A.End-to-end delay is the sum of propagation delays，processing delays，serialization delays，and queuing delays.
B.Coast-to-coast end-to-end delay over an optical link is about 20 ms.
C.Processing delay depends on various factors，which include CPU speed，CPU utilization，IP switching mode， and router architecture.
D.Propagation and serialization delays are related to the media.
E.Propagation delay is the time it takes to transmit a packet and is measured in bits-per-second （bps）.
F.Serialization delay is the time it takes for a router to take the packet from an input interface and put it into the output queue of the output interface.

A.class-based weighted fair queuing （CBWFQ）
B.low latency queuing （LLQ）
C.priority queuing （PQ） or custom queuing （CQ）
D.Real-Time Transport Protocol （RTP） header compression
E.TCP header compression
F.UDP header compression