5 ms·

Multi-path TCP is not only about throughput, but also about providing redundancy to improve stability. And to me, redundant stream is more attractive. It happe

by songgao 14y ago

Multi-path TCP is not only about throughput, but also about providing redundancy to improve stability. And to me, redundant stream is more attractive. It happens a lot when I am with my iPhone at boundary of a Wi-Fi network coverage, the network is very unstable with oscillations between Wi-Fi and 4G. The phone stays in the status with connected Wi-Fi but it's actually not working. If there was multi-path TCP, mobile devices can establish simultaneous streams on both Wi-Fi and 4G. When Wi-Fi is not responsive, the data stream can be automatically offloaded onto 4G seamlessly without causing latency in application layer. Another protocol that may achieve this is SCTP[1]. And it's been around for years[2]. But migrating existing services to another transport protocol is a challenge, which makes it difficult to adopt SCTP. I'm curious how multi-path handles this. Is it an extension to TCP that can handle backward compatibility with TCP, or yet another new transport protocol? [1]: http://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocol http://en.wikipedia.org/wiki/Stream_Control_Transmission_Pro... [2]: http://www.sctp.org/implementations.html http://www.sctp.org/implementations.html --- EDIT: More details about its design decisions and goals: http://multipath-tcp.org/data/MultipathTCP-netsys.pdf http://multipath-tcp.org/data/MultipathTCP-netsys.pdf

aray 14y ago
The tech talk (http://www.youtube.com/watch?v=VWN0ctPi5cw http://www.youtube.com/watch?v=VWN0ctPi5cw) explains how MPTCP can be implemented on top of existing TCP without interrupting the client, the server, or both.
signa11 14y ago
with two antennas (antennae ?) simultaneously broadcasting/receiving, i think battery life would be pretty low...
- brokenparser 14y ago
  Bugs have antennae, radios have antennas (or aerials).
- songgao 14y ago
  Not necessarily antennas. Antennas are in physical layer, not transport or network layer. 802.11n can have multiple antennas but if you are at the boundary of the coverage, multiple antennas won't help much. Multi-path TCP is more about multiple transport streams. Of course it would require separate antennas for Wi-Fi and 4G but that's already the case on current mobile devices. So nothing changes in this sense. It won't affect battery life much from aspect of antenna power consumption because you can only set 4G to backup link, and MPTCP won't offload to 4G until Wi-Fi is not responsive. If you are using full MPTCP (using two links all the time), then that's the tradeoff between performance and power consumption.
- Dylan16807 14y ago
  In my experience a data link takes far more power than wifi, so the extra use won't be very notable.
  - krzyk 14y ago
    I think that the opposite is true (but depends on the type of connection). Mobile stations are focused on low power, they were designed that way from the beginning (e.g. they constantly try to reduce the transmit power if you have "too good" reception so it will be just good and use a lot less power) unlike wifi. I remember the first mobile prototypes that were used around Motorola were dying of battery after few hours if used wifi instead of mobile data (that was about 8 years ago - so probably we are talking GPRS here).
- aray 14y ago
  That's not exactly how this works; you can just maintain simultaneous connections over both network methods. This consumes a very small amount of data on both, but will intelligently shift the bulk of data between the two as connectivity/packet loss/etc changes. It's about being able to seamlessly go from one to the other and back again without having to halt and re-open TCP connections every time, not about using both connections full-out all the time. Checkout the tech talk if you want to know more.

by songgao 14y ago

aray 14y ago

The tech talk (http://www.youtube.com/watch?v=VWN0ctPi5cw http://www.youtube.com/watch?v=VWN0ctPi5cw) explains how MPTCP can be implemented on top of existing TCP without interrupting the client, the server, or both.

signa11 14y ago

with two antennas (antennae ?) simultaneously broadcasting/receiving, i think battery life would be pretty low...

brokenparser 14y ago
Bugs have antennae, radios have antennas (or aerials).
songgao 14y ago
Not necessarily antennas. Antennas are in physical layer, not transport or network layer. 802.11n can have multiple antennas but if you are at the boundary of the coverage, multiple antennas won't help much. Multi-path TCP is more about multiple transport streams. Of course it would require separate antennas for Wi-Fi and 4G but that's already the case on current mobile devices. So nothing changes in this sense. It won't affect battery life much from aspect of antenna power consumption because you can only set 4G to backup link, and MPTCP won't offload to 4G until Wi-Fi is not responsive. If you are using full MPTCP (using two links all the time), then that's the tradeoff between performance and power consumption.
Dylan16807 14y ago
In my experience a data link takes far more power than wifi, so the extra use won't be very notable.
- krzyk 14y ago
  I think that the opposite is true (but depends on the type of connection). Mobile stations are focused on low power, they were designed that way from the beginning (e.g. they constantly try to reduce the transmit power if you have "too good" reception so it will be just good and use a lot less power) unlike wifi. I remember the first mobile prototypes that were used around Motorola were dying of battery after few hours if used wifi instead of mobile data (that was about 8 years ago - so probably we are talking GPRS here).
aray 14y ago
That's not exactly how this works; you can just maintain simultaneous connections over both network methods. This consumes a very small amount of data on both, but will intelligently shift the bulk of data between the two as connectivity/packet loss/etc changes. It's about being able to seamlessly go from one to the other and back again without having to halt and re-open TCP connections every time, not about using both connections full-out all the time. Checkout the tech talk if you want to know more.