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


Teaching Note:


Sample Question:


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Images needed!

Why does transmission speed vary?

General Point: Networks are Complex

Why does the speed of data transmission across a network vary? It seems like a simple enough question, but there are a myriad of reasons why this is so. So first of all, 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.

So 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:

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


Non-changing Factors for Network Speed

Hardware: (just think of everything mentioned in the scenario above)

- The transmitting hardware:

- The receiving hardware:

- The transmission media on your network

By this 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.


- If the data being sent is allowed to be, or has to be, compressed (in spite of the up-front cost in terms of processing, compressed files will speed up the network since they are smaller)

- The speed of transfer allowed by the protocol, and if it allows for different speeds

- How the protocol manages and prevents congestion

- If the protocol being used sacrifices speed for security, or vice versa

- If the protocol allows the use of IPv6. This can speed up overall network activity, because more devices can have dedicated IP addresses. (The limit for IPv4 is 4 billion addresses, and an almost infinite number with IPv6.)

ISP Considerations

- Distance from the ISP (Internet Service Provider).

- Kind of transmission service - fiber op, cable, microwave etc.

- Your ISP's maximum Internet connection speed, measured in Mbps (Mega Bits per Second).

- With certain ISPs, the more requests a computer requires from a network, the more priority it gets from the network. So if one computer is hogging the network that can slow down others' access speed. "Net neutrality" issues come into play here, where ISPs can slow down certain activities on the Internet at their discretion. Most believe this is wrong.

An example a violaion of net neutrality with some throttling of of internet speed by Verizon. Hulu is often throttled as well, aparently. Though with such issues, there is a solution: the use of a VPN!


Constantly Changing Factors for Network Speed

- The number of people using the network at any given moment.

- 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.

- 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.

- 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.











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: