Understanding Bandwidth

Hello again everybody!

I felt it was about time to dust off the blog and give it a go. I think I should start a series on the essentials of networking and what you should know about it, to make an informed decision about what to buy, etc.

This could get very technical, so try to follow along as I take you through all this.

How do I know this: Years in college and hands-on experience working I.T. in my local area. I've seen the effects of everything I'll be discussing.

When deciding on a network type, you really have to start with, what will I be doing with the network. For many, the answer is easy, I want to get on the internet; for others, the answer is a bit more complicated.

When talking about speed, it's important to note that there are two major measurements of indicating speed, they're closely related but give very different numbers. Think about it like temperature, Celsius and Fahrenheit, if the temperature goes up, both will rise, if it goes down, they both will fall, but not necessarily at the same speed, or to the same numbers, or by the same amounts.
These two are in bits per second (bps) and Bytes per second (Bps)

Confused yet? you should be.
The way this works is that a bit is a single 1 or 0 in a computer system; a byte is a set of 8 bits that contains information, one value of a possible 255. Why the strange numbers? because a bit has two options, either be a 1, or a 0. which means that if you want 3 options, you need to use two bits, but two bits gives you 4 options, one of which is simply invalid. but what if you want 5 options? you need 3 bits, but three bits means you have 8 options (000, 001, 010, 011, 100, 101, 110, 111), 3 of which will simply be invalid. It's because of this (factoring by 2), which is why we see the same numbers cropping up with computers a lot.

2, 4, 8, 16, 32, 64, 128...

so what happens when bps meets Bps?

well, the speed in bps, is much higher in number than the speed in Bps.

For simplicity, lets use a value very close to the national average, that divides nicely, so it's easy to follow: 16. a majority of internet connections in north america are running at aproximately 16 megabits per second. that means, at any given second, 16,000,000 bits can travel across your internet link. sound like a lot? it used to be.
Truth is, 16,000,000 bits is only 2MB (megabytes in this case)

I want to point something out before moving further. the difference between bits and bytes is supposed to be indicated by the use of capital or lower case lettering. eg. 16 megabits per second is supposed to be indicated with 16 mbps (with a capital on the M being optional), and 16 megabytes per second is supposed to be indicated with 16 mBps (again, capital on the M is optional). the capital "B" indicates bytes, where the lower-case "b" indicates bits. Unfortunately, not everyone (especially marketing departments) understand this; so we get ISPs selling 16MBPS speeds, which is actually in bits.

so, with an average connection speed of 16mbps, that means we get 2MBps (16/8, because there's 8 bits per byte)

This trend of using bits per second, penetrates the telecom world. whenever dealing with communication speeds between two points, whether they are connected by ethernet, wireless, fiber optics, or a string with two cans, generally, we use bits per second. The problem with this, of course, is that everyone else uses bytes per second.

Example: in windows, all file transfer dialogs are in bytes per second, not bits. This means if you have a 16mbps line to the internet and download something, windows will show your speed (given that you're using the entire thing for just this download) as 2MBps. This has caused (in the past) a lot of confusion about what actual speed consumers are getting and what they should expect to get.
one of the most common misconceptions I've seen with internet is "I pay for 10mb service, but I can only download at 1.2mbps" - that's about what you should expect from 10mb service...

Bandwidth is a crazy thing too, since we have USB 2.0 which, in theory, runs at 480mbps, and the fastest I've seen it transfer has been about 200mbps (aproximately 25MBps) - what they don't tell you is that some of these connection types require overhead, USB more than most. Ethernet is actually rather slim on it's overhead, running about 40 bytes of overhead per packet (1500bytes or so): about 2.5% overhead. obviously it's much higher with USB.

So how much bandwidth do you need? depends on what you're doing. For an example, let's talk about HD video. If, by chance, you wanted to stream full-frame HD video from a blu-ray disk to a computer across a network, you would need to be able to sustain a minimum transfer speed, which is the same or greater than the amount of data per second in the blu-ray video files. Luckily, the specifications for these formats are published: first some facts from the specs.

BluRay disks when playing video, have a defined maximum bitrate of 54mbit/s - so, for example, if you wanted to send the bluray to a media player on wireless, you're going to have a bad time, depending on the wifi.

I say that because of duplexing. Full-Duplex is when you have a dedicated line of communication to/from a source, Half-Duplex is when you have to share a send/receive channel. Think of this like trying to shout over someone: nobody can understand either of you, so one person can talk at a time - this is half-duplex. If you have a direct line to someone's ear, and they have a direct line to yours, you and they can both talk, hearing only the other's voice, which makes more sense.

okay, so the example broke down at the end, give me a break. :)

so wireless, by nature (since you're only using one channel) is half-duplex, meaning the theoretical 54mbps on Wireless G (802.11g) is shared amongst send and receive, which would be fine, if you didn't have to send confirmations that you received information, and requests for more. This means your real-bandwidth on wireless will be significantly less than the 54mbps as advertised. This is the reason behind Wireless N being recommended for 'streaming' media.

wired networking could definitely handle it, transferring, on average, 100mbps in full-duplex mode. This far out performs the 54mbps coming off the blu-ray, and stutter-free playback should be possible... provided the rest of the network is fairly quiet.


Bandwidth is a topic that seems to confuse many people, here I'm talking about bandwidth in your house, and I hope that clears things up for you and yours. Soon I'll have discussions more in-depth about why wireless bandwidth isn't nearly what it should be, moreso than just being half-duplex. why we don't have full-duplex wireless, as well as internet bandwidth (why so slow). All this among many other topics to help clarify your digital life.

