A Framework for Supporting Emergency Telecommunications Services (ETS) within a Single Administrative Domain
RFC 4958
| Document | Type | RFC - Informational (July 2007) Errata | |
|---|---|---|---|
| Author | Ken Carlberg | ||
| Last updated | 2020-01-21 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | RFC 4958 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Jon Peterson | ||
| Send notices to | kimberly.s.king@saic.com |
RFC 4958
Network Working Group K. Carlberg
Request for Comments: 4958 G11
Category: Informational July 2007
A Framework for Supporting Emergency Telecommunications Services (ETS)
within a Single Administrative Domain
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 Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document presents a framework discussing the role of various
protocols and mechanisms that could be considered candidates for
supporting Emergency Telecommunication Services (ETS) within a single
administrative domain. Comments about their potential usage as well
as their current deployment are provided to the reader. Specific
solutions are not presented.
Carlberg Informational [Page 1]
RFC 4958 ETS Single Domain Framework July 2007
Table of Contents
1. Introduction ....................................................3
1.1. Differences between Single and Inter-Domain ................3
2. Common Practice: Provisioning ...................................4
3. Objective .......................................................5
3.1. Scenarios ..................................................5
4. Topic Areas .....................................................6
4.1. MPLS .......................................................6
4.2. RSVP .......................................................7
4.2.1. Relation to ETS .....................................8
4.3. Policy .....................................................8
4.4. Subnetwork Technologies ....................................9
4.4.1. IEEE 802.1 VLANs ....................................9
4.4.2. IEEE 802.11e QoS ...................................10
4.4.3. Cable Networks .....................................10
4.5. Multicast .................................................11
4.5.1. IP Layer ...........................................12
4.5.2. IEEE 802.1d MAC Bridges ............................12
4.6. Discovery .................................................13
4.7. Differentiated Services (Diffserv) ........................14
5. Security Considerations ........................................14
6. Summary Comments ...............................................15
7. Acknowledgements ...............................................15
8. References .....................................................15
8.1. Normative Reference .......................................15
8.2. Informative References ....................................15
Carlberg Informational [Page 2]
RFC 4958 ETS Single Domain Framework July 2007
1. Introduction
This document presents a framework for supporting Emergency
Telecommunications Services (ETS) within the scope of a single
administrative domain. This narrow scope provides a reference point
for considering protocols that could be deployed to support ETS.
[rfc4375] is a complementary effort that articulates requirements for
a single administrative domain and defines it as "collection of
resources under the control of a single administrative authority".
We use this other effort as both a starting point and guide for this
document.
A different example of a framework document for ETS is [rfc4190],
which focused on support for ETS within IP telephony. In this case,
the focal point was a particular application whose flows could span
multiple autonomous domains. Even though this document uses a
somewhat more constrained perspective than [rfc4190], we can still
expect some measure of overlap in the areas that are discussed.
1.1. Differences between Single and Inter-Domain
The progression of our work in the following sections is helped by
stating some key differences between the single and inter-domain
cases. From a general perspective, one can start by observing the
following.
a) Congruent with physical topology of resources, each domain is
an authority zone, and there is currently no scalable way to
transfer authority between zones.
b) Each authority zone is under separate management.
c) Authority zones are run by competitors; this acts as further
deterrent to transferring authority.
As a result of the initial statements in (a) through (c) above,
additional observations can be made that distinguish the single and
inter-domain cases, as follows.
d) Different policies might be implemented in different
administrative domains.
e) There is an absence of any practical method for ingress nodes
of a transit domain to authenticate all of the IP network layer
packets that have labels indicating a preference or importance.
Carlberg Informational [Page 3]
RFC 4958 ETS Single Domain Framework July 2007
f) Given item (d) above, all current inter-domain QoS mechanisms
at the network level generally create easily exploited and
significantly painful Denial of Service (DoS) / Distributed
Denial of Service (DDoS) attack vectors on the network.
g) A single administrative domain can deploy various mechanisms
(e.g., access control lists) into each and every edge device
(e.g., ethernet switch or router) to ensure that only
authorized end-users (or layer 2 interfaces) are able to emit
frames/packets with non-default QoS labels into the network.
This is not feasible in the inter-domain case because the
inter-domain link contains aggregated flows. In addition, the
dissemination of access control lists at the network level is
not scalable in the inter-domain case.
h) A single domain can deploy mechanisms into the edge devices to
enforce its domain-wide policies -- without having to trust any
third party to configure things correctly. This is not
possible in the inter-domain case.
