Why Latency is so Important
Tuesday, 16 March 2010
Technical people always say bandwidth isn't everything as latency can kill even the biggest link. But why is that?
Consider a 3 lane highway (3 lanes each way). Now imagen everyone driving their own car to work everyday. One person per car. If everyone observes the speed limit and keeps a safe distance, there's only so many cars that will fit on the highway and drive at 100kph. Once the limit is reached, the only way to fit more cars, is to shorten the distance between cars, and lower the speed otherwise it wouldn't be safe anymore.
Even then, there's a saturation point. When cars are bumper to bumper, movement slows to a crawl. At that point, the maximum capacity of the highway has been reached. Networks work pretty much in a similar fashion. And similar to a highway, one way to solve that issue is to compress traffic.
Rather than everyone travelling in their own car, we put people in buses. One bus holds 40 people, and takes the space of 3 cars at 100kph. That's pretty good!
However, at some point, even those buses will slow down as they start to congest the highway. Distance between buses has to be greater because of their increased mass, so traffic will slow down quicker.
The solution here is to use an auto pilot of sorts that connects the buses together and effectively allows them to travel at 100kph with one meter distance. Because it's all computer controlled, there's no sudden braking causing collisions.
Again, the same works on data networks. A network optimizer will ensure maximum bandwidth is used.
Unfortunately, one aspect in network optimization that can't be used in the above example is caching, where data is cached at either end, and instead of re-sending data that has already been transported across, it's simply pulled from a cache. In the highway example that could work, if you made every person that works in the city sleep there as well. Effectively putting a bed next to his/her desk...
There goes your traffic congestion problem.
Network Latency
Friday, 23 January 2009
Especially on remote networks, latency can be a real problem. Unfortunately, until space folding becomes mainstream, we'll have to learn to live with latency and develop our applications accordingly.
Calculating the minimum latency you can expect between two points isn't hard if you know what to consider. The fastest you could go (well, at least for now anyway) is at the speed of light, which is about 300.000km/s. Except that speed can only be reached in a vacuum, and that's pretty hard to come by down on planet Earth. We're stuck with fibre and light in fibre goes at around 200.000km/s, still pretty good, but certainly slower.
200.000km/s equals to 200km/ms (remember, 1s equals 1000ms). The distance between Australia and Europe or USA (sorry, to me Australia is the centre of the world...) is about 15.000km (exact numbers don't really matter too much).
So, the time it takes for a signal to travel 15.000km on earth in fibre, is 75ms (15.000/200=75ms). You just can't go any faster than that. Unfortunately, I haven't seen lengths of 15.000km fibre cables yet. The switching/routing equipment that is involved at various junctions, introduces another bit of latency, which is harder to calculate, but a safe bet is to double the number we found in our previous calculation.
Which comes to 150ms. So that's the absolute minimum delay we can expect. Additional delays can occur due to slower links, extra junctions, traffic not routed the physically shortest path, too many people using a link, etc.
Pretty much it comes down to per 1000km, add 15ms delay to calculate the minimum delay you'll experience.
Running Windows Vista
Thursday, 3 April 2008
So I tried Vista, configure it and see how it went. Not on my machine though. But the laptop that came with it (an Asus F5RL) just had too many problems running Windows XP (hibernation and standby just wouldn't go, and when the USB ports weren't doing as one would expect, I gave up and chucked the Vista Restore CD in).
My first hurdle was the disk. It came with a 160GB disk that was divided in two (equal partitions of around 80GB) and that just wasn't suitable. The second partition (I always have two partitions on any machine, a boot and apps partition and a data partition) would be used for video editing so it needed to be as big as possible. Vista has a handy feature where you can shrink volumes (partitions) on the fly and I thought I'd give it a go. Yeah right. Going with the recommended shrink value didn't work (shrink from 80G to 50G something), as it didn't enough free space. Crap, as there was only 15G of data installed. And I had thought to go to 20G or something.
