QOS targets of existing services is still met. This is done by expressing each requested Standardisation of broadband started in CCITT during the 1985 - connection in terms of a set of Flow Enforcement Parameters 1988 study period which, by its close had resulted in the choice of (FEPs) and on each link through the network, an admission control ATM as the transfer mode to be used at the broadband User/Net- algorithm decides whether or not to accept the connection. (FEPs work Interface (B-UNI) and as the basic switching mechanism for could be based on estimates of the average and peak bit-rates and all B-ISDN services, this being defined in the first version of expressions of the burstiness.) recommendation I.121. A set of standards for Broadband ISDN is being established in CCITT within Study group XVIII during the current study period 41.3.4.2 Flow conditioning (1989 - 1992) under the I-series recommendations and 13 recom- mendations dealing with ATM parameters are being processed Having 'admitted' a connection, to ensure that actual cell flows under accelerated procedures. Inputs to this process derive, amongst conform to the parameters negotiated during connection admission, other sources, from the regional standardisation organisations flow conditioning procedures are required. Without these, the QOS (ETSI in Europe and T1 committee in North America) and from the of other connections could be disrupted. major European Community communications R&D initiative Flow conditioning has two components: flow enforcement (other- known as RACE (Research in Advanced Communications techno- wise 'Police function' or 'Usage parameter control') which is man- logies in Europe). datory and located just within the network periphery and flow Other CCITT Study Groups are now becoming concerned with throttling, which is optional and located between the source and the broadband, for example SG XI is active in considering the signall- network boundary. (Figure 41.8, Andersen, 1990). Throttling is ing requirements. However SG XVIII r