Multi-Tech Systems MMV1600 owner manual Appendix F, Flow Control Background

Page 95

Appendix F

Flow Control Background

Flow control refers to the techniques used by computer devices and multiplexers to stop and restart the flow of data from each other. Flow control is necessary so that a channel device does not receive more data than it can handle or vice versa (the MultiMux receives more data than its buffers can accommodate). Flow control by the mux to control data flow from a channel device is called Mux Initiated Flow Control. Such flow control might be needed if a mux was connected to a minicomputer that could output more data than the mux could handle. Flow control by the channel device to control data flow from the mux is called Channel Device Initiated Pacing. Such pacing might be required by a printer channel device which could not print data as fast as the mux might send it or might go off-line for some reason like running out of paper. To state it simply, “Flow Control” is something the mux does to the channel device, while “pacing” is something the channel device does to the mux.

MUX INITIATED

FLOW CONTROL

Channel

 

DATA

 

 

 

Mux

Device

 

 

 

 

 

 

 

 

 

 

Flow control stops the input of data to the mux

CHANNEL DEVICE

INITIATED PACING

DATA

Channel

MuxDevice

Pacing stops the output of data from the mux

Flow control can be software or hardware based. In software flow control, special characters (Xon and Xoff) are used to stop and start the flow of data. In hardware flow control the Clear To Send (CTS) signal on the RS232C interface (pin

5)is brought low to stop data and high to restart it. When you select a flow control method with a mux command you are also selecting the corresponding pacing method.

In the example below we have an eight port multi-user minicomputer connected to a MultiMux on one end of a link and seven terminals plus a printer connected to another MultiMux on the other end of the link. The MultiMux at the printer end needs Flow Control and Pace on the printer channel to stop and restart data from the minicomputer. The MultiMux at the minicomputer end needs Flow Control on to all channels to stop and restart data from the minicomputer so that the mux’s buffer capacity is not exceeded. We chose Xon/Xoff flow control for this example and are setting pace ON for all channel devices.

NODE 1

Channel 1 2

3

Mini- 4

Computer 5

6

7

8

Mux

Link

NODE 2

 

Channel

 

 

 

 

 

 

1

 

Printer

 

2

PC

 

 

Mux

3

PC

 

4

PC

 

