One document matched: draft-ietf-psamp-framework-04.txt
Differences from draft-ietf-psamp-framework-03.txt
Internet Draft
Document: <draft-psamp-framework-04.txt>
Expires: April 2004
Nick Duffield (Editor)
AT&T Labs – Research
October 2003
A Framework for Packet Selection and Reporting
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
A wide range of traffic engineering and troubleshooting tasks rely
on timely and detailed traffic measurements that can be
consistently interpreted. This document describes a framework for
packet sampling that is (a) general enough to serve as the basis
for a wide range of operational tasks, and (b) needs only a small
set of packet selectors that facilitate ubiquitous deployment in
router interfaces or dedicated measurement devices, even at very
high speeds. The framework also covers reporting and exporting
functions used by the sampling host, and configuration of the
sampling PSAMP functions.
Comments on this document should be addressed to the PSAMP Working
Group mailing list: psamp@ops.ietf.org
To subscribe: psamp-request@ops.ietf.org, in body: subscribe
Archive: https://ops.ietf.org/lists/psamp/
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Table of Contents
1. Motivation...................................................3
2. Elements, Terminology and Architecture.......................4
3. Requirements.................................................7
3.1 Selection Process Requirements...............................7
3.2 Reporting Process Requirements...............................8
3.3 Export Process Requirements..................................8
3.4 Configuration Requirements...................................9
4. Packet Selection.............................................9
4.1 Packet Selection Terminology.................................9
4.2 PSAMP Packet Selection Operations...........................11
4.3 Input Sequence Numbers for Primitive Selection Processes....13
4.4 Composite Selectors.........................................13
4.5 Constraints on the Sampling Frequency.......................13
4.6 Criteria for Choice of Selection Operations.................13
5. Reporting Process...........................................15
5.1 Mandatory Contents of Packet Reports (MUST).................15
5.2 Extended Packet Reports.....................................15
5.3 PSAMP Extended Packet Reports in the Presence of IPFIX......16
5.4 Report Interpretation.......................................16
5.5 Report Timeliness...........................................17
6. Parallel Measurement Processes..............................17
7. Export Process..............................................18
7.1 Collector Destination.......................................18
7.2 Local Export................................................18
7.3 Reliable vs. Unreliable Transport...........................18
7.4 Limiting Delay for Export Packets...........................18
7.5 Configurable Export Rate Limit..............................19
7.6 Congestion-aware Unreliable Transport.......................19
7.7 Collector-based Rate Reconfiguration........................20
7.7.1 Changing the Export Rate and Other Rates...................20
7.7.2 Notions of Fairness........................................21
7.7.3 Behavior Under Overload and Failure........................21
8. Configuration and Management................................22
9. Feasibility and Complexity..................................22
9.1 Feasibility.................................................22
9.1.1 Filtering..................................................22
9.1.2 Sampling...................................................23
9.1.3 Hashing....................................................23
9.1.4 Reporting..................................................23
9.1.5 Export.....................................................23
9.2 Potential Hardware Complexity...............................23
10. Applications................................................24
10.1 Baseline Measurement and Drill Down.........................25
10.2 Passive Performance Measurement.............................25
10.3 Troubleshooting.............................................26
11. Security Considerations.....................................27
12. References..................................................27
13. Authors' Addresses..........................................28
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14. Intellectual Property Statement.............................29
15. Full Copyright Statement....................................30
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document is an Internet-Draft and is in full conformanc with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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.
1. Motivation
This document describes a framework in which to define a standard
set of capabilities for network elements to select subsets of
packets by statistical and other methods. The framework
accommodates ongoing work to (i) specify a set of selectors by
which packets are sampled; (ii) specify the information that is to
be made available for reporting on sampled packets; (iii) describe
a protocol by which information on sampled packets is reported to
applications; (iv) describe a protocol by which packet selection
and reporting are configured.
The motivation to standardize these capabilities comes from the
need for measurement-based support for network management and
control across multivendor domains. This requires domain wide
consistency in the types of selection schemes available, the manner
in which the resulting measurements are presented, and
consequently, consistency of the interpretation that can be put on
them.
The capabilities are positioned as suppliers of packet samples to
higher level consumers, including both remote collectors and
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applications, and on board measurement-based applications. Indeed,
development of the standards within the framework described here
should be open to influence by the requirements of standards in
related IETF Working Groups, for example, IP Performance Metrics
(IPPM) [RFC2330] and Internet Traffic Engineering (TEWG) [LCTV02].
Conversely, we expect that aspects of this framework not
specifically concerned with the central issue of packet selection
and report formation may be able to leverage work in other Working
Groups. Potential examples are the format and export of reports on
selected packets, which may leverage the information model and
export protocols of IP Flow Information Export (IPFIX) [QZCZ03],
and work in congestion aware unreliable transport in the Datagram
Congestion Control Protocol (DCCP) [FHK02], and related work in The
Stream Control Transmission Protocol (SCTP) [SCTP] and [PR-SCTP].
2. Elements, Terminology and Architecture
This section defines the basic elements of the PSAMP framework. At
the highest level, the architecture comprises observation points
(at which packets are observed), measurement processes (which
select packets and construct reports on them) and export processes
(which export reports to collectors). The full definitions of these
terms now follow.
* Observation Point: a location in the network where a packet
stream is observed. Examples include:
- a line to which a probe is attached;
- a shared medium, such as an Ethernet-based LAN;
- a single port of a router, or set of interfaces (physical or
logical) of a router;
- an embedded measurement subsystem within an interface.
* Observed Packet Stream: the set of all packets observed at the
observation point.
* Packet Stream: either the observed packet stream, or a subset of
it.
Note that packets selected from a stream, e.g. by sampling, do
not necessarily possess a property by which they can be
distinguished from packets that have not been selected. For this
reason the term “stream” is favored over “flow”, which is defined
as set of packets with common properties [QuZC02].
* Selection Process: takes a packet stream as its input and selects
a subset of that stream as its output.
* Packet Content: the union of the packet header (which includes
link layer, network layer and other encapsulation headers) and
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the packet payload.
* Selection State: a selection process may maintain state
information for use by the selection process and/or the reporting
process. At a given time, the selection state may depend on
packets observed at and before that time, and other variables.
Examples include:
- sequence numbers of packets at the input of selectors;
- a timestamp of observation of the packet at the observation
points;
- iterators for pseudorandom number generators;
- hash values calculated during selection;
- indicators of whether the packet was selected by a given
selector;
Selection processes may change portions of the selection state as
a result of processing a packet.
