained in a request, including identities of 652 both the receiving entity and the sending entity. Second, the 653 importance of authentication varies when different identities of a 654 request are concerned. This specification defines new identity 655 conditions that can accommodate the granularity of specific SIP 656 identity header fields. The requirement for authentication depends 657 on which field is to be matched. 659 The identity condition for load control is specified by the element and its sub-element . The element 661 itself contains sub-elements representing SIP sending and receiving 662 identity header fields: , , and , each is of the same type as the element in 664 [RFC4745]. Therefore, they also inherit the sub-elements of the 665 element, including , , and . 667 The [RFC4745] and elements may contain an "id" 668 attribute, which is the URI of a single entity to be included or 669 excluded in the condition. When used in the , , and elements, this "id" value is the URI 671 contained in the corresponding SIP header field, i.e., From, To, 672 Request-URI, and P-Asserted-Identity. 674 When the element contains multiple sub- 675 elements, the result is combined using logical OR. When the , 676 , and elements contain 677 multiple , , or sub-elements, the result is also 678 combined using logical OR, similar to that of the element 679 in [RFC4745]. However, when the element contains multiple of 680 the , , and sub- 681 elements, the result is combined using logical AND. This allows the 682 call identity to be specified by multiple fields of a SIP request 683 simultaneously, e.g., both the From and the To header fields. 685 The following shows an example of the element. 687 688 689 690 691 692 693 694 696 This example matches call requests whose To header field contains the 697 SIP URI "sip:alice@hotline.example.com", or the 'tel' URI 698 "tel:+1-212-555-1234". 700 The [RFC4745] and elements may take a "domain" 701 attribute. The "domain" attribute specifies a domain name to be 702 matched by the domain part of the candidate identity. Thus, it 703 allows matching a large and possibly unknown number of entities 704 within a domain. The "domain" attribute works well for SIP URIs. 706 A URI identifying a SIP user, however, can also be a 'tel' URI. We 707 therefore need a similar way to match a group of 'tel' URIs. 708 According to [RFC3966], there are two forms of 'tel' URIs for global 709 numbers and local numbers, respectively. All phone numbers must be 710 expressed in global form when possible. The global number 'tel' URIs 711 start with a "+". The rest of the numbers are expressed as local 712 numbers, which must be qualified by a "phone-context" parameter. The 713 "phone-context" parameter may be labelled as a global number or any 714 number of its leading digits, or a domain name. Both forms of the 715 'tel' URI make the resulting URI globally unique. 717 'Tel' URIs of global numbers can be grouped by prefixes consisting of 718 any number of common leading digits. For example, a prefix formed by 719 a country code or both the country and area code identifies telephone 720 numbers within a country or an area. Since the length of the country 721 and area code for different regions are different, the length of the 722 number prefix is also variable. This allows further flexibility such 723 as grouping the numbers into sub-areas within the same area code. 724 'Tel' URIs of local numbers can be grouped by the value of the 725 "phone-context" parameter. 727 To include the two forms of 'tel' URI grouping in the and 728 elements, one approach is to add a new attribute similar to 729 the "domain" attribute. In this specification, we decided on a 730 simpler approach. There are basically two types of grouping 731 attribute values for both SIP URIs and 'tel' URIs: domain name and 732 number prefix starting with "+". Both of them can be expressed as 733 strings. Therefore, we re-interpret the existing "domain" attribute 734 of the and elements to allow it to contain both types 735 of grouping attribute values. In particular, when the "domain" 736 attribute value starts with "+", it denotes a number prefix, 737 otherwise, the value denotes a domain name. Note that the tradeoff 738 of this simpler approach is the overlap in matching different types 739 of URIs. Specifically, a domain name in the "domain" attribute could 740 be matched by both a SIP URI with that domain name and a local number 741 'tel' URI containing the same domain name in the "phone-context". On 742 the other hand, a number prefix in the "domain" attribute could be 743 matched by both global number 'tel' URIs starting with those leading 744 digits, and local number 'tel' URIs having the same prefix in the 745 "phone-context" parameter. These overlap situations would not be a 746 big problem because of two reasons. First, when the "phone-context" 747 coincides with the SIP domain name or the global number prefix, it is 748 usually the case that the related phone numbers indeed belong to the 749 same domain or the same area, which means the overlap is not 750 inappropriate. Second, use of the local number 'tel' URI in practice 751 is expected to be rare. As a result, the chance of such overlap 752 happening is very small. 