Ƙididdige fakiti ɗaya na G.729 ta hanyar ramin IPsec

Ana ambaton murya a kan IPsec a matsayin bitrate na codec, kuma wannan adadi ba daidai ba ne a kowane iyaka sai na codec ɗin kansa. Sauti 8 kbit/s ne, fakitin da ke ɗauke da shi ya fi girma, rufin ESP ya fi girma, kuma firam ɗin Ethernet yana ƙara firam ɗin da hoton da aka ɗauka a ramin ba ya nunawa. Ƙididdige fakiti ɗaya daga tsari da aka bayyana ita ce hanya ɗaya tilo ta sanin abin da haɗin jiki zai ɗauka a zahiri. Bayanin da ke ƙasa yana yin haka don shugabanci ɗaya kawai, kuma kowane adadi a nan lissafi ne, ba awo ba.

Fara da zaɓin fakiti, ba da adadin codec ba

Tebur na codec yana ba da saurin kaya kawai: G.729 yana fitar da 8 kbit/s, wato bytes 30 na sauti kowace 30 ms. Ba ya faɗin komai game da kawuna, kariya ko firam, kuma waɗannan uku ne suka fi rinjaye a sakamakon. Tazarar zaɓi ne na manufa wanda dole ɓangarorin biyu su amince da shi, don haka zaɓe shi da farko kuma ka bayyana shi, domin kowane adadi na gaba ya dogara da wannan shawara ɗaya.

Wannan misali yana amfani da 30 ms, don haka saurin fakiti 33.3 ne a cikin daƙiƙa. Yana ɗauka kawun RTP na bytes 12, kawun UDP na bytes 8 da kawun IPv4 na ciki na bytes 20 ba tare da zaɓuɓɓuka ba, kuma babu SRTP, matsewar kawuna ko cikar sirrin kwararar zirga-zirga; kowane canji yana motsa kasafin kuɗi tare da shi, shi ya sa zato suke kusa da amsar.

Ƙara kawunan ciki, sannan rufin ESP

Manhajar tana aika kaya da RTP da UDP da IP, wanda a wannan fakiti ke zama bytes 70. Wannan kwarara ta ciki ta kai 18.7 kbit/s, wanda ya riga ya fi ninki biyu na saurin codec, domin kawuna ne ba sauti ba ke yin yawancin fakitin. Babu ɗaya daga cikin waɗannan bytes ɗin murya; su ne kuɗin adireshi da jeri. Hoton da aka ɗauka a saman ramin yana nuna wannan adadi daidai, kuma shi ne adadin da mutane ke ambata idan sun ce kiran ƙarami ne.

Shi ne kuma adadin da ba ya taɓa isa waya. Yanayin ramin ESP yana ƙara SPI da lambar jeri na bytes 8, IV bayyananne na bytes 8 don AES-GCM, wutsiya na bytes 2 da alamar tabbatarwa na bytes 16. Kayan bytes 70 da wutsiya sun kai 72, wanda ya riga ya cika daidaiton bytes huɗu, don haka ba a buƙatar ƙarin cikawa a nan.RFC 4106 yana ƙayyade girmar IV da alamar GCM, kuma duka biyu suna cikin lissafi, ba a cikin bayanin ƙasa ba:

30  payload, G.729 at 30 ms
12  RTP
 8  UDP
20  inner IPv4
--
70  inner IP packet
 8  ESP SPI and sequence
 8  explicit IV
 2  pad length and next header
16  authentication tag
--
104 ESP packet

Ƙara kawunan waje da wucewar NAT ke buƙata

A wajen rufin ESP akwai kawun IPv4 na waje na bytes 20 da kawun UDP na bytes 8 don wucewar NAT, don haka fakitin ya zama bytes 132. Rufin UDP yana nan domin fakitin dole ya tsallake na'urar fassara tsakanin abokan tarayya, kuma yana canza siffar waje ba tare da taɓa kayan da aka kare ba. A fakiti 33.3 a cikin daƙiƙa, bytes 132 kusan 35.2 kbit/s ne, wato kusan ninki huɗu na saurin codec.

Ba za a iya cire alamar ko IV daga kimantawa don a ƙara ƙarami ba, domin duka biyu suna cikin abin da haɗin zai ɗauka a zahiri. Kimantawa da ta bar su tana bayyana fakitin da mai karɓa zai ƙi. Haka ma wutsiyar, wadda take don nuna iyakar kaya da kawun na gaba cikin yankin da aka kare.

Faɗi iyakar kafin ka ambaci adadin

Adadin IP na waje har yanzu ba ya haɗa firam ɗin Ethernet. Haɗin shiga mai alama ko marar alama yana ƙara kawun MAC na bytes 14 da jerin duba firam na bytes 4, wanda ke mai da firam ɗin bytes 150, wanda shine girman da tashar switch ke ƙididdigewa. A wannan saurin fakiti wannan 40 kbit/s ne, ninki biyar na saurin codec, kuma bambancin ba ɓarna ba ne illa kuɗin ɗauka.

Adadin 40 kbit/s har yanzu ba ya haɗa preambul, tazarar tsakanin firam, alamar VLAN, rufin mai bayarwa, RTCP, sigina da sautin da ke tafiya ɗaya ɓangaren. Kimantawa ce ta kowane shugabanci, ba ajiyar haɗi ba, kuma ambatonsa a matsayin ajiya yana ƙara abin da haɗin zai ajiye a wuri ɗaya yayin da yake rage shi a wani. Hoton da aka ɗauka a kan mai masauki yana iya rasa firam ɗin da haɗin ke ƙarawa, shi ya sa dole a faɗi iyakar tare da adadin, kuma shi ya sa teburin iyakoki ya fi amfani fiye da adadi ɗaya na kanun labari. Yi ajiya daban don shugabancin da ba ka ƙididdige shi ba.

Duba lissafin da ke gaban maɗaurin

Kafin ka amince da kimantawa, kwatanta ta da abin da maɗaurin ke bayarwa don adadin fakiti da aka sani. Ɗauki hoton a maɗaurin jiki ba na'urar rami ba, domin firam ɗin da kake ƙoƙarin lissafta ya kasance ciki, kuma ka yi tsammanin ɗan bambanci ba cikakkiyar daidaituwa ba.

sudo tcpdump -ni eth0 -c 50 'udp port 4500'
ip -s link show eth0

Hoton yana tabbatar da girman fakitin waje, yayin da ma'aunin maɗaurin ke nuna saurin tare da firam. Idan biyun sun bambanta kusan gwargwadon izinin Ethernet, lissafin daidai ne kuma iyakar ce kawai aka yi wa suna mara kyau. Bambancin da ya fi kawun firam ɗaya girma yana nuni ga wani abu a haɗin, kamar sake aikawa ko wata kwarara da ke raba maɗaurin. Rubuta tazarar fakiti, rukunin kariya da iyakar kusa da adadin, domin kimantawa ba tare da waɗannan uku ba ana ambatonta a matsayin awo daga mai karatu na gaba.