The following is a small part of net packets when I download a file from a FTP server(ip is IPS for short) to a client(ip is IPC for short):
===Begin===
NO. SRC DST Info
1 IPC IPS [SYN] Seq=0
2 IPS IPC [SYN,ACK] Seq=0 Ack=1
3 IPC IPS [ACK] Seq=1 ACK=1
...
2201 IPS IPC [PSH,ACK] Seq=1952593 ACK=1 DataSize(1200bytes)
2202 IPC IPS [ACK] Seq=1,Ack=1953793 DataSize(0) "ACK TO seg2201
2203 IPS IPC [ACK] Seq=1953793,ACK=1 DataSize(1448bytes) "ACK To Seg2202"
2204 IPS IPC [ACK] Seq=1955241,ACK=1 DataSize(1448bytes)
2205 IPC IPS [ACK] Seq=1,ACK=1956689 DataSize(0) "ACK to Seg2204"
2206 IPS IPC [PSH,ACK] Seq=1956689,ACK=1 DataSize(1200bytes) "ACK to Seg2205"
2207 IPS IPC [ACK] Seq=1957889,ACK=1 DataSize(1448bytes)
...
===End===
In fact, I am not very clear about packets from 2201 to 2207. To my own point of view:
(1) IPS sends data 2201 to IPC, and IPC sends ACK 2202 to IPS;
(2) IPS sends "two" data 2203 and 2204 to IPC, and IPC send ACK 2205 to IPS;
...
If my understanding is correct, then I have three questions:
1. Why every two from-server-side data packets ask one Client-side ACK packet, rather than one-to-one? Is it a solid thing?
2.Since 2203 is also a data packet, why it has "ACK To Seg2202" flag?
3.2203 and 2204 are two from-server-side packets,they both have [ACK] flag. But, 2206 and 2207 are also two from-server-side packets, they have [PSH, ACK] and [ACK] separately.What is the difference?
Thanks!
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