 describes user reaction to FECN and BECN. 12.5.6.2.1 End-User Equipment Employing Destination-Controlled Transmitters. End-user reaction to implicit congestion detection or explicit congestion notification (FECN indications), when supported, is based on the values of FECN indications that are received over a period of time. The method is consistent with commonly used destination- controlled protocol suites, such as OSI class 4 transport protocol operated over the OSI connectionless service. 12.5.6.2.2 End-User Equipment Employing Source-Controlled Transmitters. End- user reaction to implicit congestion notification (BECN indication), when supported, is immediate when a BECN indication or a CLLM is received. This method is consistent with implementation as a function of data-link layer elements of procedure commonly used in source-controlled protocols such as CCITT Rec. Q.922 elements of procedure. 12.5.6.3 Consolidated Link Layer Management (CLLM) Message. The CLLM utilizes a special type of frame which has been appropriated from the HDLC protocol. This is the XID frame, commonly called an exchange identification frame. In HDLC it was used just as the name implied, for exchange identification. In frame relay, however, it may be used for network management as an alternative to congestion control. CLLM messages originate at network nodes, near the frame relay interface, usually housed in a router or otherwise incorporated with operational equipment. As mentioned, BECN/FECN bits in frames must pass congested nodes in the forward or backward direction. Suppose that, for a given user, no frames pass in either direction, and that the user therefore has no knowledge of network congestion because at that moment the user is not transmitting or receiving frames. Frame relay standards do not permit network to generate frames with the DLCI of the congested circuit. CLLM covers this contingency. It has DLCI = 1023 reserved. The use of CLLM is optional. If it is used, it may or may not operate in conjunction with BECN/FECN. T