* Selector: defines the action of a selection process on a single
packet of its input. A selected packet becomes an element of the
output packet stream of the selection process.
The selector can make use of the following information in
determining whether a packet is selected:
- the packet’s content;
- information derived from the packet's treatment at the
observation point;
- any selection state that may be maintained by the selection
process.
* Composite Selection Process: an ordered composition of selection
processes, in which the output stream issuing from one component
forms the input stream for the succeeding component.
* Primitive Selection Process: a selection process that is not a
composite selection process.
* Composite Selector: the selector of a composite selection
process.
* Primitive Selector: the selector of a primitive selection
process.
* Reporting Process: creates a report stream on packets selected by
a selection process, in preparation for export. The input to the
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reporting process comprises that information available to the
selection process per selected packet, specifically:
- the selected packet’s content;
- information derived from the selected packet's treatment at
the observation point;
- any selection state maintained by the inputting selection
process, reflecting any modifications to the selection state
made during selection of the packet.
* Report Stream: the output of a reporting process is a report
stream, comprising two distinguished types of information: packet
reports, and report interpretation.
* Packet Reports: a configurable subset of the per packet input to
the reporting process.
* Report Interpretation: subsidiary information relating to one or
more packets, that is used for interpretation of their packet
reports. Examples include configuration parameters of the
selection process and of the reporting process.
* Measurement Process: the composition of a selection process that
takes the observed packet stream as its input, followed by a
reporting process.
* Export Process: sends the output of one or more reporting
processes to one or more collectors.
* Collector: a collector receives a report stream exported by one
or more export processes. In some cases, the host of the
measurement and/or export processes may also serve as the
collector.
* Export packets: one or packet reports, and perhaps report
interpretation, are bundled by the export process into a export
packet for export to a collector.
Various possibilities for the high level architecture of these
elements are as follows.
MP = Measurement Process, EP = Export Process
+---------------------+ +------------------+
|Observation Point(s) | | Collector(1) |
|MP(s)--->EP----------+---------------->| |
|MP(s)--->EP----------+-------+-------->| |
+---------------------+ | +------------------+
|
+---------------------+ | +------------------+
|Observation Point(s) | +-------->| Collector(2) |
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|MP(s)--->EP----------+---------------->| |
+---------------------+ +------------------+
+---------------------+
|Observation Point(s) |
|MP(s)--->EP---+ |
| | |
|Collector(3)<-+ |
+---------------------+
The PSAMP measurement process can be viewed as analogous to the
IPFIX metering process. The PSAMP measurement process takes an
observed packet stream as its input, and produces packet reports as
its output. The IPFIX metering process produces flow records as its
output. The distinct name “measurement process” has been retained
in order to avoid potential confusion in settings where IPFIX and
PSAMP coexist, and in order to avoid the implicit requirement that
the PSAMP version satisfy the requirements of an IPFIX metering
process (at least while these are under development). The relation
between PSAMP and IPFIX is further discussed in [QC03].
3. Requirements
3.1 Selection Process Requirements.
* Ubiquity: The selectors must be simple enough to be implemented
ubiquitously at maximal line rate.
* Applicability: the set of selectors must be rich enough to
support a range of existing and emerging measurement based
applications and protocols. This requires a workable trade-off
between the range of traffic engineering applications and
operational tasks it enables, and the complexity of the set of
capabilities.
* Extensibility: to allow for additional packet selectors to
support future applications.
* Flexibility: to support selection of packets using different
network protocols or encapsulation layers (e.g. IPv4, IPv6, MPLS,
etc).
* Robust Selection: packet selection MUST be robust with respect to
attempts to craft an observed packet stream from which packets
are selected disproportionately (e.g. to evade selection, or
overload measurement systems).
* Parallel Measurement Processes: multiple independent measurement
processes at the same host, able to operate simultaneously.
* Non-contingency: in order to satisfy the ubiquity requirement,
the selection decision for each packet MUST NOT depend on future
packets. Rather, the selection decision MUST be capable of being
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made on the basis of the selection process input up to and
including the packet in question. This excludes selection
functions that require caching of packet for selection contingent
on subsequent packets. See also the timeliness requirement
following.
Selectors are outlined in Section 4, and described in more detail
in the companion document [ZMRD03].
3.2 Reporting Process Requirements
* Transparency: allow transparent interpretation of the report
stream, without any need to obtain additional information
concerning the observed packet stream.
* Robustness to Information Loss: allow robust interpretation of
the report stream with respect to packet reports missing due to
data loss, e.g. in transport, or within the selection, reporting
or exporting processes. Inclusion in reporting of information
that enables the accuracy of measurements to be determined.
* Faithfulness: all reported quantities that relate to the packet
treatment MUST reflect the router state and configuration
encountered by the packet at the time it is received by the
measurement process.
* Privacy: selection of the content of packet reports will be
cognizant of privacy and anonymity issues while being responsive
to the needs of measurement applications, and in accordance with
RFC 2804 [RFC2804]. Full packet capture of arbitrary packet
streams is explicitly out of scope.
A specific reporting processes meeting these requirements, and th e
requirement for ubiquity, is described in Section 5.
3.3 Export Process Requirements
* Timeliness: packet reports SHOULD be made available to the
collector quickly enough to support near real time applications.
Specifically, any report on a packet SHOULD be dispatched within
1 second of the time of receipt of the packet by the measurement
process. See Section 5.5 for further discussion of this point
* Congestion Avoidance: export of a report stream across a network
MUST be congestion avoiding in compliance with RFC 2914 [RFC
2914].
* Secure Export:
- confidentiality: the option to encrypt exported data MUST be
provided. [MUST vs. SHOULD needs further WG discussion].
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- integrity: alterations in transit to exported data MUST be
detectable at the collector
- authenticity: authenticity of exported data MUST be
verifiable by the collector in order to detect forged data.
The motivation here is the same as for security in IPFIX export;
see Sections 6.3 and 10 of [QZCZ03].
3.4 Configuration Requirements
* Ease of Configuration: of sampling and export parameters, e.g.
for automated remote reconfiguration in response to collected
reports.
* Secure Configuration: the option to configure via protocols that
prevent unauthorized reconfiguration or eavesdropping on
configuration communications MUST be available. Eavesdropping on
configuration might allow an attacker to gain knowledge that
would be helpful in crafting a packet stream to (for example)
evade subversion, or overload the measurement infrastructure.
