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# System prepended metadata

title: '<center><i class="fa fa-edit"></i> Network Fundamentals: Networking </center>'
tags: [Internship]

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# <center><i class="fa fa-edit"></i> Network Fundamentals: Networking </center>
###### tags: `Internship`
:::info
**Goal:**
To gain a basic understanding of the components behind network technologies. Focus on vocabulary and systems overview.
- [x] How Networks Work

**Resources:**
[Juniper Online Learning Modules](https://learningportal.juniper.net/juniper/user_activity_info.aspx?id=769)
[Pre-Internship Notes by Jessica Chen](https://hackmd.io/@j-chen/SyfRATOmD)
[Daily Report by Lin Yen-Ting](https://hackmd.io/@8KbRc796SnuYA2Dvsvk_BA/SJU_CawIL)
:::
## Module 1: How Networks Work

### Overview
 - Network: conduit that connects two or more computers or other devices
 - Local Area Network (LAN): any group of computers on a single, geographically limited network
     - wired (switch)
     - wireless (access point)
 - Wide Area Network (WAN): a network that connects LANs over large geographic distrances 
- Open Systems Interconnection Reference Model (OSI): Identifies seven layers (network stack) of functionality computers use to communicate over a network 
    - Does not define specific procedures or protocols; theoretical in nature
    - Sending Computer: data flows downward. Protocols are added as headers or footers before passed onto the next layer (encapsulation)
    - Receiving Computer: data flows upward. Protocols are examined and removed layer by layer (deencapsulation)
- Transmission Control Protocol/Internet Protocol Reference Model (TCP/IP)
    - Simple, four layer model 
    - Defines specific protocols at each layer 
    - Mergers top three layers of OSI into Application Layer
    - Transport and Network layers map 
    - Merges lower two of OSI into Network Access Layer
- Five-Layer Model 
    - Combo of OSI and TCP/IP
    - Unmerges Network Access Layer back into Data Link and Physical 
![](https://i.imgur.com/AESPZHJ.png)

### Traversing the Five-Layer Model
- Application Layer: data processed using protocols on sending computer
    - How data should be encoded, compressed, or encrpyted
    - How sessions should be managed
    - Commonly used Application Layer Protocols
        - Simple Mail Transport Protocol (SMTP): most popular for sending email 
        - Hypertext Transder Protocol (HTTP): communications; Internet to WWW
        - File Transfer Protol (FTP): network; computer to another computer (i.e. the Internet)
        - Domain Name System (DNS): associates various info with domain names; serves as phone book for internet; hostnames to IP addresses
    - Letter with no envelope and only sender info
- Transport Layer: specifies Application Layer Protocol on receiving computer
    - Port: Unique numberical indetifier for the protocol
        - address of recipient 
        - multiple programs at same port analogous to multiple people living at same address
    - Destination port number: specifies which Application Layer protocol to be used on receiving computer so incoming data can find the right program
        - name of recipient
    - Source port number: identifies source
        - putting return name
    - Transport Layer Protocols
        - User Datagram Protocol (UDP): simple and fast "best effort" delivery service; commonly used for short messages and time-sensitive data; allows for packet loss with high impact on performance (i.e. DNS, online gaming, Voice over, streaming video)
        - Transmission Control Protocol (TCP): provides delivery notifcation, error checking, recovery procedures; more robust than UDP
            - cuts data into segments to ensure steady flow of data regardless of differences in bandwith
            - ![](https://i.imgur.com/9CouzVG.png)
- Network Layer: recevies data segments and adds a header to create a packet
    - Header contains destination and source IP address; identifies a Transport layer protocol
    - add recipient name and return address
    - ![] (https://i.imgur.com/dr3iTEI.png)
- Data Link Layer: receives packets and adds its won header to each packet to create a frame
    - Headers includes another address (Layer 2 address, physical address, MAC address)
    - Checksum: data integrity check method added to trailer at end of frame
    - Converts data into ones and zeroes for digital communication
    - post office sorting containers
    - ![](https://i.imgur.com/wExWvOC.png)
- Physical Layer: specifications define characteristics (i.e. cabling specs, voltage levels, physical data rates, max transmission distances, physical connectors)
- carries of letters between post offices
:::success
### Module 1 Summary
![](https://i.imgur.com/mEMYRWe.png)
:::
