Observe the number of packets exchanged between the Linux PCs for each keystroke? Describe the payload of the packets. Use your knowledge of delayed acknowledgements to explain the sequence of segment transmissions. Explain why you do not see four packets per typed character.
What will be an ideal response?
There are three packets exchanged between the PCs for each keystroke. For example, the
packets exchanged when the command ls are typed are shown as follows: Frame 64,65,66 for ‘l’
and Frame 67,68,69 for ‘s’. The payload of the packets are the characters, one at a time.
The first packet Frame 64 is from PC1 (10.0.5.11) to PC2 (10.0.5.22). It has a sequence number
1157588017 and sends 1 byte of payload data, which is character ‘l’. The second packet Frame 65 is from PC2 (10.0.5.22) to PC1 (10.0.5.11). It echoes character ‘l’ and piggybacks the ACK of the first packet, which is shown by the Sequence number 1148870047 and Acknowledgement number 1157588018. The payload of this packet contains a ‘l’. The last packet Frame 66 is from PC1 (10.0.5.11) to PC2 (10.0.5.22). It is an ACK to the echo sent back from PC2 to PC1. So it has an Acknowledgement number: 1148870048 and contains no payload data. TCP waits up to 200 ms before sending the delayed ACK. If during this period there is data to send, TCP sends ACK along with the data. The ACK to the first packet is piggybacked in the second packet, so here only see three packets instead of four.
Frame 64
```
(67 bytes on wire, 67 bytes captured)
Arrival Time: Aug 23, 2003 04:27:02.918459000
Time delta from previous packet: 1.108040000 seconds
Time relative to first packet: 4.620756000 seconds
Frame Number: 64
Packet Length: 67 bytes
Capture Length: 67 bytes
Ethernet II, Src: 00:06:5b:4b:e0:dd, Dst: 00:06:5b:4b:e1:da
Destination: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Source: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.11 (10.0.5.11), Dst Addr: 10.0.5.22
(10.0.5.22)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 53
Identification: 0xf615
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x267d (correct)
Source: 10.0.5.11 (10.0.5.11)
Destination: 10.0.5.22 (10.0.5.22)
Transmission Control Protocol, Src Port: 3115 (3115), Dst Port: 23 (23), Seq:
1157588017, Ack: 1148870047, Len: 1
Source port: 3115 (3115)
Destination port: 23 (23)
Sequence number: 1157588017
Next sequence number: 1157588018
Acknowledgement number: 1148870047
Header length: 32 bytes
Flags: 0x0018 (PSH, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 1... = Push: Set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0x4f14 (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611793, tsecr 1611489
Telnet
```
Frame 65
```
(67 bytes on wire, 67 bytes captured)
Arrival Time: Aug 23, 2003 04:27:02.919209000
Time delta from previous packet: 0.000750000 seconds
Time relative to first packet: 4.621506000 seconds
Frame Number: 65
Packet Length: 67 bytes
Capture Length: 67 bytes
Ethernet II, Src: 00:06:5b:4b:e1:da, Dst: 00:06:5b:4b:e0:dd
Destination: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Source: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.22 (10.0.5.22), Dst Addr: 10.0.5.11
(10.0.5.11)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 53
Identification: 0xc93f
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x5353 (correct)
Source: 10.0.5.22 (10.0.5.22)
Destination: 10.0.5.11 (10.0.5.11)
Transmission Control Protocol, Src Port: 23 (23), Dst Port: 3115 (3115), Seq:
1148870047, Ack: 1157588018, Len: 1
Source port: 23 (23)
Destination port: 3115 (3115)
Sequence number: 1148870047
Next sequence number: 1148870048
Acknowledgement number: 1157588018
Header length: 32 bytes
Flags: 0x0018 (PSH, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 1... = Push: Set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5792
Checksum: 0x4ed5 (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611599, tsecr 1611793
Telnet
```
Frame 66
```
(66 bytes on wire, 66 bytes captured)
Arrival Time: Aug 23, 2003 04:27:02.919256000
Time delta from previous packet: 0.000047000 seconds
Time relative to first packet: 4.621553000 seconds
Frame Number: 66
Packet Length: 66 bytes
Capture Length: 66 bytes
Ethernet II, Src: 00:06:5b:4b:e0:dd, Dst: 00:06:5b:4b:e1:da
Destination: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Source: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.11 (10.0.5.11), Dst Addr: 10.0.5.22
