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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ECRIT B. Rosen 3 Internet-Draft 4 Intended status: Standards Track H. Schulzrinne 5 Expires: October 19, 2019 Columbia U. 6 H. Tschofenig 7 ARM Limited 8 R. Gellens 9 Core Technology Consulting 10 April 17, 2019 12 Data-Only Emergency Calls 13 draft-ietf-ecrit-data-only-ea-18 15 Abstract 17 RFC 6443 'Framework for Emergency Calling Using Internet Multimedia' 18 describes how devices use the Internet to place emergency calls and 19 how Public Safety Answering Points (PSAPs) handle Internet multimedia 20 emergency calls natively. The exchange of multimedia traffic for 21 emergency services involves a Session Initiation Protocol (SIP) 22 session establishment starting with a SIP INVITE that negotiates 23 various parameters for that session. 25 In some cases, however, the transmission of application data is all 26 that is needed. Examples of such environments include alerts issued 27 by a temperature sensor, burglar alarm, or chemical spill sensor. 28 Often these alerts are conveyed as one-shot data transmissions. 29 These type of interactions are called 'data-only emergency calls'. 30 This document describes a container for the data based on the Common 31 Alerting Protocol (CAP) and its transmission using the SIP MESSAGE 32 transaction. 34 Status of This Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at https://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on October 19, 2019. 50 Copyright Notice 52 Copyright (c) 2019 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 69 3. Architectural Overview . . . . . . . . . . . . . . . . . . . 4 70 4. Protocol Specification . . . . . . . . . . . . . . . . . . . 6 71 4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 6 72 4.2. Profiling of the CAP Document Content . . . . . . . . . . 7 73 4.3. Sending a Data-Only Emergency Call . . . . . . . . . . . 8 74 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 9 75 5.1. 425 (Bad Alert Message) Response Code . . . . . . . . . . 9 76 5.2. The AlertMsg-Error Header Field . . . . . . . . . . . . . 9 77 6. Call Backs . . . . . . . . . . . . . . . . . . . . . . . . . 11 78 7. Handling Large Amounts of Data . . . . . . . . . . . . . . . 11 79 8. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 80 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 81 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 82 10.1. Registration of the 83 'application/EmergencyCallData.cap+xml' MIME type . . . 17 84 10.2. IANA Registration of 'cap' Additional Data Block . . . . 18 85 10.3. IANA Registration for 425 Response Code . . . . . . . . 18 86 10.4. IANA Registration of New AlertMsg-Error Header Field . . 19 87 10.5. IANA Registration for the SIP AlertMsg-Error Codes . . . 19 88 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 90 12.1. Normative References . . . . . . . . . . . . . . . . . . 20 91 12.2. Informative References . . . . . . . . . . . . . . . . . 21 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 94 1. Introduction 96 [RFC6443] describes how devices use the Internet to place emergency 97 calls and how Public Safety Answering Points (PSAPs) handle Internet 98 multimedia emergency calls natively. The exchange of multimedia 99 traffic for emergency services involves a SIP session establishment 100 starting with a SIP INVITE that negotiates various parameters for 101 that session. 103 In some cases, however, there is only application data to be conveyed 104 from the end devices to a PSAP or an intermediary. Examples of such 105 environments includes sensors issuing alerts, or certain types of 106 medical monitors. These messages may be one-shot alerts to emergency 107 authorities and do not require establishment of a session. These 108 type of interactions are called 'data-only emergency calls'. In this 109 document, we use the term "call" so that similarities between data- 110 only (non-interactive) alerts and sessions with interactive media are 111 more obvious. 