5PC

6PC

7PC

8PC

MiniComputer Flow Control

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Contents MultiMux Page Record of Revisions RevisionDescription MultiMux #MMV1600C #MMV3200CTable of Contents Service, Warranty and Tech Support CommandsOperating Procedures TroubleshootingTables AboutThisManual Service, Warranty and Tech Support 1.1 Statistical Multiplexing BackgroundDescription of Statistical Multiplexing Product Description CommunicationsMultiMux MMV1600/3200 Series Block Diagram Page Dynamic Load Balance System Features Voice/FaxNetworking Dual Composite LinksParameter Memory Channel SwitchingCommand Modem DiagnosticsSynchronous Data Channel Dynamic BufferingResponse Time Control AU7USA-20328-MD-E FCC Regulations for Telephone Line InterconnectionDOC Terminal Equipment AU7USA-18883-DE-N DSUInternal DSU Specifications Async Data ChannelsSystem Control Composite LinkDtmf Voice ChannelsElectrical/Physical CompatibilityModel Description Configuration DescriptionConfiguration Configuration 1 Composite Link Configuration Configuration 1 Local Site Channel ParametersConfiguration 1 Remote Site Channel Parameters Configuration 2 Composite Link Configuration Remote Site Configuration 3 Remote Site 2 Channel Parameters Configuration 3 Local Site Channel ParametersConfiguration 3 Remote Site 1 Channel Parameters Configuration 4 Local Site Voice/Fax Channel Parameters Configuration 4 FXO to FXSConfiguration 4 Remote Site Voice/Fax Channel Parameters Configuration 5 E&M Configuration 5 Remote Site Voice/Fax Channel Parameters Configuration 5 Local site Voice/Fax Channel ParametersConfiguration 6 FXS to FXS Configuration 6 Remote Site Voice/Fax Channel Parameters Configuration 6 Local Site Voice/Fax Channel ParametersRemote Site Configuration 7 Remote Site Voice/Fax Channel Parameters Configuration 7 Local Site Voice/Fax Channel ParametersConfiguration 8 LAN to LAN Page External Modem/DSU with RS232C Interface InstallationProcedureCabling Procedure StepProcedureAsync Channel Step ProcedureV.35 Interface Sync Data Channel Port B onlyComposite Link Cabling Supervisory Console Configuration ProcedureCommand Modem Step Procedure Voice/Fax Channels Step Procedure Async ChannelsPage ATC1B4800P1F1E0 Command SummaryType Command Description $DSUASP SNGA..H$DSUACL $DSUBCL#MA CommandDescriptionGeneral Commands Help H command menu is as follows General HelpStore New ParametersH7 menu is as follows H4 menu is as followsH5 menu is as follows H6 menu is as followsChannel Parameter Commands DTR ENQ/ACKMLA/B/D SB2 SB1$ Muxacli Composite Link Speed and Clocking Commands$DSUCL $DSUSP$MUXB Additional Composite Link Commands#RBxxxxx Retransmit TimerList Composite ReportVoice/Fax Channel Commands Command Level ATV1/2LIFXO WireSilence Suppression Local InterfaceATV1/2RIFXSG Test CommandsATV1/2LIFXSL ATV1/2RIFXOT12 Command Modem CommandsT11 Configuration of Port B Composite Link MultiMuxOperatingProceduresMultiMux Operating Procedures Configuration of Port a Composite LinkConfiguration of Port B Sync Data Voice/Fax Operating Procedures Voice/Fax Operating ProceduresCommand Modem Access on Command Modem Operating ProceduresCommand Modem Operating Procedures Command modem operation and put Introduction ImportanceofCompositeStatisticsTestCables TroubleshootingGuideData Troubleshooting Guide RD LED on RD OFF Voice/fax channel Voice/Fax Troubleshooting GuideCannot communicate Local Loop Test #4 ChannelDeviceTestingChannel Device Testing Procedure Remote Digital Loop Test #5 DSUandCommunicationsLineTestingDSU and Communications Line Testing Procedure Watch DOG Test Passed MultiMuxFunctionalTestingProceduresMultiMux Functional Testing Procedures VOICE/FAX Loopback Test #12 Voice/FaxChannelTestingVoice/Fax Channel Testing Procedure Sync Data Channel Testing Procedure SyncDataChannelTestingService, Warranty and Tech Support Repair Procedures for International Distributors AppendixA Ascii Character Code/Hex/Decimal Conversion ChartAppendix B Signal Information Negative PositiveAppendix C Cabling DiagramsDCE to DTE cabling Command Port CablesComposite Link Cabling RJ48 Cabling for Internal DSU I-V Voice/Fax Channel Cable RJ45 Spade Lug Wire Color FunctionVoice/Fax Channel Connectors Description FXO Description FXS DescriptionLast Command Name DefaultAnswer a RepeatATQ1 ATH1ATH0 ATOWrite ATD5551212RRegister Read orStore Active Configuration displaysView Active User ProfilesATX2 ATX0ATX1 After Dial Command ExecutionMode While Returning toAppendix E Table E-1. LED IndicatorsIndicator Description FCR LED Indicators DescriptionBack Panel Command Port TERMINAL/PC Connector ON/OFF SwitchPower Connector BPS Modem DIAL-UP Line ConnectorVOICE/FAX Channel 1 FXS Connector VOICE/FAX Channel 2 FXS ConnectorVOICE/FAX Channel 2 FXO Connector VOICE/FAX Channel 1 E&M ConnectorChannel # Channel Board Number of Channels SwitchRS232C/V.35 Shunt Flow Control Background Appendix FOff Printer pacing and Flow Control Glossary of Terms Page Format Page Parameter Page Page Symbols DSU DOCLads External Composite LinkFXO FXS Link Protocol List Channel Parameters CommandLoad DSU Factory Defaults Command MultiMux Functional Testing ProcedureRJ48S PDNPstn RENStdm Stop Bit Command SB1-SB2Transmit XMT Indicator Voice/Fax Channels Voice/Fax Channel Testing ProcedureVoice/Fax Input Level Gain Command Word Length Select Command WL5-8
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