scope:

This European Telecommunication Standard (ETS) describes traffic control and congestion control procedures for the Broadband Integrated Services Digital Network (B-ISDN):

- the main body describes the objectives and mechanisms of traffic control and congestion control (see CCITT Recommendation I.371 [1]);

- examples of application of monitoring functions are given in annex A.

In B-ISDN, congestion is defined as a state of network elements (e.g. switches, concentrators, crossconnects and transmission links) in which the network is not able to meet the negotiated NP objectives for the already established connections and/or for the new connection requests.

In general congestion can be caused by:

- unpredictable statistical fluctuations of traffic flows; - fault conditions within the network.

Congestion should be distinguished from the state where buffer overflow is causing cell losses, but still meets the negotiated Quality of Service (QoS).

Asynchronous Transfer Mode (ATM) layer traffic control refers to the set of actions taken by the network to avoid congested conditions.

ATM layer congestion control refers to the set of actions taken by the network to minimize the intensity, spread and duration of congestion. These actions are triggered by congestion in one or more network elements.