TWAMP Server: Two packets received but not reflected back to client #104
Description
Hello,
During TWAMP test sessions, I detected that two test packets were received by the TWAMP server but were not reflected back to the client.
Environment:
- Ubuntu 22.04 for twamp server and android 15 for twamp client
- Client implementation: custom native TWAMP client (Android)
Test configuration:
- Number of packets: 10000
- Inter-packet interval: 0.001 seconds (1 ms)
- Payload size: 1300 bytes
- Transport: UDP (TWAMP-Test)
The issue was observed during a high-rate TWAMP test (10000 packets with an inter-packet interval of 1 ms) using a near-MTU payload size (1300 bytes).
According to tcpdump captures on the server interface, two packets were successfully received by the server but were not reflected back to the client.
The missing reflected packets correspond to sequence numbers 3546 and 3548. These are the only two packets not received by the Android TWAMP client, which reported receiving 9998 out of 10000 packets (2 packets lost). The missing sequence numbers are exactly 3546 and 3548.
Server-side packet capture confirms that these packets arrived at the TWAMP server. However, no corresponding reflected TWAMP-Test packets were observed in the outgoing traffic.
Please see the attached PCAP capture for more details.
Packet 3546 was received by the server (filtered in Wireshark using: twamp.test.seq_number == 3546).
The packet is clearly visible in the server-side capture, confirming that it arrived at the TWAMP server. However, No corresponding reflected packet with the same sequence number was observed in the outgoing traffic.
Packet 3546 was not sent by the server to the Android device (filtered using: twamp.test.sender_seq_number == 3546).
The same behavior was observed for packet 3548.