Kind of! They allow systems with slightly different clock rates to adjust. A system sending data nominally at 10 Gb/s can actually run slightly faster to a system running slightly slower b/c their timing bases (crystals) oscillate at slight different frequencies.
>"They allow systems with slightly different clock rates to adjust."
Adjust to what? Ethernet is not synchronous its asynchronous. There is no shared clock.
The interframe gap goes back to the days of CSMA/CD. The interframe gap was the period during which end stations would contend for the shared medium. Without this an end station could continuously stream and monopolize the network.
Back when I worked at Chevron in the early 90s, I noticed that new SGI workstations were way faster NFS servers than anything else, even the Suns. It took me a bit in those days (Ethernet network analyzers were over $50K then, so hard to borrow even in a big, rich company) to figure out why:
It took 6 Ethernet frames to send a single 8K NFS block, and regaining the carrier could be pretty time-consuming if there was other traffic. So SGI implemented a really elegant cheat that technically violated the Ethernet standards, but dramatically improved performance for the entire network, and especially their NFS servers: They simply never let anyone else get a chance to talk until they'd sent the entire block, "hogging" the carrier by going straight from the last bit of the previous frame to the preamble of the next one. It was a very clever way of more-or-less getting jumbo frames years before they became part of the standard!
Interesting. I knew someone that worked for an ISP in 90's who had an odd SGI workstation amongst their standard SUN boxes for hosting customer sites. The SGI box was regarded to be faster than the newer SUN boxes. Eventually all customers were migrated off of the SGI box except one customer who refused and threatened to sue. I wonder if the reason for the performance gains of the SGI were the same as yours.
I believe 802.11n reduced the interframe gap down to a two microseconds for transmissions to the same receiver.
No, that's incorrect. The preamble is used to denote the start of a frame. It's used by the receive circuit to sync to - i.e it derives its clock from those preamble bits. It's also how the receiver distinguishes between a frame an noise.
Actually, even though most connections are switched point-to-point these days, any properly functioning implementation (definitely up through 100Mbps) must still implement CSMA/CD. It's required for proper functioning of Ethernet hubs and some bridges!
In ethernet (at least at higher speeds; I can't speak offhand for <=1G), an average IPG of 12 bytes is used to let the start of frame symbol be 8-byte aligned. So for example a series of 65 byte frames would be separated by alternating 11 and 13 byte IPGs.