Rychlost USB sitovky?

[Jozef Racek]

Ethernet karta 100 Mbit vo full duplex mode moze prijimat 100 Mbit a 
sucasne vysielat 100 Mbit. TEORETICKY.
Co je teoreticky 12.5 MByte/s prenos.. na vysielani a 12,5 MB/s na prijme

V zargone marketingu je to teda 200 Mbit karta s prenosom 25 MB/s ;-)))

USB pouziva ten isty par vodicov na vysielanie aj prijem...

*4. How fast is USB 2.0?*
USB 2.0 has a raw data rate at 480Mbps, and it is rated 40 times faster 
than its predecessor interface, USB 1.1, which tops at 12Mbps. 
Originally, USB 2.0 was intended to go only as fast as 240Mbps, but in 
October 1999, USB 2.0 Promoter Group pumped up the speed to 480Mbps.

As far as we know, effective rate reaches at 40MBps or 320Mbps for bulk 
transfer on a USB 2.0 hard drive with no one else is sharing the bus. 
*Flash Drives* 
<http://www.everythingusb.com/hardware/Storage/USB_Flash_Drives.htm> 
seem to be catching up too with the some hitting 30MB/s milestone. For 
all we know, USB interface could become become the bottleneck for flash 
drives as early as 2008.

/Additional notes from Alex Esquenet - our engineer friend based in 
Belgium: "A fast usb host can achieve 40 MBytes/sec. The theorical 60 
MB/sec cannot be achieved, because of the margin taken between the sof's 
(125 us), so if a packet cannot take place before the sof, the packet 
will be rescheduled after the next sof. On top of that, all the USB 
transactions are handled by software on the PC. For instance, a USB host 
on a PCI bus will send or receive the data via the PCI bus; the stack 
will prepare the next data in memory and receive interrupt from the host."/


Ak zapojite USB devices 1.0, alebo 1.1, tak mate teoreticky prenosovu 
rytchlost 12 Mbit/s ( po jednom- jedinom ) pare. ( klavesnice, mysi a 
podobne pomale zariadenia )
Teda cisto velmi teoreticky 6Mbit/s vysielanie a 6Mbit/s prijem. 
To je 0.75 MB/s  na vysielani.
Tolko teoria.

Prax hovori, ze na prepinanie medzi vysielanim a prijmom treba nejaky 
cas, normy a protokoly hovora o nejakych casoch pred a po framoch a pod.
Nejaky cas  samozrejme zhltnu drivery...

Realita je teda taka, ze USB je velmi pomale zariadenie ( aj ked je to 
USB 2.0 ) a nema zmysel za neho vesat rychlejsie zariadenia ako napr 
LAN, FireWire a pod.
Je to len pre pripad velkej nudze...

Dodo

Jiri Sladek wrote:
> Zdravím.
>
> Nevíte náhodou, jestli síťová karta v provedení USB může dosáhnout podobné 
> rychlosti přenosu dat, jako klasická síťovka 100Mbit na mainboardu?
>
> Mám notebook a chci minimalizovat počet nutných kabelů. Domíval jsem se, že 
> na jeden port USB připojím HUB a na něj USB sťovku, klávesnici, myš a čtečku 
> bankovních karet, a že to pojede slušně rychle. Ale ouha, rychlost takto 
> připojené USB síťovky je jen zlomkem rychlosti onboard síťovky.
>
> Poradí někdo něco? Díky.
>
> J.Sládek 
>
>
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