One document matched: draft-karagiannis-conex-throughput-exposure-00.txt
ConEx G. Karagiannis
Internet-Draft University of Twente
Intended status: Informational April 2, 2011
Expires: October 2, 2011
Exposing Conex Throughput
draft-karagiannis-conex-throughput-exposure-00
Abstract
This document describes a possible implementation complexity problem
associated with the current Conex concept defined by the ConEx WG
and it proposes a solution to this. This problem occurs due
to the fact that it is complex to measure the congestion rate,
at each intermediate Conex enabled device.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 2, 2011.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Implementation Complexity Problem . . . . . . . . . . . . . . . 4
3. Conex Throughput Solution . . . . . . . . . . . . . . . . . . . 4
3.1. Requirements for the Conex signal . . . . .. . . . . . . . 6
3.2. Codepoint Encoding . . . . . . . . . . . . . . . . . . . . 6
3.3. Conex Throughput Components . . . . . . . . . . . . . . . 6
3.3.1. Modified Senders . . . . . . . . . . . . . . . . . . . 7
3.3.2. Intermediate Conex Enabled Devices . . . . . . . . . 7
3.3.1. Modified Receivers . .. . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The ConEx working group is defining how IP packets will carry
additional ConEx information. This document describes a possible
implementation complexity problem associated with the current
Conex concept defined by the ConEx WG and it proposes a solution to
this. This problem occurs due to the fact that it is complex
to measure the congestion rate, at each intermediate
Conex enabled device. A conex enabled device can be for example, a
policer or an audit device. Moreover, this document provides a
solution to this problem, by measuring and monitoring the per flow
throughput on each intermediate Conex enabled device instead of
measuring and monitoring the per flow congestion rate on each
intermediate Conex enabled device.
1.1. Terminology
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].
In addition to the terminology specified in [draft-ietf-conex-
abstract-mech-01] and [draft-ietf-conex-concepts-uses-01] the
following terms are used and defined in this document.
O transport path throughput calculated at the sender: The per flow
transport sending rate as a function of the congestion rate, round-
trip time, and segment size. The transport path throughput
calculated at the sender using the TCP throughput equation
specified in [RFC5348]. Note that in [RFC5348] the term congestion
rate is denoted as loss event rate. According to [RFC5348] a loss
event is defined as one or more lost or marked packets from a
window of data, where a marked packet refers to a congestion
indication (CE) from Explicit Congestion Notification (ECN)
[RFC3168];
O throughput exposure signal (Conex-Throughput): a ConEx signal
encoded in IP packet headers from the sender to the network to
exposure the transport path throughput calculated at the sender.
O intermediate Conex enabled device: each Conex enabled device
located on a communication path between a sender and a receiver.
O measured per flow throughput at intermediate Conex enabled devices:
the per flow rate of packets that are passing through the output
buffer of an intermediate Conex enabled device and
are not dropped, (2) are not ECN CE marked. Each Conex enabled
device is only holding state on a flow if it first receives a
Throughput exposure signal.
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O throughput exposure rate at intermediate Conex devices: the
per flow rate of the received throughput exposure signals (Conex-
Throughput). Each Conex enabled device is only holding state on a
flow if it first receives a Throughput exposure signal (Conex-
Throughput).
2. Implementation Complexity Problem
The mentioned problem is related to the fact that in the context of
Conex it is complex to measure the congestion rate, see [RFC5348] at
each intermediate Conex enabled device, see Figure 1. A conex enabled
device, can be a policer or an audit device. In particular, the main
solution proposed in [draft-ietf-conex-abstract-mech-01] on measuring
the congestion rate on an audit device is: "The auditor could monitor
TCP flows or aggregates of flows, only holding state on a flow if it
first sends a Credit or a Re-Echo-Loss marking. The auditor could
detect retransmissions by monitoring sequence numbers. It would
assure that (volume of retransmitted data) <= (volume of data marked
Re-Echo-Loss). Traffic would only be auditable in this way if it
conformed to the standard TCP protocol and the IP payload was not
encrypted (e.g. with IPsec). ", from
[draft-ietf-conex-abstract-mech-01].
In other words, an audit device needs to keep per flow (individual or
aggregated) state after it receives a credit or Re-echo-Loss marking
in order to measure the per flow congestion rate. In addition to this
the audit device must be able to read the TCP header in order to
observe the TCP header numbers. This is complex to be implemented and
it is not always possible, e.g., when the IP payload is
encrypted (e.g. with IPsec). In this way the audit device is also
able to take into consideration also the number of ECN CE marked
packets that were dropped by nodes located upstream.
