1. Negotiation of traffic contract before transmission 
 Traffic contract involves traffic parameters and QoS parameters
 
 2. Traffic control mechanisms (enforcement of contract)
 Connection Admission Control (CAC): the network decides if a connection
 request can be accepted
 Usage Parameter Control (UPC): the network detects violations of
 negotiated parameters and takes appropriate action (e.g. cell discarding
 or cell tagging => CLP bit) 
 Feedback control (flow control
 of ABR service)