Network Working Group K. Carlberg
Request for Comments: 3689 UCL
Category: Informational R. Atkinson
General Requirements for
Emergency Telecommunication Service (ETS)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document presents a list of general requirements in support of
Emergency Telecommunications Service (ETS). Solutions to these
requirements are not presented in this document. Additional
requirements pertaining to specific applications, or types of
applications, are to be specified in separate document(s).
Effective telecommunications capabilities can be imperative to
facilitate immediate recovery operations for serious disaster events,
such as, hurricanes, floods, earthquakes, and terrorist attacks.
Disasters can happen any time, any place, unexpectedly. Quick
response for recovery operations requires immediate access to any
public telecommunications capabilities at hand. These capabilities
include: conventional telephone, cellular phones, and Internet
access via online terminals, IP telephones, and wireless PDAs. The
commercial telecommunications infrastructure is rapidly evolving to
Internet-based technology. Therefore, the Internet community needs
to consider how it can best support emergency management and recovery
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 BCP 14, RFC 2119 .
The term label has been used for a number of years in various IETF
protocols. It is simply an identifier. It can be manifested in
the form of a numeric, alphanumeric value, or a specific bit
pattern, within a field of a packet header. The exact form is
dependent on the protocol in which it is used.
An example of a label can be found in RFC 3031; the Multiprotocol
Label Switching Architecture. Another example can be found in RFC
2597 (and updated by RFC 3260); a bit pattern for the Assured
Forwarding PHB group. This latter case is a type of label that
does not involve routing. Note that specification of labels is
outside the scope of this document. Further comments on labels
are discussed below in section 3.
1.2. Existing Emergency Related Standards
The following are standards from other organizations that are
specifically aimed at supporting emergency communications. Most
of these standards specify telephony mechanisms or define
telephony related labels.
Standard / Organization
1) T1.631 / ANSI
2) E.106 / ITU
3) F.706 / ITU
4) H.460.4 / ITU
5) I.255.3 / ITU
The first specifies an indicator for SS7 networks that signals the
need for a High Probability of Completion (HPC) service. This
indicator is termed National Security / Emergency Preparedness
(NS/EP) The T1.631 standard  is the basis for the U.S. Government
Emergency Telecommunications Service (GETS) .
The second standard describes functional capabilities for the Public
Switched Telephone Network (PSTN) to support International Emergency
Preparedness System (IEPS) . From the PSTN perspective, one can
view NS/EP as a standard with national boundaries, while IEPS is an
extension to international boundaries for telephony.
The third standard extends IEPS beyond the scope of telephony into
other forms that encompass multimedia .
The fourth and fifth standard focuses on a multi-level labeling
mechanism distinguishing emergency type traffic from that which is
not. The former case focuses on call signaling for H.323 networks
, while the latter has been applied for both SS7  and data
While the above standards are outside the scope of the IETF, they do
represent existing efforts in the area of emergency communications,
as opposed to conceptual of potential possibilities. They act as
example manifestations of Emergency Telecommunications Service (ETS).
One problem faced by the IEPREP working group entails how, and to
what degree, support for these standards are to be realized within
the Internet architecture and the existing suite of IETF standards
and associated working groups. This support could be in the form of
interoperability with corresponding IETF protocols.
A subsequent problem is to ensure that requirements associated with
potential support is not focused just on IP telephony applications.
The I-Am-Alive (IAA) database system is an example of an ETS type
application used in Japan that supports both signaled and non-
signaled access by users . It is a distributed database system
that provides registration, querying, and reply primitives to
participants during times of an emergency (e.g., an earthquake) so
that others can make an after-the-event determination about the
status of a person. In this case, a separate signaling protocol like
SIP is not always required to establish or maintain a connection.
Given the case where signaling is optional, requirements and
subsequent solutions that address these problems must not assume the
existence of signaling and must be able to support applications that
only have labels in data packets. These label(s) may be in various
places, such as the application or IP header.
This document defines a set of general system requirements to achieve
support for ETS and addressing the problem space presented in Section
1.3. In defining these requirements, we consider known systems such
as GETS and IAA that represent existing manifestations of emergency
related systems. These two examples also represent a broad spectrum
of characteristics that range from signaling & interactive non-
elastic applications to non-signaled & elastic applications.
