Exit Zen
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../../principles/sharing.rst:778
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Various types of rate adaption algorithms are possible. `Dah Ming Chiu`_ and `Raj Jain`_ have analyzed, in [CJ1989]_, different types of algorithms that can be used by a source to adapt its transmission rate to the feedback received from the network. Intuitively, such a rate adaptation algorithm increases the transmission rate when the network is not congested (ensure that the network is efficiently used) and decrease the transmission rate when the network is congested (to avoid congestion collapse).
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../../glossary.rst:203
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The Secure Shell (SSH) Transport Layer Protocol is defined in :rfc:`4253`
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../../principles/linkstate.rst:19
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Usually, the same weight is associated to the two directed edges that correspond to a physical link (i.e. :math:`R1 \rightarrow R2` and :math:`R2 \rightarrow R1`). However, nothing in the link state protocols requires this. For example, if the weight is set in function of the link bandwidth, then an asymmetric ADSL link could have a different weight for the upstream and downstream directions. Other variants are possible. Some networks use optimization algorithms to find the best set of weights to minimize congestion inside the network for a given traffic demand [FRT2002]_.
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../../principles/reliability.rst:712
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Sliding window example
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../../principles/sharing.rst:780
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The simplest form of feedback that the network can send to a source is a binary feedback (the network is congested or not congested). In this case, a `linear` rate adaptation algorithm can be expressed as :
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../../glossary.rst:301
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standard query
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../../principles/linkstate.rst:24
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When a link-state router boots, it first needs to discover to which routers it is directly connected. For this, each router sends a HELLO message every `N` seconds on all its interfaces. This message contains the router's address. Each router has a unique address. As its neighboring routers also send HELLO messages, the router automatically discovers to which neighbors it is connected. These HELLO messages are only sent to neighbors that are directly connected to a router, and a router never forwards the HELLO messages that it receives. HELLO messages are also used to detect link and router failures. A link is considered to have failed if no HELLO message has been received from a neighboring router for a period of :math:`k \times N` seconds.
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../../principles/reliability.rst:715
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In practice, as the frame header includes an `n` bits field to encode the sequence number, only the sequence numbers between :math:`0` and :math:`2^{n}-1` can be used. This implies that, during a long transfer, the same sequence number will be used for different frames and the sliding window will wrap. This is illustrated in the figure below assuming that `2` bits are used to encode the sequence number in the frame header. Note that upon reception of `OK1`, the sender slides its window and can use sequence number `0` again.
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../../principles/sharing.rst:782
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:math:`rate(t+1)=\alpha_C + \beta_C rate(t)` when the network is congested
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../../glossary.rst:303
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For DNS servers and resolvers, a standard query is a query for a `A` or a `AAAA` record. Such a query typically returns an IP address.
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../../principles/reliability.rst:722
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Utilisation of the sliding window with modulo arithmetic
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../../principles/sharing.rst:783
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:math:`rate(t+1)=\alpha_N + \beta_N rate(t)` when the network is *not* congested
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../../glossary.rst:177
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switch
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../../principles/linkstate.rst:33
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Once a router has discovered its neighbors, it must reliably distribute all its outgoing edges to all routers in the network to allow them to compute their local view of the network topology. For this, each router builds a `link-state packet` (LSP) containing the following information:
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../../principles/reliability.rst:727
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Unfortunately, frame losses do not disappear because a reliable protocol uses a sliding window. To recover from losses, a sliding window protocol must define :
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../../principles/sharing.rst:785
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With a linear adaption algorithm, :math:`\alpha_C,\alpha_N, \beta_C` and :math:`\beta_N` are constants. The analysis of [CJ1989]_ shows that to be fair and efficient, such a binary rate adaption mechanism must rely on `Additive Increase and Multiplicative Decrease`. When the network is not congested, the hosts should slowly increase their transmission rate (:math:`\beta_N=1~and~\alpha_N>0`). When the network is congested, the hosts must multiplicatively decrease their transmission rate (:math:`\beta_C < 1~and~\alpha_C = 0`). Such an AIMD rate adaptation algorithm can be implemented by the pseudo-code below.
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../../glossary.rst:179
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A relay operating in the datalink layer.
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../../principles/linkstate.rst:35
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LSP.Router: identification (address) of the sender of the LSP
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../../principles/reliability.rst:729
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a heuristic to detect frame losses
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../../principles/sharing.rst:799
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Which binary feedback ?
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