Chapter 2: EIU messaging protocols 63
cause TCP to drop the existing connections, which could cause a temporary outage of all TCP applications.
FTP session control
Similar to the concept of TCP numbers, FTP sessions (client and server) on each node are managed by the parameters FTPSVCON and FTPCLCON in table IPHOST. These parameters control the number of FTP server and client sessions allowed on a particular node.
There is no maximum limit defined for these numbers, but they are governed by the number of TCP connections allowed on the node. Since each FTP session consumes two TCP connections (control and data), the total number of FTP client and server sessions taken together cannot exceed half the number of TCP connections allowed on that node. This restriction obviously does not take into account other TCP applications on the node. The operating company must ensure that the values in datafill are adequate for all other TCP applications (telnet, MDR7, ROSP, and so on).
The number of FTP server and client sessions are tightly coupled with the number of server and client processes respectively. Each server and client process manages one FTP server/client session. The number of FTP server sessions also restricts the number of server processes that can be reserved by the applications for security reasons. The total number of servers that can be reserved by different applications cannot exceed the number of servers allowed on the node.
If the number of client and server sessions for a node in table IPHOST is modified, the existing sessions are dropped immediately and the FTP client users are duly notified. FTP layer remains out of service until all the resources are reallocated to conform to the new datafill. If the number of FTP server and client sessions is datafilled as zero, FTP cannot provide its services.
This functionality must be exercised cautiously since it causes FTP to drop the existing sessions, which could cause a temporary outage of all FTP clients and servers. Similar consequences are observed if the IP address of the node is modified while the node is in service. Reducing the number of FTP servers removes defined owner and userID information as necessary. It is up to the user or application to restore the information when the number of sessions is increased.
Protocol buffer engineering
The buffer engineering for receiving and transmitting IP packets is a critical part of the buffer management for the protocol stack. A default number of buffers is allocated for IP receive and transmit purposes. The buffers are divided into three categories:
•small (128 bytes)