Configuration is discussed in Section 8. Feasibility and complexity
of PSAMP operations is discussed in Section 9.
Reuse of existing protocols will be encouraged provided the
protocol capabilities are compatible with the requirements laid out
in this document.
4. Packet Selection
4.1 Packet Selection Terminology.
* Filtering: a filter is a selection operation that selects a
packet deterministically based on the packet content, its
treatment, and functions of these occurring in the selection
state. Examples include mask/match filtering, and hash-based
selection.
* Sampling: a selection operation that is not a filter is called a
sampling operation. This reflects the intuitive notion that if
the selection of a packet cannot be determined from its content
alone, there must be some type of sampling taking place.
* Content-independent Sampling: a sampling operation that does not
use packet content (or quantities derived from it) as the basis
for selection is called a content-independent sampling operation.
Examples include systematic sampling, and uniform pseudorandom
sampling driven by a pseudorandom number whose generation is
independent of packet content. Note that in content-independent
sampling it is not necessary to access the packet content in
order to make the selection decision.
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* Content-dependent Sampling: a sampling operation where selection
is dependent on packet content is called a content-dependent
sampling operation. Examples include pseudorandom selection
according to a probability that depends on the contents of a
packet field; note that this is not a filter.
* Hash Domain: a subset of the packet content and the packet
treatment, viewed as an N-bit string for some positive integer N.
* Hash Range: a set of M-bit strings for some positive integer M.
* Hash Function: a deterministic map from the hash domain into the
hash range.
* Hash Selection Range: a subset of the hash range. The packet is
selected if the action of the hash function on the hash domain
for the packet yields a result in the hash selection range.
* Hash-based Selection: filtering specified by a hash domain, a
hash function, and hash range and a hash selection range.
* Approximative Selection: selection operations in any of the above
categories may be approximated by operations in the same or
another category for the purposes of implementation. For example,
uniform pseudorandom sampling may be approximated by hash-based
selection, using a suitable hash function and hash domain. In
this case, the closeness of the approximation depends on the
choice of hash function and hash domain.
* Population size: the number of packets in a subset of a packet
stream.
* Sample size: the number of packets selected from a subset of a
packet stream by a selection operation.
* Attained Selection Frequency: the actual frequency with which
packets are selected by a selection process. The attained
sampling frequency is calculated as ratio of the size of a sample
size to the size of the population from which it was selected.
* Target Selection Frequency: the long-term frequency with which
packets are expected to be selected, based on selector parameter
settings. Depending on the selector, the target selection
frequency may be count-based or time-based.
For sampling operations, due to the inherent statistical
variability of sampling decisions, the target and attained
selection frequencies will not in general be equal, although they
may be close in some circumstances, e.g., when the population
size is large. In hash-based selection, the target selection
frequency is the quotient of size of the hash selection range by
the size of the hash range.
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4.2 PSAMP Packet Selection Operations
A spectrum of packet selection operations is described in detail in
[ZMRD03]. Here we only briefly summarize the meanings for
completeness.
A PSAMP selection process MUST support at least one of the
following selectors.
* Systematic Time Based Sampling: packet selection is triggered at
periodic instants separated by a time called the Spacing. All
packets that arrive within a certain time of the trigger (called
the Interval Length) are selected.
* Systematic Count Based Sampling: similar to systematic time based
expect that selection is reckoned with respect to packet count
rather than time. Packet selection is triggered periodically by
packet count, a number of successive packets being selected
subsequent to each trigger.
* Uniform Probabilistic Sampling: packets are selected
independently with fixed sampling probability p.
* Non-uniform Probabilistic Sampling: packets are selected
independently with probability p that depends on packet content.
* Probabilistic n-out-of-N Sampling: form each count-based
successive block of N packets, n are selected at random
* Mask/match Filtering: this entails taking the masking portions of
the packet (i.e. taking the bitwise AND with a binary mask) and
selecting the packet if the result falls in a range specified in
the selection parameters of the filter. This specification
doesn't preclude the future definition of a high level syntax for
defining filtering in a concise way (e.g. TCP port taking a
particular value) providing that syntax can be compiled into the
bitwise expression.
Mask/match operations SHOULD be available for different protocol
portions of the packet header:
- the IP header (excluding options in IPv4, stacked headers in
IPv6)
- transport header
- encapsulation headers (including MPLS label stack, ATOM, if
present)
When the host of a selection process offers mask/match filtering,
and, in its usual capacity other than in performing PSAMP
functions, identifies or processes information from one or more
of the above protocols, then the information SHOULD be made
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available for filtering. For example, when a host routes based on
destination IP address, that field should be made available for
filtering. Conversely, a host that does not route is not expected
to be able to locate an IP address within a packet, or make it
available for filtering, although it MAY do so.
* Hash-based Selection: Hash-based selection will employ one or
more hash functions to be standardized. The hash domain is
specified by a bitmaps on the IP packet header and the IP
payload.
When the hash function is sufficiently good, hash-based selection
can be used to approximate uniform random sampling over the hash
domain. The target sampling frequency is then the ratio of the
size of the selection range to the hash range.
Applications of hash-based selection include:
- Trajectory Sampling: all routers use the same hash selector;
the hash domain includes only portions of the packet that do
not change from hop to hop. (For example, in an IP packet,
TTL is excluded.) Hence packets are consistently selected in
the sense that they are selected at all routers on their
path or none. Reports packets also include a second hash
(the label hash) that distinguishes different packets.
Reports of a given packet reaching the collector from
different routers can be used to reconstruct the path taken
by the packet. Trajectory sampling is proposed in [DuGr01];
further description is found in [ZMRD03]; some applications
are described in Section 10.
- Consistent Flow Sampling: the hash domain is a flow key. For
a given flow, either all or none of its packets are sampled.
This is accomplished without the need to maintain flow
state.
Some applications need to calculate packet hashes for purpose
other than selection (e.g. the label hash in trajectory
sampling). This can be achieved by placing a calculated hash
in the selection state, and setting the selection range to be
the whole of the hash range.
