ECRIT B. Rosen
Internet-Draft NeuStar, Inc.
Intended status: Experimental H. Schulzrinne
Expires: April 28, 2011 Columbia U.
H. Tschofenig
Nokia Siemens Networks
October 25, 2010
Common Alerting Protocol (CAP) based Data-Only Emergency Alerts using
the Session Initiation Protocol (SIP)
draft-ietf-ecrit-data-only-ea-01.txt
Abstract
The Common Alerting Protocol (CAP) is a document format for
exchanging emergency alerts and public warnings. CAP is mainly used
for conveying alerts and warnings between authorities and from
authorities to citizen/individuals. This document describes how
data-only emergency alerts allow devices to issue alerts using the
CAP document format.
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 http://datatracker.ietf.org/drafts/current/.
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 April 28, 2011.
Copyright Notice
Copyright (c) 2010 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Rosen, et al. Expires April 28, 2011 [Page 1]
Internet-Draft Data-Only Emergency Alerts October 2010
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 . . . . . . . . . . . . . . . . . . . . 5
4. Protocol Specification . . . . . . . . . . . . . . . . . . . . 7
4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Profiling of the CAP Document Content . . . . . . . . . . 7
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Forgery . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 10
6.3. Injecting False Alerts . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7.1. Registration of the
'application/common-alerting-protocol+xml' MIME type . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Rosen, et al. Expires April 28, 2011 [Page 2]
Internet-Draft Data-Only Emergency Alerts October 2010
1. Introduction
The Common Alerting Protocol (CAP) [cap] is an XML document format
for exchanging emergency alerts and public warnings. CAP is mainly
used for conveying alerts and warnings between authorities and from
authorities to citizen/individuals. This document describes how
data-only emergency calls are able to utilize the same CAP document
format.
Data-only emergency alerts are similar to regular emergency calls in
the sense that they require emergency call routing functionality and
may even have the same location requirements. On the other hand, the
initial communication interaction will not lead to the establishment
of a voice or video channel.
Based on the deployment experience with non-IP based systems we
distinguish between two types of environments, namely (1) data-only
emergency alerts that are targeted directly to a recipient
responsible for evaluating the alerts and for taking the necessary
steps, including triggering an emergency call towards a Public Safety
Answering Point (PSAP) and (2) alerts that are targeted to a Service
URN as used for regular IP-based emergency calls where the recipient
is not known to the originator. We describe these two cases in more
detail in Section 3.
Rosen, et al. Expires April 28, 2011 [Page 3]
Internet-Draft Data-Only Emergency Alerts October 2010
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document utilizes terminology introduced in
[I-D.ietf-atoca-requirements].
Rosen, et al. Expires April 28, 2011 [Page 4]
Internet-Draft Data-Only Emergency Alerts October 2010
3. Architectural Overview
This section illustrates two envisioned usage modes; targeted and
location-based emergency alert routing. Figure 1 shows a deployment
variant where a sensor, as the author and originator of the alert, is
pre-configured (using techniques outside the scope of this document)
to issue an alert to a receiver or an aggregator, a special form of
mediator, that processes these messages and performs whatever steps
are necessary to appropriately react on the alert. For example, a
security firm may use different sensor inputs to dispatch their
security staff to a building they protect.
+------------+ +------------+
| Sensor | | Aggregator |
| | | |
+---+--------+ +------+-----+
| |
Sensors |
trigger |
emergency |
alert |
| MESSAGE with CAP |
|----------------------------->|
| |
| Aggregator
| processes
| emergency
| alert
| 200 (OK) |
|<-----------------------------|
| |
| |
Figure 1: Targeted Emergency Alert Routing
In Figure 2 a scenario is shown whereby the alert is routed using
location information and the Service URN. In case the LoST
resolution is done at an emergency services routing proxy rather than
at the entity issuing the alert since it may not know the address of
the receiver. A possible receiver is a PSAP and the recipient of the
alert may be call taker. In the generic case, there is very likely
no prior relationship between the originator and the receiver, e.g.
PSAP. A PSAP, for example, is likely to receive and accept alerts
from entities it cannot authorize. This scenario corresponds more to
the classical emergency services use case and the description in
[I-D.ietf-ecrit-phonebcp] is applicable.
