💾 Archived View for radia.bortzmeyer.org › rfc-mirror › rfc9064.txt captured on 2024-05-10 at 12:13:08.
⬅️ Previous capture (2023-06-14)
-=-=-=-=-=-=-
Internet Research Task Force (IRTF) D. Oran
Request for Comments: 9064 Network Systems Research and Design
Category: Informational June 2021
ISSN: 2070-1721
Considerations in the Development of a QoS Architecture for CCNx-Like
Information-Centric Networking Protocols
Abstract
This is a position paper. It documents the author's personal views
on how Quality of Service (QoS) capabilities ought to be accommodated
in Information-Centric Networking (ICN) protocols like Content-
Centric Networking (CCNx) or Named Data Networking (NDN), which
employ flow-balanced Interest/Data exchanges and hop-by-hop
forwarding state as their fundamental machinery. It argues that such
protocols demand a substantially different approach to QoS from that
taken in TCP/IP and proposes specific design patterns to achieve both
classification and differentiated QoS treatment on both a flow and
aggregate basis. It also considers the effect of caches in addition
to memory, CPU, and link bandwidth as resources that should be
subject to explicitly unfair resource allocation. The proposed
methods are intended to operate purely at the network layer,
providing the primitives needed to achieve transport- and higher-
layer QoS objectives. It explicitly excludes any discussion of
Quality of Experience (QoE), which can only be assessed and
controlled at the application layer or above.
This document is not a product of the IRTF Information-Centric
Networking Research Group (ICNRG) but has been through formal Last
Call and has the support of the participants in the research group
for publication as an individual submission.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Research Task Force
(IRTF). The IRTF publishes the results of Internet-related research
and development activities. These results might not be suitable for
deployment. This RFC represents the individual opinion(s) of one or
more members of the Information-Centric Networking Research Group of
the Internet Research Task Force (IRTF). Documents approved for
publication by the IRSG are not candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9064.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction
1.1. Applicability Assessment by ICNRG Chairs
2. Requirements Language
3. Background on Quality of Service in Network Protocols
3.1. Basics on How ICN Protocols like NDN and CCNx Work
3.2. Congestion Control Basics Relevant to ICN
4. What Can We Control to Achieve QoS in ICN?
5. How Does This Relate to QoS in TCP/IP?
6. Why Is ICN Different? Can We Do Better?
6.1. Equivalence Class Capabilities
6.2. Topology Interactions with QoS
6.3. Specification of QoS Treatments
6.4. ICN Forwarding Semantics Effect on QoS
6.5. QoS Interactions with Caching
7. Strawman Principles for an ICN QoS Architecture
7.1. Can Intserv-Like Traffic Control in ICN Provide Richer QoS
Semantics?
8. IANA Considerations
9. Security Considerations
10. References
10.1. Normative References
10.2. Informative References
Author's Address
1. Introduction
The TCP/IP protocol suite used on today's Internet has over 30 years
of accumulated research and engineering into the provisioning of QoS
machinery, employed with varying success in different environments.
ICN protocols like NDN [NDN] and CCNx [RFC8569] [RFC8609] have an
accumulated ten years of research and very little deployment. We
therefore have the opportunity to either recapitulate the approaches
taken with TCP/IP (e.g., Intserv [RFC2998] and Diffserv [RFC2474]) or
design a new architecture and associated mechanisms aligned with the
properties of ICN protocols, which differ substantially from those of
TCP/IP. This position paper advocates the latter approach and
comprises the author's personal views on how QoS capabilities ought
to be accommodated in ICN protocols like CCNx or NDN. Specifically,
these protocols differ in fundamental ways from TCP/IP. The
important differences are summarized in Table 1:
+=============================+====================================+
| TCP/IP | CCNx or NDN |
+=============================+====================================+
| Stateless forwarding | Stateful forwarding |
+-----------------------------+------------------------------------+
| Simple packets | Object model with optional caching |
+-----------------------------+------------------------------------+
| Pure datagram model | Request-response model |
+-----------------------------+------------------------------------+
| Asymmetric routing | Symmetric routing |
+-----------------------------+------------------------------------+
| Independent flow directions | Flow balance (see note below) |
+-----------------------------+------------------------------------+
| Flows grouped by IP prefix | Flows grouped by name prefix |
| and port | |
+-----------------------------+------------------------------------+
| End-to-end congestion | Hop-by-hop congestion control |
| control | |
+-----------------------------+------------------------------------+
Table 1: Differences between IP and ICN Relevant to QoS Architecture
| Note: Flow balance is a property of NDN and CCNx that ensures
| one Interest packet provokes a response of no more than one
| Data packet. Further discussion of the relevance of this to
| QoS can be found in [FLOWBALANCE].
This document proposes specific design patterns to achieve both flow
classification and differentiated QoS treatment for ICN on both a
flow and aggregate basis. It also considers the effect of caches in
addition to memory, CPU, and link bandwidth as resources that should
be subject to explicitly unfair resource allocation. The proposed
methods are intended to operate purely at the network layer,
providing the primitives needed to achieve both transport and higher-
layer QoS objectives. It does not propose detailed protocol
machinery to achieve these goals; it leaves these to supplementary
specifications, such as [FLOWCLASS] and [DNC-QOS-ICN]. It explicitly
excludes any discussion of QoE, which can only be assessed and
controlled at the application layer or above.
Much of this document is derived from presentations the author has
given at ICNRG meetings over the last few years that are available
through the IETF datatracker (see, for example, [Oran2018QoSslides]).
1.1. Applicability Assessment by ICNRG Chairs
QoS in ICN is an important topic with a huge design space. ICNRG has
been discussing different specific protocol mechanisms as well as
conceptual approaches. This document presents architectural
considerations for QoS, leveraging ICN properties instead of merely
applying IP-QoS mechanisms, without defining a specific architecture
or specific protocol mechanisms yet. However, there is consensus in
ICNRG that this document, clarifying the author's views, could
inspire such work and should hence be published as a position paper.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Background on Quality of Service in Network Protocols
Much of this background material is tutorial and can be simply
skipped by readers familiar with the long and checkered history of
quality of service in packet networks. Other parts of it are
polemical yet serve to illuminate the author's personal biases and
technical views.
