alt Hacker NewsThe Nagle algorithm was created back in the day of multi-point networking. Multiple hosts were all tied to the same communications (Ethernet) channel, so they would use CSMA (https://en.wikipedia.org/wiki/Carrier-sense_multiple_access_...) to avoid collisions. CSMA is no longer necessary on Ethernet today because all modern connections are point-to-point with only two "hosts" per channel. (Each host can have any number of "users.") In fact, most modern (copper) (Gigabit+) Ethernet connections have both ends both transmitting and receiving AT THE SAME TIME ON THE SAME WIRES. A hybrid is used on the PHY at each end to subtract what is being transmitted from what is being received. Older (10/100 Base-T) can do the same thing because each end has dedicated TX/RX pairs. Fiber optic Ethernet can use either the same fiber with different wavelengths, or separate TX/RX fibers. I haven't seen a 10Base-2 Ethernet/DECnet interface for more than 25 years. If any are still operating somewhere, they are still using CSMA. CSMA is also still used for digital radio systems (WiFi and others). CSMA includes a "random exponential backoff timer" which does the (poor) job of managing congestion. (More modern congestion control methods exist today.) Back in the day, disabling the random backoff timer was somewhat equivalent to setting TCP_NODELAY.
Dumping the Nagle algorithm (by setting TCP_NODELAY) almost always makes sense and should be enabled by default.
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False. It really was just intended to coalesce packets.
I’ll be nice and not attack the feature. But making that the default is one of the biggest mistakes in the history of networking (second only to TCP’s boneheaded congestion control that was designed imagining 56kbit links)
Just to add, ethernet uses csma/cd, WiFi uses csma/ca.
Upgraded our DC switches to new ones around 2014 and needed to keep a few old ones because the new ones didn't support 10Mbit half duplex.
Nagle is quite sensible when your application isn't taking any care to create sensibly-sized packets, and isn't so sensitive to latency. It avoids creating stupidly small packets unless your network is fast enough to handle them.
I think you are confusing network layers and their functionality.
"CSMA is no longer necessary on Ethernet today because all modern connections are point-to-point with only two "hosts" per channel."
Ethernet really isn't ptp. You will have a switch at home (perhaps in your router) with more than two ports on it. At layer 1 or 2 how do you mediate your traffic, without CSMA? Take a single switch with n ports on it, where n>2. How do you mediate ethernet traffic without CSMA - its how the actual electrical signals are mediated?
"Ethernet connections have both ends both transmitting and receiving AT THE SAME TIME ON THE SAME WIRES."
That's full duplex as opposed to half duplex.
Nagle's algo has nothing to do with all that messy layer 1/2 stuff but is at the TCP layer and is an attempt to batch small packets into fewer larger ones for a small gain in efficiency. It is one of many optimisations at the TCP layer, such as Jumbo Frames and mini Jumbo Frames and much more.
Are you theorizing a CSMA related motivation or benefit in the Nagle algorithm or is this a tangential anecdote of those times?