Exit Zen
182
../../principles/sharing.rst:878
English
Consider now a window of two segments. Host `A` can send two segments within 2 msec on its 1 Mbps link. If the first segment is sent at time :math:`t_{0}`, it reaches host `D` at :math:`t_{0}+4`. Host `D` replies with an acknowledgment that opens the sending window on host `A` and enables it to transmit a new segment. In the meantime, the second segment was buffered by router `R1`. It reaches host `D` at :math:`t_{0}+6` and an acknowledgment is returned. With a window of two segments, host `A` transmits at roughly 500 Kbps, i.e. the transmission rate of the bottleneck link.
0/5800 · 580
182
../../protocols/email.rst:293
English
000101 000000
0/130 · 13
182
../../protocols/ipv6.rst:639
English
the source MAC address
0/220 · 22
182
../../protocols/wifi.rst:146
English
Two types of encapsulation schemes were defined to support IP in Ethernet networks : the original encapsulation scheme, built above the Ethernet DIX format is defined in :rfc:`894` and a second encapsulation :rfc:`1042` scheme, built above the LLC/SNAP protocol [IEEE802.2]_. In 802.11 networks, the situation is simpler and only the :rfc:`1042` encapsulation is used. In practice, this encapsulation adds 6 bytes to the 802.11 header. The first four bytes correspond to the LLC/SNAP header. They are followed by the two bytes Ethernet Type field (`0x800` for IP and `0x806` for ARP). The figure below shows an IP packet encapsulated in an 802.11 frame.
0/6530 · 653
183
../../glossary.rst:84
English
TCP/IP
0/100 · 6
183
../../principles/linkstate.rst:61
English
A router that implements flooding must be able to detect whether a received LSP is newer than the stored LSP. This requires a comparison between the sequence number of the received LSP and the sequence number of the LSP stored in the link state database. The ARPANET routing protocol [MRR1979]_ used a 6 bits sequence number and implemented the comparison as follows :rfc:`789`
0/3770 · 377
183
../../principles/reliability.rst:757
English
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.
0/3540 · 354
183
../../principles/sharing.rst:951
English
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.
0/13900 · 1390
183
../../protocols/email.rst:295
English
5 0
0/100 · 7
183
../../protocols/ipv6.rst:640
English
the destination MAC address
0/270 · 27
183
../../protocols/wifi.rst:152
English
IP over IEEE 802.11
0/190 · 19
183
../../protocols/tcp.rst:620
English
Footnotes
0/100 · 9
184
../../glossary.rst:86
English
refers to the :term:`TCP` and :term:`IP` protocols
0/500 · 50
184
../../principles/linkstate.rst:69
English
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`.
0/13070 · 1307
184
../../principles/reliability.rst:763
English
Go-back-n : example
0/190 · 19
184
../../protocols/email.rst:297
English
F A \= \=
0/170 · 17
184
../../protocols/ipv6.rst:641
English
some multiplexing information to indicate the network layer protocol that is responsible for the payload of the frame
0/1170 · 117
184
../../protocols/wifi.rst:154
English
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.
0/7830 · 783
184
../../protocols/tcp.rst:621
English
A detailed presentation of all standardization documents concerning TCP may be found in :rfc:`4614`
0/990 · 99
185
../../glossary.rst:204
English
telnet
0/100 · 6