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ECRIT B. Rosen
Internet-Draft
Intended status: Standards Track H. Schulzrinne
Expires: August 2, 2020 Columbia U.
H. Tschofenig
ARM Limited
R. Gellens
Core Technology Consulting
January 30, 2020
Non-Interactive Emergency Calls
draft-ietf-ecrit-data-only-ea-20
Abstract
RFC 6443 'Framework for Emergency Calling Using Internet Multimedia'
describes how devices use the Internet to place emergency calls and
how Public Safety Answering Points (PSAPs) handle Internet multimedia
emergency calls natively. The exchange of multimedia traffic for
emergency services involves a Session Initiation Protocol (SIP)
session establishment starting with a SIP INVITE that negotiates
various parameters for that session. These calls involve a person,
who uses the interactive media to communicate with the PSAP.
In some cases, however, the transmission of application data is all
that is needed, and no interactive media channel is established.
Examples of such environments include alerts issued by a temperature
sensor, burglar alarm, or chemical spill sensor. Often these alerts
are conveyed as one-shot data transmissions. These type of
interactions are called 'non-interactive emergency calls'. This
document describes use of a SIP MESSAGE transaction containing a
container for the data based on the Common Alerting Protocol (CAP).
MESSAGE does not establish a session, which differentiates this type
of emergency request from a SIP INVITE, which would. Any device that
needs to initiate a request for emergency services where no
interactive media channel will be established would use the
mechanisms in this document.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 2, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architectural Overview . . . . . . . . . . . . . . . . . . . 4
4. Protocol Specification . . . . . . . . . . . . . . . . . . . 6
4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Profiling of the CAP Document Content . . . . . . . . . . 7
4.3. Sending a non-interactive Emergency Call . . . . . . . . 8
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. 425 (Bad Alert Message) Response Code . . . . . . . . . . 9
5.2. The AlertMsg-Error Header Field . . . . . . . . . . . . . 9
6. Call Backs . . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Handling Large Amounts of Data . . . . . . . . . . . . . . . 11
8. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10.1. Registration of the
'application/EmergencyCallData.cap+xml' MIME type . . . 17
10.2. IANA Registration of 'cap' Additional Data Block . . . . 18
10.3. IANA Registration for 425 Response Code . . . . . . . . 18
10.4. IANA Registration of New AlertMsg-Error Header Field . . 19
10.5. IANA Registration for the SIP AlertMsg-Error Codes . . . 19
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . 20
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12.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
[RFC6443] describes how devices use the Internet to place emergency
calls and how Public Safety Answering Points (PSAPs) handle Internet
multimedia emergency calls natively. The exchange of multimedia
traffic for emergency services involves a SIP session establishment
starting with a SIP INVITE that negotiates various parameters for
that session.
In some cases, however, there is only application data to be conveyed
from the end devices to a PSAP or an intermediary. Examples of such
environments includes sensors issuing alerts, or certain types of
medical monitors. These messages may be one-shot alerts to emergency
authorities and do not require establishment of a session. These
type of interactions are called 'non-interactive emergency calls'.
In this document, we use the term "call" so that similarities between
non-interactive alerts and sessions with interactive media are more
obvious.
Non-Interactive emergency calls are similar to regular emergency
calls in the sense that they require the emergency indications,
emergency call routing functionality and may even have the same
location requirements. However, the communication interaction will
not lead to the exchange of interactive media, that is, Real-Time
Protocol packets, such as voice, video data or real-time text.
The Common Alerting Protocol (CAP) [cap] is a format for exchanging
emergency alerts and public warnings. CAP is mainly used for
conveying alerts and warnings between authorities and from
authorities to citizens/individuals. This document is concerned with
citizen to authority "alerts", where the alert is a call without any
interactive media.
