Which protocol ensures reliable delivery?

Transmission Control Protocol (TCP) is a connection-oriented protocol that provides reliable, ordered, and error-checked delivery of a stream of octets between applications. Reliability is achieved through several mechanisms: a three-way handshake to establish a connection, sequence numbers to track data segments and reassemble them in the correct order, and acknowledgments (ACKs) to confirm receipt. If an ACK is not received for a segment within a certain time, the sender retransmits the lost segment, thus guaranteeing delivery. This makes TCP suitable for applications where data integrity is critical, such as file transfers and web browsing.

A. UDP (User Datagram Protocol) is a connectionless protocol that offers "best-effort" delivery. It does not use acknowledgments or retransmissions, prioritizing speed over reliability.

B. IP (Internet Protocol) is a network layer protocol responsible for addressing and routing packets. It is inherently unreliable and provides no guarantee of packet delivery, order, or integrity.

D. ICMP (Internet Control Message Protocol) is used by network devices to send error messages and operational information. It is not designed for reliable end-to-end data transport for applications.

1. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. In Chapter 3, Section 3.4, "Connection-Oriented Transport: TCP," the text states, "TCP is said to be connection-oriented because before one application process can begin to send data to another, the two processes must first 'handshake' with each other... The TCP connection is also a full-duplex service... After a connection is established, the two application processes can send data to each other. The connection is also a reliable data transfer service." (p. 225).

2. Postel, J. (Ed.). (1981). RFC 793: Transmission Control Protocol. Internet Engineering Task Force (IETF). The abstract explicitly states, "The Transmission Control Protocol (TCP) is intended for use as a highly reliable host-to-host protocol between hosts in packet-switched computer communication networks..." Section 1.5, "Operation," further details the mechanisms like sequence numbers and acknowledgments that ensure reliability.

3. Odom, W. (2019). CCNA 200-301 Official Cert Guide, Volume 1. Cisco Press. Chapter 3, "Fundamentals of TCP/IP Transport and Applications," explains, "TCP uses acknowledgments to know whether the other host received the data. If the sender does not receive an acknowledgment, the sender retransmits the data... TCP provides services that check for errors and retransmit any data that is not received correctly. For these reasons, TCP is a reliable protocol." (p. 62).