All networking systems provide some degree of "quality of service" in
that they exhibit nonzero utility when offered traffic to carry. In
other words, the network is totally useless if it never delivers any
of the traffic injected by applications. The term QoS is therefore
more correctly applied in a more restricted sense to describe systems
that control the allocation of various resources in order to achieve
_managed unfairness_. Absent explicit mechanisms to decide which
traffic to treat unfairly, most systems try to achieve some form of
"fairness" in the allocation of resources, optimizing the overall
utility delivered to all traffic under the constraint of available
resources. From this, it should be obvious that you cannot use QoS
mechanisms to create or otherwise increase resource capacity! In
fact, all known QoS schemes have nonzero overhead and hence may
(albeit slightly) decrease the total resources available to carry
user traffic.
Further, accumulated experience seems to indicate that QoS is helpful
in a fairly narrow range of network conditions:
* If your resources are lightly loaded, you don't need it, as
neither congestive loss nor substantial queuing delay occurs.
* If your resources are heavily oversubscribed, it doesn't save you.
So many users will be unhappy that you are probably not delivering
a viable service.
* Failures can rapidly shift your state from the first above to the
second, in which case either:
- Your QoS machinery cannot respond quickly enough to maintain
the advertised service quality continuously, or
- Resource allocations are sufficiently conservative to result in
substantial wasted capacity under non-failure conditions.
Nevertheless, though not universally deployed, QoS is advantageous at
least for some applications and some network environments. Some
examples include:
* Applications with steep utility functions [Shenker2006], such as
real-time multimedia
* Applications with safety-critical operational constraints, such as
avionics or industrial automation
* Dedicated or tightly managed networks whose economics depend on
strict adherence to challenging service level agreements (SLAs)
Another factor in the design and deployment of QoS is the scalability
and scope over which the desired service can be achieved. Here there
are two major considerations, one technical, the other economic/
political:
* Some signaled QoS schemes, such as the Resource reSerVation
Protocol (RSVP) [RFC2205], maintain state in routers for each
flow, which scales linearly with the number of flows. For core
routers through which pass millions to billions of flows, the
memory required is infeasible to provide.
* The Internet is comprised of many minimally cooperating autonomous
systems [AS]. There are practically no successful examples of QoS
deployments crossing the AS boundaries of multiple service
providers. In almost all cases, this limits the applicability of
QoS capabilities to be intra-domain.
This document adopts a narrow definition of QoS as _managed
unfairness_ (see note below). However, much of the networking
literature uses the term more colloquially, applying it to any
mechanism that improves overall performance. One could use a
different, broader definition of QoS that encompasses optimizing the
allocation of network resources across all offered traffic without
considering individual users' traffic. A consequence would be the
need to cover whether (and how) ICN might result in better overall
performance than IP under constant resource conditions, which is a
much broader goal than that attempted here. The chosen narrower
scope comports with the commonly understood meaning of "QoS" in the
research community. Under this scope, and under constant resource
constraints, the only way to provide traffic discrimination is in
fact to sacrifice fairness. Readers assuming the broader context
will find a large class of proven techniques to be ignored. This is
intentional. Among these are seamless producer mobility schemes like
MAP-Me [Auge2018] and network coding of ICN data as discussed in
[NWC-CCN-REQS].
| Note: The term _managed unfairness_ used to explain QoS is
| generally ascribed to Van Jacobson, who in talks in the late
| 1990s said, "[The problem we are solving is to] Give 'better'
| service to some at the expense of giving worse service to
| others. QoS fantasies to the contrary, it's a zero-sum game.
| In other words, QoS is _managed unfairness_."
Finally, the relationship between QoS and either accounting or
billing is murky. Some schemes can accurately account for resource
consumption and ascertain to which user to allocate the usage.
Others cannot. While the choice of mechanism may have important
practical economic and political consequences for cost and workable
business models, this document considers none of those things and
discusses QoS only in the context of providing managed unfairness.
For those unfamiliar with ICN protocols, a brief description of how
NDN and CCNx operate as a packet network is in Section 3.1. Some
further background on congestion control for ICN follows in
Section 3.2.
3.1. Basics on How ICN Protocols like NDN and CCNx Work
The following summarizes the salient features of the NDN and CCNx ICN
protocols relevant to congestion control and QoS. Quite extensive
tutorial information may be found in a number of places, including
material available from [NDNTutorials].
In NDN and CCNx, all protocol interactions operate as a two-way
handshake. Named content is requested by a _consumer_ via an
_Interest message_ that is routed hop-by-hop through a series of
_forwarders_ until it reaches a node that stores the requested data.
This can be either the _producer_ of the data or a forwarder holding
a cached copy of the requested data. The content matching the name
in the Interest message is returned to the requester over the
_inverse_ of the path traversed by the corresponding Interest.
Forwarding in CCNx and NDN is _per-packet stateful_. Routing
information to select next hop(s) for an Interest is obtained from a
_Forwarding Information Base (FIB)_, which is similar in function to
the FIB in an IP router except that it holds name prefixes rather
than IP address prefixes. Conventionally, a _Longest Name Prefix
Match (LNPM)_ is used for lookup, although other algorithms are
possible, including controlled flooding and adaptive learning based
on prior history.
Each Interest message leaves a trail of "breadcrumbs" as state in
each forwarder. This state, held in a data structure known as a
_Pending Interest Table (PIT)_, is used to forward the returning Data
message to the consumer. Since the PIT constitutes per-packet state,
it is therefore a large consumer of memory resources, especially in
forwarders carrying high traffic loads over long Round-Trip Time
(RTT) paths, and hence plays a substantial role as a QoS-controllable
resource in ICN forwarders.
In addition to its role in forwarding Interest messages and returning
the corresponding Data messages, an ICN forwarder can also operate as
a cache, optionally storing a copy of any Data messages it has seen
in a local data structure known as a _Content Store (CS)_. Data in
the CS may be returned in response to a matching Interest rather than
forwarding the Interest further through the network to the original
Producer. Both CCNx and NDN have a variety of ways to configure
caching, including mechanisms to avoid both cache pollution and cache
poisoning (these are clearly beyond the scope of this brief
introduction).
3.2. Congestion Control Basics Relevant to ICN
In any packet network that multiplexes traffic among multiple sources
and destinations, congestion control is necessary in order to:
1. Prevent collapse of utility due to overload, where the total
offered service declines as load increases, perhaps
precipitously, rather than increasing or remaining flat.
2. Avoid starvation of some traffic due to excessive demand by other
traffic.
3. Beyond the basic protections against starvation, achieve
"fairness" among competing traffic. Two common objective
functions are max-min fairness [minmaxfairness] and proportional
fairness [proportionalfairness], both of which have been
implemented and deployed successfully on packet networks for many
years.
