Oracle SDU and TDU parameters
The session data unit (SDU)
specifies the size of the packets to send over the network. The
maximum transmission unit (MTU) is a fixed value that depends on the actual network
implementation used. Ideally, SDU should not surpass the size of
the MTU. Oracle recommends that SDU be set equal to the MTU. The tnsnames.ora and
listener.ora files house the SDU and TDU parameters.
To group data together, the TDU value is the default
packet size used within Oracle*Net. The
default value for both SDU and TDU is 2,048 bytes and
the maximum value is 32,767 bytes. The TDU parameter should
ideally be a multiple of the SDU parameter. For SDU and TDU,
the following guidelines apply:
On fast network connections such as T1 or T3
lines, SDU and
TDU should be set
equal to the MTU for the network. On standard Ethernet networks, the default
MTU size should be set to
1,514 bytes. On standard token ring networks, the default
MTU size is 4,202 bytes.
If the users are connecting via dial-up modem
lines, it may be desirable to set SDU and TDU to smaller values in consideration of the frequent resends that
occur over modem connections.
mts_dispatchers must also be set
with the proper MTU - TDU configuration, if a Multi-Threaded Server (MTS) is used.
As a rule, SDU should not be set greater than the
network resources will be wasted by shipping wasted space in
This brief review of network-related parameters was intended
provide an introduction to the scope and complexity of network
tuning. It is important to understand that Oracle*Net is simply a layer in the OSI model that is above
the network-specific protocol stack, and therefore, virtually
all network tuning is external to Oracle.