Customized USS tables are used by both VTAM® and Telnet, with any product-specific character substitutions converted to blanks. For example, @@SSCPNM is blank for Telnet and @@PRT is blank for VTAM. Telnet USS processing also supports system symbolic substitution. VTAM does no substitution for system symbolics. The tables must be in a data set that is in the system's linklist or is in the STEPLIB statement of the TCP/IP startup procedure. Any changes to a Telnet USS table should be made with supplementary user-defined USS tables. The IBM-supplied USS table should not be changed as it provides a good example of coding most commands and messages. Telnet loads the first table that is found with the name EZBTPUST and defines it as the default USS table. If this table is not found, there is no default USS table. Whether to include a default USS table depends on the wanted message output. When writing a USS Message, Telnet searches the USS table that is mapped to the client first. If the message does not exist in the mapped table, Telnet searches the default table. If the message does not exist in the default table, Telnet writes USSMSG14. If no default table exists, Telnet generates a USSMSG14. For 3270 format USSMSGs, the user can get back to the USSMSG10 from any message by pressing the CLEAR key. The default table does not affect the USS commands. The command entered must be in the mapped table or it is not recognized. The sample SCS USS table found in SEZAINST(EZBTPSCS) is not assembled and linked, and it is not loaded into Telnet as a default SCS USS table. The table must be assembled, linked, loaded, and mapped in the Telnet profile to be used.