Before moving on to QoS, it is useful to consider how congestion
control works in NDN or CCNx. Unlike the IP protocol family, which
relies exclusively on end-to-end congestion control (e.g., TCP
[RFC0793], DCCP [RFC4340], SCTP [RFC4960], and QUIC [RFC9000]), CCNx
and NDN can employ hop-by-hop congestion control. There is per-
Interest/Data state at every hop of the path, and therefore
outstanding Interests provide information that can be used to
optimize resource allocation for data returning on the inverse path,
such as bandwidth sharing, prioritization, and overload control. In
current designs, this allocation is often done using Interest
counting. By accepting one Interest packet from a downstream node,
this implicitly provides a guarantee (either hard or soft) that there
is sufficient bandwidth on the inverse direction of the link to send
back one Data packet. A number of congestion control schemes have
been developed for ICN that operate in this fashion, for example,
[Wang2013], [Mahdian2016], [Song2018], and [Carofiglio2012]. Other
schemes, like [Schneider2016], neither count nor police Interests but
instead monitor queues using AQM (active queue management) to mark
returning Data packets that have experienced congestion. This later
class of schemes is similar to those used on IP in the sense that
they depend on consumers adequately reducing their rate of Interest
injection to avoid Data packet drops due to buffer overflow in
forwarders. The former class of schemes is (arguably) more robust
against misbehavior by consumers.
Given the stochastic nature of RTTs, and the ubiquity of wireless
links and encapsulation tunnels with variable bandwidth, a simple
scheme that admits Interests only based on a time-invariant estimate
of the returning link bandwidth will perform poorly. However, two
characteristics of NDN and CCNx-like protocols can help substantially
to improve the accuracy and responsiveness of the bandwidth
allocation:
1. RTT is bounded by the inclusion of an _Interest Lifetime_ in each
Interest message, which puts an upper bound on the RTT
uncertainty for any given Interest/Data exchange. If Interest
Lifetimes are kept reasonably short (a few RTTs), the allocation
of local forwarder resources do not have to deal with an
arbitrarily long tail. One could in fact do a deterministic
allocation on this basis, but the result would be highly
pessimistic. Nevertheless, having a cutoff does improve the
performance of an optimistic allocation scheme.
2. A congestion marking scheme like that used in Explicit Congestion
Notification (ECN) can be used to mark returning Data packets if
the inverse link starts experiencing long queue occupancy or
other congestion indication. Unlike TCP/IP, where the rate
adjustment can only be done end-to-end, this feedback is usable
immediately by the downstream ICN forwarder, and the Interest
shaping rate is lowered after a single link RTT. This may allow
rate adjustment schemes that are less pessimistic than the
Additive Increase, Multiplicative Decrease (AIMD) scheme with .5
multiplier that is commonly used on TCP/IP networks. It also
allows the rate adjustments to be spread more accurately among
the Interest/Data flows traversing a link sending congestion
signals.
A useful discussion of these properties and how they demonstrate the
advantages of ICN approaches to congestion control can be found in
[Carofiglio2016].
4. What Can We Control to Achieve QoS in ICN?
QoS is achieved through managed unfairness in the allocation of
resources in network elements, particularly in the routers that
forward ICN packets. Hence, the first-order questions are the
following: Which resources need to be allocated? How do you
ascertain which traffic gets those allocations? In the case of CCNx
or NDN, the important network element resources are given in Table 2:
+=============================+===================================+
| Resource | ICN Usage |
+=============================+===================================+
| Communication link capacity | buffering for queued packets |
+-----------------------------+-----------------------------------+
| CS capacity | to hold cached data |
+-----------------------------+-----------------------------------+
| Forwarder memory | for the PIT |
+-----------------------------+-----------------------------------+
| Compute capacity | for forwarding packets, including |
| | the cost of FIB lookups |
+-----------------------------+-----------------------------------+
Table 2: ICN-Related Network Element Resources
For these resources, any QoS scheme has to specify two things:
1. How do you create _equivalence classes_ (a.k.a. flows) of traffic
to which different QoS treatments are applied?
2. What are the possible treatments and how are those mapped to the
resource allocation algorithms?
Two critical facts of life come into play when designing a QoS
scheme. First, the number of equivalence classes that can be
simultaneously tracked in a network element is bounded by both memory
and processing capacity to do the necessary lookups. One can allow
very fine-grained equivalence classes but not be able to employ them
globally because of scaling limits of core routers. That means it is
wise to either restrict the range of equivalence classes or allow
them to be _aggregated_, trading off accuracy in policing traffic
against ability to scale.
Second, the flexibility of expressible treatments can be tightly
constrained by both protocol encoding and algorithmic limitations.
The ability to encode the treatment requests in the protocol can be
limited -- as it is for IP where there are only six of the Type of
Service (TOS) bits available for Diffserv treatments. However, an
equal or more important issue is whether there are practical traffic
policing, queuing, and pacing algorithms that can be combined to
support a rich set of QoS treatments.
The two considerations above in combination can easily be
substantially more expressive than what can be achieved in practice
with the available number of queues on real network interfaces or the
amount of per-packet computation needed to enqueue or dequeue a
packet.
5. How Does This Relate to QoS in TCP/IP?
TCP/IP has fewer resource types to manage than ICN, and in some
cases, the allocation methods are simpler, as shown in Table 3:
+===============+=============+================================+
| Resource | IP Relevant | TCP/IP Usage |
+===============+=============+================================+
| Communication | YES | buffering for queued packets |
| link capacity | | |
+---------------+-------------+--------------------------------+
| CS capacity | NO | no CS in IP |
+---------------+-------------+--------------------------------+
| Forwarder | MAYBE | not needed for output-buffered |
| memory | | designs (see note below) |
+---------------+-------------+--------------------------------+
| Compute | YES | for forwarding packets, but |
| capacity | | arguably much cheaper than ICN |
+---------------+-------------+--------------------------------+
Table 3: IP-Related Network Element Resources
| Note: In an output-buffered design, all packet buffering
| resources are associated with the output interfaces, and
| neither the receiver interface nor the internal forwarding
| buffers can be over-subscribed. Output-buffered switches or
| routers are common but not universal, as they generally require
| an internal speedup factor where forwarding capacity is greater
| than the sum of the input capacity of the interfaces.
