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Differences from draft-ietf-atoca-requirements-00.txt
ATOCA H. Schulzrinne
Internet-Draft Columbia University
Intended status: Informational S. Norreys
Expires: July 19, 2011 BT Group
B. Rosen
NeuStar, Inc.
H. Tschofenig
Nokia Siemens Networks
January 15, 2011
Requirements, Terminology and Framework for Exigent Communications
draft-ietf-atoca-requirements-01.txt
Abstract
Before, during and after emergency situations various agencies need
to provide information to a group of persons or to the public within
a geographical area. While many aspects of such systems are specific
to national or local jurisdictions, emergencies span such boundaries
and notifications need to reach visitors from other jurisdictions.
This document provides terminology, requirements and an architectural
description for protocols exchanging alerts between IP-based end
points.
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 July 19, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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
1.1. Classical Early Warning Situations . . . . . . . . . . . . 3
1.2. Exigent Communications . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Alert Delivery Architecture . . . . . . . . . . . . . . . . . 5
3.1. Responsible Actor Roles . . . . . . . . . . . . . . . . . 5
3.1.1. User Actors . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Message Handling Service (MHS) Actors . . . . . . . . 6
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Requirements for Alert Subscription . . . . . . . . . . . 9
4.2. Requirements for Alert Message Delivery . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
1.1. Classical Early Warning Situations
During large-scale emergencies, public safety authorities need to
reliably communicate with citizens in the affected areas, to provide
warnings, indicate whether citizens should evacuate and how, and to
dispel misinformation. Accurate information can reduce the impact of
such emergencies.
Traditionally, emergency alerting has used church bells, sirens,
loudspeakers, radio and television to warn citizens and to provide
information. However, techniques, such as sirens and bells, provide
limited information content; loud speakers cover only very small
areas and are often hard to understand, even for those not hearing
impaired or fluent in the local language. Radio and television offer
larger information volume, but are hard to target geographically and
do not work well to address the "walking wounded" or other
pedestrians. Both are not suitable for warnings, as many of those
needing the information will not be listening or watching at any
given time, particularly during work/school and sleep hours.
This problem has been illustrated by the London underground bombing
on July 7, 2006, as described in a government report [July2005]. The
UK authorities could only use broadcast media and could not, for
example, easily announce to the "walking wounded" where to assemble.
1.2. Exigent Communications
With the usage of the term 'Exigent Communications' this document
aims to generalize the concept of conveying alerts to IP-based
systems and at the same time to re-define the actors that participate
in the messaging communication. More precisely, exigent
communications is defined as:
Communication that requirs immediate action or remedy.
Information about the reason for action and details about the
steps that have to be taken are provided in the alert message.
An alert message (or warning message) is a cautionary advice about
something imminent (especially imminent danger or other
unpleasantness). In the context of exigent communication such an
alert message refers to a future, ongoing or past event as the
signaling exchange itself may relate to different stages of the
lifecycle of the event. The alert message itself, and not the
signaling protocol that convey it, provides sufficient context
about the specific state of the lifecycle the alert message refers
to.
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Communication typically occurs in two phases:
Subscription: In this step Recipients express their interest to
receive certain types of alerts and happens prior to the actual
delivery of the alert. This expression of interest may be in form
of an explicit communication step by having the Receiver sending a
subscription message potentially with an indication of the type of
alerts they are interested in, the duration of the subscription
and a number of other indicators. For example, parents may want
to be alerted of emergencies affecting the school attended by
their children and adult children may need to know about
emergencies affecting elderly parents. The subscription step may,
however, also happen outside the Internet communication
infrastructure but rather by the Recipient signing a contract and
thereby agreeing to receive certain alerts. Additionally, certain
subscriptions may happen without the Recipient's explicit consent
and without the Receiver sending a subscription. For example, a
Tsunami flood alert may be delievered to Recipients in case they
are located in a specific geographical area.
It is important to note that a protocol interaction initiated by
the Receiver may need to take place to subscribe to certain types
of alerts. In some other cases the subscription does not require
such interaction from the Receiver. Orthogonal to the need to
have a protocol interaction is the question of opt-in vs. opt-out.
