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Versions: 00 01 02 03 04 RFC 5160

Network Working Group                                           P. Levis
Internet-Draft                                              M. Boucadair
Intended status: Informational                            France Telecom
Expires: November 12, 2007                                  May 11, 2007

Considerations of provider-to-provider agreements for Internet-scale QoS

Status of this Memo

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This memo analyzes provider-to-provider QoS agreements suited for a
   global QoS-enabled Internet.  It defines terminology relevant to
   inter-domain QoS models.  It introduces a new concept denoted by
   Meta-QoS-Class.  This new concept drives and federates the way QoS
   inter-domain relationships are built.  It opens up new perspectives
   for a QoS-enabled Internet that retains, as much as possible, the
   openness of the existing best-effort Internet.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4

   3.  Weaknesses of provider-to-provider QoS agreements based on
       SP chains  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  IP connectivity services . . . . . . . . . . . . . . . . .  5
     3.2.  Similarity between provider and customer agreements  . . .  6
     3.3.  Liability for service disruption . . . . . . . . . . . . .  6
     3.4.  SP chain trap leading to glaciation  . . . . . . . . . . .  7

   4.  Provider-to-provider agreements based on Meta-QoS-Class  . . .  7
     4.1.  Single domain covering . . . . . . . . . . . . . . . . . .  7
     4.2.  Binding l-QCs  . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  MQC-based Binding process  . . . . . . . . . . . . . . . . 10

   5.  The Internet as MQC planes . . . . . . . . . . . . . . . . . . 11

   6.  Towards end-to-end QoS services  . . . . . . . . . . . . . . . 12

   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14

   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14

   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     10.2. Informative References . . . . . . . . . . . . . . . . . . 15

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 18

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1.  Introduction

   Three different areas can be distinguished in IP QoS service
   offerings.  The first area is the single domain where a provider
   delivers QoS services inside the boundaries of its own network.  The
   second area is multi domains where a small set of providers, with
   mutual business interests, cooperate to deliver QoS services inside
   the boundaries of their network aggregate.  The third area, which has
   very seldom been put forward, is the Internet where QoS services can
   be delivered from almost any source to any destination.  Both multi
   domains and Internet areas deal with inter-domain aspects.  However
   they differ greatly in many ways, such as the number of domains and
   QoS paths involved, which are much higher and dynamic for the
   Internet area.  Multi domains and Internet areas are therefore likely
   to differ in their respective solutions.

   Most of the work on QoS implementation as well as standardization and
   research, has gone into the single domain area.  A number of issues
   still appear to need further elaboration [RFC2990], before we could
   have operational deployment of QoS services that include inter-domain

   This memo deals only with QoS solutions globally suited for the
   Internet.  Any Internet-wide solutions should apply locally in order
   to be usable as soon as deployed in a small set of domains.  Any
   Internet-wide solutions should be scalable in order to allow a global
   deployment to almost all Internet domains, with the ability to
   establish QoS communications between any two end-users.  Any
   Internet-wide solutions should also maintain a best-effort service
   that should remain the pre-eminent service as a consequence of the
   end-to-end argument [E2E].  If there is no path available within the
   requested QoS to reach a destination, this destination must remain
   reachable through the best-effort service.

   This memo does not place any specific requirements on the intra-
   domain traffic engineering policies and the way they are enforced.  A
   provider may deploy any technique to ensure QoS inside its network.
   This memo assumes only that QoS capabilities inside a provider's
   network can be represented as local-QoS-Classes (l-QCs).  When
   crossing a domain, traffic experiences conditions characterized by
   the values of delay, jitter, and packet loss rate that correspond to
   the l-QC selected for that traffic within that domain.  Capabilities
   can differ from one provider to another by the number of deployed
   l-QCs, by their respective QoS characteristics, and also by the way
   they have been implemented and engineered.

   This memo analyzes provider-to-provider QoS agreements.  To avoid a
   great deal of complexity and scalability issues we assume these

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   agreements are negotiated only between two adjacent domains that are
   directly accessible to each other (immediate neighbors).  We also
   assume, because they exchange traffic, that these neighbors are BGP
   [RFC4271] peers.

