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Challenges within Transport Protocols Åke Arvidsson, Ph.D., Prof. Disclaimer › Few or no new research results (save for Bilbao). › Focus on (more or less) open problems. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 2 Overview › Drivers behind challenges: – Higher cellular uptake. – Higher bit rates. – New environments. › Current research efforts: – End-to-end control. – Network assisted control. – TCP/NC. – QUIC and HTTP2. – MPTCP. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 3 Overview › Not discussed: – Data centres. – SDN and service chaining. – Internet of Things. – SCTP track. – Security aspects. – Middle box issues. – ... Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 4 Challenges › Quality Engineering for a Reliable Internet of Services. – Quality in terms of experience and reliability. › Continuous improvements: – Improve experience. – Increase utilisation. – More flexibility. – ... › Had enough? – Too much of a good thing can be wonderful. [Mae West] – Besides, conditions have changed. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 5 Drivers › Higher cellular uptake: Source: Ericsson Mobility Report June 2016. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 6 DRIVERS › Technological evolution: › Source: Performance of Wireless Networks, Chapter 7, O’Reilly. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 7 DRIVERS › Technological evolution: 5G 0.01–10 Gb/s 1 ms › Additional source: Ericsson White Paper 2016. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 8 DRIVERS › Technology adoption: Source: Ericsson Mobility Report June 2016. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 9 Drivers › Integrated services: – Real time (voice, gaming, …). › Data centres: – Short distances. › Software defined networks: – Service chaining. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 10 HIGH VOLTE Overall Target › Make the most out of new technology. › Support demands from new services. › Maximum goodput. – Only useful bytes contribute to user experience. › Minimum queuing. – Real time, handover, abandonment (cf. above). › Basic problem: – Achieve both at the same time. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 11 End-to-end Control › Some attempts to exercise end-to-end control: Source: ”TCP ex Machina: Computer-Generated Congestion Control”, Keith Winstein et al., MIT Computer Science and Artificial Intelligence Laboratory (2014). Source: ”TCP Congestion Avoidance Algorithm Identification”, Peng Yang et al. , IEEE/ACM Trans. Netw., vol. 22, no. 4 (2014). Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 12 End-to-end Control › Loss-based, delay-based, hybrid, … › Are we done? › No: – Recent papers point to several problems. › So: – Beat TCP by opening multiple, parallel connections. – Beat TCP by tweaking slow start. – Beat TCP by adding pacing. – Give up and design yourself. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 13 End-to-end Control › Improvements: – Reduce sensitivity to RTT variations. – E.g., Cubic hybrid slow start. › Development: – Use static pre-information? – Use temporary pre-information? – Fast start instead of slow start? – Are two phases necessary? › Only packet format is standardised. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 14 Network assisted control › Some attempts to provide network assisted control: Source: ”TCP ex Machina: Computer-Generated Congestion Control”, Keith Winstein et al., MIT Computer Science and Artificial Intelligence Laboratory (2014). Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 15 Network assisted control › Renewed interest in ECN, explicit congestion notification. › Congestion flags propagated back to the source. › Flags set based on AQM, active queue management. – RED (random early discard): Based on queue length. – CoDel (controlled delay): Based on minimum delay in time window. – ... › Work on both ECN, AQM and their interworking to be done. › Different track: DASH-friendly transport (support or enable rate estimation). Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 16 Network coding › Simplified idea: – For a file of N packets, compute M N linear combinations. – Send new combinations until N packets have been received. – Re-compute packets from combinations. › Example: – PAP1+P2, PBP1-P2, PCP1+2*P2 – P12*PA-PC, P2PC-PA › Benefits: – Packets are replaceable. – No need to identify lost packets. – No need to maintain packet order. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 17 SPDY, HTTP/2 and Quic › SPDY allows parallel objects over single (TCP) flows. › HTTP/2 adds server push and standardises these ideas. › QUIC adds encryption and more to a complete protocol. › Congestion control, wireless and middle boxes... Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 18 MPTCP › Multi-path TCP. › Let different packets follow different paths. – Normally invisible to end points. – Split and reassembly handled by gateways. › Load distribution for optimal throughput. › Load distribution for temporary (cost based) offload. › Minimise reordering at receiver. Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 19 ”Controlled environments” › Access networks (in particular cellular): – Under control of (largely) a single operator. – High efficiency (bit rate/queuing) more important. › Bridging functionality between gateway (GGSN or PGW) and base station (Node B or eNode B). – Split transport (faster feedback; higher rate and more accurate). – Limited uncertainty (path may be more or less known); better CC. – New features (limited need for compatibility); ECN, NC, MPTCP, Rate notification… › No need to feel constrained by ossification. – Large enough gains are always interesting! Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 20 SOME Recent IETF Publications › Duke et al., ”A Roadmap for Transmission Control Protocol (TCP) Specification Documents”, IETF RFC 7805 (2015). › Kuehlewind et al., “Problem Statement and Requirements for Increased Accuracy in Explicit Congestion Notification (ECN) Feedback”, IETF RFC 7560 (2015). › Baker et al., ”IETF Recommendations Regarding Active Queue Management”, IETF RFC 7567 (2015). › Detchart et al., ”Tetrys, an On-the-Fly Network Coding protocol”, IETF Draft (2016). › Hamilton et al., “QUIC: A UDP-Based Multiplexed and Secure Transport”, IETF Draft (2016). › Bagnulo et al., “Analysis of Residual Threats and Possible Fixes for Multipath TCP (MPTCP)”, IETF RFC 7430 (2015). Challenges within Transport Protocols | Ericsson Internal | 2016-08-29 | Page 21