Ubuninzi beYunithi yokuThumela (MTU)
Kuthungelwano lwecompyuter, igama elithi Ubuninzi boThumelo lweYunithi (MTU) lubhekisa kubungakanani (kwii-byte) zeyona PDU inkulu apho umaleko onikiweyo wenkqubo yonxibelelwano unokudlula uye phambili. Iiparamitha zeMTU zihlala zivela ngokudibana nonxibelelwano lonxibelelwano (i-NIC, uthotho lwezibuko, njl.njl.). I-MTU inokulungiswa ngemigangatho (njengoko kunjalo nge-Ethernet) okanye igqitywe ngexesha lokudibanisa (njengoko kuhlala kunjalo ngamakhonkco e-point-to-point serial). I-MTU ephezulu izisa ukusebenza ngakumbi kuba ipakethi nganye ithwala idatha engaphezulu yomsebenzisi ngelixa iiprothokholi zentloko, ezinje ngezihloko okanye ukulibaziseka kwepakethi nganye zihlala zilungisiwe, kwaye ukusebenza okuphezulu kuthetha ukuphucuka okuncinci kokuhamba kweprotocol enkulu. Nangona kunjalo, iipakethi ezinkulu zinokuhlala kwikhonkco elicothayo kangangexesha elithile, zibangela ukulibaziseka okukhulu ekulandeleni iipakethi kunye nokwandisa i-lag kunye ne-latency encinci. Umzekelo, ipakethi ye-1500 ye-byte, eyeyona inkulu evunyelwe yi-Ethernet kuludwe lwenethiwekhi (yiyo ke loo nto uninzi lwe-Intanethi), ibinokubopha imodem eyi-14.4k malunga nomzuzwana omnye.
Indlela yokufumanisa i-MTU
IProtokholi ye-Intanethi ichaza “umendo we-MTU” wendlela yosasazo ye-Intanethi njengeyona MTU incinci kuyo nayiphi na i-IP hops "yendlela" phakathi komthombo kunye nendawo ekuyiwa kuyo. Beka enye indlela, umendo we-MTU ngowona ubungakanani bepakethe bukhulu ohamba kule ndlela ngaphandle kokubandezeleka kokuqhekeka.
I-RFC 1191 ichaza "ukufunyanwa kwe-MTU Path", indlela yokumisela indlela ye-MTU phakathi kweendawo ezimbini ze-IP. Isebenza ngokuseta ukhetho lwe-DF (Musa ukuQhekeza) kwiintloko ze-IP zeepakethi eziphumayo. Nasiphi na isixhobo ecaleni kwendlela esincinci i-MTU kunepakethi siyakulahla iipakethi ezinjalo kwaye sithumele kwakhona i-ICMP "Indawo ekuYiwa kuyo engenakufikeleleka (iDatagram Enkulu kakhulu)" umyalezo oqukethe i-MTU yayo, uvumela umphathi womthombo ukuba anciphise indlela yakhe ye-MTU ngokufanelekileyo. Inkqubo iphinda ide i-MTU incinci ngokwaneleyo ukuba ihambe yonke indlela ngaphandle kokuqhekeka.
Ngelishwa, ukwanda kwamanani othungelwano alahla ukugcwala kwe-ICMP (umz. Ukuthintela uhlaselo lwenkonzo), ethintela indlela yokufunyanwa kweMTU ekusebenzeni. Umntu uhlala ebona ubhloklo olunjalo kwimeko apho unxibelelwano lusebenzela idatha yevolumu esezantsi kodwa ixhonywe kwakamsinya nje xa umphathi ebethumela ibhloko enkulu yedatha ngexesha. Umzekelo, nge-IRC umxhasi onxibelelanayo unokubona umyalezo we-ping, kodwa ungafumani mpendulo emva koko. Kungenxa yokuba iseti enkulu yemiyalezo eyamkelekileyo ithunyelwa kwiipakethi ezinkulu kuneMTU yokwenyani. Kwakhona, kwinethiwekhi ye-IP, indlela esuka kwidilesi yomthombo kwidilesi ekuyiwa kuyo ihlala iguqulwa ngamandla, ekuphenduleni kwimicimbi eyahlukeneyo (ukulungelelanisa umthwalo, ukuxinana, iziphumo, njl. Iphindaphindwe) ngexesha lokuhambisa, elinokuthi lazise ukuhla kwepakethe ngaphambi kokuba umamkeli afumane iMTU entsha ekhuselekileyo.
Uninzi lwee-LAN ze-Ethernet zisebenzisa i-MTU ye-1500 byte (ii-LAN zangoku zingasebenzisa izakhelo zeJumbo, ukuvumela i-MTU ukuya kuthi ga kwi-9000 byte), nangona kunjalo iiprotokholi zomda njengePPPoE ziyakukunciphisa oku. Oku kubangela ukuba ukufunyanwa kwe-MTU kusebenze kunye nesiphumo esinokubakho sokwenza ezinye iisayithi ngasemva kweendawo zokucima umlilo ezingafikelelekiyo. Umntu unokusebenza ngokujikeleza oku, kuxhomekeke ekubeni leliphi na inethiwekhi elilawulayo; Umzekelo umntu unokutshintsha iMSS (ubukhulu becandelo elininzi) kwipakethi yokuqala emisela uqhagamshelo lwe-TCP kwi-firewall yakho.
