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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):

• At the remote destination, the data you have requested is taken out of the web server's hard drive (so the server must have a fast CPU and internal bus system to get the data out)
• The server must have software that operates effectively to chop the file up and prepare the packets to be sent through the network
• The server puts the packets onto the Internet through some sort of Network Access Server
• The packets travel through various communications medium all around the world, with potentially many hops through a variety of routers along with various transmission media including:
  • Fiber optic Cable
  • Coaxial Cable
  • Satellite Signals
  • Twisted Pair metal wires
• The packets reach your LAN through the LAN's gateway/firewall computer  
• A MODEM converts the signal from analogue back to digital
• The data goes into a wireless router and is translated into modulated radio frequency which fills the air all around the router
• The laptop picks up this signal and translates it back into a digital signal
• The packets are then re-assembled into the file, which you are downloading, and this process involves software, CPU power and Memory of your laptop

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 CPU specifications
• amount of RAM/cache
• The speed of the Routers and or Switches involved in switching packets across the network

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

• The CPU specifications
• amount of RAM/cache
• network card specifications
• The speed of your modem

- 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:

• compression: compression can both slow down and speed up network activity...
  • There is an up-front cost of processing the compression, but compressed files will speed up the network since they are smaller.
• speed: of transfer allowed by the protocol, and if it allows for different speeds
• congestion: how it manages and prevents congestion
• security: increased security usually results in decreased speed
  • For example the UDP protocol is used by gamers because even though it's not too secure, it is fast.
  • Whereas TCP/IP is used by most people on the Internet and is much more secure, and has good error checking, but it is therefore slow. The good analogy is having a package delivered in a big congested city by one of those "Messenger" guys on a motor bike, versus the local postal service - the postal service is more reliable, but not as fast.

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

• Distance from the ISP
• Kind of transmission service - fiber op, cable, microwave etc.
• Maximum speed provided by the ISP, measured in Mbps (Mega Bits per Second).
  
  • There have been many examples recently of ISPs, at their own discresion, deciding which websites get the most bandwidth; usually these would be their most important customers. And if one set of servers is hogging the network in this way, that can obviously slow down others' access speed. Meantime, the ISPs can limit the access of other servers by "throttling" them. As a result of this, "net neutrality" principles have been developed, which state that everyone should be treated the same.
  • An example violation of net neutrality was some targeted throttling of internet speeds recently by Verizon. Hulu is often throttled as well, apparently. Though with such issues, there is a solution: the use of a VPN!

 

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ADDITIONAL INFORMATION ONLY

 

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:

• Nodal processing:
  By this we mean everything which has to be done at each node along the network. A good analogy is the processing time it takes a person going through various airports on their journey; their "nodal processing" is going through security and passport control etc. For packets on their journey, that which holds them up at each network node (i.e. router or repeater) includes security and error checking as stipulated by the network protocol it is following.)
  • Check bit errors
  • Determine output link
• Queuing:
  • Time waiting at output link for transmission
  • Depends on congestion level of router
• Transmission delay:
  • R=Link bandwidth (bit/s)
  • L=Packet length (bits)
  • Time to send bits into link = L/R
• Propagation delay:
  • d = Length of physical link
  • s = Propagation speed in medium
  • Propagation delay = d/s