754 The following example shows the use of the re-interpreted "domain" 755 attribute. 757 758 759 760 761 762 763 764 765 766 767 769 770 772 This example matches those requests calling to the number "+1-202- 773 999-1234" but are not calling from a "+1-212" prefix or a SIP From 774 URI domain of "manhattan.example.com". 776 6.3.2. Validity 778 A rule is usually associated with a validity period condition. This 779 specification reuses the element of [RFC4745], which 780 specifies a period of validity time by pairs of and 781 sub-elements. When multiple time periods are defined, the validity 782 condition is evaluated to TRUE if the current time falls into any of 783 the specified time periods. i.e., it represents a logical OR 784 operation across all validity time periods. 786 The following example shows a element specifying a valid 787 period from 12:00 to 15:00 US Eastern Standard Time on 2008-05-31. 789 790 2008-05-31T12:00:00-05:00 791 2008-05-31T15:00:00-05:00 792 794 6.3.3. Method 796 The load created on a SIP server depends on the type of an initial 797 SIP request for a dialog or standalone transaction. The 798 element specifies the SIP method to which a particular action 799 applies. When this element is not included, the rule actions are 800 applicable to all initial methods. 802 The following example shows the use of the element. 804 INVITE 806 6.4. Actions 808 As [RFC4745] specified, conditions form the 'if'-part of rules, while 809 actions and transformations form the 'then'-part. Transformations 810 are not used in the load control document. The actions for load 811 control are defined by the element, which takes any one of 812 the three sub-elements , , and . The 813 element denotes an absolute value of the maximum acceptable request 814 rate in requests per second; the element specifies the 815 relative percentage of incoming requests that should be accepted; the 816 element describes the acceptable window size supplied by the 817 receiver, which is applicable in window-based load control. In 818 static load filter configuration scenarios, using the sub- 819 element is RECOMMENDED because it is hard to enforce the percentage 820 rate or window-based control when the incoming load from upstream or 821 the reactions from downstream are uncertain. (See 822 [I-D.ietf-soc-overload-control] [RFC6357] for more details on rate- 823 based, loss-based and window-based load control) 825 In addition, the element takes an optional "alt-action" 826 attribute which can be used to explicitly specify the desired action 827 in case a request cannot be accepted. The possible "alt-action" 828 values are "drop" for simple drop, "reject" for explicit rejection 829 (e.g., sending a "500 Server Internal Error" response message to an 830 INVITE request), and "forward". The default value is "reject" in 831 order to avoid possible SIP retransmissions when an unreliable 832 transport is used. If the "alt-action" value is "forward", an "alt- 833 target" attribute MUST be defined. The "alt-target" specifies a URI 834 where the request should be forwarded (e.g., an answering machine 835 with explanation of why the request cannot be accepted). 837 In the following element example, the server accepts 838 maximum of 100 call requests per second. The remaining calls are 839 forwarded to an answering machine. 841 842 844 100 845 846 848 6.5. Complete Examples 850 This section presents two complete examples of load control documents 851 vliad with respect to the XML schema defined in Section 7. 853 The first example assumes that a set of hotlines are set up at 854 "sip:alice@hotline.example.com" and "tel:+1-212-555-1234". The 855 hotlines are activated from 12:00 to 15:00 US Eastern Standard Time 856 on 2008-05-31. The goal is to limit the incoming calls to the 857 hotlines to 100 requests per second. Calls that exceed the rate 858 limit are explicitly rejected. 860 861 865 866 867 868 869 870 871 872 873 874 875 876 2008-05-31T12:00:00-05:00 877 2008-05-31T15:00:00-05:00 878 879 880 881 882 100 883 884 886 887 889 The second example considers optimizing server resource usage of a 890 three-day period during the aftermath of an earthquake. Incoming 891 calls to the earthquake domain "pompeii.example.com" will be limited 892 to a rate of 100 requests per second, except for those calls 893 originating from a particular rescue team domain 894 "rescue.example.com". Outgoing calls from the earthquake domain or 895 calls within the local domain are never limited. All calls that are 896 throttled due to the rate limit will be forwarded to an answering 897 machine with updated earthquake rescue information. 