This document describes a method of including a CAP message in a SIP
transaction by defining it as a block of "additional data" as defined
in [RFC7852]. The CAP message is included either by value (the CAP
message is in the body of the message, using a CID) or by reference
(a URI is included in the message, which when dereferenced returns
the CAP message). The additional data mechanism is also used to send
alert specific data beyond that available in the CAP message. This
document also describes how a SIP MESSAGE [RFC3428] transaction can
be used to send a non-interactive call.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
SIP is the Session Initiation Protocol [RFC3261]
PIDF-LO is Presence Information Data Format - Location Object, a data
structure for carrying location [RFC4119]
LoST is the Location To Service Translation protocol [RFC5222]
CID is Content InDirection [RFC2392]
CAP is the Common Alerting Protocol [cap]
PSAP is a Public Safety Answering Point, the call center for
emergency calls.
ESRP is an Emergency Services Routing Proxy, a type of SIP Proxy
Server used in some emergency services networks
3. Architectural Overview
This section illustrates two envisioned usage modes: targeted and
location-based emergency alert routing.
1. Emergency alerts containing only data are targeted to an
intermediary recipient responsible for evaluating the next steps.
These steps could include:
1. Sending a non-interactive call containing only data towards a
Public Safety Answering Point (PSAP);
2. Establishing a third-party initiated emergency call towards a
PSAP that could include audio, video, and data.
2. Emergency alerts may be targeted to a Service URN used for IP-
based emergency calls where the recipient is not known to the
originator. In this scenario, the alert may contain only data
(e.g., a CAP, Geolocation header field and one or more Call-Info
header fields containing Additional Data [RFC7852] in a SIP
MESSAGE).
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Figure 1 shows a deployment variant where a sensor is pre-configured
(using techniques outside the scope of this document) to issue an
alert to an aggregator that processes these messages and performs
whatever steps are necessary to appropriately react to the alert.
For example, a security firm may use different sensor inputs to
dispatch their security staff to a building they protect or to
initiate a third-party emergency call.
+------------+ +------------+
| Sensor | | Aggregator |
| | | |
+---+--------+ +------+-----+
| |
Sensors |
trigger |
emergency |
alert |
| SIP MESSAGE with CAP |
|----------------------------->|
| |
| Aggregator
| processes
| emergency
| alert
| SIP 200 (OK) |
|<-----------------------------|
| |
| |
Figure 1: Targeted Emergency Alert Routing
In Figure 2 a scenario is shown whereby the alert is routed using
location information and a Service URN. An emergency services
routing proxy (ESRP) may use LoST (a protocol defined by [RFC5222]
which translates a location to a URI used to route an emergency call)
to determine the next hop proxy to route the alert message to. A
possible receiver is a PSAP and the recipient of the alert may be a
call taker. In the generic case, there is very likely no prior
relationship between the originator and the receiver, e.g., a PSAP.
A PSAP, for example, is likely to receive and accept alerts from
entities it has no previous relationship with. This scenario
corresponds to the classic emergency services use case and the
description in [RFC6881] is applicable. In this use case, the only
difference between an emergency call and an emergency non-interactive
call is that the former uses INVITE, creates a session, and
negotiates one or more media streams, while the latter uses MESSAGE,
does not create a session, and does not have interactive media.
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+----------+ +----------+ +-----------+
|Sensor or | | ESRP | | PSAP |
|Aggregator| | | | |
+----+-----+ +---+------+ +----+------+
| | |
Sensors | |
trigger | |
emergency | |
alert | |
| | |
| | |
| SIP MESSAGE w/CAP | |
| (including Service URN, |
| such as urn:service:sos) |
|------------------>| |
| | |
| ESRP performs |
| emergency alert |
| routing |
| | MESSAGE with CAP |
| | (including identity info) |
| |----------------------------->|
| | |
| | PSAP
| | processes
| | emergency
| | alert
| | SIP 200 (OK) |
| |<-----------------------------|
| | |
| SIP 200 (OK) | |
|<------------------| |
| | |
| | |
Figure 2: Location-Based Emergency Alert Routing
4. Protocol Specification
4.1. CAP Transport
A CAP message may be sent in the initial message of any SIP
transaction. However, this document only addresses sending a CAP
message in a SIP MESSAGE transaction for a one-shot, non-interactive
emergency call. Behavior with other transactions is not defined.
