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../../glossary.rst:65
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a frame is the unit of information transfer in the datalink layer
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../../exercises/network.rst:363 • ../../exercises/network.rst:364 • ../../exercises/network.rst:365 • ../../exercises/network.rst:366 • ../../exercises/network.rst:367
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0
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../../exercises/sockets.rst:335
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Besides 16 and 32 bit words, some applications need to exchange data structures containing bit fields of various lengths. For example, a message may be composed of a 16 bits field followed by eight, one bit flags, a 24 bits field and two 8 bits bytes. Internet protocol specifications will define such a message by using a representation such as the one below. In this representation, each line corresponds to 32 bits and the vertical lines are used to delineate fields. The numbers above the lines indicate the bit positions in the 32-bits word, with the high order bit at position `0`.
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../../principles/reliability.rst:199
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If the physical layer were perfect, the problem would be very simple. We would simply need to define how to encode each frame as a sequence of consecutive bits. The receiver would then easily be able to extract the frames from the received bits. Unfortunately, the imperfections of the physical layer make this framing problem slightly more complex. Several solutions have been proposed and are used in practice in different network technologies.
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../../principles/transport.rst:99
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Message format
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../../bibliography.rst:311
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Ramakrishnan, K.K. and Henry Yang, `The Ethernet Capture Effect: Analysis and Solution <http://www2.research.att.com/~kkrama/papers/capture_camera.pdf>`_, Proceedings of IEEE 19th Conference on Local Computer Networks, MN, Oct. 1994.
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../../glossary.rst:229
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Frame-Relay
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../../exercises/network.rst:363
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1 via A
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../../exercises/sockets.rst:341
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Message format
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../../principles/referencemodels.rst:162
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Footnotes
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../../principles/reliability.rst:202
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Framing
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../../principles/transport.rst:101
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The message mentioned above will be transmitted starting from the upper 32-bits word in network byte order. The first field is encoded in 16 bits. It is followed by eight one bit flags (`A-H`), a 24 bits field whose high order byte is shown in the first line and the two low order bytes appear in the second line followed by two one byte fields. This ASCII representation is frequently used when defining binary protocols. We will use it for all the binary protocols that are discussed in this book.
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../../bibliography.rst:312
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Roberts, L., `ALOHA packet system with and without slots and capture <http://doi.acm.org/10.1145/1024916.1024920>`_. SIGCOMM Computer Communication Review 5, 2 (Apr. 1975), 28-42.
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../../exercises/network.rst:363 • ../../exercises/network.rst:365
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2 via B
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../../exercises/sockets.rst:343
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The message mentioned above will be transmitted starting from the upper 32-bits word in network byte order. The first field is encoded in 16 bits. It is followed by eight one bit flags (`A-H`), a 24 bits field whose high order byte is shown in the first line and the two low order bytes appear in the second line followed by two one byte fields. This ASCII representation is frequently used when defining binary protocols. We will use it for all the binary protocols that are discussed in this book.
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../../principles/network.rst:187
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By inspecting the source and destination addresses of packets, network nodes can automatically derive their forwarding tables. As we will discuss later, this technique is used in :term:`Ethernet` networks. Despite being widely used, it has two important drawbacks. First, packets sent to unknown destinations are broadcasted in the network even if the destination is not attached to the network. Consider the transmission of ten packets destined to `Z` in the network above. When a node receives a packet towards this destination, it can only broadcast that packet. Since `Z` is not attached to the network, no node will ever receive a packet whose source is `Z` to update its forwarding table. The second and more important problem is that few networks have a tree-shaped topology. It is interesting to analyze what happens when a port-address table is used in a network that contains a cycle. Consider the simple network shown below with a single host.
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../../principles/referencemodels.rst:163
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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.
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../../principles/reliability.rst:204
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The `framing` problem can be defined as : "`How does a sender encode frames so that the receiver can efficiently extract them from the stream of bits that it receives from the physical layer`".
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../../principles/sharing.rst:191
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Discarding packets is a frequent reaction to network congestion. Unfortunately, discarding packets is not optimal since a packet which is discarded on a network node has already consumed resources on the upstream nodes. There are other ways for the network to inform the end hosts of the current congestion level. A first solution is to mark the packets when a node is congested. Several networking technologies have relied on this kind of packet marking.
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../../principles/transport.rst:105
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The peer-to-peer model emerged during the last ten years as another possible architecture for networked applications. In the traditional client-server model, hosts act either as servers or as clients and a server serves a large number of clients. In the peer-to-peer model, all hosts act as both servers and clients and they play both roles. The peer-to-peer model has been used to develop various networked applications, ranging from Internet telephony to file sharing or Internet-wide filesystems. A detailed description of peer-to-peer applications may be found in [BYL2008]_. Surveys of peer-to-peer protocols and applications may be found in [AS2004]_ and [LCP2005]_.
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