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Learn How and Why
How Downloads Work
This is a brief (layman's) explanation of how Internet access works.
Data is sent along a phone line from the ISP's modem to your modem, and it is then passed to your computer. The speed of transfer depends on the connection hardware-rating of your modem (e.g. a 56K modem), on the capacity of the phone line, and on the ISP's own capabilities.
While phone lines use a modulated analogue wave form, PCs use digital data. However modems convert digital data to a modulated analogue wave form and visaversa. This allows two digital computers to 'talk' to each other over an analogue phone line. Modem is an acronym for Modulator-Demodulator.
The following diagram and explanation show how a download works when Hardware Compression is used :
Following the route
Target Site < = = Routers = = > ISP modem
When you send a request for data (a file to download, get an email, view a page), many snippets of information are included with your request. These include such routine items as the file name, your address, your ISP's address, and so on.
When the Internet is overcrowded then the overstretched network routers start dropping (discarding) data Packets, or route them onto slower, more congested links. It now takes time for the target to notice that the requester hasn't ACKnowledged Packets that had been sent - the target has to resend those Packets (which may also get dropped). The result is a general slowdown in apparent transmission speed, often with long gaps or pauses.
Your ISP modem
The ISP will receive the data Packets and relay them to you in the agreed Protocol manner - provided there is agreement. It can be worthwhile checking with your ISP as to the Protocols he requires, just in case he does not adhere to the international standards.
ISP modem < = = = > your modem
This is your 'line connection' to the ISP and is referred to as the DCE speed. Its greatest speed is totally controlled by the hardware specifications of your modem e.g. a 28.8K, 33.6K or 56K modem (provided the ISP can, and does, service that speed).
There is little else you can do here, EXCEPT ensuring you have the correct modem selection made when setting up your modem - do not select 28,800 if you have a 33,600!, and do not use 'generic' when you can nominate the correct modem!
The basic function of the modem is to send data (a) to another modem and (b) in the opposite direction to the computer. To achieve either of these it must first alter the nature of the signal - change it to analogue ue for transmission along the phone line, and change it to digital when sending to the computer - computers are digital in nature, and this is how they 'talk' to each other over an analogue ue phone line.
Modem < = = = > Port
What arrives at your modem is likely to be mostly compressed data. It is de-compressed by the modem (it is expanded to its natural size) and then sent along the serial cable to the Serial Com Port.
It makes sense that this speed should be close to, but not be greater than, the Port speed.
Serial Com Port
Think of the Port as a nautical port receiving a constant stream of cargo (requested packets of data), and the CPU as the stevedore who brings each cargo item (data) to, or from, its final destination (memory) - all very very rapidly.
The newly arrived data is available to your Application software (browser, email, etc) after its arrival in memory. Winsock is a .DLL (Dynamic Link Library) and is the interface to TCP/IP and, from there, on out to the Internet.
Winsock.dll acts as a "layer" between your WinSock applications and your TCP/IP stack. Your Application tells Winsock.dll what to do; Winsock translates these commands to your TCP/IP stack, and your TCP/IP stack passes them on to the Internet.
As the TCP/IP Protocols work hand-in-hand with the Winsock software, it is likely a TCI/IP upgrade will also require a Winsock upgrade - they are a matching pair. If you have multiple versions of Winsock.dll floating on your hard disk, you may have problems. The Winsock.dll you're using must match the version of TCP/IP that you're running. Don't assume that because all Winsocks are called Winsock.dll that they're all the same--they're not - if you are using Microsoft's TCP/IP, you can't use Trumpet Winsock.
If Software Compression have been implemented, then decompression occurs in memory - Hardware Compression occurs at the modems.
Up to How It Works
This section provides simple
explanations of some
[ listed in order of association, rather than alphabetically ]
Packets or Frames:
Bits & Bytes:
Serial COM(munication) Port. This is the point of connection between the modem and the computer (even with internal modems). A Serial Port is a male-pin adapter. The serial is MALE, the parallel is FEMALE
For downloads, when data flows from the modem it passes through the port on its way to the computer, and visa versa for uploads. Therefore is it important to use the correct setting, and this needs to be substantially higher than the speed of your modem e.g. a 33.6K modem. However setting the port speed excessively high will give no noticeable gain, and may actually cause problems (more on this elsewhere).
- - < = = = > PORT UART [ <= FIFO => ] < = = = > CPU < = = = > Memory
UART (& FIFO):
FIFO and Overruns:
Higher Port Speed
Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.
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