   This memo defines terminology relevant to inter-domain QoS models and
   introduces a new concept denoted by Meta-QoS-Class(MQC) that drives
   and federates the way QoS inter-domain relationships are built.  The
   rationale for the MQC concept relies on a universal and common
   understanding of QoS-sensitive application needs.  Wherever end-users
   are connected, they experience the same QoS difficulties and are
   likely to express very similar QoS requirements to their respective
   providers.  Globally confronted with the same customer requirements,
   providers are likely to design and operate similar network
   capabilities.  Note that this document does not specify any protocols
   or systems.

2.  Terminology

   (D, J, L)

      D: one-way transit delay [RFC2679], J: one-way transit delay
      variation or jitter [RFC3393], and L: packet loss rate [RFC2680].


      A network infrastructure composed of one or several Autonomous
      Systems (AS) managed by a single administrative entity.

   IP connectivity service

      IP transfer capability characterized by a (Destination, D, J, L)
      tuple where Destination is a group of IP addresses and (D, J, L)
      is the QoS performance to get to Destination.

   Local-QoS-Class (l-QC)

      A QoS transfer capability across a single domain, characterized by
      a set of QoS performance parameters denoted by (D, J, L).  From a
      Diffserv [RFC2475] perspective, an l-QC is an occurrence of a Per
      Domain Behavior (PDB) [RFC3086].

   L-QC binding

      Two l-QCs from two neighboring domains are bound together once the
      two providers have agreed to transfer traffic from one l-QC to the

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   L-QC thread

      Chain of neighboring bound l-QCs.

   Meta-QoS-Class (MQC)

      An MQC provides the boundaries of the QoS parameters values, two
      l-QCs must respect in order to be bound together.  An MQC is used
      as a label that certifies the support of a set of applications
      that bear similar network QoS requirements.

   Service Provider (SP)

      An entity that provides Internet connectivity.  This document
      assumes that an SP owns and administers an IP network called a
      domain.  Sometimes simply referred to as provider.

   SP chain

      The chain of Service Providers whose domains are used to convey
      packets for a given IP connectivity service.

3.  Weaknesses of provider-to-provider QoS agreements based on SP chains

   This section analyzes provider-to-provider QoS agreements based on
   guarantees that span several domains.  In this approach the basic
   service element that a provider offers to its neighboring providers
   is called an IP connectivity service.  It uses the notion of SP
   chains.  We first define what an IP connectivity service is, and then
   we point out several weaknesses of such an approach, especially the
   SP chain trap problem that leads to the so-called Internet glaciation

3.1.  IP connectivity services

   An IP connectivity service is a (Destination, D, J, L) tuple where
   Destination is a group of IP addresses reachable from the domain of
   the provider offering the service, and (D, J, L) is the QoS
   performance to get from this domain to Destination.  Destination is
   typically located in a remote domain.

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   Provider-               /--------------SP chain---------------\
   view         /--Agreement--\
              +----+       +----+    +----+    +----+       +----+
              |SP  +-------+SP  +----+SP  +----+SP  +- ... -+SP  |
              |n+1 |       |n   |    |n-1 |    |n-2 |       |1   |
              +----+       +----+    +----+    +----+       +----+
   Domain-            -----> packet flow                      /
   oriented                                              Destination
   view                    <----------- Guarantee Scope --------->

                     Figure 1: IP connectivity service

   In Figure 1 Provider SPn guarantees provider SPn+1 the level of QoS
   for crossing the whole chain of providers' domains (SPn, SPn-1,
   SPn-2, ...,SP1).  SPi denotes a provider as well as its domain.  The
   top of the figure is the provider-oriented view, the ordered set of
   providers (SPn, SPn-1, SPn-2, ...,SP1) is called an SP chain.  The
   bottom of the figure is the domain-oriented view.