For these resources, IP has specified three fundamental things, as
shown in Table 4:
+=============+====================================================+
| What | How |
+=============+====================================================+
| Equivalence | subset+prefix match on IP 5-tuple {SA,DA,SP,DP,PT} |
| classes | SA=Source Address |
| | DA=Destination Address |
| | SP=Source Port |
| | DP=Destination Port |
| | PT=IP Protocol Type |
+-------------+----------------------------------------------------+
| Diffserv | (very) small number of globally-agreed traffic |
| treatments | classes |
+-------------+----------------------------------------------------+
| Intserv | per-flow parameterized _Controlled Load_ and |
| treatments | _Guaranteed_ service classes |
+-------------+----------------------------------------------------+
Table 4: Fundamental Protocol Elements to Achieve QoS for TCP/IP
Equivalence classes for IP can be pairwise, by matching against both
source and destination address+port, pure group using only
destination address+port, or source-specific multicast with source
address+port and destination multicast address+port.
With Intserv, RSVP [RFC2205] carries two data structures: the Flow
Specifier (FLOWSPEC) and the Traffic Specifier (TSPEC). The former
fulfills the requirement to identify the equivalence class to which
the QoS being signaled applies. The latter comprises the desired QoS
treatment along with a description of the dynamic character of the
traffic (e.g., average bandwidth and delay, peak bandwidth, etc.).
Both of these encounter substantial scaling limits, which has meant
that Intserv has historically been limited to confined topologies,
and/or high-value usages, like traffic engineering.
With Diffserv, the protocol encoding (six bits in the TOS field of
the IP header) artificially limits the number of classes one can
specify. These are documented in [RFC4594]. Nonetheless, when used
with fine-grained equivalence classes, one still runs into limits on
the number of queues required.
6. Why Is ICN Different? Can We Do Better?
While one could adopt an approach to QoS that mirrors the extensive
experience with TCP/IP, this would, in the author's view, be a
mistake. The implementation and deployment of QoS in IP networks has
been spotty at best. There are, of course, economic and political
reasons as well as technical reasons for these mixed results, but
there are several architectural choices in ICN that make it a
potentially much better protocol base to enhance with QoS machinery.
This section discusses those differences and their consequences.
6.1. Equivalence Class Capabilities
First and foremost, hierarchical names are a much richer basis for
specifying equivalence classes than IP 5-tuples. The IP address (or
prefix) can only separate traffic by topology to the granularity of
hosts and cannot express actual computational instances nor sets of
data. Ports give some degree of per-instance demultiplexing, but
this tends to be both coarse and ephemeral, while confounding the
demultiplexing function with the assignment of QoS treatments to
particular subsets of the data. Some degree of finer granularity is
possible with IPv6 by exploiting the ability to use up to 64 bits of
address for classifying traffic. In fact, the Hybrid Information-
Centric Networking (hICN) project [HICN], while adopting the request-
response model of CCNx, uses IPv6 addresses as the available
namespace, and IPv6 packets (plus "fake" TCP headers) as the wire
format.
Nonetheless, the flexibility of tokenized (i.e., strings treated as
opaque tokens), variable length, hierarchical names allows one to
directly associate classes of traffic for QoS purposes with the
structure of an application namespace. The classification can be as
coarse or fine-grained as desired by the application. While not
_always_ the case, there is typically a straightforward association
between how objects are named and how they are grouped together for
common treatment. Examples abound; a number can be conveniently
found in [FLOWCLASS].
6.2. Topology Interactions with QoS
In ICN, QoS is not pre-bound to network topology since names are non-
topological, unlike unicast IP addresses. This allows QoS to be
applied to multi-destination and multipath environments in a
straightforward manner, rather than requiring either multicast with
coarse class-based scheduling or complex signaling like that in RSVP
Traffic Engineering (RSVP-TE) [RFC3209] that is needed to make point-
to-multipoint Multiprotocol Label Switching (MPLS) work.
Because of IP's stateless forwarding model, complicated by the
ubiquity of asymmetric routes, any flow-based QoS requires state that
is decoupled from the actual arrival of traffic and hence must be
maintained, at least as soft state, even during quiescent periods.
Intserv, for example, requires flow signaling on the order of
O(number of flows). ICN, even worst case, requires order of O(number
of active Interest/Data exchanges), since state can be instantiated
on arrival of an Interest and removed (perhaps lazily) once the data
has been returned.
6.3. Specification of QoS Treatments
Unlike Intserv, Diffserv eschews signaling in favor of class-based
configuration of resources and queues in network elements. However,
Diffserv limits traffic treatments to a few bits taken from the TOS
field of IP. No such wire encoding limitations exist for NDN or
CCNx, as the protocol is completely TLV (Type-Length-Value) based,
and one (or even more than one) new field can be easily defined to
carry QoS treatment information.
Therefore, there are greenfield possibilities for more powerful QoS
treatment options in ICN. For example, IP has no way to express a
QoS treatment like "try hard to deliver reliably, even at the expense
of delay or bandwidth". Such a QoS treatment for ICN could invoke
native ICN mechanisms, none of which are present in IP, such as the
following:
* Retransmitting in-network in response to hop-by-hop errors
returned from upstream forwarders
* Trying multiple paths to multiple content sources either in
parallel or serially
* Assigning higher precedence for short-term caching to recover from
downstream (see note below) errors
* Coordinating cache utilization with forwarding resources
| Note: _Downstream_ refers to the direction Data messages flow
| toward the consumer (the issuer of Interests). Conversely,
| _Upstream_ refers to the direction Interests flow toward the
| producer of data.
Such mechanisms are typically described in NDN and CCNx as
_forwarding strategies_. However, there is little or no guidance for
which application actions or protocol machinery a forwarder should
use to select the appropriate forwarding strategy for arriving
Interest messages. See [BenAbraham2018] for an investigation of
these issues. Associating forwarding strategies with the equivalence
classes and QoS treatments directly can make them more accessible and
useful to implement and deploy.
Stateless forwarding and asymmetric routing in IP limits available
state/feedback to manage link resources. In contrast, NDN or CCNx
forwarding allows all link resource allocation to occur as part of
Interest forwarding, potentially simplifying things considerably. In
particular, with symmetric routing, producers have no control over
the paths their Data packets traverse; hence, any QoS treatments
intended to influence routing paths from producer to consumer will
have no effect.
One complication in the handling of ICN QoS treatments is not present
in IP and hence worth mentioning. CCNx and NDN both perform
_Interest aggregation_ (see Section 2.4.2 of [RFC8569]). If an
Interest arrives matching an existing PIT entry, but with a different
QoS treatment from an Interest already forwarded, it can be tricky to
decide whether to aggregate the Interest or forward it, and how to
keep track of the differing QoS treatments for the two Interests.
Exploration of the details surrounding these situations is beyond the
scope of this document; further discussion can be found for the
general case of flow balance and congestion control in [FLOWBALANCE]
and specifically for QoS treatments in [DNC-QOS-ICN].
