QUIC Working Group B. Trammell, Ed.
Internet-Draft M. Kuehlewind
Intended status: Standards Track ETH Zurich
Expires: December 30, 2019 June 28, 2019
The QUIC Latency Spin Bit
draft-ietf-quic-spin-exp-latest
Abstract
This document specifies the addition of a latency spin bit to the
QUIC transport protocol and describes how to use it to measure end-
to-end latency.
Note to Readers
This document specifies an experimental delta to the QUIC transport
protocol. Specifically, this experimentation is intended to
determine:
o the impact of the addition of the latency spin bit on
implementation and specification complexity; and
o the accuracy and value of the information derived from spin bit
measurement on live network traffic.
The information generated by this experiment will be used by the QUIC
working group as input to a decision about the standardization of the
latency spin bit. Although this is a Working Group document, it is
currently NOT a Working Group deliverable.
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=quic [1].
Working Group information can be found at https://github.com/quicwg
[2]; source code and issues list for this draft can be found at
https://github.com/quicwg/base-drafts/labels/-spin [3].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
Trammell & Kuehlewind Expires December 30, 2019 [Page 1]
Internet-Draft QUIC Spin Bit June 2019
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on December 30, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Spin Bit Mechanism . . . . . . . . . . . . . . . . . . . 3
2.1. Proposed Short Header Format Including Spin Bit . . . . . 3
2.2. Setting the Spin Bit on Outgoing Packets . . . . . . . . 4
2.3. Resetting Spin Value State . . . . . . . . . . . . . . . 4
3. Using the Spin Bit for Passive RTT Measurement . . . . . . . 4
4. Disabling the Spin Bit . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security and Privacy Considerations . . . . . . . . . . . . . 6
7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Since draft-ietf-spin-exp-00 . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
Trammell & Kuehlewind Expires December 30, 2019 [Page 2]
Internet-Draft QUIC Spin Bit June 2019
1. Introduction
The QUIC transport protocol [QUIC-TRANSPORT] uses Transport Layer
Security (TLS) [TLS] to encrypt most of its protocol internals. In
contrast to TCP where the sequence and acknowledgement numbers and
timestamps (if the respective option is in use) can be seen by on-
path observers and used to estimate end-to-end latency, QUIC's wire
image (see [WIRE-IMAGE]) currently does not expose any information
that can be used for passive latency measurement techniques that rely
on this information (e.g. [CACM-TCP], [TMA-QOF]).
This document adds an explicit signal for passive latency
measurability to the QUIC short header: a "spin bit". Passive
observation of the spin bit provides one RTT sample per RTT to
passive observers of QUIC traffic. This document describes the
mechanism, how it can be added to QUIC, and how it can be used by
passive measurement facilities to generate RTT samples.
2. The Spin Bit Mechanism
The latency spin bit enables latency monitoring from observation
points on the network path throughout the duration of a connection.
Since it is possible to measure handshake RTT without a spin bit, it
is sufficient to include the spin bit in the short packet header.
The spin bit therefore appears only after version negotiation and
connection establishment are completed.
2.1. Proposed Short Header Format Including Spin Bit
[QUIC-TRANSPORT] specifies using the third most significant bit of
the first byte in the short header for the spin bit (0x20, labeled S
in Figure 1). The Spin bit is set 0 or 1 depending on the stored
spin value that is updated on packet reception as explained in
Section 2.2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
|0|1|S|R|R|K|P P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Connection ID (0..144) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Number (8/16/24/32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protected Payload (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Short Header Packet Format
Trammell & Kuehlewind Expires December 30, 2019 [Page 3]
Internet-Draft QUIC Spin Bit June 2019
2.2. Setting the Spin Bit on Outgoing Packets
Each endpoint, client and server, maintains a spin value, 0 or 1, for
each QUIC connection, and sets the spin bit in the short header to
the currently stored value when a packet with a short header is sent
out. The spin value is initialized to 0 at each endpoint, client and
server, at connection start. Each endpoint also remembers the
highest packet number seen from its peer on the connection.
