Normally your ISP provider will supply you with the operating
parameters you require. However, if you are experimenting and connecting two
PC's together you should bear the following in mind.
On end of the link should supply the line clock. At one end
set CLOCK=ext in the ifcfg-hdlcX file.
One end needs to be LMI DTE and the other LMI dce. At one
end set DCE=y in the ifcfg-hdlcX file.
Use dlci number of 16 and above. You are not prevented
using any dlci, but remember that some are reserved.
If your ISP only supports Cisco's LMI protocol, then turn
off LMI altogether. set LMI=none in the ifcfg-hdlcX file.