Note that in the opinion of the authors of this draft the same method
of measuring the congestion rate at a policer is required as the one
applied at the audit device.
3. Conex Throughput Solution
This document provides a solution to this problem, see Figure 2, by
measuring and monitoring the per flow throughput on each intermediate
Conex enabled device instead of measuring and monitoring the per flow
congestion rate on each intermediate Conex enabled device.
In addition to this, a sender calculates the per flow transport path
throughput, which describes the sending rate as a function of the
congestion rate, round-trip time, and segment size. The transport
path throughput calculated at the sender can be accomplished using
the TCP throughput equation specified in [RFC5348].
Moreover, the sender uses the throughput exposure signal (Conex-
Throughput) that is a ConEx signal encoded in IP packet headers from
the sender to the network to exposure the transport path throughput
calculated at the same sender.
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Each intermediate Conex enabled device measures the per flow
throughput, which is the per flow rate of packets that are passing
through the output buffer of an intermediate Conex enabled device and
(1) not dropped, (2) are not ECN CE marked. Each Conex enabled device
is only holding state on a flow if it first receives a Throughput
exposure signal (Conex-Throughput). Note that in this way the
intermediate Conex enabled device can also take into account the ECN
CE marked packets that were dropped by nodes located upstream.
Furthermore, each intermediate Conex enabled device measures
the throughput exposure rate at intermediate Conex devices, which is
the per flow rate of the received throughput exposure signals (Conex-
Throughput). Each Conex enabled device is only holding state on a
flow if it first receives a Throughput exposure signal (Conex-
Throughput).
It is important to note that the per flow throughput measured by
intermediate Conex enabled devices located closer to the sender can
be higher than the per flow throughput measured by Conex enabled
devices located closer to the receiver.
Identical use cases and applications can be used as the ones
described in [draft-ietf-conex-concepts-uses-01], using the same
semantics related to the exposed and measured congestion. The only
difference is now that the intermediate Conex enabled devices can
monitor and process the "Measured per flow throughput" and the
"Throughput exposure rate", instead of monitoring and processing the
measured congestion rate and the signaled exposed congestion rate,
respectively. An example of this is that each intermediate Congestion
enabled device ensures that the "Throughput exposure rate" is always
less or equal to the "Measured per flow throughput".
{More details will be provided in a next version of this draft}
+---------+ +---------+
|Transport| +-----------+ |Transport|
| Sender |>=Data=Path=>|(Congested)|>=====Data=Path=====>| Receiver|
| | | Network |>-Congestion-Signal->|---. |
| | | Device | | | |
| | +-----------+ | | |
| | | | |
| |<==Feedback=Path==============================<| | |
| ,---|<--Transport Layer returned Congestion Signal-<|<--' |
| V | | |
||-------|| | |
||Congest|| | |
||rate || +-----------+ |Transport|
||calcul.||>=Data=Path=>|(Congested)|>=====Data=Path=====>| Receiver|
|| |->(new)Conex->| Network |-(new)Conex signal)->| |
|+-------+| | Device | (carried in data | |
| | +-----------+ packet headers) | |
+---------+ +---------+
Figure 1: Overview ConEx architecture, based on
[draft-ietf-conex-abstract-mech-01]
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+---------+ +---------+
|Transport| +-----------+ |Transport|
| Sender |>=Data=Path=>|(Congested)|>=====Data=Path=====>| Receiver|
| | | Network |>-Congestion-Signal->|---. |
| | | Device | | | |
| | +-----------+ | | |
| | | | |
| |<==Feedback=Path==============================<| | |
| ,---|<--Transport Layer returned Congestion Signal-<|<--' |
| V | | |
||-------|| | |
||Througp|| | |
|| || +-----------+ |Transport|
||calcul.||>=Data=Path=>|(Congested)|>=====Data=Path=====>| Receiver|
|| |->(new)Conex->| Network |-(Throughp. signal)->| |
|+-------+| | Device | (carried in data | |
| | +-----------+ packet headers) | |
+---------+ +---------+
Figure 2: Overview ConEx architecture, with Conex throughput
exposure
3.1. Requirements for the ConEx Signal
The following requirements apply to the Conex-Throughput signal,
which are in line with most of the requirements presented in
[draft-ietf-conex-abstract-mech-01]:
o) The ConEx Signal SHOULD be visible to internetwork layer
devices along the entire path from the transport sender to the
transport receiver.
o) The ConEx Signal SHOULD be useful under only partial
deployment.
o) The ConEx Signal SHOULD be timely.
o) The ConEx Signal SHOULD be accurate.
