Most everything there is to say about console servers is said here,
along with a description of how "screen" can be of value:

	http://www.eng.auburn.edu/users/doug/console.html

Note that to properly connect two hosts with a three-wire lead you need
to build a full hand-shake 3-wire null modem.  Connect RX1 (port 1, pin
2) to TX2 (port 2, pin 3) and TX1 to RX2, connect GND1 (port 1, pin 7)
to GND2 (port 2, pin 7), connect RTS (pin 4) and CTS (pin 5) and DCD
(pin 8) together on each port, and finally connect DTR (pin 20) to DSR
(pin 6) on each port.

Some people also recommend putting a 4.7K Ohm resistor between pin 3 and
pin 25 (which has -5v on most Sun systems) on host end when connecting
to a Sun SPARC host.  This should have the effect of stifling any
appearance of a break signal when the console server machine is either
disconnected or power cycled.  I've never actually tried this myself
though....