Kunonyanyisa Transmission Unit (MTU)

Kunonyanyisa Transmission Unit (MTU)

Mumakomputa network, izwi rekuti Maximum Transmission Unit (MTU) rinoreva saizi (mumabheti) yePDU hombe iyo nhanho yakapihwa yeprotocol yekutaurirana inogona kupfuura. MTU parameter inowanzoonekwa mukubatana neyekutaurirana interface (NIC, serial port, nezvimwewo). Iyo MTU inogona kugadziriswa nematanho (sezvazvakaita neEthernet) kana kusarudzwa panguva yekubatanidza (sezvazvinowanzoitika nenyaya yekunongedzera-kunongedzera serial link). Yakakwira MTU inounza kugona kukuru nekuti paseti yega yega inotakura yakawanda mushandisi data nepo protocol iri pamusoro, senge misoro kana kunonoka kwepakiti kunonoka kunogadziriswa, uye kugona kwepamusoro kunoreva kusimudzira kudiki mukuwandisa kweprotocol kubudikidza. Nekudaro, mapakeji mahombe anogona kutora chinononoka chinongedzo kwechinguva, zvichikonzera kunonoka kukuru kukutevera mapaketi uye kuwedzera lag uye kushoma kwekupedzisira. Semuenzaniso, 1500 byte packet, iyo hombe inobvumidzwa neEthernet pane network network (uye nekudaro yakawanda yeInternet), yaigona kusunga 14.4k modem kweinenge sekondi imwe chete.

Nzira MTU kuwanikwa
IInternet Protocol inotsanangura "nzira MTU" yeiyo nzira yekufambisa yeInternet seMTU diki pane chero ei IP hops e "nzira" pakati peinobva nekuenda. Isa imwe nzira, iyo nzira MTU ndiyo yakakura pasuru saizi iyo inopfuura nenzira iyi isina kutambura kupatsanurwa.

RFC 1191 inotsanangura "Path MTU kuwanikwa", nzira yekumisikidza nzira MTU pakati pemaviri IP mauto. Inoshanda nekumisikidza iyo DF (Usatsemure) sarudzo mune iyo IP misoro yemapaketi anobuda. Chero mudziyo uri munzira iyo MTU iri diki pane iyo packet inodonhedza mapaketi akadaro uye ndokutumira zvakare ICMP "Destination Unreachable (Datagram Too Big)" meseji ine yayo MTU, ichibvumidza iyo sosi inomiririra kudzikisira nzira yayo yainofungidzirwa MTU nenzira kwayo. Maitiro acho anodzokorora kudzamara MTU iri diki zvakakwana kuyambuka nzira yese pasina kupatsanurwa.

Nehurombo, kuwanda kwenhamba yemasaiti inodonhedza ICMP traffic (semuenzaniso kudzivirira kuramba-kwe-sevhisi kurwiswa), iyo inodzivirira nzira kuwanikwa kweMTU kushanda. Mumwe anowanzoona kuvharirwa kwakadai mumamiriro apo kubatana kunoshandira yakaderera-vhoriyamu data asi kunorembera nekukurumidza panongotumirwa inomiririra dhata hombe yedata panguva. Semuenzaniso, ne IRC inobatanidza mutengi inogona kuona kumusoro kune iyo ping meseji, asi isingawane mhinduro mushure meizvozvo. Izvi imhaka yekuti hombe seti yemameseji anotumirwa anotumirwa mumaphakeji akakura kupfuura iwo chaiwo MTU. Zvakare, mune IP network, iyo nzira kubva kukero kero kuenda kune yekuenda kero inowanzo gadziridzwa musimba, mukupindura kune akasiyana zviitiko (mutoro-kuenzanisa, kuzara, zvinobuda, nezvimwewo) - izvi zvinogona kukonzera nzira iyo MTU ichichinja (dzimwe nguva inodzokororwa) panguva yekufambisa, iyo inogona kuburitsa mamwe mapakeji madonhwe mugashiri asati awana iyo itsva yakachengeteka MTU.

Mazhinji Ethernet LANs anoshandisa iyo MTU ye1500 mabheti (maLAN azvino anogona kushandisa Jumbo mafuremu, achibvumidza iyo MTU inosvika kuma9000 mabheti), zvisinei mabumbiro epamuganhu sePPPoE anozodzora izvi. Izvi zvinokonzeresa nzira yekuwanikwa kweMTU kuti iite kushanda pamwe nemhedzisiro inogoneka yekuita mamwe masayiti kuseri kwemashure-akagadziriswa firewalls asinga svikike. Mumwe anogona kushanda akatenderedza izvi, zvinoenderana nechikamu chipi che network chakadzora. semuenzaniso munhu anogona kushandura iyo MSS (yakakura chikamu chikamu) mupaketi rekutanga iro rinomisa kubatana kweTCP pane firewall yemumwe.

