TDA4VM: Some problems about using EST

hello，

I use SDK8.5，TDA4VH board as sender，using eth3. TDA4VH board as receiver，using eth0. Between two boards, use network cables directly

first， I didn‘t use TAS function，Then I sends 80 bytes of UDP packets through plget. udp port is 5003

It can be seen that the interval between each message is 15us，Then I enable the EST configuration.

ifconfig eth4 down
ifconfig eth1 down
ifconfig eth2 down
ifconfig eth3 down
ethtool -L eth3 tx 3
sleep 5

ethtool --set-priv-flags eth3 p0-rx-ptype-rrobin off

#devlink dev param set platform/c000000.ethernet name switch_mode value true cmode runtime
phc2sys -s clock_realtime -c eth3 -m -O 0 > /dev/null &
ip link set dev eth3 up
sleep 5
tc qdisc replace dev eth3 parent root handle 100 taprio \
num_tc 3 \
map 0 0 1 2 0 0 0 0 0 0 0 0 0 0 0 0 \
queues 1@0 1@1 1@2 \
base-time 0 \
sched-entry S 4 400000 \
sched-entry S 2 200000 \
sched-entry S 1 100000 \
flags 2

Use Plget to send the same message again，the result is

According to the above results, I have the following questions

1. Why is there no configuration EST, the time interval is 15US, after configured EST, the time interval will be 0.8us?

2. Why is the interval between the early stages of the news 0.8, and the later period will become 15us？