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RFC 4958 - A Framework for Supporting Emergency Telecommunicatio


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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.

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

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.

      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.

   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.

      (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.

   [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.

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].

   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.

   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).

   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-

   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.

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.

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

   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.

   [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.

   [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

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