3.2.  Similarity between provider and customer agreements

   This approach maps end-users' needs directly to provider-to-provider
   agreements.  Providers negotiate agreements to a destination because
   they know customers are ready to pay for QoS guaranteed transfer to
   this destination.  As far as service scope is concerned, the
   agreements between providers will resemble the agreements between
   customers and providers.  For instance, in Figure 1, SPn can sell to
   its own customers the same IP connectivity service it sells to SPn+1.
   There is no clear distinction between provider-to-provider agreements
   and customer-to-provider agreements.

   In order to guarantee a stable service, redundant SP chains should be
   formed to reach the same destination.  When one SP chain becomes
   unavailable, an alternate SP chain should be selected.  In the
   context of a global QoS Internet that would lead to an enormous
   number of SP chains along with the associated agreements.

3.3.  Liability for service disruption

   In Figure 1, if SPn+1 sees a disruption in the IP connectivity
   service, it can turn only against SPn, its legal partner in the
   agreement.  If SPn is not responsible, in the same way, it can only
   complain to SPn-1, and so on, until the faulty provider is found and
   eventually requested to pay for the service impairment.  The claim is
   then supposed to move back along the chain until SPn pays SPn+1.  The
   SP chain becomes a liability chain.

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   Unfortunately this process is prone to failure in many cases.  In the
   context of QoS solutions suited for the Internet, SP chains are
   likely to be dynamic and involve a significant number of providers.
   Providers (that do not all know each other) involved in a same SP
   chain can be competitors in many fields; therefore, trust
   relationships are very difficult to build.  Many complex and critical
   issues need to be resolved: How will SPn+1 prove to SPn that QoS
   level is not the level expected for a scope that can expand well
   beyond SPn?  How long will it take to find the guilty domain?  Is SPn
   ready to pay SPn+1 for something it does not control and is not
   responsible for?

3.4.  SP chain trap leading to glaciation

   In Figure 1, SPn implicitly guarantees SPn+1 the level of QoS for the
   crossing of distant domains like SPn-2.  As we saw in Section 3.2, SP
   chains will proliferate.  A provider is, in this context, likely to
   be part of numerous SP chains.  It will see the level of QoS it
   provides guaranteed by many providers it has maybe even never heard

   Any change in a given agreement is likely to have an impact on
   numerous external agreements that make use of it.  A provider sees
   the degree of freedom to renegotiate, or terminate, one of its own
   agreements being restricted by the large number of external (to its
   domain) agreements that depend on it.  This is what is referred to as
   the "SP chain trap" issue.  This solution is not appropriate for
   worldwide QoS coverage as it would lead to glaciation phenomena,
   causing a completely petrified QoS infrastructure, where nobody could
   renegotiate any agreement.

4.  Provider-to-provider agreements based on Meta-QoS-Class

   If a QoS-enabled Internet is deemed desirable, with QoS services
   available potentially to and from any destination, any solution must
   resolve the above weaknesses and scalability problems, and find
   alternate schemes for provider-to-provider agreements.

4.1.  Single domain covering

   Due to the vulnerabilities of the SP chain approach we assume
   provider-to-provider QoS agreements should be based on guarantees
   covering a single domain.  A provider guarantees its neighbors only
   the crossing performance of its own domain.  In Figure 2, the
   provider SPn guarantees the provider SPn+1 only the QoS performance
   of the SPn domain.  The remainder of this document will show that
   this approach, bringing clarity and simplicity into inter-domain

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   relationships, is better suited for a global QoS Internet than that
   based on SP chains.

     view                          /--Agreement--\
                                 +----+       +----+
                                 |SP  +-------+SP  +
                                 |n+1 |       |n   |
                                 +----+       +----+
     Domain-               -----> packet flow
     oriented                                 <---->
     view                                  Guarantee Scope

               Figure 2: provider-to-provider QoS agreement

   It is very important to note that the proposition to limit guarantees
   to only one domain hop applies exclusively to provider-to-provider
   agreements.  It does not in any way preclude end-to-end guarantees
   for communications.

