The tmnxPortMode variable indicates if the interface on this port
is configured as a service access port, a network port or a 
hybrid port.  Once the port's mode has been configured for 'access', 
'network' or 'hybrid' mode, multiple services may be configured 
on the port.

tmnxPortEncapType is defaulted based on MDA type and
Port Mode according to the following table:

MDA Type           Port Mode             tmnxPortEncapType
---------------------------------------------------------
ATM                access                atmEncap

CEM                access                cemEncap

Ethernet           access                nullEncap
                   network               nullEncap
                   hybrid                qEncap

ISA
  isa-aa           network               nullEncap
  isa-bb           access                qinqEncap
                   network               qEncap
  isa-ipsec        access                qEncap
  isa-video        access                qEncap

Sonet/SDH          access                bcpNullEncap
                   network               pppAutoEncap

TDM                access                bcpNullEncap
                   network               pppAutoEncap

VSM
   vsm-cca         access                qEncap
   vsm-cca         network               qEncap