 Advertisement messages are used to disseminate across the network the discovery of new network entities or other modifications in the network topology that influences the labels distribution. For example, if a link fails, this has to be eliminated from the topology map that each GLSR has in the routing engine. This is dis- covered by processing the absence of response to all the Hello messages that are directed toward that link and is advertised to all the network routing entities via advertisement messages. The notification messages signal errors and other events of interest. There are two kinds of notification messages: 1. Error notifications: these signal fatal errors and cause termination of the session 2. Advisory notifications: these are used to pass on GLSR information about the CR-LDP session or the status of some previous message received from the peer All CR-LDP messages have a common structure that uses a TLV encoding scheme. This TLV encoding is used to encode much of the information carried in CR-LDP messages. The Value part of a TLV-encoded object may itself contain one or more TLVs. Messages are sent as CR-LDP PDUs. Each PDU can contain more than one CR-LDP message. Each CR-LDP PDU is an CR-LDP header followed by one or more CR-LDP message. 8.3.2.6 Comparison between RSVP-TE and CR-LDP From the brief description we have done, it is quite evident that RSVP-TE and CD-LDP have almost all the same functionalities, even if they are constructed using different cri- teria. Thus a comparison between the two protocols, which are obviously alternative in a particular implementation of GMPLS, can be useful. The summary of this comparison is mainly derived from Ref. [3]. Transport Protocol: The first difference between CR-LDP and RSVP is the choice of transport protocol used to distribute the label requests. RSVP uses connectionless Convergent Network Management and Control Plane raw IP or UDP encapsulation for message exchange, whereas CR-LDP uses UDP only to discover GMPLS peers and uses connection-oriented