uting domains. The logical view is that OSPF creates something of a spider web or star topology of many areas all attached directly to area zero and IS-IS by contrast creates a logical topology of a backbone of Level 2 routers with branches of Level 1-2 and Level 1 routers forming the individual areas. 8.3.2.4 Resource Reservation Protocol with Traffic Engineering Extensions Because RSVP-TE inherits its design from the RSVP protocol, it is based on distributing various signaling objects. These signaling objects have been grouped. These groups con- tain mandatory and optional signaling objects; encapsulating the groups with a common header, distinct signaling messages are created. When a GLSR receives a signaling message, the resident objects are examined and inter- preted based upon the message type indicated by the common header. Extending the RSVP-TE protocol for GMPLS was thus a matter of generalizing existing signaling objects, including some new objects that are reported in Table 8.4, and adding some minor signal- ing enhancements. Considering the RSVP-TE protocol with GMPLS extensions for signaling, each signaling message contains a common 8-byte header. The common header defines the message type followed by the encapsulated objects. Encapsulated objects are of variable length and con- tain a 4-byte header defining the object length, class, and type within class. Convergent Network Management and Control Plane TABLE 8.4 New Objects Introduced in the Adaptation of RSVP-TE for the GMPLS Object Name Length Message Description Generalized label request 4 bytes Path describes the requested LSP IF_ID RSVP_HOP Variable Path/Resv defines what interface to label Generalized label variable 4 bytes Resv/ResvErr downstream label Upstream label variable 4 bytes Path/PathErr upstream label Label ERO 2 bits + label Path/Resv explicit label control Suggested label variable 4 bytes Path/PathErr label suggestion Label set Variable Path label selection restriction The first signaling activity of RSVP-TE is to distribute the l