IGP extensions are defined in RFC 4124. Diff-Serv TE advertises link available bandwidth, referred to as unreserved bandwidth, by OSPF TE or IS-IS TE on a per TE class basis. A TE class is a combination of a class type and an LSP priority. To reduce the amount of per TE class flooding required in the network, the number of TE classes is set to eight. This means that eight class types can be supported with a single priority or four class types with two priorities, and so on. In that case, the operator configures the wanted class type on the LSP such that RSVP-TE can signal it in the class-type object in the path message.
IGP continues to advertise the existing Maximum Reservable Link Bandwidth TE parameter to mean the maximum bandwidth that can be booked on a specified interface by all classes. The value advertised is adjusted with the link subscription factor.