Exit Zen
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../../principles/sharing.rst:163
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Let us first explore which mechanisms can be used inside a network to control congestion and how these mechanisms can influence the behavior of the end hosts.
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../../principles/transport.rst:74
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The :term:`ASCII` characters are encoded as a seven bits field, but transmitted as an eight-bits byte whose high order bit is usually set to `0`. Bytes are always transmitted starting from the high order or most significant bit.
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../../bibliography.rst:117
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Leffler, S., Fabry, R., Joy, W., Lapsley, P., Miller, S., Torek, C., `An Advanced 4.4BSD Interprocess Communication Tutorial <http://docs.freebsd.org/44doc/psd/21.ipc/paper.pdf>`_, 4.4 BSD Programmer's Supplementary Documentation
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../../glossary.rst:152
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Exterior Gateway Protocol. Synonym of interdomain routing protocol
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../../exercises/ex-sharing.rst:641
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Consider a CSMA/CD network that contains hosts that generate frames at a regular rate. When the transmission rate increases, the amount of collisions increases. For a given network load, measured in bits/sec, would the number of collisions be smaller, equal or larger with short frames than with long frames ?
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../../exercises/network.rst:356
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If you compute the routing tables of all routers in this network, you would obtain a table such as the table below :
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../../exercises/reliability.rst:80
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ten frames
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../../exercises/sockets.rst:290
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A program can use the ``struct sockaddr_in6`` to represent IPv6 socket addresses. The following program creates a ``struct sockaddr_in6`` that identifies the program that reserved the port number ``55555`` on the computer identified by the ``::1`` IPv6 address.
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../../principles/network.rst:136
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An alternative to manually computed forwarding tables is to use a network management platform that tracks the network status and can push new forwarding tables on the routers when it detects any modification to the network topology. This solution gives some flexibility to the network managers in computing the paths inside their network. However, this solution only works if the network management platform is always capable of reaching all routers even when the network topology changes. This may require a dedicated network that allows the management platform to push information on the forwarding tables. Openflow is a modern example of such solutions [MAB2008]_. In a nutshell, Openflow is a protocol that enables a network controller to install specific entries in the forwarding tables of remote routers and much more.
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../../principles/referencemodels.rst:138
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the Internet layer which is equivalent to the network layer of our reference model
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../../principles/reliability.rst:160
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Many other types of encodings have been defined to transmit information over an electrical cable. All physical layers are able to send and receive physical symbols that represent values `0` and `1`. However, for various reasons that are outside the scope of this chapter, several physical layers exchange other physical symbols as well. For example, the Manchester encoding used in several physical layers can send four different symbols. The Manchester encoding is a differential encoding scheme in which time is divided into fixed-length periods. Each period is divided in two halves and two different voltage levels can be applied. To send a symbol, the sender must set one of these two voltage levels during each half period. To send a `1` (resp. `0`), the sender must set a high (resp. low) voltage during the first half of the period and a low (resp. high) voltage during the second half. This encoding ensures that there will be a transition at the middle of each period and allows the receiver to synchronize its clock to the sender's clock. Apart from the encodings for `0` and `1`, the Manchester encoding also supports two additional symbols : `InvH` and `InvB` where the same voltage level is used for the two half periods. By definition, these two symbols cannot appear inside a frame which is only composed of `0` and `1`. Some technologies use these special symbols as markers for the beginning or end of frames.
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../../principles/sharing.rst:165
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As explained earlier, one of the first manifestation of congestion on network nodes is the saturation of the network links that leads to a growth in the occupancy of the buffers of the node. This growth of the buffer occupancy implies that some packets will spend more time in the buffer and thus in the network. If hosts measure the network delays (e.g. by measuring the round-trip-time between the transmission of a packet and the return of the corresponding acknowledgment) they could start to sense congestion. On low bandwidth links, a growth in the buffer occupancy can lead to an increase of the delays which can be easily measured by the end hosts. On high bandwidth links, a few packets inside the buffer will cause a small variation in the delay which may not necessarily be larger that the natural fluctuations of the delay measurements.
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../../principles/transport.rst:76
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Most applications exchange strings that are composed of fixed or variable numbers of characters. A common solution to define the character strings that are acceptable is to define them as a grammar using a Backus-Naur Form (:term:`BNF`) such as the Augmented BNF defined in :rfc:`5234`. A BNF is a set of production rules that generate all valid character strings. For example, consider a networked application that uses two commands, where the user can supply a username and a password. The BNF for this application could be defined as shown in the figure below.
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../../bibliography.rst:120
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Leboudec, J.-Y., `Rate Adaptation Congestion Control and Fairness : a tutorial <http://ica1www.epfl.ch/PS_files/LEB3132.pdf>`_, Dec. 2008
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../../glossary.rst:159
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EIGRP
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../../exercises/ex-sharing.rst:643
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Slotted ALOHA improves the performance of ALOHA by dividing the time in slots. However, this basic idea raises two interested questions. First how would you enforce the duration of these slots ? Second, should a slot include the time to transmit a data frame or the time to transmit a data frame and the corresponding acknowledgment ?
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../../exercises/network.rst:360
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Destination
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../../exercises/reliability.rst:81
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hundred frames
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../../exercises/sockets.rst:301
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Now, we have built everything we need to send a message to the remote program. The ``create_socket_and_send_message`` function below assembles all the building blocks we created until now in order to send the message ``"hello"`` to the program running on port ``55555`` on the computer identified by the ``::1`` IPv6 address.
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../../principles/naming.rst:152
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It is interesting to note that to prevent any homograph attack, Google Inc. registered the `g00gle.com` domain name but does not apparently use it.
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