6.4. ICN Forwarding Semantics Effect on QoS
IP has three forwarding semantics, with different QoS needs (Unicast,
Anycast, Multicast). ICN has the single forwarding semantic, so any
QoS machinery can be uniformly applied across any request/response
invocation. This applies whether the forwarder employs dynamic
destination routing, multi-destination forwarding with next hops
tried serially, multi-destination with next hops used in parallel, or
even localized flooding (e.g., directly on Layer 2 multicast
mechanisms). Additionally, the pull-based model of ICN avoids a
number of thorny multicast QoS problems that IP has (see [Wang2000],
[RFC3170], and [Tseng2003]).
The Multi-destination/multipath forwarding model in ICN changes
resource allocation needs in a fairly deep way. IP treats all
endpoints as open-loop packet sources, whereas NDN and CCNx have
strong asymmetry between producers and consumers as packet sources.
6.5. QoS Interactions with Caching
IP has no caching in routers, whereas ICN needs ways to allocate
cache resources. Treatments to control caching operation are
unlikely to look much like the treatments used to control link
resources. NDN and CCNx already have useful cache control directives
associated with Data messages. The CCNx controls include the
following:
ExpiryTime: time after which a cached Content Object is considered
expired and MUST no longer be used to respond to an Interest from
a cache.
Recommended Cache Time: time after which the publisher considers the
Content Object to be of low value to cache.
See [RFC8569] for the formal definitions.
ICN flow classifiers, such as those in [FLOWCLASS] can be used to
achieve soft or hard partitioning (see note below) of cache resources
in the CS of an ICN forwarder. For example, cached content for a
given equivalence class can be considered _fate shared_ in a cache
whereby objects from the same equivalence class can be purged as a
group rather than individually. This can recover cache space more
quickly and at lower overhead than pure per-object replacement when a
cache is under extreme pressure and in danger of thrashing. In
addition, since the forwarder remembers the QoS treatment for each
pending Interest in its PIT, the above cache controls can be
augmented by policy to prefer retention of cached content for some
equivalence classes as part of the cache replacement algorithm.
| Note: With hard partitioning, there are dedicated cache
| resources for each equivalence class (or enumerated list of
| equivalence classes). With soft partitioning, resources are at
| least partly shared among the (sets of) equivalence classes of
| traffic.
7. Strawman Principles for an ICN QoS Architecture
Based on the observations made in the earlier sections, this summary
section captures the author's ideas for clear and actionable
architectural principles for incorporating QoS machinery into ICN
protocols like NDN and CCNx. Hopefully, they can guide further work
and focus effort on portions of the giant design space for QoS that
have the best trade-offs in terms of flexibility, simplicity, and
deployability.
*Define equivalence classes using the name hierarchy rather than
creating an independent traffic class definition*. This directly
associates the specification of equivalence classes of traffic with
the structure of the application namespace. It can allow
hierarchical decomposition of equivalence classes in a natural way
because of the way hierarchical ICN names are constructed. Two
practical mechanisms are presented in [FLOWCLASS] with different
trade-offs between security and the ability to aggregate flows.
Either the prefix-based mechanism (the equivalence class component
count (EC3) scheme) or the explicit name component-based mechanism
(the equivalence class name component type (ECNCT) scheme), or both,
could be adopted as the part of the QoS architecture for defining
equivalence classes.
*Put consumers in control of link and forwarding resource
allocation*. Base all link buffering and forwarding (both memory and
CPU) resource allocations on Interest arrivals. This is attractive
because it provides early congestion feedback to consumers and allows
scheduling the reverse link direction for carrying the matching data
in advance. It makes enforcement of QoS treatments a single-ended
(i.e., at the consumer) rather than a double-ended problem and can
avoid wasting resources on fetching data that will be dropped when it
arrives at a bottleneck link.
*Allow producers to influence the allocation of cache resources*.
Producers want to affect caching decisions in order to do the
following:
* Shed load by having Interests served by CSes in forwarders before
they reach the producer itself
* Survive transient producer reachability or link outages close to
the producer
For caching to be effective, individual Data objects in an
equivalence class need to have similar treatment; otherwise, well-
known cache-thrashing pathologies due to self-interference emerge.
Producers have the most direct control over caching policies through
the caching directives in Data messages. It therefore makes sense to
put the producer, rather than the consumer or network operator, in
charge of specifying these equivalence classes.
See [FLOWCLASS] for specific mechanisms to achieve this.
*Allow consumers to influence the allocation of cache resources*.
Consumers want to affect caching decisions in order to do the
following:
* Reduce latency for retrieving data
* Survive transient outages of either a producer or links close to
the consumer
Consumers can have indirect control over caching by specifying QoS
treatments in their Interests. Consider the following potential QoS
treatments by consumers that can drive caching policies:
* A QoS treatment requesting better robustness against transient
disconnection can be used by a forwarder close to the consumer (or
downstream of an unreliable link) to preferentially cache the
corresponding data.
* Conversely, a QoS treatment together with, or in addition to, a
request for short latency indicating that the forwarder should
only pay attention to the caching preferences of the producer
because caching requested data would be ineffective (i.e., new
data will be requested shortly).
* A QoS treatment indicating that a mobile consumer will likely
incur a mobility event within an RTT (or a few RTTs). Such a
treatment would allow a mobile network operator to preferentially
cache the data at a forwarder positioned at a _join point_ or
_rendezvous point_ of their topology.
*Give network operators the ability to match customer SLAs to cache
resource availability*. Network operators, whether closely tied
administratively to producer or consumer, or constituting an
independent transit administration, provide the storage resources in
the ICN forwarders. Therefore, they are the ultimate arbiters of how
the cache resources are managed. In addition to any local policies
they may enforce, the cache behavior from the QoS standpoint emerges
from the mapping of producer-specified equivalence classes onto cache
space availability, including whether cache entries are treated
individually or fate-shared. Forwarders also determine the mapping
of consumer-specified QoS treatments to the precedence used for
retaining Data objects in the cache.
