Question

FTP and HTTP need underlying layers for Reliability Service and hence TCP is used at the Transport Layer, what protocol will FTP and HTTP use at Network Layer ?
Since IP is an unreliable protocol,it does not guarantee the delivery of a datagram to its destination, how application layer data in ensured reliability @ this Network level ?

Comments

1. i think IP self uses TCP for reliability at network layer TCP/IP suite
2.  the "unreliability" of IP does not negate the "reliability" of TCP. TCP simply uses IP with smart acknowledgements to make communication using TCP/IP reliable. TCP by itself can not handle sending packets from one host to another, all it can do is apply certain rules to an 'end to end' delivery scheme (like IP), to make that delivery scheme more reliable.

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Another new variant of HTTP is HTTPR - for Reliable HTTP. This new protocol is being developed by IBM for adoption as a standard by the Internet Engineering Task Force (IETF).

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TCP is connection-oriented. A connection-oriented transport protocol establishes a virtual path between the source and destination. All the segments belonging to a message are then sent over this virtual path. Using a single virtual pathway for the entire message facilitates the acknowledgment process as well as retransmission ofdamaged or lost frames. You may wonder how TCP, which uses the services ofIP, a connectionless protocol, can be connection-oriented. The point is that a TCP connection is virtual, not physical. TCP operates at a higher level. TCP uses the services ofIP to deliver individual segments to the receiver, but it controls the connection itself. If a segment is lost or corrupted, it is retransmitted. Unlike TCP, IP is unaware of this retransmission. If a segment arrives out of order, TCP holds it until the missing segments arrive; IP is unaware ofthis reordering.
 

Behrouz A. Forouzan
 

TCP, on the other hand, offers several additional services to applications. First and foremost, it provides reliable data transfer. Using flow control, sequence numbers, acknowledgments, and timers , TCP ensures that data is delivered from sending process to receiving process,
correctly and in order. TCP thus converts IP’s unreliable service between end systems into a reliable data transport service between processes.
 

Computer networking : a top-down approach / James F. Kurose, Keith W. Ross