Property

1. format of sending message --> <portS, addS, portD, addD, flag>
2. flag type --> SYN, FIN, URG, PUSH, RESET, ACK
3. SeqNum reset (ISN) --> consecutive number --> change ISN over time
4. ACK的時候 SeqNum 要加一
5. FIN needs the handshake --> 兩次Fin and FinACK --> needs to close two connection
6. Handshake --> no data flow

SW Algorithm

Sender

    --> Last Byte Acked, Sent, Written
    --> Sent - Acked <= AD window
    --> EffectWindwo = AD W - (Sent - Acked)

Receiver

    --> Last Byte Read, Expected (receive in order), receive
    --> MaxReceiveBuffer --> received - read
    --> Advertise W --> MRB - (Expeted-1-Read) ==? Received - Exp +1

SeqNum

AD window 16bit --> 2^16
SNUM --> 2^32 --> 傳送BW太大的時候會低於TTL
Add TimeStamp --> if SeqNum fixed but timestamp are earlier, drop it.

Retransmission - Time out
Solution A

• SampleRTTi = a
• ERTTi = x*ERTTi-1+ SampleRTTi
• Timeout = 2 ERTTi
  
  

Karn/ Patridge --> Drop bad sample , double timeout

Jacobson/Karel --> 考量 deviation

TCP extension
--> timestamps
--> timestamps + SeqNum
--> extend window size
--> selectiveAck --> 不正常的時候才用

Network Model --> Best Effort Services

Resources Allocation

• router and host-centric --> 不同在一個是router分析, 一個是end-host作分析, are not mutually exclusive
• reserved and feedback based --> in advance or not
• window or rate based
• fair index --> 越接近1越公平
• Max-unin fairness --> 先從最壅擠的開始, 滿了之後再來看別的地方
  
  

First Input First Output

• problems --> rate 比較快的可以占滿大部分的頻寬
• Fair Queuing --> round-robin --> 某個queue滿了丟掉部分檔案就好 --> 新問題 --> 別人檔案比較大怎麼半? --> bit-by-bit RR --> 原則 : 小的先傳送 / 舊的先傳送

Congestion control

• AIMD algorithm --> if lost CW = CW/2, else if ACKed CW = CW + (WSS)^2/CW
• Slow Start --> exponential growth --> drop , to 1 --> exponential 成長到一半 --> 線性成長
• performance of platform --> fast retransmit --> 3 duplicate ACK --> retransmission
• fast recovery --> use slow start only on begining

Congestion Avoidance --> predict BW
DEC-bit scheme

• Router --> 偵測packet --> if >= 1, set 1
• Sources --> if lower than 50% of packets own the DEC-bit --> increase, else --> CW =0.875CW
• Can use with AIMD
  Random Early Detection
  Source-based congestion avoidance
  

Information Security

• classical cryptography -> 5 tuple, plaintext set, ciphertext set, key set, encryption set, descryption
• Definition of secure encryption --> 別人看到加密文後無法直接恢復key, 無法用加密文來找出加密公式 (encryption function)
• Shift cipher, substitution cipher, affine (y=ax+b) cipher

Cryptanalysis

• Kerckhoffs’ principle --> EVE knows every thing
• attacker model -> ciphertext only attack/ chosen plaintext attack/ known plaintext attack/ chosen ciphertext attack --> cipher only 最爛

Symmetric Key Model

• k = P{k1, k2, k3.....}
• 用key來加密 --> substitution box 改變順序
• hard to be attack

Authentication

• symmetric key --> 用 public key來encrypt --> 另一方認證
• asymmetric key --> public key, authentication --> private key, signature, verify
• certificate --> signature IDA and Pka, ver (CertA, IDA || PKA