CSEE 145A Reliable Transmission over Unreliable Channel

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CS/EE 145AReliable Transmission over Unreliable
Channel

• Netlab.caltech.edu/course

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Lab 1

• QA
• What happens if the udp client cannot receive my
  message?
• Shall I receive and print the message on the
  client side?
• I did some extra work
• How do you grade my work?

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Lab 1

• Clients

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Lab 1

• Server (Basic Functions)

5
Lab 1

• Server (Advanced Function 1, Multi-connection)

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Lab 1

• Server (Advanced Function 2, 3-connections)

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Lab 1 Multiplexing

• Multiple Processes
• One process for each active TCP connection, one
  UDP process and one Listening process
• How to tell the main process when the child
  processes finish the TCP connection?
• SIGCHILD (with a handler in the main function)

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Lab 1 Multiplexing

• Multiple Threads
• Similar to Multiple Processes
• pthread_create

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Lab 1 Multiplexing

• Single Process
• Check status of all ports with a single select
  function
• Timeout of the select?

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Topics of this thread

• How does TCP/IP work? (roughly)
• Design and implementation of protocols

Lab 1
Lab 2, 3, 4
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Reliable Transmission over Unreliable Channel (I)
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Reliable Transmission over Unreliable Channel (I)
Stream
Stream
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Reliable Transmission over Unreliable Channel (I)
Stream
Stream
P1, P2,
???
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Reliable Transmission over Unreliable Channel
Goals

• We want the file to be transmitted without any
  error.
• We cannot make any assumption on the channel (The
  packet may be dropped, re-ordered, duplicated in
  the middle).
• We dont want to waste time.
• We dont want to waste bandwidth.

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Reliable Transmission over Unreliable Channel
Difficulties

• How to split a file into packets?
• How to detect errors (packet corruption, packet
  loss, duplication, reordering)?
• How to recover from packets reordering?
• How to recover from loss?
• How to use the bandwidth efficiently?
• How to share the bandwidth fairly?

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Lab 2

• How to split a file into packets?
• How to detect errors (packet corruption, packet
  loss, duplication, reordering)?
• How to recover from packets reordering?
• How to recover from loss?
• How to use the bandwidth efficiently?
• How to share the bandwidth fairly?

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Lab 3

• How to split a file into packets?
• How to detect errors (packet corruption, packet
  loss, duplication, reordering)?
• How to recover from packets reordering?
• How to recover from loss?
• How to use the bandwidth efficiently?
• How to share the bandwidth fairly?

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Lab 4

• How to split a file into packets?
• How to detect errors (packet corruption, packet
  loss, duplication, reordering)?
• How to recover from packets reordering?
• How to recover from loss?
• How to use the bandwidth efficiently?
• How to share the bandwidth fairly?

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Split a file
Sender
Whats inside a packet?
File
File
Receiver
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Inside a packet

• Data
• Header
• Help to reassembly
• Help to detect errors

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(No Transcript)
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One Example TCP Header
Packet Identification
Detect Packet Corruption

• Source http//linux-ip.net/gl/tcng/node39.html

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Sequence Number (Packet ID)
Sender
File
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
File
Receiver
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In case of packet loss
Sender
Why?
File
1
2
3
4
5
6
7
8
1
2
4
5
6
7
8
Please Retransmit packet 3
Receiver
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In case of packets reordering
Sender
Why?
File
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Receiver
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Packet duplication
Sender
Why?
File
1
2
3
4
5
6
7
8
8
1
3
4
2
5
6
7
2
1
2
3
4
6
7
8
5
Receiver
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Sequence Number (Packet ID)

• With the packet ID, the receiver side can recover
  from packet reordering and packet duplication.
• The receiver can detect packet loss. But it has
  to call sender for retransmission.

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CS/EE 145A Lab 2Packet

• Netlab.caltech.edu/course

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Tasks for Lab 2( Not a network programming! ? )

• Assume there is no packet corruption
• Design a packet format that can be used to
  transmit data reliably, over unreliable channels
• Implement conversion from a file to packets, at
  sender side.
• Implement error detection and file reassembly, at
  receiver side.

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Sequence Number (Packet ID)
Sender
File
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
File
Receiver
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Sender

• sender ltfilenamegt ltPacketSizegt
• Read the file specified by ltfilenamegt (The file
  contains English characters and numbers only)
• Convert this file into packets, each packet has
  at most ltPacketSizegt bytes, including header.
• Save each packet to one file, with a file name as
  P0000001.txt, P0000002.txt,

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Receiver

• receiver ltnumber of packetsgt ltPacketSizegt
  ltfilenamegt
• Read the files for packets ( P0000001.txt,
  P0000002.txt)
• WARNING The filenames are always from 1 to
  ltnumber of packetsgt. But packets may not have the
  same filenames assigned by the sender, due to
  packet loss, packet reordering or packet
  duplication.
• Convert the packets into a file, specified by
  ltfilenamegt. Use one character to indicate
  each lost packet.

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Example

• File abcdefg
• Packet Size10 bytes
• Header size 7 bytes
• Payload 3 bytes
• Sender Output 3 files
• P0000001.txt ltheadergt abc
• P0000002.txt ltheadergt def
• P0000003.txt ltheadergt g

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Example

• After reordering (by a program written by TA)
• P0000001.txt ltheadergt abc
• P0000002.txt ltheadergt g
• P0000003.txt ltheadergt def
• Receiver
• Output a file abcdefg

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Example

• After packet loss (by a program written by TA)
• P0000001.txt ltheadergt g
• P0000002.txt ltheadergt def
• Receiver
• Output a file defg

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Tips

• For the unknown commands, use man/ info.
• Be careful of the data structures
• Testing design some small examples to test your
  program
• Start Earlier!

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Submission (due Nov 7th 235959)

• Task sender.c receiver.c readme.txt
• Mailto weixl_at_cs.caltech.edu
• Documents
• How to use the programs compile, run
• Design, testing cases, the problems you met
• Any other comments

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Grading

• Correctness (70)
• Documentation and comments (20)
• Program style (10)

TA Hours

• Tue 2000 2200 JRG 170
• Thu 2000 2200 JRG 170