ATM WAN Architecture

ATM WAN architecture uses two traffic control parameters and mechanisms for congestion control: Connection Admission Control (CAC) and Usage Parameter Control (UPC). The primary role of these traffic control parameters is to protect the network and the end-users so that network performance objectives are met.

ATM CoS relate quality requirements and traffic characteristics to network behavior parameters and mechanisms. ATM CoS must be declared when the connection with the network service provider is initially provisioned. CoS categories apply to both VCCs and Virtual Path Connections (VPCs); for example, a VP cannot be provisioned as UBR and carry VCs that are provisioned for Constant Bit Rate.

CAC and UPC are used within the ATM switch for each Service Category, guaranteeing the provisioned CoS.

CAC

CAC is the process the ATM network uses during the VP/VC setup to determine whether a connection can be made. If available, network resources (port bandwidth and buffer space) are reserved for the incoming connection at each ATM switch in the connection path. CAC maintains the end-to-end connection QoS of an ATM connection, ensuring the QoS of other network connections is not compromised by the new connection.

UPC

UPC, or policing, is the ATM network process monitoring and controlling the traffic at the UNI. UPC is a requirement for any ATM network supporting multiple CoS. UPC has the primary purpose to protect network resources from malicious and unintentional misbehavior, which can affect the QoS of other established connections. Traffic shaping can be applied to each cell arrival to assess conformance to the traffic contract for each ATM connection. Violations of negotiated parameters are either discarded or tagged for possible discard.