Re: Is nagle disabled?
Le quintidi 25 fructidor, an CCXXIV, Rob van der Putten a écrit : > I use netcat6. From man nc; > nc6 --continuous --exec cat -l -p > So the data goes from nc to cat and then back to nc. > > Timestamps (epoch.microseconds) are dumped to a file on transmission and to > an other file on reception of the 'echo'. Further check with tcpdump. > Experiment on LAN and experiment over DSL; > When the time between the bits of data is larger then the RTT, data is send > at two bytes per TCP packet. With that kind of test, the reply comes immediately, the ACK is bundled with the reply, therefore making delayed ACK invisible. The way you implemented the echo server, with several applications communicating with each other, is irrelevant because it is all invisible to the network stack. If you want to observe delayed ACK, you need to use a kind of server where the reply does not come immediately in the same TCP stream. A discard server would be the simplest example. Regards, -- Nicolas George signature.asc Description: Digital signature
Re: Is nagle disabled?
Hi there On 10/09/16 13:37, Nicolas George wrote: Le quintidi 25 fructidor, an CCXXIV, Rob van der Putten a écrit : So the question should have been 'Is delayed ack disabled'. I have a hard finding decent information on the subject, so I did a bit of experimentation; I send tiny bits of data (two bytes at a time) to a little echo server. As it turns out, the use of delayed acks and therefore nagle, depends on the time between sending the bits of data and the RTT. I do not think you can really test delayed ACK with an echo server: the principle of delayed ACK is to leave a little time to the application to send a reply, because then the ACK can be bundled with the reply, saving a packet. With an echo server, the reply comes immediately, never letting the delay for the ACK expire. I use netcat6. From man nc; nc6 --continuous --exec cat -l -p So the data goes from nc to cat and then back to nc. Timestamps (epoch.microseconds) are dumped to a file on transmission and to an other file on reception of the 'echo'. Further check with tcpdump. Experiment on LAN and experiment over DSL; When the time between the bits of data is larger then the RTT, data is send at two bytes per TCP packet. Regards, Rob
Re: Is nagle disabled?
Le quintidi 25 fructidor, an CCXXIV, Rob van der Putten a écrit : > So the question should have been 'Is delayed ack disabled'. > I have a hard finding decent information on the subject, so I did a bit of > experimentation; > I send tiny bits of data (two bytes at a time) to a little echo server. As > it turns out, the use of delayed acks and therefore nagle, depends on the > time between sending the bits of data and the RTT. I do not think you can really test delayed ACK with an echo server: the principle of delayed ACK is to leave a little time to the application to send a reply, because then the ACK can be bundled with the reply, saving a packet. With an echo server, the reply comes immediately, never letting the delay for the ACK expire. Regards, -- Nicolas George signature.asc Description: Digital signature
Re: Is nagle disabled?
Hi there On 09/09/16 19:57, Rob van der Putten wrote: I thought I overlooked something. And this is it. Thanks! So the question should have been 'Is delayed ack disabled'. I have a hard finding decent information on the subject, so I did a bit of experimentation; I send tiny bits of data (two bytes at a time) to a little echo server. As it turns out, the use of delayed acks and therefore nagle, depends on the time between sending the bits of data and the RTT. Regards, Rob
Re: Is nagle disabled?
Hi there On 09/09/16 18:19, Stefan Monnier wrote: I suggest you re-read https://en.wikipedia.org/wiki/Nagle's_algorithm Nagle only kicks in when there are un-acknowledged packets. So on the first packet, there is no delay. There will be a delay on the *second* packet if it's small and we haven't yet received confirmation that the first packet was received. I thought I overlooked something. And this is it. Thanks! Regards, Rob
Re: Is nagle disabled?
> I'm experimenting with TCP to see how long it takes to send a small amount > of data from A to B. One would expect a latency of a few hundred > milliseconds, but it's a few hundred microseconds instead. It is as if > Nagle's algorithm has been disabled. I suggest you re-read https://en.wikipedia.org/wiki/Nagle's_algorithm Nagle only kicks in when there are un-acknowledged packets. So on the first packet, there is no delay. There will be a delay on the *second* packet if it's small and we haven't yet received confirmation that the first packet was received. Stefan
Is nagle disabled?
Hi there I'm experimenting with TCP to see how long it takes to send a small amount of data from A to B. One would expect a latency of a few hundred milliseconds, but it's a few hundred microseconds instead. It is as if Nagle's algorithm has been disabled. Regards, Rob
