This value signifies the role of an RSVP session with
respect to the start and end points of the session. This value
MUST be set to ingress(1) at the head-end (source) of this session.
This value MUST be set to egress(3) at the tail-end (destination)
of the RSVP session. This value MUST be set to transit(2) on any
other intermediate nodes that this RSVP session exists on.