Internet DRAFT - draft-moiseenko-icnrg-flowclass
draft-moiseenko-icnrg-flowclass
ICNRG I. Moiseenko
Internet-Draft Apple Computer
Intended status: Informational D. Oran
Expires: July 17, 2021 Network Systems Research and Design
January 13, 2021
Flow Classification in Information Centric Networking
draft-moiseenko-icnrg-flowclass-07
Abstract
For the ubiquitous and highly important Internet protocols (TCP, UDP,
IP), flows are conventionally identified by the "5-tuple" of source
and destination IP addresses, source and destination port, and
protocol type in an IP packet. Information Centric Networking (ICN)
is a new paradigm where network communications are accomplished by
requesting named content, instead of sending packets to destination
addresses. This document describes mechanisms allowing ICN
forwarders, consumers, producers and other ICN nodes to encode,
decode, and process equivalence class identifiers (flows) at any
desired granularity of a routable name prefix and beyond the routable
name prefix. This document is a product of the IRTF Information-
Centric Networking Research Group (ICNRG).
Status of This Memo
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Flow Identification Challenges and Opportunities in ICN . . . 3
3. Flow Encoding Schemes . . . . . . . . . . . . . . . . . . . . 4
3.1. Equivalence class component count (EC3) . . . . . . . . . 5
3.2. Equivalence class name component type (ECNCT) . . . . . . 6
4. Producer operation . . . . . . . . . . . . . . . . . . . . . 7
5. Consumer operation . . . . . . . . . . . . . . . . . . . . . 8
6. Forwarder operation . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The problem of identifying groups of packets that get consistent
treatment in a network and allowing that treatment to be independent
and isolated from the treatment of other groups of packets, is
ubiquitous and long-standing. The purposes to which this
identification can be put is highly varied, including such functions
are providing differentiated quality of service, traffic engineering,
traffic filtering for security functions like intrusion detection and
firewalling, etc.
Providing the capability to apply different functions to groupings
(formally equivalence classes) of packets is generally known as the
"flow identification problem" where the definition of what
constitutes a "flow" is highly dependent on the particular protocol
or protocols carrying the packets. Some of the above uses of flows
also bring a mechanism requirement that the flow identification
technique be useful to have not just equivalence classes, but the
ability to apply some useful notion of fairness among the instances
of each equivalence class. There are many possible flow
identification techniques that are either too granular (spatially or
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temporally) to establish fairness, or conversely too coarse and
cannot separate traffic a fine enough level to have useful fairness.
For the ubiquitous and highly important Internet protocols (TCP, UDP,
IP), flows are conventionally identified by the "5-tuple" of source
and destination IP addresses, source and destination port, and
protocol type in an IP packet. Some systems augment this by further
distinguishing equivalence classes by the TOS/DSCP field, but this is
secondary to the 5-tuple methods. 2-party flows are present where the
source and destination addresses are unicast IP addresses. Multi-
party flows can exist when the destination IP address is a multicast
address. One key common characteristic is that the identification of
flows depends in a very deep way on the presence of source addresses
in the packets, and the limited richness of IP addresses is
correspondingly constraining as a means to classify traffic in a
semantically meaningful way.
The purpose of this document is to devise a mechanism allowing ICN
forwarders, consumers, producers and other ICN nodes to encode,
decode, and process equivalence class identifiers (flows) at any
desired granularity of a routable name prefix and beyond the routable
name prefix.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Flow Identification Challenges and Opportunities in ICN
ICN systems differ from IP-based designs in a number of ways, three
of which are quite fundamental.
1. The packets are addressed to a rich namespace of packets, which
is hierarchical and carry semantic information that can be useful
for classification of flows.
2. Conversely, the packets do not contain source addresses of any
kind, which means that identifying flows as groups of packets
between a single pair of endpoints (in the unicast case) is not
possible for intermediate forwarders (other than possibly the
first-hop forwarder if it serves a single consumer per
interface).
3. Instead of group-based multicast, ICN systems use multi-
destination delivery semantics. This allows a different way to
map packets to flows, and in fact in the IP world multicast has
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been difficult to use partly because there is no good way to make
use of flow identification for multicast flows (for a variety of
reasons).
These differences lead to a need to find a different method to
identify flows than used in the IP protocol suite. Ideally, the
method would provide semantics that map well with the expected uses
of ICN to build applications. It would also use native capabilities
in the ICN protocols rather than having to change the protocol
architecture in ways that affect the semantics or utility of an ICN
approach to networking.
In NDN and CCN protocols, Interest and Data names are the only
identifiers in the network; neither source addresses nor destination
addresses are employed. Each Interest packet is responded by exactly
one Data packet, producing a useful property known as "flow balance".
This means that flow identification can be tied directly to the
Interest/Data exchanges. The key to having useful flow
identification is for the equivalence classes to be associated with
the names in the corresponding Interest and Data packets, and to be
stable over multiple exchanges using different names that share some
common "handle" that can be used to separate the names into
equivalence classes. As mentioned above, simply using the routing
state that maps name prefixes to routes does not provide a useful set
of equivalence classes, because:
o in general, routing prefixes are too coarse; many equivalence
classes of packets are generally covered by a single routing
prefix because they are present at the same set of destinations
from a routing perspective;
o practical, scalable routing needs to do route aggregation, which
further blurs the discrimination of the equivalence classes.