This is a pure policy decision and largely outside the scope of a
technical specification.
Alert Delivery In this step the alert message is distributed to one
or multiple Receivers. The Receiver as a software module then
presents the alert message to the Receipient. The alert encoding
is accomplished via the Common Alerting Protocol (CAP) and such an
alert message contains useful information needed for dealing with
the imminent danger.
Note that alert Receivers as software modules may not necessarily
only be executed on end devices humans typically carry around, such
as mobile phones, Internet tablets, or laptops. Instead, alert
distribution may well directly communicate with displays in subway
stations, or electronic bill boards. When a Receiver obtains such an
alert then it may not necessarily need to interact with a human (as
the Recipient) but may instead use the alert as input to another
process to trigger automated behaviors, such as closing vents during
a chemical spill or activating sirens or other warning systems in
commercial buildings.
This document provides terminology, requirements and an architectural
description. Note that the requirements focus on the communication
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protocols for subscription and alert delivery rather than on the
content of the alert message itself. With the usage of CAP these
alert message content requirements are delegated to the authors and
originators of alerts.
2. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119], with the
important qualification that, unless otherwise stated, these terms
apply to the design of a protocol conveying warning messages, not its
implementation or application.
3. Alert Delivery Architecture
This section illustrates the roles useful for alert delivery.
3.1. Responsible Actor Roles
The communication system used for the dissemination of alert messages
builds on top of existing communication infrastructure. At the time
of writing this underlying communication infrastructure is the
Session Initiation Protocol (SIP) and the Extensible Messaging and
Presence Protocol (XMPP). These distributed services consist of a
variety of actors playing different roles. On a high level we
differentiate between the User, and the Message Handling Service
(MHS) actors. We will describe them in more detail below.
3.1.1. User Actors
Users are the sources and sinks of alert messages. We differentiate
between two types of users:
o Authors
o Recipients
From the user perspective, all alert message transfer activities are
performed by a monolithic Message Handling Service (MHS), even though
the actual service can be provided by many independent organizations.
3.1.1.1. Author
The Author is a human responsible for creating the alert message, its
contents, and its intended recipients, even though the exact list of
recipients may be unknown to the Author at the time of writing the
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alert message. The MHS transfers the alert message from the Author
and delivers it to the Recipients.
3.1.1.2. Recipient
The Recipient is a consumer of the delivered alert message. It is a
human reading the alert message.
3.1.2. Message Handling Service (MHS) Actors
The Message Handling Service (MHS) performs a single end-to-end
transfer of warning messages on behalf of the Author to reach the
Recipient. As a pragmatic heuristic MHS actors actors generate,
modify or look at only transfer data, rather than the entire message.
Figure 1 shows the relationships among transfer participants.
Although it shows the Originator as distinct from the Author and
Receiver as distinct from Recipient, each pair of roles usually has
the same actor. Transfers typically entail one or more Relays.
However, direct delivery from the Originator to Receiver is possible.
Delivery of warning messages within a single administrative boundary
usually only involve a single Relay.
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++==========++ ++===========++
|| Author || || Recipient ||
++====++====++ ++===========++
|| /\
|| ||
\/ ||
+----------+ +---++----+
| | | |
/-+----------+----------------------------+---------+---\
| | | Message Handling | | |
| |Originator| System (MHS) |Receiver | |
| | | | | |
| +---++-----+ +---------+ |
| || /\ |
| || || |
| \/ || |
| +---------+ +---------+ +-+--++---+ |
| | Relay +======-=>| Relay +=======>| Relay | |
| +---------+ +----++---+ +---------+ |
| || |
| || |
| \/ |
| +---------+ |
| | Gateway +--> |
| +---------+ |
\-------------------------------------------------------/
Legend: === and || lines indicate primary (possibly
indirect) transfers or roles
Figure 1: Relationships Among MHS Actors
3.1.2.1. Originator
The Originator ensures that a warning message is valid for transfer
and then submits it to a Relay. A message is valid if it conforms to
both communication and warning message encapsulation standards and
local operational policies. The Originator can simply review the
message for conformance and reject it if it finds errors, or it can
create some or all of the necessary information.
