cnp3-ebook/principles/referencemodels

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30 ../../principles/referencemodels.rst:219

	English The TCP/IP reference model 26/10000 · 26
31 ../../principles/referencemodels.rst:221

	English In contrast with OSI, the TCP/IP community did not spend a lot of effort defining a detailed reference model; in fact, the goals of the Internet architecture were only documented after TCP/IP had been deployed [Clark88]_. :rfc:`1122`, which defines the requirements for Internet hosts, mentions four different layers. Starting from the top, these are : 352/10000 · 352
32 ../../principles/referencemodels.rst:223

	English the Application layer 21/10000 · 21
33 ../../principles/referencemodels.rst:224

	English the Transport layer 19/10000 · 19
34 ../../principles/referencemodels.rst:225

	English the Internet layer which is equivalent to the network layer of our reference model 82/10000 · 82
35 ../../principles/referencemodels.rst:226

	English the Link layer which combines the functions of the physical and datalink layers of our five-layer reference model 113/10000 · 113
36 ../../principles/referencemodels.rst:228

	English Besides this difference in the lower layers, the TCP/IP reference model is very close to the five layers that we use throughout this document. 142/10000 · 142
37 ../../principles/referencemodels.rst:233

	English The OSI reference model 23/10000 · 23
38 ../../principles/referencemodels.rst:235

	English Compared to the five layers reference model explained above, the :term:`OSI` reference model defined in [X200]_ is divided in seven layers. The four lower layers are similar to the four lower layers described above. The OSI reference model refined the application layer by dividing it in three layers : 302/10000 · 302
39 ../../principles/referencemodels.rst:237

	English the `Session layer`. The Session layer contains the protocols and mechanisms that are necessary to organize and to synchronize the dialogue and to manage the data exchange of presentation layer entities. While one of the main functions of the transport layer is to cope with the unreliability of the network layer, the session's layer objective is to hide the possible failures of transport-level connections to the upper layer higher. For this, the Session Layer provides services that allow establishing a session-connection, to support in-order data exchange (including mechanisms that allow recovering from the abrupt release of an underlying transport connection), and to release the connection in an orderly manner. 721/10000 · 721
40 ../../principles/referencemodels.rst:238

	English the `Presentation layer` was designed to cope with the different ways of representing information on computers. There are many differences in the way computer store information. Some computers store integers as 32 bits field, others use 64 bits field and the same problem arises with floating point number. For textual information, this is even more complex with the many different character codes that have been used [#funicode]_. The situation is even more complex when considering the exchange of structured information such as database records. To solve this problem, the Presentation layer provides a common representation of the data transferred. The :term:`ASN.1` notation was designed for the Presentation layer and is still used today by some protocols. 762/10000 · 762
41 ../../principles/referencemodels.rst:239

	English the `Application layer` that contains the mechanisms that do not fit in neither the Presentation nor the Session layer. The OSI Application layer was itself further divided in several generic service elements. 209/10000 · 209
42 ../../principles/referencemodels.rst:275

	English Footnotes 9/10000 · 9
43 ../../principles/referencemodels.rst:276

	English An interesting historical discussion of the OSI-TCP/IP debate may be found in [Russel06]_ 89/10000 · 89
44 ../../principles/referencemodels.rst:278

	English There is now a rough consensus for the greater use of the Unicode_ character format. Unicode can represent more than 100,000 different characters from the known written languages on Earth. Maybe one day, all computers will only use Unicode to represent all their stored characters and Unicode could become the standard format to exchange characters, but we are not yet at this stage today. 389/10000 · 389
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