PCI Express System Architecture

Arbitration

Two types of transaction arbitration provide the method for managing isochronous transactions and differentiated services:

• Virtual Channel (VC) Arbitration — determines the priority of transactions being transmitted from the same port, based on their VC ID.

• Port Arbitration — determines the priority of transactions with the same VC assignment at the egress port, based on the priority of the port at which the transactions arrived. Port arbitration applies to transactions that have the same VC ID at the egress port, therefore a port arbitration mechanism exists for each virtual channel supported by the egress port.

Arbitration is also affected by the requirements associated with transaction ordering and flow control. These additional ...