What are all those T1, T2, N2 and things ?

Not every AX.25 implementation is a TNC2. Linux uses nomenclature that differs in some respects from that you will be used to if your sole experience with packet is a TNC. The following table should help you interpret what each of the configurable items are, so that when you come across them later in this text you'll understand what they mean.

Linux	TAPR TNC	Description
T1	FRACK	How long to wait before retransmitting an unacknowledged frame.
T2	RESPTIME	The minimum amount of time to wait for another frame to be received before transmitting an acknowledgement.
T3	CHECK	The period of time we wait between sending a check that the link is still active.
N2	RETRY	How many times to retransmit a frame before assuming the connection has failed.
Idle		The period of time a connection can be idle before we close it down.
Window	MAXFRAME	The maximum number of unacknowledged transmitted frames.