While the above is not an all-inclusive set of differences, it does
provide some rationale why one may wish to focus efforts in the more
constrained scenario of a single administrative domain.
2. Common Practice: Provisioning
The IEPREP working group and mailing list have had extensive
discussions about over-provisioning. Many of these exchanges have
debated the need for QoS mechanisms versus over-provisioning of
links.
In reality, most IP network links are provisioned with a percentage
of excess capacity beyond that of the average load. The 'shared'
resource model together with TCP's congestion avoidance algorithms
helps compensate for those cases where spikes or bursts of traffic
are experienced by the network.
The thrust of the debate within the IEPREP working group is whether
it is always better to over-provision links to such a degree that
spikes in load can still be supported with no loss due to congestion.
Advocates of this position point to many ISPs in the US that take
this approach instead of using QoS mechanisms to honor agreements
with their peers or customers. These advocates point to cost
effectiveness in comparison to complexity and security issues
associated with other approaches.
Carlberg Informational [Page 4]
RFC 4958 ETS Single Domain Framework July 2007
Proponents of QoS mechanisms argue that the relatively low cost of
bandwidth enjoyed in the US (particularly, by large ISPs) is not
necessarily available throughout the world. Beyond the subject of
cost, some domains are comprised of physical networks that support
wide disparity in bandwidth capacity -- e.g., attachment points
connected to high capacity fiber and lower capacity wireless links.
This document does not advocate one of these positions over the
other. The author does advocate that network
administrators/operators should perform a cost analysis between
over-provisioning for spikes versus QoS mechanisms as applied within
a domain and its access link to another domain (e.g., a customer and
its ISP). This analysis, in addition to examining policies and
requirements of the administrative domain, should be the key to
deciding how (or if) ETS should be supported within the domain.
If the decision is to rely on over-provisioning, then some of the
following sections will have little to no bearing on how ETS is
supported within a domain. The exception would be labeling
mechanisms used to convey information to other communication
architectures (e.g., SIP-to-SS7/ISUP gateways).
3. Objective
The primary objective is to provide a target measure of service
within a domain for flows that have been labeled for ETS. This level
may be better than best effort, the best available service that the
network (or parts thereof) can offer, or a specific percentage of
resource set aside for ETS. [rfc4375] presents a set of requirements
in trying to achieve this objective.
This framework document uses [rfc4375] as a reference point in
discussing existing areas of engineering work or protocols that can
play a role in supporting ETS within a domain. Discussion of these
areas and protocols are not to be confused with expectations that
they exist within a given domain. Rather, the subjects discussed in
Section 4 below are ones that are recognized as candidates that can
exist and could be used to facilitate ETS users or data flows.
3.1. Scenarios
One of the topics of discussion on the IEPREP mailing list and in the
working group meetings is the operating environment of the ETS user.
Many variations can be dreamed of with respect to underlying network
technologies and applications. Instead of getting lost in hundreds
of potential scenarios, we attempt to abstract the scenarios into two
simple case examples.
Carlberg Informational [Page 5]
RFC 4958 ETS Single Domain Framework July 2007
(a) A user in their home network attempts to use or leverage any
ETS capability within the domain.
(b) A user visits a foreign network and attempts to use or
leverage any ETS capability within the domain.
We borrow the terms "home" and "foreign" network from that used in
Mobile IP [rfc3344]. Case (a) is considered the normal and vastly
most prevalent scenario in today's Internet. Case (b) above may
simply be supported by the Dynamic Host Configuration Protocol (DHCP)
[rfc2131], or a static set of addresses, that are assigned to
'visitors' of the network. This effort is predominantly operational
in nature and heavily reliant on the management and security policies
of that network.
A more ambitious way of supporting the mobile user is through the use
of the Mobile IP (MIP) protocol. MIP offers a measure of
application-transparent mobility as a mobile host moves from one
subnetwork to another while keeping the same stable IP address
registered at a global anchor point. However, this feature may not
always be available or in use. In any case, where it is in use, at
least some of the packets destined to and from the mobile host go
through the home network.
4. Topic Areas
The topic areas presented below are not presented in any particular
order or along any specific layering model. They represent
capabilities that may be found within an administrative domain. Many
are topics of on-going work within the IETF.
It must be stressed that readers of this document should not expect
any of the following to exist within a domain for ETS users. In many
cases, while some of the following areas have been standardized and
in wide use for several years, others have seen very limited
deployment.
