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Data Communication and Host Modes
Rev 3.0B Feb.08 57
remoteIP/portuntilnodataissentorreceivedforthetime
intervaldefinedinthe UDPautoanswertime‐out(S83).
Duringthissession,packetsfromotherIP/portaddresseswill
berejected,unless*UALLisset.Whetherornotanincoming
packetwillcausethemodemtoenteraUDP
sessionisalways
dependentontheS53andAIPsettings.
TheNormalUDPMode(MD3)canbecombinedwithUDP
autoanswertocausetheincomingserialdatatobesentin
UDPpackets(insteadofbeingtreatedasATcommands),while
allowingsessionstobeestablishedfromdifferentUDP
sources.AUDPsessionwillbeinitiatedeitherbyincoming
serial
dataorbyanincomingUDPpacket.Thesession,started
byeithermethod,willbeterminatedwhennodatahasbeen
sentorreceivedfortheS82period.Oncethesessiontermi
‐
nates,anothermaybeinitiatedbyeithermeans.
Whenidle,afterthetime‐outhasoccurred,themodemisinAT
commandmodeontheserialport,andanyvalidATcommand
maybeenteredduringthistime.
Tip: It is best to ensure the idle time-outs for TCP and UDP are never
0 if you're going to be using auto-answer, or either PAD mode. In
those circumstances, you will want the modem to close the socket if
the connection goes idle for too long, particularly if the other side
doesn’t normally close the connection.
Whenthesessionisinitiatedbyserialdata,thenewsession
willbeestablishedusingthedestinationaddressspecifiedin
S53.TheS53settingcanbe changediftheconnecttolastUDP
setting(*UDPLAST=1)isset.TheaddressinS53willbe
updatedtoreflecttheaddressofthelast
sessioninitiatedbyan
incomingUDPpacket.Sothatwhennewdataisreceivedover
thehostserialportwhileintheidlestate,asessionwillbere‐
establishedwiththelastaddress.(Thisbehavioristhesameas
thepreviousHybrid2(MD6)mode).
Tip: TCP auto answer (S0) may also be set simultaneously with UDP
auto answer. Then, when in the idle state, the modem will accept
either a TCP or UDP incoming packet, and enter a TCP or UDP
session as appropriate.
Reliable UDP
ReliableUDPaddsasimpleprotocolontopofUDPtoprovide
reliabledeliveryofdata.Whendataisreceivedfromthehost
serialport,a2byteheaderisaddedtothedata,containinga
messagetypeandasequencenumber.TheRavenwillcontinue
tosendthisdata(buffering
anyreceiveddatainthemeantime)