(10.0.5.22)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 52
Identification: 0xf616
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x267d (correct)
Source: 10.0.5.11 (10.0.5.11)
Destination: 10.0.5.22 (10.0.5.22)
Transmission Control Protocol, Src Port: 3115 (3115), Dst Port: 23 (23), Seq:
1157588018, Ack: 1148870048, Len: 0
Source port: 3115 (3115)
Destination port: 23 (23)
Sequence number: 1157588018
Acknowledgement number: 1148870048
Header length: 32 bytes
Flags: 0x0010 (ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0xbaad (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611793, tsecr 1611599
Frame 67 (67 bytes on wire, 67 bytes captured)
Arrival Time: Aug 23, 2003 04:27:03.305393000
Time delta from previous packet: 0.386137000 seconds
Time relative to first packet: 5.007690000 seconds
Frame Number: 67
Packet Length: 67 bytes
Capture Length: 67 bytes
Ethernet II, Src: 00:06:5b:4b:e0:dd, Dst: 00:06:5b:4b:e1:da
Destination: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Source: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.11 (10.0.5.11), Dst Addr: 10.0.5.22
(10.0.5.22)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 53
Identification: 0xf617
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x267b (correct)
Source: 10.0.5.11 (10.0.5.11)
Destination: 10.0.5.22 (10.0.5.22)
Transmission Control Protocol, Src Port: 3115 (3115), Dst Port: 23 (23), Seq:
1157588018, Ack: 1148870048, Len: 1
Source port: 3115 (3115)
Destination port: 23 (23)
Sequence number: 1157588018
Next sequence number: 1157588019
Acknowledgement number: 1148870048
Header length: 32 bytes
Flags: 0x0018 (PSH, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 1... = Push: Set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0x477e (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611831, tsecr 1611599
Telnet
Data: s
Frame 68 (67 bytes on wire, 67 bytes captured)
Arrival Time: Aug 23, 2003 04:27:03.306106000
Time delta from previous packet: 0.000713000 seconds
Time relative to first packet: 5.008403000 seconds
Frame Number: 68
Packet Length: 67 bytes
Capture Length: 67 bytes
Ethernet II, Src: 00:06:5b:4b:e1:da, Dst: 00:06:5b:4b:e0:dd
Destination: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Source: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.22 (10.0.5.22), Dst Addr: 10.0.5.11
(10.0.5.11)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 53
Identification: 0xc940
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x5352 (correct)
Source: 10.0.5.22 (10.0.5.22)
Destination: 10.0.5.11 (10.0.5.11)
Transmission Control Protocol, Src Port: 23 (23), Dst Port: 3115 (3115), Seq:
1148870048, Ack: 1157588019, Len: 1
Source port: 23 (23)
Destination port: 3115 (3115)
Sequence number: 1148870048
Next sequence number: 1148870049
Acknowledgement number: 1157588019
Header length: 32 bytes
Flags: 0x0018 (PSH, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 1... = Push: Set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5792
Checksum: 0x4786 (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611638, tsecr 1611831
Telnet
Data: s
Frame 69 (66 bytes on wire, 66 bytes captured)
Arrival Time: Aug 23, 2003 04:27:03.306153000
Time delta from previous packet: 0.000047000 seconds
Time relative to first packet: 5.008450000 seconds
Frame Number: 69
Packet Length: 66 bytes
Capture Length: 66 bytes
Ethernet II, Src: 00:06:5b:4b:e0:dd, Dst: 00:06:5b:4b:e1:da
Destination: 00:06:5b:4b:e1:da (00:06:5b:4b:e1:da)
Source: 00:06:5b:4b:e0:dd (00:06:5b:4b:e0:dd)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.5.11 (10.0.5.11), Dst Addr: 10.0.5.22
(10.0.5.22)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 52
Identification: 0xf618
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x267b (correct)
Source: 10.0.5.11 (10.0.5.11)
Destination: 10.0.5.22 (10.0.5.22)
Transmission Control Protocol, Src Port: 3115 (3115), Dst Port: 23 (23), Seq:
1157588019, Ack: 1148870049, Len: 0
Source port: 3115 (3115)
Destination port: 23 (23)
Sequence number: 1157588019
Acknowledgement number: 1148870049
Header length: 32 bytes
Flags: 0x0010 (ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0xba5e (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 1611831, tsecr 1611638
```
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