4.1. MPLS
Multiprotocol Label Switching (MPLS) is generally the first protocol
that comes to mind when the subject of traffic engineering is brought
up. MPLS signaling produces Labeled Switched Paths (LSPs) through a
network of Label Switch Routers [rfc3031]. When traffic reaches the
ingress boundary of an MPLS domain (which may or may not be congruent
with an administrative domain), the packets are classified, labeled,
scheduled, and forwarded along an LSP.
Carlberg Informational [Page 6]
RFC 4958 ETS Single Domain Framework July 2007
[rfc3270] describes how MPLS can be used to support Differentiated
Services. The RFC discusses the use of the 3-bit EXP (experimental)
field to convey the Per Hop Behavior (PHB) to be applied to the
packet. As we shall see in later sections, this 3-bit field can be
mapped to fields in several other protocols.
The inherent features of classification, scheduling, and labeling are
viewed as symbiotic, and therefore, they are often integrated with
other protocols and architectures. Examples of this include RSVP and
Differentiated Services. Below, we discuss several instances where a
given protocol specification or mechanism has been known to be
complemented with MPLS. This includes the potential labels that may
be associated with ETS. However, we stress that MPLS is only one of
several approaches to support traffic engineering. In addition, the
complexity of the MPLS protocol and architecture may make it suited
only for large domains.
4.2. RSVP
The original design of RSVP, together with the Integrated Services
model, was one of an end-to-end signaling capability to set up a path
of reserved resources that spanned networks and administrative
domains [rfc2205]. Currently, RSVP has not been widely deployed by
network administrators for QoS across domains. Today's limited
deployment by network administrators has been mostly constrained to
boundaries within a domain, and commonly in conjunction with MPLS
signaling. Early deployments of RSVP ran into unanticipated scaling
issues; it is not entirely clear how scalable an RSVP approach would
be across the Internet.
[rfc3209] is one example of how RSVP has evolved to complement
efforts that are scoped to operate within a domain. In this case,
extensions to RSVP are defined that allow it to establish intra-
domain Labeled Switched Paths (LSPs) in Multiprotocol Label Switching
(MPLS).
[rfc2750] specifies extensions to RSVP so that it can support generic
policy-based admission control. This standard goes beyond the
support of the POLICY_DATA object stipulated in [rfc3209], by
defining the means of control and enforcement of access and usage
policies. While the standard does not advocate a particular policy
architecture, the IETF has defined one that can complement [rfc2750]
-- we expand on this in Section 4.3 below.
Carlberg Informational [Page 7]
RFC 4958 ETS Single Domain Framework July 2007
4.2.1. Relation to ETS
The ability to reserve resources correlates to an ability to provide
preferential service for specifically classified traffic -- the
classification being a tuple of 1 or more fields which may or may not
include an ETS specific label. In cases where a tuple includes a
label that has been defined for ETS usage, the reservation helps
ensure that an emergency-related flow will be forwarded towards its
destination. Within the scope of this document, this means that RSVP
would be used to facilitate the forwarding of traffic within a
domain.
We note that this places an importance on defining a label and an
associated field that can be set and/or examined by RSVP-capable
nodes.
Another important observation is that major vendor routers currently
constrain their examination of fields for classification to the
network and transport layers. This means that application layer
labels will mostly likely be ignored by routers/switches.
4.3. Policy
The Common Open Policy Service (COPS) protocol [rfc2748] was defined
to provide policy control over QoS signaling protocols, such as RSVP.
COPS is based on a query/response model in which Policy Enforcement
Points (PEPs) interact with Policy Decision Points (i.e., policy
servers) to exchange policy information. COPS provides application-
level security and can operate over IPsec or TLS. COPS is also a
stateful protocol that supports a push model. This means that
servers can download new policies or alter existing ones to known
clients.
[rfc2749] articulates the usage of COPS with RSVP. It specifies COPS
client types, context objects, and decision objects. Thus, when an
RSVP reservation is received by a PEP, the PEP decides whether to
accept or reject it based on policy. This policy information can be
stored a priori to the reception of the RSVP PATH message, or it can
be retrieved on an on-demand basis. A similar course of action could
be applied in cases where ETS-labeled control flows are received by
the PEP. This of course would require an associated (and new) set of
documents that first articulates types of ETS signaling and then
specifies its usage with COPS.