The CAP message is included in a SIP message as an additional-data
block [RFC7852]. Accordingly, it is introduced to the SIP message
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with a Call-Info header field with a purpose of
"EmergencyCallData.cap". The header field may contain a URI that is
used by the recipient (or in some cases, an intermediary) to obtain
the CAP message. Alternatively, the Call-Info header field may
contain a Content Indirect url [RFC2392] and the CAP message included
in the body of the message. In the latter case, the CAP message is
located in a MIME block of the type 'application/
emergencyCallData.cap+xml'.
If the SIP server does not support the functionality required to
fulfill the request then a 501 Not Implemented will be returned as
specified in [RFC3261]. This is the appropriate response when a User
Agent Server (UAS) does not recognize the request method and is not
capable of supporting it for any user.
The 415 Unsupported Media Type error will be returned as specified in
[RFC3261] if the SIP server is refusing to service the request
because the message body of the request is in a format not supported
by the server for the requested method. The server MUST return a
list of acceptable formats using the Accept, Accept-Encoding, or
Accept-Language header fields, depending on the specific problem with
the content.
4.2. Profiling of the CAP Document Content
The usage of CAP MUST conform to the specification provided with
[cap]. For usage with SIP the following additional requirements are
imposed:
sender: The following restrictions and conditions apply to setting
the value of the <sender> element:
* Originator is a SIP entity, Author indication irrelevant: When
the alert was created by a SIP-based originator and it is not
useful to be explicit about the author of the alert, then the
<sender> element MUST be populated with the SIP URI of the user
agent.
* Originator is a non-SIP entity, Author indication irrelevant:
When the alert was created by a non-SIP based entity and the
identity of this original sender is to be preserved, then this
identity MUST be placed into the <sender> element. In this
situation it is not useful to be explicit about the author of
the alert. The specific type of identity being used will
depend on the technology used by the original originator.
* Author indication relevant: When the author is different from
the actual originator of the message and this distinction
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should be preserved, then the <sender> element MUST NOT contain
the SIP URI of the user agent.
incidents: The <incidents> element MUST be present. This incident
identifier MUST be chosen in such a way that it is unique for a
given <sender, expires, incidents> combination. Note that the
<expires> element is optional and may not be present.
scope: The value of the <scope> element MAY be set to "Private" if
the alert is not meant for public consumption. The <addresses>
element is, however, not used by this specification since the
message routing is performed by SIP and the respective address
information is already available in other SIP header fields.
Populating information twice into different parts of the message
may lead to inconsistency.
parameter: The <parameter> element MAY contain additional
information specific to the sender, conforming to the CAP message
syntax.
area: It is RECOMMENDED to omit this element when constructing a
message. If the CAP message already contains an <area> element,
then the specified location information SHOULD be copied into a
PIDF-LO structure (the data format for location used by emergency
calls on the Internet) referenced by the SIP 'Geolocation' header
field. If there is a need to copy the PIDF-LO structure
referenced by 'geolocation' to <area>, implementers must be aware
that <area> is limited to a circle or polygon, and conversion of
other shapes will be required. Points SHOULD be converted to a
circle with a radius equal to the uncertainty of the point. Arc-
bands and ellipses SHOULD be converted to an equivalent polygon.
3D locations SHOULD be converted to their equivalent 2D forms.
4.3. Sending a non-interactive Emergency Call
A non-interactive emergency call is sent using a SIP MESSAGE
transaction with a CAP URI or body part as described above in a
manner similar to how an emergency call with interactive media is
sent, as described in [RFC6881]. The MESSAGE transaction does not
create a session nor establish interactive media streams, but
otherwise, the header content of the transaction, routing, and
processing of non-interactive calls are the same as those of other
emergency calls.
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5. Error Handling
This section defines a new error response code and a header field for
additional information.
5.1. 425 (Bad Alert Message) Response Code
This SIP extension creates a new location-specific response code,
defined as follows:
425 (Bad Alert Message)
The 425 response code is a rejection of the request due to its
included alert content, indicating that it was malformed or not
satisfactory for the recipient's purpose.
A SIP intermediary can also reject an alert it receives from a User
Agent (UA) when it detects that the provided alert is malformed.
Section 5.2 describes an AlertMsg-Error header field with more
details about what was wrong with the alert message in the request.
This header field MUST be included in the 425 response.
It is only appropriate to generate a 425 response when the responding
entity has no other information in the request that is usable by the
responder.
