he CLLM frame format has one octet for the cause of congestion such as excessive traffic, equipment or facility failure, preemption, or maintenance action. This same octet indicates whether the cause is expected to be short or long term. Short term is on the order of seconds or minutes, and anything greater is long term. There is also a bit sequence in this octet indicating an unknown cause of congestion and whether short or long term. CLLM octets 19 and above give the DLCI values that identify logical links that have encountered congestion. This field must accommodate DLCI length such as two-octet, three-octet, and four-octet DLCI fields. ENTERPRISE NETWORKS II: WIDE AREA NETWORKS 12.5.6.4 Action at a Congested Node. When a node is congested, it has several alternatives it may use to mitigate or eliminate the problem. It may set the FECN and BECN bits to a binary 1 in the address field and/or use the CLLM message. Of course, the purpose of explicit congestion notification is: To inform the "edge" node at the network ingress of congestion SO that edge node can take the appropriate action to reduce the congestion; or To notify the source that the negotiated throughput has been exceeded; or To do both. One of the strengths of the CLLM is that it contains a list of DLCIs that correspond to the congested frame relay bearer connections. These DLCIs indicate not only the sources currently active causing the congestion, but also those sources that are not active. The reason for the latter is to prevent those sources that are not active from becoming active and thus causing still further congestion. It may be necessary to send more than one CLLM message if all the affected DLCIs cannot fit into a single frame. 12.5.7 Quality of Service Parameters The quality that frame-relaying service provides is characterized by the values of the following parameters. ANSI adds in Ref. 18 that the specific list of negotiable parameters is for further study. 1. Throughput 2. Transit delay 3. Information integrity 4. Residual error rate 