A complementary document to the COPS protocols is COPS Usage for
Policy Provisioning (COPS-PR) [rfc3084].
Carlberg Informational [Page 8]
RFC 4958 ETS Single Domain Framework July 2007
As a side note, the current lack of deployment by network
administrators of RSVP has also played at least an indirect role in
the subsequent lack of implementation and deployment of COPS-PR.
[rfc3535] is an output from the IAB Network Management Workshop in
which the topic of COPS and its current state of deployment was
discussed. At the time of that workshop in 2002, COPS-PR was
considered a technology/architecture that did not fully meet the
needs of network operators. It should also be noted that at the 60th
IETF meeting held in San Diego in 2004, COPS was discussed as a
candidate protocol that should be declared as historic because of
lack of use and concerns about its design. In the future, an altered
design of COPS may emerge that addresses the concern of operators,
but speculation on that or other possibilities is beyond the scope of
this document.
4.4. Subnetwork Technologies
This is a generalization of work that is considered "under" IP and
for the most part outside of the IETF standards body. We discuss
some specific topics here because there is a relationship between
them and IP in the sense that each physical network interacts at its
edge with IP.
4.4.1. IEEE 802.1 VLANs
The IEEE 802.1q standard defined a tag appended to a Media Access
Controller (MAC) frame for support of layer 2 Virtual Local Area
Networks (VLANs). This tag has two parts: a VLAN identifier (12
bits) and a Prioritization field of 3 bits. A subsequent standard,
IEEE 802.1p, later incorporated into a revision of IEEE 802.1d,
defined the Prioritization field of this new tag [iso15802]. It
consists of 8 levels of priority, with the highest priority being a
value of 7. Vendors may choose a queue per priority codepoint, or
aggregate several codepoints to a single queue.
The 3-bit Prioritization field can be easily mapped to the old ToS
field of the upper-layer IP header. In turn, these bits can also be
mapped to a subset of differentiated codepoints. Bits in the IP
header that could be used to support ETS (e.g., specific Diffserv
codepoints) can in turn be mapped to the Prioritization bits of
802.1p. This mapping could be accomplished in a one-to-one manner
between the 802.1p field and the IP ToS bits, or in an aggregate
manner if one considers the entire Diffserv field in the IP header.
In either case, because of the scarcity of bits, ETS users should
expect that their traffic will be combined or aggregated with the
same level of priority as some other types of "important" traffic.
In other words, given the existing 3-bit Priority Field for 802.1p,
there will not be an exclusive bit value reserved for ETS traffic.
Carlberg Informational [Page 9]
RFC 4958 ETS Single Domain Framework July 2007
Certain vendors are currently providing mappings between the 802.1p
field and the ToS bits. This is in addition to integrating the
signaling of RSVP with the low-level inband signaling offered in the
Priority field of 802.1p.
It is important to note that the 802.1p standard does not specify the
correlation of a layer 2 codepoint to a physical network bandwidth
reservation. Instead, this standard provides what has been termed as
"best effort QoS". The value of the 802.1p Priority codepoints is
realized at the edges: either as the MAC payload is passed to upper
layers (like IP), or as it is bridged to other physical networks like
Frame Relay. Either of these actions help provide an intra-domain
wide propagation of a labeled flow for both layer 2 and layer 3
flows.
4.4.2. IEEE 802.11e QoS
The 802.11e standard is a proposed enhancement that specifies
mechanisms to provide QoS to the 802.11 family of protocols for
wireless LANs.
Previously, 802.11 had two modes of operation. One was Distributed
Coordination Function (DCF) , which is based on the classic collision
detection schema of "listen before sending". A second optional mode
is the Point Coordination Function (PCF). The modes splits access
time into contention-free and contention-active periods --
transmitting data during the former.
The 802.11e standard enhances DCF by adding support for 8 different
traffic categories or classifications. Each higher category waits a
little less time than the next lower one before it sends its data.
In the case of PCF, a Hybrid Coordination Function has been added
that polls stations during contention-free time slots and grants them
a specific start time and maximum duration for transmission. This
second mode is more complex than enhanced DCF, but the QoS can be
more finely tuned to offer specific bandwidth and jitter control. It
must be noted that neither enhancement offers a guarantee of service.
