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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