A 425 response code MUST NOT be sent in response to a request that
lacks an alert message, as the user agent in that case may not
support this extension.
A 425 response is a final response within a transaction, and MUST NOT
terminate an existing dialog.
5.2. The AlertMsg-Error Header Field
The AlertMsg-Error header field provides additional information about
what was wrong with the original request. In some cases the provided
information will be used for debugging purposes.
The AlertMsg-Error header field has the following ABNF [RFC5234]:
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message-header /= AlertMsg-Error
; (message-header from 3261)
AlertMsg-Error = "AlertMsg-Error" HCOLON
ErrorValue
ErrorValue = error-code
*(SEMI error-params)
error-code = 1*3DIGIT
error-params = error-code-text
/ generic-param ; from RFC3261
error-code-text = "code" EQUAL quoted-string ; from RFC3261
HCOLON, SEMI, and EQUAL are defined in [RFC3261]. DIGIT is defined
in [RFC5234].
The AlertMsg-Error header field MUST contain only one ErrorValue to
indicate what was wrong with the alert payload the recipient
determined was bad.
The ErrorValue contains a 3-digit error code indicating what was
wrong with the alert in the request. This error code has a
corresponding quoted error text string that is human readable. The
text string is OPTIONAL, but RECOMMENDED for human readability,
similar to the string phrase used for SIP response codes. The
strings in this document are recommendations, and are not
standardized -- meaning an operator can change the strings -- but
MUST NOT change the meaning of the error code. Similar to how RFC
3261 specifies, there MUST NOT be more than one string per error
code.
The AlertMsg-Error header field MAY be included in any response if an
alert message was in the request part of the same transaction. For
example, a UA includes an alert in a MESSAGE to a PSAP. The PSAP can
accept this MESSAGE, thus creating a dialog, even though its UA
determined that the alert message contained in the MESSAGE was bad.
The PSAP merely includes an AlertMsg-Error header field value in the
200 OK to the MESSAGE, thus informing the UA that the MESSAGE was
accepted but the alert provided was bad.
If, on the other hand, the PSAP cannot accept the transaction without
a suitable alert message, a 425 response is sent.
A SIP intermediary that requires the UA's alert message in order to
properly process the transaction may also sends a 425 with an
AlertMsg-Error code.
This document defines an initial list of AlertMsg-Error values for
any SIP response, including provisional responses (other than 100
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Trying) and the new 425 response. There MUST be no more than one
AlertMsg-Error code in a SIP response.
AlertMsg-Error: 100 ; code="Cannot Process the Alert Payload"
AlertMsg-Error: 101 ; code="Alert Payload was not present or could
not be found"
AlertMsg-Error: 102 ; code="Not enough information to determine the
purpose of the alert"
AlertMsg-Error: 103 ; code="Alert Payload was corrupted"
Additionally, if an entity cannot or chooses not to process the alert
message from a SIP request, a 500 (Server Internal Error) SHOULD be
used with or without a configurable Retry-After header field.
6. Call Backs
This document does not describe any method for the recipient to call
back the sender of a non-interactive call. Usually, these alerts are
sent by automata, which do not have a mechanism to receive calls of
any kind. The identifier in the 'From' header field may be useful to
obtain more information, but any such mechanism is not defined in
this document. The CAP message may contain related contact
information for the sender.
7. Handling Large Amounts of Data
It is not atypical for sensors to have large quantities of data that
they may wish to send. Including large amounts of data (tens of
kilobytes) in a MESSAGE is not advisable, because SIP entities are
usually not equipped to handle very large messages. In such cases,
the sender SHOULD make use of the by-reference mechanisms defined in
[RFC7852], which involves making the data available via HTTPS (either
at the originator or at another entity), placing a URI to the data in
the 'Call-Info' header field, and the recipient uses HTTPS to
retrieve the data. The CAP message itself can be sent by-reference
using this mechanism, as well as any or all of the Additional Data
blocks that may contain sensor-specific data.