899 900 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 79-08-24T09:00:00+01:00 921 79-08-27T09:00:00+01:00 922 923 924 925 927 100 928 929 931 932 934 7. XML Schema Definition for Load Control 936 This section defines the XML schema for the load control document. 937 It extends the Common Policy schema in [RFC4745] in two ways. 938 Firstly, it defines two mandatory attributes for the ruleset element: 939 version and state. The version attribute allows the recipient of the 940 notification to properly order them. Versions start at 0, and 941 increment by one for each new document sent to a subscriber within 942 the same subscription. Versions MUST be representable using a non- 943 negative 32 bit integer. The state attribute indicates whether the 944 document contains the full control policy update, or whether it 945 contains only state delta as partial update. Secondly, it defines 946 new members of the and elements. 948 949 956 958 959 966 968 8. Related Work 970 8.1. Relationship with Load Filtering in PSTN 972 It is known that the existing PSTN network also uses a load filtering 973 mechanism to prevent overload and the filter configuration is done 974 manually. This specification defines a SIP events framework based 975 distribution mechanism which allows automated filter distribution in 976 suitable environments. 978 There are control messages associated with PSTN overload control 979 which would specify an outgoing control list, call gap duration and 980 control duration [AINGR]. These items could be roughly correlated to 981 the identity, action and time fields of the SIP load filter defined 982 in this specification. However, the filter defined in this 983 specification is much more generic and flexible as opposed to its 984 PSTN counterpart. 986 Firstly, PSTN load filtering only applies to telephone numbers, and 987 the number of prefix to be matched for a group of telephone numbers 988 is usually a fixed set. The SIP filter identity allows both SIP URI 989 and telephone numbers (through Tel URI) to be specified. The 990 identities can be arbitrarily grouped by SIP domains or any number of 991 leading prefix of the telephone numbers. 993 Secondly, the PSTN filtering action is usually limited to call 994 gapping with a fixed set of allowed gapping intervals. The action 995 field in the SIP load filter allows more flexible rate throttle and 996 other possibilities. 998 Thirdly, the duration field in PSTN filtering specifies a value in 999 seconds for the control duration only, and the allowed values are 1000 mapped into a value set. The time field in the SIP load filter may 1001 specify not only a duration, but also a future activation time which 1002 could be especially useful for automating load control for 1003 predictable overloads. 1005 PSTN filtering can be performed in both edge switches and transit 1006 switches; SIP filtering can also be applied in both edge proxy 1007 servers and core proxy servers, and even in capable user agents. 1009 PSTN overload control also has special accommodation for High 1010 Probability of Completion (HPC) calls, which would be similar to the 1011 calls designated by the SIP Resource Priority Headers [RFC4412]. SIP 1012 filtering mechanism can also prioritize the treatment of these calls 1013 by specifying favorable actions for these calls. 1015 PSTN filtering also provides administrative option for routing failed 1016 call attempts to either Recorder Tone or a special announcement. 1017 Similar capability can be provided in the SIP filtering mechanism by 1018 specifying the appropriate "alt-action" attribute in the SIP 1019 filtering action field. 1021 8.2. Relationship with Other IETF SIP Load Control Efforts 1023 The load filtering rules in this specification consists of identity, 1024 action and time. The identity can range from a single specific user 1025 to an arbitrary user aggregate, domains or areas. The user can be 1026 identified by either the source or the destination. When the user is 1027 identified by the source and a favorable action is specified, the 1028 result is to some extent similar to identifying a priority user based 1029 on authorized Resource Priority Headers [RFC4412] in the requests. 1030 Specifying a source user identity with an unfavorable action would 1031 cause an effect to some extent similar to an inverse SIP resource 1032 priority mechanism. 