Rosen, et al. Expires April 28, 2011 [Page 5]
Internet-Draft Data-Only Emergency Alerts October 2010
+-----------+ +----------+
+--------+ | SIP Proxy | | PSAP as |
| Sensor | | as Relay | | Receiver |
+---+----+ +---+-------+ +---+------+
| | |
Sensors | |
trigger | |
emergency | |
alert | |
| | |
| | |
| MESSAGE with CAP | |
| (including Service URN, |
| such as urn:service:sos) |
|------------------->| |
| | |
| SIP Proxy performs |
| emergency alert |
| routing |
| | MESSAGE with CAP |
| | (including identity info) |
| |----------------------------->|
| | |
| | PSAP
| | processes
| | emergency
| | alert
| | 200 (OK) |
| |<-----------------------------|
| | |
| 200 (OK) | |
|<-------------------| |
| | |
| | |
Figure 2: Location-Based Emergency Alert Routing
Rosen, et al. Expires April 28, 2011 [Page 6]
Internet-Draft Data-Only Emergency Alerts October 2010
4. Protocol Specification
4.1. CAP Transport
Since alerts structured via CAP require a "push" medium, they SHOULD
be sent via the SIP MESSAGE. The MIME type is set to 'application/
common-alerting-protocol+xml'.
Alternatively, the SIP PUBLISH mechanism or other SIP messages
could be used. However, the usage of SIP MESSAGE is a simple
enough approach from an implementation point of view.
4.2. Profiling of the CAP Document Content
The usage of CAP MUST conform to the specification provided with
[cap]. For the usage with SIP the following additional requirements
are imposed:
sender: When the CAP was created by a SIP-based entity then the
element MUST be populated with the SIP URI of that entity.
incidents: The <incidents> element MUST be present whenever there is
a possibility that alert information needs to be updated. The
initial message will then contain an incident identifier carried
in the <incidents> element. 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 MUST be set to "private" as
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 the geolocation header.
Populating location information twice into different parts of the
message can quickly lead to inconsistency.
parameter: The <parameter> element MAY contain additional
information specific to the sensor.
area: It is RECOMMENDED to omit this element when constructing a
message. In case that the CAP message already contained an <area>
element then the specified location information MUST be copied
into the PIDF-LO structure of the geolocation header element.
Rosen, et al. Expires April 28, 2011 [Page 7]
Internet-Draft Data-Only Emergency Alerts October 2010
5. Example
Figure 3 shows a CAP document indicating a BURLARY alert issued by a
sensor with the identity 'sensor1@domain.com'. The location of the
sensor can be obtained from the attached geolocation information
provided via the geolocation header contained in the SIP MESSAGE
structure. Additionally, the sensor provided some data long with the
alert message using proprietary information elements only to be
processed by the receiver, a SIP entity acting as an aggregator.
This example reflects the description in Figure 1.
MESSAGE sip:aggregator@domain.com SIP/2.0
Via: SIP/2.0/TCP sensor1.domain.com;branch=z9hG4bK776sgdkse
Max-Forwards: 70
From: sip:sensor1@domain.com;tag=49583
To: sip:aggregator@domain.com
Call-ID: asd88asd77a@1.2.3.4
Geolocation: <cid:abcdef@domain.com>
;routing-allowed=yes
Supported: geolocation
Accept: application/pidf+xml, application/common-alerting-protocol+xml
CSeq: 1 MESSAGE
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: common-alerting-protocol+xml
Content-ID: <abcdef2@domain.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@domain.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>
Rosen, et al. Expires April 28, 2011 [Page 8]
Internet-Draft Data-Only Emergency Alerts October 2010
<parameter>
<valueName>SENSOR-DATA-NAMESPACE1</valueName>
<value>123</value>
</parameter>
<parameter>
<valueName>SENSOR-DATA-NAMESPACE2</valueName>
<value>TRUE</value>
</parameter>
</info>
</alert>
--boundary1
Content-Type: application/pidf+xml
Content-ID: <abcdef2@domain.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:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
entity="pres:sensor1@domain.com">
<tuple id="12345">
<dm:device id="sensor1">
<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>
<gp:retransmission-allowed>yes
</gp:retransmission-allowed>
<gp:retention-expiry>2010-07-30T20:00:00Z
</gp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-07-28T20:57:29Z</dm:timestamp>
</dm:device>
</tuple>
</presence>
--boundary1--
Figure 3: Example Message conveying an Alert
Rosen, et al. Expires April 28, 2011 [Page 9]
Internet-Draft Data-Only Emergency Alerts October 2010
6. Security Considerations
This section discusses security considerations when using SIP to make
data-only emergency alerts utilizing CAP. Location specific threats
are not unique to this document and the discussion in
[I-D.ietf-ecrit-trustworthy-location].
6.1. Forgery
Threat:
An adversary could forge or alter a CAP document to report false
emergency alarms.