The spin value is then determined at each endpoint within a single
connection as follows:
o When the server receives a packet from the client, if that packet
has a short header and if it increments the highest packet number
seen by the server from the client, the server sets the spin value
to the value observed in the spin bit in the received packet.
o When the client receives a packet from the server, if the packet
has a short header and if it increments the highest packet number
seen by the client from the server, it sets the spin value to the
opposite of the spin bit in the received packet.
This procedure will cause the spin bit to change value in each
direction once per round trip. Observation points can estimate the
network latency by observing these changes in the latency spin bit,
as described in Section 3. See [QUIC-SPIN] for further illustration
of this mechanism in action.
2.3. Resetting Spin Value State
Each client and server resets it spin value to zero when sending the
first packet of a given connection with a new connection ID. This
reduces the risk that transient spin bit state can be used to link
flows across connection migration or ID change.
3. Using the Spin Bit for Passive RTT Measurement
When a QUIC flow sends data continuously, the latency spin bit in
each direction changes value once per round-trip time (RTT). An on-
path observer can observe the time difference between edges (changes
from 1 to 0 or 0 to 1) in the spin bit signal in a single direction
to measure one sample of end-to-end RTT.
Note that this measurement, as with passive RTT measurement for TCP,
includes any transport protocol delay (e.g., delayed sending of
acknowledgements) and/or application layer delay (e.g., waiting for a
request to complete). It therefore provides devices on path a good
instantaneous estimate of the RTT as experienced by the application.
Trammell & Kuehlewind Expires December 30, 2019 [Page 4]
Internet-Draft QUIC Spin Bit June 2019
A simple linear smoothing or moving minimum filter can be applied to
the stream of RTT information to get a more stable estimate.
However, application-limited and flow-control-limited senders can
have application and transport layer delay, respectively, that are
much greater than network RTT. When the sender is application-
limited and e.g. only sends small amount of periodic application
traffic, where that period is longer than the RTT, measuring the spin
bit provides information about the application period, not the
network RTT.
Simple heuristics based on the observed data rate per flow or changes
in the RTT series can be used to reject bad RTT samples due to lost
or reordered edges in the spin signal, as well as application or flow
control limitation; for example, QoF [TMA-QOF] rejects component RTTs
significantly higher than RTTs over the history of the flow. These
heuristics may use the handshake RTT as an initial RTT estimate for a
given flow.
An on-path observer that can see traffic in both directions (from
client to server and from server to client) can also use the spin bit
to measure "upstream" and "downstream" component RTT; i.e, the
component of the end-to-end RTT attributable to the paths between the
observer and the server and the observer and the client,
respectively. It does this by measuring the delay between a spin
edge observed in the upstream direction and that observed in the
downstream direction, and vice versa.
4. Disabling the Spin Bit
Implementations SHOULD allow administrators of clients and servers to
disable the spin bit either globally or on a per-connection basis.
Even when the spin bit is not disabled by the administrator
implementations SHOULD disable the spin bit on a randomly chosen
fraction of connections.
The selection process SHOULD be designed such that on average the
spin bit is disabled for at least one eighth of network paths. The
selection process SHOULD be externally unpredictable but consistent
for any given combination of source and destination address/port.
For instance, the implementation might have a static key which it
uses to key a pseudorandom function over these values and use the
output to determine whether to send the spin bit. The selection
process performed at the beginning of the connection SHOULD be
applied for all paths used by the connection.
Trammell & Kuehlewind Expires December 30, 2019 [Page 5]
Internet-Draft QUIC Spin Bit June 2019
Note that where multiple connections use the same path, the use of
the spin bit MAY be coordinated by endpoints, recognizing that this
might not be possible in many cases.
When the spin bit is disabled, endpoints MAY set the spin bit to any
value, and MUST accept any incoming value. It is RECOMMENDED that
they set the spin bit to a random value either chosen independently
for each packet, or chosen independently for each path and kept
constant for that path.
