fxp performance with POLLING

sthaug at nethelp.no sthaug at nethelp.no
Tue Oct 7 19:24:58 UTC 2008

> However, ethernet at 100Mbit is 4B5B coded at a 125mhz rate. So the raw 
> synchronous data rate really is 12.5Mbytes/s.  Minus the sync preamble 
> of 8 bytes per packet and the mandatory inter-frame-gap of 12 bytes 
> that's a physical layer rate of (12.5M * (1500/(1500+20))) or 12.34Mbyte/s.

You need add Ethernet header (14 bytes) + CRC (4 bytes). This means you
have a maximum data rate, assuming 1500 byte MTU, of 12.5M * 1500/1538
= 12.19 Mbyte/s. And for those used to powers of two, M here means one
million, not 1048576.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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