FECN and BECN are congestion avoidance techniques used in network communication to manage traffic flow and prevent network congestion.
Understanding FECN and BECN
As described in the reference, both FECN and BECN serve as signaling mechanisms within a network. Their primary goal is to notify different points in the network about the presence of congestion, allowing adjustments to be made to reduce traffic load and prevent further issues.
BECN (Backward Explicit Congestion Notification)
- Role: BECN is used to notify the sender that congestion has occurred along the path the data is taking.
- Mechanism: When a network device (like a router or switch) experiences congestion on a link, it can mark frames or packets with a BECN signal on traffic traveling backward towards the source.
- Purpose: Upon receiving a frame marked with BECN, the sending device understands that there is congestion ahead and should reduce its transmission rate or take other congestion control measures.
FECN (Forward Explicit Congestion Notification)
- Role: FECN is used to inform the receiver of the traffic that congestion has occurred on the path from the sender.
- Mechanism: Similar to BECN, a network device experiencing congestion can mark frames or packets with a FECN signal on traffic traveling forward towards the destination.
- Purpose: When the receiving device gets a frame marked with FECN, it learns about the congestion. While the receiver doesn't typically adjust the sender's rate directly, it can use this information, potentially relaying it back to the sender through a higher-layer protocol or simply being aware of potential delays or packet loss due to the network condition.
Key Differences
The core distinction between BECN and FECN lies in who they explicitly notify about congestion:
| Feature | BECN | FECN |
|---|---|---|
| Notified Party | Sender (Source) | Receiver (Destination) |
| Direction | Signal travels backward to the sender | Signal travels forward to the receiver |
| Primary Action | Triggers sender to reduce rate | Informs receiver about congestion status |
Why are they used?
Networks can become congested when the volume of data traffic exceeds the capacity of network links or devices. This leads to increased delays, packet loss, and reduced overall performance. Techniques like FECN and BECN provide explicit signaling methods, allowing network devices and end systems to react proactively to congestion signals rather than waiting for packet loss to occur (which is implicit congestion notification). This proactive approach helps in maintaining better network stability and performance.
Historically, these techniques were notably used in Frame Relay networks, although the general concepts of explicit congestion notification exist in various forms in modern networking (like ECN in IP).
These techniques are fundamental examples of how networks use signaling to manage shared resources effectively.