Googling told me why. Often, the MFT sector gets in the way. I mean, why place that at the beginning of the harddisk when it fits near the end too? That way, it also defeats shrinking. Nobody does that anyway, right? You also want to disable as many systems files as you can (turn off paging and hibernation). I still don't know how to turn of hibernation.
Anyway, cost me a lot of hours but I got the boot disk down to 27G. Then try installing Firefox or Thunderbird. Hehe, nononono. Microsoft doesn't like that. More googling reveals UAC gets in the way here. Even more googling also shows how to disable UAC. After that I also end up disabling the Security Center (service) and set it to not alert and whinge and not display the icon. Ah the peace and quiet of not having popups asking for permissions or alerting that UAC ain't running....
After that, Vista turns out to be fairly usuable. Haven't seen any further issues. UAC and SC, that's the secret...
Opening an Asus M5N Lappie
Wednesday, 9 January 2008
So you wanna open up your Asus Lappie do you? Just remember, I only provide the knowhow, I don't take any responsebility for using this information. It's completely your decision to use this. And also remember, if you still have warranty on your machine, say goodbye to it, I doubt Asus will still service it when you've taken it completely apart. My machine was well out of warranty, so I didn't really care. And since Asus was reluctant to provide me with this info, I decided to make a small howto out of it.
OK, here goes. Refer to the photo's whenever something is not clear, I've tried to make some nice ones which should clarify enough. Oh, before I forget, make sure you have thermal paste handy, you'll need it.
First of all, turn on the lappie and press on the CD eject button. When the CD drive is open, turn off the lappie and unplug any power and remove the battery. Now turn over the lappie and look at the bunch of screws. Some you may already have touched. There are 2 screws to release the CD drive (having the darn thing open makes it heaps easier to pull it out), just unscrew them and carefully pull out the drive.
Next open the HD lid (2 screws) and disconnect the harddrive. Now open the CPU/Memory lid (1 screw). Fantastic! You're almost there!
Now turn the lappie back to normal again and open the screen. There are 3 little locks at the top of the keyboard that hold it in place. Yes, the keyboard needs to come out. With a small flat screwdriver, carefully push the locks (or whatever you feel like caling it) and carefully lift the keyboard with your nail (hooking behind a key). Once all 3 are free the keyboard should come out easily. Disconnect the keyboard from the mobo (that's a motherboard if you didn't grasp that) by carefully pushing the lighter coloured edge away from the connector (only a few mm). This releases the cable. There are a few other similar but smaller connectors that also need to be disconnected.
Right in the middle of where the keyboard lives there's a screw that needs removing, and to the left, over the CD bay, there are an additional 3 screws.
Good good, we're getting somewhere now. Close the screen again, turn the lappie upside down again. First remove the 4 screws around the CPU. One will be covered by a label, this tells Asus that you've been a bad boy (or girl) if you decide to bring it to them afterwards. We're gonna break that label and get that screw under it out of the way. You'll also have to disconnect the fan cable when the fan and cooler comes off. Now remove all the screws that are marked with "Case". Lastly, disconnect the wifi connectors (black and white cables), carefully pry them upwards with a flatscrewdriver.
Turn the lappie back over again, and open the screen. Looking at the front of the lappie there are points where the case locks into the bottom part, with a screwdriver or something similar, carefully pry these points loose. There's another one on the right side. Now the top part of the case should come off, pulling the front open first. The screen stays on the top part (which is why all the connectors had to be disconnected).
The mobo itself is screwed onto the bottom case with a few screws, you'll find those easily. Make sure you disconnect the speakers first (black rectangular thingies left and right of the harddisk bay), then carefully pull the mobo out.
And that's it! You've done it! That is, if you actually followed my lead and actually took yours apart.
When putting it back together you can basically follow the steps in reverse order. When you get to replacing the cooler, I had no issues with the original thermal paste. Although I did replace it after a couple of days just to make sure. It is better to replace the paste completely.