BLD FLASH 9508 SOURCE MATERIAL DATED: 2/95 ¦ TCP "KEEPALIVE" SUPPORT ADDED TO PSF/6000 AND PSF/2 PSF/6000 and PSF/2 offer TCP/IP attachment of several IPDS printers. Some, such as the 3935, 3130, and certain 3900 models, can be directly attached via TCP/IP. Others, such as the 3912, 3916, 3930, 3812, 3816, and 4028 can be TCP/IP-attached using the i-data 7913 as a protocol converter from TCP/IP to coax or twinax. Until now, if PSF/6000 or PSF/2 communicated with a printer that was directly attached via TCP/IP or via an i-data 7913 and the printer or i-data 7913 was abruptly powered off, TCP did not always detect connection failures and in- form PSF. PSF/6000 and PSF/2 have just added support for the TCP "KEEPALIVE" facility to enable consistent detection when a printer or i-data 7913 is ab- ruptly powered off. TCP/IP is a layered protocol. IP conveys datagrams through a network that connects two communicating IP "host" systems. TCP provides a logical con- nection that ensures data is not lost or duplicated, and is properly se- quenced. Unlike SNA, TCP does not normally "poll" connection partners. Thus, TCP only discovers that a connection partner has been lost if it sends data to the connection partner but does not receive an acknowledgement. If TCP waits for data from a connection partner but no data arrives, TCP does not differen- tiate between a connection partner that is slow to provide data and a con- nection partner that has been lost. Since this behavior is not acceptable for some applications, TCP provides a "KEEPALIVE" facility. It enables an application to direct TCP to send an empty segment to the application's connection partner if the TCP connection has remained inactive for an extended period. If the KEEPALIVE transmission is not acknowledged by the connection partner, TCP assumes that the con- nection partner has been lost. Although an application can direct TCP to send KEEPALIVE transmissions, the frequency of these transmissions depends upon system-wide TCP/IP configura- tion parameters. On both AIX and OS/2, the default values are two hours or more. Both platforms, however, allow the frequency of KEEPALIVE trans- missions to be adjusted. These values apply to all TCP applications that re- quest KEEPALIVE transmissions. PSF/6000 and PSF/2 now direct TCP to send KEEPALIVE transmissions thus enabl- ing TCP, and PSF, to detect when a printer that is directly attached via TCP/IP or an i-data 7913 is abruptly powered off, both when PSF attempts to send data and when it waits to receive data. Here are instructions for using the KEEPALIVE support that has just been added to PSF/6000 and PSF/2: PSF/6000 ________ o PSF/6000 1.2 PTF U436937 or later must be installed. o The "no" (network options) command can be used by the root user to con- figure KEEPALIVE frequencies. no -o tcp_keepidle=nnn no -o tcp_keepintvl=nnn where nnn is in half-seconds. tcp_keepidle specifies the interval of inactivity that causes TCP to gen- erate a KEEPALIVE transmission for an application that requests them. The default is 14400 (2 hours). tcp_keepintvl specifies the interval between the nine retries that are attempted if a KEEPALIVE transmission is not acknowledged. The default is 150 (75 seconds). The "no" commands must be run each time the AIX system is started. Add- ing the "no" commands to /etc/rc.net is a convenient way to automate this step. For example, adding no -o tcp_keepidle=480 no -o tcp_keepintvl=80 to /etc/rc.net causes TCP to send a KEEPALIVE transmission if a TCP con- nection has been inactive for 4 minutes and the application requested KEEPALIVE transmissions, as PSF/6000 now does. PSF/6000 recommends these TCP configuration settings for customers who use TCP/IP-attached printers and i-data 7913's. To view current settings enter no -a PSF/2 _____ o PSF/2 1.1 APAR IR28714 fix must be installed, or PSF/2 2.0 APAR IR28716 fix must be installed. o TCP/IP 2.0 CSD UN64092 or later must be installed. o The TCP/IP "inetcfg" command can be used to configure the "KEEPALIVE" pa- rameter. inetcfg KEEPALIVE=nnn where nnn is the number of minutes a TCP connection must remain inactive before TCP generates a KEEPALIVE transmission for an application that re- quests them. The default is 120 minutes. The inetcfg command must be run each time the OS/2 system is started. Adding the inetcfg command to \tcpip\bin\tcpstart.cmd is a convenient way to automate this step. For example, adding inetcfg KEEPALIVE=4 to \tcpip\bin\tcpstart.cmd causes TCP to send a KEEPALIVE transmission if a TCP connection has been inactive for 4 minutes and the application re- quested KEEPALIVE transmissions, as PSF/2 now does. PSF/2 recommends this TCP configuration setting for customers who use TCP/IP-attached printers and i-data 7913's. If the KEEPALIVE transmission is not acknowledged, TCP retries up to 9 times. The interval between these retries is fixed but short. Finally, in most cases it is not necessary to power off the i-data 7913 after a problem. Powering off the printer attached to the 7913, or pressing the "test" page on the 7913, causes the 7913 to end its TCP connection with PSF. To obtain the PTF/CSD/APAR listed above, it is recommended that the customer contact software service (1-800-237-5511 for US customers) to make sure any coreq or prereq requirements are met. $EOM