• OSI Model consists of 7 layers.

  • physical , data link, network, transport, session, presentation, application

  (Please Do Not Teach Students Pointless Abbreviation!)

  

  Source : https://www.udemy.com/course/networkplus/

Layer 1) Physical

Bits, Medium, Wiring standards, Physical topology, 
Synchronizing bits, Bandwidth usage, Multiplexing strategy 

• physical and electrical characteristics.

How are bits represented on the medium?

1. Electrical voltage or light
2. Current State
3. Transition Modulation

How are the cables wired?

• 2 std inside of network.
• TIA/EIA-568-B is standard wiring for RJ-45 cables and ports (?)
• cross over cable : A std - Bstd
• straing-thru cable : B std - B std or A std - A std

How are the cables connected?

• add pros/cons on the picture

source : https://www.conceptdraw.com/How-To-Guide/network-topologies

How is communication synchronized?

• Asynchronous : uses start/stop bits to notify transmission occured.
• Synchronous : uses a reference clock to coordinate the transmission

How is bandwidth utilized?

• broadband : like TV channel. we only pulled out the ones we wanted
• baseband : like telephone, using all of the bandwidth allocated to that phone line, reference clock. (example of synchronous communication)

Layer 1 Devices

• Cables : Ethernet, Fiber optic
• Radio frequencies : Wi-Fi, Bluetooth
• Infrastructure devices : Hubs, Wireless Access Points, Media Converters

Layer 2) Data Link

MAC, Physical addressing, Logical topology, Method of Transmission, LLC, Flow control

• consists of 2 sublayers, Media Access Control and Logical Link Control.

• data –(Data Link)–> frames

  

  (source : https://www.youtube.com/watch?v=Ilk7UXzV_Qc)

• Error detection/correction

• identification of network devices with an address (MAC)

Media Access Control (MAC)

• Many stations vying each other to occupy the cable. This is called media access, and there are several strategies.

  • Carrier Sence/Multiple Access with Collision Detection (CSMA/CD)

    If the device uses this method, then it first detect the signal on the wire(a carrier). Signal on the wire means that someone is already transmitting the data.

    1. It detects a signal on the wire.
    2. If there is no signal, then it sends signal. If other device did the same , then collision happens.
    3. After certain amount of time, It sends its signal again.

  • Token Passing

    1. The first computer turned on creates a token.

    2. The token passes around till it finds computer with data to send.

    3. The token with data has the address. Each station checks the address in the token.

    4. If the address in the token matches its own address, then it receives data, and modifies the token that it has received the data.

    5. The token is sent back to the original sender, and finally becomes free.

       No collision occurs!

  • Carrier Sense/Multiple Access with Collision Avoicance(CSMA/CA)

    This method is similar to CSMA/CD method. The difference is that It sends a request to send(RTS) packet and wait for clear to send(CTS) before sending.

    (I wonder if does have a collsion issue. It seems like, if it has a bad luck, it might happen.)

• Physical addressing. protocol-independent address

  • First 24-bits : the vendor code
  • Second 24-bits : a unique value
  • Hexadecimal number system

source : https://www.semanticscholar.org/paper/A-Study-of-MAC-Address-Randomization-in-Mobile-and-Martin-Mayberry/abae19306dfe311a2301d4cd015003414513e72a

• Logical topology

  • dictates the way the information flow. Types are the same as physical topology

  • Three main methods.

    • Contention :

      Stations seek for the chance to transmission of data. If collision occurs, the stations try to send data again.

    • Polling :

      Central device polls each device whether it has data to send or not. No collision problem.

    • Token passing :

      Token is a special data packet. If the device has a token, then it can transmit its data. No collision problem.

Logical Link Control (LLC)

• Acknowledgement of receipt of a message.
• Flow control : controls the load of data to optimize the performance.
• Error control : sends again if the data is not received or coruppted.

How is communication synchronized?

(learn more to understand fully)

• Isochronous :
  • create time slots by using a common reference clock source.
  • Less overhead(?) than other two method.
• Synchronous :
  • uses clocking method to indicate start/end of frames.
• Asynchronous :
  • uses their own internal clocks and use start/stop bits.

