TCP/IP model: Difference between revisions

Revision as of 07:11, 27 March 2012

Revision as of 07:13, 27 March 2012

Line 39:

The layers near the top are logically closer to the user application, while those near the bottom are logically closer to the physical transmission of the data. Viewing layers as providing or consuming a service is a method of [[abstraction (computer science)|abstraction]] to isolate upper layer protocols from the nitty-gritty detail of transmitting bits over, for example, [[Ethernet]] and [[Carrier sense multiple access with collision detection|collision detection]], while the lower layers avoid having to know the details of each and every application and its protocol.

This abstraction also allows upper layers to provide services that the lower layers cannot, or choose not to, provide. Again, the original [[OSI Reference Model]]model was extended to include connectionless services (OSIRM CL).<ref>[ OSI: Reference Model Addendum 1: Connectionless-mode Transmission,ISO7498/AD1],ISO7498/AD1, May 1986</ref> For example, IP is not designed to be reliable and is a [[best effort delivery]] protocol. This means that all transport layer implementations must choose whether or not to provide reliability and to what degree. UDP provides data integrity (via a [[checksum]]) but does not guarantee delivery; TCP provides both data integrity and delivery guarantee (by retransmitting until the receiver acknowledges the reception of the packet).

This model lacks the formalism of the OSI reference model and associated documents, but the IETF does not use a formal model and does not consider this a limitation, as in the comment by [[David D. Clark]], "We reject: kings, presidents and voting. We believe in: rough consensus and running code." Criticisms of this model, which have been made with respect to the OSI Reference Model, often do not consider ISO's later extensions to that model.