Cisco CCNA CCNP Certification Exam Frame Relay BECNs and FECNs
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Understanding Frame Relay BECNs and FECNs for Cisco Certification
Overview
If you're preparing for the Cisco CCNA or CCNP certification exams, comprehending Frame Relay concepts like BECNs and FECNs is crucial. These elements are not only vital for exam success but also for effectively managing congestion in today's networks.Introduction to BECNs and FECNs
In the context of Frame Relay networks, BECNs (Backward Explicit Congestion Notifications) and FECNs (Forward Explicit Congestion Notifications) play key roles in handling congestion. They enable networks to dynamically adjust their transmission rates to maintain efficiency.FECN Explained
The Forward Explicit Congestion Notification (FECN) bit, initially set to zero, is marked as 1 by a Frame Relay switch (DCE) if congestion is detected. This alteration informs the receiving router (DTE) that congestion has been encountered along the path.Understanding BECN
Conversely, if congestion is present in the opposite direction, the Backward Explicit Congestion Notification (BECN) is set to 1. The BECN is crucial as it signals the sender to slow down its data transmission rate.Practical Example
Consider a scenario where data is sent from Kansas City to Green Bay. If congestion occurs, the Frame Switch sets the FECN bit to 1. Green Bay then informs Kansas City of the issue by sending return frames with the BECN bit set. Upon receiving these frames, Kansas City knows to reduce its transmission speed.Adaptive Shaping with BECN
BECN Adaptive Shaping allows a router to adjust its transmission speed based on incoming BECN notifications. If frames from Green Bay arrive with a BECN bit set, Kansas City will reduce its data rate. As congestion clears, and BECNs cease, the router will increase its transmission speed once more.Configuration
To enable BECN Adaptive Shaping in your network, use the following commands:```plaintext
KC(config)
int s0
KC(config-if)frame-relay adaptive-shaping becn
```Monitoring with Show Frame PVC
To track frames with BECN and FECN bits, execute the `show frame pvc` command. This will display detailed statistics about packet flow and congestion indicators:```plaintext
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