When a packet is sent over a network, the sender starts a timer and expects the packet to be acknowledged before the timer expire.

Go to the TCP header and expand tree.Īs you see in the screenshot above, after SYN/ACK packet arrived, the RTT for the SYN packet has calculated as 0.229751 second.Īnalysing TCP Retransmission Timeout (RTO).

We will measure RTT for the first packet (SYN) in the flow. Let’s get our hands dirty and capture a TCP flow. Wireshark is capable of calculating and displaying TCP RTT in the header.

RTT is how long it takes to receive an ACK for data that has been sent. The similar concept can be applied to TCP as well.

Minimum = 11ms, Maximum = 37ms, Average = 18ms Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),Īpproximate round trip times in milli-seconds: My ping command displays the RTT for each packet sent and returned below. The total time is called RTT for ping.ĪLSO READ: Detect Rogue DHCP Server with Wireshark I am using Windows OS and when I ping 1.1.1.1 address, it displays an output that shows me how much time it takes to send an ICMP packet from my computer to the server and gets back an answer from the server to my computer. Before diving into retransmissions and examining the types of retransmissions, we need to explain two concepts.įor sake of simplicity, lets first go with pinging. Packet loss is mostly caused by hardware issues, software bugs, network congestion, and some other factors. Packet loss may happen due to two main reasons which can fall into many sub categories. After that, the copy gets deleted and resources are released for future use. Whenever a sender transmits a packet, it saves a copy of the packet int its buffer and it stays there until receiving side acknowledges that it has received the packet. The lost packets are recovered by retransmissions and acknowledgments while sequence numbers are used to determine correct packet reordering in the receiving side. The protocol offers packet delivery guarantees, even if some of the packets have been lost during the transmission. TCP is one of the reliable protocols working in the transport layer, in terms of Open System Interconnect (OSI) model.

Mikrotik wireshark capture