💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc5160.txt captured on 2024-06-16 at 16:58:51.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Network Working Group P. Levis
Request for Comments: 5160 M. Boucadair
Category: Informational France Telecom
March 2008
Considerations of Provider-to-Provider Agreements
for Internet-Scale Quality of Service (QoS)
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.
IESG Note
This RFC is not a candidate for any level of Internet Standard. The
IETF disclaims any knowledge of the fitness of this RFC for any
purpose and notes that the decision to publish is not based on IETF
review apart from IESG review for conflict with IETF work. The RFC
Editor has chosen to publish this document at its discretion. See
RFC 3932 for more information.
Abstract
This memo analyzes provider-to-provider Quality of Service (QoS)
agreements suitable for a global QoS-enabled Internet. It defines
terminology relevant to inter-domain QoS models. It proposes a new
concept denoted by Meta-QoS-Class (MQC). This concept could
potentially drive and federate the way QoS inter-domain relationships
are built between providers. It opens up new perspectives for a QoS-
enabled Internet that retains, as much as possible, the openness of
the existing best-effort Internet.
Levis & Boucadair Informational [Page 1]
RFC 5160 MQC and Provider QoS Agreements March 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Assumptions and Requirements . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Weaknesses of Provider-to-Provider QoS Agreements Based on
SP Chains . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. IP Connectivity Services . . . . . . . . . . . . . . . . . 6
4.2. Similarity between Provider and Customer Agreements . . . 6
4.3. Liability for Service Disruption . . . . . . . . . . . . . 7
4.4. SP Chain Trap Leading to Glaciation . . . . . . . . . . . 7
5. Provider-to-Provider Agreements Based on Meta-QoS-Class . . . 7
5.1. Single Domain Covering . . . . . . . . . . . . . . . . . . 8
5.2. Binding l-QCs . . . . . . . . . . . . . . . . . . . . . . 9
5.3. MQC-Based Binding Process . . . . . . . . . . . . . . . . 10
6. The Internet as MQC Planes . . . . . . . . . . . . . . . . . . 12
7. Towards End-to-End QoS Services . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
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 multiple 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
multiple domains and Internet areas deal with inter-domain aspects.
However, they differ significantly in many ways, such as the number
of domains and QoS paths involved, which are much higher and dynamic
for the Internet area. Multiple domains and Internet areas are
therefore likely to differ in their respective solutions. This memo
is an attempt to investigate the Internet area from the point of view
of provider-to-provider agreements. It provides a framework for
inter-domain QoS-enabled Internet.
[MESCAL]provides a set of requirements to be met by any solution
aiming to solve inter-domain QoS issues. These requirements are not
reproduced within this memo. Readers are invited to refer to
[MESCAL] for more elaborated description on the requirements.
Levis & Boucadair Informational [Page 2]
RFC 5160 MQC and Provider QoS Agreements March 2008
This memo shows that for the sake of scalability, providers need not
be concerned with what occurs more than one hop away (from their
Autonomous System) when they negotiate inter-domain QoS agreements.
They should base their agreements on nothing but their local QoS
capabilities and those of their direct neighbors. This analysis
leads us to define terminology relevant to inter-domain QoS models.
We also introduce a new concept denoted by Meta-QoS-Class (MQC) that
drives and federates the way QoS inter-domain relationships are built
between providers. The rationale for the MQC concept relies on a
universal and common understanding of QoS-sensitive applications
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.
MQC brings up a simplified view of the Internet QoS capabilities as a
set of MQC planes. This memo looks at whether the idea of MQC planes
can be helpful in certain well-known concrete inter-domain QoS
issues. The focus, however, is on the provider-to-provider QoS
agreement framework, and the intention is not to specify individual
solutions and protocols for a full inter-domain QoS system. For
discussion of a complete architecture based on the notion of parallel
Internets that extends and generalizes the notion of MQC planes, see
[AGAVE].
Note that this document does not specify any protocols or systems.
2. Assumptions and Requirements
To avoid a great deal of complexity and scalability issues, we assume
that provider-to-provider QoS agreements are negotiated only for two
adjacent domains that are directly accessible to each other. We also
assume, because they exchange traffic, that these neighbors are BGP
[RFC4271] peers. This pairwise peering is logical, therefore it can
be supported not only on physical point-to-point connections but also
on Internet exchange points (IXPs), where many operators connect to
each other using a layer 2 switch.
The QoS solutions envisaged in this document are exclusively
solutions suitable for the global Internet. As far as Internet-wide
solutions are concerned, this document assumes that:
o Any solutions should apply locally in order to be usable as soon
as deployed in a small set of domains.
