Comprehensive and Detailed Explanation:

Key Factors Affecting FTP Performance:

Tail Drop and TCP Synchronization (A)✅

Tail Dropcauses TCPglobal synchronization, reducing FTP speeds drastically when congestion occurs.

Since FTP isTCP-based, packet loss due to tail drop forcesTCP retransmissions, further degrading performance.

Priority Preemption by Video Traffic (D)✅

UDP-based real-time video trafficis often prioritized overTCP-based trafficto avoid jitter and packet loss.

If video traffic hashigher QoS priority, FTP bandwidth may bepreempted, leading toslow speeds.

Incorrect Options:

❌Option B:PQ scheduling typically prioritizes latency-sensitive traffic (VoIP), but this scenario does not mention priority queuing for FTP.

❌Option C:No information about an explicitrate limiton FTP traffic.

????Reference:Huawei HCIE Datacom – QoS and Congestion Control