When you execute the shell or ! command, ppp
executes a shell (or if you've passed any arguements, ppp
will execute those arguements). Ppp will wait for the command
to complete before continuing. If you attempt to use the
ppp link while running the command, the link will appear to have
frozen. This is because ppp is waiting for the command
to complete.
If you wish to execute commands like this, use the
!bg command instead. This will execute the given command
in the background, and ppp can continue to service the link.