113 Data-only emergency calls are similar to regular emergency calls in 114 the sense that they require the emergency indications, emergency call 115 routing functionality and may even have the same location 116 requirements. However, the communication interaction will not lead 117 to the exchange of interactive media, that is, Real-Time Protocol 118 packets, such as voice, video data or real-time text. 120 The Common Alerting Protocol (CAP) [cap] is a format for exchanging 121 emergency alerts and public warnings. CAP is mainly used for 122 conveying alerts and warnings between authorities and from 123 authorities to citizen/individuals. This document is concerned with 124 citizen to authority "alerts", where the alert is a call without any 125 interactive media. 127 This document describes a method of including a CAP message in a SIP 128 transaction by defining it as a block of "additional data" as defined 129 in [RFC7852]. The CAP message is included either by value (the CAP 130 message is in the body of the message, using a CID) or by reference 131 (a URI is included in the message, which when dereferenced returns 132 the CAP message). The additional data mechanism is also used to send 133 alert specific data beyond that available in the CAP message. This 134 document also describes how a SIP MESSAGE [RFC3428] transaction can 135 be used to send a data-only call. 137 2. Terminology 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 141 document are to be interpreted as described in [RFC2119]. 143 3. Architectural Overview 145 This section illustrates two envisioned usage modes: targeted and 146 location-based emergency alert routing. 148 1. Emergency alerts containing only data are targeted to an 149 intermediary recipient responsible for evaluating the next steps. 150 These steps could include: 152 1. Sending a non-interactive call containing only data toward a 153 Public Safety Answering Point (PSAP); 155 2. Establishing a third-party initiated emergency call towards a 156 PSAP that could include audio, video, and data. 158 2. Emergency alerts may be targeted to a Service URN used for IP- 159 based emergency calls where the recipient is not known to the 160 originator. In this scenario, the alert may contain only data 161 (e.g., a CAP, Geolocation header field and one or more Call-Info 162 header fields containing Additional Data [RFC7852] in a SIP 163 MESSAGE). 165 Figure 1 shows a deployment variant where a sensor is pre-configured 166 (using techniques outside the scope of this document) to issue an 167 alert to an aggregator that processes these messages and performs 168 whatever steps are necessary to appropriately react to the alert. 169 For example, a security firm may use different sensor inputs to 170 dispatch their security staff to a building they protect or to 171 initiate a third-party emergency call. 173 +------------+ +------------+ 174 | Sensor | | Aggregator | 175 | | | | 176 +---+--------+ +------+-----+ 177 | | 178 Sensors | 179 trigger | 180 emergency | 181 alert | 182 | MESSAGE with CAP | 183 |----------------------------->| 184 | | 185 | Aggregator 186 | processes 187 | emergency 188 | alert 189 | 200 (OK) | 190 |<-----------------------------| 191 | | 192 | | 194 Figure 1: Targeted Emergency Alert Routing 196 In Figure 2 a scenario is shown whereby the alert is routed using 197 location information and a Service URN. An emergency services 198 routing proxy (ESRP) may use LoST to determine the next hop proxy to 199 route the alert message to. A possible receiver is a PSAP and the 200 recipient of the alert may be a call taker. In the generic case, 201 there is very likely no prior relationship between the originator and 202 the receiver, e.g., a PSAP. A PSAP, for example, is likely to 203 receive and accept alerts from entities it cannot authorize. This 204 scenario corresponds to the classic emergency services use case and 205 the description in [RFC6881] is applicable. In this use case, the 206 only difference between an emergency call and an emergency data-only 207 call is that the former uses INVITE, creates a session, and 208 negotiates one or more media streams, while the latter uses MESSAGE, 209 does not create a session, and does not have interactive media. 