1034 The load filter defined in this specification is generic and expected 1035 to be applicable not only to the load filtering mechanism but also to 1036 the feedback overload control mechanism in 1037 [I-D.ietf-soc-overload-control]. In particular, both mechanisms 1038 could use specific or wildcard filter identities for load control and 1039 could share well-known load control actions. The time duration field 1040 in the load filter could also be used in both mechanisms. As 1041 mentioned in Section 1, the load filter distribution mechanism and 1042 the feedback overload control mechanism address complementary areas 1043 in the load control problem space. Load filtering is more proactive 1044 and focuses on distributing the filter towards the source of the 1045 traffic; the hop-by-hop feedback based approach is reactive and 1046 targets more at traffic already accepted in the network. Therefore, 1047 they could also make different use of the generic filter components. 1048 For example, the load filtering mechanism may use the time field in 1049 the filter to specify not only a control duration but also a future 1050 activation time to accommodate a predicable overload such as the one 1051 caused by Mother's Day greetings or a viewer-voting program; the 1052 feedback-based control might not need to use the time field or might 1053 use the time field to specify an immediate control duration. 1055 9. Discussion of this specification meeting the requirements of RFC5390 1057 This section evaluates whether the load control event package defined 1058 in this specification satisfies the various SIP overload control 1059 requirements set forth by RFC5390 [RFC5390]. Not all RFC5390 1060 requirements are found applicable due to the scope of this document. 1061 Therefore, we categorize the assessment results into Yes (meet the 1062 requirement), P/A (partially applicable), No (must be used in 1063 conjunction with another mechanism to meet the requirement), and N/A 1064 (not applicable). 1066 REQ 1: The overload mechanism shall strive to maintain the overall 1067 useful throughput (taking into consideration the quality-of- 1068 service needs of the using applications) of a SIP server at 1069 reasonable levels, even when the incoming load on the network is 1070 far in excess of its capacity. The overall throughput under load 1071 is the ultimate measure of the value of an overload control 1072 mechanism. 1074 P/A. The goal of the load filtering is to prevent overload or 1075 maintain overall goodput during the time of overload, but it is 1076 dependent on the advance predictions of the load. If the predictions 1077 are incorrect, in either direction, the effectiveness of the 1078 mechanism will be affected. 1080 REQ 2: When a single network element fails, goes into overload, or 1081 suffers from reduced processing capacity, the mechanism should 1082 strive to limit the impact of this on other elements in the 1083 network. This helps to prevent a small-scale failure from 1084 becoming a widespread outage. 1086 N/A if filter values are installed in advance and do not change 1087 during the potential overload period. P/A if filter values are 1088 dynamically adjusted due to the specific filter computation 1089 algorithm. The dynamic filter computation algorithm is outside the 1090 scope of this specification, while the distribution of the updated 1091 filters uses the event package mechanism of this specification. 1093 REQ 3: The mechanism should seek to minimize the amount of 1094 configuration required in order to work. For example, it is 1095 better to avoid needing to configure a server with its SIP message 1096 throughput, as these kinds of quantities are hard to determine. 1098 No. This mechanism is entirely dependent on advance configuration, 1099 based on advance knowledge. In order to satisfy Req 3, it should be 1100 used in conjunction with other mechanisms which are not based on 1101 advance configuration. 1103 REQ 4: The mechanism must be capable of dealing with elements that 1104 do not support it, so that a network can consist of a mix of 1105 elements that do and don't support it. In other words, the 1106 mechanism should not work only in environments where all elements 1107 support it. It is reasonable to assume that it works better in 1108 such environments, of course. Ideally, there should be 1109 incremental improvements in overall network throughput as 1110 increasing numbers of elements in the network support the 1111 mechanism. 1113 No. This mechanism is entirely dependent on the participation of all 1114 possible neighbors. In order to satisfy Req 4, it should be used in 1115 conjunction with other mechanisms, some of which are described in 1116 Section 4.4. 1118 REQ 5: The mechanism should not assume that it will only be 1119 deployed in environments with completely trusted elements. It 1120 should seek to operate as effectively as possible in environments 1121 where other elements are malicious; this includes preventing 1122 malicious elements from obtaining more than a fair share of 1123 service. 1125 No. This mechanism is entirely dependent on the non-malicious 1126 participation of all possible neighbors. In order to satisfy Req 5, 1127 it should be used in conjunction with other mechanisms, some of which 1128 are described in Section 4.4. 