   There is a clear distinction between provider-to-provider and
   customer-to-provider QoS agreements.  We expect a great deal of
   difference in dynamicity between the two.  Most provider-to-provider
   agreements should have been negotiated, and should remain stable,
   before end-users can dynamically request end-to-end guarantees.  The
   number of provider agreements is largely independent of the number of
   end-user requests and does not increase dramatically as with SP

   The simple fact that SP chains do not exist makes the AS chain trap
   problem and the associated glaciation threat vanish.

   The liability issue is restricted to a one hop distance.  A provider
   is responsible for its own domain only, and is controlled only by all
   the neighbors with whom it has a direct contract.

4.2.  Binding l-QCs

   When a provider wants to contract with another provider, the main
   concern is to decide which l-QC(s) in its own domain it will bind to
   which l-QC(s) in the neighboring downstream domain.  The l-QC Binding
   process becomes the basic inter-domain process.

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                    Upstream          Downstream
                     domain            domain

                     l-QC21   ----->   l-QC11

                     l-QC22   ----->   l-QC12

                     l-QC23   ----->
                     l-QC24   ----->

                          Figure 3: l-QC Binding

   If one l-QC was to be bound to two (or more) l-QCs it would be very
   difficult for packets to know whether they should jump to one l-QC or
   the other.  This could imply a flow classification at the border of
   the domains based on granularity as fine as the application flows.
   For the sake of scalability we assume one l-QC should not be bound to
   several l-QCs [Lev].  On the contrary, several l-QCs can be bound to
   the same l-QC, in the way that l-QC23 and l-QC24 are bound to l-QC13
   in Figure 3.

   A provider decides the best match between l-QCs based exclusively on:

   - What it knows about its own l-QCs;

   - What it knows about its neighboring l-QCs.

   It does not use any information related to what is happening more
   than one domain away.

   Despite this one hop, short-sighted approach, the consistency and the
   coherency of the QoS treatment must be ensured on an l-QC thread
   formed by neighboring bound l-QCs.  Packets leaving a domain that
   applies a given l-QC, should experience similar treatment when
   crossing external domains up to their final destination.  A provider
   should bind its l-QC with the neighboring l-QC that has the closest
   performance.  The criteria for l-QC binding should be stable along
   any l-QC thread.  For example, two providers should not bind two
   l-QCs for minimizing the delay whereas further on, on the same
   thread, two other providers have bound two l-QCs for minimizing
   errors.  Constraints should be put on l-QC QoS performance parameters
   to confine their values to an acceptable and expected level on an
   l-QC thread scale.  These constraints should depend on domain size,
   for example restrictions on delay should authorize a bigger value for
   a national domain than for a regional one.  Some rules must therefore
   be defined to establish in which conditions two l-QCs can be bound

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   together.  These rules are provided by the notion of Meta-QoS-Class

4.3.  MQC-based Binding process

   An MQC provides the limits of the QoS parameters two l-QCs must
   respect in order to be bound together.  A provider goes through
   several steps to extend its internal l-QCs through the binding
   process.  Firstly, it classifies its own l-QCs based on MQCs.  An MQC
   is used as a label that certifies the support of a set of
   applications that bear similar network QoS requirements.  It is a
   means to make sure that an l-QC has the appropriate QoS
   characteristics to convey the traffic of this set of applications.
   Secondly, it learns about available MQCs advertised by its neighbors.
   To advertise an MQC, a provider must have at least one compliant l-QC
   and should be ready to reach agreements to let neighbor traffic
   benefit from it.  Thirdly, it contracts an agreement with its
   neighbor to send some traffic that will be handled according to the
   agreed MQCs.

   The following attributes should be documented in any specification of
   an MQC.  This is not a closed list, other points can be added if

   o  A set of applications (e.g.  VoIP) the MQC is particularly suited

   o  Boundaries or intervals for each QoS performance attribute (D, J,
      L), whenever required.  An MQC can be focused on a single
      parameter (e.g. low delay).  Several levels can be specified
      depending on the size of the network provider, for instance a
      small domain (e.g. regional) needs lower delay than a large domain
      (e.g. national) to match a given MQC.

   o  Constraints on traffic (e.g. only TCP-friendly).

   o  Constraints on the ratio: network resources for the class /
      overall traffic using this class (e.g. less resources than peak

   Two l-QCs can be bound together if, and only if, they conform to the
   same MQC.

