OSI Model

7 Layers In Detail

7 Layers In Detail

Layer 7

Layer 7

1. OSI Model, Layer 7, supports application and end-user processes. 
2. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. 
3. Everything at this layer is application-specific. 
4. This layer provides application services for file transfers, e-mail, and other network software services.

WWW browsers, NFS, SNMP, Telnet, HTTP, FTP

Layer 6

1. Provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. 
2. Works to transform data into the form that the application layer can accept. 
3. Formats and encrypts data to be sent across a network, providing freedom from compatibility problems. 
4. It is sometimes called the syntax layer.

encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI

Layer 5

1. Establishes, manages and terminates connections between applications.
2. Sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. 
3. Deals with session and connection coordination.

NFS, NetBios names, RPC, SQL

Layer 4

1. Provides transparent transfer of data between end systems, or hosts
2. Responsible for end-to-end error recovery and flow control. 
3. Ensures complete data transfer.

SPX, TCP, UDP

Layer 3

1. Provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. 
2. Routing and forwarding are functions of this layer.
3. Additional functions include addressing, internetworking, error handling, congestion control and packet sequencing.

AppleTalk DDP, IP, IPX

Layer 2

1. Data packets are encoded and decoded into bits. 
2. Furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. 
3. It is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. 
4. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. 
5. The LLC layer controls frame synchronization, flow control and error checking.

PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay.

Layer 1

1.Conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level. 
2. Provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. 

Ethernet, FDDI, B8ZS, V.35, V.24, RJ45
Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Next Steps

1.How does Browser Work ?.
2. How does Javascript Work ?
3. How does Node Js Work ?
4. How middle ware works ?
5. Before that post a curl and examine what each of those mean ?
6. Post couple of stack trace errors and explain various OSI elements at play.
7. How to apply this OSI model in trouble shooting ?


References Used:
1.https://www.webopedia.com/quick_ref/OSI_Layers.asp#OSI-7
2. https://en.wikipedia.org/wiki/OSI_model
3. https://www.youtube.com/watch?v=sxiRFwQ1RJ4
https://www.sohamkamani.com/blog/2018/05/30/understanding-how-expressjs-works/

https://blog.risingstack.com/your-first-node-js-http-server/

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