The TCP/IP and OSI Networking Models
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By Cbrzana |
The TCP/IP and OSI Networking Models
| TCP/IP Layer | Example Protocols |
| Application | HTTP, POP3, FTP, SMTP |
| Transport | TCP,UDP |
| Internetwork | IP |
| Network Interface | Ethernet, Frame Relay |
The Application Layer: Provide services to the application software running on a computer. Defines the services the application needs to run, not the application itself. An interface between software and the network itself.
The Transport Layer: Consists of 2 main protocol options -TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Reliable or unreliable transport of data across a network. TCP uses acknowledgements, error recovery, etc.
The Internetwork Layer: IP defines the addresses so each host computer can have different IP address, defines the process of routing (the path to take to get data from point A to point 
.
The Network Interface Layer: Defines how to connect the host computer to the network. Includes cabling, connectors, voltage levels, and protocols used to deliver data (Ethernet, Token Ring, etc).
Data Encapsulation
The process of putting headers and trailers around data on each individual layer.
| Data | Application Layer |
| [TCP]'''[Data] | Transport |
| [IP]'''[TCP][Data] | Internetwork |
| [Link Header] [IP][TCP][Data] [Link Trailer] | Network Interface |
| Transmit Bits | |
Protocol Data Units (PDU)
Frame = All encapsulated data
Packet = IP header, no data link header
Segment = TCP or UDP header, but not the IP header
OSI Layers & Thier Purpose
Layer 7 (Application): Defines interface between communications software and any applications that need to communicate on a network.
Layer 6 (Presentation): Define data formats, encryption, and compression.
Layer 5 (Session): Defines how to start, control, and end conversations (sessions).
Layer 4 (Transport): Error recovery, segmentation of large data blocks into smaller ones, reassembly of small data blocks to large ones.
Layer 3 (Network): End-to-end delivery of packets, logical addressing, defines how routing works.
Layer 2 (Data link): Deliver data across one particular link/medium.
Layer 1 (Physical): Deal with physical characteristics of the transmission medium.
Benefits of OSI Layering
Easier to learn
Easier to develop
Multivendor interoperability (same networking standards)
Modular engineering (one vendor works on one layer, another works on another layer)
Cisco’s Three-Layer Hierarchical Model
Access Layer: Uses switches, point where users are connected..
Distribution Layer: Routes traffic, segments the network, translates between media types.
Core Layer: Switches traffic as fast as possible to the appropriate service
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