RE: [ethmac] About FlowControl and VLAN

["NewsGroup" <nbase@nbase.com>]

6-Oct-00

   Hi,

	Just had a new machine and got some of the old email that was stored on the
server however some mail got lost so hope I don't say something that was
already said.


>-> FlowControl:
>Well I found the corresponding information in the standard. I think it's
nice to
>have a FlowControl implemention on receiver side to disable the
transmitter. But
>what's about transmitter side - should there be any hardware support for
sending
>FlowControl frames?

Just as you have in the reciver a simple counter that hold the transmiter,
if your back side have no more space you should send a flow control to stop
the other side from keep sending data.

the simplest and as far as I know most used technique is simple to send
either flow control packet with timer equal ffff or timer equal 0000 so it
work in sort of Xon/Xoff .

This methode is not only the simplest to impliment but in most case will
give just the same performance as sending a calculated timer.

>-> VLAN:
>Thanks for the reply. I also found some info about VLAN at one website
mentioned
>on the link page. But the knowledge about the VLAN tag is not all. How is
it
>used? What if the MAC removes the VLAN tag? How does the host respond?
Great if
>someone can give additional advice!

the vlan is used for few thing, starting in "grouping" meaning that let say
on the net are 4 computer A,B, C, and D and you want mail from A to go only
to B and simplar from C only to D but also you want A to be able to send to
everyone, in this case you can for example put A and B on vlan #1 and C and
D on vlan #2 and all on vland #3.
now if A send packet with Vlan #1 it will go only to B but if he send packet
with Vlan #3 it will go to everyone.
there are more use for it like for multicast and even security EVEN tho' you
should be EXTREMLY carefull if you want to do security as the std of VLAN
was NOT intent for security and it thus have several drawback.

in removeing Vlan you should be aware that the packet might go BELOW the
minimum and therefore it is YOUR responsibility to add pad so it will go
back to at least minimum packet size.

have a nice day

   Illan