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MSL
Maximum Segment Lifetime (MSL) is the time a TCP segment can exist in the network, and is defined as two minutes. 2MSL is twice this lifetime. It is the maximum lifetime of a TCP segment on the network because it supposes segment transmission and acknowledgment.
Currently, Micrium does not support multiple sockets with identical connection information. This prevents new sockets from binding to the same local addresses as other sockets. Thus, for TCP sockets, each close() incurs the TCP 2MSL timeout and prevents the next bind() from the same client from occurring until after the timeout expires. This is why the 2MSL value is used. This can lead to a long delay before the socket resource is released and reused. µC/TCP-IP configures the TCP connection's default maximum segment lifetime (MSL) timeout value, specified in integer seconds. A starting value of 3 seconds is recommended.
If TCP connections are established and closed rapidly, it is possible that this timeout may further delay new TCP connections from becoming available. Thus, an even lower timeout value may be desirable to free TCP connections and make them available for new connections as rapidly as possible. However, a 0 second timeout prevents µC/TCP-IP from performing the complete TCP connection close sequence and will instead send TCP reset (RST) segments.
For UDP sockets, the sockets close() without delay. Thus, the next bind() is not blocked.