211 +----------+ +----------+ +-----------+ 212 |Sensor or | | ESRP | | PSAP | 213 |Aggregator| | | | | 214 +----+-----+ +---+------+ +----+------+ 215 | | | 216 Sensors | | 217 trigger | | 218 emergency | | 219 alert | | 220 | | | 221 | | | 222 | MESSAGE with CAP | | 223 | (including Service URN, | 224 | such as urn:service:sos) | 225 |-------------------| | 226 | | | 227 | ESRP performs | 228 | emergency alert | 229 | routing | 230 | | MESSAGE with CAP | 231 | | (including identity info) | 232 | |----------------------------->| 233 | | | 234 | | PSAP 235 | | processes 236 | | emergency 237 | | alert 238 | | 200 (OK) | 239 | |<-----------------------------| 240 | | | 241 | 200 (OK) | | 242 |<------------------| | 243 | | | 244 | | | 246 Figure 2: Location-Based Emergency Alert Routing 248 4. Protocol Specification 250 4.1. CAP Transport 252 A CAP message may be sent in the initial message of any SIP 253 transaction. However, this document only addresses sending a CAP 254 message in a SIP INVITE that initiates an emergency call, or in a SIP 255 MESSAGE transaction for a one-shot, data-only emergency call. 256 Behavior with other transactions is not defined. 258 The CAP message is included in a SIP message as an additional-data 259 block [RFC7852]. Accordingly, it is introduced to the SIP message 260 with a Call-Info header field with a purpose of 261 "EmergencyCallData.cap". The header field may contain a URI that is 262 used by the recipient (or in some cases, an intermediary) to obtain 263 the CAP message. Alternative, the Call-Info header field may contain 264 a Content Indirect url [RFC2392] and the CAP message included in the 265 body of the message. In the latter case, the CAP message is located 266 in a MIME block of the type 'application/emergencyCallData.cap+xml'. 268 If the SIP server does not support the functionality required to 269 fulfill the request then a 501 Not Implemented MUST be returned as 270 specified in [RFC3261]. This is the appropriate response when a User 271 Agent Server (UAS) does not recognize the request method and is not 272 capable of supporting it for any user. 274 The 415 Unsupported Media Type error MUST be returned as specified in 275 [RFC3261] if the SIP server is refusing to service the request 276 because the message body of the request is in a format not supported 277 by the server for the requested method. The server MUST return a 278 list of acceptable formats using the Accept, Accept-Encoding, or 279 Accept-Language header fields, depending on the specific problem with 280 the content. 282 4.2. Profiling of the CAP Document Content 284 The usage of CAP MUST conform to the specification provided with 285 [cap]. For usage with SIP the following additional requirements are 286 imposed: 288 sender: The following restrictions and conditions apply to setting 289 the value of the element: 291 Originator is a SIP entity, Author indication irrelevant: When 292 the alert was created by a SIP-based originator and it is not 293 useful to be explicit about the author of the alert, then the 294 element MUST be populated with the SIP URI of the user 295 agent. 297 Originator is a non-SIP entity, Author indication irrelevant: 298 When the alert was created by a non-SIP based entity and the 299 identity of this original sender is to be preserved, then this 300 identity MUST be placed into the element. In this 301 situation it is not useful to be explicit about the author of the 302 alert. The specific type of identity being used will depend on 303 the technology used by the original originator. 305 Author indication relevant: When the author is different from the 306 actual originator of the message and this distinction should be 307 preserved, then the element MUST NOT contain the SIP URI 308 of the user agent. 310 incidents: The element MUST be present. This incident 311 identifier MUST be chosen in such a way that it is unique for a 312 given combination. Note that the 313 element is optional and may not be present. 315 scope: The value of the element MAY be set to "Private" if 316 the alert is not meant for public consumption. The 317 element is, however, not used by this specification since the 318 message routing is performed by SIP and the respective address 319 information is already available in other SIP header fields. 320 Populating information twice into different parts of the message 321 may lead to inconsistency. 323 parameter: The element MAY contain additional 324 information specific to the sender. 