Things You Should Know About PFC

What Is PFC?

PFC, or Priority-based Flow Control, is a pivotal technology in managing network traffic effectively to prevent packet loss and establish intelligent, lossless networks. Enabled within network queues, PFC ensures that queues operate without loss, even amidst congestion. When congestion occurs in a queue on a downstream device, instructions are promptly sent to the upstream device, directing it to cease traffic transmission in the affected queue. This seamless coordination guarantees zero packet loss, maintaining smooth network operation.

Advantages of PFC

Disadvantages of Traditional Flow Control Technology

The most basic flow control technique is the Ethernet pause mechanism defined in IEEE 802.3. When a downstream device detects that its receiving capabilities are lower than the transmission capabilities of its upstream device, it sends a pause frame to the upstream device, requesting the upstream device to stop sending traffic for a while.

However, the disadvantage is that the Ethernet pause mechanism stops all traffic on the link (for the entire interface). This in turn affects link sharing, which is critical to the actual service. Link sharing requires:

• One type of burst traffic cannot affect the forwarding of other types of traffic.

• There is too much traffic of a certain type in the queue and it cannot occupy the buffer resources of other types of traffic.

Advantages of PFC

Compared with traditional flow control methods, PFC can deal with network congestion and data loss more effectively. Traditional technologies often use a general pause mechanism, causing data transmission across the entire network interface to stagnate, affecting service continuity and efficiency. PFC instructs the upstream device to pause transmission so that traffic transmission is stopped only when needed, thereby avoiding unnecessary stagnation and ensuring network continuity. In addition, PFC can also optimize the service quality of the network through priority sorting and dynamic management, ensure the priority transmission of key data, and improve the reliability and performance of the network.

How Does PFC Work?

PFC, or Priority-based Flow Control, operates by managing traffic flow across network interfaces in a targeted and flexible manner. Illustrated in the setup, eight priority queues on the transmit interface of DeviceA correspond to eight receive buffers on the receiving interface of DeviceB. In the event of congestion in a receive buffer on DeviceB, a backpressure signal labeled "STOP" is sent to DeviceA, signaling it to halt traffic transmission in the corresponding priority queue.

PFC working mechanism

One of the key advantages of PFC lies in its ability to reconcile conflicts between the Ethernet Pause mechanisms and the need for efficient link sharing. Unlike traditional methods that halt traffic across entire interfaces, PFC precisely controls traffic within specific priority queues, allowing for more granular management. Moreover, PFC offers the flexibility to pause or restart individual queues without disrupting traffic flow in other queues. This capability facilitates the sharing of a single link among various types of traffic, promoting efficient utilization of network resources.

The Role of PFC in Switches

PFC (Priority Flow Control) is a mechanism used for traffic control in network switches, commonly employed in Ethernet switches. Its purpose is to ensure that during network congestion, the transmission priority of critical data flows is protected, thereby enhancing network performance and reliability.

Specifically, PFC addresses packet loss issues stemming from congestion. Traditionally, when the output buffers of switch ports are full, packet loss is alleviated by either discarding packets or using random packet drop methods. However, for certain applications such as data transmission in Storage Area Networks (SANs), losing any packet can lead to severe data loss or performance degradation.

PFC enables the sender to temporarily pause data transmission, allowing the data in the buffer to be processed rather than discarding packets outright. PFC adheres to the IEEE 802.1Qbb standard, defining priorities through the Priority Code Point (PCP) field in Ethernet frame headers. PFC control frames are exchanged between switches to implement this mechanism. Thus, when congestion is detected by the receiver, PFC control frames can be sent to the sender, requesting the suspension of data transmission.

How FS Can Help

In conclusion, Priority-based Flow Control (PFC) stands out as a crucial technology in modern networking, effectively managing traffic flow to prevent packet loss and establish intelligent, lossless networks. By precisely controlling traffic within specific priority queues, PFC ensures seamless coordination, guaranteeing zero packet loss even amidst congestion. Its ability to reconcile conflicts between flow control mechanisms and the need for efficient link sharing makes PFC an indispensable tool for optimizing network performance and reliability.

As a leading communication company, FS provides data center switches that support PFC functionality, ensuring our customers have access to cutting-edge solutions for their networking needs. With FS, you can trust in the reliability and efficiency of your network infrastructure, backed by advanced technologies like PFC to meet the demands of today's dynamic digital landscape.