10. TCP Properties
10
● Provides an effective abstraction of a reliable network running over
an unreliable channel
○ in-order delivery
○ data integrity
○ Retransmission of lost data
○ congestion control and avoidance
13. TCP Fast Open (TFO)
● an extension of TCP that helps
reduce network latency
● enabling data to be exchanged
during the sender’s initial TCP SYN.
Ref: https://www.keycdn.com/support/tcp-fast-open
13
14. TCP Fast Open (TFO)
1. The sender sends a SYN packet along with a cookie
request
2. The receiver generates the requested cookie and
sends a SYN-ACK along with the cookie back to the
sender
3. The client caches the cookie for the particular
server’s IP
Ref: https://www.keycdn.com/support/tcp-fast-open
1. The sender sends a packet containing a SYN, TFO
cookie, and data
2. The receiver validates the TFO cookie and sends
back a SYN-ACK and continues to send more data
packets to the client
3. The client sends an ACK back to the receiver
14
15. Enable TFO on Linux
echo 3 > /proc/sys/net/ipv4/tcp_fastopen
# 在/etc/sysctl.conf中添加
net.ipv4.tcp_fastopen = 3
https://www.wikiwand.com/zh-tw/TCP%E5%BF%AB%E9
%80%9F%E6%89%93%E5%BC%80 15
16. Network Congestion
16
● Network congestion in data networking and queueing theory is the reduced
quality of service that occurs when a network node or link is carrying more data
than it can handle. Typical effects include queueing delay, packet loss or the
blocking of new connections. A consequence of congestion is that an incremental
increase in offered load leads either only to a small increase or even a decrease in
network throughput.[1]
● Network protocols that use aggressive retransmissions to compensate for packet
loss due to congestion can increase congestion, even after the initial load has
been reduced to a level that would not normally have induced network
congestion. Such networks exhibit two stable states under the same level of load.
The stable state with low throughput is known as congestive collapse.
17. Congestion Avoidance and Control
17
● Flow Control (傳送端與接收端的事)
● Congestion Control (整體網路的事)
○ Slow Start
○ Congestion Avoidance
24. UDP Properties
24
● UDP 屬於不可靠的協定,因此並無法保證封包一定可以到達目的地
○ No guarantee of message delivery
○ No guarantee of order of delivery
○ No connection state tracking
○ No congestion control
27. HyperText Transfer Protocol Secure
(HTTPS)
27
● Unencrypted communication—via HTTP and other
protocols—creates a large number of privacy, security, and
integrity vulnerabilities.
● With HTTPS
○ protects the integrity of the website
○ protects the privacy and security of the user
○ enables powerful features on the web
■ 取得 user 地理資訊
■ 拍照、錄影
■ 使用者喜好
■ 有可靠的安全性,使用者才敢使用