NonBlocking.io - Malte Ubl's Asynchronous Identity Disorder

Here's the whole implementation of nextTick ba...

2011-07-13T16:56:03.557-07:00

Here's the whole implementation of nextTick based on MessageChannel.

var channel = new MessageChannel();
// linked list of tasks (single, with head node)
var head = {}, tail = head;
channel.port1.onmessage = function () {
var next = head.next;
var task = next.task;
head = next;
task();
};
var nextTick = function (task) {
tail = tail.next = {task: task};
channel.port2.postMessage();
};

Thanks, interesting variants! Not rendering is ac...

2011-06-16T07:54:02.384-07:00

Thanks, interesting variants!

Not rendering is actually a nice property.

requestAnimationFrame should be used for that anyway.

This is slightly faster than window.postMessage an...

2011-06-16T07:09:29.744-07:00

This is slightly faster than window.postMessage and doesn't interfere with other onmessage listeners.

var mc = new MessageChannel;
function nextTick(callback){
mc.port1.onmessage = callback;
mc.port2.postMessage(0);
}

HOWEVER, some browsers (at least Opera) does not redraw after each postMessage async operation, so it can't be used for animation.

I think it's best to do what JSDeferred does.

function nextTick(callback){
var img = new Image;
img.onerror = callback;
img.src = 'data:image/png,' + Math.random();
}

(need special care for IE)

Update: So extending this a bit. SpiderMonkey code...

2011-06-12T06:46:15.274-07:00

Update: So extending this a bit.
SpiderMonkey code is at http://hg.mozilla.org/tracemonkey.
To understand the naming and some internals, i recommend reading Mapping the monkeysphere by cdleary.

For TraceMonkey (our tracing JIT) getting the cases we don't optimize is kinda easy. Please notice that code we don't trace is fed into our Jägermonkey (the whole method JIT), so it's most of the time equally and often even faster.

>grep LeaveTrace *
When we trace into some function, that can't be traced, we stop tracing.
>grep RETURN_STOP jstracer.cpp
General operations that can't be traced.

Jägermonkey accepts nearly everything, only a few things like |with| aren't compiled.
But you can get a list of stuff we can't "inline cache" (again read this article by cdleary, when you don't know what this is)
>grep disable methodjit/*

@Erik: Sorry, yeah. Typo corrected.

2011-06-12T06:21:41.435-07:00

@Erik: Sorry, yeah. Typo corrected.

It's Mr Aleph rather than Mr Raleph. See http...

2011-06-12T06:19:57.633-07:00

It's Mr Aleph rather than Mr Raleph. See http://en.wikipedia.org/wiki/Aleph I guess.

2011-06-12T06:02:10.467-07:00

This comment has been removed by the author.

There aren't eleven channels available
2011-05-20T09:11:34.817-07:00
There aren't eleven channels available .Channels overlap, and putting users on opposite channels will cause loss of throughput.

One trick I learned from the Xirrus reps is to use...

2011-05-19T14:20:15.045-07:00

One trick I learned from the Xirrus reps is to use the same SSID for both 5Ghz and 2.4Ghz, but turn 5Ghz up much louder. There's a lot more channel space in 5Ghz and much less interference from the preponderance of 2.4Ghz gear that always bleeds into the conference space on channel 3 and 8... Clients that run 5Ghz will select the stronger signal, and clients that don't wind up on a less-congested 2.4Ghz.

@Matt: For connectivity and AP hardware expect som...

2011-05-16T06:08:29.651-07:00

@Matt: For connectivity and AP hardware expect something in the order of $3000 to $10000 depending on what you need. We can't and we won't measure the time it took to build this because it includes two complex open source projects and we do it for the love of it.

@Jak: You look for a new venue and follow the instructions in this article.

If you are doing events and at the whim of an even...

2011-05-16T06:03:12.150-07:00

If you are doing events and at the whim of an event venue's A/V supplier, what can you do to ensure the best setup?

I do events of ~300 with 1.5 connections per person on average. Should I ask for:
- # of AP
- speed of AP
- placement of AP in rooms/hallways
?

How much would you say you paid in total to provid...

2011-05-16T05:38:28.314-07:00

How much would you say you paid in total to provide wifi to all of your conference users, including the time of your dedicated resource? What did this break down to as a cost per user? Finally, was that cost worth it?

