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../../exercises/sockets.rst:322
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Note that we can reuse our ``send_hello_to_peer`` function without any modification as we wrote it to handle any kind of sockets, including sockets using the IPv6 network protocol.
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../../principles/referencemodels.rst:141
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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.
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../../exercises/reliability.rst:85
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Is it possible for a selective-repeat receiver to inter-operate with a go-back-n sender ? Justify your answer.
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../../exercises/network.rst:360
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Routes on B
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../../exercises/sockets.rst:326
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Endianness: exchanging integers between different computers
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../../principles/referencemodels.rst:146
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The OSI reference model
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../../principles/network.rst:143
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Computing forwarding tables
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../../principles/reliability.rst:180
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All the functions related to the physical transmission or information through a wire (or a wireless link) are usually known as the `physical layer`. The physical layer allows thus two or more entities that are directly attached to the same transmission medium to exchange bits. Being able to exchange bits is important as virtually any information can be encoded as a sequence of bits. Electrical engineers are used to processing streams of bits, but computer scientists usually prefer to deal with higher level concepts. A similar issue arises with file storage. Storage devices such as hard-disks also store streams of bits. There are hardware devices that process the bit stream produced by a hard-disk, but computer scientists have designed filesystems to allow applications to easily access such storage devices. These filesystems are typically divided into several layers as well. Hard-disks store sectors of 512 bytes or more. Unix filesystems group sectors in larger blocks that can contain data or `inodes` representing the structure of the filesystem. Finally, applications manipulate files and directories that are translated in blocks, sectors and eventually bits by the operating system.
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../../principles/transport.rst:86
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Besides character strings, some applications also need to exchange 16 bits and 32 bits fields such as integers. A naive solution would have been to send the 16- or 32-bits field as it is encoded in the host's memory. Unfortunately, there are different methods to store 16- or 32-bits fields in memory. Some CPUs store the most significant byte of a 16-bits field in the first address of the field while others store the least significant byte at this location. When networked applications running on different CPUs exchange 16 bits fields, there are two possibilities to transfer them over the transport service :
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../../exercises/network.rst:360
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Routes on C
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../../exercises/sockets.rst:328
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Besides character strings, some applications also need to exchange 16 bits and 32 bits fields such as integers. A naive solution would have been to send the 16- or 32-bits field as it is encoded in the host's memory. Unfortunately, there are different methods to store 16- or 32-bits fields in memory. Some CPUs store the most significant byte of a 16-bits field in the first address of the field while others store the least significant byte at this location. When networked applications running on different CPUs exchange 16 bits fields, there are two possibilities to transfer them over the transport service :
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../../principles/referencemodels.rst:148
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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 :
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../../principles/reliability.rst:184
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Computer networks use a similar approach. Each layer provides a service that is built above the underlying layer and is closer to the needs of the applications. The datalink layer builds upon the service provided by the physical layer. We will see that it also contains several functions.
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../../principles/transport.rst:88
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send the most significant byte followed by the least significant byte
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../../exercises/network.rst:360
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Routes on D
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../../exercises/sockets.rst:330
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send the most significant byte followed by the least significant byte
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../../principles/reliability.rst:188
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The datalink layer
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../../principles/transport.rst:89
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send the least significant byte followed by the most significant byte
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../../exercises/network.rst:360
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Routes on E
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../../exercises/sockets.rst:331
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send the least significant byte followed by the most significant byte
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