Introduction to Standardization
Communication between heterogeneous computer systems requires the adoption of standardized and rigorous rules, defined as architectural models.
The OSI Model by ISO
The Open Systems Interconnection (OSI) model, defined by ISO, describes the network architecture by structuring it into seven distinct logical levels.
Level 1 - Physical: Manages the transmission of raw bits on the physical communication channel, dealing with electrical voltages, cables, and radio frequencies.
Level 2 - Data Link (Data Link): Ensures reliable data transfer on the physical channel, managing MAC addresses and error detection.
Level 3 - Network (Network): Deals with packet routing, defining IP address logic and selecting the best path to the destination.
Level 4 - Transport (Transport): Offers end-to-end data transfer, managing flow control and error correction via TCP or UDP.
Level 5 - Session (Session): Establishes, maintains, and synchronizes connections and communication sessions between different network hosts.
Level 6 - Presentation (Presentation): Translates data into standardized formats, dealing with encryption, decryption, and information compression.
Level 7 - Application (Application): Provides services directly usable by the end-user or application programs, such as HTTP, SMTP, and FTP.
The TCP/IP Model
The TCP/IP model, on which today's Internet is entirely based, is a leaner model composed of only four fundamental levels.
Network Access Level: Combines the concepts of levels 1 and 2 of the OSI model, controlling physical hardware and link protocols.
Internet Level: Exactly corresponds to the OSI network level, managing IP addresses and global packet routing.
Transport Level: Identical to the OSI level, provides reliable or fast end-to-end communication channels for applications.
Application Level: Summarizes the functions of levels 5, 6, and 7 of the OSI model, offering direct communication protocols.
Comparison between the Two Models
While the OSI model is a theoretical and academic scheme, extremely rigorous, the TCP/IP model was born in the field and constitutes its practical application.
Conclusions
Both models are fundamental to understanding how bits are transformed into web pages, emails, and complex multimedia streams.