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Exercício em Tamanho de Janelas na Internet

Você está agindo como um emissor em uma conexão TCP, e você tem 217k bytes de dados para enviar. Na conexão, você concorda que o TCP utiliza o algoritmo de inicialização lenta (slow start) com um terceiro parâmetro, o limitante (threshold):– Tamanho do segmento inicial: 2K.– Parâmetro limitante inicial: 16K.

Destino tem 24K de buffer (janela do receptor).– Usuário destino somente pega os dados quando o buffer

receptor estiver cheio. – Para um buffer parcialmente cheio, a janela de controle de

fluxo é reduzida para o espaço atual restante no buffer.

O tempo expira na 14a mensagem, mas esta é reenviada com sucesso antes de enviar a 15a mensagem.

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Você pode preencher essa tabela?

Depois dessas mensagens…

A janela de congestiona-mento é …

A janela de controle de fluxo é …

O número de bytes dessa mensagem

0 (valor inicial) (valor inicial) (não aplicável) 1 ? ? ? 2 ? ? ? … … … … n ? ? ?

3

2K4K

Mensagem 1

2KQuantidade deixada para enviar:

217K

Janela de Controle de Congestionamento :

Janela Limitante de Congestionamento:

16K

Janela de Controle de Fluxo:

24K

2K215K

22K

4

22K18K

4K8K

215K211K

Mensagem 2

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

4K2K

2K

5

211K203K

18K10K

8K16K

Message 3

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

8K

2K

2K

2K

2K

2K

2K

6

16K

10K0K

203K193K

Message 4

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

10K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

7

0K24K

193K

16K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

8

24K8K

16K18K

193K177K

Message 5

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

16K2K2K

2K 2K

2K 2K

2K 2K

9

8K0K

18K

177K169K

Message 6

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

8K

2K2K

2K 2K

2K 2K

2K 2K

2K 2K

2K 2K

10

0K24K

169K

18K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

11

169K151K

18K20K

24K6K

Message 7

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

18K2K2K

2K 2K

2K 2K

2K 2K

2K

12

151K145K

20K

6K0K

Message 8

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

6K

2K2K

2K

2K 2K

2K 2K

2K 2K

2K 2K

2K

13

0K24K

145K

20K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

14

145K125K

24K

20K22K

4K

Message 9

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

20K2K2K

2K 2K

2K 2K

2K 2K

2K 2K

15

125K121K

4K0K

22K

Message 10

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

4K

2K2K

2K 2K

2K 2K

2K 2K

2K 2K

2K 2K

16

0K24K

121K

22K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

17

121K99K

22K24K

24K2K

Message 11

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

22K2K2K

2K 2K

2K 2K

2K 2K

2K 2K

2K

18

99K97K

2K0K

24K

Message 12

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K 2K

2K 2K

2K 2K

2K 2K

2K 2K

2K

19

0K24K

97K

24K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

20

97K73K

24K26K

24K0K

Message 13

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

24K2K2K

2K 2K

2K 2K

2K 2K

2K 2K

2K 2K

21

0K24K

73K

26K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

22

26K

73K

24K

Message 14

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

24K

23

73K49K

24K0K

26K2K

Re-send message 14

Amount left to send:

Congestion control window:

Congestion threshold:

16K

Flow control window:

24K2K2K

2K 2K

2K 2K

2K 2K

2K 2K

2K 2K

13K

24

0K24K

49K

2K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

25

49K47K

2K4K

Message 15

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

24K

2K

22K

26

47K43K

22K18K

4K8K

Message 16

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

4K2K

2K

27

43K35K

18K10K

8K13K

Message 17

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

8K

2K

2K

2K

2K

2K

2K

28

35K25K

13K

10K0K

Message 18

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

10K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

29

0K24K

25K

13K

Receiver picks up data

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

30

24K11K

25K12K

13K15K

Message 19

2KAmount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

13K

1K

2K

2K

2K

2K

2K

31

12K1K

15K

11K0K

Message 20

2K

Amount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

11K

1K

2K

2K 2K

2K2K

1K

2K

2K2K

2K2K

32

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

2K

1K 1K

0K24K

1K

15K

Receiver picks up data

Amount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

33

1K0K

15K

24K23K

Message 21

Amount left to send:

Congestion control window:

Congestion threshold:

13K

Flow control window:

1K

1K

34

After thismanymessages…

Congestionwindow is…

Flow controlwindow is…

Number ofbytes in thismessage

0 2K 24K (not applicable)1 4K 22K 2K2 8K 18K 4K3 16K 10K 8K4 16K 24K 10K5 18K 8K 16K6 18K 24K 8K7 20K 6K 18K8 20K 24K 6K9 22K 4K 20K

10 22K 24K 4K11 24K 2K 22K

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After thismanymessages…

Congestionwindow is…

Flow controlwindow is…

Number ofbytes in thismessage

11 24K 2K 22K12 24K 24K 2K13 26K 24K 24K14 2K 24K 24K15 4K 22K 2K16 8K 18K 4K17 13K 10K 8K18 13K 24K 10K19 15K 11K 13K20 15K 24K 11K21 15K 23K 1K

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