Exit Zen
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../../glossary.rst:306
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For DNS servers and resolvers, an inverse query is a query for the domain name that corresponds to a given IP address.
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sending a control packet back to the source if a router detects that a packet is looping inside the network
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**1** **2** **3** **DLE** **STX** **4**
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[Abramson1970]_ analyzed the performance of ALOHANet under particular assumptions and found that ALOHANet worked well when the channel was lightly loaded. In this case, the frames are rarely retransmitted and the `channel traffic`, i.e. the total number of (correct and retransmitted) frames transmitted per unit of time is close to the `channel utilization`, i.e. the number of correctly transmitted frames per unit of time. Unfortunately, the analysis also reveals that the `channel utilization` reaches its maximum at :math:`\frac{1}{2 \times e}=0.186` times the channel bandwidth. At higher utilization, ALOHANet becomes unstable and the network collapses due to collided retransmissions.
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../../principles/transport.rst:447
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To ensure a reliable delivery of the SDUs sent by each user over a connection, we need to consider the two streams that compose a connection as independent. A user should be able to release the stream that it uses to send SDUs once it has sent all the SDUs that it planned to send over this connection, but still continue to receive SDUs over the opposite stream. This `graceful` connection release is usually performed as shown in the figure below. One user issues a `Disconnect.request` primitive to its provider once it has issued all its `Data.request` primitives. The service provider will wait until all `Data.indication` primitives have been delivered to the receiving user before issuing the `Disconnnect.indication` primitive. This primitive informs the receiving user that it will no longer receive SDUs over this connection, but it is still able to issue `Data.request` primitives on the stream in the opposite direction. Once the user has issued all of its `Data.request` primitives, it issues a `Disconnnect.request` primitive to request the termination of the remaining stream. The service provider will process the request and deliver the corresponding `Disconnect.indication` to the other user once it has delivered all the pending `Data.indication` primitives. At this point, all data has been delivered, the two streams have been released successfully and the connection is completely closed.
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../../glossary.rst:75
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IP
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verifying that packets can reach a given destination
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`DLE STX` **1** **2** **3** **DLE** `DLE` **STX** `4` `DLE ETX`
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Amateur packet radio
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../../principles/transport.rst:487
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Reliability of the connection-oriented service
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../../glossary.rst:77
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Internet Protocol is the generic term for the network layer protocol in the TCP/IP protocol suite. IP version 4 is widely used but IP version 6 is being deployed globally.
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We will discuss these functions in more details when we will describe the protocols that are used in the network layer of the TCP/IP protocol suite.
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**DLE STX DLE ETX**
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../../principles/sharing.rst:343
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Packet radio technologies have evolved in various directions since the first experiments performed at the University of Hawaii. The Amateur packet radio service developed by amateur radio operators is one of the descendants ALOHANet. Many amateur radio operators are very interested in new technologies and they often spend countless hours developing new antennas or transceivers. When the first personal computers appeared, several amateur radio operators designed radio modems and their own datalink layer protocols [KPD1985]_ [BNT1997]_. This network grew and it was possible to connect to servers in several European countries by only using packet radio relays. Some amateur radio operators also developed TCP/IP protocol stacks that were used over the packet radio service. Some parts of the `amateur packet radio network <http://www.ampr.org/>`_ are connected to the global Internet and use the `44.0.0.0/8` IPv4 prefix.
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../../glossary.rst:78
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IPv4
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../../principles/network.rst:353
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Virtual circuit organization
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`DLE STX` **DLE** `DLE` **STX** **DLE** `DLE` ETX** `DLE ETX`
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../../principles/sharing.rst:347
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Many improvements to ALOHANet have been proposed since the publication of [Abramson1970]_, and this technique, or some of its variants, are still found in wireless networks today. The slotted technique proposed in [Roberts1975]_ is important because it shows that a simple modification can significantly improve channel utilization. Instead of allowing all terminals to transmit at any time, [Roberts1975]_ proposed to divide time into slots and allow terminals to transmit only at the beginning of each slot. Each slot corresponds to the time required to transmit one fixed size frame. In practice, these slots can be imposed by a single clock that is received by all terminals. In ALOHANet, it could have been located on the central mainframe. The analysis in [Roberts1975]_ reveals that this simple modification improves the channel utilization by a factor of two.
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../../principles/transport.rst:494
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The request-response service
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../../glossary.rst:80
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is the version 4 of the Internet Protocol, the connectionless network layer protocol used in most of the Internet today. IPv4 addresses are encoded as a 32 bits field.
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