Therefore, NDN and CCN protocols need to have something that both
relates to the name structure but provides finer granularity for flow
classification purposes. This document describes two alternative
mechanisms addressing these issues.
3. Flow Encoding Schemes
Flow encoding schemes described in this document allow ICN systems to
perform flow identification at any desired granularity of a routable
name prefix and beyond the routable name prefix. Techniques
described herein permit both consumer nodes and forwarders to use
equivalence classes to perform per-flow functions. The encoding to
achieve the flow classification is lightweight and does not require
changes to the protocol architecture in ways that affect the
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semantics or utility of an ICN approach to networking. Furthermore,
equivalence classes can be specified by the data producer, in
contrast to IP protocols in which the data producer can only control
the destination port as an equivalence-class discriminator.
No matter what method is used to identify equivalence classes that
can be treated as flows, there is the independent but critically
important issue of how to scale any state that is kept on a per-flow
basis when the flow count is very high. For consumers and producers,
this state scales naturally with the number of applications and
application interactions are going on simultaneously. Therefore the
scaling limit is not likely to be in the producers or consumers. For
ICN forwarders this state could scale quadratically or worse if the
forwarders need classic prior resource reservation to
deterministically partition resources on a producer/consumer pair
basis. This need not be the case however. Practical resource
control algorithms exist that keep state only for "active" flows
(those with packets either currently or recently moving through the
network). Further state reduction is also possible with some loss of
accuracy using approximate techniques, like stochastic fair queuing
(SFQ). If the ICN forwarder cannot keep all the state due to memory
or processing limitations, it faces the common problem of which flows
to remember and which to forget. This problem is fundamental, and is
mostly independent of the choice of flow identification method in the
protocol. Flow encoding schemes described in this document provide a
method for identifying equivalence classes using protocol machinery
that already has to scale (e.g. name parsing and lookup) and hence
does not introduce a new class of problems not inherently present.
3.1. Equivalence class component count (EC3)
For this encoding scheme a new field called equivalence class
component count (EC3) is introduced into the Data packets. It is set
by a producer and counts the number of name components in the
corresponding name that are to be considered, when grouped together
under the same prefix part of the name, to be one equivalence class
instance. This allows either finer (or coarser) granularity than
provided by routing prefixes. Because the EC3 is a separate field of
the packet (Figure 1), producers can "regroup" equivalence classes
dynamically by including more or fewer levels of the name hierarchy
when they respond to Interests for the corresponding Data packets.
This brings a set of clear advantages and disadvantages. The primary
advantage is flexibility in re-grouping equivalence classes,
especially in aggregating flows at different granularities. The main
disadvantage is that the binding of the equivalence class into the
namespace is not explicit, and hence it is harder to enforce
consistent interpretation among producers, consumers and forwarders.
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An additional consideration with the EC3 encoding scheme is whether
or not the field is inside or outside the security envelope that
provides cryptographic packet integrity to the name and data in the
data packet. Either approach is possible; however having the field
outside the security envelope would allow ICN forwarders to modify
it, allowing the aggregation/disaggregation of flows to be performed
by the forwarders as well as the consumers. Conversely, leaving the
field outside the security envelope may enhance certain attack
scenarios against flow classification when employed for quality of
service differentiation or firewall filtering.
+-------------------------------------------------------------------+
| /youtube | /<mediaID> | /video OR | <frameID> | <segment#> |
| | | /audio | | |
+-----------+--------------+-------------+-------------+------------+
| Name | Name | Name | Name | Segment |
| component | component | component | component | component |
| type | type | type | type | type |
+-----------+--------------+-------------+-------------+------------+
| |
| Equivalence Class Component Count = 2 (up to MediaID stream) |
| OR |
| Equivalence Class Component Count = 3 (video or audio substream) |
+-------------------------------------------------------------------+
An example of EC3 encoding of flow information.
Figure 1
3.2. Equivalence class name component type (ECNCT)
For this scheme the equivalence class information is encoded directly
in the name, by adding a name component to the name of the Interest
and Data packets. This new typed named component is called
equivalence class name component type (ECNCT). It is set by the
producer as part of constructing all Data packets in the desired
equivalence class and is therefore immutable for the lifetime of the
associated named data. A consequence of this is that the ECNCT is
present in Interest packets as well, and hence may affect both PIT
matching and FIB matching. The Equivalence Class name component both
names the equivalence class explicitly, and implicitly makes all Data
packets named below it in the hierarchy part of that equivalence
class. In other words, the name can have multiple equivalence class
(e.g. flow and subflows) markings using this scheme (Figure 2). As
in EC3 encoding scheme, depending where in the name component
hierarchy the ECNCT is placed, one can have either finer or coarser
granularity than provided by routing prefixes.
