PCI Express System Architecture

The Previous Chapter

This previous chapter discussed Traffic Classes, Virtual Channels, and Arbitration that supports Quality of Service concepts in PCI Express implementations. The concept of Quality of Service in the context of PCI Express is an attempt to predict the bandwidth and latency associated with the flow of different transaction streams traversing the PCI Express fabric. The use of QoS is based on application-specific software assigning Traffic Class (TC) values to transactions, which define the priority of each transaction as it travels between the Requester and Completer devices. Each TC is mapped to a Virtual Channel (VC) that is used to manage transaction priority via two arbitration schemes called port and VC arbitration.