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. 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 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 October 20, 2021. Copyright Notice Copyright (c) 2021 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 Deutschmann, et al. Expires October 20, 2021 [Page 1] Internet-Draft Satellite/Terrestrial Multipath April 2021 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 . . . . . . . . . . . . . . . . . . . . . . . . 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 Deutschmann, et al. Expires October 20, 2021 [Page 2] Internet-Draft Satellite/Terrestrial Multipath April 2021 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 Deutschmann, et al. Expires October 20, 2021 [Page 3] Internet-Draft Satellite/Terrestrial Multipath April 2021 [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 Deutschmann, et al. Expires October 20, 2021 [Page 4] Internet-Draft Satellite/Terrestrial Multipath April 2021 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, . [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, . Deutschmann, et al. Expires October 20, 2021 [Page 5] Internet-Draft Satellite/Terrestrial Multipath April 2021 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, . [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, . [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, . [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, . 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 Deutschmann, et al. Expires October 20, 2021 [Page 6] Internet-Draft Satellite/Terrestrial Multipath April 2021 Reinhard German Univ. of Erlangen-Nuernberg Email: reinhard.german@fau.de Deutschmann, et al. Expires October 20, 2021 [Page 7]