Exit Zen
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../../principles/linkstate.rst:100
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As link state packets are flooded regularly, routers are able to measure the quality (e.g. delay or load) of their links and adjust the metric of each link according to its current quality. Such dynamic adjustments were included in the ARPANET routing protocol [MRR1979]_ . However, experience showed that it was difficult to tune the dynamic adjustments and ensure that no forwarding loops occur in the network [KZ1989]_. Today's link state routing protocols use metrics that are manually configured on the routers and are only changed by the network operators or network management tools [FRT2002]_.
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../../principles/reliability.rst:790
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The `selective repeat` sender maintains a sending buffer that can store up to `W` unacknowledged frames. These frames are sent as long as the sending buffer is not full. Several implementations of a `selective repeat` sender are possible. A simple implementation associates one retransmission timer to each frame. The timer is started when the frame is sent and canceled upon reception of an acknowledgment that covers this frame. When a retransmission timer expires, the corresponding frame is retransmitted and this retransmission timer is restarted. When an acknowledgment is received, all the frames that are covered by this acknowledgment are removed from the sending buffer and the sliding window is updated.
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../../protocols/email.rst:346
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SMTP is a text-based protocol like many other application-layer protocols on the Internet. It relies on the byte-stream service. Servers listen on port `25`. Clients send commands that are each composed of one line of ASCII text terminated by `CR+LF`. Servers reply by sending ASCII lines that contain a three digit numerical error/success code and optional comments.
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../../protocols/ipv6.rst:682
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MAC addresses are allocated in blocks of :math:`2^{20}`. When a company registers for a block of MAC addresses, it receives an identifier. company identifier is then used to populated the `c` bits of the MAC addresses. The company can allocate all addresses in starting with this prefix and manages the `m` bits as it wishes.
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../../protocols/tcp.rst:646
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This TCP segment is then placed in an IP header. We describe IPv6 in the next chapter. The minimum size of the IPv6 (resp. IPv4) header is 40 bytes (resp. 20 bytes).
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../../glossary.rst:20
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a transmission mode where an information is sent from one source to one recipient
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../../principles/linkstate.rst:104
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When a link fails, the two routers attached to the link detect the failure by the absence of HELLO messages received during the last :math:`k \times N` seconds. Once a router has detected the failure of one of its local links, it generates and floods a new LSP that no longer contains the failed link. This new LSP replaces the previous LSP in the network. In practice, the two routers attached to a link do not detect this failure exactly at the same time. During this period, some links may be announced in only one direction. This is illustrated in the figure below. Router `E` has detected the failure of link `E-B` and flooded a new LSP, but router `B` has not yet detected this failure.
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../../principles/reliability.rst:792
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The figure below illustrates the operation of `selective repeat` when frames are lost. In this figure, `C(OK,x)` is used to indicate that all frames, up to and including sequence number `x` have been received correctly.
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../../protocols/email.rst:348
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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.
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../../protocols/ipv6.rst:687
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A MAC address converted into a 64 bits host identifier
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../../protocols/tcp.rst:649
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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.
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../../glossary.rst:292
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vnc
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../../principles/reliability.rst:798
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Selective repeat : example
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../../principles/sharing.rst:1331
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Some networking technologies allow to adjust dynamically the bandwidth of links. For example, some devices can reduce their bandwidth to preserve energy. We ignore these technologies in this basic course and assume that all links used inside the network have a fixed bandwidth.
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../../protocols/email.rst:354
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BNF specification of the SMTP commands
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../../protocols/ipv6.rst:689
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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.
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../../protocols/tcp.rst:651
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See http://fasterdata.es.net/tuning.html for more information on how to tune a TCP implementation
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../../glossary.rst:294
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A networked application that allows to remotely access a computer's Graphical User Interface. See https://en.wikipedia.org/wiki/Virtual_Network_Computing
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../../principles/reliability.rst:802
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Pure cumulative acknowledgments work well with the `go-back-n` strategy. However, with only cumulative acknowledgments a `selective repeat` sender cannot easily determine which frames have been correctly received after a data frame has been lost. For example, in the figure above, the second `C(OK,0)` does not inform explicitly the sender of the reception of `D(2,c)` and the sender could retransmit this frame although it has already been received. A possible solution to improve the performance of `selective repeat` is to provide additional information about the received frames in the acknowledgments that are returned by the receiver. For example, the receiver could add in the returned acknowledgment the list of the sequence numbers of all frames that have already been received. Such acknowledgments are sometimes called `selective acknowledgments`. This is illustrated in the figure above.
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../../principles/sharing.rst:1333
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In this section, we focus on congestion control mechanisms that regulate the transmission rate of the hosts. Other types of mechanisms have been proposed in the literature. For example, `credit-based` flow-control has been proposed to avoid congestion in ATM networks [KR1995]_. With a credit-based mechanism, hosts can only send packets once they have received credits from the routers and the credits depend on the occupancy of the router's buffers.
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