5. IANA Considerations
This document has no actions for IANA.
6. Security and Privacy Considerations
The spin bit is intended to expose end-to-end RTT to observers along
the path, so the privacy considerations for the latency spin bit are
essentially the same as those for passive RTT measurement in general.
It has been shown [PAM-RTT] that RTT measurements do not provide more
information for geolocation than is available in the most basic,
freely-available IP address based location databases. The risk of
exposure of per-flow network RTT to on-path devices is in most cases
negligible.
There is however an exception, when parts of the path from client to
server are hidden from observers. An example would be a server
accessed through a proxy. The spin bit allows for measurement of the
end-to-end RTT, and will thus enable adversaries near the endpoint to
discover that the connection does not terminate at the visible
destination address.
Endpoints that want to hide their use of a proxy or a relay will want
to disable the spin bit. However, if only privacy-sensitive clients
or servers ever disabled the spin bit, they would stick out. The
probabilistic disabling behavior explained in Section 4 ensures that
other endpoints will also disable the spin bit some of the time, thus
hiding the privacy sensitive endpoints in a large anonymity set. It
also provides for a minimal greasing of the spin bit, in order to
mitigate risks of ossification.
7. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
Trammell & Kuehlewind Expires December 30, 2019 [Page 6]
Internet-Draft QUIC Spin Bit June 2019
7.1. Since draft-ietf-spin-exp-00
Adding section on disabling the spin bit and privacy considerations.
Acknowledgments
This document is derived from [QUIC-SPIN], which was the work of the
following authors in addition to the editor of this document:
o Piet De Vaere, ETH Zurich
o Roni Even, Huawei
o Giuseppe Fioccola, Telecom Italia
o Thomas Fossati, Nokia
o Marcus Ihlar, Ericsson
o Al Morton, AT&T Labs
o Emile Stephan, Orange
The QUIC Spin Bit was originally specified in a slightly different
form by Christian Huitema.
This work is partially supported by the European Commission under
Horizon 2020 grant agreement no. 688421 Measurement and Architecture
for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
for Education, Research, and Innovation under contract no. 15.0268.
This support does not imply endorsement.
9. References
9.1. Normative References
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport-latest (work in progress).
9.2. Informative References
[CACM-TCP]
Strowes, S., "Passively Measuring TCP Round-Trip Times (in
Communications of the ACM)", October 2013.
Trammell & Kuehlewind Expires December 30, 2019 [Page 7]
Internet-Draft QUIC Spin Bit June 2019
[PAM-RTT] Trammell, B. and M. Kuehlewind, "Revisiting the Privacy
Implications of Two-Way Internet Latency Data (in Proc.
PAM 2018)", March 2018.
[QUIC-SPIN]
Trammell, B., Vaere, P., Even, R., Fioccola, G., Fossati,
T., Ihlar, M., Morton, A., and S. Emile, "Adding Explicit
Passive Measurability of Two-Way Latency to the QUIC
Transport Protocol", draft-trammell-quic-spin-03 (work in
progress), May 2018.
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[TMA-QOF] Trammell, B., Gugelmann, D., and N. Brownlee, "Inline Data
Integrity Signals for Passive Measurement (in Proc. TMA
2014)", April 2014.
[WIRE-IMAGE]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", draft-trammell-wire-image-04 (work in
progress), April 2018.
9.3. URIs
[1] https://mailarchive.ietf.org/arch/search/?email_list=quic
[2] https://github.com/quicwg
[3] https://github.com/quicwg/base-drafts/labels/-spin
Authors' Addresses
Brian Trammell (editor)
ETH Zurich
Email: ietf@trammell.ch
Mirja Kuehlewind
ETH Zurich
Email: mirja.kuehlewind@tik.ee.ethz.ch
Trammell & Kuehlewind Expires December 30, 2019 [Page 8]