1130 REQ 6: When overload is signaled by means of a specific message, 1131 the message must clearly indicate that it is being sent because of 1132 overload, as opposed to other, non overload-based failure 1133 conditions. This requirement is meant to avoid some of the 1134 problems that have arisen from the reuse of the 503 response code 1135 for multiple purposes. Of course, overload is also signaled by 1136 lack of response to requests. This requirement applies only to 1137 explicit overload signals. 1139 N/A. This mechanism signals anticipated overload, not actual 1140 overload. However the signals in this mechanism are not used for any 1141 other purpose. 1143 REQ 7: The mechanism shall provide a way for an element to 1144 throttle the amount of traffic it receives from an upstream 1145 element. This throttling shall be graded so that it is not all- 1146 or-nothing as with the current 503 mechanism. This recognizes the 1147 fact that "overload" is not a binary state and that there are 1148 degrees of overload. 1150 Yes. This event package allows rate/loss/windows-based overload 1151 control options as discussed in Section 6.4. 1153 REQ 8: The mechanism shall ensure that, when a request was not 1154 processed successfully due to overload (or failure) of a 1155 downstream element, the request will not be retried on another 1156 element that is also overloaded or whose status is unknown. This 1157 requirement derives from REQ 1. 1159 N/A to the load control event package itself. 1161 REQ 9: That a request has been rejected from an overloaded element 1162 shall not unduly restrict the ability of that request to be 1163 submitted to and processed by an element that is not overloaded. 1164 This requirement derives from REQ 1. 1166 Yes. For example, the load filter [Section 4.1] allows the inclusion 1167 of alternative forwarding destinations for rejected requests. 1169 REQ 10: The mechanism should support servers that receive requests 1170 from a large number of different upstream elements, where the set 1171 of upstream elements is not enumerable. 1173 No. Because this mechanism requires advance configuration of 1174 specifically identified neighbors, it does not support environments 1175 where the number and identity of the upstream neighbors are not known 1176 in advance. In order to satisfy Req 10, it should be used in 1177 conjunction with other mechanisms. 1179 REQ 11: The mechanism should support servers that receive requests 1180 from a finite set of upstream elements, where the set of upstream 1181 elements is enumerable. 1183 Yes. See also answer to REQ 10. 1185 REQ 12: The mechanism should work between servers in different 1186 domains. 1188 Yes. The load control event package is not limited by domain 1189 boundaries. However, it is likely more applicable in intra-domain 1190 scenarios than in inter-domain scenarios due to security and other 1191 concerns (See also Section 4.4). 1193 REQ 13: The mechanism must not dictate a specific algorithm for 1194 prioritizing the processing of work within a proxy during times of 1195 overload. It must permit a proxy to prioritize requests based on 1196 any local policy, so that certain ones (such as a call for 1197 emergency services or a call with a specific value of the 1198 Resource-Priority header field [RFC4412]) are given preferential 1199 treatment, such as not being dropped, being given additional 1200 retransmission, or being processed ahead of others. 1202 P/A. This mechanism does not specifically address the prioritizing of 1203 work during times of overload. But it does not preclude any 1204 particular local policy. 1206 REQ 14: The mechanism should provide unambiguous directions to 1207 clients on when they should retry a request and when they should 1208 not. This especially applies to TCP connection establishment and 1209 SIP registrations, in order to mitigate against avalanche restart. 1211 N/A to the load control event package itself. 1213 REQ 15: In cases where a network element fails, is so overloaded 1214 that it cannot process messages, or cannot communicate due to a 1215 network failure or network partition, it will not be able to 1216 provide explicit indications of the nature of the failure or its 1217 levels of congestion. The mechanism must properly function in 1218 these cases. 1220 P/A. Because the filters are provisioned in advance, they are not 1221 affected by the overload or failure of other nodes. But, on the 1222 other hand, they may not, in those cases, be able to protect the 1223 overloaded node (see Req 1). 1225 REQ 16: The mechanism should attempt to minimize the overhead of 1226 the overload control messaging. 1228 Yes. The standardized SIP event package mechanism RFC3265 [RFC3265] 1229 is used. 1231 REQ 17: The overload mechanism must not provide an avenue for 1232 malicious attack, including DoS and DDoS attacks. 