Internet DRAFT - draft-deutschmann-sat-ter-multipath
draft-deutschmann-sat-ter-multipath
Internet Engineering Task Force J. Deutschmann
Internet-Draft K-S. Hielscher
Intended status: Informational R. German
Expires: October 20, 2021 Univ. of Erlangen-Nuernberg
April 18, 2021
Multipath Communication with Satellite and Terrestrial Links
draft-deutschmann-sat-ter-multipath-01
Abstract
Multipath communication enables the combination of low data rate, low
latency terrestrial links and high data rate, high latency links
(e.g., geostationary satellite links) to provide a full-fledged
Internet access. However, the combination of such heterogeneous
links is challenging from a technical point of view. This document
describes a possible solution, i.e. an architecture and scheduling
mechanism. The applicability of this approach to encrypted transport
protocols (e.g., Multipath QUIC) is also discussed.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Comparison of Link Characteristics . . . . . . . . . . . . . 4
4. Backlog-Based Scheduling . . . . . . . . . . . . . . . . . . 4
5. Applicability non-TCP / Enrypted Traffic and QUIC . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Some areas (e.g., rural areas) suffer from poor Internet connectivity
(e.g., low data rate DSL lines or old generation cellular networks).
On the other hand, geostationary satellite Internet access is
available all over the world with data rates of up to 50 Mbit/s and
more. Obviously, the combination of both Internet access types seems
beneficial.
high data rate, ______
high latency \
+-----> high data rate,
low data rate, _______/ low latency
low latency
Motivation for combining very heterogeneous Internet access links.
Figure 1
However, the combination of very heterogeneous link types is
challenging given currently deployed transport protocols. Some
applications could be strictly assigned to either the high data rate,
high latency link (e.g., bulk data transfer) or the low data rate,
low latency link (e.g., VoIP). Other applications, especially
Internet browsing, have more versatile requirements. Connection
setup and interactive content require low latency, but transferring
large objects requires high data rate. The combination of links as
shown in Figure 1 cannot outperform a fast terrestrial Internet
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access which is able to provide high data rate and low latency
simultaneously (e.g, as required for video conferencing or cloud
gaming), but there still can be a significant improvement regarding
quality of service and quality of experience.
Multipath protocols (e.g., Multipath TCP [RFC8684]) can be used for
simultaneously using multiple Internet access links. However,
scheduling is non-trivial in case of very heterogeneous links. In
this document, an architecture based on Performance Enhancing Proxies
and a scheduling mechanism called back-log based scheduling is
described.
This document is based on the publication [MMB2020], which also
contains performance evaluation results obtained with the discrete
event simulator ns-3. Performance evaluation results with a Linux-
based implementation and real networks will be published as soon as
possible.
2. Architecture
Sat
/ \
#######___/ \___########
#Local# #Remote#
Host(s)----# PEP #-------------# PEP #----Host(s)
####### Ter ########
Multipath-enabled PEPs in access network.
Figure 2
A PEP-based architecture, similar to Hybrid Access networks [HA2020],
as shown in Figure 2 is chosen because of several reasons:
o For the satellite link, PEPs and protocols suitable for high-
latency links are required, anyway.
o As the PEPs are located at the Access network, there is better
knowledge of the link characteristics used for multipath
communication.
o The presence of PEPs enables the aggregation of transport layer
data which can be used for scheduling decisions, as described
later in Section 4.
Unlike Multipath TCP [RFC8684], the multipath connection between both
PEPs is provisioned statically. A way to interoperate between PEPs
is out of scope for this document, configurations with SOCKS
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[RFC1928] or the 0-RTT TCP Convert Protocol [RFC8803] are under
investigation.
