# Transport Layer ![[Transport layer - Wikipedia#^py4jfc]] **The transport layer is in charge of transferring variable-length data sequences between two hosts**. ^x3iupj The protocol data unit of the transport layer is called a *segment*. We can say that the transport layer is responsible for relaying variable-length data sequences between two hosts. It does this by splitting the data stream into segments which are packaged into internet layer packets. ^52a8xw ## Transport Layer Protocols TCP, UDP, and QUIC are the most commonly used transport layer protocols. ^22htty ![[Transport layer - Wikipedia#^a54g6l]] ![[QUIC - Wikipedia#^m7itwi]] For more information about TCP and UDP see [[Introduction to Networking - TCP and UDP Connections]]. ## Ports **Ports belong to the transport layer. They are used to indicate the host OS which application should be used to process the segment.** ![[Fawn Write-up#^vksftl]] ![[Network Foundations - Network Communication#^itmotj]] For a breakdown of the port range and port number classification see [[Network Foundations - Network Communication]]. ![[Explosion Write-up#^wn0pd1]]