* Router State Filtering: the selection process MAY support
filtering based on the following conditions, which may be
combined with the AND, OR or NOT operators:
- Ingress interface at which packet arrives equals a specified
value
- Egress interface to which packet is routed to equals a
specified value
- Packet violated Access Control List (ACL) on the router
- Failed Reverse Path Forwarding (RPF)
- Failed Resource Reservation (RSVP)
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- No route found for the packet
- Origin Autonomous System (AS) equals a specified value or
lies within a given range
- Destination AS equals a specified value or lies within a
given range
Router architectural considerations may preclude some information
concerning the packet treatment, e.g. routing state, being
available at line rate for selection of packets. However, if
selection not based on routing state has reduced down from line
rate, subselection based on routing state may be feasible.
4.3 Input Sequence Numbers for Primitive Selection Processes.
Each instance of a primitive selection process MUST maintain a
count of packets presented at its input. The counter value is to be
included as a sequence number for selected packets. The sequence
numbers are considered as part of the packet's selection state.
Use of input sequence numbers enables applications to determine the
attained frequency at which packets are selected, and hence
correctly normalize network usage estimates regardless of loss of
information, regardless of whether this loss occurs because of
discard of packet reports in the measurement or reporting process
(e.g. due to resource contention in the host of these processes),
or loss of export packets in transmission or collection. See
[RFC3176] for further details.
4.4 Composite Selectors
The ability to compose selectors in a selection process SHOULD be
provided. The following combinations appear to be most useful for
applications:
* filtering followed by sampling
* sampling followed by filtering
Composite selectors are useful for drill down applications. The
first component of a composite selector can be used to reduce the
load on the second component. In this setting, the advantage to be
gained from a given ordering can depend on the composition of the
packet stream.
4.5 Constraints on the Sampling Frequency
Sampling at full line rate, i.e. with probability 1, is not
excluded in principle, although resource constraints may not
support it in practice.
4.6 Criteria for Choice of Selection Operations
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In current practice, sampling has been performed using particular
algorithms, including:
* pseudorandom independent sampling with probability 1/N;
* systematic sampling of every Nth packet.
The question arises as to whether both of these should be
standardized as distinct selection operations, or whether they can
be regarded as different implementations of a single selection
operation.
To determine the answer to this question, we need to consider
(a) measured or assumed statistical properties of the packet
stream, e.g., one or more of the following:
- contents of different packets are statistically independent
- correlations between contents of different packets decay at
a specified rate
- contents of certain fields within the same packet are
significantly variable and exhibit small cross correlation
(b) the desired reference sampling model, e.g., one of:
- sample packets with long term probability 1/N
- sample packets independent with probability 1/N
(c) the set of possible alternatives and implementations, e.g., one
of:
- pseudorandom independent sampling with probability 1/N
- systematic sampling with period N
- hash-based sampling with target probability 1/N
(d) the tolerance for error in the applications that use the
collected packet reports.
We can say that a given alternative from (c) reproduces a reference
model (b) for the applications if the results obtained using them
are sufficiently accurate in (d) for traffic satisfying an assumed
statistical properties in (a). Clearly, application to evaluate
methods in (c) requires developing agreement on the relevant
properties in (a), (b) and (d).
Example: systematic sampling with period N will not count the
occurrence of closely space packets (less than N counts apart) from
the same flow. Thus for applications that are concerned with the
joint statistics of multiple packets within flows, systematic
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sampling may not reproduce the results obtained with random
sampling sufficiently accurately.
5. Reporting Process
5.1 Mandatory Contents of Packet Reports (MUST)
The reporting process MUST include the following in each packet
report:
(i) the input sequence number(s) of any sampling operation
that acted on the packet in the instance of a measurement
process of which the reporting process is a component.
The reporting process MUST be able to include the following in each
packet report, as a configurable option:
(ii) some number of contiguous bytes from the start of the
packet, including the packet header (which includes link
layer, network layer and other encapsulation headers) and some
subsequent bytes of the packet payload.
Some devices hosting reporting processes may not have the resource
capacity or functionality to provide more detailed packet reports
that those in (i) and (ii) above. Using this minimum required
reporting functionality, the reporting process places the burden of
interpretation on the collector, or on applications that it
supplies.
5.2 Extended Packet Reports (MAY)
The reporting process MAY provide for the inclusion in packet
reports of the following information, inclusion any or all being
configurable as a option.
(iii) fields relating to the following protocols used in the
packet, specifically: IPv4, IPV6, transport protocols, MPLS,
ATOM. Note that optional reporting of field contents may be
used to reduce reporting bandwidth, in which case the option
to not report information in (ii) above would be exercised.
(iv) packet treatment, including:
- identifiers for any input and output interfaces of the
observation point that were traversed by the packet
- source and destination AS
(v) selection state associated with the packet, including:
- the timestamp of observation of the packet at the
observation point
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- hashes, where calculated.
5.3 Extended Packet Reports in the Presence of IPFIX
If IPFIX is supported at the observation point, then in order to be
PSAMP compliant, extended packet reports MUST be able to include
all fields required in the IPFIX information model [QZCZ03], with
modifications appropriate to reporting on single packets rather
than flows.
5.4 Report Interpretation
Information for use in report interpretation MUST include
(i) configuration parameters of the selectors of the packets
reported on.
(ii) format of the packet report;
(iii) indication of the inherent accuracy of the reported
quantities, e.g., of the packet timestamp.
(iv) identifiers for observation point, measurement process,
and export process.
The accuracy measure in (iii) is of fundamental importance for
estimating the likely error attached to estimates formed from the
packet reports by applications.
Identifiers in (iv) are necessary, e.g., in order to match packet
reports to the selection process that selected them. For example,
when packet reports due to a sampling operation suffer loss (either
during export, or in transit) it may be desirable to reconfigure
downwards the sampling rate on the selection process that selected
them.
The requirements for robustness and transparency are motivations
for including report interpretation in the report stream. Inclusion
makes the report stream self-defining. The PSAMP framework
excludes reliance on an alternative model in which interpretation
is recovered out of band. This latter approach is not robust with
respect to undocumented changes in selector configuration, and may
give rise to future architectural problems for network management
systems to coherently manage both configuration and data
collection.
It is not envisaged that all report interpretation be included in
every packet report. Many of the quantities listed above are
expected to be relatively static; they could be communicated
periodically, and upon change.
To conserve network bandwidth and resources at the collector, the
export packets may be compressed before export. Compression is
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expected to be quite effective since the sampled packets may share
many fields in common, e.g. if a filter focuses on packets with
certain values in particular header fields. Using compression,
however, could impact the timeliness of packet reports. Any
consequent delay MUST not violate the timeliness requirement for
availability of packet reports at the collector.
