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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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../../protocols/email.rst:272
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00010100 11111011 10011100 00000011 11011001 01111110
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../../protocols/ipv6.rst:576
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When a TCP segment is transported in an IP packet that is fragmented in the network, the loss of a single fragment forces TCP to retransmit the entire segment (and thus all the fragments). If TCP was able to send only packets that do not require fragmentation in the network, it could retransmit only the information that was lost in the network. In addition, IP reassembly causes several challenges at high speed as discussed in :rfc:`4963`. Using IP fragmentation to allow UDP applications to exchange large messages raises several security issues [KPS2003]_.
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../../protocols/wifi.rst:109
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802.11 control frames are simpler than data frames. They contain a `Frame Control`, a `Duration` field and one or two addresses. The acknowledgment frames are very small. They only contain the address of the destination of the acknowledgment. There is no source address and no `Sequence Control` field in the acknowledgment frames. This is because the acknowledgment frame can easily be associated to the previous frame that it acknowledges. Indeed, each unicast data frame contains a `Duration` field that is used to reserve the transmission channel to ensure that no collision will affect the acknowledgment frame. The `Sequence Control` field is mainly used by the receiver to remove duplicate frames. Duplicate frames are detected as follows. Each data frame contains a 12 bits sequence number in the `Sequence Control` field and the `Frame Control` field contains the `Retry` bit flag that is set when a frame is transmitted. Each 802.11 receiver stores the most recent sequence number received from each source address in frames whose `Retry` bit is reset. Upon reception of a frame with the `Retry` bit set, the receiver verifies its sequence number to determine whether it is a duplicated frame or not.
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../../protocols/tcp.rst:561
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When an `RST` segment is sent by a TCP entity, it should contain the current value of the `sequence number` for the connection (or 0 if it does not belong to any existing connection) and the `acknowledgment number` should be set to the next expected in-sequence `sequence number` on this connection.
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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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../../protocols/email.rst:274 • ../../protocols/email.rst:293 • ../../protocols/email.rst:307
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6-bit
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../../protocols/ipv6.rst:578
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ICMPv6 is used by TCP implementations to discover the largest MTU size that is allowed to reach a destination host without causing network fragmentation. A TCP implementation parses the `Packets Too Big` ICMP messages that it receives. These ICMP messages contain the MTU of the router's outgoing link in their `Data` field. Upon reception of such an ICMP message, the source TCP implementation adjusts its Maximum Segment Size (MSS) so that the packets containing the segments that it sends can be forwarded by this router without requiring fragmentation.
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../../protocols/wifi.rst:115
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IEEE 802.11 ACK and CTS frames
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../../protocols/tcp.rst:563
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TCP `RST` wars
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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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../../protocols/email.rst:274
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000101 001111 101110 011100 000000 111101 100101 111110
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../../protocols/ipv6.rst:583
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Two types of informational ICMPv6 messages are defined in :rfc:`4443` : `echo request` and `echo reply`, which are used to test the reachability of a destination by using :manpage:`ping6(8)`. Each host is supposed [#fpingproblems]_ to reply with an ICMP `Echo reply` message when it receives an ICMP `Echo request` message. A sample usage of :manpage:`ping6(8)` is shown below.
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