Ethernet yana ko'ina, kuma dubun dubatar masana'antun suna samar da kayan aikin da ke goyan bayan sa. Duk da haka, kusan dukkanin waɗannan na'urori suna da abu guda ɗaya - :
$ ip l
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP
link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
MTU (Mafi girman Sashin watsawa) yana bayyana matsakaicin girman fakitin bayanai guda. Gabaɗaya, lokacin da kuke musayar saƙonni da na'urori a cikin LAN ɗinku, MTU zai kasance akan tsari 1500 bytes, kuma kusan gabaɗayan Intanet yana aiki akan 1500 bytes. Duk da haka, wannan ba yana nufin cewa waɗannan fasahohin sadarwa ba za su iya watsa manyan fakiti masu girma dabam ba.
Misali, 802.11 (wanda aka fi sani da WiFi) yana da MTU na bytes 2304, kuma idan cibiyar sadarwar ku tana amfani da FDDI, to MTU ɗin ku shine 4352 bytes. Ethernet kanta yana da ra'ayi na "giant Frames", inda MTU za a iya sanya girman har zuwa 9000 bytes (tare da goyon bayan wannan yanayin ta hanyar NICs, masu sauyawa da masu amfani da hanyoyi).
Koyaya, akan Intanet wannan ba lallai bane musamman. Tunda manyan kashin bayan Intanet sun kasance da haɗin gwiwar Ethernet, an saita iyakar girman fakitin da ba na hukuma ba zuwa 1500B don guje wa rarrabuwar fakiti akan wasu na'urori.
Lamba 1500 da kanta baƙon abu ne - wanda zai yi tsammanin ci gaba a cikin duniyar kwamfuta ya dogara da iko na biyu, misali. To daga ina 1500B ya fito kuma me yasa har yanzu muke amfani dashi?
Lambar sihiri
Babban ci gaban Ethernet na farko a cikin duniya ya zo ta hanyar ma'auni. (bakin ciki) kuma (kauri), lambobin da a cikinsu ke nuna ɗaruruwan mita nawa wani ɓangaren cibiyar sadarwa zai iya rufewa.
Tun da akwai ka'idoji da yawa masu fafatawa a lokacin, kuma hardware yana da iyakokin sa, mahaliccin tsarin ya yarda cewa buƙatun ƙwaƙwalwar ajiyar fakitin buffer ya taka rawa wajen bayyanar lambar sihirin 1500:
A cikin hangen nesa, a bayyane yake cewa mafi girma mafi girma na iya zama mafi kyawun mafita, amma idan mun haɓaka farashin NICs da wuri, da zai hana Ethernet ya zama yaɗuwa.
Duk da haka, wannan ba duka labarin ba ne. IN "Ethernet: Canjawar Fakitin Rarraba a cikin Cibiyoyin Sadarwar Kwamfuta na Gida," 1980, yana ba da ɗaya daga cikin farkon nazarin tasirin amfani da manyan fakiti a cikin cibiyoyin sadarwa. A wancan lokacin, wannan yana da mahimmanci musamman ga hanyoyin sadarwa na Ethernet, tunda suna iya haɗa dukkan tsarin tare da kebul na coaxial guda ɗaya, ko kuma sun ƙunshi cibiyoyi masu iya aika fakiti ɗaya zuwa duk nodes akan sashe ɗaya lokaci ɗaya.
Ya zama dole a zaɓi lambar da ba za ta haifar da jinkiri mai yawa ba yayin aika saƙonni a cikin sassa (wani lokaci ma aiki sosai), kuma a lokaci guda ba zai ƙara adadin fakiti da yawa ba.
A bayyane yake, injiniyoyi a wancan lokacin sun zaɓi lamba 1500 B (kimanin 12000 bits) a matsayin zaɓin “aminci”.
Tun daga wannan lokacin, wasu tsarin saƙo daban-daban sun zo sun tafi, amma a cikinsu, Ethernet yana da mafi ƙarancin ƙimar MTU tare da Bytes 1500. Ya wuce mafi ƙarancin ƙimar MTU a cikin hanyar sadarwa yana nufin ko dai haifar da rarrabuwar fakiti ko shiga cikin PMTUD [gano matsakaicin girman fakitin. don hanyar da aka zaɓa]. Duk zaɓuɓɓukan biyu suna da nasu matsaloli na musamman. Ko da a wasu lokuta manyan masana'antun OS sun saukar da ƙimar MTU ko da ƙasa.
Fasali mai inganci
Yanzu mun san cewa MTU na Intanet yana iyakance ga 1500B, galibi saboda ma'aunin latency na gado da iyakokin kayan aiki. Nawa ne wannan ya shafi ingancin Intanet?
Idan muka kalli bayanai daga babban wurin musayar Intanet AMS-IX, za mu ga cewa aƙalla 20% na fakitin da aka watsa suna da matsakaicin girman. Hakanan zaka iya duba jimlar zirga-zirgar LAN:
Idan kun haɗa hotuna biyu, kuna samun wani abu kamar haka (ƙididdigar zirga-zirga na kowane girman fakiti):
Ko, idan muka kalli zirga-zirgar duk waɗannan kanun labarai da sauran bayanan sabis, muna samun jadawali ɗaya tare da sikelin daban:
Ana kashe babban kaso na bandwidth akan kanun labarai don fakiti a cikin mafi girman aji. Tunda mafi girman abin hawa a kololuwar zirga-zirgar ababen hawa shine 246 GB/s, ana iya ɗauka cewa idan duk mun canza zuwa "firam ɗin jumbo" lokacin da irin wannan zaɓin har yanzu ya kasance, wannan saman zai zama kusan 41 GB/s.
Amma ina tsammanin a yau ga mafi girman ɓangaren Intanet wanda jirgin ya riga ya tafi. Kuma ko da yake wasu masu samarwa suna aiki tare da MTU na 9000, yawancin ba su goyi bayan shi ba, kuma ƙoƙarin canza wani abu a duniya akan Intanet ya tabbatar da cewa yana da wuyar gaske akai-akai.
source: www.habr.com