326 area: It is RECOMMENDED to omit this element when constructing a 327 message. If the CAP message already contains an element, 328 then the specified location information SHOULD be copied into a 329 PIDF-LO structure referenced by the 'geolocation' header field. 330 If there is a need to copy the PIDF-LO structure referenced by 331 'geolocation' to , implementers must be aware that is 332 limited to a circle or polygon, and conversion of other shapes 333 will be required. Points SHOULD be converted to a circle with a 334 radius equal to the uncertainty of the point. Arc-bands and 335 ellipses SHOULD be converted to an equivalent polygon. 3D 336 locations SHOULD be converted to their equivalent 2D forms. 338 4.3. Sending a Data-Only Emergency Call 340 A data-only emergency call is sent using a SIP MESSAGE transaction 341 with a CAP URI or body part as described above in a manner similar to 342 how an emergency call with interactive media is sent, as described in 343 [RFC6881]. The MESSAGE transaction does not create a session nor 344 establish interactive media streams, but otherwise, the header 345 content of the transaction, routing, and processing of data-only 346 calls are the same as those of other emergency calls. 348 5. Error Handling 350 This section defines a new error response code and a header field for 351 additional information. 353 5.1. 425 (Bad Alert Message) Response Code 355 This SIP extension creates a new location-specific response code, 356 defined as follows: 358 425 (Bad Alert Message) 360 The 425 response code is a rejection of the request due to its 361 included alert content, indicating that it was malformed or not 362 satisfactory for the recipient's purpose. 364 A SIP intermediary can also reject an alert it receives from a User 365 Agent (UA) when it understands that the provided alert is malformed. 367 Section 5.2 describes an AlertMsg-Error header field with more 368 details about what was wrong with the alert message in the request. 369 This header field MUST be included in the 425 response. 371 It is only appropriate to generate a 425 response when the responding 372 entity has no other information in the request that is usable by the 373 responder. 375 A 425 response code MUST NOT be sent in response to a request that 376 lacks an alert message, as the user agent in that case may not 377 support this extension. 379 A 425 response is a final response within a transaction, and MUST NOT 380 terminate an existing dialog. 382 5.2. The AlertMsg-Error Header Field 384 The AlertMsg-Error header field provides additional information about 385 what was wrong with the original request. In some cases the provided 386 information will be used for debugging purposes. 388 The AlertMsg-Error header field has the following ABNF [RFC5234]: 390 message-header /= AlertMsg-Error 391 ; (message-header from 3261) 392 AlertMsg-Error = "AlertMsg-Error" HCOLON 393 ErrorValue 394 ErrorValue = error-code 395 *(SEMI error-params) 396 error-code = 1*3DIGIT 397 error-params = error-code-text 398 / generic-param ; from RFC3261 399 error-code-text = "code" EQUAL quoted-string ; from RFC3261 401 HCOLON, SEMI, and EQUAL are defined in [RFC3261]. DIGIT is defined 402 in [RFC5234]. 404 The AlertMsg-Error header field MUST contain only one ErrorValue to 405 indicate what was wrong with the alert payload the recipient 406 determined was bad. 408 The ErrorValue contains a 3-digit error code indicating what was 409 wrong with the alert in the request. This error code has a 410 corresponding quoted error text string that is human understandable. 411 The text string is OPTIONAL, but RECOMMENDED for human readability, 412 similar to the string phrase used for SIP response codes. That said, 413 the strings are complete enough for rendering to the user, if so 414 desired. The strings in this document are recommendations, and are 415 not standardized -- meaning an operator can change the strings -- but 416 MUST NOT change the meaning of the error code. Similar to how RFC 417 3261 specifies, there MUST NOT be more than one string per error 418 code. 420 The AlertMsg-Error header field MAY be included in any response if an 421 alert message was in the request part of the same transaction. For 422 example, a UA includes an alert in a