Thanks! Great article!

There are 3 non-overlapping wifi channels, not 11....

2011-05-16T05:13:26.279-07:00

There are 3 non-overlapping wifi channels, not 11. That's important to know when you lay out the APs. Channel 4 and 5 are 85% overlapping.

I second the recommendation to avoid dlink/netgear/apple kind of stuff and avoid encryption wherever possible.

Another good idea is to set up the 5 GHz band as well. A portion of your users will use that band instead (10-20%?) which means less stress on your 2 GHz equipment.

Thanks for the article and congrats on your succes...

2011-05-16T04:48:58.849-07:00

Thanks for the article and congrats on your success.

A few observations though:

1.) Having personel supporting the network is a must, no matter the equipment used. Good point!

2). Have your specific requirements written down and presented to the organizer. Make sure that the organizer is responsible if the expectations are not met. Make it clear that this super important! (Apple does this for their events and training for example).
And have a plan B prepared!

3). RF planning is the most underrated in setting up the WiFi networks. Having to many AP can be as counterproductive as not having them enough. One has to understand that RF is a shared medium (collision domains). Lovering the AP Tx power is okay but you have to remember that signal at lover data rates travel far. A proper design incorporates that.

I think providing security for your attendees is very important so I would provide them with secure connection. While WPA2 is not crackable by it self it is not a secure solution because WPA2 PSK is given to all atendes and attacker can easily sniff the 4way handshake and than decrypt in real time. One can use 802.1X security but than you will need some extra equipment (AAA server) and very good step by step tutorial for your attendees. Third, the easiest, is using personal personal pre shared keys but this is proprietary and only used with Ruckus and Aerohive products.

Most controller based systems provide with load balancing and band steering functionalities. DOSing your clients is effective but very crude way of doing it.

4.) I do not understand what you mean by effective bandwidth per channel (per channel and not AP as some people understand). The throughput depends on the technology used. HR-DSSS (802.11b) has about 5 Mbps throughput, ERP-OFDM (802.11g) has about 20 Mbps and HT (802.11n) has about 70 Mbps (using 20 Mhz channel width and 2 spacial streams). One has to remember though that it takes two to tango. The lovest denominator will determine the maximum throughput per communication path.

Using airtime fairness is also very important in throughput. If a 802.11n AP supports b/g/n clients (they are active on the network) the speed will be reduced to 802.11b speeds. Airtime fairness corrects that.

There are only 3 non overlapping channels in the 2,4 band (1,6,11 or 1,7,14...). So you get the aggregate throughput of 3 channels not 11. In contrast all channels in 5 Ghz band are non overlapping. In some cases one can use 4 channels (1,5,10,14) but there is overlap between the channels and there will be collision. On highly used networks this setup is debatable. There is also an advantage of using 1,6,11 setup. This setup will support clients (stations) from all over the world. For example FCC (US) allows only channels 1-11. Channel above ch. 11 will not be recognized by an FCC approved device.

There are ways of designing the network so you can provide more bandwidth. Using sector antennas or sectorised array products (such as Xirrus) or smart antennas system like Ruckus wireless beam forming. But this can get pretty complicated and is a reason why a good WLAN engineer is payed good money.

There is always a problem with Apple devices so you should pretest your network as best as you can and optimize accordingly. 5 Ghz is a good way to speed up your network.

Also using as few SSIDs as possible will reduce overhead. If one needs segmentation, dynamic VLANs are preferable.

Just my 5 cents :).

Regards,

Gregor

I immediately send it to my system admin. The down...

2011-05-16T02:15:54.647-07:00

I immediately send it to my system admin. The down speed in the place I come from is a premium at 8 MBps and up speed would be 5 costing around $100 for a month or so with a cap of 50 GB. And if we have a tech conference with around 300 attendees with atleast 200 wifi devices lets say at the rate of 200 X 100 Kbps it comes to 20000 Kbps , 20 Mbps ... We will have to go for 4 connections.. Just calculating.. Thanks

Xirrus rocks we are using them on the Bon Jovi Tou...

