Suggest an editImprove this articleRefine the answer for “What is the transport layer responsible for in an end-to-end connection?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)In an **end-to-end connection**, the transport layer is responsible for **the entire logic of transferring data between two end applications** - from sending to correct receipt. In simpler terms, the transport layer makes sure data reaches from one program to another correctly, in the right order, and at the right speed (when required). **Key point:** transfer control happens at the ends of the connection, the network in between stays as simple as possible, and reliability and order are the responsibility of the transport layer (L4).Shown above the full answer for quick recall.Answer (EN)Image**In an end-to-end connection**, the transport layer is responsible for **the entire logic of transferring data between two end applications** - from sending to correct receipt. In simpler terms: **the transport layer makes sure data reaches from one program to another correctly, in the right order, and at the right speed (when required)**. --- ## What exactly the transport layer is responsible for (end-to-end) ### 1. Identifying applications (ports) The transport layer: - uses **ports** - precisely determines: - which application the data came from - which application it is intended for Without this, end-to-end communication between programs would be impossible. --- ### 2. Establishing and closing the connection (TCP) If TCP is used: - a connection is established before the transfer - it is closed correctly after the exchange ends This happens **between the end nodes**, not inside the network. --- ### 3. Reliable delivery (TCP) The transport layer provides: - acknowledgment of received data - retransmission of lost segments - protection against duplicates Important: - all of this happens **only between the sender and the receiver** - routers do not take part in this --- ### 4. Order of data delivery The transport layer: - numbers segments - assembles them in the correct sequence - passes data to the application already in the correct form --- ### 5. Flow control The transport layer makes sure that: - the sender does not transmit data faster - than the receiver can accept it This protects the **receiver**, not the network. --- ### 6. Network congestion control (TCP) The transport layer: - reduces transmission speed when congested - increases it when the network is free Decisions are made: - based on end-to-end observations - without the involvement of intermediate nodes --- ### 7. Segmentation and reassembly of data The transport layer: - splits application data into segments - reassembles them on the receiver's side Applications receive: - a complete data stream - without needing to know how it was transmitted --- ## What the transport layer does NOT do in end-to-end Important for the interview. The transport layer: - does not choose the route (that is L3) - does not manage the transfer at every network segment - does not work with MAC addresses - does not guarantee physical delivery of signals --- ## The key idea of end-to-end - transfer control is **at the ends** - the network inside is **as simple as possible** - reliability and order are the job of L4For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.