Ngalaba Nnyefe Kachasị (MTU)

Ngalaba Nnyefe Kachasị (MTU)

Na ịkparịta ụka n'Ịntanet, okwu ahụ Nkeji Nnyefe Kachasị (MTU) na -ezo aka nha (n'ime octets) nke PDU kachasị nke otu usoro nkwukọrịta nwere ike ịga n'ihu. Ogwe MTU na -apụtakarị na njikọ nkwukọrịta (NIC, ọdụ ụgbọ mmiri, wdg). Enwere ike idozi MTU site n'ụkpụrụ (dịka ọ dị na Ethernet) ma ọ bụ kpebie n'oge njikọta (dịka ọ na-adịkarị na njikọ njikọta isi-ruo-isi). MTU dị elu na-eweta arụmọrụ ka ukwuu n'ihi na ngwugwu nke ọ bụla na-ebu data ndị ọrụ karịa ka usoro nchịkwa, dị ka nkụnye eji isi mee ma ọ bụ na-egbu oge kwa-paket na-adịgide, yana ịrụ ọrụ dị elu pụtara ntakịrị nkwalite na nnukwu usoro mmepụta. Agbanyeghị, nnukwu ngwugwu nwere ike ịnwe njikọ nwayọ ruo oge ụfọdụ, na -ebute igbu oge dị ukwuu n'ịgbaso ngwugwu yana ịbawanye lag na ntakịrị latency. Dịka ọmụmaatụ, ngwugwu baiti 1500, nke Ethernet kwere ka ọ dị na oyi akwa netwọkụ (ya mere ọtụtụ n'ime ịntanetị), ga -ejikọ modem 14.4k maka ihe dị ka otu sekọnd.

Nchọpụta ụzọ MTU
Protocol Internet na -akọwa “ụzọ MTU” nke ụzọ mbufe ịntanetị dị ka MTU kacha nta nke ọ bụla n'ime hops IP nke “ụzọ” n'etiti isi mmalite na ebe njedebe. N'ikwu ya n'ụzọ ọzọ, ụzọ MTU bụ nha kacha ibu na -agafe n'ụzọ a na -enweghị nkewa.

RFC 1191 na -akọwa "ụzọ MTU nchọpụta", usoro maka ịchọpụta ụzọ MTU n'etiti ndị ọbịa IP abụọ. Ọ na -arụ ọrụ site na ịtọlite ​​nhọrọ DF (Emela Ederede) na nkụnye eji isi mee IP nke ngwugwu na -apụ apụ. Ngwa ọ bụla dị n'okporo ụzọ nke MTU pere mpe karịa ngwugwu ga -agbada ụdị ngwugwu ahụ wee zite ozi ICMP “Ebe a na -apụghị iru (Datagram Too Big)” nke nwere MTU ya, na -enye ohere ka onye ọbịa wee belata ụzọ echere ya MTU n'ụzọ dabara adaba. Usoro a na -emegharị ruo mgbe MTU pere mpe iji gafee okporo ụzọ niile na -enweghị nkewa.

Ọ bụ ihe nwute, ọnụ ọgụgụ na-abawanye nke netwọkụ na-agbada okporo ụzọ ICMP (dịka iji gbochie mwakpo nke ọrụ), nke na-egbochi ụzọ nchọpụta MTU na-arụ ọrụ. Otu na-achọpụtakarị ụdị mkpọchi a n'ọnọdụ ebe njikọ na-arụ ọrụ maka data nwere obere olu mana ọ na-akwụgide ozugbo onye ọbịa zigara nnukwu ngọngọ data n'otu oge. Dịka ọmụmaatụ, site na IRC onye ahịa na -ejikọ nwere ike ịhụ ozi ping, mana ọ nweghị nzaghachi mgbe nke ahụ gasịrị. Nke a bụ n'ihi na a na -ezipụ nnukwu ozi nnabata n'akpa buru ibu karịa ezigbo MTU. Ọzọkwa, na netwọkụ IP, a na-agbanwekarị ụzọ site na isi mmalite gaa na adreesị ebe ọ na-aga, na nzaghachi maka ihe omume dị iche iche (ịhazi ibu, mkpọchi, ntinye, wdg)-nke a nwere ike ibute ụzọ MTU na-agbanwe (mgbe ụfọdụ ugboro ugboro) n'oge nnyefe, nke nwere ike ibubata ngwugwu ọzọ tupu onye nnabata ahụ achọta MTU nchekwa ọhụrụ.

Imirikiti LANs Ethernet na -eji MTU nke octets 1500 (LANs ọgbara ọhụrụ nwere ike iji okpokolo agba Jumbo, na -enye ohere maka MTU ruo 9000 bytes), agbanyeghị usoro oke ala dịka PPPoE ga -ebelata nke a. Nke a na-ebute ụzọ nchọpụta MTU na-arụ ọrụ na nsonaazụ nwere ike ime nke mere ka saịtị ụfọdụ n'azụ ogwe ọkụ ahaziri nke ọma enweghị ike iru. Otu nwere ike rụọ ọrụ na nke a, dabere na akụkụ netwọkụ nke otu na -achịkwa; dịka ọmụmaatụ mmadụ nwere ike ịgbanwe MSS (nha nke kacha) na ngwugwu mbụ nke na -edobe njikọ TCP na firewall mmadụ.