The Originator serves the Author and can be the same entity in
absence of a human crafting alert messages.
The Originator also performs any post-submission, Author-related
administrative tasks associated with message transfer and delivery.
Notably, these tasks pertain to sending error and delivery notices,
enforcing local policies, and dealing with messages from the Author
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that prove to be problematic for the Internet. The Originator is
accountable for the message content, even when it is not responsible
for it. The Author creates the message, but the Originator handles
any transmission issues with it.
3.1.2.2. Relay
The Relay performs MHS-level transfer-service routing and store-and-
forward, by transmitting or retransmitting the message to its
Recipients. The Relay may add history information (e.g., as
available with SIP History Info [RFC4244]) or security related
protection (e.g., as available with SIP Identity [RFC4474]) but does
not modify the envelope information or the message content semantics.
A Message Handling System (MHS) network consists of a set of Relays.
This MHS network is above any underlying packet-switching network
that might be used and below any Gateways.
3.1.2.3. Gateway
A Gateway is a hybrid of User and Relay that connects heterogeneous
communication infrastructures. Its purpose is to emulate a Relay and
the closer it comes to this, the better. A Gateway operates as a
User when it needs the ability to modify message content.
Differences between the different communication systems can be as
small as minor syntax variations, but they usually encompass
significant, semantic distinctions. Hence, the Relay function in a
Gateway presents a significant design challenge, if the resulting
performance is to be seen as nearly seamless. The challenge is to
ensure user-to-user functionality between the communication services,
despite differences in their syntax and semantics.
The basic test of Gateway design is whether an Author on one side of
a Gateway can send a useful warning message to a Recipient on the
other side, without requiring changes to any components in the
Author's or Receiver's communication service other than adding the
Gateway. To each of these otherwise independent services, the
Gateway appears to be a native participant.
3.1.2.4. Receiver
The Receiver performs final delivery or sends the warning message to
an alternate address. In case of warning messages it is typically
responsible for ensuring that the appropriate user interface
interactions are triggered to interact with the Recipient.
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4. Requirements
4.1. Requirements for Alert Subscription
The requirements listed below refer to the alert subscription phase.
Req-S1:
The protocol solution MUST allow a potential Recipient to indicate
the language used by alert messages.
Req-S2:
The protocol solution MUST allow a potential Recipient to express
the geographical area it wants to receive alerts about.
Req-S3:
The protocol solution MUST allow a potential Recipient to indicate
preferences about the type of alerts it wants to receive.
Req-S4:
The protocol solution MUST allow a potential Recipient to express
preference for certain media types. The support for different
media types depends on the content of the warning message but also
impacts the communication protocol. This functionality is, for
example, useful for hearing and vision impaired persons.
4.2. Requirements for Alert Message Delivery
The requirements listed below refer to the delivery of alerts.
Req-D1:
The protocol solution MUST allow delivery of alerts by utilizing
the lower layer infrastructure ensuring congestion control being
considered. Note that congestion does not only focus on over-
utilization of a network caused by a large number of alerts but
also in relationship with other traffic not related to exigent
communication. Network layer multicast, anycast or broadcast
mechanisms may be utilized. The topological network structure may
be used for efficient alert distribution.
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Req-D2:
The protocol solution MUST allow delivery of messages
simultaneously to a large audience.
Req-D3:
The protocol solution MUST be independent of the underlying link
layer technology.
Req-D4:
The protocol solution MUST allow targeting notifications to
specific individuals and to groups of individuals.
Req-D5:
The protocol solution MUST allow a Recipient to learn the identity
of the Author of the alert message.
5. IANA Considerations
This document does not require actions by IANA.
