Hacker News Reader

Comment by ken | Hacker News Reader

In 2005, Jeff Atwood reported that 100M ethernet is 10x as fast as 10M ethernet, but 1G ethernet is only about 30% faster than 100M, even for a simple loopback test.

http://www.codinghorror.com/blog/2005/07/gigabit-ethernet-an...

Is this still true? What's the bottleneck?

View on HN

Assuming you arent CPU or memory limited, the bottleneck was originally largely due to gigabit Ethernet's support of unswitched hubs and as such uses CSMA to detect collisions. In order for this to work there is a minimum transmit timeslot to ensure that collisions can be detected at the full round trip delay of a ~100m network.

Effectively a 1Gbit Ethernet node must transmit at least 512 bytes during its timeslot. If it has that much to send then it all goes out at 1gbit. If it only has a few bytes to send (a tcp ack for example) then it must idle for a bit to make sure there wasn't a collision.

In theory gigabit Ethernet should perform at 1gbit for sustained transfers but much worse for workloads with more sporadic sets of smaller packets. In practice, especially on core switches and routers, modern techniques like frame bursting (sending multiple small packets going to the same destination back to back) even things out more.

10gbit Ethernet and above get rid of the carrier sense collision detection support all together and require the entire network to be point to point with switches. It has no minimum timeslots or packet lengths.

No, its not true. Regularly saturating a 1Gbps Ethernet port is quite possible on many systems, and happens often in datacenter installations.

The bottleneck is really the computer buses (memory included) and implementation of protocols.

Reply on news.ycombinator.com