A Frame Relay interface has been configured for adaptive shaping with a minimum rate of 15 kbps. The current maximum transmit rate is 56 kbps. If three FECNs are received over the next 4 seconds, what will be the maximum transmit rate after the last FECN has been received?

A.
7 kbps

B.
10 kbps

C.
15 kbps

D.
28 kbps

E.
37 kbps

F.
56 kbps

Explanation:

User specified traffic shaping can be performed on a Frame Relay interface or sub-interface with the traffic-shape rate command. The traffic-shape adaptive command can be specified to allow the shape of the traffic to dynamically adjust to congestion experienced by the Frame-Relay provider. This is achieved through the reception of Backward Explicit Congestion Notifications (BECN) from the Frame Relay switch. When a Frame Relay switch becomes congested it sends BECNs in the direction the traffic is coming from and it generates Forward Explicit Congestion Notifications (FECN) in the direction the traffic is flowing to.
If the traffic-shape fecn-adapt command is configured at both ends of the link, the far end will reflect FECNs as BECNs. BECNs notify the sender to decrease the transmission rate. If the traffic is one-way only, such as multicast traffic, there is no reverse traffic with BECNs to notify the sender to slow down. Therefore, when a DTE device receives a FECN, it first determines if it is sending any data in return. If it is sending return data, this data will get marked with a BECN on its way to the other DTE device. However, if the DTE device is not sending any data, the DTE device can send a Q.922 TEST RESPONSE message with the BECN bit set.