3 ms·

None of this applies to modern gigabit ethernet installations, which are full-duplex and switched so that collisions don't occur. Maximum cable length is limite

by tlb 14y ago

None of this applies to modern gigabit ethernet installations, which are full-duplex and switched so that collisions don't occur. Maximum cable length is limited by signal degradation, so the limit is soft. With good quality cables you can go a little beyond the rated maximum.

ajross 14y ago
Exactly. The switches buffer packets. The article is talking about a CSMA limitation of the old unbuffered hub architecture (and the "real electrical bus" coax networks before that) which have been irrelevant for over a decade now. And my experience is that you can actually get well beyond the official lengths for most signal types even with comparatively cheap cables as long as you're willing to test and throw out the odd cable or connector. Standards are written with conservatism in mind.
- jcr 14y ago
  > Exactly. The switches buffer packets. In most cases, you're right. The vast majority of switches use a sore-and-forward design (buffering), but when you get into latency-critical applications, another type of switch design is used, typically called a cross-bar switch. http://www.researchgate.net/publication/220055485_A_low-latency_modular_switch_for_CMP_systems http://www.researchgate.net/publication/220055485_A_low-late... http://www.google.com/patents/US5339396 http://www.google.com/patents/US5339396 I think opinions vary on whether or not crossbar designs "buffer" but it mostly depends on how you define buffering. None the less, the low-latency crossbar designs try to eliminate the latency caused by buffering in the older but more common store-and-forward designs.
  - ajross 14y ago
    This is a valid point and I should have been more precise. But AFAICT all those interconnects are single duplex point-to-point links, and thus not subject to the CSMA issues of asymmetric collision detection detailed in the linked article.
sliverstorm 14y ago
With good quality cables you can go a little beyond the rated maximum This sort of thing is designed with a very, very comfortable margin. I'd expect if you wanted, you could get quite a lot beyond the rated maximum.
vineel 14y ago
You seem to have a lot of knowledge about this. If I wanted to acquire similar knowledge, where would I go? I know embarrassingly little about networks.
- smithian 14y ago
  Not the OP, but I would pick up a copy of Ethernet: the Definitive Guide. Then move on to TCP/IP Illustrated, 1&2.

by tlb 14y ago

ajross 14y ago

Exactly. The switches buffer packets. The article is talking about a CSMA limitation of the old unbuffered hub architecture (and the "real electrical bus" coax networks before that) which have been irrelevant for over a decade now. And my experience is that you can actually get well beyond the official lengths for most signal types even with comparatively cheap cables as long as you're willing to test and throw out the odd cable or connector. Standards are written with conservatism in mind.

jcr 14y ago
> Exactly. The switches buffer packets. In most cases, you're right. The vast majority of switches use a sore-and-forward design (buffering), but when you get into latency-critical applications, another type of switch design is used, typically called a cross-bar switch. http://www.researchgate.net/publication/220055485_A_low-latency_modular_switch_for_CMP_systems http://www.researchgate.net/publication/220055485_A_low-late... http://www.google.com/patents/US5339396 http://www.google.com/patents/US5339396 I think opinions vary on whether or not crossbar designs "buffer" but it mostly depends on how you define buffering. None the less, the low-latency crossbar designs try to eliminate the latency caused by buffering in the older but more common store-and-forward designs.
- ajross 14y ago
  This is a valid point and I should have been more precise. But AFAICT all those interconnects are single duplex point-to-point links, and thus not subject to the CSMA issues of asymmetric collision detection detailed in the linked article.

sliverstorm 14y ago

With good quality cables you can go a little beyond the rated maximum This sort of thing is designed with a very, very comfortable margin. I'd expect if you wanted, you could get quite a lot beyond the rated maximum.

vineel 14y ago

You seem to have a lot of knowledge about this. If I wanted to acquire similar knowledge, where would I go? I know embarrassingly little about networks.

smithian 14y ago
Not the OP, but I would pick up a copy of Ethernet: the Definitive Guide. Then move on to TCP/IP Illustrated, 1&2.