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The truth about bandwidth?


kiramanell

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There's a very persistent behavior going around, especially on ingame groups, telling people that Linden caps your bandwidth at 1500 kbps, and that you shouldn't go higher. Then I found this, straight from the mouth of Linden themselves:

http://community.secondlife.com/t5/Tips-and-Tricks/QUICKTIP-Get-less-lag-in-seconds-by-increasing-your-Maximum/ba-p/670217

Pay particular attention to this: "Supposedly years ago, setting your Max. Bandwidth too high would result in bad packet loss and overall decreased performance, but tell me if you still notice that. It may not even be true anymore."

And, indeed, having a 30Mbps connection, I can set it at 10,000 kbps easily (and get way increased rez-times), with 0.000% packet loss. And my bandwidth meter generally hovers between ca. 5,000-9,000 kbps.

Not meaning to sound too paranoid, but often inworld support groups seem more motivated to have you play fair ("Don't set your draw distance to 512m: you'll use too many server resources!") than they are at simply telling you what is, and is not, technically optimal for your connection. Nothing wrong with that, per se, but with Linden apparently dispelling the 1500 kbps rumor (in 2010 already), I wouldn't mind hearing the truth about bandwidth settings for a change.

^^ Well, that still came out too paranoid. :) Nonetheless I would love to get a definitive answer, from the Lindens, preferably, on whether indeed the cap has been lifted, and whether the whole 1500 kbps story still holds true.

Thanks,

- Kira

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It used to be that you got everything from the sim server you were connected to, using UDP, and there was a per-user limit set by the server. The tech has changed, and now the sim server sends you a URL, with textures, in particular, downloaded from a server cluster using HTTP.

A large HTTP server cluster is a well-understood technology and can put out a lot of data. So I reckon some of the advice is obsolete.

But not everything uses HTTP 

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WolfBaginski Bearsfoot wrote:

It used to be that you got everything from the sim server you were connected to, using UDP, and there was a per-user limit set by the server. The tech has changed, and now the sim server sends you a URL, with textures, in particular, downloaded from a server cluster using HTTP.

A large HTTP server cluster is a well-understood technology and can put out a lot of data. So I reckon some of the advice is obsolete.

But not everything uses HTTP 

What if you have HTTP textures turned off?

Jeanne

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Why would you turn off HTTP Get Textures?

Some time ago the Lab has more servers handling the UDP channels and  people could solve problems and get better performance using UDP. There were not enough servers handling HTTP Texture Gets. That has changed. 

When you change from UDP to HTTP clear your cache. The PH/FS support team and some others recommend the clear on change.

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There is no simple answer that works for every computer and location. Try different values and see what works for you.

If you get on a laggy server, one making less than 30 FPS or Time Dilation under 0.7, you may have fewer problems with a low bandwidth setting.

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Nalates Urriah wrote:

Why would you turn off HTTP Get Textures?

Some time ago the Lab has more servers handling the UDP channels and  people could solve problems and get better performance using UDP. There were not enough servers handling HTTP Texture Gets. That has changed. 

When you change from UDP to HTTP clear your cache. The PH/FS support team and some others recommend the clear on change.

Ok Nalantes. Thanks!

Awhile back textures were slow to load & someone suggested turning off HTTP textures. This seemed to have helped. If it's better now I'll try turning it back on & clearing cache. Thanks again!

Jeanne

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 know switching back to UDP sort out lag problems, but times are changing. To be honest, I don't recall much ever being said about the pros and cons.

I do wonder if residents outside North America, with inevitably longer ping times, can see that as limiting the speed of HTTP texture gets. There's a limit on simultaneous texture loads. But one HTTP request involves 6 packets, and three round trips, minimum. Which for me is between 750ms and 900ms, on top of the time needed to actually transmit the packets.

It looks horribly complicated. It ends up depending on packet sizes, and how many packets the server will send without acknowledgement before it pauses to wait. Small textures will have a higher overhead from the setup, but might not be affected by that pausing.

And when you TP into a new region, there might be a lot of textures to download. Let's say there are 48. I think there are 8 simultanous streams possible. And the packet size I assume trivial at whatever beandwidth is set.

I can see a fivefold increase in the total time needed to download textures.

HTTP Get is more reliable. It avoids a sim-server bottleneck. But I am not convinced it is inherently faster.

 

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WolfBaginski Bearsfoot wrote:

But one HTTP request involves 6 packets, and three round trips, minimum. 

Um, HTTP is a stateless protocol, there is no handshake. Perhaps you were thinking of the TCP handshake, but that is only 3 packets (SYN, SYN+ACK, ACK), and the client can include its request in the SYN packet and the server can include its reply (or the first part of it) in the SYN+ACK packet. So only 1 round trip is needed to start getting data.

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  • 2 weeks later...

But what happens when everyone switches their Max speed from 1000k to 10000k/s?..  Does the Grid have enough overhead to increase speeds 10x overnight?

All that would happen is a few people with it set higher would ruin it for everyone else by taking up 10 user worth of bandwidth while also increasing server loads to keep up with more connection demand.  Almost like a leecher in that u dont stick to ur fair share.

 

I doubt theres enough overhead to basically increase the load by 10x on the Grid when ingame the servers can barely keep up if theres more than 20 people in the area anyways...

 

Also, I dont think any LL viewers allow u to set it too high, Only 3rd party viewer have it uncapped or set very high..

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Another comment that is made in the same breadth as it were is, if you use a wireless LAN inside the house set max BW at 500.

Thats in spite of the fact that if I run speed tests on my pc (on the wireless lan), I get download speeds in the 14 - 20 MBPS range.   Even the slow data centre in the deep south (I forget which) doesnt ususally go below 8 MBPS.

Is this another myth?

Standing back a bit ... there is a tun of settings that we each need to optimise for out setup.  In many cases the advice seems to be. try it and see.  (EG http textures).   But we can never really do controlled experiments to be sure that when we change something the benefit we see (or not) is due to precisely that factor; as opposed to some persion with a gazillion scripts or prims logging off or leaving the region.

 

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"All that would happen is a few people with it set higher would ruin it for everyone else by taking up 10 user worth of bandwidth while also increasing server loads to keep up with more connection demand.  Almost like a leecher in that u dont stick to ur fair share."

And yet, separating the (in itself not per se unreasonable) request to play fair, and the naked truth about what bandwidth is really available, is precisely why I started this thread.

N.B. As for playing fair, I pay the Lindens upward to $300 USD a month in tier alone. From my perspective, 'fair' is not b*tching about people who actually want to use what you let thm pay thru their noses for to get. But hey, that's just me. :)

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Wi-Fi has a few things that can mess you up, and the latest standards do have a higher speed.

I would say that Wi-Fi does need more margin between the nominal speed and the bandwidth used by SL. It's not just the effect from another Wi-Fi system nearby (which is why changing from the default channel can make a big difference). There are other things using the same frequencies, and effectively adding to background noise, which reduces bandwidth.

The reduced speed advice is maybe a safe starting point: cut your bandwidth, check your wi-fi set-up, and then see if you can increase the speed. There can be a lot of trial and error in it.

 

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