At 03:17 AM 9/11/00, you wrote:
>What do you mean by interfame gap? is it the address?
The interframe gap (IFG) is the required gap between frames. Per the IEEE
802.3 (Ethernet) specification, between frames, there must be silence on
the wire for the time to transmit 96 bits, which is 9.6 microseconds on 10
Mbps Ethernet. (I'll let you do the math for the higher speed Ethernets).
The IFG gave NICs the time to recover in the olden days when they weren't
as fast as they are today.
>What about ingress and egress issue? how do they calculate it?
Counting ingress would be cheating, if you ask me. I've never heard of a
vendor doing that, but I wouldn't put it past them. As we have said, this
is all marketing showmanship.
Priscilla
>Thanks a lot
>
> Bye
>
>
>
>
>On Sun, 10 Sep 2000 19:41:13 -0700, Priscilla Oppenheimer wrote:
>
> > Wire speed means the switch can pump out packets as fast as the medium
>can
> > handle. For example, the maximum packets-per-second rate on 10-Mbps
> > Ethernet with 64-byte packets is 14,880 packets per second. This comes
>from
> >
> > Preamble = 64 bits
> > 64 Byte frame = 512 bits
> > Interframe gap = 96 bits
> >
> > Total = 672 bits
> >
> > Max packets per second on 10 Mbps Ethernet = 10,000,000 / 672 = 14,880
> > packets per second. A wire-speed switch, which most are, would have no
> > problem outputting that number of packets per second.
> >
> > If you were to use 1024 byte packets, the number is 1197 packets per
>second
> > on 10Mbps Ethernet.
> >
> > So, yes, vendors do tend to use 64-byte packets when quoting their
>results,
> > because it gives them better numbers.
> >
> > The other thing vendors do is quote the results when using Gigabit
> > Ethernet. That's where numbers like millions of packets per second come
> > from. In addition, if the vendor's numbers are based on tests that output
>
> > to multiple ports, then you can get astronomical numbers, for example,
>1.48
> > million packets per second multiplied by 100 ports. As you can probably
> > guess, this is a rudimentary way of specifying the performance of a
>switch
> > that is fraught with the over-zealousness of marketing drones. &;-)
> >
> > Priscilla
> >
> >
> > At 02:12 PM 9/10/00, Kent wrote:
> > >Hi all,
> > >
> > >Any body knows what they mean by saying "wire-speed"
> > >forwarding about a switch?
> > >Also, when Cisco says a switch can forward at 100
> > >million pps or something like this, what the size of
> > >the packets they usually refer to of the PPS(packet
> > >per second)? 64byte?
> > >
> > >Thanks
> > >
> > >Kent
> > >
> > >
> > >
> > >
> > >__________________________________________________
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