8. Example
The following example shows a CAP document indicating a BURGLARY
alert issued by a sensor called 'sensor1@example.com'. The location
of the sensor can be obtained from the attached location information
provided via the 'geolocation' header field contained in the SIP
MESSAGE structure. Additionally, the sensor provided some data along
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with the alert message, using proprietary information elements
intended only to be processed by the receiver, a SIP entity acting as
an aggregator.
MESSAGE sip:aggregator@example.com SIP/2.0
Via: SIP/2.0/TCP sensor1.example.com;branch=z9hG4bK776sgdkse
Max-Forwards: 70
From: sip:sensor1@example.com;tag=49583
To: sip:aggregator@example.com
Call-ID: asd88asd77a@2001:DB8:0:0FF
Geolocation: <cid:abcdef@example.com>
;routing-allowed=yes
Supported: geolocation
Accept: application/pidf+xml,application/EmergencyCallData.cap+xml
CSeq: 1 MESSAGE
Call-Info: cid:abcdef2@example.com;purpose=EmergencyCallData.cap
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/EmergencyCallData.cap+xml
Content-ID: <abcdef2@example.com>
Content-Disposition: by-reference;handling=optional
<?xml version="1.0" encoding="UTF-8"?>
<alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
<identifier>S-1</identifier>
<sender>sip:sensor1@example.com</sender>
<sent>2008-11-19T14:57:00-07:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Private</scope>
<incidents>abc1234</incidents>
<info>
<category>Security</category>
<event>BURGLARY</event>
<urgency>Expected</urgency>
<certainty>Likely</certainty>
<severity>Moderate</severity>
<senderName>SENSOR 1</senderName>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE1</valueName>
<value>123</value>
</parameter>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE2</valueName>
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<value>TRUE</value>
</parameter>
</info>
</alert>
--boundary1
Content-Type: application/pidf+xml
Content-ID: <abcdef2@example.com>
Content-Disposition: by-reference;handling=optional
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp=
"urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="sensor">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--
Figure 3: Example Message conveying an Alert to an aggregator
The following shows the same CAP document sent as a non-interactive
emergency call towards a PSAP.
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MESSAGE urn:service:sos SIP/2.0
Via: SIP/2.0/TCP sip:aggreg.1.example.com;branch=z9hG4bK776abssa
Max-Forwards: 70
From: sip:aggregator@example.com;tag=32336
To: 112
Call-ID: asdf33443a@example.com
Route: sip:psap1.example.gov
Geolocation: <cid:abcdef@example.com>
;routing-allowed=yes
Supported: geolocation
Accept: application/pidf+xml,application/EmergencyCallData.cap+xml
Call-info: cid:abcdef2@example.com;purpose=EmergencyCallData.cap
CSeq: 1 MESSAGE
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/EmergencyCallData.cap+xml
Content-ID: <abcdef2@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
<identifier>S-1</identifier>
<sender>sip:sensor1@example.com</sender>
<sent>2008-11-19T14:57:00-07:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Private</scope>
<incidents>abc1234</incidents>
<info>
<category>Security</category>
<event>BURGLARY</event>
<urgency>Expected</urgency>
<certainty>Likely</certainty>
<severity>Moderate</severity>
<senderName>SENSOR 1</senderName>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE1</valueName>
<value>123</value>
</parameter>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE2</valueName>
<value>TRUE</value>
</parameter>
</info>
</alert>
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--boundary1
Content-Type: application/pidf+xml
Content-ID: <abcdef2@example.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp=
"urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="sensor">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--
Figure 4: Example Message conveying an Alert to a PSAP
9. Security Considerations
This section discusses security considerations when SIP user agents
issue emergency alerts utilizing MESSAGE and CAP. Location specific
threats are not unique to this document and are discussed in
[RFC7378] and [RFC6442].
The ECRIT emergency services architecture [RFC6443] considers classic
individual-to-authority emergency calling where the identity of the
emergency caller does not play a role at the time of the call
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establishment itself, i.e., a response to the emergency call does not
depend on the identity of the caller. In the case of emergency
alerts generated by devices such as sensors, the processing may be
different in order to reduce the number of falsely generated
emergency alerts. Alerts could get triggered based on certain sensor
input that might have been caused by factors other than the actual
occurrence of an alert-relevant event. For example, a sensor may
simply be malfunctioning. For this reason, not all alert messages
are directly sent to a PSAP, but rather may be pre-processed by a
separate entity, potentially under supervision by a human, to filter
alerts and potentially correlate received alerts with others to
obtain a larger picture of the ongoing situation.
