2 ms·

I'd argue that the legacy of CSMA/CD still alive in ethernet is what makes it harder to implement efficient networks, as the switched network kinda tries to emu

by p_l 5y ago

I'd argue that the legacy of CSMA/CD still alive in ethernet is what makes it harder to implement efficient networks, as the switched network kinda tries to emulate the shared bus behaviour.

dragontamer 5y ago
I admit that I'm not actually a network engineer at this point. I took a networking course back in college and what I've discussed so far is largely just the basics and how I've internalized my lessons from back then. Looking at CSMA/CD more specifically, as well as "full-duplex Ethernet" (which are 100Mbit, 1Gbit, and 10Gbit modern Ethernet), it seems like CSMA/CD is no longer used in any full-duplex Ethernet Protocol. I'm not 100% sure about that, since its outside the scope of my old studies. But it makes sense to me. It seems like "full duplex Ethernet" can only work with point-to-point communications. If you have point-to-point connections between exactly two stations, there's no need for carrier-sense (CS), multiple-access (MA), or collision-detection (CD) protocols at all. CS: Wait for the current person on the walkie-talkie to say "over" before you yourself start talking. MA: Walkie talkies: many people can access the same channel. CD: If two people accidentally start talking at exactly the same time, they need to independently try to restart-talking. A random-number generator with exponential backoff is common for this sort of thing IIRC, though I'm not keen on the exact details.
- p_l 5y ago
  The problem is that the switched network has to emulate behaviours that were free on CSMA/CD system. So we get MAC learning, Spanning-Tree Protocol, and ultimately if you want performant large scale ethernet switching (and not just terminate ethernet at point2point) you end up with complex software directly managing forwarding tables (all sorts of SDNs) or essentially turn ethernet into routed network (using IS-IS routing, two standards exists for implementing it, one of them - TRILL - is reportedly backbone of Cisco Nexus Fabric system). There's a reason why another name of Layer 2 ethernet network is "broadcast area".

by p_l 5y ago

I'd argue that the legacy of CSMA/CD still alive in ethernet is what makes it harder to implement efficient networks, as the switched network kinda tries to emulate the shared bus behaviour.

dragontamer 5y ago

I admit that I'm not actually a network engineer at this point. I took a networking course back in college and what I've discussed so far is largely just the basics and how I've internalized my lessons from back then. Looking at CSMA/CD more specifically, as well as "full-duplex Ethernet" (which are 100Mbit, 1Gbit, and 10Gbit modern Ethernet), it seems like CSMA/CD is no longer used in any full-duplex Ethernet Protocol. I'm not 100% sure about that, since its outside the scope of my old studies. But it makes sense to me. It seems like "full duplex Ethernet" can only work with point-to-point communications. If you have point-to-point connections between exactly two stations, there's no need for carrier-sense (CS), multiple-access (MA), or collision-detection (CD) protocols at all. CS: Wait for the current person on the walkie-talkie to say "over" before you yourself start talking. MA: Walkie talkies: many people can access the same channel. CD: If two people accidentally start talking at exactly the same time, they need to independently try to restart-talking. A random-number generator with exponential backoff is common for this sort of thing IIRC, though I'm not keen on the exact details.

p_l 5y ago
The problem is that the switched network has to emulate behaviours that were free on CSMA/CD system. So we get MAC learning, Spanning-Tree Protocol, and ultimately if you want performant large scale ethernet switching (and not just terminate ethernet at point2point) you end up with complex software directly managing forwarding tables (all sorts of SDNs) or essentially turn ethernet into routed network (using IS-IS routing, two standards exists for implementing it, one of them - TRILL - is reportedly backbone of Cisco Nexus Fabric system). There's a reason why another name of Layer 2 ethernet network is "broadcast area".