MESSAGE to a PSAP. The PSAP can 423 accept this MESSAGE, thus creating a dialog, even though its UA 424 determined that the alert message contained in the MESSAGE was bad. 425 The PSAP merely includes an AlertMsg-Error header field value in the 426 200 OK to the MESSAGE, thus informing the UA that the MESSAGE was 427 accepted but the alert provided was bad. 429 If, on the other hand, the PSAP cannot accept the transaction without 430 a suitable alert message, a 425 response is sent. 432 A SIP intermediary that requires the UA's alert message in order to 433 properly process the transaction may also sends a 425 with an 434 AlertMsg-Error code. 436 This document defines an initial list of AlertMsg-Error values for 437 any SIP response, including provisional responses (other than 100 438 Trying) and the new 425 response. There MUST be no more than one 439 AlertMsg-Error code in a SIP response. 441 AlertMsg-Error: 100 ; code="Cannot Process the Alert Payload" 443 AlertMsg-Error: 101 ; code="Alert Payload was not present or could 444 not be found" 446 AlertMsg-Error: 102 ; code="Not enough information to determine the 447 purpose of the alert" 449 AlertMsg-Error: 103 ; code="Alert Payload was corrupted" 451 Additionally, if an entity cannot or chooses not to process the alert 452 message from a SIP request, a 500 (Server Internal Error) SHOULD be 453 used with or without a configurable Retry-After header field. 455 6. Call Backs 457 This document does not describe any method for the recipient to call 458 back the sender of a data-only call. Usually, these alerts are sent 459 by automata, which do not have a mechanism to receive calls of any 460 kind. The identifier in the 'From' header field may be useful to 461 obtain more information, but any such mechanism is not defined in 462 this document. The CAP message may contain related contact 463 information for the sender. 465 7. Handling Large Amounts of Data 467 It is not atypical for sensors to have large quantities of data that 468 they may wish to send. Including large amounts of data in a MESSAGE 469 is not advisable, because SIP entities are usually not equipped to 470 handle very large messages. In such cases, the sender SHOULD make 471 use of the by-reference mechanisms defined in [RFC7852], which 472 involves making the data available via HTTPS (either at the 473 originator or at another entity), placing a URI to the data in the 474 'Call-Info' header field, and the recipient using HTTPS to retrieve 475 the data. The CAP message itself can be sent by-reference using this 476 mechanism, as well as any or all of the Additional Data blocks that 477 may contain sensor-specific data. 479 8. Example 481 The following example shows a CAP document indicating a BURGLARY 482 alert issued by a sensor called 'sensor1@example.com'. The location 483 of the sensor can be obtained from the attached location information 484 provided via the 'geolocation' header field contained in the SIP 485 MESSAGE structure. Additionally, the sensor provided some data along 486 with the alert message, using proprietary information elements 487 intended only to be processed by the receiver, a SIP entity acting as 488 an aggregator. 490 MESSAGE sip:aggregator@example.com SIP/2.0 491 Via: SIP/2.0/TCP sensor1.example.com;branch=z9hG4bK776sgdkse 492 Max-Forwards: 70 493 From: sip:sensor1@example.com;tag=49583 494 To: sip:aggregator@example.com 495 Call-ID: asd88asd77a@2001:DB8:0:0FF 496 Geolocation: 497 ;routing-allowed=yes 498 Supported: geolocation 499 Accept: application/pidf+xml,application/EmergencyCallData.cap+xml 500 CSeq: 1 MESSAGE 501 Call-Info: cid:abcdef2@example.com;purpose=EmergencyCallData.cap 502 Content-Type: multipart/mixed; boundary=boundary1 503 Content-Length: ... 