Chapter 2

• OSI Model - Open System Interconnection. It is a framework/basis to understand overall flow of network communication. Not actual implementation. Provides standard that will become the basis for network design
• OSI was Introduced in 1983 and adapted by ISO(International Organization for Standardization) in 1984
• Without OSI - there will be no standard procedure, no compatibility there will be problem sa communication unless same manufacturer ang devices
• 1. Why there’s layered approach  - networking is complex so layered to breakdown into more manageable chunks to isolate parts and will not affect other layer if there’s problem
• 1. Transmission Control Protocol /Internet Protocol - actual implementation of reference model. first to exist. has 4 layers (Application, Transport, Internet, Network Access)
• 1. Encapsulation - process of adding additional info to data as it goes down the layer. sending
• Decapsulation - process of removing info. receiving
• 1. Layer 7 Application Layer - supplies network services to end user application. gives idea how to communicate kay network through protocols. serves as a medium interface between user application and network
  2. Protocols example - HTTP, HTTP, SMTP, POP, FTP
• 1. Layer 6 - Presentation layer - syntax, translation, formation layer. Format in a form na magiging readable in both end. Functions: Translation, Compression and Decompression, Encryption and Decryption
  2. Compression - reducing bits. Decompression to become readable again
  3. Encryption - convert data into unrecognizable code, for security. Decryption babalik sa original text
• Layer 5 - Session Layer creates logical connection between devices. Creates session, reestablishment, maintaining, terminating
• 1. Layer 4 - Transport Layer end-to-end delivery between host. 
  2. data segmentation - breaks into manageable chunk
  3. flow control - both end parties must have same speed para di maoverwhelm si receiver
  4. Protocol - TCP (High reliability) UDP(speed and efficiency)
• Layer 6 Added header: sequence number for order of segment, port number to ensure sa correct session marereceive
• Layer 3 - Network Layer . function : routing - finding the best route or path because data have limited hops lang, logical addressing (IP Address) - to know where network belong ang isang device
• Layer 2 - Data link layer.  allows the upper layer to access the media/cables. acts as a medium between upper layers and physical layer. Controls how data is placed into the media, light pulses, electromagnetic etc.
• Layer 1 - Physical Layer. responsible for the actual physical connection between devices. Data will be converted to bits. Roles: interacting with the actual hardware, determining the signaling mechanism to be used
• 1. Protocol Data Unit(PDU) - information in every layer. Each layer adds header and trailer so, PDU in every layer change
  2. Layer 7, 6, 5 - DATA
  3. Layer 4 - Segment. header: Port numbers and Sequence number
  4. Layer 3 - packet. header: IP Address
  5. Layer 2 - frame. header: MAC Address, trailer: Error checking
  6. Layer 1 - bits