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The exact details of how to encode the ECNCT name component may
differ among ICN architectures. The CCN design has explicitly typed
name components, so for that protocol an explicit name component type
can be assigned straightforwardly. The NDN design eschews typed name
components and instead uses textual naming conventions for name
components. In that case an architectural constant string would be
chosen to distinguish ECNCT from other name component semantics.
+------------------------------------------------------------+
| /youtube | /<mediaID> | /video OR | <frameID> | <segment#> |
| | | /audio | | |
+----------+------------+-----------+-----------+------------+
| Name | Flow | Flow | Name | Segment |
| component| component | component | component | component |
| type | type | type | type | type |
+----------+------------+-----------+-----------+------------+
An example of ECNCT encoding of flow information.
Figure 2
When an ICN forwarder receives a packet with a name carrying
ECNCT(s), it can be processed on a component-by-component basis, and
substreams can be identified according to name prefixes indicated by
the equivalence class identifiers. The identification of substreams
enables special treatment of selected substreams. For example, video
substreams can be discriminated from other substreams, such as audio
substreams. In the example in Figure 2, two name components include
equivalence class identifiers to define a hierarchy of flows (or
substreams). Specifically, two flow components are encoded to define
the following hierarchy of flows:
First level name prefix: /youtube/<mediaID>
Second level name prefix: /youtube/<mediaID>/video
Second level name prefix: /youtube/<mediaID>/audio
4. Producer operation
In ECNCT encoding scheme, an ICN producer receives an Interest packet
carrying equivalence class identifiers in the name. A producer might
use the equivalence class identifiers for demultiplexing, load
sharding and other purposes, and reply with a Data packet matching
the Interest name.
In EC3 encoding scheme, an ICN producer receives an Interest packet
that might not carry an equivalence class identifier. In such case,
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the producer may refer to the name schemas used in a particular
application to dynamically determine the equivalence class identifier
for Interest demultiplexing, load sharding and other purposes, and
for replying with a Data packet carring the equivalence class
identifer in EC3 field.
5. Consumer operation
An ICN consumer may also use the knowledge of equivalence classes of
packets to take certain actions. For example, when a Data packet
with a name specifying a particular equivalence class arrives at a
consumer in response to a previously sent Interest packet, the
consumer can associate the data packet with the correct equivalence
class. Consequently, the consumer can manage subsequent Interest/
Data exchanges with the same name prefix and equivalence class
identifier (e.g., EC3 or ECNCT) as one flow. Associated measurements
such as round trip time (RTT) or marginal delay can be leveraged to
perform flow and congestion management for the equivalence class as a
whole.
6. Forwarder operation
A flow table may be provisioned in ICN node to enable the node to
make decisions about performing actions on Interest and/or Data
packets based on one or more equivalence classes. The flow table can
include name prefixes mapped to equivalence class identifiers
obtained from previous Interest-Data exchanges. In ECNCT encoding
scheme, Interest packets carry the equivalence class identifier,
therefore flow table may only include name prefixes. Typically, name
prefixes in flow table are more granular than prefixes in the FIB,
but less granular than names in the PIT. Flow table could be
separate from other elements of ICN node or could be integrated with
FIB or PIT.
Flow management logic can be configured to treat flows having the
same equivalence class similarly. Actions taken that are related to
flows or objects having a similar equivalence class can include, but
are not limited to, dropping a packet, using a particular interface
for a packet, security related actions (e.g., filtering traffic for
security functions like intrusion detection and firewalling), quality
of service (QoS) related actions (e.g., types of resources to
allocate to the packets, moving a packet up in the queue for
forwarding purposes, etc.), and/or traffic engineering (e.g.,
selecting one path over another path). Flow management logic can
enable such actions to be taken on a particular flow based on the
equivalence class associated with the flow or object and policies
related to the equivalence class.
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Specific examples of how ICN node can use the knowledge of
equivalence classes of packets include, but are not limited to, the
following:
1. Enforce rate control for the equivalence class as a whole (e.g.,
dropping packets, queuing packets, etc.);
2. Estimate the number of simultaneous flows traversing a bottleneck
link, which can improve the performance of many congestion
control schemes; and
3. Make more intelligent selections of which packets to cache at the
ICN forwarder, for example, to prefer to cache many packets of
the same equivalence class.
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
Certain attack scenarios against flow classification for quality of
service or firewall filtering may be prevented if the EC3 field
located inside the security envelope. ICN forwarders can read, but
not change, the EC3 value, because the EC3 field is covered by a
security signature and not encrypted.
If the EC3 field is outside of the security envelope, it can be
placed in the hop-by-hop headers and, therefore, be modified by the
transit ICN forwarders. This allows the transit ICN forwarders to
override the flow definitions set by the producer applications, but
opens the system to various attack scenarios.
Modification of equivalence class identifiers in ECNCT encoding
scheme effectively modifies the packet name, and therefore, ECNCT
does not introduce any additional security threats.
9. 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>.
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Authors' Addresses
Ilya Moiseenko
Apple Computer
USA
Email: imoiseenko@apple.com
Dave Oran
Network Systems Research and Design
4 Shady Hill Square
Cambridge, MA 02138
USA
Email: daveoran@orandom.net
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