Layer 2 Devices

• Network Interface Cards (NIC)
• Bridges
• Switches

Layer 3) Network

Logical address, Switching (not SWITCH), Route discovery and selection, Connection services, Bandwidth usage, Multiplexing strategy 

• forward traffic with logical address such as IP Address.
• Every device has an assigned address by factory. This

Logical address

• Internet Protocol(IP) is dominantly used. (IP v4, IP v6)

How should data be forwarded or routed?

(learn more to understand fully)

• Packet swtiching (routing) : Data is divided into packets and forwarded.
• Circuit switching : Dedicated communication link is established between two devices
• Message switching : Data is divided into messages.

? what is the difference between Packet switching and Message switching?

Static routing : The network admin manually updates the router’s routing tables.

Dynamic routing : uses route discovery protocols to talk to other routeres.

Route Discovery and Selection

Routing table, Routing Protocol

• A routing table contains info about where to forward a packet based on destination IP address.
• Manually configured as a static route or dynamically through a routing protocol (RIP, OSPF, EIGRP) –> ?

Connection Services

• Layer 3 augment Layer 2 to improve reliability
• Flow control, Packet reordering (how does it work in detail? with LLC in layer 2?)

Internet Control Message Protocol (ICMP)

• sends error messages and operational info about an IP destination
• Used in troubleshooting (ping and traceroute)

Layer 3 Devices/Protocols

• Routers
• Multilayer switches
• IPv4 protocol / IPv6 protocol / Internet Control Message Protocol (ICMP)

Layer 4) Transport

TCP/UDP, Windowing, Buffering

• The start of upper layer.

Transmission Control Protocol (TCP)

• Connection-oriented protocol

• If segment is not sent well, then protocol will resend segment

• Acknowledgements recevied for succssful communications

• Three way handshake

  

• Source : https://www.udemy.com/course/networkplus/

User Datagram Protocol (UDP)

• Connectionless protocol
• Even though data is not sent well, sender does not know
• Good for audio/video streaming

Source : https://www.udemy.com/course/networkplus/

Windowing

• It helps client to send the right amount of data in each segment by evaluating how often retransmisions occured.

(Ex. Downloading Videos. The downloading speed keeps changing)

Buffering

• If bandwdith is not available, Device allocate memory to store segements.
• If bandwidth is available, it transmits the contents of the buffer.
• If the buffer overflows, then segments will be dropped.

Layer 4 Devices/Protocols

• TCP
• UDP
• WAN Accelerators
• Load Balancers
• Firewalls

Layer 5) Session

Setting up session, Maintaining sessions, Tearing down sessions

• Session layer is different from Transport layer in that it sees a bigger picture, and focus on entire conversation rather than one sentence.

Setting up a Session

• Assign numbers to session to identify them
• Negotiate services needed for session and who begins sending data

Maintaining a Session

• Transfer the data (respond/request)
• Restart a disconnected session

Tearing Down a Session

• After the transfer is over, the session ends with mutual agreement.

Layer 5 Devices/Protocols

• H.323
• NetBIOS

Layer 6) Presentation

Encryption, Data compression, network redirectors, Data format

• It converts data format for both upper and lower layer, so they can understand each other, like a translator.

Data Formatting

• Formats data for proper compatibility between devices

• Ensures data is readable by receiving system.

  • Most standard computer systems use the ASCII, but some other computer uses EBCDIC.

    Protocol at the transport layer can translate between the two.

