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Data Communication and Host Modes
Rev 3.0B Feb.08 68
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.ThePinPointXwill
continuetosendthisdata
(bufferinganyreceiveddatainthe
meantime)untilitreceivesanacknowledgementwiththis
sequencenumber.Ifanacknowledgementisnotreceived
withinthetime‐outperiod(specifiedinS7),thedatawillbe
retransmitted.Thiswillcontinueuntilanacknowledgementis
receivedorthemodemisreset.Likewiseany
UDPpackets
receivedbythePinPointXareexpectedtohavethissimple
header.ThePinPointXwillissueanacknowledgementforany
validpacketswhicharereceived.
ToconfigurethePinPointXforanormalUDPsession,you
needtosettheStartup ModeDefaultto73(ATMD73).Ifyou
areusingtwomodems,configuretheDestinationIPandPort
ineachtopointtoeachother.Serialdatawillthenbesent
reliablybetweenthetwo.
Caution: Although it adds reliability, the simple implementation of the
Reliable UDP mode in the does not check for duplicate packets.