Exit Zen
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../../protocols/email.rst:248
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q
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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/ipv6.rst:391
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The `Destinations Option` header uses the same format as the `Hop-by-Hop Options` header. It has some usages, e.g. to support mobile nodes :rfc:`6275`, but these are outside the scope of this document.
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../../protocols/ethernet.rst:373
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Handles data frames
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../../protocols/tcp.rst:335 • ../../protocols/tcp.rst:348
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10 msec
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../../glossary.rst:280
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modem
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../../principles/linkstate.rst:128 • ../../principles/network.rst:505
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Footnotes
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../../principles/reliability.rst:405
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The only solution to protect against transmission errors is to add redundancy to the frames that are sent. `Information Theory` defines two mechanisms that can be used to transmit information over a transmission channel affected by random errors. These two mechanisms add redundancy to the transmitted information, to allow the receiver to detect or sometimes even correct transmission errors. A detailed discussion of these mechanisms is outside the scope of this chapter, but it is useful to consider a simple mechanism to understand its operation and its limitations.
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../../principles/transport.rst:650
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A classical solution to avoid remembering the previous transport connections to detect duplicates is to use a clock inside each transport entity. This `transport clock` has the following characteristics :
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../../principles/sharing.rst:527
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The figure below shows the basic operation of CSMA/CA devices. Before transmitting, host `A` verifies that the channel is empty for a long enough period. Then, its sends its data frame. After checking the validity of the received frame, the recipient sends an acknowledgment frame after a short SIFS delay. Host `C`, which does not participate in the frame exchange, senses the channel to be busy at the beginning of the data frame. Host `C` can use this information to determine how long the channel will be busy for. Note that as :math:`SIFS<DIFS<EIFS`, even a device that would start to sense the channel immediately after the last bit of the data frame could not decide to transmit its own frame during the transmission of the acknowledgment frame.
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../../protocols/bgp.rst:422
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`AS4` advertises `U(p,AS4:AS1:AS0)` to `AS3`.
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../../protocols/email.rst:248
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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/ipv6.rst:395
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The `Fragment Options` header is more important. An important problem in the network layer is the ability to handle heterogeneous datalink layers. Most datalink layer technologies can only transmit and receive frames that are shorter than a given maximum frame size. Unfortunately, all datalink layer technologies use different maximum frames sizes.
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../../protocols/ethernet.rst:375
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Blocked
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../../protocols/tcp.rst:335
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52.4 Mbps
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../../glossary.rst:282
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A modem (modulator-demodulator) is a device that encodes (resp. decodes) digital information by modulating (resp. demodulating) an analog signal. Modems are frequently used to transmit digital information over telephone lines and radio links. See https://en.wikipedia.org/wiki/Modem for a survey of various types of modems
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../../principles/network.rst:506
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We will see later a more detailed description of Multiprotocol Label Switching, a networking technology that is capable of using one or more labels.
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../../principles/reliability.rst:407
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`Information theory` defines `coding schemes`. There are different types of coding schemes, but let us focus on coding schemes that operate on binary strings. A coding scheme is a function that maps information encoded as a string of `m` bits into a string of `n` bits. The simplest coding scheme is the (even) parity coding. This coding scheme takes an `m` bits source string and produces an `m+1` bits coded string where the first `m` bits of the coded string are the bits of the source string and the last bit of the coded string is chosen such that the coded string will always contain an even number of bits set to `1`. For example :
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../../principles/transport.rst:652
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the `transport clock` is implemented as a `k` bits counter and its clock cycle is such that :math:`2^k \times cycle >> MSL`. Furthermore, the `transport clock` counter is incremented every clock cycle and after each connection establishment. This clock is illustrated in the figure below.
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