There are many ways in which to connect up networks.
A network is simply one or more computer users who are in touch with one another, using any applications they prefer (chat, mail, file transfer, web pages, remote execution, and so on)
To assist matters of networking there are a number of different protocols. There is a useful heirarchical model for these, known as the ISO 7-layer model.
At the low levels (below about level 3) we deal with hardware. Above it, we are in the realm of software.
The layer of interest firstly are levels 1 and 2. (the physical layer and the Data link layers)
These often relate to the electrical properties of the link and to the abilities of the circuitry to present useful frameworks for the layers above to deal with.
DSL, Satellite etc are examples of non-broadcast level-1 and they are all interchangeable. There are quite a number of protocols used to impose a line discipline on one of these links. They may be based on broadcasting principles: 802.2 Ethernet 802.11 Wireless lan Or they may verge to narrowcasting: 802.5 Token ring
At least 802.2 and 802.5 are able to be run down UTP cables at speeds up to 132Mbits/s (802.5) and 100Mbits/s (802.2). 802.11 is true broadcast at level 1, for it uses radio signals, but at layer 2 it looks rather less so.
These are useful technologies to implement LANs (Local Area Networks). But to interconnect the LANs to make Wide Area Networks (WANs) like the Internet, we need also to establish point-to-point links between geographically-remote sites, and we need to sensibly be able to route traffic between them.
Technologies like DSL give us faster point-to-point links than moems could.
The general topology is:
PC ---v PC -> hub ---> router --> Internet PC ---^
(plus the reverse :-))
Where it says 'router', you can have a cable modem router, a DSL router, a satellite on, or whatever.
The key is the speed between *your* router, and the router of your ISP, and the speed of any other routers to get to the destination (there can be up to 30 or 40)
Of the different linds of links:
DSL = Digital Subscriber Line.
These "borrow" the unused bandwidth available on many phone lines. An average voice connection uses about 3.5KHz of the phone line's available capacity. Based on this, in the 60s/70s, the theoretical bandwidth over the same wiring was up to ~3000 / 10 = 300 bps for an asynchronous link. Then, using Quadrature Amplitude Encoding (Trellis Encoding) instead of the old-style FSK (Frequency Shift Key) this was raised in the early 1990s up to 9600bps. And then the theoretical max was boosted again by adding dynamic compression/decompression to the data stream, bringing us up to 14400kbits/s
The next move was the realisation that nearly all phone lines had pretty good cabling. There was actually *way* more bandwidth there than the 3.5kHz needed for an old bakelite phone graphite voice coil handset. So let's use it!!
After 28.8 and 33.6 and then 56k modems, it all seemed silly. Economies of scale kicked in.
They started to treat the lines as digital lines, and at the subscriber put in line filters to catch the odd phone call, and relegate those via fairly crude hardware compansion to the low frequencies, so hence we now have our delightful high-speed DSL network. Here in Belgium it normally goes at 3Mbps download. You can pay them more to have up to about 5. As a guideline, simple Ethernet (802.2) is 10Mbps and a simple Token Ring goes at 16.
To really boost throughput, ADSL pairs both Tx and Rx lines to shunt through twice as much info at a time in one direction only (half-duplex mode) and the ratio of the Tx->Rx may typically be 3.0Mbps Rx (download) vs 768kbps (upload)
These have routers at the end of each street, running coax. cable into each home. and they can be treated just like old-style Ethernet.
The real problem with this set-up is that traffic is often not routed. So, at peak times, even though you theoretically have 10Mbps bandwidth, once all your neighbours have had their bits, the connection speed may be low.
The cheap way to do this is with a modem uplink and a satellite downlink, or so I am told, but I am still awaiting more details...
Re: looking for info#131972 12/08/0407:37 PM12/08/0407:37 PM
When you get a download goin of a large file, you see speeds such as 20 or even 30 instead of ones of 2 to 5, as per modem, with typical ADSL speeds. It's a *lot* faster.
My pal up in Mechelen, and others I know in Antwerp, who use cable modem, they say thir *peak* speeds are OK, in relation to the above. But we've worked out using BJ's line, up in Mechelen (which is more or less central Belgium) that it is a bad throughput compared to ADSL.
The main difference is in their sharing the bus far sooner, I think.
Are you worried about a 3mbps throughput? I think you should not be. Try to enjoy also the lovely http://www.bbc.co.uk/bbc7 and on the page 'listen again' there are all old books like Cold Comfort Farm. With a 3mbps throughput, you can enjoy it :-)
Re: looking for info#131974 01/14/0508:48 PM01/14/0508:48 PM