[f-nsp] 1G speed-duplex concept FESX

[Mark Tech]

Hi
If I want to enable port speed to 1Gbps, I get the following options, 

telnet#speed-duplex?
  10-full  10M, full duplex
  10-half  10M, half duplex
  100-full  100M, full duplex
  100-half  100M, half duplex
  1000-full-master 1G, full duplex, master
  1000-full-slave 1G, full duplex, slave
  auto   Autonegotiation

What is the difference/concept behind the master - slave config?

Regards

Mark