505 --boundary1 507 Content-Type: application/EmergencyCallData.cap+xml 508 Content-ID: 509 Content-Disposition: by-reference;handling=optional 510 512 513 S-1 514 sip:sensor1@example.com 515 2008-11-19T14:57:00-07:00 516 Actual 517 Alert 518 Private 519 abc1234 520 521 Security 522 BURGLARY 523 Expected 524 Likely 525 Moderate 526 SENSOR 1 527 528 SENSOR-DATA-NAMESPACE1 529 123 530 531 532 SENSOR-DATA-NAMESPACE2 533 TRUE 534 535 536 538 --boundary1 540 Content-Type: application/pidf+xml 541 Content-ID: 542 Content-Disposition: by-reference;handling=optional 543 544 553 554 555 556 557 558 32.86726 -97.16054 559 560 561 562 563 false 564 565 2010-11-14T20:00:00Z 566 567 568 802.11 569 570 2010-11-04T20:57:29Z 571 572 573 --boundary1-- 575 Figure 3: Example Message conveying an Alert to an aggregator 577 The following shows the same CAP document sent as a data-only 578 emergency call towards a PSAP. 580 MESSAGE urn:service:sos SIP/2.0 581 Via: SIP/2.0/TCP sip:aggreg.1.example.com;branch=z9hG4bK776abssa 582 Max-Forwards: 70 583 From: sip:aggregator@example.com;tag=32336 584 To: 112 585 Call-ID: asdf33443a@example.com 586 Route: sip:psap1.example.gov 587 Geolocation: 588 ;routing-allowed=yes 589 Supported: geolocation 590 Accept: application/pidf+xml,application/EmergencyCallData.cap+xml 591 Call-info: cid:abcdef2@example.com;purpose=EmergencyCallData.cap 592 CSeq: 1 MESSAGE 593 Content-Type: multipart/mixed; boundary=boundary1 594 Content-Length: ... 596 --boundary1 598 Content-Type: application/EmergencyCallData.cap+xml 599 Content-ID: 600 602 603 S-1 604 sip:sensor1@example.com 605 2008-11-19T14:57:00-07:00 606 Actual 607 Alert 608 Private 609 abc1234 610 611 Security 612 BURGLARY 613 Expected 614 Likely 615 Moderate 616 SENSOR 1 617 618 SENSOR-DATA-NAMESPACE1 619 123 620 621 622 SENSOR-DATA-NAMESPACE2 623 TRUE 624 625 626 627 --boundary1 629 Content-Type: application/pidf+xml 630 Content-ID: 631 632 641 642 643 644 645 646 32.86726 -97.16054 647 648 649 650 651 false 652 653 2010-11-14T20:00:00Z 654 655 656 802.11 657 658 2010-11-04T20:57:29Z 659 660 661 --boundary1-- 663 Figure 4: Example Message conveying an Alert to a PSAP 665 9. Security Considerations 667 This section discusses security considerations when SIP user agents 668 issue emergency alerts utilizing MESSAGE and CAP. Location specific 669 threats are not unique to this document and are discussed in 670 [RFC7378] and [RFC6442]. 672 The ECRIT emergency services architecture [RFC6443] considers classic 673 individual-to-authority emergency calling where the identity of the 674 emergency caller does not play a role at the time of the call 675 establishment itself, i.e., a response to the emergency call does not 676 depend on the identity of the caller. In the case of emergency 677 alerts generated by devices such as sensors, the processing may be 678 different in order to reduce the number of falsely generated 679 emergency alerts. Alerts could get triggered based on certain sensor 680 input that might have been caused by factors other than the actual 681 occurrence of an alert-relevant event. For example, a sensor may 682 simply be malfunctioning. For this reason, not all alert messages 683 are directly sent to a PSAP, but rather may be pre-processed by a 684 separate entity, potentially under supervision by a human, to filter 685 alerts and potentially correlate received alerts with others to 686 obtain a larger picture of the ongoing situation. 688 In any case, for alerts initiated by sensors, the identity could play 689 an important role in deciding whether to accept or ignore an incoming 690 alert message. With the scenario shown in Figure 1 it is very likely 691 that only authorized sensor input will be processed. For this 692 reason, it needs to be possible to refuse to accept alert messages 693 from an unknown origin. Two types of information elements can be 694 used for this purpose: 696 1. SIP itself provides security mechanisms that allow the 697 verification of the originator's identity. These mechanisms can 698 be re-used, such as P-Asserted-Identity [RFC3325] or SIP Identity 699 [RFC8224]. The latter provides a cryptographic assurance while 700 the former relies on a chain of trust model. 702 2. CAP provides additional security mechanisms and the ability to 703 carry further information about the sender's identity. 704 Section 3.3.4.1 of [cap] specifies the signing algorithms of CAP 705 documents. 707 In addition to the desire to perform identity-based access control, 708 the classic communication security threats need to be considered, 709 including integrity protection to prevent forgery or replay of alert 710 messages in transit. To deal with replay of alerts, a CAP document 711 contains the mandatory , , elements and an 712 optional element. Together, these elements make the CAP 713 document unique for a specific sender and provide time restrictions. 