Dambudziko iri rakabuda kakawanda kubva pakaunzwa Windows Vista iyo inosuma iyo 'Inotevera Chizvarwa TCP / IP Stack'. Izvi zvinoshandisa "Gamuchira Window Auto-Tuning iyo inoramba ichitarisa yakanakisa yekugamuchira hwindo saizi nekuyera bandwidth-kunonoka chigadzirwa uye iyo application yekudzosa chiyero, uye inogadzirisa yakakwira yekugamuchira hwindo saizi zvichienderana nekuchinja kweneti mamiriro." [2] Izvi zvakaonekwa zvichikundikana pamwe chete nevakuru ma routers uye firewalls ayo airatidzika kushanda nemamwe masisitimu anoshanda. Inowanzoonekwa muADSL mairaira uye inogona kugadziriswa neyakagadziriswa firmware.

ATM backbones, muenzaniso we MTU tuning
Dzimwe nguva zvinosarudzika kubva pakuona kwekugona kuita zvine hungwaru kuzivisa yakaderedzwa MTU mune software pazasi pechokwadi chaiyo urefu hunogona kutsigirwa. Mumwe muenzaniso weizvi inyaya iyo IP traffic inotakurwa pamusoro peATM (Asynchronous Transfer Mode) network. Vamwe vanopa, kunyanya avo vane nharembozha, vanoshandisa ATM pane yavo yepashure musana network.

Kushandisa ATM pakunyatsoita basa kunowanikwa kana pakiti pakureba kuwanda kwema 48 mabheti. Izvi zvinodaro nekuti ATM inotumirwa senge rukova rweakagadzika-akareba mapaketi (anozivikanwa se'maseru '), rimwe nerimwe rayo rinogona kutakura mubhadharo wemakumi mana nemasere edata remushandisi nema48 mabheti epamusoro pamutengo wakazara wemakumi mashanu nematatu pasero. Saka hurefu hwese hweyakafambiswa dhata urefu i5 * ncells byte, uko ncells = nhamba yemasero anodikanwa e = INT ((payload_length + 53) / 53). Saka mune yakaipisisa kesi, uko huwandu hwakazara = (47 * n + 48) mabheti, rimwe sero rekuwedzera rinodiwa kufambisa rimwe rekupedzisira reti rekubhadhara, sero rekupedzisira rinobhadhara mamwe makumi mashanu nematatu akapfuudzwa mabheti makumi mashanu nemashanu ayo ari padding. Neichi chikonzero, kwekunyepedzera kuzivisa yakaderedzwa MTU mune software kunowedzera protocol kunyatso paATM rukoko nekuita iyo ATM AAL48 yakazara payload kureba kuve kuwanda kwemakumi mana nemasere pese pazvinogoneka.

Semuenzaniso, makumi matatu nemasere akazara maATM masero anotakura mubhadharo we31 * 31 = 48 byte. Tichitora huwandu uhu hwa1488 uye tichitora kubva pahwo chero hupamhi hwepamusoro hwakapihwa neese akakodzera maprotocol tinogona kuwana yakatarwa kukosha kune yakanyatso kuderedzwa zvakakwana MTU. Muchiitiko chekuti mushandisi anowanzo tumira mapeketi mazana gumi nemashanu, kutumira pakati pe1488 ne1500 mabheti kunoda imwezve mari yakatarwa yemakumi mashanu nematatu anotapurirana, muchimiro cheimwe ATM sero.

Semuenzaniso we IP pamusoro peDSL kubatana uchishandisa PPPoA / VC-MUX, zvakare kusarudza kuzadza makumi matatu nemasere eATM sepakutanga, isu tinowana inodikanwa zvakaringana yakaderedzwa MTU nhamba ye31 = 1478 * 31-48 tichifunga pamusoro pemakumi gumi emabheti ane yePoint-to-Point Protocol pamusoro pemabheti maviri, uye AAL10 pamusoro pemasere masere. Izvi zvinopa mutengo wakazara we10 * 2 = 5 mabheti anotapurirana kuburikidza neATM kubva pa8 byte paketi rakapfuudzwa kuPPPoA. Panyaya ye IP yakatumirwa pamusoro peADSL ichishandisa PPPoA huwandu hwe31 hwaizove hwakazara urefu hwepaketi yePI kusanganisira IP misoro. Saka mune uyu muenzaniso kuchengeta kune yakazvimisikidza yakadzikiswa MTU ye53 kupesana nekutumira IP mapakeji ehurefu hwese 1643 inochengetedza 1478 mabheti pakiti pane iyo ATM dura pamutengo we1478 byte kudzikiswa kwehurefu hwe IP mapaketi.

Yepamusoro MTU yePPPoE / DSL yekubatana ndeye 1492, paRFC 2516: 6 mabheti ari PPPoE musoro, ichisiya nzvimbo yakakwana ye1488 byte payload, kana makumi matatu nemasere maATM akazara.

Pakupedzisira: Iko kukosha kwakaringana kweMTU ndeyekuve 1492 .... uye kana paine matambudziko ekubhurawuza kana eMSN ekubatanidza matambudziko anofanirwa kudzikiswa kusvika kuhunhu 1422 na1420.

Dheuteronomio: Wikipedia

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