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../../principles/transport.rst:684
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The first scenario is when the remote entity receives an old `CR` segment. It considers this `CR` segment as a connection establishment attempt and replies by sending a `CA` segment. However, the initiating host cannot match the received `CA` segment with a previous connection attempt. It sends a control segment (`REJECT` in the figure below) to cancel the spurious connection attempt. The remote entity cancels the connection attempt upon reception of this control segment.
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../../principles/sharing.rst:617
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During the 1970s and 1980s, there were huge debates in the networking community about the best suited Medium Access Control algorithms for Local Area Networks. The optimistic algorithms that we have described until now were relatively easy to implement when they were designed. From a performance perspective, mathematical models and simulations showed the ability of these optimistic techniques to sustain load. However, none of the optimistic techniques are able to guarantee that a frame will be delivered within a given delay bound and some applications require predictable transmission delays. The deterministic MAC algorithms were considered by a fraction of the networking community as the best solution to fulfill the needs of Local Area Networks.
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../../protocols/bgp.rst:444
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Based on these studies and [ATLAS2009]_, the AS-level Internet topology can be summarized as shown in the figure below.
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../../protocols/ethernet.rst:406
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The figure below illustrates a switched Ethernet network with three Virtual LANs. `VLAN2` and `VLAN3` only require a local configuration of switch `S1`. Host `C` can exchange frames with host `D`, but not with hosts that are outside of its VLAN. `VLAN1` is more complex as there are ports of this VLAN on several switches. To support such VLANs, local configuration is not sufficient anymore. When a switch receives a frame from another switch, it must be able to determine the VLAN in which the frame originated to use the correct MAC table to forward the frame. This is done by assigning an identifier to each Virtual LAN and placing this identifier inside the headers of the frames that are exchanged between switches.
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../../protocols/tcp.rst:364
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In a go-back-n transport protocol such as TCP, the retransmission timeout must be correctly set in order to achieve good performance. On one hand, if the retransmission timeout expires too early, then bandwidth is wasted by retransmitting segments that have already been correctly received. On the other hand, if the retransmission timeout expires too late, then bandwidth is wasted because the sender is idle waiting for the expiration of its retransmission timeout.
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../../glossary.rst:217
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NFS
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../../principles/reliability.rst:429
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Even parity
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../../principles/transport.rst:690
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Three-way handshake : recovery from a duplicate `CR`
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../../protocols/bgp.rst:450
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The layered structure of the global Internet
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../../protocols/email.rst:252
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../../protocols/ipv6.rst:409
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FDDI
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../../protocols/ethernet.rst:413
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Virtual Local Area Networks in a switched Ethernet network
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../../protocols/tcp.rst:366
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A good setting of the retransmission timeout clearly depends on an accurate estimation of the round-trip-time of each TCP connection. The round-trip-time differs between TCP connections, but may also change during the lifetime of a single connection. For example, the figure below shows the evolution of the round-trip-time between two hosts during a period of 45 seconds.
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../../glossary.rst:219
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The Network File System is defined in :rfc:`1094`
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../../principles/reliability.rst:431 • ../../principles/reliability.rst:448
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../../principles/transport.rst:692
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A second scenario is when the initiating entity sends a `CR` segment that does not reach the remote entity and receives a duplicate `CA` segment from a previous connection attempt. This duplicate `CA` segment cannot contain a valid acknowledgment for the `CR` segment as the sequence number of the `CR` segment was extracted from the transport clock of the initiating entity. The `CA` segment is thus rejected and the `CR` segment is retransmitted upon expiration of the retransmission timer.
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../../principles/sharing.rst:621
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The IEEE 802.5 Token Ring technology is defined in [IEEE802.5]_. We use Token Ring as an example to explain the principles of the token-based MAC algorithms in ring-shaped networks. Other ring-shaped networks include the defunct FDDI [Ross1989]_ or Resilient Pack Ring [DYGU2004]_ . A good survey of the early token ring networks may be found in [Bux1989]_ .
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../../protocols/bgp.rst:454
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The domains on the Internet can be divided in about four categories according to their role and their position in the AS-level topology.
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