4.4.3. Cable Networks
The Data Over Cable Service Interface Specification (DOCSIS) is a
standard used to facilitate the communication and interaction of the
cable subnetwork with upper-layer IP networks [docsis]. Cable
subnetworks tend to be asynchronous in terms of data load capacity:
typically, 27 M downstream, and anywhere from 320 kb to 10 M upstream
(i.e., in the direction of the user towards the Internet).
Carlberg Informational [Page 10]
RFC 4958 ETS Single Domain Framework July 2007
The evolution of the DOCSIS specification, from 1.0 to 1.1, brought
about changes to support a service other than best effort. One of
the changes was indirectly added when the 802.1d protocol added the
Priority field, which was incorporated within the DOCSIS 1.1
specification. Another change was the ability to perform packet
fragmentation of large packets so that Priority-marked packets (i.e.,
packets marked with non-best effort labels) can be multiplexed in
between the fragmented larger packet.
It's important to note that the DOCSIS specifications do not specify
how vendors implement classification, policing, and scheduling of
traffic. Hence, operators must rely on mechanisms in Cable Modem
Termination Systems (CMTS) and edge routers to leverage indirectly or
directly the added specifications of DOCSIS 1.1. As in the case of
802.1p, ETS-labeled traffic would most likely be aggregated with
other types of traffic, which implies that an exclusive bit (or set
of bits) will not be reserved for ETS users. Policies and other
managed configurations will determine the form of the service
experienced by ETS labeled traffic.
Traffic engineering and management of ETS labeled flows, including
its classification and scheduling at the edges of the DOCSIS cloud,
could be accomplished in several ways. A simple schema could be
based on non-FIFO queuing mechanisms like class-based weighted fair
queuing (or combinations and derivations thereof). The addition of
active queue management like Random Early Detection could provide
simple mechanisms for dealing with bursty traffic contributing to
congestion. A more elaborate scheme for traffic engineering would
include the use of MPLS. However, the complexity of MPLS should be
taken into consideration before its deployment in networks.
4.5. Multicast
Network layer multicast has existed for quite a few years. Efforts
such as the Mbone (multicast backbone) have provided a form of
tunneled multicast that spans domains, but the routing hierarchy of
the Mbone can be considered flat and non-congruent with unicast
routing. Efforts like the Multicast Source Discovery Protocol
[rfc3618] together with the Protocol Independent Multicast - Sparse
Mode (PIM-SM) have been used by a small subset of Internet Service
Providers to provide forms of inter-domain multicast [rfc4601].
However, network layer multicast has not been accepted as a common
production level service by a vast majority of ISPs.
In contrast, intra-domain multicast in domains has gained more
acceptance as an additional network service. Multicast can produce
denial-of-service attacks using the any sender model, with the
problem made more acute with flood and prune algorithms. Source-
Carlberg Informational [Page 11]
RFC 4958 ETS Single Domain Framework July 2007
specific multicast [rfc3569], together with access control lists of
who is allowed to be a sender, reduces the potential and scope of
such attacks.
4.5.1. IP Layer
The value of IP multicast is its efficient use of resources in
sending the same datagram to multiple receivers. An extensive
discussion on the strengths of and concerns about multicast is
outside the scope of this document. However, one can argue that
multicast can very naturally complement the push-to-talk feature of
land mobile radio (LMR) networks.
Push-to-talk is a form of group communication where every user in the
"talk group" can participate in the same conversation. LMR is the
type of network used by First Responders (e.g., police, firemen, and
medical personnel) that are involved in emergencies. Currently,
certain vendors and providers are offering push-to-talk service to
the general public in addition to First Responders. Some of these
systems are operated over IP networks or are interfaced with IP
networks to extend the set of users that can communicate with each
other. We can consider at least a subset of these systems as either
closed IP networks, or domains, since they do not act as transits to
other parts of the Internet.
The potential integration of LMR talk groups with IP multicast is an
open issue. LMR talk groups are established in a static manner with
man-in-the-loop participation in their establishment and teardown.
The seamless integration of these talk groups with multicast group
addresses is a feature that has not been discussed in open forums.
4.5.2. IEEE 802.1d MAC Bridges
The IEEE 802.1d standard specifies fields and capabilities for a
number of features. In Section 4.3.2 above, we discussed its use for
defining a Prioritization field. The 802.1d standard also covers the
topic of filtering MAC layer multicast frames.
One of the concerns about multicast is that broadcast storms can
arise and generate a denial of service against other users/nodes.