Levis & Boucadair Informational [Page 3]
RFC 5160 MQC and Provider QoS Agreements March 2008
o Any 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 and all end-users.
o Any solutions should also maintain a best-effort service that
should remain the preeminent service as a consequence of the end-
to-end argument [E2E].
o 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 own
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.
3. 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].
Domain
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 the Destination.
Levis & Boucadair Informational [Page 4]
RFC 5160 MQC and Provider QoS Agreements March 2008
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
other.
L-QC thread
Chain of neighboring bound l-QCs.
Meta-QoS-Class (MQC)
An MQC provides the limits of the QoS parameter values that 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.
4. Weaknesses of Provider-to-Provider QoS Agreements Based on SP Chains
The objective of this section is to show, by a sort of reductio ad
absurdum proof, that within the scope of Internet services, provider-
to-provider QoS agreements should be based on guarantees that span a
single domain.
We therefore analyze provider-to-provider QoS agreements based on
guarantees that span several domains and emphasize their
vulnerabilities. In this case, 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
Levis & Boucadair Informational [Page 5]
RFC 5160 MQC and Provider QoS Agreements March 2008
several weaknesses of such an approach, especially the SP chain trap
problem that leads to the so-called Internet glaciation era.
4.1. 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.
Provider- /--------------SP chain---------------\
oriented
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.
4.2. 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 alternative 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.
Levis & Boucadair Informational [Page 6]
RFC 5160 MQC and Provider QoS Agreements March 2008
4.3. 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.
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 the 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 the 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?
4.4. 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 4.2, 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 perhaps has never even heard
of.
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.
5. Provider-to-Provider Agreements Based on Meta-QoS-Class
If a QoS-enabled Internet is deemed desirable, with QoS services
potentially available to and from any destination, any solution must
resolve the above weaknesses and scalability problems and find
alternate schemes for provider-to-provider agreements.
Levis & Boucadair Informational [Page 7]
RFC 5160 MQC and Provider QoS Agreements March 2008
5.1. 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
relationships, is better suited for a global QoS Internet than one
based on SP chains.
Provider-
oriented
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.
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 by all the
neighbors with whom it has a direct contract.
Levis & Boucadair Informational [Page 8]
RFC 5160 MQC and Provider QoS Agreements March 2008
5.2. Binding l-QCs
When a provider wants to contract with another provider, the main
concern is deciding 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.
Upstream Downstream
domain domain
l-QC21 -----> l-QC11
l-QC22 -----> l-QC12
l-QC23 ----->
l-QC13
l-QC24 ----->
Figure 3: l-QC Binding
If one l-QC were to be bound to two (or more) l-QCs, it would be very
difficult to know which l-QC the packets should select. 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 to minimize the delay whereas further on, on the same thread,
two other providers have bound two l-QCs to minimize errors.
Levis & Boucadair Informational [Page 9]
RFC 5160 MQC and Provider QoS Agreements March 2008
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
together. These rules are provided by the notion of Meta-QoS-Class
(MQC).
5.3. 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 attributes can be added if
needed.
o A set of applications (e.g., VoIP) the MQC is particularly suited
for.
o Boundaries or intervals of a set of QoS performance attributes
whenever required. For illustration purposes, we propose to use
in this document attribute (D, J, L) 3-tuple. An MQC could be
focused on a single parameter (e.g., suitable to convey delay
sensitive traffic). Several levels could also 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
traffic).
Levis & Boucadair Informational [Page 10]
RFC 5160 MQC and Provider QoS Agreements March 2008
Two l-QCs can be bound together if, and only if, they conform to the
same MQC.
Provider-to-provider agreements, 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 agreements will also be negotiated for transporting
traffic in the opposite direction. Note that uni-directional
provider-to-provider agreements do not preclude having end-to-end
services with bi-directional guarantees, when you consider the two
directions of the traffic separately.
Two providers negotiating an agreement based on MQC will have to
agree on several other parameters that are outside the definition of
MQC. One such obvious parameter is bandwidth. The two providers
agree to exchange up to a given level of QoS traffic. This bandwidth
level can then be further renegotiated, inside the same MQC
agreement, to reflect an increase in the end-user QoS requests.
Other clauses of inter-domain agreements could cover availability of
the service, time of repair, etc.
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.
There is a need for some form of standardization to control QoS
agreements between providers [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 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 only involved when a provider
Levis & Boucadair Informational [Page 11]
RFC 5160 MQC and Provider QoS Agreements March 2008
wants to negotiate an agreement with a neighboring provider. MQC
is completely indifferent to the way networks are engineered as
long as the MQC QoS attribute (e.g., (D, J, L)) values are reached.
