yeah sorry I've packed a hell of a lot into there now I look at it. One of the best analogies is speech.
If two people who are sober aged say 30 sit close in a small quiet room, then they can communicate quickly at a low speech level.
If they went to a large hall and sat at each end, then they have to speak louder and more slowly. This is because communication energy disspipates over distance, and audible/inaudible echo will also interfere.
If several more couples come into the hall, then the communication rate of all couples depends on distance between each couple and the "noise" level they each inadvertently produce on one another.
There are several ways around this, here are the 5 most widely used.
1-CSMA (Carrier Sense Multiple Access) - in this system, as soon as one couple communicates, the others wait for a pause, and when there is a pause, another couple grabs the time and the others wait until there is a pause, etc, etc. So the overall communcation rate goes down when more people are trying to talk in the same space. This is an Ethernet Bus system (Virgin Media Cable). WiFi also uses CSMA, but in a house with a few users you won't notice.
2-FDMA (Frequency Divison Multiple Access) - in this system, the couples would split to using narrower frequency bands per couple, and then they can all talk at once, but their rate would still be slower as the energy per word is less. The first generation mobile phones (AMPS/TACS) used FDMA and was too narrow for data transmissions.
3-TDMA (Time Division Multiple Access) - in this system , each couple takes it in turn to talk for a fixed period (say 10 seconds each for human speech). Thus their overall communication rate is still slow. 2G/GSM/GPRS uses this system.
4-CDMA (Code Division Multiple Access) - in this system, each couple uses a different language (German, French, etc, etc) and they all talk at once, and provided the distance between each couple is the same and their speech levels are the same, then this will work. However, if one couple talks louder, or if the distance between a couple is bigger then the others, well hard luck. 3G/UMTS/HSPA uses this system.
5-OFDM (Orthogonal Frequency Division Multiplexing) - this system is a bit like FDMA, but the frequencies used have to be very carefully arranged so that they do not cause interference to one another. In electronics reality, no filter has a sharp characteristic, each characteristic overlaps in space and time, but in OFDM the digital filters and frequencies are extremely precise to limit the overlap in space and time. The amount of OFDM adaptation (frequency choices and bits per hertz) is limited as distance increases, so comms rate will reduce with distance. There is no equivalent in human speech (birds, whales, elephants might be able to do this). DSL and 4G/LTE uses this system.
All of this is summarised in
the Shannon-Hartley Theorem from the 1920's. Noise is anything unwanted in the channel between two communication points on a link, this includes other talkers, echo, noise from other sources, etc, etc. Communication rate is affected by noise. And this also applies to writing, whereby writing style can inadvertently produce noise. If you don't understand any of this, a part of it may be down to my writing style. You can't please all of the people all of the time
So the screen shot by Father Ted (Marty) shows he has a very good CSMA WiFi link between laptop and router.
If you are using DSL from router to the outside workd over twisted copper pair. then the rate you get depends on how well the OFDM mush is banging around on those wires. This can also be affected by other users, if it's a lot better in the early hours of the monrning, that's why.
If you are using Cable from router to the outside workd over co-ax, your CSMA rate is affected by other users on the same cable, if it's a lot better in the early hours of the monrning, that's why.
If you are using 3G HSPA to the outside workd, your CDMA quality might depend on other users, if it's a lot better in the early hours of the monrning, that's why.
And finally, if your internet access is shit whatever time of day, if it's 3G you don't have HSPA. if it's DSL or Cable, either the twisted-pair/co-ax is shit, or their modem/multiplexer at the far end is shit.