Nsogbu a apụtala ọtụtụ oge kemgbe iwebata Windows Vista nke na -ewebata 'Ọgbọ ọzọ TCP/IP Stack'. Nke a na-arụ ọrụ "Nata na-akpaghị aka na-emegharị windo nke na-ekpebi nha windo kacha mma site na ịlele ngwaahịa na-egbu oge bandwidth na ngwa iweghachite ngwa, wee mezie nha windo kacha dabere na ọnọdụ netwọkụ na-agbanwe agbanwe." [2] A hụla nke a ka ọ daa na njikọta ndị na -anya ụgbọ elu ochie na firewalls nke yiri ka ọ na -arụ ọrụ na sistemụ arụmọrụ ndị ọzọ. A na -ahụkarị ya na ndị na -anya ụgbọ elu ADSL ma nwelite firmware nwere ike idozi ya.

Ọkpụkpụ azụ ATM, ọmụmaatụ nke ịmegharị MTU
Mgbe ụfọdụ ọ ka mma site n'echiche nke ịrụ ọrụ nke ọma iji kwuwapụta MTU belatara na ngwanrọ n'okpuru ezigbo ogologo ogologo enwere ike kwado. Otu ihe atụ nke a bụ ikpe ebe a na -ebufe okporo ụzọ IP n'elu netwọkụ ATM (Asynchronous Transfer Mode). Ụfọdụ ndị na -enye ọrụ, ọkachasị ndị nwere ekwentị ekwentị, na -eji ATM na netwọkụ azụ ha dị n'ime.

A na -enweta ATM na arụmọrụ kacha mma mgbe ogologo ngwugwu bụ otutu nke octets 48. Nke a bụ n'ihi na a na-eziga ATM ka ọ bụrụ iyi nke ngwugwu nwere ogologo-ogologo (nke a maara dị ka 'sel'), nke ọ bụla nwere ike iburu ụgwọ ọrụ nke octets 48 nke data onye ọrụ ya na octets 5 dị n'elu maka ngụkọta ọnụ ahịa 53 baiti n'otu sel. Yabụ ngụkọta ogologo nke data ebugharị ebugharị bụ 53 * ncells bytes, ebe ncells = ọnụọgụ sel achọrọ = INT ((payload_length+47)/48). Yabụ n'ọnọdụ kachasị njọ, ebe ngụkọta ogologo = (48*n+1) bytes, a chọrọ otu sel ọzọ iji bufee otu octets ikpeazụ nke ụgwọ ọrụ, sel nke ikpeazụ na -efu 53 ọzọ na -ebugharị bytes 47 nke bụ padding. Maka nke a, ịkọwapụta MTU belatara na ngwanrọ na -eme ka arụmọrụ protocol dị mma na oyi akwa ATM site na ime ka ogologo oge ịkwụ ụgwọ nke ATM AAL5 bụrụ ọnụọgụ nke baiti 48 mgbe ọ bụla enwere ike.

Dịka ọmụmaatụ, mkpụrụ ego ATM iri atọ na otu juru eju na -ebu ibu nke 31*31 = 48 bytes. Iwere onyonyo a nke 1488 ma wepu ya ihe ọ bụla karịrị akarị sitere na usoro iwu dị elu niile anyị nwere ike nweta uru atụpụtara maka mbelata nke ọma MTU. N'ọnọdụ ebe onye ọrụ ga -ezigakarị ngwugwu 1488 byte, izipu n'etiti 1500 na 1489 bytes chọrọ ọnụ ahịa atọrọ ọzọ nke 1536 otetes na -ebufe, n'ụdị otu ekwentị ATM ọzọ.

Maka ọmụmaatụ IP karịa njikọ DSL site na iji PPPoA/VC-MUX, ọzọ na-ahọrọ imeju mkpụrụ ndụ ATM 31 dị ka ọ dị na mbụ, anyị na-enweta ọnụ ọgụgụ MTU nke chọrọ belata nke ọma nke 1478 = 31*48-10 na-eburu n'uche isi 10 bits gụnyere. nke Protocol-to-Point Protocol karịrị 2 bytes, yana AAL5 dị elu nke octets 8. Nke a na -enye ngụkọta ego nke 31*53 = 1643 octets na -ebugharị site na ATM site na ngwugwu otele 1478 gafere PPPoA. N'ihe gbasara IP zitere ADSL site na iji PPPoA, ọnụ ọgụgụ nke 1478 ga -abụ mkpokọta ngwugwu IP gụnyere nkụnye eji isi mee IP. Yabụ na ihe atụ a na-edebe MTU nke 1478 ewepụtara n'onwe ya ewezuga iziga ngwugwu IP n'ogologo ogologo 1500 na-azọpụta 53 bytes kwa ngwugwu na oyi akwa ATM na ọnụ ahịa mbelata 22 byte nke ogologo ngwugwu IP.

Oke MTU maka njikọ PPPoE/DSL bụ 1492, na RFC 2516: 6 bytes bụ isi PPPoE, na -ahapụ ohere zuru ezu maka ụgwọ ịkwụ ụgwọ 1488, ma ọ bụ mkpụrụ ego ATM 31 zuru ezu.

N'ikpeazụ: Ụkpụrụ ọkọlọtọ nke MTU ga -abụ 1492 .... ma ọ bụrụ na enwere nsogbu nchọgharị ma ọ bụ nsogbu njikọta MSN, ekwesịrị ibelata ya na ụkpụrụ 1422 na 1420.

Ntughari: Wikipedia

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