3. Comparison of Link Characteristics
There is a great difference between both delay and data rate of
aforementioned links.
o Low data rate, low latency terrestrial link: Suitable for
connection setups and small objects. Unsuitable for large amounts
of data. The transmission duration can be a approximated as
TransmissionDurationTer = DelayTer + Size/DatarateTer
o High data rate, high latency link (geostationary satellite):
Favorable for large objects. Unsuitable for latency-sensitive
data. The transmission duration can be approximated as
TransmissionDurationSat = DelaySat + Size/DatarateSat
By putting both together
TransmissionDurationTer = TransmissionDurationSat
a threshold size can be obtained, which describes over which link a
transmission finishes first:
ThresholdTerSat
= (DelaySat - DelayTer) / ((1/DatarateTer) - (1/DatarateSat))
with the assumption that DatarateSat > DatarateTer and DelaySat >
DatarateTer.
Example:
DatarateTer = 1 Mbit/s, DelayTer = 15 ms,
DatarateSat = 20 Mbit/s, DelaySat = 300ms,
leads to ThresholdTerSat = 37.5 kByte, which means that a sum of
packets smaller than this size finishes on the terrestrial link
first, whereas a sum of packets greater than this size finishes on
the satellite link first.
4. Backlog-Based Scheduling
With the help of PEPs, data from TCP senders can be aggregated.
Packets are then sent on the appropriate link based on
ThresholdTerSat. As PEPs handle individual TCP flows, new
connections and flows with little backlog are sent via the
terrestrial connection, flows with large backlog are sent via the
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satellite link. For a detailed description and performance
evaluation see [MMB2020]. Other multipath schedulers are currently
also under investigation, as the combination of very heterogeneous
links requires specialized scheduling strategies.
5. Applicability non-TCP / Enrypted Traffic and QUIC
The architecture described in Section 2 only works for non-encrypted
TCP traffic. As it is the case for every PEP, it does not work for
enrypted traffic (e.g., VPNs or QUIC).
However, the use case of bonding very heterogenous links and the
scheduling mechanism can also be applied to end-to-end protocols
(e.g., Multipath QUIC [I-D.deconinck-quic-multipath]), which is
currently work in progress.
With Multipath QUIC, data and acknowledgements can be sent on
different paths. By this, data sent over the high-latency satellite
link can be acknowledged by the low-latency satellite link,
effectively halving the round trip time.
6. Acknowledgements
This work has been funded by the Federal Ministry of Economics and
Technology of Germany in the project Transparent Multichannel IPv6
(FKZ 50YB1705).
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
The same security considerations as in [RFC3135] apply.
9. References
9.1. Normative References
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928,
DOI 10.17487/RFC1928, March 1996,
<https://www.rfc-editor.org/info/rfc1928>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>.
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9.2. Informative References
[HA2020] Keukeleire, N., Hesmans, B., and O. Bonaventure,
"Increasing Broadband Reach with Hybrid Access Networks",
IEEE Communications Standards Magazine vol. 4, no. 1, pp.
43-49, 2020,
<https://doi.org/10.1109/MCOMSTD.001.1900036>.
[I-D.deconinck-quic-multipath]
Coninck, Q. and O. Bonaventure, "Multipath Extensions for
QUIC (MP-QUIC)", draft-deconinck-quic-multipath-06 (work
in progress), November 2020.
[MMB2020] Deutschmann, J., Hielscher, KS., and R. German, "An ns-3
Model for Multipath Communication with Terrestrial and
Satellite Links", In: Hermanns H. (eds) Measurement,
Modelling and Evaluation of Computing Systems. Lecture
Notes in Computer Science, vol 12040. Springer, Cham,
2020, <https://doi.org/10.1007/978-3-030-43024-5_5>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>.
[RFC8803] Bonaventure, O., Ed., Boucadair, M., Ed., Gundavelli, S.,
Seo, S., and B. Hesmans, "0-RTT TCP Convert Protocol",
RFC 8803, DOI 10.17487/RFC8803, July 2020,
<https://www.rfc-editor.org/info/rfc8803>.
Authors' Addresses
Joerg Deutschmann
Univ. of Erlangen-Nuernberg
Email: joerg.deutschmann@fau.de
Kai-Steffen Hielscher
Univ. of Erlangen-Nuernberg
Email: kai-steffen.hielscher@fau.de
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Reinhard German
Univ. of Erlangen-Nuernberg
Email: reinhard.german@fau.de
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