Be safe, enjoy.

Network Speeds - GBe, Wireless N and how they affect you.

A very significant debate in my mind, between different wireless (and wired) network technologies has been relating to effective speed.

What I mean by effective speed is two things; first, the speed you can literally get from the network (after overhead, crosstalk, and other factors). Second, the speed that's useful to the end-user.

Because of this, I end up in quite a conundrum... with server and back-end topologies and technologies, you generally know what kind of speed you'll need and what you can use. When connecting servers together, whether from scratch or to an existing network, you can surmise whether you'll need GBe, 802.2ad linked GBe, or a multi-GB connection (or even a 100MBit connection) for your server, depending on application. For example, a high-performance file server or database, you may want to put some of the more expensive connections onto, especially if the system will be used concurrently by many users, and the drive array can handle multiple gigabits of sustained simultaneous output to multiple destinations...

For servers, the job is pretty easy to deduce what you need, the hard part is not only finding the hardware you need (since 90% of computer shops carry consumer oriented products only), but getting management to sign-off on the purchase...

For client access roles and points, you really have to start debating, is one technology really better than another? let's review.

Almost all network access by end users (or consumers) is internet bound. not many people exist in a world where an intranet even exists, nevermind having servers setup on it, or accessing any "local" resources. With this in mind, I quickly begin to consider two things, first, how many people will be using the service, and what is the WAN speed?

WAN speed: most consumer based systems are using consumer based internet lines, which are generally not terribly fast. In North America, most consumer based broadband lines are between 3Mbit and 15Mbit. There are some exceptions to this, in cases of extremely fast or extremely slow internet lines, but for the most part, they fit into this model. In these cases I have to debate on the validity of buying the latest GBe router or switch, or the newest fanciest dual-band Wireless N router or AP. Since 90% of traffic is going to be internet bound, the fastest any one users connection will go, is 3-15Mbit. Current standards for wired internet technology is 100Mbit full duplex (or 100BaseTX), and currently the standard for wireless is 802.11g (or Wireless G) which runs at 54Mbit. Both of these show standard connection speeds that are 3-8 times FASTER than current internet speeds.

Factor all that into the fact that consumer based internet lines don't really seem to be getting any significant bump in speed, neither now, or in the near future, and you've found yourself in my debate.

If you're not using any resources on your local network, why do you need anything more than a 100BaseTX or 802.11g network? ... to be fair, wireless technologies will never run as fast as advertised, due to the fact that the send and receive happens on the same frequency, making the system half-duplex by nature (meaning you can only send OR receive, not both) but still, a half duplex connection can still sustain, even in high-traffic situations, something near 30-40% of it's maximum bandwidth (except in extreme scenarios).

Additionally, a lot of the technology that is touted as "Wireless N" is really just a beefed up Wireless G, that's been given similar encoding technology to Wireless N (making it possible to encode more data per wavelength of transmission, and therefore increasing throughput)... What I mean is that: 802.11n is designed to run on (or was originally designed to run on) higher frequencies, with shorter wavelengths (eventually, they settled on 5.8Ghz). With shorter wavelengths, and better encoding, it became possible to encode a significant amount of extra data into the stream than wave previously possible.

Allowing Wireless N on the same frequency as Wireless G, causes additional interference, since wireless G would take more time to transmit, and create more noise on the channels that Wireless N would be trying to use, and at the same time, Wireless N would be unintelligible noise to any Wireless G implementations nearby. The real conundrum is that to use Wireless N on 2.4Ghz effectively, you have to bump the channel width from 20Mhz, to 40Mhz. While using 'Channel 6' (the midpoint in N.America for wireless), with a "fat channel" (40Mhz), the radio then crosses over into almost every other wireless frequency, causing interference on every wireless "channel".

The bottom line with 2.4Ghz Wireless N, is that it would only really work in a controlled environment, where there is nearly no other 2.4Ghz networks or devices (this includes cordless phones).

Add that to the fact that the extra speed isn't making anything go faster, because you're using the 150-300Mbit 2.4Ghz Wireless N to access the internet, and you end up with this mis-mash of different, competing technologies, that completely ruin the experience for everyone (since they cause so much interference).

The only true benefit you could ever obtain from Wireless N, is in it's intended implimentation at 5.8Ghz (where there's very little demand, aka interference currently), while using dedicated 5.8Ghz ONLY devices and nodes. Additionally, you would have to use that wireless for accessing local resources; not just that, but you would have to make sure that your AP, and every link between you and the system you're talking to, is GBe, since Wireless N can fully saturate 100Mbit Ethernet... Then, on top of that, you almost have to be accessing an array of drives to really take full advantage of the throughput, since, even good conventional drives max out around 400ish MBit... That's not even touching how useless GBe would be to most users...

Yeah, I understand that, despite the bandwidth being not really necessary, GBe can reduce ping times because the speed of the transaction to transmit each packet is so short, however, the difference in real-world scenarios is negligible at best.

The real baffling thing, for me, is when there's respectable companies, that actually have intranets, with dozens of client systems, roaming profiles, network shares, VoIP, Internet, etc, all connected to the same network fiber, and they're still running on MB Ethernet. Thats. Just. Amazing. Upgrading to GBe in those scenarios would have massive impact, and the upgrade costs would be minimal at best. Since a lot of unmanaged switches are rather cheap, even with massive numbers of ports... Managed switches aren't too far behind in cost.

And really, in those scenarios, isn't the cost of the switch far outweighed by the increase in productivity of the workers? since now they don't have to wait forever for a roaming profile to load before they can actually do some work?

Food for thought.