cnp3-ebook/principles/referencemodels

Exit Zen

17 ../../principles/referencemodels.rst:131

	English The Transport layer 19/10000 · 19
18 ../../principles/referencemodels.rst:133

	English The network layer enables hosts to reach each others. However, different communication flows can take place between the same hosts. These communication flows might have different needs (some require reliable delivery, other not) and need to be distinguished. Ensuring an identification of a communication flow between two given hosts is the task of the `transport layer`. `Transport layer` entities exchange `segments`. A segment is a finite sequence of bytes that are transported inside one or more packets. A transport layer entity issues segments (or sometimes part of segments) as `Data.request` to the underlying network layer entity. 639/10000 · 639
19 ../../principles/referencemodels.rst:135

	English There are different types of transport layers. The most widely used transport layers on the Internet are :term:`TCP`, that provides a reliable connection-oriented bytestream transport service, and :term:`UDP`, that provides an unreliable connection-less transport service. 272/10000 · 272
20 ../../principles/referencemodels.rst:164

	English The Application layer 21/10000 · 21
21 ../../principles/referencemodels.rst:168

	English The upper layer of our architecture is the `Application layer`. This layer includes all the mechanisms and data structures that are necessary for the applications. We will use Application Data Unit (ADU) or the generic Service Data Unit (SDU) term to indicate the data exchanged between two entities of the Application layer. 325/10000 · 325
22 ../../principles/referencemodels.rst:201

	English In the remaining chapters of this text, we will often refer to the information exchanged between entities located in different layers. To avoid any confusion, we will stick to the terminology defined earlier, i.e. : 215/10000 · 215
23 ../../principles/referencemodels.rst:203

	English physical layer entities exchange bits 37/10000 · 37
24 ../../principles/referencemodels.rst:204

	English datalink layer entities exchange frames 41/10000 · 41
25 ../../principles/referencemodels.rst:205

	English network layer entities exchange packets 41/10000 · 41
26 ../../principles/referencemodels.rst:206

	English transport layer entities exchange segments 44/10000 · 44
27 ../../principles/referencemodels.rst:207

	English application layer entities exchange SDUs 42/10000 · 42
28 ../../principles/referencemodels.rst:212

	English Reference models 16/10000 · 16
29 ../../principles/referencemodels.rst:215

	English Two reference models have been successful in the networking community : the OSI reference model and the TCP/IP reference model. We discuss them briefly in this section. 168/10000 · 168
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

Shortcut	Action
`?`	Open available keyboard shortcuts.
`Alt` + `Home`	Navigate to the first translation in the current search.
`Alt` + `End`	Navigate to the last translation in the current search.
`Alt` + `PageUp` or `Ctrl` + `↑` or `Alt` + `↑` or `Cmd` + `↑` or	Navigate to the previous translation in the current search.
`Alt` + `PageDown` or `Ctrl` + `↓` or `Alt` + `↓` or `Cmd` + `↓` or	Navigate to the next translation in the current search.
`Ctrl` + `Enter` or `Cmd` + `Enter`	Submit current form; this works the same as pressing Save and continue while editing translation.
`Ctrl` + `Shift` + `Enter` or `Cmd` + `Shift` +`Enter`	Unmark translation as Needing edit and submit it.
`Alt` + `Enter` or `Option` + `Enter`	Submit the string as a suggestion; this works the same as pressing Suggest while editing translation.
`Ctrl` + `E` or `Cmd` + `E`	Focus on translation editor.
`Ctrl` + `U` or `Cmd` + `U`	Focus on comment editor.
`Ctrl` + `M` or `Cmd` + `M`	Shows Automatic suggestions tab.
`Ctrl` + `1` to `Ctrl` + `9` or `Cmd` + `1` to `Cmd` + `9`	Copies placeable of a given number from source string.
`Ctrl` + `M` followed by `1` to `9` or `Cmd` + `M` followed by `1` to `9`	Copy the machine translation of a given number to current translation.
`Ctrl` + `I` followed by `1` to `9` or `Cmd` + `I` followed by `1` to `9`	Ignore one item in the list of failing checks.
`Ctrl` + `J` or `Cmd` + `J`	Shows the Nearby strings tab.
`Ctrl` + `S` or `Cmd` + `S`	Focus on search field.
`Ctrl` + `O` or `Cmd` + `O`	Copy the source string.
`Ctrl` + `Y` or `Cmd` + `Y`	Toggle the Needs editing checkbox.
`→`	Browse the next translation string.
`←`	Browse the previous translation string.