A quick run down of the internal structure.

main.c:
	main() Just sets things up. Opens socket, and set terminal
		to non-blocking. calls main_loop();

	main_loop() program sits here until exit.
		Runs in a loop doing select().
		calls do_serial_out() to set data to modem.
		do_link_out() to queue packets.
		update_time() to maintain 1/20th second clock.
		do_serial_in() to build packets from raw serial.
		

serial.c
	do_serial_out(). Runs down the list of queued packets looking for
		one to send. Picks the one that has been waiting the longest
		for an ack.
	do_serial_in(). a FSM, that builds packets from serial. Tries
		to find a header, then uses header to get length of packet
		and reads in that packet. calls get_serial() which may	
		return -1 if there is nothing in serial in buffer.

	do_ack(). Takes an outgoing packet of the queue. It has been acked.
		
	send_ack(). We correctly received a packet, so send an ack.

	check_sum() is not a good one. Someone write a better one. :)

link.c:
	do_link_out(). Builds a packet if there is space on the queue.
		calls get_data() to build the packets.

	do_link_in(). Takes a packet of the in queue, uncompress it if
		necessary, and gives it to put_data().

	get_data(). Call get_client_byte until we have a full packet, or
		have run out of data, and then (optionally) compress it.
	
	do_control(). Handle control messages. This routine handle only
		remote control messages. I.e. messages sent from the other
		end.

	get_next_client() returns the struct for the next client ready to 
		give data.

	get_client_data returns the next byte from the client.

	put_client_data() handles control messages calling do_control(), and
		puts non-control data in client buffer.

	
	get_client_byte() returns the next bytes from the client. handles
		local control messages. Handles stream switching. Yet another
		finite state machine...

	
	put_data(). Put data to clients. Handles stream switching, switch
		char escaping, and thats about it. calls put_client_data()
		to send actual data or client control messages.

	
		

	
Protocols:
Closing down.
	state is 1 while running.
	if an error on read or write occurs then state goes to 2.
	then when buffer is empty, a C_CLOSE is sent, and state goes
	to 3.

	if a C_CLOSE is received, then state goes to 3.