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Document ID: 13791
Contents
Introduction
Prerequisites
Requirements
Components Used
Conventions
Definition
Related Information
Introduction
This document provides the definition for the Congestion Notification Function.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
This document is not restricted to specific software and hardware versions.
Conventions
For more information on document conventions, refer to Cisco Technical Tips Conventions.
Definition
ISO 8473, Section 6.17 defines the Congestion Notification Function as follows:
To allow Network Services (NS) Users to take appropriate action when congestion is experienced within the NS provider, intermediate systems may inform the destination network entity of congestion using a flag in the Quality of Service (QoS) Maintenance parameter in the options part of the protocol data unit (PDU) header. The value of this flag is initially set to zero by the originator of the PDU and may be set to one by any intermediate system that processes the PDU to indicate that it is experiencing congestion. The criteria for determining when this action is to be taken are a local matter.
Note: Congestion typically corresponds to unavailability of buffer space to maintain output queues. An appropriate policy for indicating congestion may be based on the depth of the output queue selected for the PDU (according to its destination address or other routing information). When the depth of a particular output queue exceeds a certain proportion of the depth of that queue, an intermediate system starts to discard PDUs. The intermediate system sets the Congestion Experienced flag in the next PDU to be forwarded and may continue to do so until the condition is alleviated.
Related Information
| Updated: Aug 10, 2005 | Document ID: 13791 |