This attribute indicates the role of this link in the PNNI hierarchy.
The following values are possible:
unknown: the Hello protocol has not yet determined the role of the
link.
lowestLevelHorizLink: the link is a horizontal link between two
lowest level nodes.
lowestLevelOutsideLink: the link is an outside link between two
border nodes.
horizontalLinkToLgn: the link is a horizontal link to a Logical
Group Node (LGN).
uplink: the link is a uplink to a higher level LGN.