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

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?

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

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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

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

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

Possible scenario: Mobile client Mobile client 3G celltower Server

Scenario: Mobile Client Mobile client Server Wifi

Scenario: Mobile Client Mobile client Server Wifi

Scenario: Mobile Client Mobile client Server Wifi

Feb 19, 2009Trilogy – Re-architecting the Internet12 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

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

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

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

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