5.5 Report Timeliness
Low measurement latency allows the traffic monitoring system to be
more responsive to real-time network events, for example, in
quickly identifying sources of congestion. Timeliness is generally
a good thing for devices performing the sampling since it minimizes
the amount of memory needed to buffer samples.
Keeping the packet dispatching delay to under 1 second has other
benefits besides limiting buffer requirements. For many
applications a 1 second time resolution is sufficient. Applications
in this category would include: identifying sources associated with
congestion; tracing denial of service attacks through the network
and constructing traffic matrices.
A dispatch delay of 1 second in these situations eliminates the
need for timestamping by synchronized clocks at observation points
devices, or for the observation points and collector to maintain
bi-directional communication in order to track clock offsets. The
collector can simply process packet reports in the order that they
are received---using its own clock as a "global" time base---
avoiding the complexity of buffering and reordering samples. See
[DuGeGr02] for an example.
6. Parallel Measurement Processes
Because of the increasing number of distinct measurement
applications, with varying requirements, it is desirable to set up
parallel measurement processes on given observed packet stream. A
device capable of hosting a measurement process SHOULD be able to
support more than one independently configurable measurement
process simultaneously. Each such measurement process SHOULD have
the option of being equipped with its own export process; otherwise
the parallel measurement processes MAY share the same export
process.
Each of the parallel measurement processes SHOULD be independent.
However, resource constraints may prevent complete reporting on a
packet selected by multiple selection processes. In this case,
reporting for the packet MUST be complete for at least one
measurement process; other measurement processes need only record
that they selected the packet, e.g., by incrementing a counter. The
priority amongst measurement processes under resource contention
SHOULD be configurable.
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It is not proposed to standardize the number of parallel
measurement processes.
7. Export Process
7.1 Collector Destination
When exporting to a remote collector, the collector is identified
by IP address, transport protocol, and transport port number.
7.2 Local Export
The report stream may be directly exported to on-board measurement
based applications, for example those that form composite
statistics from more than one packet. Local export may be presented
through an interface direct to the higher level applications, i.e.,
through an API, rather than employing the transport used for off-
board export. Specification of such an API is outside the scope of
the PSAMP framework.
A possible example of local export could be that packets selected
by the PSAMP measurement process serve as the input for the IPFIX
protocol, which then forms flow records out of the stream of
selected packets. Note that IPFIX being still developed; this is
given only as a possible example.
7.3 Reliable vs. Unreliable Transport
The export of the report stream does not require reliable export.
On the contrary, retransmission of lost export packets consumes
additional network resources and requires maintenance of state by
the export process. As such, the export process would have to be
able to receive and process acknowledgments, and to store
unacknowledged data. Furthermore, the host of the export process
may not possess its own network address at which to receive
acknowledgments. For example an autonomous embedded measurement
subsystem in an interface may simply inject export packets into the
interface packet stream, designating the interface address as the
source address of the export packets). These requirements would be
a significant impediment to having ubiquitous support PSAMP.
Instead, it is proposed that the export process support unreliable
export. Sequence numbers on the export packets would indicate when
loss has occurred, and the analysis of the surviving report stream
can be used to determine the degree of loss. In some sense, packet
loss becomes another form of sampling (albeit a less desirable, and
less controlled, form of sampling).
7.4 Limiting Delay for Export Packets
The export process may queue the report stream in order to export
multiple packet reports in a single export packet. Any consequent
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delay MUST still allow for timely availability of packet reports at
the collector as described in Section 5.4.
7.5 Configurable Export Rate Limit
The export process MUST be able to limit its export rate; otherwise
it could overload the network and/or the collector. Note this
problem would be exacerbated using reliable transport mode, since
any lost packets would be retransmitted, thereby imposing an
additional load on the network.
At times, the reporting process may generate new packet reports or
report interpretation faster than the allowed export rate. In this
situation, the export process MUST discard the excess packet
reports rather than transmitting them to the collector. Sequence
numbers reported for selector input enable correction for lost
packet reports. An additional sequence number for dispatched export
packets enables the collector to determine the degree of loss in
transmission.
There are two options for a configurable rate limit. First, if the
transport protocol has a configurable rate limit, that can be used.
The second option is to limit the rate at which export packets are
supplied to the transport protocol. A candidate for implementation
of rate limiting is the leaky bucket, with tokens corresponding
e.g. to bytes or packets.
The export rate limit MUST be configurable per export process. Note
that since congestion loss can occur at any link on the export
path, it is not sufficient to limit rate simply as a function of
the bandwidth of the interface out of which export takes place.
7.6 Congestion-aware Unreliable Transport
Export packets compete for resources with other Internet transfers.
Congestion-aware export is important to ensure that the export
packets do not overwhelm the capacity of the network or unduly
degrade the performance of other applications, while making good
use of available bandwidth resources.
Choice of transport for PSAMP has to be made under the following
constraints:
(i) IESG has mandated that all transport in new protocols must
be congestion aware
(ii) reliable transport is too onerous for general entities
that support PSAMP (see Section 7.3)
(iii) there currently exists no IETF standardized unreliable
congestion-aware transport
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In the absence of an existing IETF standardized unreliable
congestion-aware protocol, PSAMP will provisionally nominate the
reliable congestion aware transport protocol TCP as the interim
transport protocol for export. From the preceding arguments, TCP is
unsatisfactory for final standardization in PSAMP. In the meantime,
the PSAMP Working Group will evaluate (at least) the following
alternatives for congestion aware unreliable transport, as they
become available, with a view to selecting one of them and
discarding TCP:
(i) unreliable transport protocols adopted in the future by
the IPFIX Working Group,
(ii) the Datagram Congestion Control Protocol (DCCP);
currently under development; see [FHK02]
(iii) The Stream Control Transmission Protocol (SCTP) under
development [SCTP]. SCTP is by default reliable, but has the
capability to operate in unreliable and partially reliable
modes [PR-SCTP]. See [D03] for description of its potential
use in flow export.
(iv) collector-based rate reconfiguration, described below.
7.7 Collector-based Rate Reconfiguration
Since collector-based rate reconfiguration is a new proposal, this
draft will discuss it in some detail.
