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Explain why the speed of data transmission across a network can vary.


Teaching Note:


Sample Question:


JSR Notes:

JSR point: network pictures or videos reminder.

Images needed!

Why does transmission speed vary?

There are actually a couple of ways to look at this. We could only look at things that change speed of network access in a continual way - the "Constantly Changing Factors". But we could also consider all the other myriad hardware/software/protocol things that speed up and slow down networks more generally.

This assessment statement is more likely focused on the constantly changing factors. But we'll look all the other more static effects, too, if only because it will consolidate, and string together a lot of the knowledge we have gained so far about networks. But for starters:

I. Constantly Changing Factors for Network Speed

1. The number of people using the network at any given moment. ("....how many people are now...?")

2. The geographic distribution of the current connections. They may happen to be concentrated from the area where you are connecting from. So it's not just the number of people using the overall network you are part of, but the network activity of the people closest to you, at any given time. ("...where?...")

3. The particular kind of activity by people on the network at any given time. For example, is it a time of the day where many are downloading big files or watching videos at the same time. i.e. Netflix!! Other bandwidth hogs which slow down everyone's Internet speed must necessarily include networked games such as Battlefiled, and Steam games. ("... doing what?...")

4. Interference/noise on the connection medium (which can happen with any of: Twisted pair, Ethernet, or Coaxial cables, as well as WiFi) - resulting in packets getting lost and needing to be resent. ("...with or without noise?...")


So in summary, in terms of constantly changing factors affecting network speed:

"How many people, where, doing what, with or without noise, all continually changes and affects network speed."
(In fact, you can think: "who, what, when, where, why?")


II. Non-changing Factors for Network Speed

General Point: Networks are Complex

So not only are there the above continually saning factors affecting network speed. Consider just how complex sending a file across a the Internet is. And the point is that any one of the stages can cause delay. For fast, consistent data transfer, ALL of the parts of the system must be capable of high speed, error free transmission. All Hardware, Software, Protocols, and the ISP (Internet Service Provider), all can help speed up, or just as likely slow down network activity.

As an example, imagine a laptop computer within a wireless LAN downloading a file from a website somewhere on the other side of the world. Here are the steps (and these, only after the request for that file has been sent, received and processed):

Again, if ANY ONE of the stages is slow then it will have an impact on the speed that the file is downloaded.


1. (Non-changing) Hardware: (just think of everything mentioned in the scenario above)

- The transmitting hardware: the server you are connected to, including

- The receiving hardware: the receiving computer or laptop, including

- The transmission media on your network
By transmission media, we mean, if wired, the kind of material the wires are made of, or if it's wireless transmission the kind, i.e. Ethernet cable, fiber optic cable, ISDN/cable, microwaves etc.

2. (Non-changing) Protocols:

- How the protocol manages:

3. (Non-changing) ISP (Internet Service Provider) Considerations










And getting specific, as the St. Julian's site does, this is directly from Wikipedia, and an article called Packet Transfer Delay

There are four sources of packet transfer delay: