Which of the following statements best describe why WRED is useful for networks where the majority of traffic uses TCP? (Select 2 choices.)

A. TCP packets that are dropped must be retransmitted.

B. TCP packets cannot arrive out of sequence.
C. TCP packets have large header sizes.

D. TCP sources reduce traffic flow when congestion occurs.

E. TCP packets must have priority over UDP packets.

Explanation:

Weighted random early detection (WRED) is useful for networks where themajority of traffic uses Transmission Control Protocol (TCP) because TCP packets that are dropped must be retransmitted. Additionally, TCP sources reduce traffic flow when congestion occurs, thereby further slowing down the network.
WRED is a congestion avoidance mechanism that addresses packet loss caused by tail drop, which occurs when new incoming packets are dropped because a router’s queues are too full to accept them. Tail drop causes a problem called global TCP synchronization, whereby all of the TCPsources on a network reduce traffic flow during periods of congestion and then the TCP sources increase traffic flow when the congestion is reduced, which again causes congestion and dropped packets. When WRED is implemented, you can configure different tail drop thresholds for each IP precedence or Differentiated Services Code Point (DSCP) value so that lowerpriority traffic is more likely to be dropped than higher priority traffic, thereby avoiding global TCP synchronization.
WRED does not address headersize. To compress the header of TCP packets, you should implement TCP header compression. Because TCP header compression compresses only the header, not the entire packet, TCP header compression works best for packets with small payloads, such as those carrying interactive data.
WRED does not address the order in which TCP packets arrive. TCP packets can arrive in any order because each packet is numbered with a sequence number. When the TCP packets arrive at their destination, TCP rearranges the packets into the correct order.
Although it is possible for TCP packets to require a higher priority than User DatagramProtocol (UDP) packets, it is also possible for UDP packets to require a higher priority than TCP packets. UDP traffic that requires a high priority includes Voice over IP (VoIP) traffic and realtime multimedia traffic. You should avoid placing TCP and UDP traffic in the same traffic class, because doing so can cause TCP starvation. UDP traffic is not aware of packet loss due to congestion control mechanisms, so devices sending UDP traffic might not reduce their transmission rates. This behavior causes the UDP traffic to dominate the queue and prevent TCP traffic from resuming a normal flow.