1234 P/A. This mechanism does provide a potential avenue for malicious 1235 attacks. Therefore the security mechanisms for SIP event packages in 1236 general [RFC3265] and of section 10 of this specification should be 1237 used. 1239 REQ 18: The overload mechanism should be unambiguous about whether 1240 a load indication applies to a specific IP address, host, or URI, 1241 so that an upstream element can determine the load of the entity 1242 to which a request is to be sent. 1244 Yes. The identity of load indication is covered in the filter format 1245 definition in Section 4.1. 1247 REQ 19: The specification for the overload mechanism should give 1248 guidance on which message types might be desirable to process over 1249 others during times of overload, based on SIP-specific 1250 considerations. For example, it may be more beneficial to process 1251 a SUBSCRIBE refresh with Expires of zero than a SUBSCRIBE refresh 1252 with a non-zero expiration (since the former reduces the overall 1253 amount of load on the element), or to process re-INVITEs over new 1254 INVITEs. 1256 N/A to the load control event package itself. 1258 REQ 20: In a mixed environment of elements that do and do not 1259 implement the overload mechanism, no disproportionate benefit 1260 shall accrue to the users or operators of the elements that do not 1261 implement the mechanism. 1263 No. This mechanism is entirely dependent on the participation of all 1264 possible neighbors. In order to satisfy Req 20, it should be used in 1265 conjunction with other mechanisms, some of which are described in 1266 Section 4.4. 1268 REQ 21: The overload mechanism should ensure that the system 1269 remains stable. When the offered load drops from above the 1270 overall capacity of the network to below the overall capacity, the 1271 throughput should stabilize and become equal to the offered load. 1273 N/A to the load control event package itself. 1275 REQ 22: It must be possible to disable the reporting of load 1276 information towards upstream targets based on the identity of 1277 those targets. This allows a domain administrator who considers 1278 the load of their elements to be sensitive information, to 1279 restrict access to that information. Of course, in such cases, 1280 there is no expectation that the overload mechanism itself will 1281 help prevent overload from that upstream target. 1283 N/A to the load control event package itself. 1285 REQ 23: It must be possible for the overload mechanism to work in 1286 cases where there is a load balancer in front of a farm of 1287 proxies. 1289 Yes. The load control event package does not preclude its use in a 1290 scenario with server farms. 1292 10. Security Considerations 1294 Two aspects of security considerations arise from this specification. 1295 One is the SIP event framework based filter distribution mechanism, 1296 the other is the filter enforcement mechanism. 1298 Security considerations for SIP event framework based mechanisms are 1299 covered in Section 5 of [RFC3265]. A particularly relevant security 1300 concern for this event package is that if the notifiers can be 1301 spoofed, attackers can send fake notifications asking subscribers to 1302 throttle all traffic, leading to Denial-of-Service attacks. 1303 Therefore, all load control notification MUST be authenticated and 1304 authorized before being accepted. Standard authentication and 1305 authorization mechanisms recommended in [RFC3261] such as TLS 1306 [RFC5246] and IPSec [RFC4301] may serve this purpose. On the other 1307 hand, if a legitimate notifier is itself compromised, additional 1308 mechanisms will be needed to detect the attack. 1310 Security considerations for filter enforcements vary depending on the 1311 filter itself. This specification defines possible filter match of 1312 the following SIP header fields: , , and 1313 . The exact requirement to authenticate and 1314 authorize these fields is up to the service provider. In general, if 1315 the identity field represents the source of the request, it SHOULD be 1316 authenticated and authorized; if the identity field represents the 1317 destination of the request, the authentication and authorization is 1318 optional. 1320 11. IANA Considerations 1322 This specification registers a SIP event package, a new MIME type, a 1323 new XML namespace, and a new XML schema. 1325 11.1. Load Control Event Package Registration 1327 This section registers an event package based on the registration 1328 procedures defined in [RFC3265]. 1330 Package name: load-control 1332 Type: package 1334 Published specification: This specification 1336 Person to contact: Charles Shen, charles@cs.columbia.edu 1338 11.2. application/load-control+xml MIME Registration 1339 This section registers a new MIME type based on the procedures 1340 defined in [RFC4288] and guidelines in [RFC3023]. 