cs441-lecture-20240827

Lecture Notes - CS441

Tuesday, August 27th 2024

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• Previous slides are posted on Canvas
• Important: packet switching and circuit switching
• Very important: OSI Model
  • Application (Data)
  • Presentation (Data)
  • Session (Data)
  • Transport (Segments)
  • Network (Packets)
  • Data Link (Frames)
  • Physical (Bits)
    • Above is a translation for what the OSI Model layers would do
    • 
    • Transport: why we compress: bandwidth, our valued real estate

• Understanding the big picture:

• 

• End-to-end: before we send the data to the other party, we make sure the other party is there
  • Same bandwidth
  • Valid point of communication
• Transport: check if there is any error, cuts into segments
• Cuts into packets
• Physical: 0s and 1s are transported, then on the “other side”, the reverse happens:
  • packets → segments → turns into message → shown to user
  • We’ll cover standard packet size later

• Application Layer

• HTTP
• 
• DoorDash uses Google Maps API
• Example protocol: Security Session

• Session Layer

• Least respected in the whole list
• Like a wedding: wedding holder is thankless hero in holding the wedding, everybody busy thanking the bride/groom
  • Establishing and keeping alive communications link
  • Keeping communications secure
  • Identify session participants
  • Synchronizing dialogue between two nodes
    • Video chat, audio delay during talking
• “Still there”
  • Possibility the connection will continue even if no communication is going on

• Transport Layer

• TCP/IP
  • Suite of protocols
  • NEEDED if you want to connect to the internet
  • Layer 4
  • IP: Layer 3 (Network)
• MTU (Maximum transmission unit)
• Accepts data from Session Layer, they are trusting the Session Layer
• Manage end-to-end data delivery
  • Like Amazon taking pictures of delivered package
  • Acknowledgement of delivery
  • Relying on “Still there → still there → still there”, aka async communication wouldn’t ever end
• Handle flow control
  • Warehouse dumping/loading area; if warehouse is accepting 10 trucks a day and there’s suddenly 15, there’s traffic, aka overflow
  • Stops intake unless processing is finished
• Quality of Service (QoS)
• Has a priority
  • Ex. CFO, CEO has a zoom meeting, thus, bandwidth of an intern watching YouTube is lowered
• Examples of TCP
  • Checksum
  • Segmentation

• Network Layer

• Routers/Switches
• IP
  • IPv4 - $2^{32}$
  • IPv6 - $2^{128}$
  • What is the difference?
    • IPv4 is 32bit, IPv6 is 128bit.
  • What happened to IPv5?
    • Was created to be a protocol for streaming services
    • Don’t ever reuse the same term
    • Example with Operating Systems
      • Windows 7/8/10/11
      • We didn’t have Windows 9 because of Windows 95/98
      • Windows in the system is represented as 9x

• Data Link Layered

• Two sublayers
  • Logical Link Control (LLC)
  • MAC (Media Access Control)

• Physical Layer

• Copper transmission medium
  • Signals issued as voltage
• Fiber-optic cable
  • Signals issued as light pulses
• Wireless transmission medium
  • Signals issued as electromagnetic signals