Besides utilizing cache resources to meet the QoS goals of individual
producers and consumers, network operators also want to manage their
cache resources in order to do the following:
* Ameliorate congestion hotspots by reducing load converging on
producers they host on their network
* Improve Interest satisfaction rates by utilizing caches as short-
term retransmission buffers to recover from transient producer
reachability problems, link errors, or link outages
* Improve both latency and reliability in environments when
consumers are mobile in the operator's topology
*Rethink how to specify traffic treatments -- don't just copy
Diffserv*. Some of the Diffserv classes may form a good starting
point, as their mappings onto queuing algorithms for managing link
buffering are well understood. However, Diffserv alone does not
capture more complex QoS treatments, such as:
* Trading off latency against reliability
* Trading off resource usage against delivery probability through
controlled flooding or other forwarding mechanisms
* Allocating resources based on rich TSPEC-like traffic descriptions
that appear in signaled QoS schemes like Intserv
Here are some examples:
* A "burst" treatment, where an initial Interest gives an aggregate
data size to request allocation of link capacity for a large burst
of Interest/Data exchanges. The Interest can be rejected at any
hop if the resources are not available. Such a treatment can also
accommodate Data implosion produced by the discovery procedures of
management protocols like [CCNINFO].
* A "reliable" treatment, which affects preference for allocation of
PIT space for the Interest and CS space for the Data in order to
improve the robustness of IoT data delivery in a constrained
environment, as is described in [IOTQOS].
* A "search" treatment, which, within the specified Interest
Lifetime, tries many paths either in parallel or serially to
potentially many content sources, to maximize the probability that
the requested item will be found. This is done at the expense of
the extra bandwidth of both forwarding Interests and receiving
multiple responses upstream of an aggregation point. The
treatment can encode a value expressing trade-offs like breadth-
first versus depth-first search, and bounds on the total resource
expenditure. Such a treatment would be useful for instrumentation
protocols like [ICNTRACEROUTE].
| As an aside, loose latency control (on the order of seconds or
| tens of milliseconds as opposed milliseconds or microseconds)
| can be achieved by bounding Interest Lifetime as long as this
| lifetime machinery is not also used as an application mechanism
| to provide subscriptions or to establish path traces for
| producer mobility. See [Krol2018] for a discussion of the
| network versus application timescale issues in ICN protocols.
7.1. Can Intserv-Like Traffic Control in ICN Provide Richer QoS
Semantics?
Basic QoS treatments such as those summarized above may not be
adequate to cover the whole range of application utility functions
and deployment environments we expect for ICN. While it is true that
one does not necessarily need a separate signaling protocol like RSVP
given the state carried in the ICN data plane by forwarders, simple
QoS treatments applied per Interest/Data exchanges lack some
potentially important capabilities. Intserv's richer QoS
capabilities may be of value, especially if they can be provided in
ICN at lower complexity and protocol overhead than Intserv plus RSVP.
There are three key capabilities missing from Diffserv-like QoS
treatments, no matter how sophisticated they may be in describing the
desired treatment for a given equivalence class of traffic. Intserv-
like QoS provides all of these:
1. The ability to *describe traffic flows* in a mathematically
meaningful way. This is done through parameters like average
rate, peak rate, and maximum burst size. The parameters are
encapsulated in a data structure called a "TSPEC", which can be
placed in whatever protocol needs the information (in the case of
TCP/IP Intserv, this is RSVP).
2. The ability to perform *admission control*, where the element
requesting the QoS treatment can know _before_ introducing
traffic whether the network elements have agreed to provide the
requested traffic treatment. An important side effect of
providing this assurance is that the network elements install
state that allows the forwarding and queuing machinery to police
and shape the traffic in a way that provides a sufficient degree
of _isolation_ from the dynamic behavior of other traffic.
Depending on the admission-control mechanism, it may or may not
be possible to explicitly release that state when the application
no longer needs the QoS treatment.
3. The ability to specify the permissible *degree of divergence* in
the actual traffic handling from the requested handling. Intserv
provides two choices here: the _controlled load_ service and the
_guaranteed_ service. The former allows stochastic deviation
equivalent to what one would experience on an unloaded path of a
packet network. The latter conforms to the TSPEC
deterministically, at the obvious expense of demanding extremely
conservative resource allocation.
Given the limited applicability of these capabilities in today's
Internet, the author does not take any position as to whether any of
these Intserv-like capabilities are needed for ICN to be successful.
However, a few things seem important to consider. The following
paragraphs speculate about the consequences of incorporating these
features into the CCNx or NDN protocol architectures.
Superficially, it would be quite straightforward to accommodate
Intserv-equivalent traffic descriptions in CCNx or NDN. One could
define a new TLV for the Interest message to carry a TSPEC. A
forwarder encountering this, together with a QoS treatment request
(e.g., as proposed in Section 6.3), could associate the traffic
specification with the corresponding equivalence class derived from
the name in the Interest. This would allow the forwarder to create
state that not only would apply to the returning Data for that
Interest when being queued on the downstream interface but also be
maintained as soft state across multiple Interest/Data exchanges to
drive policing and shaping algorithms at per-flow granularity. The
cost in Interest message overhead would be modest; however, the
complications associated with managing different traffic
specifications in different Interests for the same equivalence class
might be substantial. Of course, all the scalability considerations
with maintaining per-flow state also come into play.
Similarly, it would be equally straightforward to have a way to
express the degree of divergence capability that Intserv provides
through its controlled load and guaranteed service definitions. This
could either be packaged with the traffic specification or encoded
separately.
In contrast to the above, performing admission control for ICN flows
is likely to be just as heavyweight as it is with IP using RSVP. The
dynamic multipath, multi-destination forwarding model of ICN makes
performing admission control particularly tricky. Just to
illustrate:
* Forwarding next-hop selection is not confined to single paths (or
a few ECMP equivalent paths) as it is with IP, making it difficult
to know where to install state in advance of the arrival of an
Interest to forward.
* As with point-to-multipoint complexities when using RSVP for MPLS-
TE, state has to be installed to multiple producers over multiple
paths before an admission-control algorithm can commit the
resources and say "yes" to a consumer needing admission-control
capabilities.
* Knowing when to remove admission-control state is difficult in the
absence of a heavyweight resource reservation protocol. Soft
state timeout may or may not be an adequate answer.
Despite the challenges above, it may be possible to craft an
admission-control scheme for ICN that achieves the desired QoS goals
of applications without the invention and deployment of a complex,
separate admission-control signaling protocol. There have been
designs in earlier network architectures that were capable of
performing admission control piggybacked on packet transmission.
| The earliest example the author is aware of is [Autonet].
Such a scheme might have the following general shape (*warning:*
serious hand-waving follows!):
* In addition to a QoS treatment and a traffic specification, an
Interest requesting admission for the corresponding equivalence
class would indicate this via a new TLV. It would also need to do
the following: (a) indicate an expiration time after which any
reserved resources can be released, and (b) indicate that caches
be bypassed, so that the admission-control request arrives at a
bona fide producer.