Countermeasures:
To avoid this kind of attack, the entities must assure that proper
mechanisms for protecting the CAP documents are employed, e.g.,
signing the CAP document itself. Section 3.3.2.1 of [cap]
specifies the signing of CAP documents. This does not protect
against a legitimate sensor sending phrank alerts after being
compromised.
6.2. Replay Attack
Threat:
An adversary could eavesdrop alerts and reply them at a later
time.
Countermeasures:
A CAP document contains the mandatory <identifier>, <sender>,
<sent> elements and an optional <expire> element. These
attributes make the CAP document unique for a specific sender and
provide time restrictions. An entity that has received a CAP
message already 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 [RFC4474], to tie the CAP message
to the SIP message.
Rosen, et al. Expires April 28, 2011 [Page 10]
Internet-Draft Data-Only Emergency Alerts October 2010
6.3. Injecting False Alerts
Threat:
When an entity receives a CAP message it has to determine whether
the entity distributing the CAP messages is genuine to avoid
accepting messages that are injected by adversaries. In scenario
Countermeasures:
For some types of data-only emergency calls author/originator and
the receiver/recipient have a relationship with each other and
hence it is possible (using cryptographic techniques) to verify
whether a message was indeed issued by an authorized entity.
Figure 1 is such an environment. Standard SIP security mechanisms
can be re-used for this purpose. For example, identity based
access control is a viable approach utilizing the asserted
identity of the alert originator using P-Asserted-Identity
[RFC3325] or SIP Identity [RFC4474].
There are, however, other types of data-only emergency calls where
there is no such relationship between the author/originator and
the receiver/recipient. Incoming alerts need to be treated more
carefully than multi-media emergency calls that contain additional
information, such as audio, to allow a call taker to sort out
phrank calls.
Rosen, et al. Expires April 28, 2011 [Page 11]
Internet-Draft Data-Only Emergency Alerts October 2010
7. IANA Considerations
7.1. Registration of the 'application/common-alerting-protocol+xml'
MIME type
To: ietf-types@iana.org
Subject: Registration of MIME media type application/ common-
alerting-protocol+xml
MIME media type name: application
MIME subtype name: common-alerting-protocol+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 RFC
3023 [RFC3023], Section 3.2.
Security considerations: This content type is designed to carry
payloads of the Common Alerting Protocol (CAP).
Interoperability considerations: This content type provides a way to
convey CAP payloads.
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.
Rosen, et al. Expires April 28, 2011 [Page 12]
Internet-Draft Data-Only Emergency Alerts October 2010
Additional information: OASIS has published the Common Alerting
Protocol at http://www.oasis-open.org/committees/
documents.php&wg_abbrev=emergency
Person & email address to contact for further information: Hannes
Tschofenig, Hannes.Tschofenig@nsn.com
Intended usage: Limited use
Author/Change controller: IETF SIPPING working group
Other information: This media type is a specialization of
application/xml RFC 3023 [RFC3023], and many of the considerations
described there also apply to application/
common-alerting-protocol+xml.
Rosen, et al. Expires April 28, 2011 [Page 13]
Internet-Draft Data-Only Emergency Alerts October 2010
8. 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.
Rosen, et al. Expires April 28, 2011 [Page 14]
Internet-Draft Data-Only Emergency Alerts October 2010
9. References
9.1. 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.
1.1", October 2005.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension
for Event State Publication", RFC 3903, October 2004.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[I-D.ietf-ecrit-trustworthy-location]
Tschofenig, H., Schulzrinne, H., and B. Aboba,
"Trustworthy Location Information",
draft-ietf-ecrit-trustworthy-location-01 (work in
progress), October 2010.
9.2. Informative References
[I-D.ietf-ecrit-phonebcp]
Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling",
draft-ietf-ecrit-phonebcp-15 (work in progress),
July 2010.
[I-D.ietf-atoca-requirements]
Schulzrinne, H., Norreys, S., Rosen, B., and H.
Tschofenig, "Requirements, Terminology and Framework for
Exigent Communications", draft-ietf-atoca-requirements-00
(work in progress), September 2010.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Rosen, et al. Expires April 28, 2011 [Page 15]
Internet-Draft Data-Only Emergency Alerts October 2010
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
Rosen, et al. Expires April 28, 2011 [Page 16]
Internet-Draft Data-Only Emergency Alerts October 2010
Authors' Addresses
Brian Rosen
NeuStar, Inc.
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
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Rosen, et al. Expires April 28, 2011 [Page 17]
