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A Little-Heralded New iOS 7 Feature: Multipath TCP

Olivier Bonaventure Re:Wait, isn't this... (172 comments)

Having Multipath TCP inside the operating system allows all applications to automatically benefit from its features without forcing each application to reinvent the wheel. Operating system services help application developers by providing them with reusable services through standard APIs. In the case of Multipath TCP, at least on Linux, the standard API is the socket API.

about 10 months ago
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A Little-Heralded New iOS 7 Feature: Multipath TCP

Olivier Bonaventure Re:Wait, isn't this... (172 comments)

MOSH only works with ssh, while Multipath TCP works with any unmodified application that runs on top of TCP. ssh is one of them of course.

about 10 months ago
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A Little-Heralded New iOS 7 Feature: Multipath TCP

Olivier Bonaventure Re:Why not SCTP? (172 comments)

SCTP is cleaner than Multipath TCP, but unfortunately there are on today's Internet many devices such as NATs that do not understand SCTP and simply block SCTP packets.

about 10 months ago
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A 50 Gbps Connection With Multipath TCP

Olivier Bonaventure Re:You're supposed to get an AS number. (150 comments)

The main benefit of Multipath TCP when used in multihoming scenarios compared to BGP-based multihoming is that Multipath TCP capable hosts can use different paths simultaneously while BGP-based multihoming would provide one path for each client server pair.

With Multipath TCP, multihoming must be exposed to the server. For example, consider a small enterprise network connected to two different providers, A and B. With BGP-based multihoming, you assign address C to your server and advertise it through the two providers via BGP. BGP decides which path will be used and the ASPath metric used by BGP is far from being the most accurate metric to evaluate the quality of a path.

With Multipath TCP, you should ask a block of addresses from both A and B and assign one address from each provider you your server, say A.1 and B.1. Both addresses are advertised in the DNS. Address A.1 is always reachable via provider A and B.1 always reachable via provider B. When a TCP connection reaches the server, say over A.1, it will also advertise address B.1 using Multipath TCP and a second subflow will be established. Multipath TCP will then regulate the usage of the two paths in function of the amount of congestion on each path. If one path fails, Multipath TCP will perform failover automatically.

about a year ago
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A 50 Gbps Connection With Multipath TCP

Olivier Bonaventure Re:API support (150 comments)

Multipath TCP supports transparently IPv4 and IPv6. A Multipath TCP connection can start over IPv4 and then use IPv6 without the application being aware of the utilisation of IPv6. This could help the utilisation of IPv6 paths by IPv6 unaware TCP applications.

about a year ago
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A 50 Gbps Connection With Multipath TCP

Olivier Bonaventure Re:API support (150 comments)

The current implementation in the Linux kernel only exposes the first address used in the connection to the application. If the addresses change, the application is not informed but the TCP connection remains alive. Exposing addresses to the application is an old mistake of the socket interface. The socket interface does not expose packet losses because TCP deals with them and provides a bytestream abstraction to the application. Multipath TCP does the same, it handles all changes in address transparently to the application.

about a year ago
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A 50 Gbps Connection With Multipath TCP

Olivier Bonaventure Re:Bad math? (150 comments)

The limit here is the CPU and on the sender and the receiver. Both servers used in the test reached 98% CPU load to achieve 52 Gbps. Note that 52 Gbps is the googput at the application and not the bandwidth used on the links (which is higher due to the various overheads)

about a year ago
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A 50 Gbps Connection With Multipath TCP

Olivier Bonaventure Re:what's happening with SCTP? (150 comments)

SCTP is cleaner than Multipath TCP, but it suffers from two drawbacks that hinder its deployment in today's Internet : - many middleboxes only support IP, ICMP and TCP and discard SCTP packets (or do not perform NAT correctly) - applications need to be modified to support SCTP Multipath TCP is an evolution to TCP that works with unmodified applications and unmodified middleboxes.

about a year ago

Submissions

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Multipath TCP inside iOS7

Olivier Bonaventure Olivier Bonaventure writes  |  about 10 months ago

Olivier Bonaventure (2873367) writes "Besides changes in UI, multitasking and other features that the press discusses, iOS7 also includes support for Multipath TCP. Multipath TCP is a major extension to TCP that is able to use different interfaces for the same connection. Until now, Multipath TCP has been mainly used by researchers with a modified Linux kernel. iOS7 changes with millions of Multipath-TCP enabled devices that can switch from 3G to WiFi without losing existing TCP connections. This is not yet the case on iOS7 that currently seems to only enable it for SIRI, but other use cases will likely appear in the future."
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A 50 Gbps TCP connection with Multipath TCP

Olivier Bonaventure Olivier Bonaventure writes  |  about a year ago

Olivier Bonaventure (2873367) writes "The TCP protocol is closely coupled with the underlying IP protocol.
Once a TCP connection has been established through one IP address,
the other packets of the connection must be sent from this address. This
makes mobility and load balancing difficult. Multipath TCP is
a new extension that solves these old problems by decoupling TCP from
the underlying IP. A Multipath TCP connection can send packets over
several interfaces/addresses simultaneously while remaining backward
compatible with existing TCP applications. Multipath TCP has several use
cases including smartphones that can use both WiFi and 3G or servers
that can pool multiple high-speed interfaces. Christoph Paasch, Gregory
Detal and their colleagues who develop the implementation of
Multipath TCP in the Linux kernel have achieved 50 Gbps for a single TCP
connection by pooling together six 10 Gbps interfaces. See here for
technical details and full source code."

Link to Original Source

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