This selects which specific bundle of ATM traffic-descriptor parameters -- which combination of PCR, SCR, MBS, and tagging behavior -- governs this circuit, a shorthand code for a whole traffic-contract profile rather than the admin configuring each parameter type individually. An admin choosing between profiles like pcr-01-bestEffort and pcr-01-scr-01-mbs-01 is deciding whether this circuit gets a full traffic-descriptor-based admission and policing treatment or a simpler best-effort profile. For example, selecting cktAtmTfdType as pcr-0-01-tag(2) tells the switch to police this circuit using only PCR-based enforcement at both CLP0 and CLP1 levels, tagging out-of-contract cells rather than dropping them outright.