Exit Zen
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../../glossary.rst:30
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MAN
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../../principles/network.rst:417
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Since a packet received with `label=1` must be forwarded to `R5` with `label=1`, `R2`'s `label forwarding table` could contain :
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../../principles/reliability.rst:391
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The datalink layer must deal with the transmission errors. In practice, we mainly have to deal with two types of errors in the datalink layer :
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../../principles/sharing.rst:477
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In the second and third cases, both hosts have flipped different coins. The delay chosen by the host that defers its retransmission should be long enough to ensure that its retransmission will not collide with the immediate retransmission of the other host. However the delay should not be longer than the time necessary to avoid the collision, because if both hosts decide to defer their transmission, the network will be idle during this delay. The `slot time` is the optimal delay since it is the shortest delay that ensures that the first host will be able to retransmit its frame completely without any collision.
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../../principles/transport.rst:571
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To support the connection-oriented service, the transport layer needs to include several mechanisms to enrich the connectionless network-layer service. We discuss these mechanisms in the following sections.
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../../glossary.rst:32
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Metropolitan Area Network
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../../principles/network.rst:427
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Two virtual circuits pass through `R3`. They both need to be forwarded to `R4`, but `R4` expects `label=1` for packets belonging to the virtual circuit originated by `R2` and `label=0` for packets belonging to the other virtual circuit. `R3` could choose to leave the labels unchanged.
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../../principles/reliability.rst:393
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Frames can be corrupted by transmission errors
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../../principles/sharing.rst:479
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If two hosts are competing, the algorithm above will avoid a second collision 50% of the time. However, if the network is heavily loaded, several hosts may be competing at the same time. In this case, the hosts should be able to automatically adapt their retransmission delay. The `binary exponential back-off` performs this adaptation based on the number of collisions that have affected a frame. After the first collision, the host flips a coin and waits 0 or 1 `slot time`. After the second collision, it generates a random number and waits 0, 1, 2 or 3 `slot times`, etc. The duration of the waiting time is doubled after each collision. The complete pseudo-code for the CSMA/CD algorithm is shown in the figure below.
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../../principles/transport.rst:575
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Connection establishment
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../../glossary.rst:253
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MIME
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../../principles/network.rst:432 • ../../principles/network.rst:434
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->R4
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../../principles/reliability.rst:394
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Frames can be lost or unexpected frames can appear
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../../principles/sharing.rst:504
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The inter-frame delay used in this pseudo-code is a short delay corresponding to the time required by a network adapter to switch from transmit to receive mode. It is also used to prevent a host from sending a continuous stream of frames without leaving any transmission opportunities for other hosts on the network. This contributes to the fairness of CSMA/CD. Despite this delay, there are still conditions where CSMA/CD is not completely fair [RY1994]_. Consider for example a network with two hosts : a server sending long frames and a client sending acknowledgments. Measurements reported in [RY1994]_ have shown that there are situations where the client could suffer from repeated collisions that lead it to wait for long periods of time due to the exponential back-off algorithm.
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../../glossary.rst:255
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The Multipurpose Internet Mail Extensions (MIME) defined in :rfc:`2045` are a set of extensions to the format of email messages that allow to use non-ASCII characters inside mail messages. A MIME message can be composed of several different parts each having a different format.
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../../principles/sharing.rst:507
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This name should not be confused with the duration of a transmission slot in slotted ALOHA. In CSMA/CD networks, the slot time is the time during which a collision can occur at the beginning of the transmission of a frame. In slotted ALOHA, the duration of a slot is the transmission time of an entire fixed-size frame.
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../../principles/transport.rst:579
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An important difference between the connectionless service and the connection-oriented one is that the transport entities in the latter maintain some state during lifetime of the connection. This state is created when a connection is established and is removed when it is released.
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../../glossary.rst:277
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MIME document
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../../principles/network.rst:442
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->R3
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../../principles/reliability.rst:399
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To deal with these types of imperfections, reliable protocols rely on different types of mechanisms. The first problem is transmission errors. Data transmission on a physical link can be affected by the following errors :
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