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Glossary of Terms

What is Layer 4 of the OSI Model?

Layer 4 of the OSI Model Handles Transport Protocols Like TCP and UDP

Layer 4 of the OSI model, also known as the transport layer, manages network traffic between hosts and end systems to ensure complete data transfers. Transport-layer protocols such as TCP, UDP, DCCP, and SCTP are used to control the volume of data, where it is sent, and at what rate.

By providing standardized access to communication services such as connection-oriented communication, reliability, flow control, and multiplexing, layer 4 eliminates the need for the application-oriented layers 5 – 7 to consider the characteristics of the communications network itself. Layer 4 is also responsible for end-to-end error recovery.

Because layer 4 coordinates data transfer without visibility into message content, layer 4 load balancing can make routing decisions without the need to decrypt or inspect network traffic. This makes layer 4 load balancing a quick and efficient approach for packet-level load balancing based on simple algorithms such as round-robin routing.

To route traffic based on media type, localization rules, application, or other criteria where message inspection is required, layer 7 load balancing must be used.

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