* Each forwarder processing the Interest would check for resource
availability. If the resources are not available, or the
requested service is not feasible, the forwarder would reject the
Interest with an admission-control failure. If resources are
available, the forwarder would record the traffic specification as
described above and forward the Interest.
* If the Interest successfully arrives at a producer, the producer
would return the requested Data.
* Upon receiving the matching Data message and if the resources are
still available, each on-path forwarder would allocate resources
and would mark the admission control TLV as "provisionally
approved". Conversely, if the resource reservation fails, the
admission control would be marked "failed", although the Data
would still be passed downstream.
* Upon the Data message arrival, the consumer would know if
admission succeeded or not, and subsequent Interests could rely on
the QoS state being in place until either some failure occurs, or
a topology or other forwarding change alters the forwarding path.
To deal with this, additional machinery is needed to ensure
subsequent Interests for an admitted flow either follow that path
or an error is reported. One possibility (also useful in many
other contexts), is to employ a _Path Steering_ mechanism, such as
the one described in [Moiseenko2017].
8. IANA Considerations
This document has no IANA actions.
9. Security Considerations
There are a few ways in which QoS for ICN interacts with security and
privacy issues. Since QoS addresses relationships among traffic
rather than the inherent characteristics of traffic, it neither
enhances nor degrades the security and privacy properties of the data
being carried, as long as the machinery does not alter or otherwise
compromise the basic security properties of the associated protocols.
The QoS approaches advocated here for ICN can serve to amplify
existing threats to network traffic. However:
* An attacker able to manipulate the QoS treatments of traffic can
mount a more focused (and potentially more effective) denial-of-
service attack by suppressing performance on traffic the attacker
is targeting. Since the architecture here assumes QoS treatments
are manipulatable hop-by-hop, any on-path adversary can wreak
havoc. Note, however, that in basic ICN, an on-path attacker can
do this and more by dropping, delaying, or misrouting traffic
independent of any particular QoS machinery in use.
* When equivalence classes of traffic are explicitly revealed via
either names or other fields in packets, an attacker has yet one
more handle to use to discover linkability of multiple requests.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8569] Mosko, M., Solis, I., and C. Wood, "Content-Centric
Networking (CCNx) Semantics", RFC 8569,
DOI 10.17487/RFC8569, July 2019,
<https://www.rfc-editor.org/info/rfc8569>.
[RFC8609] Mosko, M., Solis, I., and C. Wood, "Content-Centric
Networking (CCNx) Messages in TLV Format", RFC 8609,
DOI 10.17487/RFC8609, July 2019,
<https://www.rfc-editor.org/info/rfc8609>.
10.2. Informative References
[AS] Wikipedia, "Autonomous system (Internet)", May 2021,
<https://en.wikipedia.org/w/index.php?title=Autonomous_sys
tem_(Internet)&oldid=1025244754>.
[Auge2018] Augé, J., Carofiglio, G., Grassi, G., Muscariello, L.,
Pau, G., and X. Zeng, "MAP-Me: Managing Anchor-Less
Producer Mobility in Content-Centric Networks", in IEEE
Transactions on Network and Service Management, Vol. 15,
No. 2, DOI 10.1109/TNSM.2018.2796720, June 2018,
<https://ieeexplore.ieee.org/document/8267132>.
[Autonet] Schroeder, M., Birrell, A., Burrows, M., Murray, H.,
Needham, R., Rodeheffer, T., Satterthwaite, E., and C.
Thacker, "Autonet: a High-speed, Self-configuring Local
Area Network Using Point-to-point Links", in IEEE Journal
on Selected Areas in Communications, Vol. 9, No. 8,
DOI 10.1109/49.105178, October 1991,
<https://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-
59.pdf>.
[BenAbraham2018]
Ben Abraham, H., Parwatikar, J., DeHart, J., Dresher, A.,
and P. Crowley, "Decoupling Information and Connectivity
via Information-Centric Transport", in ICN '18:
Proceedings of the 5th ACM Conference on Information-
Centric Networking, Boston, MA, USA,
DOI 10.1145/3267955.3267963, September 2018,
<https://conferences.sigcomm.org/acm-icn/2018/proceedings/
icn18-final31.pdf>.
[Carofiglio2012]
Carofiglio, G., Gallo, M., and L. Muscariello, "Joint Hop-
by-hop and Receiver-Driven Interest Control Protocol for
Content-Centric Networks", in ACM SIGCOMM Computer
Communication Review, DOI 10.1145/2377677.2377772,
September 2012,
<http://conferences.sigcomm.org/sigcomm/2012/paper/icn/
p37.pdf>.
[Carofiglio2016]
Carofiglio, G., Gallo, M., and L. Muscariello, "Optimal
multipath congestion control and request forwarding in
information-centric networks: Protocol design and
experimentation", in Computer Networks, Vol. 110,
DOI 10.1016/j.comnet.2016.09.012, December 2016,
<https://doi.org/10.1016/j.comnet.2016.09.012>.
[CCNINFO] Asaeda, H., Ooka, A., and X. Shao, "CCNinfo: Discovering
Content and Network Information in Content-Centric
Networks", Work in Progress, Internet-Draft, draft-irtf-
icnrg-ccninfo-06, 9 March 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-icnrg-
ccninfo-06>.
[DNC-QOS-ICN]
Jangam, A., Ed., Suthar, P., and M. Stolic, "QoS
Treatments in ICN using Disaggregated Name Components",
Work in Progress, Internet-Draft, draft-anilj-icnrg-dnc-
qos-icn-02, 9 March 2020,
<https://datatracker.ietf.org/doc/html/draft-anilj-icnrg-
dnc-qos-icn-02>.
[FLOWBALANCE]
Oran, D., "Maintaining CCNx or NDN flow balance with
highly variable data object sizes", Work in Progress,
Internet-Draft, draft-oran-icnrg-flowbalance-05, 14
February 2021, <https://datatracker.ietf.org/doc/html/
draft-oran-icnrg-flowbalance-05>.
[FLOWCLASS]
Moiseenko, I. and D. Oran, "Flow Classification in
Information Centric Networking", Work in Progress,
Internet-Draft, draft-moiseenko-icnrg-flowclass-07, 13
January 2021, <https://datatracker.ietf.org/doc/html/
draft-moiseenko-icnrg-flowclass-07>.
[HICN] Muscariello, L., Carofiglio, G., Augé, J., Papalini, M.,
and M. Sardara, "Hybrid Information-Centric Networking",
Work in Progress, Internet-Draft, draft-muscariello-
intarea-hicn-04, 20 May 2020,
<https://datatracker.ietf.org/doc/html/draft-muscariello-
intarea-hicn-04>.
