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7.5 Transport Layer 7.6 Network Layer 7.7 Link Layer

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By So Hee Park 2 min read

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💡 Layer 3: Transport Layer

  • Service in charge of breaking information into pieces.
  • Pieces must be less than or equal to 64 KB.

  • Pieces can travel using:

    • TCP
    • UDP
  • The protocol used depends on the application/service.

✅ TCP (Transfer Control Protocol)

  • Reliable communication protocol.
  • Every piece requires confirmation.
  • Confirmations themselves are also confirmed.

☑️ TCP Communication Phases

✔️ 1. Establishment of Connection (SYNC)

  • Machines establish communication first.
  • Uses 3-way handshaking.

☑️ Process

✔️ Step 1

  • Machine 1 requests communication with Machine 2.

✔️ Step 2

  • Machine 2 confirms request.

✔️ Step 3

  • Machine 2 also requests communication.

✔️ Step 4

  • Machine 1 confirms.

☑️ Notes

  • Made of 4 messages functioning as 3.

✔️ 2. Flow

  • Data pieces begin transmission.

  • Every sent piece requires:

    • ACK
    • ACK of the ACK

✔️ 3. Termination (FIN)

  • Communication is closed properly.

  • Both sides:

    • announce termination
    • confirm termination

☑️ Notes

  • Composed of 3 messages.

✅ Protocols that Use TCP

  • FTP
  • SMTP
  • POP3
  • IMAP

☑️ Reason

  • They require ACK confirmations.

✅ UDP (User Data Protocol)

  • Fast but unreliable protocol.

☑️ Characteristics

  • No SYNC.
  • No ACK.
  • No FIN.
  • Data is simply sent.

☑️ Important Note

  • Nobody checks if pieces arrive correctly.

✅ Protocols that Use UDP

  • TFTP

☑️ Reason

  • TFTP does not use ACK confirmations.

✅ Ports to Remember

☑️ Socket

  • Combination of:

    • IP address
    • port

  • Represents:

    • machine + service

☑️ Example

✔️ 192.10.8.6:25

  • Sending an email.
  • Port 25 = SMTP/email service.

💡 Layer 2: Network Layer

  • Layer responsible for mixing communication portions in channels and sending them.
  • Usually handled by routers.

✅ IP (Internet Protocol)

  • Checks whether IP addresses are correct.

✅ ICMP (Internet Control Message Protocol)

  • Warns about communication problems.
  • Detects dangerous events.

☑️ Examples

  • Destination not reachable.
  • Communication delay.

☑️ Ping Command

  • Uses ICMP.
  • Checks whether destination is safely reachable.

✅ ARP (Address Resolution Protocol)

  • Identifies which IP belongs to which MAC address.

☑️ Characteristics

  • Requires huge database containing:

    • machines
    • IPs
    • MAC addresses

☑️ Important Note

  • Modifying database can detach IP from MAC.

💡 Layer 1: Link Layer

  • Checks for transmission errors in bits.

☑️ FCS (Frame Checking Sequence)

  • Redundancy information added to portions.
  • Guarantees correction and error detection.

✅ Layer 1 Techniques

☑️ ECC

  • Error Correction Code.
  • Technique for correcting errors.

☑️ CRC

  • Cyclic Redundancy Check.
  • Technique for detecting transmission errors.

☑️ Important Note

  • Layer 1 does not really use protocols/rules.
  • Mainly based on correction and checking techniques.
DAW bilingual, Computer System
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