IP-Lab | Interactive TCP/IP Protocol Simulator

IP-Lab is a free, browser-based lab for networking students. The TCP Simulation module animates a real TCP connection step by step: the three-way handshake, sliding-window flow control, congestion control (slow start, congestion avoidance, fast retransmit and fast recovery), loss recovery, and connection teardown — with an AI tutor on hand to explain whatever just happened on the wire.

TCP state machine — RFC 793

Client
CLOSED→
SYN_SENT→
ESTABLISHED→
FIN_WAIT_1→
FIN_WAIT_2→
TIME_WAIT
Server
CLOSED→
LISTEN→
SYN_RECEIVED→
ESTABLISHED→
CLOSE_WAIT→
LAST_ACK
Client
CLOSED

Packet Flow

t = 0.0s
Server
CLOSED
No packets in transitStart the simulation from the control bar.
DataACKSYNFINRetransmitLost