ip - the internet protocol

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1、IP-TheInternetProtocolRelatestoLab2.AmoduleontheInternetProtocol.1IP(InternetProtocol)isaNetworkLayerProtocol.IP’scurrentversionisVersion4(IPv4).ItisspecifiedinRFC891.Orientation2IP:ThewaistofthehourglassIPisthewaistofthehourglassoftheInternetprotocolar

2、chitectureMultiplehigher-layerprotocolsMultiplelower-layerprotocolsOnlyoneprotocolatthenetworklayer.3ApplicationprotocolIPisthehighestlayerprotocolwhichisimplementedatbothroutersandhosts4IPServiceDeliveryserviceofIPisminimalIPprovideprovidesanunreliable

3、connectionlessbesteffortservice(alsocalled:“datagramservice”).Unreliable:IPdoesnotmakeanattempttorecoverlostpacketsConnectionless:Eachpacket(“datagram”)ishandledindependently.IPisnotawarethatpacketsbetweenhostsmaybesentinalogicalsequenceBesteffort:IPdoe

4、snotmakeguaranteesontheservice(nothroughputguarantee,nodelayguarantee,…)Consequences:HigherlayerprotocolshavetodealwithlossesorwithduplicatepacketsPacketsmaybedeliveredout-of-sequence5IPsupportsthefollowingservices:one-to-one(unicast)one-to-all(broadcas

5、t)one-to-several(multicast)IPmulticastalsosupportsamany-to-manyservice.IPmulticastrequiressupportofotherprotocols(IGMP,multicastrouting)IPServiceunicastbroadcastmulticast620bytes≤HeaderSize<24x4bytes=60bytes20bytes≤TotalLength<216bytes=65536bytesIPDatag

6、ramFormat7IPDatagramFormatQuestion:InwhichorderarethebytesofanIPdatagramtransmitted?Answer:TransmissionisrowbyrowForeachrow:1.Firsttransmitbits0-72.Thentransmitbits8-153.Thentransmitbits16-234.Thentransmitbits24-31Thisiscallednetworkbyteorderorbigendian

7、byteordering.Note:Manycomputers(incl.Intelprocessors)store32-bitwordsinlittleendianformat.Others(incl.Motorolaprocessors)usebigendian.8Bigendianvs.smallendianLittleEndianStoresthelow-orderbyteatthelowestaddressandthehighestorderbyteinthehighestaddress.B

8、aseAddress+0Byte0BaseAddress+1Byte1BaseAddress+2Byte2BaseAddress+3Byte3IntelprocessorsusethisorderBigEndianStoresthehigh-orderbyteatthelowestaddress,andthelow-orderbyteatthehighestaddress.BaseAddress+0Byte3BaseAddress+1Byte2