6. Security Considerations
Figure 1 shows the actors for delivering an alert message assuming
that a prior subscription has taken place already. The desired
security properties of an MHS for conveying alerts will depend on the
number of administrative domains involved. Each administrative
domain can have vastly different operating policies and trust-based
decision-making. One obvious example is the distinction between
alert messages that are exchanged within an closed group (such as
alert messages received by parents affecting the school attended by
their children) and alert messages that are exchanged between
independent organizations (e.g., in case of large scale disasters).
The rules for handling both types of communication architectures tend
to be quite different. That difference requires defining the
boundaries of each.
Operation of communication systems that are used to convey alert
messages are typically carried out by different providers (or
operators). Since each be in operated in an independent
administrative domain it is useful to consider administrative domain
boundaries in the description to facilitate discussion about designs,
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policies and operations that need to distinguish between internal
issues and external entities. Most significant is that the entities
communicating across administrative boundaries typically have the
added burden of enforcing organizational policies concerning external
communications. For example, routing alerts between administrative
domains can create requirements, such as needing to route alert
messages between organizational partners over specially trusted
paths.
The communication interactions are subject to the policies of that
domain, which cover concerns such as these:
o Reliability
o Access control
o Accountability
o Content evaluation, adaptation, and modification
Many communication system make the distinction of administrative
domains since they impact the requirements on security solutions.
However, with the distribution of alert messages a number of
additional security threats need to be addressed. Due to the nature
of alerts it is quite likely that end device implementations will
offer user interface enhancements to get the Recipients attention
whenever an alert arrives, which is an attractive property for
adversaries to exploit. Below we list the most important threats any
solution will have to deal with.
Originator Impersonation:
An attacker could then conceivably attempt to impersonate the
Originator of an alert message. This threat is particularly
applicable to those deployment environments where authorization
decisions are based on the identity of the Originator.
Alert Message Forgery:
An attacker could forge or alter an alert message in order to
convey custom messages to Recipients to get their immediate
attention.
Replay:
An attacker could obtain previously distributed alert messages and
to replay them at a later time in the hope that Recipients could
be tricked into believing they are fresh.
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Unauthorized Distribution:
When a Receiver receives an alert message it has to determine
whether the Author distributing the alert messages is genuine to
avoid accepting messages that are injected by malicious entities
with the potential desire to at least get the immediate attention
of the Recipient.
Amplification Attack:
An attacker may use the Message Handling System to inject a single
alert message for distribution that may then be instantly turned
into potentially millions of alert messages for distribution.
One important security challenge is related to authorization. When
an alert message arrives at the Receiver then certain security checks
may need to be performed to ensure that the alert message meets
certain criteria. The final consumer of the alert message is,
however, the Recipient - a human. From a security point of view the
work split between the Recipient and the Receiver for making the
authorization decision is important, particularly when an alert
message is rejected due to a failed security verfication by the
Receiver. False positives may be fatal but accepting every alert
message lowers the trustworthiness in the overall system.
7. Acknowledgments
This document re-uses text from [RFC5598]. The authors would like to
thank Dave Crocker for his work.
The authors would like to thank Martin Thomson, Carl Reed, Leopold
Murhammer, and Tony Rutkowski for their comments.
At IETF#79 the following persons provided feedback leading to changes
in this document: Keith Drage, Scott Bradner, Ken Carberg, Keeping
Li, Martin Thomson, Igor Faynberg, Mark Wood, Peter Saint-Andre.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009.
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8.2. Informative References
[July2005]
, ., "Report of the 7 July Review Committee, ISBN 1
85261 878 7", (PDF document), http://www.london.gov.uk/
assembly/reports/7july/report.pdf, June 2006.
[RFC4244] Barnes, M., "An Extension to the Session Initiation
Protocol (SIP) for Request History Information", RFC 4244,
November 2005.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
Authors' Addresses
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
Steve Norreys
BT Group
1 London Road
Brentwood, Essex CM14 4QP
UK
Phone: +44 1277 32 32 20
Email: steve.norreys@bt.com
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Brian Rosen
NeuStar, Inc.
470 Conrad Dr
Mars, PA 16046
US
Phone:
Email: br@brianrosen.net
Hannes Tschhofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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