2. cnp3-ebook
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4. Zen

193 ../../principles/linkstate.rst:334
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — When a link is reported in the LSP of only one of the attached routers, routers consider the link as having failed and they remove it from the directed graph that they compute from their LSDB. This is called the `two-way connectivity check`. This check allows link failures to be quickly flooded as a single LSP is sufficient to announce such bad news. However, when a link comes up, it can only be used once the two attached routers have sent their LSPs. The `two-way connectivity check` also allows for dealing with router failures. When a router fails, all its links fail by definition. These failures are reported in the LSPs sent by the neighbors of the failed router. The failed router does not, of course, send a new LSP to announce its failure. However, in the graph that represents the network, this failed router appears as a node that only has outgoing edges. Thanks to the `two-way connectivity check`, this failed router cannot be considered as a transit router to reach any destination since no outgoing edge is attached to it. 1041/10000 · 1041
194 ../../glossary.rst:47
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The world wide web consortium was created to standardize the protocols and mechanisms used in the world wide web. It is thus focused on a subset of the application layer. See https://www.w3.org 193/10000 · 193
194 ../../principles/reliability.rst:990
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Maximum window size with `go-back-n` and `selective repeat` 59/10000 · 59
194 ../../principles/linkstate.rst:336
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — When a router has failed, its LSP must be removed from the LSDB of all routers [#foverload]_. This can be done by using the `age` field that is included in each LSP. The `age` field is used to bound the maximum lifetime of a link state packet in the network. When a router generates a LSP, it sets its lifetime (usually measured in seconds) in the `age` field. All routers regularly decrement the `age` of the LSPs in their LSDB and a LSP is discarded once its `age` reaches `0`. Thanks to the `age` field, the LSP from a failed router does not remain in the LSDBs forever. 573/10000 · 573
194 ../../protocols/email.rst:348
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The SMTP protocol, like most text-based protocols, is specified as a :term:`BNF`. The full BNF is defined in :rfc:`5321`. The main SMTP commands are defined by the BNF rules shown in the figure below. 200/10000 · 200
194 ../../protocols/ipv6.rst:687
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A MAC address converted into a 64 bits host identifier 54/10000 · 54
194 ../../protocols/tcp.rst:649
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A precise estimation of the maximum bandwidth that can be achieved by a TCP connection should take into account the overhead of the TCP and IP headers as well. 159/10000 · 159
195 ../../glossary.rst:33
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — WAN 3/10000 · 3
195 ../../principles/reliability.rst:992
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A reliable protocol that uses `n` bits to encode its sequence number can send up to :math:`2^n` successive frames. However, to ensure a reliable delivery of the frames, `go-back-n` and `selective repeat` cannot use a sending window of :math:`2^n` frames. Consider first `go-back-n` and assume that a sender sends :math:`2^n` frames. These frames are received in-sequence by the destination, but all the returned acknowledgments are lost. The sender will retransmit all frames. These frames will all be accepted by the receiver and delivered a second time to the user. It is easy to see that this problem can be avoided if the maximum size of the sending window is :math:`{2^n}-1` frames. A similar problem occurs with `selective repeat`. However, as the receiver accepts out-of-sequence frames, a sending window of :math:`{2^n}-1` frames is not sufficient to ensure a reliable delivery. It can be easily shown that to avoid this problem, a `selective repeat` sender cannot use a window that is larger than :math:`\frac{2^n}{2}` frames. 1035/10000 · 1035
195 ../../principles/linkstate.rst:338
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — To compute its forwarding table, each router computes the spanning tree rooted at itself by using Dijkstra's shortest path algorithm [Dijkstra1959]_. The forwarding table can be derived automatically from the spanning as shown in the figure below. 247/10000 · 247
195 ../../protocols/email.rst:354
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — BNF specification of the SMTP commands 38/10000 · 38
195 ../../protocols/ipv6.rst:689
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Inside a MAC address, the two bits indicated as `0` and `g` in the figure above play a special role. The first bit indicates whether the address is universal or local. The `g` bit indicates whether this is a multicast address or a unicast address. The MAC address can be converted into a 64 bits host identifier by flipping the value of the `0` bit and inserting ``FFFE``, i.e. ``1111111111111110`` in binary, in the middle of the address as shown in the figure below. The `c`, `m` and `g` bits of the MAC address are not modified. 531/10000 · 531
195 ../../protocols/tcp.rst:651
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — See http://fasterdata.es.net/tuning.html for more information on how to tune a TCP implementation 97/10000 · 97
196 ../../glossary.rst:35
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Wide Area Network 17/10000 · 17
196 ../../principles/reliability.rst:1038
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Reliable protocols often need to send data in both directions. To reduce the overhead caused by the acknowledgments, most reliable protocols use `piggybacking`. Thanks to this technique, a datalink entity can place the acknowledgments and the receive window that it advertises for the opposite direction of the data flow inside the header of the data frames that it sends. The main advantage of piggybacking is that it reduces the overhead as it is not necessary to send a complete frame to carry an acknowledgment. This is illustrated in the figure below where the acknowledgment number is underlined in the data frames. Piggybacking is only used when data flows in both directions. A receiver will generate a pure acknowledgment when it does not send data in the opposite direction as shown in the bottom of the figure. 821/10000 · 821
196 ../../principles/linkstate.rst:380
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — It should be noted that link state routing assumes that all routers in the network have enough memory to store the entire LSDB. The routers that do not have enough memory to store the entire LSDB cannot participate in link state routing. Some link state routing protocols allow routers to report that they do not have enough memory and must be removed from the graph by the other routers in the network, but this is outside the scope of this e-book. 449/10000 · 449
196 ../../protocols/email.rst:356
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In this BNF, `atext` corresponds to printable ASCII characters. This BNF rule is defined in :rfc:`5322`. The five main commands are `EHLO` [#fehlo]_, `MAIL FROM:`, `RCPT TO:`, `DATA` and `QUIT`. `Postmaster` is the alias of the system administrator who is responsible for a given domain or SMTP server. All domains must have a `Postmaster` alias. 346/10000 · 346
196 ../../protocols/ipv6.rst:692
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The next step is to connect the LAN to the Internet. For this, a router is attached to the LAN. 95/10000 · 95
196 ../../protocols/tcp.rst:653
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In theory, a TCP implementation could store the timestamp of each data segment transmitted and compute a new estimate for the round-trip-time upon reception of the corresponding acknowledgment. However, using such frequent measurements introduces a lot of noise in practice and many implementations still measure the round-trip-time once per round-trip-time by recording the transmission time of one segment at a time :rfc:`2988` 429/10000 · 429
197 ../../glossary.rst:211
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — X.25 4/10000 · 4