   Provider-to-provider SLSs, as defined here, are uni-directional.
   They are established for transporting traffic in a given direction.
   However, from a business perspective, it is likely that reverse SLSs
   will also be negotiated for transporting traffic in the opposite

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   A hierarchy of MQCs can be defined for a given type of service (e.g.
   VoIP with different qualities: VoIP for residential and VoIP for
   business).  A given l-QC can be suitable for several MQCs (even
   outside the same hierarchy).  Several l-QCs in the same domain can be
   classified as belonging to the same MQC.  There is an MQC with no
   specific constraints called the best-effort MQC.

   The need for standardization is great in respect of inter-domain QoS
   agreements [RFC3387].  Each provider must have the same understanding
   of what a given MQC is about.  We need a global agreement on a set of
   MQC standards.  The number of classes to be defined must remain very
   small to avoid overwhelming complexity.  We also need a means to
   certify that the l-QC classification made by a provider conforms to
   the MQC standards.  So the standardization effort should be
   accompanied by investigations on conformance testing requirements.

   The three notions of PDB, Service Class [RFC4594], and MQC are
   related; what MQC brings is the inter-domain aspect:

   - PDB is how to engineer a network;

   - Service Class is a set of traffic with specific QoS requests;

   - MQC is a standardized way to classify the QoS capabilities (l-QCs,
   through Diffserv or any other protocols or mechanisms) in order to
   reach agreements with neighbors.  MQCs are involved only when an ISP
   wants to agree an SLS with a neighboring ISP.  MQC is completely
   indifferent to the way networks are engineered as long as the (D, J,
   L) values are reached.

5.  The Internet as MQC planes

   The resulting QoS Internet can be viewed as a set of parallel
   Internets or MQC planes.  Each plane consists of all the l-QCs bound
   according to the same MQC.  An MQC plane can have holes and isolated
   domains because QoS capabilities do not cover all Internet domains.
   When an l-QC maps to several MQCs, it belongs potentially to several

   When a provider contracts with another provider based on the use of
   MQCs, it simply adds a logical link to the corresponding MQC plane.
   This is basically what current traditional inter-domain agreements
   mean for the existing Internet.  Figure 4a) depicts the physical
   layout of a fraction of the Internet, comprising four domains with
   full-mesh connectivity.

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                +----+    +----+               +----+    +----+
                |SP  +----+SP  |               |SP  +----+SP  |
                |1   |    |2   |               |1   |    |2   |
                +-+--+    +--+-+               +-+--+    +----+
                  |   \  /   |                   |      /
                  |    \/    |                   |     /
                  |    /\    |                   |    /
                  |   /  \   |                   |   /
                +-+--+    +--+-+               +-+--+    +----+
                |SP  +----+SP  |               |SP  |    |SP  |
                |4   |    |3   |               |4   |    |3   |
                +----+    +----+               +----+    +----+
                a) physical configuration      b) an MQC plane

                           Figure 4: MQC planes

   Figure 4 b) depicts how these four domains are involved in a given
   MQC plane.  SP1, SP2 and SP4 have at least one compliant l-QC (SP3
   maybe has or not) for this MQC.  A bi-directional agreement exists
   between SP1 and SP2, SP1 and SP4, SP2 and SP4.