We stress that ETS, and its associated requirements, is not the only
means of supporting authorized emergency communications. It is
simply an approach influenced by existing systems and standards.
Solutions to requirements are not defined. This document does not
specify protocol enhancements or specifications. Requirements for
specific types of applications that go beyond the general set stated
in section 3 are to be specified in other document(s). At the
current writing of this document,  has been written for the case
of IP telephony.
The current IEPREP charter stipulates that any proposed solution to
support ETS that responds to the requirements of this document are to
be developed in other working groups. We note that other specific
requirements (like that of IP telephony) may be defined as an
extension of the general requirements presented in section 3 below.
2.1. Out of Scope
While the problem space stated in section 1.3 includes standards
related to telephony, this document is meant to be broader in scope.
Hence, emulation of specific architectures, like the PSTN, or focus
on a specific application is out of scope. Further, the
specifications of requirements that are aimed at adhering to
regulations or laws of governments is also out of the scope of this
document. The focus of the IETF and its working groups is technical
positions that follow the architecture of the Internet.
Another item that is not in scope of this document is mandating
acceptance and support of the requirements presented in this
document. There is an expectation that business contracts, (e.g.,
Service Level Agreements), will be used to satisfy those requirements
that apply to service providers. Absence of an SLA implies best
effort service is provided.
3. General Requirements
These are general requirements that apply to authorized emergency
telecommunications service. The first requirement is presented as a
conditional one since not all applications use or are reliant on
IF signaling is to be used to convey the state or existence of
emergency, then signaling mechanism(s) MUST exist to carry
Labels may exist in various forms at different layers. They might
be carried as part of signaling, and/or as part of the header of a
data packet. Labels from different layers are NOT required to be
the same, but MAY be related to each other.
Policy MUST be kept separate from label(s). This topic has
generated a fair amount of debate, and so we provide additional
guidance from the following:
A set of labels may be defined as being related to each other.
Characteristics (e.g., drop precedence) may also be attributed to
these labels.  is an example of a related set of labels based
on a specific characteristic.
However, the mechanisms used to achieve a stated characteristic
MUST NOT be stated in the definition of a label. Local policy
determines mechanism(s) used to achieve or support a specific
characteristic. This allows for the possibility of different
mechanisms to achieve the same stated characteristic.
The interaction between unrelated labels MUST NOT be embedded
within the definition of a label. Local policy states the actions
(if any) to be taken if unrelated labeled traffic merges at a
Finally, labels may have additional characteristics added to them
as a result of local policy.
4) Network Functionality
Functionality to support a better than best effort SHOULD focus on
probability versus guarantees. Probability can be realized in
terms of reduced probability of packet loss, and/or minimal
jitter, and/or minimal end-to-end delay. There is NO requirement
that a better than best effort functionality MUST exist. There is
NO requirement that if a better than best effort functionality
exists then it must be ubiquitous between end users.
3.1. General Security Related Requirements
The following are security related requirements that emerge given the
requirements 1 through 4 above.
Authorization is a method of validating that a user or some
traffic is allowed by policy to use a particular service offering.
Mechanisms must be implemented so that only authorized users have
access to emergency telecommunications services. Any mechanism
for providing such authorization beyond closed private networks
SHOULD meet IETF Security Area criterion (e.g., clear-text
passwords would not generally be acceptable). Authorization
protects network resources from excessive use, from abuse, and
might also support billing and accounting for the offered service.
Such authorization mechanisms SHOULD be flexible enough to provide
various levels of restriction and authorization depending on the
expectations of a particular service or customer.
6) Integrity & Authentication
In practice, authentication and integrity for IP based
communications are generally bound within a single mechanism, even
though conceptually they are different. Authentication ensures
that the user or traffic is who it claims to be. Integrity offers
assurance that unauthorized modifications to objects can be
Authorized emergency traffic needs to have reduced risk of adverse
impact from denial of service. This implies a need to ensure
integrity of the authorized emergency network traffic. It should
be noted, though, that mechanisms used to ensure integrity can
also be subject to Denial of Service attacks.
