I need to set or get RTT in socket(AF_INET, SOCK_RAW, IPPROTO_TCP) way.
What do I need to do next to control such RTT in socket programming? In other words, how to find such RTT parameter?
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There's no function for that in the API. Just send a message to the other end, have the other end send it back, and time it. Not so hard.Filipe Gonçalves– Filipe Gonçalves2015-06-22 11:56:27 +00:00Commented Jun 22, 2015 at 11:56
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Will tcp-timestamp option help?Vikash Jain– Vikash Jain2015-06-22 12:14:15 +00:00Commented Jun 22, 2015 at 12:14
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It isn't set, it's measured, by TCP.user207421– user2074212015-06-22 12:39:22 +00:00Commented Jun 22, 2015 at 12:39
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2 Answers
On Linux you can get the RTT by calling getsockopt() with TCP_INFO:
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
/* ... */
tcp_info info;
socklen_t tcp_info_length = sizeof info;
ret = getsockopt(sock, SOL_TCP, TCP_INFO, &info, &tcp_info_length);
printf("rtt: %u microseconds\n", info.tcpi_rtt);
4 Comments
user786
Can I get the rtt time of accepted socket like this
lvella
@user786 Yes, that is the RTT as calculated by the TCP stack.
user786
so where I call
getsockopt() is it after the call to accept() or after the call to read(..)lvella
@user786 It will work in both places, but the value will change as the socket is used, because it is an estimation calculated as new packets are sent and confirmed through that connection. I am not sure
read() will have any effect on the value.To measure the Round Trip Time (RTT) write a simple client-server application where one node:
- Reads the current time with
clock_gettime() - Sends a message to the other node using
write()on the (already opened) socket - Waits the message back using
read() - Reads the current time using
clock_gettime()
RTT is the difference between the two times.
2 Comments
Filipe Gonçalves
POSIX.1-2008 marks
gettimeofday(2) as obsolescent. clock_gettime(2) should be used instead (or time(2)).
Claudio
Right. Fixed. Thank you.