   For a global QoS-based Internet, this solution will work only if MQC-
   based binding is largely accepted and becomes a current practice.
   This limitation is due to the nature of the service itself, and not
   to the use of MQCs.  Insofar as we target global services we are
   bound to provide QoS in as many SP domains as possible.  However, any
   MQC-enabled part of the Internet that forms a connected graph can be
   used for QoS communications, and be extended.  Therefore, incremental
   deployment is possible, and leads to incremental benefits.  For
   example, in Figure 4 right-hand plane, as soon as SP3 connects to the
   MQC plane it will be able to benefit from the SP1, SP2 and SP4 QoS

   The Internet as a split of different MQC planes offers an ordered and
   simplified view of the Internet QoS capabilities.  End-users can
   select the MQC plane that is the closest to their needs, as long as
   there is a path available for the destination.  One of the main
   outcomes of applying the MQC concept is that it alleviates the
   complexity and the management burden of inter-domain relationships.

6.  Towards end-to-end QoS services

   Building end-to-end QoS paths, for the purpose of QoS-guaranteed
   communications between end-users, is going a step further in the QoS
   process.  The full description of customer-to-provider QoS
   agreements, and the way they are enforced, is outside the scope of
   this memo.  However, in this section, we will list some important

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   issues and state whether MQC can help to find solutions.

   Route path selection within a selected MQC plane can be envisaged in
   the same way as the traditional routing system used by Internet
   routers.  Thus, we can rely on the BGP protocol, basically one BGP
   occurrence per MQC plane, for the inter-domain routing process.  The
   resilience of the IP routing system is preserved.  If a QoS path
   breaks somewhere, the routing protocol enables dynamic computation of
   another QoS path, if available, in the proper MQC plane.  This
   provides a first level of QoS infrastructure that could be
   conveniently named "best-effort QoS", even if this is an oxymoron.

   On this basis, features can be added in order to select and control
   the QoS paths better.  For example, BGP can be used to convey QoS-
   related information, and to implement a process where Autonomous
   Systems add their own QoS values (D, J, L) when they propagate an AS
   path.  Then, the AS path information is coupled with the information
   on Delay, Jitter and Loss, and the decision whether or not to use the
   path selected by BGP can be taken, based on numerical values.  The
   QoS value of an AS path could also be disconnected from BGP and
   computed via an off-line process.

   If we use QoS routing, we can incorporate the (D, J, L) information
   in the BGP decision process, but that raises the issue of composing
   performance metrics in order to select appropriate paths [Chau].
   When confronted by multiple incompatible objectives, the local
   decisions taken to optimize the targeted parameters could give rise
   to a set of incomparable paths, where no path is strictly superior to
   the others.  The existence of provider-to-provider SLSs based on MQC
   offers a homogenous view of the QoS parameters, and should therefore
   bring coherency, and restrict the risk of such non optimal choices.

   Almost any useful end-to-end service is bi-directional, so one must
   measure the composite performance in both directions.  Many inter-
   domain paths are asymmetric, and usually, some providers involved in
   the forward path are not in the reverse path, and vice versa.  That
   means that no assumptions can be made about the reverse path.
   Although MQC-based provider-to-provider SLSs are likely to be
   negotiated bi-directionally, they allow the inter-domain routing
   protocol to compute the forward and the reverse paths separately, as
   usual.  The only constraint MQC puts on routing is that the selected
   paths must use the chosen MQCs throughout the selected domains.
   There might be a different MQC requirement in the reverse direction
   than in the forward direction.  To address this problem, we can use
   application level communication between the two parties (customers)
   involved in order to specify the QoS requirements in both directions.

   We can go a step further in the control of the path to ensure the

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   stability of QoS parameters such as, for example, enforcing an
   explicit routing scheme, making use of RSVP-TE/MPLS-TE requests
   [RFC3209], before injecting the traffic into an l-QC thread.
   However, currently, several problems must be resolved before ready
   and operational solutions for inter-domain route pinning, inter-
   domain TE, fast failover, and so forth, are available.  See for
   example the BGP slow convergence problem in [Kushman].

   Multicast supports many applications such as audio and video
   broadcasting (e.g.  IPTV, streaming applications) with QoS
   requirements.  Along with solutions at the IP or Application level,
   such as Forward Error Correction (FEC), the inter-domain multicast
   routing protocol with Multiprotocol Extensions for BGP-4 [RFC4760],
   could be used to advertise MQC capabilities for multicast source
   reachability.  If an inter-domain tree that spans several domains
   remains in the same MQC plane, it would be possible to benefit from
   the consistency and the coherency conferred by MQC.