6. 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
planes.
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.
+----+ +----+ +----+ +----+
|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 for
this MQC; SP3 may or may not have one. A bi-directional agreement
exists between SP1 and SP2, SP1 and SP4, SP2 and SP4.
MQC brings 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.
Provider agreements do not directly map end-users' needs; therefore,
the number of provider agreements is largely independent of the
Levis & Boucadair Informational [Page 12]
RFC 5160 MQC and Provider QoS Agreements March 2008
number of end-user requests and does not increase as dramatically as
with SP chains.
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 can be extended. Therefore,
incremental deployment is possible, and leads to incremental
benefits. For example, in Figure 4 b), as soon as SP3 connects to
the MQC plane it will be able to benefit from the SP1, SP2, and SP4
QoS capabilities.
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.
7. 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
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 made, based on numerical values. For
Levis & Boucadair Informational [Page 13]
RFC 5160 MQC and Provider QoS Agreements March 2008
example, for destination N, an AS path (X, Y) is advertised to AS Z.
During the propagation of this AS path by BGP, X adds the information
concerning its own delay, say 30 ms, and Y adds the information
concerning its own delay, say 20 ms. Z receives the BGP
advertisement (X, Y, N, 50 ms). One of Z's customers requests a
delay of 100 ms to reach N. Z knows its own delay for this customer,
say 20 ms. Z computes the expected maximum delay from its customer
to N: 70 ms, and concludes that it can use the AS path (X, Y). 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 made 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 agreements 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.
A lot of end-to-end services are 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 agreements 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
stability of QoS parameters such as, e.g., 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. For example, see the
BGP slow convergence problem in [Kushman].
Multicast supports many applications such as audio and video
distribution (e.g., IPTV, streaming applications) with QoS
Levis & Boucadair Informational [Page 14]
RFC 5160 MQC and Provider QoS Agreements March 2008
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.
Note that the use of some QoS parameters to drive the route selection
process within an MQC plane may induce QoS deterioration since the
best QoS-inferred path will be selected by all Autonomous System
Border Routers (ASBRs) involved in the inter-domain path computation
(i.e., no other available routes in the same MQC plane will have a
chance to be selected). This problem was called the QoS Attribute-
rush (QA-rush) in [Grif]. This drawback may be avoided if all
involved ASes in the QoS chain implement some out-of-band means to
control the inter-domain QoS path consistency (MQC compliance).
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.
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
the MESCAL (Management of End-to-End Quality of Service Across the
Internet At Large) and AGAVE (A liGhtweight Approach for Viable End-
to-end IP-based QoS Services) projects. The authors would like to
thank all the other partners for the fruitful discussions.
We are grateful to Brian Carpenter, Jon Crowcroft, and Juergen
Quittek for their helpful comments and suggestions for improving this
document.
Levis & Boucadair Informational [Page 15]
RFC 5160 MQC and Provider QoS Agreements March 2008
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., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
January 2006.
10.2. Informative References
[AGAVE] Boucadair, et al., "Parallel Internets Framework", IST
AGAVE project public deliverable D1.1, September 2006.
[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.
[Grif] Griffin, D., Spencer, J., Griem, J., Boucadair, M.,
Morand, P., Howarth, M., Wang, N., Pavlou, G., Asgari, A.,
and P. Georgatsos, "Interdomain routing through QoS-class
planes [Quality-of-Service-Based Routing Algorithms for
Heterogeneous Networks]", IEEE Communications
Magazine, Vol 45, Issue 2, pp 88-95, February 2007.
[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.
Levis & Boucadair Informational [Page 16]
RFC 5160 MQC and Provider QoS Agreements March 2008
[MESCAL] Flegkas, et al., "Specification of Business Models and a
Functional Architecture for Inter-domain QoS Delivery",
IST MESCAL project public deliverable D1.1, May 2003.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[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., Ed., Floyd, S., Ed., 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.
Levis & Boucadair Informational [Page 17]
RFC 5160 MQC and Provider QoS Agreements March 2008
Authors' Addresses
Pierre Levis
France Telecom
42 rue des Coutures
BP 6243
Caen Cedex 4 14066
France
EMail: pierre.levis@orange-ftgroup.com
Mohamed Boucadair
France Telecom
42 rue des Coutures
BP 6243
Caen Cedex 4 14066
France
EMail: mohamed.boucadair@orange-ftgroup.com
Levis & Boucadair Informational [Page 18]
RFC 5160 MQC and Provider QoS Agreements March 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78 and at http://www.rfc-editor.org/copyright.html,
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.
Levis & Boucadair Informational [Page 19]