network_models

OSI

• Open System Interconnection model
• It is a general model and has 7-layers
  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data Link
  • Physical

Layer	Name	Devices	Protocols	PDU
7	Application	About: What interpreted characters do Using ASCII in L6 you interpret GET /simple which will mean GET request on /simple endpoint	HTTP, SMTP, FTP DHCP, DNS, Telnet
6	Presentation	About: Interpreting 1s and 0s Encoding/Decoding for example ASCII, Encryption/Decryption, Compression/Decompression	TLS, SSL, MIME
5	Session		RPC???, NetBIOS
4	Transport	About: Service to Service delivery Achieved using Ports+Other info Data streams is routed to correct program	TCP, UDP	Segment
3	Network	About: End-to-End delivery Routers, Hosts, Anything with IP Bridge and other L1, L2 devices may have IP address but not required for its operation	IP Address ICMP	Packet
2	Data Link	About: Hop-to-Hop delivery NIC Card, WiFi Access Card, Switch, Bridge Routers have multiple NICs	MAC address - Ethernet (802.3) - WiFi (802.11) ARP	Frame
1	Physical	About: Transporting Bits Devices: Repeaters, Hubs, WiFi Wires and Cables: Ethernet, Fiber, Coaxial	Ethernet (IEEE 802.3), Wifi (IEEE 802.11), USB, Infrared	Frame

• Notes
  • IEEE 802.3, IEEE 802.11, USB are all specs and contain multiple protocols that can span multiple layers in OSI model
  • routers or in general other devices may work with multiple layers, OSI model is just conceptualization not rigid rules
  • TCP and UDP protocols have ports in their specification which is used to distinguish different data streams with programs
  • Layer 5, 6, 7 are considered universally as Application Layer
  • Layer 1, 2 are combined as Network Access Layer in TCP/IP-5 layer model

TCP/IP

• protocol based model
• were built to offer highly reliable end-to-end data delivery over an unreliable network, such as the internet.
• incorporates the rules created when the internet developed
• The names of layers are not consistently used everywhere
  • Application Layer
  • Transport Layer
  • Internet Layer
  • Network Access Layer

Common TCP/IP Layer Names

• 4 Layer Model

Layer	Most Common Name	Alternate Names
4	Application	Application/Presentation
3	Transport	Host-to-Host
2	Internet	Network, Networking
1	Network Access	Data Link, Physical, Network Interface, Link

• 5 Layer Model

Layer	Most Common Name
5	Application
4	Transport
3	Network
2	Data Link
1	Physical