Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Reliable data delivery services are designed to provide guaranteed and accurate delivery of data over unreliable or best-effort networks. This is done by implementing additional protocols that track packet deliveries and retransmit lost packets. Other services include monitoring the network for congestion and throttling back senders that are contributing to congestion.

IP networks are best-effort networks, meaning that the network will deliver packets but provides no guarantees. Packets may be dropped due to congestion. They may also take alternate routers that cause them to arrive after the sender has already sent a replacement packet, causing duplicates at the receiver.

The main point is that the IP network itself does not provide any services to recover from these problems. However, end systems do provide these services. This is a major design feature of the Internet.

This topic continues in "The Encyclopedia of Networking and Telecommunications" with a discussion of the following:

• End-to-end architecture
• Connection setup and multiplexing
• Positive acknowledgments and flow control
• Sequencing of packets
• Congestion control mechanisms
• Error checking to detect corrupted packets
• Partial Reliable Services

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