Which three traffic descriptors are typically used as QoS markings for packets or frames entering the network？（）

A.QoS preclassification is only supported on generic routing encapsulation （GRE） and IPsec VPNs
B.QoS preclassification is not required in Layer 2 Tunneling Protocol （L2TP）， Layer2 Forwarding （L2F）， and Point-to-Point Tunneling Protocol （PPTP） VPNs
C.QoS preclassification is supported on IPsec AH VPNs， but not on IPsec ESP VPNs
D.the QoS-for-VPNs feature （QoS preclassification） is designed for VPN transport interfaces
E.with IPsec tunnel mode， the type of service （ToS） byte value is copied automatically from the original IP header to the tunnel header

A.timing
B.queuing
C.differential
D.serialization
E.packetization
F.propagation

A.latency must be kept below 150 ms
B.latency is not a concern as long as jitter is kept below 30 ms
C.voice packets do not require a specific type of queuing
D.voice packets are rather small
E.voice packets require TCP for rapid retransmission of dropped packets
F.voice packets require a fairly constant bandwidth reserved for voice control traffic as well as forthe voice payload