Some administrators purposely filter out multicast frames in cases
where the subnetwork resource is relatively small (e.g., 802.11
networks). Operational considerations with respect to ETS may wish
to consider doing this on an as-needed basis, balancing the
conditions of the network with the perceived need for multicast. In
cases where filtering out multicast can be activated dynamically,
COPS may be a good means of providing consistent domain-wide policy
control.
Carlberg Informational [Page 12]
RFC 4958 ETS Single Domain Framework July 2007
4.6. Discovery
If a service is being offered to explicitly support ETS, then it
would seem reasonable that discovery of the service may be of
benefit. For example, if a domain has a subset of servers that
recognize ETS-labeled traffic, then dynamic discovery of where these
servers are (or even if they exist) would be more beneficial than
relying on statically configured information.
The Service Location Protocol (SLP) [rfc2608] is designed to provide
information about the existence, location, and configuration of
networked services. In many cases, the name of the host supporting
the desired service is needed to be known a priori in order for users
to access it. SLP eliminates this requirement by using a descriptive
model that identifies the service. Based on this description, SLP
then resolves the network address of the service and returns this
information to the requester. An interesting design element of SLP
is that it assumes that the protocol is run over a collection of
nodes that are under the control of a single administrative
authority. This model follows the scope of this framework document.
However, the scope of SLP may be better suited for parts of an
enterprise network versus an entire domain.
Anycasting [rfc1546] is another means of discovering nodes that
support a given service. Interdomain anycast addresses, propagated
by BGP, represent anycast in a wide scope and have been used by
multiple root servers for a while. Anycast can also be realized in a
more constrained and limited scope (i.e., solely within a domain or
subnet), and as in the case of multicast, it may not be supported.
[rfc4291] covers the topic of anycast addresses for IPv6. Unlike
SLP, users/applications must know the anycast address associated with
the target service. In addition, responses to multiple requests to
the anycast address may come from different servers. Lack of
response (not due to connectivity problems) correlates to the
discovery that a target service is not available. Detailed tradeoffs
between this approach and SLP are outside the scope of this framework
document.
The Dynamic Delegation Discovery System (DDDS) is used to implement a
binding of strings to data in order to support dynamically configured
delegation systems [rfc3401]. The DDDS functions by mapping some
unique string to data stored within a DDDS Database by iteratively
applying string transformation rules until a terminal condition is
reached. The potential then exists that a client could specify a set
of known tags (e.g., RetrieveMail:Pop3) that would identify/discover
the appropriate server with which it can communicate.
Carlberg Informational [Page 13]
RFC 4958 ETS Single Domain Framework July 2007
4.7. Differentiated Services (Diffserv)
There are a number of examples where Diffserv [rfc2474] has been
deployed strictly within a domain, with no extension of service to
neighboring domains. Various reasons exist for Diffserv not being
widely deployed in an inter-domain context, including ones rooted in
the complexity and problems in supporting the security requirements
for Diffserv codepoints. An extensive discussion on Diffserv
deployment is outside the scope of this document.
[Baker] presents common examples of various codepoints used for
well-known applications. The document does not recommend these
associations as being standard or fixed. Rather, the examples in
[Baker] provide a reference point for known deployments that can act
as a guide for other network administrators.
An argument can be made that Diffserv, with its existing codepoint
specifications of Assured Forwarding (AF) and Expedited Forwarding
(EF), goes beyond what would be needed to support ETS within a
domain. By this we mean that the complexity in terms of maintenance
and support of AF or EF may exceed or cause undue burden on the
management resources of a domain. Given this possibility, users or
network administrators may wish to determine if various queuing
mechanisms, like class-based weighted fair queuing, is sufficient to
support ETS flows through a domain. Note, as we stated earlier in
Section 2, over-provisioning is another option to consider. We
assume that if the reader is considering something like Diffserv,
then it has been determined that over-provisioning is not a viable
option given their individual needs or capabilities.
5. Security Considerations
Services used to offer better or best available service for a
particular set of users (in the case of this document, ETS users) are
prime targets for security attacks or simple misuse. Hence,
administrators that choose to incorporate additional
protocols/services to support ETS are strongly encouraged to consider
new policies to address the added potential of security attacks.
These policies, and any additional security measures, should be
considered independent of any mechanism or equipment that restricts
access to the administrative domain.