Encryption

• Used to scramble the data in transit to keep it secure from prying eyes

• TLS to secure data between your PC and website (lock shows that it is encrypted)

  

Layer 6 Protocols

• HTML, XML, PHP, JavaScript, …
• ASCII, EBCDIC, UNICODE, …
• GIF, JPG, TIF, SVG, PNG, …
• MPG, MOV, …
• TLS, SSL, …

Layer 7) Application

Application services, Network management activities

• Provides application level services
• Layer where the users communicate with the computer (not notepad, not word, not eclipse…)

Application Services

• Application services unite communicating components from more than one network application
• Examples
  • E-mail (POP3, IMAP, SMTP)
  • File Transfer Protocol (FTP, FTPS)
  • Remote Access (TELNET, SSH)
  • Web Browsing (HTTP, HTTPS)
  • Domain Name Service (DNS)

Network management activities

• Client/server processes
• States the services they offer on the network (Printers ,File servers)
• Examples
  • Simple Network Management Protocol (SNMP)

• Mistakes
  • did not check the range of i in while statement.

Resources :

1. First Person View PC BUILD Guide!(POV)- Linus Tech Tips
2. https://www.wired.com/story/how-to-build-a-pc/
3. Hands-on practice

Components

Motherboard, CPU, Memory, Power supply, GPU, Storage

Motherboard : The follow a standard layout but can have different configurations depending on the use case.

Q) So if I wanted to build a gaming or AI specific computer, would I need to choose a different motherboard for each purpose?

CPU : Central Processing Unit, this is where the numbers get crunched and is what is core to a computer, it is socketed directly to the motherboard.

Memory : RAM (Random Access Memory, not REM, that is Rapid Eye Movement.)

PSU : Power Supply, it converts AC power to DC power to run the components of your computer.

GPU : Graphics Processing Unit, it handles the processing of visual aspects of a game or works as high core processing for AI

Storage : The two main types are HDD (Hard Disk Drive - mechanical) and SSD (Solid State Drive - no moving parts) and can vary in capacity and form factor.

I/O Devices : Such as a mouse, keyboard, monitor and so on, the devices used to interface with the computer.

Before getting started,

Connect yourself to a grounded power supply part using an anti-static strap. It will prevent ESD sensitive components from getting damaged.

** ESD : Electrostatic-Sensitive Device

Most computer components only require a size 2 Philips-head screwdriver to install.

Learning from YT video

1. Place the CPU in the CPU socket making sure it’s in the correct orientation.

   

2. Install the two RAM modules and note the notch for correct installation, after this install the M.2 SDD and screw it down.

   

3. When installing the cooler check to see if thermal compound has been pre-applied, if not apply only a pea sized amount on the center of the CPU, the pressure from installing the cooler will spread the compound. If you have an overclockable CPU a cooler that is higher rated would give better results when doing so.

1. The motherboard has a CPU fan pin which the cooler fan needs to be connected to, some computers will not boot if no CPU fan is detected.

   

2. The power supply should come with all the power cables necessary to run the computer.

3. If you plan to install a lot of fans you would need to have a fan splitter and to connect SATA power to the splitter.

   

4. Install the motherboard into the case. but before this, make sure to put the IO shield first into the case.

   

5. Once the motherboard has been screwed in securely you can start to plug in all the necessary power cables.

   

6. Take note of which cables are used for which devices.

7. Insert SATA SSD into the case, depending on the mount it should slot in or would need to be screwed in. Then connect the SATA data cable to motherboard and SSD.

8. Install the power supply and connect all the needed power supply cables to the motherboard.

   

9. PCI express power connector -> connects the graphics card and power supply

   

10. SATA power (SSD, hard drive, integrated RGB controller)

11. Put the graphics card in the PCI slot on the motherboard. Note the graphics card has it’s own IO shield so remove the IO plates corresponding to where the graphics card will be.

    

** PCI express : an interface that connects internal expansion cards such as graphics cards, sound cards, Ethernet and Wi-Fi adapters to the motherboard. source

** Overclocking : Overclocking is the action of increasing a component’s clock rate, running it at a higher speed than it was designed to run. This is usually applies to the CPU or GPU, but other components can also be overclocked. source

Try to learn about what is ipv4, ipv6, CIDR, OSI Model, what are ports, Switch vs Router vs firewall

그래프 기초

Direct-Address Tables

알고리즘 설명

알고리즘 설명

알고리즘 설명

힙의 형태 : 완전 이진 트리에 가깝다.