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../../principles/reliability.rst:757
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The operation of `go-back-n` is illustrated in the figure below. In this figure, note that upon reception of the out-of-sequence frame `D(2,c)`, the receiver returns a cumulative acknowledgment `C(OK,0)` that acknowledges all the frames that have been received in sequence. The lost frame is retransmitted upon the expiration of the retransmission timer.
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../../principles/sharing.rst:951
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Our last example is a window of four segments. These segments are sent at :math:`t_{0}`, :math:`t_{0}+1`, :math:`t_{0}+2` and :math:`t_{0}+3`. The first segment reaches host `D` at :math:`t_{0}+4`. Host `D` replies to this segment by sending an acknowledgment that enables host `A` to transmit its fifth segment. This segment reaches router `R1` at :math:`t_{0}+5`. At that time, router `R1` is transmitting the third segment to router `R2` and the fourth segment is still in its buffers. At time :math:`t_{0}+6`, host `D` receives the second segment and returns the corresponding acknowledgment. This acknowledgment enables host `A` to send its sixth segment. This segment reaches router `R1` at roughly :math:`t_{0}+7`. At that time, the router starts to transmit the fourth segment to router `R2`. Since link `R1-R2` can only sustain 500 Kbps, packets will accumulate in the buffers of `R1`. On average, there will be two packets waiting in the buffers of `R1`. The presence of these two packets will induce an increase of the round-trip-time as measured by the transport protocol. While the first segment was acknowledged within 4 msec, the fifth segment (`data(4)`) that was transmitted at time :math:`t_{0}+4` is only acknowledged at time :math:`t_{0}+11`. On average, the sender transmits at 500 Kbps, but the utilization of a large window induces a longer delay through the network.
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../../protocols/email.rst:295
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5 0
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../../protocols/ipv6.rst:640
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the destination MAC address
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../../protocols/wifi.rst:152
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IP over IEEE 802.11
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../../protocols/tcp.rst:620
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Footnotes
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../../glossary.rst:86
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refers to the :term:`TCP` and :term:`IP` protocols
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../../principles/linkstate.rst:69
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This comparison takes into account the modulo :math:`2^{6}` arithmetic used to increment the sequence numbers. Intuitively, the comparison divides the circle of all sequence numbers into two halves. Usually, the sequence number of the received LSP is equal to the sequence number of the stored LSP incremented by one, but sometimes the sequence numbers of two successive LSPs may differ, e.g. if one router has been disconnected for some time. The comparison above worked well until October 27, 1980. On this day, the ARPANET crashed completely. The crash was complex and involved several routers. At one point, LSP `40` and LSP `44` from one of the routers were stored in the LSDB of some routers in the ARPANET. As LSP `44` was the newest, it should have replaced LSP `40` on all routers. Unfortunately, one of the ARPANET routers suffered from a memory problem and sequence number `40` (`101000` in binary) was replaced by `8` (`001000` in binary) in the buggy router and flooded. Three LSPs were present in the network and `44` was newer than `40` which is newer than `8`, but unfortunately `8` was considered to be newer than `44`... All routers started to exchange these three link state packets forever and the only solution to recover from this problem was to shutdown the entire network :rfc:`789`.
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../../principles/reliability.rst:763
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Go-back-n : example
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../../protocols/email.rst:297
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F A \= \=
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../../protocols/ipv6.rst:641
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some multiplexing information to indicate the network layer protocol that is responsible for the payload of the frame
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../../protocols/wifi.rst:154
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The second important utilization of the management frames is to allow a WiFi station to be associated with an access point. When a WiFi station starts, it listens to beacon frames to find the available SSIDs. To be allowed to send and receive frames via an access point, a WiFi station must be associated to this access point. If the access point does not use any security mechanism to secure the wireless transmission, the WiFi station simply sends an `Association request` frame to its preferred access point (usually the access point that it receives with the strongest radio signal). This frame contains some parameters chosen by the WiFi station and the SSID that it requests to join. The access point replies with an `Association response frame` if it accepts the WiFI station.
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../../protocols/tcp.rst:621
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A detailed presentation of all standardization documents concerning TCP may be found in :rfc:`4614`
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../../glossary.rst:204
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telnet
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../../principles/linkstate.rst:71
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Current link state routing protocols usually use 32 bits sequence numbers and include a special mechanism in the unlikely case that a sequence number reaches the maximum value (with a 32 bits sequence number space, it takes 136 years to cycle the sequence numbers if a link state packet is generated every second).
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../../principles/reliability.rst:766
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The main advantage of `go-back-n` is that it can be easily implemented, and it can also provide good performance when only a few frames are lost. However, when there are many losses, the performance of `go-back-n` quickly drops for two reasons :
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../../protocols/email.rst:303
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0x14b9
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../../protocols/ipv6.rst:643
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LANs also provide a broadcast and a multicast service. The broadcast service enables a device to send a single frame to all the devices attached to the same LAN. This is done by reserving a special broadcast MAC address (typically all bits of the address are set to one). To broadcast a frame, a device simply needs to send a frame whose destination is the broadcast address. All devices attached to the datalink network will receive the frame.
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../../protocols/wifi.rst:158
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The 802.11 working group defined the `basic service set (BSS)` as a group of devices that communicate with each other. We continue to use `network` when referring to a set of devices that communicate.
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../../protocols/tcp.rst:623
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Several researchers have analyzed the utilization of TCP and UDP in the global Internet. Most of these studies have been performed by collecting all the packets transmitted over a given link during a period of a few hours or days and then analyzing their headers to infer the transport protocol used, the type of application, ... Recent studies include http://www.caida.org/research/traffic-analysis/tcpudpratio/, https://research.sprintlabs.com/packstat/packetoverview.php or http://www.nanog.org/meetings/nanog43/presentations/Labovitz_internetstats_N43.pdf
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