The collector can detect congestion loss along the path from the
exporting device to the collector by observing packet loss,
manifest as gaps in the sequence numbers, or the absence of packets
for a period of time. The server can run an appropriate congestion-
control algorithm to compute a new export rate limit, then
reconfigure the export process with the new rate. This is an
attractive alternative to requiring the export process to receive
acknowledgment packets. Implementing the congestion control
algorithm in the collector has the added advantages of flexibility
in adapting the sending rate and the ability to incorporate new
congestion-control algorithms as they become available.
7.7.1 Changing the Export Rate and Other Rates
Forcing the export process to discard excess packet reports is an
effective control under short term congestion. Alternatively, the
selection process could be reconfigured to select fewer packets, or
the reporting process could be reconfigured to send smaller reports
on each selected packet. This may be a more appropriate reaction to
long-term congestion. In some cases, a collector may receive export
packets due to more than one export process, and could decide to
reduce the export or other rates associated with one export process
rather than another, in order to prioritize the export packets.
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This type of flexibility is valuable for network operators that
collect export packets from multiple locations to drive multiple
applications.
7.7.2 Notions of Fairness
In some cases, it may be reasonable to allow the collector to have
flexibility in deciding how aggressively to respond to congestion.
For example, the host of the export process and the collector may
have a very small round-trip time (RTT) relative to other traffic.
Conventional TCP-friendly congestion control would allocate a very
large share of the bandwidth to the PSAMP export traffic. Instead,
the collector could apply an algorithm that reacts more
aggressively to congestion to give a larger share of the bandwidth
to other traffic (with larger RTTs).
In other cases, the export packets may require a larger share of
the bandwidth than other flows. For example, consider a link that
carries tens of thousands of flows, including some non TCP-friendly
DoS attack traffic. Restricting the PSAMP traffic to a fair share
allocation may be too restrictive, and might limit the collection
of the data necessary to diagnose the DoS attack which overloads
links over which export packets are carried. In order to maintain
report collection during periods of congestion, PSAMP report
streams may claim more than a fair share of link bandwidth,
provided the number of report streams in competition with fair
sharing traffic is limited. The collector could also employ
policies that allocate bandwidth in certain proportions amongst
different measurement processes.
Note that the ability to control differential bandwidth usage in
the manner described in this section may be partially or wholly
lost if congestion control is performed by other means purely at
the transport level.
7.7.3 Behavior Under Overload and Failure
The congestion control algorithm has to be robust to severe
overload or complete loss of connectivity between the host of the
export process and the collector, and also to the failure of host
of the export process or the collector. For example, in a scenario
where the collector is unable to reconfigure the export rate
because of loss of reverse (collector to exporting host)
connectivity, it is desirable for the exporting host to reduce the
export rate autonomously. Similarly, if no export packets reach
the collector because of loss of forward connectivity, the
collector should not react to this by increasing the export rate.
This problem may be solved through periodic heartbeat packets in
both directions (i.e., export packets in the forward direction,
configuration refresh messages in the reverse direction). This
allows each side to detect a loss in connectivity or outright
failure and to react appropriately.
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8. Configuration and Management
A key requirement for PSAMP is the easy reconfiguration of the
parameters of the measurement process: those for selection, packet
reports and export. Examples are
(i) support of measurement-based applications that want to
drill-down on traffic detail in real-time;
(ii) collector-based rate reconfiguration.
To facilitate reconfiguration and retrieval of parameters, they are
to reside in a Management Information Base (MIB). Mandatory
configuration, capabilities and monitoring objects will cover all
minimum required (MUST) PSAMP functionality.
Secondary objects will cover the recommended PSAMP functionality
(SHOULD), and MUST be provided only when such functionality is
offered by a host. Such PSAMP functionality includes configuration
of offered selectors, composite selectors, multiple measurement
processes, and report format including the choice of fields to be
reported. For further details concerning the PSAMP MIB, see
[DRC03].
PSAMP requires a uniform mechanism with which to access and
configure the MIB. SNMP access MUST be provided by the host of the
MIB.
9. Feasibility and Complexity
In order for PSAMP to be supported across the entire spectrum of
networking equipment, it must be simple and inexpensive to
implement. One can envision easy-to-implement instances of the
mechanisms described within this draft. Thus, for that subset of
instances, it should be straightforward for virtually all system
vendors to include them within their products. Indeed, sampling and
filtering operations are already realized in available equipment.
Here we give some specific arguments to demonstrate feasibility and
comment on the complexity of hardware implementations. We stress
here that the point of these arguments is not to favor or recommend
any particular implementation, or to suggest a path for
standardization, but rather to demonstrate that the set of possible
implementations is not empty.
9.1 Feasibility
9.1.1 Filtering
Filtering consists of a small number of mask (bit-wise logical),
comparison and range (greater than) operations. Implementation of
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at least a small number of such operations is straightforward. For
example, filters for security access control lists (ACLs) are
widely implemented. This could be as simple as an exact match on
certain fields, or involve more complex comparisons and ranges.
9.1.2 Sampling
Sampling based on either counters (counter set, decrement, test for
equal to zero) or range matching on the hash of a packet (greater
than) is possible given a small number of selectors, although there
may be some differences in ease of implementation for hardware vs.
software platforms.
9.1.3 Hashing
Hashing functions vary greatly in complexity. Execution of a small
number of sufficient simple hash functions is implementable at line
rate. Concerning the input to the hash function, hop-invariant IP
header fields (IP address, IP identification) and TCP/UDP header
fields (port numbers, TCP sequence number) drawn from the first 40
bytes of the packet have been found to possess a considerable
variability; see [DuGr01].
9.1.4 Reporting
The simplest packet report would duplicate the first n bytes of the
packet. However, such an uncompressed format may tax the bandwidth
available to the reporting process for high sampling rates;
reporting selected fields would save on this bandwidth. Thus there
is a trade-off between simplicity and bandwidth limitations.
9.1.5 Export
Ease of exporting export packets depends on the system
architecture. Most systems should be able to support export by
insertion of export packets, even through the software path.
9.2 Potential Hardware Complexity
We now comment on the complexity of possible hardware
implementations. Achieving low constants for performance while
minimizing hardware resources is, of course, a challenge,
especially at very high clock frequencies. Most of these
operations, however, are very basic and their implementations very
well understood; in fact, the average ASIC designer simply uses
canned library instances of these operations rather than design
them from scratch. In addition, networking equipment generally does
not need to run at the fastest clock rates, further reducing the
effort required to get reasonably efficient implementations.