In any case, for alerts initiated by sensors, the identity could play
an important role in deciding whether to accept or ignore an incoming
alert message. With the scenario shown in Figure 1 it is very likely
that only authorized sensor input will be processed. For this
reason, it needs to be possible to refuse to accept alert messages
from an unknown origin. Two types of information elements can be
used for this purpose:
1. SIP itself provides security mechanisms that allow the
verification of the originator's identity. These mechanisms can
be re-used, such as P-Asserted-Identity [RFC3325] or SIP Identity
[RFC8224]. The latter provides a cryptographic assurance while
the former relies on a chain of trust model.
2. CAP provides additional security mechanisms and the ability to
carry further information about the sender's identity.
Section 3.3.4.1 of [cap] specifies the signing algorithms of CAP
documents.
In addition to the desire to perform identity-based access control,
the classic communication security threats need to be considered,
including integrity protection to prevent forgery or replay of alert
messages in transit. To deal with replay of alerts, a CAP document
contains the mandatory <identifier>, <sender>, <sent> elements and an
optional <expire> element. Together, these elements make the CAP
document unique for a specific sender and provide time restrictions.
An entity that has already received a CAP message within the
indicated timeframe is able to detect a replayed message and, if the
content of that message is unchanged, then no additional security
vulnerability is created. Additionally, it is RECOMMENDED to make
use of SIP security mechanisms, such as SIP Identity [RFC8224], to
tie the CAP message to the SIP message. To provide protection of the
entire SIP message exchange between neighboring SIP entities, the
usage of TLS is REQUIRED.
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Note that none of the security mechanism in this document protect
against a compromised sensor sending crafted alerts. Privacy
provided for any emergency calls, including non-interactive messages,
is subject to local regulations.
10. IANA Considerations
10.1. Registration of the 'application/EmergencyCallData.cap+xml' MIME
type
To: ietf-types@iana.org
Subject: Registration of MIME media type application/
EmergencyCallData.cap+xml
MIME media type name: application
MIME subtype name: cap+xml
Required parameters: (none)
Optional parameters: charset; Indicates the character encoding of
enclosed XML. Default is UTF-8 [RFC3629].
Encoding considerations: Uses XML, which can employ 8-bit
characters, depending on the character encoding used. See
[RFC7303], Section 3.2.
Security considerations: This content type is designed to carry
payloads of the Common Alerting Protocol (CAP). RFC XXX [Replace
by the RFC number of this specification] discusses security
considerations for this.
Interoperability considerations: This content type provides a way to
convey CAP payloads.
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Published specification: RFC XXX [Replace by the RFC number of this
specification].
Applications which use this media type: Applications that convey
alerts and warnings according to the CAP standard.
Additional information: OASIS has published the Common Alerting
Protocol at http://www.oasis-open.org/committees/
documents.php&wg_abbrev=emergency
Person and email address to contact for further information: Hannes
Tschofenig, hannes.tschofenig@gmx.net
Intended usage: Limited use
Author/Change controller: IETF ECRIT working group
Other information: This media type is a specialization of
application/xml [RFC7303], and many of the considerations
described there also apply to application/cap+xml.
10.2. IANA Registration of 'cap' Additional Data Block
This document registers a new block type in the sub-registry called
'Emergency Call Data Types' of the Emergency Call Additional Data
Registry defined in [RFC7852]. The token is "cap", the Data About is
"The Call" and the reference is this document.
10.3. IANA Registration for 425 Response Code
In the SIP Response Codes registry, the following is added
Reference: RFC-XXXX (i.e., this document)
Response code: 425 (recommended number to assign)
Default reason phrase: Bad Alert Message
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Registry:
Response Code Reference
------------------------------------------ ---------
Request Failure 4xx
425 Bad Alert Message [this doc]
This SIP Response code is defined in Section 5.