714 An entity that has already received a CAP message within the 715 indicated timeframe is able to detect a replayed message and, if the 716 content of that message is unchanged, then no additional security 717 vulnerability is created. Additionally, it is RECOMMENDED to make 718 use of SIP security mechanisms, such as SIP Identity [RFC8224], to 719 tie the CAP message to the SIP message. To provide protection of the 720 entire SIP message exchange between neighboring SIP entities, the 721 usage of TLS is REQUIRED. 723 Note that none of the security mechanism in this document protect 724 against a compromised sensor sending crafted alerts. Privacy 725 provided for any emergency calls, including data-only messages, is 726 subject to local regulations. 728 10. IANA Considerations 730 10.1. Registration of the 'application/EmergencyCallData.cap+xml' MIME 731 type 733 To: ietf-types@iana.org 735 Subject: Registration of MIME media type application/ 736 EmergencyCallData.cap+xml 738 MIME media type name: application 740 MIME subtype name: cap+xml 742 Required parameters: (none) 744 Optional parameters: charset; Indicates the character encoding of 745 enclosed XML. Default is UTF-8 [RFC3629]. 747 Encoding considerations: Uses XML, which can employ 8-bit 748 characters, depending on the character encoding used. See 749 [RFC7303], Section 3.2. 751 Security considerations: This content type is designed to carry 752 payloads of the Common Alerting Protocol (CAP). RFC XXX [Replace 753 by the RFC number of this specification] discusses security 754 considerations for this. 756 Interoperability considerations: This content type provides a way to 757 convey CAP payloads. 759 Published specification: RFC XXX [Replace by the RFC number of this 760 specification]. 762 Applications which use this media type: Applications that convey 763 alerts and warnings according to the CAP standard. 765 Additional information: OASIS has published the Common Alerting 766 Protocol at http://www.oasis-open.org/committees/ 767 documents.php&wg_abbrev=emergency 769 Person and email address to contact for further information: Hannes 770 Tschofenig, hannes.tschofenig@gmx.net 772 Intended usage: Limited use 774 Author/Change controller: IETF ECRIT working group 776 Other information: This media type is a specialization of 777 application/xml [RFC7303], and many of the considerations 778 described there also apply to application/cap+xml. 780 10.2. IANA Registration of 'cap' Additional Data Block 782 This document registers a new block type in the sub-registry called 783 'Emergency Call Data Types' of the Emergency Call Additional Data 784 Registry defined in [RFC7852]. The token is "cap", the Data About is 785 "The Call" and the reference is this document. 787 10.3. IANA Registration for 425 Response Code 789 In the SIP Response Codes registry, the following is added 791 Reference: RFC-XXXX (i.e., this document) 793 Response code: 425 (recommended number to assign) 795 Default reason phrase: Bad Alert Message 796 Registry: 797 Response Code Reference 798 ------------------------------------------ --------- 799 Request Failure 4xx 800 425 Bad Alert Message [this doc] 802 This SIP Response code is defined in Section 5. 804 10.4. IANA Registration of New AlertMsg-Error Header Field 806 The SIP AlertMsg-error header field is created by this document, with 807 its definition and rules in Section 5, to be added to the IANA 808 Session Initiation Protocol (SIP) Parameters registry with two 809 actions: 811 1. Update the Header Fields registry with 813 Registry: 814 Header Name compact Reference 815 ----------------- ------- --------- 816 AlertMsg-Error [this doc] 818 2. In the portion titled "Header Field Parameters and Parameter 819 Values", add 821 Predefined 822 Header Field Parameter Name Values Reference 823 ----------------- ------------------- ---------- --------- 824 AlertMsg-Error code yes [this doc] 826 10.5. IANA Registration for the SIP AlertMsg-Error Codes 828 This document creates a new registry for SIP, called "AlertMsg-Error 829 Codes". AlertMsg-Error codes provide reasons for an error discovered 830 by a recipient, categorized by the action to be taken by the error 831 recipient. The initial values for this registry are shown below. 