2011-05-15T23:12:13.517-07:00

Xirrus rocks we are using them on the Bon Jovi Tour and for every Live event we do. 5 Arrays cover an arena with 18,000 attendees our Live-Fi platform solves every problem noted here. Try 88,000 unique devices at the US Open in 2010 or 25,000 over three day at ACL festival. We do big or small / focused events like Science On line... bring it on and get online with @SignalShare

On solving the bandwidth sharing issue: the monowa...

2011-05-15T16:54:58.098-07:00

On solving the bandwidth sharing issue: the monowall firewall distribution has a one-click "share bandwidth evenly" traffic shaper option that is really easy to use and powerful.

It also has a builtin captive portal and can integrate with radius.

I run them on yawarra.com.au devices ($300 per device but they can move around 70mbps easy)

This works for a tiny tech conference where someon...

2011-05-15T16:06:39.426-07:00

This works for a tiny tech conference where someone is dedicating themselves to managing the network full-time. What do you do at a 20,000-30,000 attendee convention?

there are only 3 non overlapping chanels for 802.1...

2011-05-15T15:54:30.145-07:00

there are only 3 non overlapping chanels for 802.11 b and g not 11!

You just need to hire some one who has done the cisco wireless CCNA

On Encryption: Most conferences will use a pre-sha...

2011-05-15T15:34:47.893-07:00

On Encryption: Most conferences will use a pre-shared key. What people don't realize is that given the PSK and observation of the handshake, an attacker can calculate the session key and decrypt all traffic between a user and the access point.

So turning off encryption is really not that bad when you consider that all it did was hog CPU and give people a false sense of security.

http://blog.jeffreymcmanus.com/157/learnings-is-a-...

2011-05-15T14:49:33.965-07:00

http://blog.jeffreymcmanus.com/157/learnings-is-a-stupid-stupid-word/

W/r/t the -B, -G, -N spot, my experience is that i...

2011-05-15T14:35:15.143-07:00

W/r/t the -B, -G, -N spot, my experience is that if you have N/B|G, clients often roam between them poorly and en-masse; By having multiple channels, people become your stochastic mechanism.

Still, very nice article!

Cheers

are we seriously talking about channel layouts in ...

2011-05-15T13:42:27.770-07:00

are we seriously talking about channel layouts in 2011? Controller based-architectures solve most of the problem (with appropriate policies) without thinking. Now focus on AP specs and density and conferences magically get much easier.

Xirrus can do it... They kept up at Interop this y...

2011-05-15T12:22:55.925-07:00

Xirrus can do it... They kept up at Interop this year nicely.

@John Adams: I was giving an upper bound for the b...

2011-05-15T12:16:08.560-07:00

@John Adams: I was giving an upper bound for the band width. In reality you are right, one can only do 4 channels. We are using that exact channel layout. The point about low power is in the article.

I personally think the redirect is a pragmatic solution. People who care about real security can use VPN.

NonBlocking.io - Malte Ubl's Asynchronous Identity Disorder

Here's the whole implementation of nextTick ba...

Thanks, interesting variants! Not rendering is ac...

This is slightly faster than window.postMessage an...

Update: So extending this a bit. SpiderMonkey code...

@Erik: Sorry, yeah. Typo corrected.

It's Mr Aleph rather than Mr Raleph. See http...

There aren't eleven channels available 2011-05-20T09:11:34.817-07:00 There aren't eleven channels available.Channels overlap, and putting users on opposite channels will cause loss of throughput.

One trick I learned from the Xirrus reps is to use...

@Matt: For connectivity and AP hardware expect som...

If you are doing events and at the whim of an even...

How much would you say you paid in total to provid...

There are 3 non-overlapping wifi channels, not 11....

Thanks for the article and congrats on your succes...

I immediately send it to my system admin. The down...

Xirrus rocks we are using them on the Bon Jovi Tou...

On solving the bandwidth sharing issue: the monowa...

This works for a tiny tech conference where someon...

there are only 3 non overlapping chanels for 802.1...

On Encryption: Most conferences will use a pre-sha...

http://blog.jeffreymcmanus.com/157/learnings-is-a-...

W/r/t the -B, -G, -N spot, my experience is that i...

are we seriously talking about channel layouts in ...

Xirrus can do it... They kept up at Interop this y...

@John Adams: I was giving an upper bound for the b...

There aren't eleven channels available
2011-05-20T09:11:34.817-07:00
There aren't eleven channels available .Channels overlap, and putting users on opposite channels will cause loss of throughput.