In the TCP/IP model, which layer provides end-to-end data transport and reliability when using TCP?

• A. Transport
• B. Application
• C. Internet
• D. Network Interface

Answer: (A)

The Transport layer provides end-to-end data transport and reliability when using TCP. TCP sits at this layer and offers a connection-oriented, reliable data stream between two hosts. It handles breaking application data into segments, numbering them, acknowledging received segments, and retransmitting any that are lost. It also manages flow control to prevent overwhelming the receiver and uses congestion control to avoid network overload. Because of these mechanisms, data is delivered reliably and in order from one endpoint to the other, across any path the IP layer may take.

The Internet layer (IP) is responsible for routing and delivering packets but does so on a best-effort basis, without guarantees of delivery or order. The Network Interface (Link) layer deals with hardware addressing and the actual transmission over the local network, not end-to-end reliability. The Application layer protocols depend on the Transport layer for delivery guarantees when TCP is used, rather than providing the end-to-end transport themselves.