2. cnp3-ebook
3. English
4. Zen

30 ../../principles/sharing.rst:212
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Let us now try to present a broad overview of the congestion problem in networks. We will assume that the network is composed of dedicated links having a fixed bandwidth [#fadjust]_. A network contains hosts that generate and receive packets and nodes (routers and switches) that forward packets. Assuming that each host is connected via a single link to the network, the largest demand is :math:`\sum{Access Links}`. In practice, this largest demand is never reached and the network will be engineered to sustain a much lower traffic demand. The difference between the worst-case traffic demand and the sustainable traffic demand can be large, up to several orders of magnitude. Fortunately, the hosts are not completely dumb and they can adapt their traffic demand to the current state of the network and the available bandwidth. For this, the hosts need to `sense` the current level of congestion and adjust their own traffic demand based on the estimated congestion. Network nodes can react in different ways to network congestion and hosts can sense the level of congestion in different ways. 1097/10000 · 1097
31 ../../exercises/ex-sharing.rst:609
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In this network, a 250 Kbps link is used between the routers. The propagation delays in the network are negligible. Host `A` sends 1000 bits long segments so that it takes one msec to transmit one segment on the `A-R1` link. Neglecting the transmission delays for the acknowledgments, what is the minimum round-trip time measured on host `A` with such segments ? 362/10000 · 362
31 ../../exercises/sockets.rst:282
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Sending a message to a remote peer using its IPv6 address 57/10000 · 57
31 ../../principles/naming.rst:141
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Footnotes 9/10000 · 9
31 ../../principles/network.rst:215
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Besides the `data plane`, a network is also characterized by its `control plane`. The control plane includes all the protocols and algorithms (often distributed) that compute the forwarding tables that are installed on all routers inside the network. While there is only one possible `data plane` for a given networking technology, different networks using the same technology may use different control planes. 410/10000 · 410
31 ../../principles/reliability.rst:106
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — With the above transmission scheme, a bit is transmitted by setting the voltage on the electrical cable to a specific value during some period of time. We have seen that due to electromagnetic interference, the voltage measured by the receiver can differ from the voltage set by the transmitter. This is the main cause of transmission errors. However, this is not the only type of problem that can occur. Besides defining the voltages for bits `0` and `1`, the above transmission scheme also specifies the duration of each bit. If one million bits are sent every second, then each bit lasts 1 microsecond. On each host, the transmission (resp. the reception) of each bit is triggered by a local clock having a 1 MHz frequency. These clocks are the second source of problems when transmitting bits over a wire. Although the two clocks have the same specification, they run on different hosts, possibly at a different temperature and with a different source of energy. In practice, it is possible that the two clocks do not operate at exactly the same frequency. Assume that the clock of the transmitting host operates at exactly 1000000 Hz while the receiving clock operates at 999999 Hz. This is a very small difference between the two clocks. However, when using the clock to transmit bits, this difference is important. With its 1000000 Hz clock, the transmitting host will generate one million bits during a period of one second. During the same period, the receiving host will sense the wire 999999 times and thus will receive one bit less than the bits originally transmitted. This small difference in clock frequencies implies that bits can "disappear" during their transmission on an electrical cable. This is illustrated in the figure below. 1749/10000 · 1749
31 ../../bibliography.rst:42
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Chiu, D., Jain, R., `Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks <https://dx.doi.org/10.1016/0169-7552(89)90019-6>`_, Computer Networks and ISDN Systems Vol 17, pp 1-14, 1989 225/10000 · 225
31 ../../exercises/network.rst:259
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The network below uses port forwarding tables. It has been running for several hours and all hosts have exchanged packets. What is the content of the port forwarding tables ? 174/10000 · 174
31 ../../exercises/reliability.rst:60
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — all errors that affect a sequence of bits which is shorter than the length of the CRC 85/10000 · 85
31 ../../principles/sharing.rst:214