Simple bit-wise logical operations are easy to implement in
hardware. Such operations (NAND/NOR/XNOR/NOT) directly translate
to four-transistor gates. Each bit of a multiple-bit logical
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operation is completely independent and thus can be performed in
parallel incurring no additional performance cost above a single
bit operation.
Comparisons (EQ/NEQ) take O(lg(M)) stages of logic, where M is the
number of bits involved in the comparison. The lg(M) is required
to accumulate the result into a single bit.
Greater than operations, as used to determine whether a hash falls
in a selection range, are a determination of the most significant
not-equivalent bit in the two operands. The operand with that
most-significant-not-equal bit set to be one is greater than the
other. Thus, a greater than operation is also an O(lg(M)) stages
of logic operation. Optimized implementations of arithmetic
operations are also O(lg(M)) due to propagation of the carry bit.
Setting a counter is simply loading a register with a state. Such
an operation is simple and fast O(1). Incrementing or decrementing
a counter is a read, followed by an arithmetic operation followed
by a store. Making the register dual-ported does take additional
space, but it is a well-understood technique. Thus, the
increment/decrement is also an O(lg(M)) operation.
Hashing functions come in a variety of forms. The computation
involved in a standard Cyclic Redundancy Code (CRC) for example are
essentially a set of XOR operations, where the intermediate result
is stored and XORed with the next chunk of data. There are only
O(1) operations and no log complexity operations. Thus, a simple
hash function, such as CRC or generalizations thereof, can be
implemented in hardware very efficiently.
At the other end of the range of complexity, the MD5 function uses
a large number of bit-wise conditional operations and arithmetic
operations. The former are O(1) operations and the latter are
O(lg(M)). MD5 specifies 256 32b ADD operations per 16B of input
processed. Consider processing 10Gb/sec at 100MHz (this processing
rate appears to be currently available). This requires processing
12.5B/cycle, and hence at least 200 adders, a sizeable number.
Because of data dependencies within the MD5 algorithm, the adders
cannot be simply run in parallel, thus requiring either faster
clock rates and/or more advanced architectures. Thus, selection
hashing functions as complex as MD5 may be precluded for ubiquitous
use at full line rate. This motivates exploring the use of
selection hash functions with complexity somewhere between that of
MD5 and CRC. However, identification hashing with MD5 on only
selected packets is feasible at a sufficiently low sampling
frequency.
10. Applications
We first describe several representative operational applications
that require traffic measurements at various levels of temporal and
spatial granularity. Some of the goals here appear similar to those
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of IPFIX, at least in the broad classes of applications supported.
However, there are two major differences:
- PSAMP aims for ubiquitous deployment of packet measurement,
including devices that are not expected to support IPFIX.
This offers broader reach for existing applications.
- PSAMP can support new applications through the type of
packet selectors that it supports
10.1 Baseline Measurement and Drill Down
Packet sampling is ideally suited to determine the composition of
the traffic across a network. The approach is to enable measurement
on a cut-set of the network links such that each packet entering
the network is seen at least once, for example, on all ingress
links. Unfiltered sampling with a relatively low frequency
establishes baseline measurements of the network traffic. Packet
reports include packet attributes of common interest: source and
destination address and port numbers, prefix, protocol number, type
of service, etc. Traffic matrices are indicated by reporting source
and destination AS matrices. Absolute traffic volumes are estimated
by renormalizing the sampled traffic volumes through division by
either the target sampling frequency, or by the attained sampling
frequency (as derived by interface packet counters included in the
report stream)
Suppose an operator or a measurement-based application detects an
interesting subset of a packet stream, as identified by a
particular packet attribute. Real-time drill-down to that subset is
achieved by instantiating a new measurement process on the same
packet stream from which the subset was reported. The selection
process of the new measurement process filters according to the
attribute of interest, and composes with sampling if necessary to
manage the frequency of packet selection.
10.2 Passive Performance Measurement
Hash-based sampling enables the tracking of the performance
experience by customer traffic, customers identified by a list of
source or destination prefixes, or by ingress or egress interfaces.
Operational uses include the verification of Service Level
Agreements (SLAs), and troubleshooting following a customer
complaint.
In this application, trajectory sampling is enabled at all network
ingress and egress interfaces. The label hash is used to match up
ingress and egress samples. Rates of loss in transit between
ingress and egress are estimated from the proportion of
trajectories for which no egress report is received. Note loss of
customer packets is distinguishable from loss of packet reports
through use of report sequence numbers. Assuming synchronization of
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clocks between different entities, delay of customer traffic across
the network may also be measured.
Extending hash-selection to all interfaces in the network would
enable attribution of poor performance to individual network links.
10.3 Troubleshooting
PSAMP can also be used to diagnose problems whose occurrence is
evident from aggregate statistics, per interface utilization and
packet loss statistics. These statistics are typically moving
averages over relatively long time windows, e.g., 5 minutes, and
serve as a coarse-grain indication of operational health of the
network. The most common method of obtaining such measurements are
through the appropriate SNMP MIBs (MIB-II and vendor-specific
MIBs.)
Suppose an operator detects a link that is persistently overloaded
and experiences significant packet drop rates. There is a wide
range of potential causes: routing parameters (e.g., OSPF link
weights) that are poorly adapted to the traffic matrix, e.g.,
because of a shift in that matrix; a denial of service attack or a
flash crowd; a routing problem (link flapping). In most cases,
aggregate link statistics are not sufficient to distinguish between
such causes, and to decide on an appropriate corrective action. For
example, if routing over two links is unstable, and the links flap
between being overloaded and inactive, this might be averaged out
in a 5 minute window, indicating moderate loads on both links.
Baseline PSAMP measurement of the congested link, as described in
Section 10.1, enables measurements that are fine grained in both
space and time. The operator has to be able to determine how many
bytes/packets are generated for each source/destination address,
port number, and prefix, or other attributes, such as protocol
number, MPLS forwarding equivalence class (FEC), type of service,
etc. This allows the precise determination of the nature of the
offending traffic. For example, in the case of a DDoS attack, the
operator would see a significant fraction of traffic with an
identical destination address.
