Exit Zen
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../../principles/reliability.rst:769
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the `go-back-n` sender retransmits all unacknowledged frames once it has detected a loss
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../../principles/sharing.rst:1060
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In the above pseudocode, `cwin` contains the congestion window stored as a real number of segments. This congestion window is updated upon the arrival of each acknowledgment and when congestion is detected. For simplicity, we assume that `cwin` is stored as a floating point number but only full segments can be transmitted.
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../../protocols/email.rst:307
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000101 001111 101100
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../../protocols/ipv6.rst:649
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Interactions between IPv6 and the datalink layer
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../../protocols/tcp.rst:627
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On many departmental networks containing Unix workstations, it was common to allow users on one of the hosts to use ``rlogin`` :rfc:`1258` to run commands on any of the workstations of the network without giving any password. In this case, the remote workstation "authenticated" the client host based on its IP address. This was a bad practice from a security viewpoint.
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../../glossary.rst:240
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A Top-level domain name. There are two types of TLDs. The ccTLD are the TLD that correspond to a two letters :term:`ISO-3166` country code. The gTLD are the generic TLDs that are not assigned to a country.
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../../principles/reliability.rst:776
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`Selective repeat` is a better strategy to recover from losses. Intuitively, `selective repeat` allows the receiver to accept out-of-sequence frames. Furthermore, when a `selective repeat` sender detects losses, it only retransmits the frames that have been lost and not the frames that have already been correctly received.
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../../principles/sharing.rst:1063
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As an illustration, let us consider the network scenario above and assume that the router implements the DECBit binary feedback scheme [RJ1995]_. This scheme uses a form of Forward Explicit Congestion Notification and a router marks the congestion bit in arriving packets when its buffer contains one or more packets. In the figure below, we use a `*` to indicate a marked packet.
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../../protocols/email.rst:309
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5 15 44
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../../protocols/ipv6.rst:653
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IPv6 hosts and routers frequently interact with the datalink layer service. To understand the main interactions, it is useful to analyze all the packets that are exchanged when a simple network containing a few hosts and routers is built. Let us first start with a LAN containing two hosts [#fMAC]_.
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../../protocols/tcp.rst:634
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Of course, such a simultaneous TCP establishment can only occur if the source port chosen by the client is equal to the destination port chosen by the server. This may happen when a host can serve both as a client as a server or in peer-to-peer applications when the communicating hosts do not use ephemeral port numbers.
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../../glossary.rst:307
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TLS
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../../principles/linkstate.rst:87
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Flooding allows LSPs to be distributed to all routers inside the network without relying on routing tables. In the example above, the LSP sent by router `E` is likely to be sent twice on some links in the network. For example, routers `B` and `C` receive `E`'s LSP at almost the same time and forward it over the `B-C` link. To avoid sending the same LSP twice on each link, a possible solution is to slightly change the pseudo-code above so that a router waits for some random time before forwarding a LSP on each link. The drawback of this solution is that the delay to flood an LSP to all routers in the network increases. In practice, routers immediately flood the LSPs that contain new information (e.g. addition or removal of a link) and delay the flooding of refresh LSPs (i.e. LSPs that contain exactly the same information as the previous LSP originating from this router) [FFEB2005]_.
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../../principles/reliability.rst:778
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A `selective repeat` receiver maintains a sliding window of `W` frames and stores in a buffer the out-of-sequence frames that it receives. The figure below shows a five-frame receive window on a receiver that has already received frames `7` and `9`.
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../../principles/sharing.rst:1218
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When the connection starts, its congestion window is set to one segment. Segment `S0` is sent an acknowledgment at roughly :math:`t_{0}+4`. The congestion window is increased by one segment and `S1` and `S2` are transmitted at time :math:`t_{0}+4` and :math:`t_{0}+5`. The corresponding acknowledgments are received at times :math:`t_{0}+8` and :math:`t_{0}+10`. Upon reception of this last acknowledgment, the congestion window reaches `3` and segments can be sent (`S4` and `S5`). When segment `S6` reaches router `R1`, its buffers already contain `S5`. The packet containing `S6` is thus marked to inform the sender of the congestion. Note that the sender will only notice the congestion once it receives the corresponding acknowledgment at :math:`t_{0}+18`. In the meantime, the congestion window continues to increase. At :math:`t_{0}+16`, upon reception of the acknowledgment for `S5`, it reaches `4`. When congestion is detected, the congestion window is decreased down to `2`. This explains the idle time between the reception of the acknowledgment for `S*6` and the transmission of `S10`.
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../../protocols/email.rst:311
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F P s \=
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../../protocols/ipv6.rst:671
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Hosts ``A`` and ``B`` are attached to the same datalink layer network. They can thus exchange frames by using the MAC addresses shown in the figure above. To be able to use IPv6 to exchange packets, they need to have an IPv6 address. One possibility would be to manually configure an IPv6 address on each host. However, IPv6 provides a better solution thanks to the `link-local` IPv6 addresses. A `link-local` IPv6 address is an address that is composed by concatenating the ``fe80:://64`` prefix with the MAC address of the device. In the example above, host A would use IPv6 `link-local` address ``fe80::0223:45FF:FE67:89ab`` and host B ``fe80::0234:56FF:FE78:9abc``. With these two IPv6 addresses, the hosts can exchange IPv6 packets.
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../../protocols/tcp.rst:636
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Sending a packet with a different source IP address than the address allocated to the host is called sending a :term:`spoofed packet`.
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../../glossary.rst:309
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Transport Layer Security, defined in :rfc:`5246` is a cryptographic protocol that is used to provide communication security for Internet applications. This protocol is used on top of the transport service but a detailed description is outside the scope of this book.
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../../principles/linkstate.rst:89
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To ensure that all routers receive all LSPs, even when there are transmissions errors, link state routing protocols use `reliable flooding`. With `reliable flooding`, routers use acknowledgments and if necessary retransmissions to ensure that all link state packets are successfully transferred to each neighboring router. Thanks to reliable flooding, all routers store in their LSDB the most recent LSP sent by each router in the network. By combining the received LSPs with its own LSP, each router can build a graph that represents the entire network topology.
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