OSI/AS Configuration and Management Manual

Performance Considerations
OSI/AS Configuration and Management Manual—424119-001
6-10
Transport Class 4 Attributes
The RECVSECURITY and SENDSECURITY attributes specify that security checking
is to be performed on incoming CR-TPDUs. The security field adds up to 16 characters
per CR-TPDU. These additional bytes increase both CPU overhead (calculating the field
and processing the additional characters) and line overhead. However, this increase in
overhead is not likely to be significant unless there is a consistently excessive number of
connections being initiated.
Transport Class 4 Attributes
Transport class 4, which implements mechanisms for error recovery, requires special
consideration. Class 4 includes a number of timeout attributes used to aid in recovery
from unsignaled errors. You should set the values for these timeout attributes high
enough that unnecessary retransmissions are not triggered and that transport connections
are not terminated unnecessarily. CCITT X.224 (ISO 8073) provides information and
recommendations on how to calculate these values.
The class 4 timeout attributes involved are as follows (these values can be set in
OSI/AS, which then passes the values to OSI/TS):
•
INACTIVETIMEOUT Attribute on page 6-10
•
REXMITTIMEOUT Attribute on page 6-10
•
WINDOWTIMEOUT Attribute on page 6-10
•
MAXREMIT Attribute on page 6-10
INACTIVETIMEOUT Attribute
The INACTIVETIMEOUT attribute defines the amount of time TSP waits before
aborting the transport connection, if no TPDU is received. You should set this value high
enough to ensure that the transport connection is not terminated unnecessarily.
REXMITTIMEOUT Attribute
The REXMITTIMEOUT attribute defines the amount of time TSP waits before
retransmitting an unacknowledged TPDU. You should set this value high enough to
ensure that TPDUs are not unnecessarily retransmitted, yet low enough to ensure that
TPDUs are retransmitted in a reasonable amount of time if any get lost.
WINDOWTIMEOUT Attribute
The WINDOWTIMEOUT attribute defines the amount of time TSP waits before
retransmitting up-to-date window information. This establishes a limit on the maximum
interval between window updates. You should set this value high enough to ensure that
update information is transmitted as often as is useful, yet low enough to ensure that it is
lower than the INACTIVETIMEOUT at the other end of the connection.
MAXREMIT Attribute
The MAXREXMIT attribute defines the maximum number of times unacknowledged
TPDUs are retransmitted. Set this value in conjunction with the INACTIVETIMEOUT