WELCOME! Multipath TCP Implementors Workshop

1. WELCOME!Multipath TCP Implementors Workshop Saturday 24th July Maastricht Philip Eardley MPTCP WG Co-chair

2. Objective • The objective of the workshop is to help make MPTCP real, i.e., to get it implemented in many operating systems and to get it used by key applications. • Interactive workshop with • Designers who would use MPTCP, • OS implementors who would implement and ship MPTCP • MPTCP WG people who are designing and standardising MPTCP • Discuss the use cases for Multipath TCP – • What are the gotchas and how can the protocol designers increase the usefulness of MPTCP? • Discuss the process through which Multipath TCP could make its way into OSes. • What are the potential stumbling blocks for MPTCP's implementation (real world requirements and constraints) and how could the protocol designers lower the deployment barriers?

3. Note • The workshop is organised under the auspices of the MPTCP working group, but is not a formal WG meeting - for instance, WG consensus calls will not be made. • Please assume that the ‘Note Well’ applies

4. Note Well • Any submission to the IETF intended by the Contributor for publication as all or part of an IETF Internet-Draft or RFC and any statement made within the context of an IETF activity is considered an "IETF Contribution". Such statements include oral statements in IETF sessions, as well as written and electronic communications made at any time or place, which are addressed to: • * The IETF plenary session • * The IESG, or any member thereof on behalf of the IESG • * Any IETF mailing list, including the IETF list itself, any working group or design team list, or any other list functioning under IETF auspices • * Any IETF working group or portion thereof • * The IAB or any member thereof on behalf of the IAB • * The RFC Editor or the Internet-Drafts function • All IETF Contributions are subject to the rules of RFC 5378 and RFC 3979 (updated by RFC 4879). • Statements made outside of an IETF session, mailing list or other function, that are clearly not intended to be input to an IETF activity, group or function, are not IETF Contributions in the context of this notice. • Please consult RFC 5378 and RFC 3979 for details. • A participant in any IETF activity is deemed to accept all IETF rules of process, as documented in Best Current Practices RFCs and IESG Statements. • A participant in any IETF activity acknowledges that written, audio and video records of meetings may be made and may be available to the public.

5. Agenda • Intro, background, assumptions • Philip Eardley • Demo of implementation • Sebastien Barre / Costin Raicu • Use cases discussion • Mobility - discussion led by Lars Eggert • Data centres - discussion led by Costin Raicu • OS implementation discussion • Led by Sebastien Barre and Costin Raicu • Changes to Linux kernel – priorities etc • How to get into mainline Linux kernel • How to get into other OS

6. Introduction • Overview of Multipath TCP (MPTCP) • Uses and benefits • Status of MPTCP • Assumptions & design decision by WG

7. MPTCP: The Basic Idea • Enable a single TCP connection to use multiple paths simultaneously • Stop hiding multihoming • Establish more than one path between the same pair of endpoints for the same connection. • Use congestion control to determine traffic on each path • Move congestion, not just spread it out over more time

8. Possible scenario: Mobile client 3G celltower Mobile client Server

9. Scenario: Mobile Client Mobile client Server Wifi Wifi

10. Server Mobile client Wifi Wifi Scenario: Mobile Client

11. Scenario: Mobile Client Server Wifi Mobile client Wifi

12. Possible scenarios & benefits A mobile node with 3G and WiFi A form of mobility A campus with 2 providers Resilience Inside a network Fast TE Increase utilisation, resource pooling Inside a data centre Load balancing Trilogy – Re-architecting the Internet 12 Feb 19, 2009

13. Status of MPTCP • WG established • Charter runs to March 2011 • output is experimental or informational • Good progress on work items • High level design decisions • Protocol • Congestion control algorithm • Security threats • Application considerations • Optional extended API • Implementations • User space, early implementation • Linux kernel ‘reference’ implementation

14. Goals & assumptions • Improve throughput • Better than regular TCP on best path • Be “fair” • To regular TCP at shared bottlenecks • Paths may not be disjoint • Improve resilience • Use multiple paths interchangeably • Paths may disappear • Assume identify paths by IP addresses • Application compatibility • Same API as regular TCP • Network compatibility • Work on current Internet • Traverse predominant middleboxes • Fallback to regular TCP

15. Design decisions • Improve throughput & Be “fair” • Congestion control: coupled increases algorithm • Improve resilience • Either end can add paths • Re-transmit on any path • Application compatibility • TCP API – no mods to apps • Modify TCP stack • Network compatibility • Subflows look like regular TCP • Connection & subflow sequence spaces, acks… • Signal “MPTCP capable” with TCP option on SYN • Sunsequent signalling under discussion • Fallback to regular TCP

16. Multipath TCP Implementors workshop • Interactive workshop to help make Multipath TCP real • to get it implemented in many operating systems and to get it used by key applications. • Intro, background, assumptions • Demo of implementation • Sebastien Barre / Costin Raicu • Use cases discussion • Mobility - discussion led by Lars Eggert • Data centres - discussion led by Costin Raicu • OS implementation discussion • Led by Sebastien Barre and Costin Raicu • Changes to Linux kernel – priorities etc • How to get into mainline Linux kernel • How to get into other OS