{More details will be provided in a next version of this draft}
3.2. Codepoint Encoding
This encoding involves signaling the following
codepoint:
Conex-Throughput: a ConEx signal
encoded in IP packet headers from the sender to the network to
exposure the transport path throughput calculated at the sender.
3.3. Conex Throughput Components
The same Conex enabled devices can be used as the ones specified in
[draft-ietf-conex-abstract-mech-01].
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3.3.1 Modified Senders
The senders should be able to support a TCP based
congestion control protocol, e.g., [RFC5681] in combination with
[RFC3168], [RFC5348]. In addition, the sender MUST be able to support
the following functionality:
O calculates the transport path throughput calculated: The per flow
transport sending rate as a function of the congestion rate, round-
trip time, and segment size. The transport path throughput
calculated at the sender using the TCP throughput equation
specified in [RFC5348]. Note that in [RFC5348] the term congestion
rate is denoted as loss event rate. According to [RFC5348] a loss
event is defined as one or more lost or marked packets from a
window of data, where a marked packet refers to a congestion
indication (CE) from Explicit Congestion Notification (ECN)
[RFC3168].
O generates and encodes ConEx-Throughput signals in IP packet headers
from the sender to the network to exposure the transport path
throughput calculated at the same sender.
3.3.2 Intermediate Conex Enabled Devices
The same intermediate Conex enabled devices could be used as the
intermediate Conex enabled devices specified in [draft-ietf-conex-
abstract-mech-01], e.g., Policer and Audit. The only difference is
now that the intermediate Conex enabled devices MUST monitor and MUST
process the "Measured per flow throughput" and the "Throughput
exposure rate", instead of monitoring and processing the measured
congestion rate and the signaled exposed congestion rate,
respectively.
3.3.3 Modified Receivers
The receivers should be able to support a TCP based
congestion control protocol, e.g., [RFC5681] in combination with
[RFC3168], [RFC5348]. In addition, the receiver MUST be able to
support the following functionality:
O Measure per flow throughput: the per flow rate of packets that are
Received and (1) are not dropped, (2) are not ECN CE marked.
O Measure throughput exposure rate at intermediate Conex devices: the
per flow rate of the received throughput exposure signals.
{More details will be provided in a next version of this draft}
4. IANA Considerations
This memo includes no request to IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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5. Security Considerations
The security consideration sections are the same as the security
considerations associated with [draft-ietf-conex-abstract-mech-01].
{More details will be provided in a next version of this draft>}
6. Conclusions
{To be done}
7. Acknowledgements
{To be done}
8. Comments Solicited
Comments and questions are encouraged and very welcome. They can be
addressed to the IETF Congestion Exposure (ConEx) working group
mailing list <conex@ietf.org>, and/or to the authors.
9. References
9.1. Normative References
[draft-ietf-conex-abstract-mech-01] M. Mathis, B. Briscoe, "Congestion
Exposure (ConEx) Concepts and
Abstract Mechanism", draft-ietf-
conex-abstract-mech-01, (work in
progress), March 2011.
[RFC2119] S. Bradner, "Key words for use in
RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119,
March 1997.
9.2. Informative References
[draft-ietf-conex-concepts-uses-01] T. Moncaster, J. Leslie, B. Briscoe,
R. Woundy, D. McDysan, "ConEx
Concepts and Use Cases", draft-
ietf-conex-concepts-uses-01, (draft
in progress), March 2011.
[RFC5348] S. Floyd, M. Handley, J. Padhye,
J. Widmer, "TCP Friendly Rate
Control (TFRC): Protocol
Specification", RFC 5348, September
2008.
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[RFC3168] K. Ramakrishnan, S. Floyd, S., and
D. Black, "The Addition of Explicit
Congestion Notification (ECN) to
IP", RFC 3168, September 2001.
[RFC5681] M. Allman, V. Paxson, and E.
E. Blanton, "TCP Congestion
Control", RFC 5681, September 2009.
Authors' Addresses
Georgios Karagiannis
University of Twente
P.O. Box 217
7500 AE Enschede,
The Netherlands
EMail: g.karagiannis@ewi.utwente.nl
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