This attribute specifies the required minimum level of security of
the trunks on the route. A value of zero represents the most secure
while seven represents the least secure. The trunk's security is
indicated by the trunkSecurity attribute of the Trunk component,
and has values identical in range and meaning to the
requiredSecurity attribute. PORS ensures that any route selected
does not contain a trunk whose trunkSecurity attribute is
numerically greater than the requiredSecurity.