[ICNTRACEROUTE]
Mastorakis, S., Gibson, J., Moiseenko, I., Droms, R., and
D. R. Oran, "ICN Traceroute Protocol Specification", Work
in Progress, Internet-Draft, draft-irtf-icnrg-
icntraceroute-02, 11 April 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-icnrg-
icntraceroute-02>.
[IOTQOS] Gundogan, C., Schmidt, T. C., Waehlisch, M., Frey, M.,
Shzu-Juraschek, F., and J. Pfender, "Quality of Service
for ICN in the IoT", Work in Progress, Internet-Draft,
draft-gundogan-icnrg-iotqos-01, 8 July 2019,
<https://datatracker.ietf.org/doc/html/draft-gundogan-
icnrg-iotqos-01>.
[Krol2018] Król, M., Habak, K., Oran, D., Kutscher, D., and I.
Psaras, "RICE: Remote Method Invocation in ICN", in ICN
'18: Proceedings of the 5th ACM Conference on Information-
Centric Networking, Boston, MA, USA,
DOI 10.1145/3267955.3267956, September 2018,
<https://conferences.sigcomm.org/acm-icn/2018/proceedings/
icn18-final9.pdf>.
[Mahdian2016]
Mahdian, M., Arianfar, S., Gibson, J., and D. Oran,
"MIRCC: Multipath-aware ICN Rate-based Congestion
Control", in ACM-ICN '16: Proceedings of the 3rd ACM
Conference on Information-Centric Networking,
DOI 10.1145/2984356.2984365, September 2016,
<http://conferences2.sigcomm.org/acm-icn/2016/proceedings/
p1-mahdian.pdf>.
[minmaxfairness]
Wikipedia, "Max-min fairness", June 2021,
<https://en.wikipedia.org/w/index.php?title=Max-
min_fairness&oldid=1028246910>.
[Moiseenko2017]
Moiseenko, I. and D. Oran, "Path Switching in Content
Centric and Named Data Networks", in ICN '17: Proceedings
of the 4th ACM Conference on Information-Centric
Networking, DOI 10.1145/3125719.3125721, September 2017,
<https://conferences.sigcomm.org/acm-icn/2017/proceedings/
icn17-2.pdf>.
[NDN] "Named Data Networking: Executive Summary",
<https://named-data.net/project/execsummary/>.
[NDNTutorials]
"NDN Tutorials",
<https://named-data.net/publications/tutorials/>.
[NWC-CCN-REQS]
Matsuzono, K., Asaeda, H., and C. Westphal, "Network
Coding for Content-Centric Networking / Named Data
Networking: Considerations and Challenges", Work in
Progress, Internet-Draft, draft-irtf-nwcrg-nwc-ccn-reqs-
05, 22 January 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-nwcrg-
nwc-ccn-reqs-05>.
[Oran2018QoSslides]
Oran, D., "Thoughts on Quality of Service for NDN/CCN-
style ICN protocol architectures", presented at ICNRG
Interim Meeting, Cambridge, MA, 24 September 2018,
<https://datatracker.ietf.org/meeting/interim-2018-icnrg-
03/materials/slides-interim-2018-icnrg-03-sessa-thoughts-
on-qos-for-ndnccn-style-icn-protocol-architectures>.
[proportionalfairness]
Wikipedia, "Proportional-fair scheduling", June 2021,
<https://en.wikipedia.org/w/index.php?title=Proportional-
fair_scheduling&oldid=1027073289>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
September 1997, <https://www.rfc-editor.org/info/rfc2205>.
[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,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2998] Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
Speer, M., Braden, R., Davie, B., Wroclawski, J., and E.
Felstaine, "A Framework for Integrated Services Operation
over Diffserv Networks", RFC 2998, DOI 10.17487/RFC2998,
November 2000, <https://www.rfc-editor.org/info/rfc2998>.
[RFC3170] Quinn, B. and K. Almeroth, "IP Multicast Applications:
Challenges and Solutions", RFC 3170, DOI 10.17487/RFC3170,
September 2001, <https://www.rfc-editor.org/info/rfc3170>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<https://www.rfc-editor.org/info/rfc4340>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[Schneider2016]
Schneider, K., Yi, C., Zhang, B., and L. Zhang, "A
Practical Congestion Control Scheme for Named Data
Networking", in ACM-ICN '16: Proceedings of the 3rd ACM
Conference on Information-Centric Networking,
DOI 10.1145/2984356.2984369, September 2016,
<http://conferences2.sigcomm.org/acm-icn/2016/proceedings/
p21-schneider.pdf>.
[Shenker2006]
Shenker, S., "Fundamental design issues for the future
Internet", in IEEE Journal on Selected Areas in
Communications, Vol. 13, No. 7, DOI 10.1109/49.414637,
September 2006,
<https://dl.acm.org/doi/10.1109/49.414637>.
[Song2018] Song, J., Lee, M., and T. Kwon, "SMIC: Subflow-level
Multi-path Interest Control for Information Centric
Networking", ICN '18: Proceedings of the 5th ACM
Conference on Information-Centric Networking,
DOI 10.1145/3267955.3267971, September 2018,
<https://conferences.sigcomm.org/acm-icn/2018/proceedings/
icn18-final62.pdf>.
[Tseng2003]
Tseng, C.-J. and C.-H. Chen, "The performance of QoS-aware
IP multicast routing protocols", in Networks, Vol. 42,
DOI 10.1002/net.10084, September 2003,
<https://onlinelibrary.wiley.com/doi/abs/10.1002/
net.10084>.
[Wang2000] Wang, B. and J. C. Hou, "Multicast routing and its QoS
extension: problems, algorithms, and protocols", in IEEE
Network, Vol. 14, Issue 1, DOI 10.1109/65.819168, January
2000, <https://ieeexplore.ieee.org/document/819168>.
[Wang2013] Wang, Y., Rozhnova, N., Narayanan, A., Oran, D., and I.
Rhee, "An improved Hop-by-hop Interest Shaper for
Congestion Control in Named Data Networking", in ACM
SIGCOMM Computer Communication Review,
DOI 10.1145/2534169.2491233, August 2013,
<https://conferences.sigcomm.org/sigcomm/2013/papers/icn/
p55.pdf>.
Author's Address
Dave Oran
Network Systems Research and Design
4 Shady Hill Square
Cambridge, MA 02138
United States of America
Email: daveoran@orandom.net