Determining how authorization is accomplished is an open issue. Many
times the choice is a function of the service that is deployed. One
example is source addresses in an access list permitting senders to
the multicast group (as described in Section 4.5). Within a single
domain environment, cases can be found where network administrators
tend to find this approach acceptable. However, other services may
Carlberg Informational [Page 14]
RFC 4958 ETS Single Domain Framework July 2007
require more stringent measures that employ detailed credentials, and
possibly multiple levels of access and authentication. Ease of use,
deployment, scalability, and susceptibility to security breach all
play a role in determining authorization schemas. The potential is
that accomplishing this for only a single domain may be easier than
at the inter-domain scope, if only in terms of scalability and trust.
6. Summary Comments
This document has presented a number of protocols and complementary
technologies that can be used to support ETS users. Their selection
is dictated by the fact that all or significant portions of the
protocols can be operated and controlled within a single
administrative domain. It is this reason why other protocols, like
those under current development in the Next Steps in Signaling (NSIS)
working group, have not been discussed.
By listing a variety of efforts in this document, we avoid taking on
the role of "king maker" and at the same time indirectly point out
that a variety of solutions exist in support of ETS. These solutions
may involve QoS, traffic engineering, or simply protection against
detrimental conditions (e.g., spikes in traffic load). Again, the
choice is up to the reader.
7. Acknowledgements
Thanks to Ran Atkinson, Scott Bradner, Jon Peterson, and Kimberly
King for comments and suggestions on this document.
8. References
8.1. Normative Reference
[rfc4375] Carlberg, K., "Emergency Telecommunications Services (ETS)
Requirements for a Single Administrative Domain", RFC
4375, January 2006.
8.2. Informative References
[Baker] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, August
2006.
[docsis] "Data-Over-Cable Service Interface Specifications: Cable
Modem to Customer Premise Equipment Interface
Specification SP-CMCI-I07-020301", DOCSIS, March 2002,
http://www.cablemodem.com.
Carlberg Informational [Page 15]
RFC 4958 ETS Single Domain Framework July 2007
[iso15802] "Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Common specifications - Part
3: Media Access Control (MAC) Bridges: Revision. This is
a revision of ISO/IEC 10038: 1993, 802.1j-1992 and
802.6k-1992. It incorporates P802.11c, P802.1p and
P802.12e." ISO/IEC 15802-3:1998"
[rfc1546] Partridge, C., Mendez, T., and W. Milliken, "Host
Anycasting Service", RFC 1546, November 1993.
[rfc2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[rfc2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[rfc2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[rfc2608] Guttman, E., Perkins, C., Veizades, J., and M. Day,
"Service Location Protocol, Version 2", RFC 2608, June
1999.
[rfc2748] Durham, D., Ed., Boyle, J., Cohen, R., Herzog, S., Rajan,
R., and A. Sastry, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
[rfc2749] Herzog, S., Ed., Boyle, J., Cohen, R., Durham, D., Rajan,
R., and A. Sastry, "COPS usage for RSVP", RFC 2749,
January 2000.
[rfc2750] Herzog, S., "RSVP Extensions for Policy Control", RFC
2750, January 2000.
[rfc3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[rfc3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, May 2002.
Carlberg Informational [Page 16]
RFC 4958 ETS Single Domain Framework July 2007
[rfc3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[rfc3344] Perkins, C., Ed., "IP Mobility Support for IPv4", RFC
3344, August 2002.
[rfc3084] Chan, K., Seligson, J., Durham, D., Gai, S., McCloghrie,
K., Herzog, S., Reichmeyer, F., Yavatkar, R., and A.
Smith, "COPS Usage for Policy Provisioning (COPS-PR)", RFC
3084, March 2001.
[rfc3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS", RFC 3401 October 2002.
[rfc3535] Schoenwaelder, J., "Overview of the 2002 IAB Network
Management Workshop", RFC 3535, May 2003.
[rfc3569] Bhattacharyya, S., Ed., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, July 2003.
[rfc3618] Fenner, B., Ed., and D. Meyer, Ed., "Multicast Source
Discovery Protocol (MSDP)", RFC 3618, October 2003.
[rfc4190] Carlberg, K., Brown, I., and C. Beard, "Framework for
Supporting Emergency Telecommunications Service (ETS) in
IP Telephony", RFC 4190, November 2005.
[rfc4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[rfc4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
Author's Address
Ken Carlberg
G11
123a Versailles Circle
Baltimore, MD
USA
EMail: carlberg@g11.org.uk
Carlberg Informational [Page 17]
RFC 4958 ETS Single Domain Framework July 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Carlberg Informational [Page 18]