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Author Topic: SCTP unfriendliness  (Read 758 times)

Chrysalis

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Re: SCTP unfriendliness
« Reply #15 on: September 22, 2018, 06:37:30 PM »

http/2 is nice and google is pushing it, but with that said its not taking over http 1.x anytime soon.
There is things that google adopted and even introduced themselves that got abandoned, one recent thing is public key pinning which is been removed in chrome after only a few years, so google are impatient to allow things to get adopted.  https://www.theregister.co.uk/2017/10/30/google_hpkp/

With that said http/2 is used on youtube and other google sites for performance reasons so their motivation will be higher than HPKP so I dont think that will get removed from chrome.

The domain hosting my line stats in my sig uses http/2 for reference.

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CarlT

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Re: SCTP unfriendliness
« Reply #16 on: September 22, 2018, 07:36:21 PM »

QUIC adapts to congestion better than normal TCP and is easily recognisable as QUIC so, although shaping it won't be clever, simple dropping of the packets has to suffice.
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CarlT

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Re: SCTP unfriendliness
« Reply #17 on: September 23, 2018, 12:37:02 AM »

As far as P2P goes the killer was the number of flows it opened. Very approximately each TCP flow on your connecting gets roughly the same bandwidth. When you've a hundred torrent flows on a 20Mb connection, eating 200kb/s each a 101st TCP flow isn't going to be getting much capacity, not least because congestion control will kick in before it can ramp up very much.

The UDP version of the protocol, UTP, was actually better behaved.
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kitz

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Re: SCTP unfriendliness
« Reply #18 on: September 23, 2018, 10:36:33 AM »

Sorry, I don't think I explained it very well.  I was pondering on the effect of the backhaul and other types of traffic for other users. When I said networks I meant network operators & service providers.

I know things will have scaled up since but I was using the BE* example because it was simple and when they started up, some of the satellite exchanges only had a 100Mbps backhaul.     After a while you may get users seeing congestion and speeds drop to 5Mbps if a lot of those users were constantly downloading.  If everything was equal (and I know it never is because you also get bursty traffic), that means you have 20 users getting 5Mb per connection.    So there's user A using his 5Mbps, but along comes user B who opens up p2p with multiple streams thus still able to get his full 24Mbps, but has the effect of pushing down the available backhaul bandwidth for other traffic (and users) even further. 

The article implied that QUIC could be challenging to shape for network providers.   I think I recall reading something somewhere else that if UDP (or the ports) were blocked then it can fall back to TCP.  So whilst its only really google using it atm, but what's to stop other applications using it in future. 
I suppose the only saving grace is that bandwidth isnt cheap on mobile networks and is quite often limited.  So if someone invents a new p2p type file sharing system using QUIC, then your'e hardly likely to do so over a mobile connection. 
   
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CarlT

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Re: SCTP unfriendliness
« Reply #19 on: September 23, 2018, 12:06:15 PM »

Ah yes!

So with TCP the headers can be manipulated to shape the flows. Mess with window sizes / MSS / ECN / whatever. Obviously QUIC not so much so you just have to drop packets to shape them.

To be honest, though, with most networks packets are just buffered then dropped now. Flow counts are getting somewhat excessive to spend resources manipulating layer 4 unless you really, really want to invest in seriously expensive kit.

I remember the ham-fisted way upstream traffic was shaped by Virgin Media's implementation of Allot equipment. Setting MSS to 536 was the thing I, as initiator of the flow, could see. No idea what else was happening. Downstream shaping was much simpler.
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