In certain circumstances, precise information about the spatial
flow of traffic through the network domain is required to detect
and diagnose problems and verify correct network behavior. In the
case of the overloaded link, it would be very helpful to know the
precise set of paths that packets traversing this link follow. This
would readily reveal a routing problem such as a loop, or a link
with a misconfigured weight. More generally, complex diagnosis
scenarios can benefit from measurement of traffic intensities (and
other attributes) over a set of paths that is constrained in some
way. For example, if a multihomed customer complains about
performance problems on one of the access links from a particular
source address prefix, the operator should be able to examine in
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detail the traffic from that source prefix which also traverses the
specified access link towards the customer.
While it is in principle possible to obtain the spatial flow of
traffic through auxiliary network state information, e.g., by
downloading routing and forwarding tables from routers, this
information is often unreliable, outdated, voluminous, and
contingent on a network model. For operational purposes, a direct
observation of traffic flow is more reliable, as it does not depend
on any such auxiliary information. For example, if there was a bug
in a router's software, direct observation would allow the
diagnosis the effect of this bug, while an indirect method would
not.
11. Security Considerations
Security considerations are addressed in:
- Section 3.1: item Robust Selection
- Section 3.3: item Secure Export
- Section 3.4: item Secure Configuration
12. References
[B88] R.T. Braden, A pseudo-machine for packet monitoring and
statistics, in Proc ACM SIGCOMM 1988
[ClPB93] K.C. Claffy, G.C. Polyzos, H.-W. Braun, Application of
Sampling Methodologies to Network Traffic Characterization,
Proceedings of ACM SIGCOMM'93, San Francisco, CA, USA,
September 13-17, 1993
[DRC03] T. Dietz, D. Romascanu, B. Claise, Definitions of
Managed Objects for Packet Sampling, Internet Draft,
draft-ietf-psamp-mib-00.txt, work in progress, June 2003.
[D03] M. Djernaes, Cisco Systems NetFlow Services Export Version
9 Transport, Internet Draft,
draft-djernaes-netflow-9-transport-00.txt, work in
progress, February 2003
[DuGr01] N. G. Duffield and M. Grossglauser, Trajectory Sampling
for Direct Traffic Observation, IEEE/ACM Trans. on
Networking, 9(3), 280-292, June 2001.
[DuGeGr02] N.G. Duffield, A. Gerber, M. Grossglauser, Trajectory
Engine: A Backend for Trajectory Sampling, IEEE Network
Operations and Management Symposium 2002, Florence, Italy,
April 15-19, 2002.
[RFC2914] S. Floyd, Congestion Control Principles, RFC 2914,
September 2000.
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[FHK02] S. Floyd, M. Handley. E. Kohler, Problem Statement for
DCCP, Internet Draft draft-ietf-dccp-problem-00.txt, work
in progress, October 2002.
[RFC2804] IAB and IESG, Network Working Group, IETF Policy on
Wiretapping, RFC 2804, May 2000
[LCTV02] W.S. Lai, B.Christian, R.W. Tibbs, S. Van den Berghe, A
Framework for Internet Traffic Engineering Measurement
Internet Draft draft-ietf-tewg-measure-05.txt, work in
progress, February 2003.
[RFC3176] P. Phaal, S. Panchen, N. McKee, InMon Corporation's
sFlow: A Method for Monitoring Traffic in Switched and
Routed Networks, RFC 3176, September 2001
[RFC2330] V. Paxson, G. Almes, J. Mahdavi, M. Mathis, Framework
for IP Performance Metrics, RFC 2330, May 1998
[QC03] J. Quittek, B. Claise, On the Relationship between PSAMP
and IPFIX, Internet Draft draft-quittek-psamp-ipfix-01.txt,
work in progress, February 2003.
[QZCZ03] J. Quittek, T. Zseby, B. Claise, S. Zander,
Requirements for IP Flow Information Export, Internet Draft
draft-ietf-ipfix-reqs-10.txt, work in progress, June 2003.
[SPSJTKS01] A. C. Snoeren, C. Partridge, L. A. Sanchez, C. E.
Jones, F. Tchakountio, S. T. Kent, W. T. Strayer, Hash-
Based IP Traceback, Proc. ACM SIGCOMM 2001, San Diego, CA,
September 2001.
[RFC2960] Stewart, R. (ed.) "Stream Control Transmission
Protocol", RFC 2960, October 2000
[PR-SCTP] Stewart, R, "SCTP Partial Reliability Extension",
Internet Draft, draft-stewart-tsvwg-prsctp-01.txt, work in
progress, June 2003.
13. Authors' Addresses
Derek Chiou
Avici Systems
101 Billerica Ave
North Billerica, MA 01862
Phone: +1 978-964-2017
Email: dchiou@avici.com
Benoit Claise
Cisco Systems
De Kleetlaan 6a b1
1831 Diegem
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Belgium
Phone: +32 2 704 5622
Email: bclaise@cisco.com
Nick Duffield
AT&T Labs - Research
Room B-139
180 Park Ave
Florham Park NJ 07932, USA
Phone: +1 973-360-8726
Email: duffield@research.att.com
Albert Greenberg
AT&T Labs - Research
Room A-161
180 Park Ave
Florham Park NJ 07932, USA
Phone: +1 973-360-8730
Email: albert@research.att.com
Matthias Grossglauser
School of Computer and Communication Sciences
EPFL
1015 Lausanne
Switzerland
Email: matthias.grossglauser@epfl.ch
Peram Marimuthu
Cisco Systems
170, W. Tasman Drive
San Jose, CA 95134
Phone: (408) 527-6314
Email: peram@cisco.com
Jennifer Rexford
AT&T Labs - Research
Room A-169
180 Park Ave
Florham Park NJ 07932, USA
Phone: +1 973-360-8728
Email: jrex@research.att.com
Ganesh Sadasivan
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
Phone: (408) 527-0251
Email: gsadasiv@cisco.com
14. Intellectual Property Statement
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AT&T Corporation may own intellectual property applicable to this
contribution. The IETF has been notified of AT&T's licensing intent
for the specification contained in this document. See
http://www.ietf.org/ietf/IPR/ATT-GENERAL.txt for AT&T's IPR
statement.
15. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain
it or assist in its implementation may be prepared, copied,
published and distributed, in whole or in part, without restriction
of any kind, provided that the above copyright notice and this
paragraph are included on all such copies and derivative works.
However, this document itself may not be modified in any way, such
as by removing the copyright notice or references to the Internet
Society or other Internet organizations, except as needed for the
purpose of developing Internet standards in which case the
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Duffield (Ed.) Expires April 2004 [Page 30]
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