833 Registry Name: AlertMsg-Error Codes 835 Reference: [this doc] 837 Registration Procedures: Specification Required 838 Code Default Reason Phrase Reference 839 ---- --------------------------------------------------- --------- 840 100 "Cannot Process the Alert Payload" [this doc] 842 101 "Alert Payload was not present or could not be found" [this doc] 844 102 "Not enough information to determine 845 the purpose of the alert" [this doc] 847 103 "Alert Payload was corrupted" [this doc] 849 Details of these error codes are in Section 5. 851 11. Acknowledgments 853 The authors would like to thank the participants of the Early Warning 854 adhoc meeting at IETF#69 for their feedback. Additionally, we would 855 like to thank the members of the NENA Long Term Direction Working 856 Group for their feedback. 858 Additionally, we would like to thank Martin Thomson, James 859 Winterbottom, Shida Schubert, Bernard Aboba, Marc Linsner, Christer 860 Holmberg and Ivo Sedlacek for their review comments. 862 12. References 864 12.1. Normative References 866 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 867 Requirement Levels", March 1997. 869 [cap] Jones, E. and A. Botterell, "Common Alerting Protocol v. 870 1.2", October 2005, . 873 [RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource 874 Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998, 875 . 877 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 878 A., Peterson, J., Sparks, R., Handley, M., and E. 879 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 880 DOI 10.17487/RFC3261, June 2002, 881 . 883 [RFC3428] Campbell, B., Ed., Rosenberg, J., Schulzrinne, H., 884 Huitema, C., and D. Gurle, "Session Initiation Protocol 885 (SIP) Extension for Instant Messaging", RFC 3428, 886 DOI 10.17487/RFC3428, December 2002, 887 . 889 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 890 Specifications: ABNF", STD 68, RFC 5234, 891 DOI 10.17487/RFC5234, January 2008, 892 . 894 [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303, 895 DOI 10.17487/RFC7303, July 2014, 896 . 898 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 899 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 900 2003, . 902 [RFC6442] Polk, J., Rosen, B., and J. Peterson, "Location Conveyance 903 for the Session Initiation Protocol", RFC 6442, 904 DOI 10.17487/RFC6442, December 2011, 905 . 907 [RFC6881] Rosen, B. and J. Polk, "Best Current Practice for 908 Communications Services in Support of Emergency Calling", 909 BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013, 910 . 912 [RFC7852] Gellens, R., Rosen, B., Tschofenig, H., Marshall, R., and 913 J. Winterbottom, "Additional Data Related to an Emergency 914 Call", RFC 7852, DOI 10.17487/RFC7852, July 2016, 915 . 917 12.2. Informative References 919 [RFC7378] Tschofenig, H., Schulzrinne, H., and B. Aboba, Ed., 920 "Trustworthy Location", RFC 7378, DOI 10.17487/RFC7378, 921 December 2014, . 923 [RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt, 924 "Authenticated Identity Management in the Session 925 Initiation Protocol (SIP)", RFC 8224, 926 DOI 10.17487/RFC8224, February 2018, 927 . 929 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 930 Extensions to the Session Initiation Protocol (SIP) for 931 Asserted Identity within Trusted Networks", RFC 3325, 932 DOI 10.17487/RFC3325, November 2002, 933 . 935 [RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, 936 "Framework for Emergency Calling Using Internet 937 Multimedia", RFC 6443, DOI 10.17487/RFC6443, December 938 2011, . 940 Authors' Addresses 942 Brian Rosen 943 470 Conrad Dr 944 Mars, PA 16046 945 US 947 Email: br@brianrosen.net 949 Henning Schulzrinne 950 Columbia University 951 Department of Computer Science 952 450 Computer Science Building 953 New York, NY 10027 954 US 956 Phone: +1 212 939 7004 957 Email: hgs+ecrit@cs.columbia.edu 958 URI: http://www.cs.columbia.edu 960 Hannes Tschofenig 961 ARM Limited 962 Austria 964 Email: Hannes.Tschofenig@gmx.net 965 URI: http://www.tschofenig.priv.at 967 Randall Gellens 968 Core Technology Consulting 970 Email: rg+ietf@coretechnologyconsulting.com 971 URI: http://www.coretechnologyconsulting.com