   To conclude this section, whatever the protocols we want to use, and
   however tightly we want to control QoS paths, MQC is a concept that
   can help to resolve problems [WIP], without prohibiting the use of
   any particular mechanism or protocol at the data, control, or
   management planes.

7.  IANA Considerations

   There are no IANA considerations.

   Note to RFC Editor: this section may be removed on publication as an

8.  Security Considerations

   This document describes a framework and not protocols or systems.
   Potential risks and attacks will depend directly on the
   implementation technology.  Solutions to implement this proposal must
   detail security issues in the relevant protocol documentation.

   Particular attention should be paid to giving access to MQC resources
   only to authorized traffic.  Unauthorized access can lead to denial
   of service when the network resources get overused [RFC3869].

9.  Acknowledgements

   This work is funded by the European Commission, within the context of

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   the MESCAL (Management of End-to-End Quality of Service Across the
   Internet At Large, http://www.mescal.org) and AGAVE (A liGhtweight
   Approach for Viable End-to-end IP-based QoS Services,
   http://www.ist-agave.org) projects.  The authors would like to thank
   all the other partners for the fruitful discussions.

   We are grateful to Brian Carpenter and Jon Crowcroft for their
   helpful comments and suggestions for improving this document.

10.  References

10.1.  Normative References

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, September 1999.

   [RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Packet Loss Metric for IPPM", RFC 2680, September 1999.

   [RFC3393]  Demichelis, C. and P. Chimento, "IP Packet Delay Variation
              Metric for IP Performance Metrics (IPPM)", RFC 3393,
              November 2002.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

10.2.  Informative References

   [Chau]     Chau, C., "Policy-based routing with non-strict
              preferences", Proceedings of the ACM SIGCOMM 2006
              Conference on Applications, Technologies, Architectures,
              and Protocols for Computer Communications, Pisa, Italy, pp
              387-398, September 2006.

   [E2E]      Saltzer, J H., Reed, D P., and D D. Clark, "End-To-End
              Arguments in System Design", ACM Transactions in Computer
              Systems, Vol 2, Number 4, pp 277-288, November 1984.

   [Kushman]  Kushman, N., Kandula, S., and D. Katabi, "Can You Hear Me
              Now?! It Must Be BGP", ACM Journal of Computer and
              Communication Review CCR, November 2007.

   [Lev]      Levis, P., Asgari, H., and P. Trimintzios, "Consideration
              on Inter-domain QoS and Traffic Engineering issues Through
              a Utopian Approach", SAPIR-2004 workshop of ICT-2004, (C)
              Springer-Verlag, August 2004.

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   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [RFC2990]  Huston, G., "Next Steps for the IP QoS Architecture",
              RFC 2990, November 2000.

   [RFC3086]  Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules for
              their Specification", RFC 3086, April 2001.

   [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.

   [RFC3387]  Eder, M., Chaskar, H., and S. Nag, "Considerations from
              the Service Management Research Group (SMRG) on Quality of
              Service (QoS) in the IP Network", RFC 3387,
              September 2002.

   [RFC3869]  Atkinson, R., Floyd, S., and Internet Architecture Board,
              "IAB Concerns and Recommendations Regarding Internet
              Research and Evolution", RFC 3869, August 2004.

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              August 2006.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              January 2007.

   [WIP]      Deleuze, G. and F. Guattari, "What Is Philosophy?",
              Columbia University Press ISBN: 0231079893, April 1996.

Authors' Addresses

   Pierre Levis
   France Telecom
   42 rue des Coutures
   BP 6243
   Caen Cedex 4  14066

   Email: pierre.levis@orange-ftgroup.com

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   Mohamed Boucadair
   France Telecom
   42 rue des Coutures
   BP 6243
   Caen Cedex 4  14066

   Email: mohamed.boucadair@orange-ftgroup.com

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