Users of emergency network services SHOULD consider deploying
end-to-end integrity and authentication, rather than relying on
services that might be offered by any single provider of emergency
network services. Users SHOULD also carefully consider which
application-layer security services might be appropriate to use.
Some emergency communications might have a requirement that they
not be susceptible to interception or viewing by others, due to
the sensitive and urgent nature of emergency response activities.
An emergency telecommunications service MAY offer options to
provide confidentiality for certain authorized user traffic.
Consistent with other IETF standards and the Internet
Architecture, this document recommends that IEPREP users SHOULD
deploy end-to-end security mechanisms, rather than rely on
security services that might be offered by a single network
operator. IEPREP users SHOULD carefully consider security
alternatives (e.g., PGP, TLS, IPsec transport-mode) at different
layers (e.g., Application Layer, Session Layer, Transport Layer)
of the Internet Architecture before deployment.
This section presents issues that arise in considering solutions for
the requirements that have been defined for ETS. This section does
not specify solutions nor is it to be confused with requirements.
Subsequent documents that articulate a more specific set of
requirements for a particular service may make a statement about the
Accounting represents a method of tracking actual usage of a
service. We assume that the usage of any service better than best
effort will be tracked and subsequently billed to the user.
Accounting is not addressed as a general requirement for ETS.
However, solutions used to realize ETS should not preclude an
2) Admission Control
The requirements of section 3 discuss labels and security. Those
developing solutions should understand that the ability labels
provide to distinguish emergency flows does not create an ability
to selectively admit flows. Admission control as it is commonly
understood in circuit-switched networks is not present in IP-based
networks, and schemes which presume the ability to selectively
admit flows when resources are scarce will fail outside of very
controlled environments. In cases where emergency related flows
occur outside of controlled environments, the development of
technologies based on admission control is not recommended as the
foundation of emergency services.
3) Digital Signatures
Verification of digital signatures is computationally expensive.
If an operator acts upon a label and hence needs to verify the
authenticity of the label, then there is a potential denial-of-
service attack on the entity performing the authentication. The
DoS attack works by flooding the entity performing the
authentication with invalid (i.e., not authentic) labelled
information, causing the victim to spend excessive amounts of
computing resources on signature validation. Even though the
invalid information might get discarded after the signature
validation fails, the adversary has already forced the victim to
expend significant amounts of computing resource. Accordingly,
any system requiring such validation SHOULD define operational and
protocol measures to reduce the vulnerability to such a DoS
5. Related Work
RFC 3487 describes requirements for resource priority mechanisms for
the Session Initiation Protocol . The requirements specified in
that RFC pertain to a specific application level protocol. In
contrast, the requirements of this document are a generalization that
are not application specific. From this blueprint (acting as a
guideline), more specific requirements may be described in future
6. Security Considerations
Security in terms of requirements is discussed sections 3.1 and 4.
7.1. Normative Reference
 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
 ANSI, "Signaling System No. 7(SS7) "High Probability of
Completion (HPC) Network Capability" , ANSI T1.631-1993 (R1999).
 "Description of an International Emergency Preference Scheme
(IEPS)", ITU-T Recommendation E.106 March, 2000.
 "Description for an International Emergency Multimedia Service",
ITU Draft Recommendation F.706, February, 2002.
 "Call Priority Designation for H.323 Calls", ITU Recommendation
H.460.4, November, 2002.
 ITU, "Multi-Level Precedence and Preemption Service, ITU,
Recommendation, I.255.3, July, 1990.
 U.S. National Communications System: http://www.ncs.gov
 Schulzrinne, H., "Requirements for Resource Priority Mechanisms
for the Session Initiation Protocol (SIP)", RFC 3487, February
 Carlberg, K. and R. Atkinson, "IP Telephony Requirements for
Emergency Telecommunications Service", RFC 3690, February 2004.
 Tada, N., et. al., "IAA System (I Am Alive): The Experiences of
the Internet Disaster Drills", Proceedings of INET-2000, June.
 Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski, "Assured
Forwarding PHB Group", RFC 2597, June 1999.
8. Authors' Addresses
University College London
Department of Computer Science
London, WC1E 6BT
3585 Monroe Street
Santa Clara, CA
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