GE PACSystems RXi User Manual

Chapter 8. Gigabit Ethernet (GbE) Interface Overview and OperationGFK-2816F August 2015 195SRTP and Modbus TCP Connection TimeoutWhen the Ethernet Interface is abruptly disconnected from a remote SRTP or Modbus TCPdevice (for example, by disconnecting the Ethernet cable), the underlying TCP connectionattempts to re-establish communication. By default, the underlying TCP connection in theEthernet Interface remains open for 7 minutes while TCP attempts to reconnect. During thisinterval, the SRTP or Modbus TCP connection is unavailable. If all the SRTP or Modbus TCPconnections in the Ethernet Interface are in use or otherwise unavailable, a new SRTP orModbus TCP server connection must wait until an existing SRTP or Modbus TCP connectiontimes out. If the SRTP server connection was used by the Programmer, any newProgrammer connection is restricted to Monitor operation until the previous connection timesout and is cleaned up.For details, refer to Section 8.4.1, SRTP Inactivity Timeout.Note that the TCP connection timeout interval applies to all TCP-based connections at thisEthernet interface. This includes all SRTP, Modbus TCP, FTP, and web servercommunications.The underlying TCP connection timeout is normal expected behavior, and is consistent withour other controller products.Sluggish Programmer Response after Network DisruptionThe network programmer attempts to use a special privileged SRTP server connection at theEthernet Interface in order to establish and maintain connection even under heavy load dueSRTP connections. The Ethernet Interface allows three privileged connections. When themaximum number of privileged connections is in use, no other privileged connections arepermitted until a current privileged connection is terminated. This normally occurs when thenetwork programmer disconnects from the target controller.As described in Section 8.4.1, SRTP Inactivity Timeout, when the programmer-controllernetwork connection is abruptly broken (not the orderly termination performed duringdisconnection), the SRTP server connection and its underlying TCP connection remain aliveuntil either an SRTP inactivity timeout occurs (20 –30 seconds), or the TCP connection timesout (about 7 minutes). If the maximum privileged connections are in use and the programmerreconnects during this interval, it obtains a new, non-privileged connection. Under heavy loadat the Ethernet Interface, the programmer may experience sluggish response over this non-privileged connection. If this occurs, you can manually disconnect and reconnect theprogrammer after the previous connection has timed out. Upon reconnection, theprogrammer should once again obtain a privileged connection.