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Let us first explore which mechanisms can be used inside a network to control congestion and how these mechanisms can influence the behavior of the end hosts. 158/10000 · 158
31 ../../principles/transport.rst:83
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In addition, the :term:`ASCII` table also defines several non-printable or control characters. These characters were designed to allow an application to control a printer or a terminal. These control characters include `CR` and `LF`, that are used to terminate a line, and the `Bell` character which causes the terminal to emit a sound. 336/10000 · 336
31 ../../principles/security.rst:367
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — a public key (:math:`K_{pub}`) that he can distribute to everyone 65/10000 · 65
31 ../../exercises/dns.rst:93
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The next three questions ask you to go one step further by predicting the values of specific fields in the DNS messages. 120/10000 · 120
31 ../../exercises/ipv6.rst:295
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``p:13/64`` for the link between ``R1`` and ``R3``. On this subnet, ``R1`` uses address ``p:13::1`` while router ``R3`` uses address ``p:13::3`` 144/10000 · 144
31 ../../exercises/tcp-2.rst:213
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — As for the establishment of a connection, it is also possible for the two communicating hosts to close the connection at the same time. This is shown in the example below where the remote host sends its own ``FIN`` when acknowledging the first one. This script is available from :download:`/exercises/packetdrill_scripts/local-close2.pkt`. 339/10000 · 339
31 ../../protocols/bgp.rst:101
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The figure below shows a simple example of the BGP routes that are exchanged between domains. In this example, prefix `2001:db8:cafe::/48` is announced by `AS1`. `AS1` advertises a BGP route towards this prefix to `AS2`. The AS-Path of this route indicates that `AS1` is the originator of the prefix. When `AS4` receives the BGP route from `AS1`, it re-announces it to `AS2` and adds its AS number to the AS-Path. `AS2` has learned two routes towards prefix `2001:db8:cafe::/48`. It compares the two routes and prefers the route learned from `AS4` based on its own ranking algorithm. `AS2` advertises to `AS5` a route towards `2001:db8:cafe::/48` with its AS-Path set to `AS2:AS4:AS1`. Thanks to the AS-Path, `AS5` knows that if it sends a packet towards `2001:db8:cafe::/48` the packet first passes through `AS2`, then through `AS4` before reaching its destination inside `AS1`. 879/10000 · 879
31 ../../protocols/congestion.rst:180
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Routers that use a single queue measure their buffer occupancy as the number of bytes of packets stored in the queue [#fslot]_. A first method to detect congestion is to measure the instantaneous buffer occupancy and consider the router to be congested as soon as this occupancy is above a threshold. Typical values of the threshold could be 40% of the total buffer. Measuring the instantaneous buffer occupancy is simple since it only requires one counter. However, this value is fragile from a control viewpoint since it changes frequently. A better solution is to measure the *average* buffer occupancy and consider the router to be congested when this average occupancy is too high. Random Early Detection (RED) [FJ1993]_ is an algorithm that was designed to support Explicit Congestion Notification. In addition to measuring the average buffer occupancy, it also uses probabilistic marking. When the router is congested, the arriving packets are marked with a probability that increases with the average buffer occupancy. The main advantage of using probabilistic marking instead of marking all arriving packets is that flows will be marked in proportion of the number of packets that they transmit. If the router marks 10% of the arriving packets when congested, then a large flow that sends hundred packets per second will be marked 10 times while a flow that only sends one packet per second will not be marked. This probabilistic marking allows marking packets in proportion of their usage of the network resources. 1524/10000 · 1524
31 ../../protocols/email.rst:174
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The `MIME-Version:` header line indicates the version of the MIME specification that was used to encode the email message. The current version of MIME is 1.0. Other versions of MIME may be defined in the future. Thanks to this header line, the software that processes email messages will be able to adapt to the MIME version used to encode the message. Messages that do not contain this header are supposed to be formatted according to the original :rfc:`822` specification. 474/10000 · 474
31 ../../protocols/ethernet.rst:172
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Thin coaxial cable, 185m 24/10000 · 24
31 ../../protocols/http.rst:123
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — a `header`, that contains additional information about the response. The response header ends with an empty line. 113/10000 · 113