10.4. IANA Registration of New AlertMsg-Error Header Field
The SIP AlertMsg-error header field is created by this document, with
its definition and rules in Section 5, to be added to the IANA
Session Initiation Protocol (SIP) Parameters registry with two
actions:
1. Update the Header Fields registry with
Registry:
Header Name compact Reference
----------------- ------- ---------
AlertMsg-Error [this doc]
2. In the portion titled "Header Field Parameters and Parameter
Values", add
Predefined
Header Field Parameter Name Values Reference
----------------- ------------------- ---------- ---------
AlertMsg-Error code yes [this doc]
10.5. IANA Registration for the SIP AlertMsg-Error Codes
This document creates a new registry for SIP, called "AlertMsg-Error
Codes". AlertMsg-Error codes provide reasons for an error discovered
by a recipient, categorized by the action to be taken by the error
recipient. The initial values for this registry are shown below.
Registry Name: AlertMsg-Error Codes
Reference: [this doc]
Registration Procedures: Specification Required
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Code Default Reason Phrase Reference
---- --------------------------------------------------- ---------
100 "Cannot Process the Alert Payload" [this doc]
101 "Alert Payload was not present or could not be found" [this doc]
102 "Not enough information to determine
the purpose of the alert" [this doc]
103 "Alert Payload was corrupted" [this doc]
Details of these error codes are in Section 5.
11. Acknowledgments
The authors would like to thank the participants of the Early Warning
adhoc meeting at IETF#69 for their feedback. Additionally, we would
like to thank the members of the NENA Long Term Direction Working
Group for their feedback.
Additionally, we would like to thank Martin Thomson, James
Winterbottom, Shida Schubert, Bernard Aboba, Marc Linsner, Christer
Holmberg and Ivo Sedlacek for their review comments.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[cap] Jones, E. and A. Botterell, "Common Alerting Protocol v.
1.2", October 2005, <https://docs.oasis-
open.org/emergency/cap/v1.2/CAP-v1.2-os.pdf>.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
<https://www.rfc-editor.org/info/rfc2392>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
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[RFC3428] Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
Huitema, C., and D. Gurle, "Session Initiation Protocol
(SIP) Extension for Instant Messaging", RFC 3428,
DOI 10.17487/RFC3428, December 2002,
<https://www.rfc-editor.org/info/rfc3428>.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, DOI 10.17487/RFC4119, December 2005,
<https://www.rfc-editor.org/info/rfc4119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
DOI 10.17487/RFC7303, July 2014,
<https://www.rfc-editor.org/info/rfc7303>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC6442] Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
for the Session Initiation Protocol", RFC 6442,
DOI 10.17487/RFC6442, December 2011,
<https://www.rfc-editor.org/info/rfc6442>.
[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in Support of Emergency Calling",
BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013,
<https://www.rfc-editor.org/info/rfc6881>.
[RFC7852] Gellens, R., Rosen, B., Tschofenig, H., Marshall, R., and
J. Winterbottom, "Additional Data Related to an Emergency
Call", RFC 7852, DOI 10.17487/RFC7852, July 2016,
<https://www.rfc-editor.org/info/rfc7852>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[RFC7378] Tschofenig, H., Schulzrinne, H., and B. Aboba, Ed.,
"Trustworthy Location", RFC 7378, DOI 10.17487/RFC7378,
December 2014, <https://www.rfc-editor.org/info/rfc7378>.
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[RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 8224,
DOI 10.17487/RFC8224, February 2018,
<https://www.rfc-editor.org/info/rfc8224>.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
DOI 10.17487/RFC3325, November 2002,
<https://www.rfc-editor.org/info/rfc3325>.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, DOI 10.17487/RFC5222, August 2008,
<https://www.rfc-editor.org/info/rfc5222>.
[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
"Framework for Emergency Calling Using Internet
Multimedia", RFC 6443, DOI 10.17487/RFC6443, December
2011, <https://www.rfc-editor.org/info/rfc6443>.
Authors' Addresses
Brian Rosen
470 Conrad Dr
Mars, PA 16046
US
Phone:
Email: br@brianrosen.net
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
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Hannes Tschofenig
ARM Limited
Austria
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Randall Gellens
Core Technology Consulting
Email: rg+ietf@coretechnologyconsulting.com
URI: http://www.coretechnologyconsulting.com
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