RECITATION 3

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RECITATION 3

• Remind CEREAL account!!!

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Project 1

• Provide TorrentFileHandle.java
• Important info from .torren file
• url of the tracker
• Name of file
• Length of file
• Pieces lthash1,hash2,.hashngt
• Piece length

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Overall Architecture
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Overall Architecture
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Overall Architecture
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Overall Architecture
Tracker
Web Server
Web page with link to .torrent
request
C
A
request
Peer Seed
Peer Leech Downloader US
B
Peer Leech
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Overall Architecture
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Project 1 Basics (cont'd)

• ? Communicate With Peer
• Handshake
• ltpstrlengtltpstrgtltreservedgtltinfo_hashgtltpeer_idgt
• General Messages
• ltlength prefix 4B decgtltmessage ID1B
  chargtltpayloadgt
• Request
• lt0013gtlt6gtltindexgtltbegingtltlengthgt
• Piece ltlength prefixgt is 0009X and message ID
  is 7. The payload is as follows
  ltindexgtltbegingtltblockgt
• X is block size

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Sample Question SWITCHING

• Considering a small network of four hosts and
  three links as depicted in the figure below. A
  1MB message is to be sent from A to D. The
  bandwidth of links is 0.8 Mbyte/second.
  Propagation delays of the links are negligible.
• Host A ----- Host B------ Host C----------Host D
• (A). Assume that circuit switching is used and
  the total circuit set-up time is 100 ms, what is
  the time to send the message from A to D?
• (B). Assume that message switching is used and
  queuing delays are negligible, what is the time
  to send the message from A to D?

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Sample Question SWITCHINGPIPELINING

• Considering a small network of four hosts and
  three links as depicted in the figure below. A
  1MB message is to be sent from A to D. The
  bandwidth of links is 0.8 Mbyte/second.
  Propagation delays of the links are negligible.
• Host A ----- Host B------ Host C----------Host D
• (C). Assume that packet switching is used, packet
  size is 240 bytes and header size is 10 bytes,
  what is the time to send the message from A to D?
  (WITH PIPELINING)

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Message Switching (contd)
Header
Transmission Delay
Time
Queueing Delay
A
B
C
D
Routers/switches
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Pipelining Parallelogram for packet switching
Host A
Switch 1
Switch 2
Host B
Packet 1
Packet 2
Packet 3
Time
Packet 4
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Sample Question Performance Analysis

• For parts A and B, assume host A is connected to
  B via a point-to-point duplex link which has a
  data rate of 1 Mbps and propagation delay of 10
  msec.
• HOST A------------------------------HOST B
• Host A has a large amount of data that must be
  reliably sent to Host B. Assuming Stop-and-Wait
  protocol is used to assure reliable delivery, the
  data frame size is 1000 bytes each, and the ACK
  frame size is 64 bytes.
• (A). Assuming that Host B takes 0 time to process
  an incoming data and send an ACK frame back to A,
  what is the smallest time the retransmission
  timer can be set to at Host A which eliminates
  unnecessary retransmissions?
• (B). Assuming there are no transmission errors,
  what is the link utilization in the direction
  from A to B?
• Hint
• Link utilization the time to send a frame
  without delay and ACK/ the time in A (OR the time
  to send a frame from A to B the time an ACK
  frame back to A)
• Link utilization size of a frame/ (the time to
  send a frame from A to B the time an ACK frame
  back to A)
• (C). A new, different channel has a bit rate of
  4 Kbps and a propagation delay of 20 msec. For
  what range of frame sizes does stop-and-wait
  protocol give an efficiency of at least 50
  percent?

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MAC address

• Network Interface Card (NIC)
• Each NIC has its own MAC address , it is stored
  on the chip!!
• Length of MAC 48 bites 6 bytes
• For examples 00C17101ABF0
• Prefix Company ID 3Com, Netgear
• Postfix Serial Number
• Command to show MAC ifconfig, ipconfig

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Ethernet Frame Structure
MAC Dest. address MAC Source address Type DATA . CRC

• Type(2 bytes) specifies the network layer
  protocol IP or Novel IPX or ARP or RARP
• CRC check sum
• Broadcast
• MAC Broadcast Address FFFFFFFFFFFF
• Host A sends a msg to host B
• MAC dest MAC B, MAC src MAC A

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HUB vs. SWITCH
Ethernet Frame
SWITCH can learn the MACs of all nodes
MAC A -gt MAC C
DATA
HUB
SWITCH
B
A
C
A
B
C
B can CAPTURE the packet from A to C !!!!
B CANT capture the packet from A to C !!!!
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How to build your own network!

• NICs
• HUB or SWITCH !!!
• 2 machines can be connected by using crossover
  cable!!!
• Assign IP address
• Static
• Dynamic

Crossover cable