- Sometimes, ICMP is not enabled on the end hosts (increasingly now)
- ICMP RTTs may not provide the right delay metric for real-world applications.
This should be a more realistic measure of RTT for real-world TCP traffic and should be possible to do on any public node.
Here are two that I found to be helpful
- TCP Ping: Download script here and more details here (requires tcptraceroute)
- Scapy TCP Ping (using Python): Doesn't seem to actually do RTT measurements... (requires python and scapy library)