[X4U] Streaming Confusion with QT Data Rates

[Stroller]

On Sep 25, 2004, at 3:49 pm, revDAVE wrote:

> On 9/20/04 2:29 AM, "Eugene Lee" <list-themacintoshguy at fsck.net> wrote:
>
>> I think you are mixing two different sets of numbers.  The first set,
>> e.g. "low-100k", probably means 100 kilobits/second (12.5 
>> kilobytes/sec).
>> The second set, e.g. "DSL-Low - video = 10k bytes per second", means
>> 10 kilobytes/second (80 kilobits/sec).
>
> If I understand you correctly-  then if my QuickTime movie plays back 
> with a
> data rate of 37.5 kBytes/sec - then is actually the data rate of 300 
> kBits
> /sec ?

37.5 * 8 = 300
Yes.

A bit is "a binary one or zero".

A byte originated as something like "enough bits that lined-up they 
represent a usable binary number, but not too many that it makes our 
processor too complicated or expensive to build" and has come to be 
standardised on 8 bits (which can be used to produce a number between 0 
& 255)

> Also - what is the ideal Kbits for your average DSL speeds ( basic 
> Internet
> standards)
>
> DSL-Low - 100kbits?
> DSL-Med - 200kbits?
> DSL-Hi - 300kbits?
> 56k modem - kbits ?

Obviously I've missed a posting here here, but DSL is typically sold, 
for marketing purposes, in kilobits, and in powers of two of them, for 
convenience of packaging & management.

In the UK we have ADSL services:
  256kbits down, 128kbits up = 32kbytes down, 16kbytes up
  512kbits down, 256kbits up = 64kbytes down, 32kbytes up
      - most domestic users are on this one, and many small offices, too.
  1024kbits down, 256kbits up = 132kbytes down, 32kbytes up   "megabit 
service"
  2048kbits down, 256kbits up = 264kbytes down, 32kbytes up   "2 megabit 
service"
  3072kbits down, 256kbits up = 384kbytes down, 32kbytes up   "3 megabit 
service"

As I recall, the DSL modem actually achieves slightly higher 
performance than this, a 512 one pushing c 600 kilobits in a second in 
order to compensate for the overhead of error-checking & routing & 
stuff. Equally one is unlikely to see one's download meter hit 64 
kilobytes on such a connection, as FTP (or whatever protocol one is 
using to get the file) has its own overheads. I'm very happy when I see 
50kilobits or so on a download.

56k modem = 56kbits = (56/8 =) 7 bytes/second, but that's misleading. 
As I recall the marketing of 56k is different - I think that figure 
allows for compression (which may not always be possible) but not for 
protocol overhead.

Stroller.