Real-world use of Linux multipath TCP [LWN.net]

LWN looked at the Linux multipath TCP implementation back in 2013. That code remains out of tree, but it now seems that it is being used in some Samsung phones in Korea. "This service enables smartphone users to reach bandwidth of up to 1 Gbps on existing smartphones. This is probably the fastest commercially deployed mobile network. They achieve this high bandwidth by combining both fast LTE (with carrier aggregation) and fast WiFi networks on Multipath TCP enabled smartphones." (Thanks to Oliver Bonaventure).

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Real-world use of Linux multipath TCP

Posted Aug 1, 2015 17:55 UTC (Sat) by MuratD (guest, #75273) [Link] (2 responses)

Korea's smartphones capable to handle such bandwidth, 1Gbits?

Real-world use of Linux multipath TCP

Posted Aug 1, 2015 22:50 UTC (Sat) by flussence (guest, #85566) [Link] (1 responses)

You're probably not going to achieve a sustained speed anywhere near that on a battery-powered ARM device. But as it's a shared medium with a huge number of concurrent users, getting bits from one end to the other faster should reduce overall congestion.

Real-world use of Linux multipath TCP

Posted Aug 2, 2015 3:43 UTC (Sun) by ssmith32 (subscriber, #72404) [Link]

According to the article, at least, they demonstrated phones reaching 800 Mbps out of the >1Gbps theoretical max. Since they've only enabled it on the S6, it was prolly one of those. So it looks like recent phones can get fairly close with arm and battery power and all...

Real-world use of Linux multipath TCP

Posted Aug 1, 2015 19:43 UTC (Sat) by Felix_the_Mac (guest, #32242) [Link]

via Wikipedia:

https://perso.uclouvain.be/olivier.bonaventure/blog/html/...

"On September 18th, 2013, Apple releases iOS7 which includes the first large scale commercial deployment of Multipath TCP"

"Packet traces collected on an iPad running iOS7 reveal that it uses Multipath TCP to reach some destinations that seem to be directly controlled by Apple."

Hopefully we'll see this merged in Linux soon and implemented in Android and, one day, by Microsoft.

Real-world use of Linux multipath TCP

Posted Aug 3, 2015 4:18 UTC (Mon) by rsidd (subscriber, #2582) [Link] (5 responses)

I'm missing something here. The Samsung phones are combining LTE and wifi to achieve 1 Gbps. If the bandwidth is additive, either each of those was already about 0.5 Gbps or one of those was already close to 1 Gbps -- an achievement in itself? What am I missing?

Real-world use of Linux multipath TCP

Posted Aug 3, 2015 4:44 UTC (Mon) by dlang (guest, #313) [Link] (4 responses)

well, 802.11ac 3x3 wifi is a theoretical 1.3Gb/s and a practical ~900Mb/s, so 500Mb each is not unreasonable.

Real-world use of Linux multipath TCP

Posted Aug 3, 2015 5:15 UTC (Mon) by rsidd (subscriber, #2582) [Link] (3 responses)

OK, so they got 800-900 Mbps from existing wifi technology and used LTE to boost it over 1 Gbps, is that it? My impression was LTE doesn't offer much beyond 50 Mbps, theoretically 100 max.

LTE-Avdanced not limited to 100mbps

Posted Aug 3, 2015 6:01 UTC (Mon) by gmatht (subscriber, #58961) [Link]

IIRC plain LTE is limited to 100mbps, but LTE with carrier aggregation can do better than that. For example 480mbps in this trial:
http://www.computerworld.com.au/article/569267/optus-cloc...

Real-world use of Linux multipath TCP

Posted Aug 3, 2015 11:12 UTC (Mon) by farnz (subscriber, #17727) [Link] (1 responses)

LTE's theoretical peak is about 30 bits/Hz (using 8x8 MIMO); currently deployed LTE modems in cellphones do 2x2 MIMO for 7.5 bits/Hz, and can aggregate 2 or 3 spectrum bands to get high peak bitrates. LTE can be deployed in 1.4, 3, 5, 10, 15 and 20 MHz wide spectrum chunks, getting a theoretical speed peak of 600 Mbit/s for a single 20 MHz carrier; a current mobile LTE modem (like the one in the Samsung Galaxy S6) can combine 3 carriers at once, each band getting 150 Mbit/s to give you a peak of 450 Mbit/s raw data rate. You can expect to lose around 50 Mbit/s of the peak rate to overheads (network management, idle users checking in, cell handoff etc), for an LTE rate of 400 Mbit/s. Note that this throughput figure depends crucially on your serving cell sites having no other clients to serve; LTE reallocates airtime (and thus carrier aggregation bands) once a millisecond to keep latency under control, but your data rate is thus constantly varying with cell load.

Your 50 to 100 figure sounds right for a modem capable of 2x2 MIMO on a single band, talking to a base station that's only capable of 2x2 MIMO itself in a 20 MHz wide carrier; you've got a cell capable of 150 Mbit/s if it dedicates itself to you, but where other users (including network overhead) bring the speed down to a more realistic 50 Mbit/s. A base station with more MIMO capability (e.g. 8x4 MIMO) can get you to 100 Mbit/s on your 2x2 MIMO device despite the other users; to go much faster, you need carrier aggregation to let you use more than 20 MHz of spectrum, or more complex MIMO systems to let you get more bits on the same spectrum.

Real-world use of Linux multipath TCP

Posted Aug 3, 2015 17:02 UTC (Mon) by billygout (guest, #70918) [Link]

My assumption is that the biggest benefit of MPTCP is not the aggregated bandwidth, but the reliability which comes from multiple points of failure, and seamless failover to one sub-stream when the other sub-stream is making no progress.

Real-world use of Linux multipath TCP

Posted Aug 13, 2015 9:50 UTC (Thu) by leni536 (guest, #103643) [Link]

MPTCP requires MPTCP aware hosts too, doesn't it? I assume they use MPTCP proxies to reach other sites, so your cell phone provider is always a middleman even if you use wifi. Also it could make sense to tune MPTCP to not to optimize for bandwidth but to optimize for some weighted average of bandwidth and cost, mobile data costs money (if this is on an unlimited plan then it doesn't matter though).