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Why...

michaelscott
Grafter
Posts: 594
Registered: 09-08-2007

Why...

do I connect to +net at 576kbps rather than 512k? Just wondering...


Mike
7 REPLIES
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Why...

I think the difference is the protocol overhead in reciving the data which is transfered in packets. Your upstream speed will be 288Kbits/s for an effective transfer speed of 256Kbits.

The actual transfer speed (the speed you can get data to/from your PC) is ultimately governed by network contention (the 50:1 or 20:1 ratio quoted in various places), exchange and line conditions.
N/A

Why...

The true speed of data transfer will be in kiloBYTES.
1 kilobyte = 8 kilobits, so with a 512Kilobit (kbps)connection (excluding transfer overhead as already mentioned) the maximum data speed you will get is 512/8 = 64kilobytes per second (64KB/s)

Confusing, isn't it........
michaelscott
Grafter
Posts: 594
Registered: 09-08-2007

Why...

i know that i'll get a max of 64KBps. i just wondered why it dialed in at 576Kbps

btw, i'm am i right in thinking that for kilobytes, u capitalise the 'B' (KB) and for kilobits, you don't (Kb)?
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Why...

Always a difficult one that....

In theory yes B = bytes and b = bits but not everyone knows that and it is often confused and misused. I always make it clear by using Kbits, Mbits or Kbytes, Mbytes - no possibility of confusion that way.
michaelscott
Grafter
Posts: 594
Registered: 09-08-2007

Why...

it'd be nice if there were only one measurement to deal with.

what idiot decided to measure bandwidth in a different way to file sizes and why? :?:
N/A

Why...

I suppose we'll have to blame Alan Turing for that.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

Why...

Hmmm. If you've got several hours to spare I could explain it Cheesy

Try not to fall asleep reading this...ZZZzzzzz

In the early days of communication over phone lines, transmission speeds were very slow compared to todays standards - the old modems (or acoustic couplers - showing my age now Cheesy) transfered at a speed of 110 baud or 110 bits/s. In order to make sure every byte (8 bits) was sent correctly and received correctly additional bits were needed. For each character (8 bits), a total of 10 or 11 bits were actually transmitted 1 start bit (synchronise), 8 data bits (the actual data being transmitted), 1 or 2 stop bits. Even todays 56K (that's 56Kbits Wink ) modem uses the same principle of transmitting data to/from your PC via the serial connection.

So in the early days, transmission speeds were always talked about in bits/s because you could actually see or hear the individual bits being sent. In time speeds got faster but it was common practice (even an industry standard) to use bits/s as the indicator of the transmission speed and it still is today, even when we reach the giga levels of Ethernet. Any communication will normally be refered to as bits/s.

With data files there were no additional bits stored and as each character could be represented in a single byte (8 bits) and files were refered to as having 100 characters or bytes as a file size. Files were never refered to as having 1000 bits because that was difficult to determin how many characters it actually contained (I won't go into the area of a byte sometimes having 7, 8, 9 or even 10 bits on some computer systems of old as that will just confuse you further) Cheesy

Still awake... No... Never mind Wink

Cheers

Peter Cool