1342 MIME media type name: application 1344 MIME subtype name: load-control+xml 1346 Mandatory parameters: none 1348 Optional parameters: Same as charset parameter application/xml in 1349 [RFC3023] 1351 Encoding considerations: Same as encoding considerations of 1352 application/xml in [RFC3023] 1354 Security considerations: See Section 10 of [RFC3023] and Section 10 1355 of this specification 1357 Interpretability considerations: None 1359 Published Specification: This specification 1361 Applications which use this media type: load control of SIP entities 1363 Additional information: 1365 Magic number: None 1367 File extension: .xml 1369 Macintosh file type code: 'TEXT' 1371 Personal and email address for further information: 1373 Charles Shen, charles@cs.columbia.edu 1375 Intended usage: COMMON 1377 Author/Change Controller: IETF SOC Working Group 1378 , as designated by the IESG 1380 11.3. Load Control Schema Registration 1382 URI: urn:ietf:params:xml:schema:load-control 1384 Registrant Contact: IETF SOC working group, Charles Shen 1385 (charles@cs.columbia.edu). 1387 XML: the XML schema to be registered is contained in Section 7. 1389 Its first line is 1391 1393 and its last line is 1395 1397 12. Acknowledgements 1399 The authors would like to thank Bruno Chatras, Keith Drage, Ashutosh 1400 Dutta, Janet Gunn, Vijay Gurbani, Volker Hilt, Geoff Hunt, Hadriel 1401 Kaplan, Paul Kyzivat, Salvatore Loreto, Timothy Moran, Eric Noel, 1402 Parthasarathi R, Shida Schubert, Robert Sparks, Phil Williams and 1403 other members of the SOC and SIPPING working group for many helpful 1404 comments. In addition, Bruno Chatras proposed the condition 1405 element. Janet Gunn provided detailed text suggestions for 1406 Section 9. Shida made many suggestions about terminology usage. 1407 Phil added support for delta updates. Ashutosh Dutta gave pointers 1408 to PSTN references. 1410 13. References 1412 13.1. Normative References 1414 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1415 Requirement Levels", BCP 14, RFC 2119, March 1997. 1417 [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. 1419 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media 1420 Types", RFC 3023, January 2001. 1422 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1423 A., Peterson, J., Sparks, R., Handley, M., and E. 1424 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1425 June 2002. 1427 [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific 1428 Event Notification", RFC 3265, June 2002. 1430 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 1431 January 2004. 1433 [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", 1434 RFC 3966, December 2004. 1436 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 1437 Registration Procedures", BCP 13, RFC 4288, December 2005. 1439 [RFC4745] Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., 1440 Polk, J., and J. Rosenberg, "Common Policy: A Document 1441 Format for Expressing Privacy Preferences", RFC 4745, 1442 February 2007. 1444 13.2. Informative References 1446 [AINGR] Bell Communications Research, "AINGR: Service Control 1447 Point (SCP) Network Traffic Management", GR-2938-CORE , 1448 December 1996. 1450 [I-D.ietf-soc-overload-control] 1451 Gurbani, V., Hilt, V., and H. Schulzrinne, "Session 1452 Initiation Protocol (SIP) Overload Control", 1453 draft-ietf-soc-overload-control-06 (work in progress), 1454 January 2012. 1456 [RFC2648] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, 1457 August 1999. 1459 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1460 Internet Protocol", RFC 4301, December 2005. 1462 [RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource 1463 Priority for the Session Initiation Protocol (SIP)", 1464 RFC 4412, February 2006. 1466 [RFC4825] Rosenberg, J., "The Extensible Markup Language (XML) 1467 Configuration Access Protocol (XCAP)", RFC 4825, May 2007. 1469 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1470 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1472 [RFC5390] Rosenberg, J., "Requirements for Management of Overload in 1473 the Session Initiation Protocol", RFC 5390, December 2008. 1475 [RFC6357] Hilt, V., Noel, E., Shen, C., and A. Abdelal, "Design 1476 Considerations for Session Initiation Protocol (SIP) 1477 Overload Control", RFC 6357, August 2011. 1479 Authors' Addresses 1480 Charles Shen 1481 AT&T Security Research Center 1482 33 Thomas Street 1483 New York, NY 10007 1484 USA 1486 Phone: +1 212 513 2081 1487 Email: shen@att.com 1489 Henning Schulzrinne 1490 Columbia University 1491 Department of Computer Science 1492 1214 Amsterdam Avenue, MC 0401 1493 New York, NY 10027 1494 USA 1496 Phone: +1 212 939 7004 1497 Email: schulzrinne@cs.columbia.edu 1499 Arata Koike 1500 NTT Service Integration Labs & 1501 3-9-11 Midori-cho Musashino-shi 1502 Tokyo, 184-0013 1503 Japan 1505 Phone: +81 422 59 6099 1506 Email: koike.arata@lab.ntt.co.jp