Exit Zen
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../../principles/reliability.rst:433 • ../../principles/reliability.rst:450
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../../principles/transport.rst:711
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Data transfer
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../../principles/sharing.rst:638
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When powered-on, Token Ring interfaces operate in two different modes : `listen` and `transmit`. When operating in `listen` mode, a Token Ring interface receives an electrical signal from its upstream neighbor on the ring, introduces a delay equal to the transmission time of one bit on the ring and regenerates the signal before sending it to its downstream neighbor on the ring.
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../../protocols/bgp.rst:473
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Several web sites collect and analyze data about the evolution of BGP in the global Internet. http://bgp.potaroo.net provides lots of statistics and analyzes that are updated daily.
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../../protocols/email.rst:254
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../../protocols/ipv6.rst:427
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IPv6 fragmentation header
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../../protocols/wifi.rst:7
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The radio spectrum is a limited resource that must be shared by everyone. During most of the twentieth century, governments and international organizations have regulated most of the radio spectrum. This regulation controls the utilization of the radio spectrum, in order to prevent interference among different users. A company that wants to use a frequency range in a given region must apply for a license from the regulator. Most regulators charge a fee for the utilization of the radio spectrum and some governments have encouraged competition among companies bidding for the same frequency to increase the license fees.
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../../protocols/tcp.rst:394
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To avoid this ambiguity in the estimation of the round-trip-time when segments are retransmitted, recent TCP implementations rely on the `timestamp option` defined in :rfc:`1323`. This option allows a TCP sender to place two 32 bit timestamps in each TCP segment that it sends. The first timestamp, TS Value (`TSval`) is chosen by the sender of the segment. It could for example be the current value of its real-time clock [#ftimestamp]_. The second value, TS Echo Reply (`TSecr`), is the last `TSval` that was received from the remote host and stored in the :term:`TCB`. The figure below shows how the utilization of this timestamp option allows for the disambiguation of the round-trip-time measurement when there are retransmissions.
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../../glossary.rst:141
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OSPF
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../../principles/dv.rst:72
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`B` and `D` process the received distance vector and update their routing table with a route towards `A`.
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../../principles/reliability.rst:434 • ../../principles/reliability.rst:451
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../../principles/transport.rst:713
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Now that the transport connection has been established, it can be used to transfer data. To ensure a reliable delivery of the data, the transport protocol will include sliding windows, retransmission timers and `go-back-n` or `selective repeat`. However, we cannot simply reuse the techniques from the datalink because a transport protocol needs to deal with more types of errors than a reliable protocol in datalink layer. The first difference between the two layers is the transport layer must face with more variable delays. In the datalink layer, when two hosts are connected by a link, the transmission delay or the round-trip-time over the link is almost fixed. In a network that can span the globe, the delays and the round-trip-times can vary significantly on a per packet basis. This variability can be caused by two factors. First, packets sent through a network do not necessarily follow the same path to reach their destination. Second, some packets may be queued in the buffers of routers when the load is high and these queuing delays can lead to increased end-to-end delays. A second difference between the datalink layer and the transport layer is that a network does not always deliver packets in sequence. This implies that packets may be reordered by the network. Furthermore, the network may sometimes duplicate packets. The last issue that needs to be dealt with in the transport layer is the transmission of large SDUs. In the datalink layer, reliable protocols transmit small frames. Applications could generate SDUs that are much larger than the maximum size of a packet in the network layer. The transport layer needs to include mechanisms to fragment and reassemble these large SDUs.
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../../principles/sharing.rst:640
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The first problem faced by a Token Ring network is that as the token represents the authorization to transmit, it must continuously travel on the ring when no data frame is being transmitted. Let us assume that a token has been produced and sent on the ring by one station. In Token Ring networks, the token is a 24 bits frame whose structure is shown below.
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../../protocols/bgp.rst:475
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See http://as-rank.caida.org/ for an analysis of the interconnections between domains based on measurements collected in the global Internet.
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../../protocols/email.rst:254
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../../protocols/ipv6.rst:429
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If a router receives a packet that is too long to be forwarded, the packet is dropped and the router returns an ICMPv6 message to inform the sender of the problem. The sender can then either fragment the packet or perform Path MTU discovery. In IPv6, packet fragmentation is performed only by the source by using IPv6 options.
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../../protocols/wifi.rst:9
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In the 1970s, after the first experiments with ALOHANet, interest in wireless networks grew. Many experiments were done on and outside the ARPANet. One of these experiments was the `first mobile phone <http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm>`_ , which was developed and tested in 1973. This experimental mobile phone was the starting point for the first generation analog mobile phones. Given the growing demand for mobile phones, it was clear that the analog mobile phone technology was not sufficient to support a large number of users. To support more users and new services, researchers in several countries worked on the development of digital mobile telephones. In 1987, several European countries decided to develop the standards for a common cellular telephone system across Europe : the `Global System for Mobile Communications` (GSM). Since then, the standards have evolved and more than three billion users are connected to GSM networks today.
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../../protocols/tcp.rst:400
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Disambiguating round-trip-time measurements with the :rfc:`1323` timestamp option
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../../glossary.rst:143
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Open Shortest Path First. A link-state intradomain routing protocol that is often used in enterprise and ISP networks. OSPF is defined in and :rfc:`2328` and :rfc:`5340`
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../../principles/dv.rst:73
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`D` sends its distance vector `[D=0,A=1]` to `A` and `E`. `E` can now reach `A` and `D`.
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