Le ngxaki ivele rhoqo ukusukela oko kwaqaliswa iWindows Vista eyazisa 'i-Next Generation TCP / IP Stack'. Oku kuphumeza "Fumana iwindow ngokuzenzekelayo ukuKhangela okuhlala kumisela ubungakanani befestile ngokulinganisa imveliso yolibaziseko-bandwidth kunye nenqanaba lokufumana kwakhona isicelo, kwaye uhlengahlengisa ubuninzi bokufumana ubungakanani bewindows ngokusekwe kwimeko zenethiwekhi eziguqukayo." [2] Oku kubonwe kusilele ngokudibeneyo kunye nee-routers ezindala kunye ne-firewall ezibonakala zisebenza nezinye iinkqubo zokusebenza. Ihlala ibonwa kwi-ADSL imizila kwaye inokulungiswa ngohlaziyo lwe-firmware.
Amathambo omqolo weATM, umzekelo wolungelelwaniso lweMTU
Ngamanye amaxesha kuyakhethwa ukusuka kwindawo yokujonga ukusebenza ngokufanelekileyo ukubhengeza ngokunganyanzelekanga ukuba kuncitshisiwe i-MTU kwisoftware engaphantsi kobude obuphezulu obunokubakho obuxhaswayo. Omnye umzekelo woku yimeko apho ukugcwala kwe-IP kuqhutywa ngaphezulu kwe-ATM (Imowudi yokuGqithisela i-Asynchronous) yenethiwekhi. Abanye ababoneleli, ngakumbi abo banemvelaphi yokufowunelwa, basebenzise i-ATM kuthungelwano lwangaphakathi lomqolo.
Sebenzisa i-ATM ekusebenzeni kakuhle kuyenzeka xa ubude beepakethi zininzi ngee-byte ezingama-48. Kungenxa yokuba i-ATM ithunyelwa njengomsinga weepakethi ezinde-ubude (ezaziwa ngokuba ziiseli), nganye inokuthi ithwale umthwalo wee-byte ezingama-48 zedatha yomsebenzisi ngee-byte ezi-5 zentloko ngexabiso lilonke lama-byte angama-53 kwiseli nganye. Ke ubude bebonke bedatha yedatha ehanjisiweyo yi-53 * ncells bytes, apho i-ncells = inani leeseli ezifunekayo ze- = INT ((payload_length + 47) / 48). Ke kweyona meko imbi kakhulu, apho ubude bebonke = (48 * n + 1) byte, iseli enye eyongezelelweyo iyafuneka ukuhambisa enye yokugqibela yokuhlawulwa komvuzo, iseli yokugqibela ixabisa ii-byte ezingama-53 ezongezelelekileyo ezingama-47. Ngesi sizathu, ukubhengeza ngokungekho mthethweni ukunciphisa i-MTU kwisoftware kwandisa ukusebenza ngokukuko komgaqo we-ATM ngokwenza i-ATM AAL5 iyonke ubude bokuhlawulwa kube zii-byte ezingama-48 xa kunokwenzeka.
Umzekelo, iiseli zeATM ezizaliswe ngokupheleleyo ezingama-31 zithwala umthwalo wee-31 * 48 = 1488 byte. Ukuthatha eli nani le-1488 kunye nokususa kulo naziphi na iintloko ezinegalelo kuzo zonke iiprothokholi ezifanelekileyo ezifanelekileyo sinokufumana ixabiso elicetyisiweyo lokuncitshiswa ngokufanelekileyo kwe-MTU. Kwimeko apho umsebenzisi aqhele ukuthumela iipakethi ze-1500 nge-byte, ukuthumela phakathi kwe-1489 kunye ne-1536 byte kufuna iindleko ezongeziweyo ezongeziweyo zee-byte ezingama-53 ezikhutshiweyo, ngohlobo lwesisele esinye seATM.
Umzekelo we-IP ngaphezulu konxibelelwano lwe-DSL usebenzisa i-PPPoA / VC-MUX, ukuphinda ukhethe ukugcwalisa iiseli ze-ATM ezingama-31 njengangaphambili, sifumana inani elincitshisiweyo elincitshisiweyo le-MTU le-1478 = 31 * 48-10 kuthathelwa ingqalelo ngaphezulu kwe-10 byte ezibandakanya yeProtokholi yokuKhomba ukuya ePointini ngaphezulu kwee-byte ezi-2, kunye ne-AAL5 ngaphezulu kwee-8 ze-byte. Oku kunika indleko zizonke ezingama-31 * 53 = 1643 byte ezithunyelwa nge-ATM ukusuka kwipakethi eyi-1478 eyidluliselwe kwi-PPPoA. Kwimeko ye-IP ethunyelwe ngaphezulu kwe-ADSL isebenzisa iPPPoA inani le-1478 iya kuba bubude bepakethi ye-IP kubandakanya iintloko ze-IP. Ke kulo mzekelo ukugcina kwi-MTU yokunciphisa ngokwakho ye-1478 ngokuchasene nokuthumela iipakethi ze-IP zobude be-1500 isindisa i-byte ezingama-53 kwipakethi nganye kumaleko we-ATM ngendleko zokuncitshiswa kwe-22 byte kubude beepakethi ze-IP.
Elona liphezulu le-MTU yoqhagamshelo lwe-PPPoE / DSL yi-1492, nge-RFC 2516: i-6 byte iyintloko ye-PPPoE, ishiya indawo eyaneleyo yokuhlawulwa kwe-1488 byte, okanye iiseli ze-ATM ezingama-31.
Okokugqibela: Ixabiso eliqhelekileyo leMTT liza kuba li-1492 .... kwaye kwimeko yeengxaki zokukhangela iincwadi okanye iingxaki zonxibelelwano ze-MSN kufanele ukuba yehliswe kwixabiso le-1422 kunye ne-1420.
Imbekiselo: Wikipedia
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