Sun Microsystems THE SUN 805-7945-10 - Manual (Page 11)

Installing and Configuring the ge Device Driver 7
Interpacket Gap Parameters
The GEM ASIC supports the programmable Interpacket Gap (IPG) parameters ipg1
and ipg2 . The total IPG is the sum of ipg1 and ipg2 : 0.096 microseconds for the
link speed of 1000 Mbps.
TABLE 4 lists the default values and allowable values for the IPG parameters, ipg1
and ipg2 .
By default, the driver sets ipg1 to 8-byte time and ipg2 to 4-byte time, which are
the standard values. (Byte time is the time it takes to transmit one byte on the link,
with a link speed of 1000 Mbps.)
If your network has systems that use longer IPG (the sum of ipg1 and ipg2 ) and if
those machines seem to be slow in accessing the network, increase the values of
ipg1 and ipg2 to match the longer IPGs of other machines.
Defining an Additional Delay Before Transmitting
a Packet Using
lance_mode and ipg0
The GEM ASIC supports a programmable mode called lance_mode . The ipg0
parameter is associated with lance_mode .
If lance_mode is enabled (the default), an additional delay is added by setting the
ipg0 parameter before transmitting the packet. This delay is in addition to the delay
set by the ipg1 and ipg2 parameters. The additional delay set by ipg0 helps to
reduce collisions. Systems that have lance_mode enabled might not have enough
transmission time on the network.
If lance_mode is disabled, the value of ipg0 is ignored and no additional delay is
set. Only the delays set by ipg1 and ipg2 are used. Disable lance_mode if other
systems keep sending a large number of back-to-back packets.
You can add the additional delay by setting the ipg0 parameter from 0 to 31, which
is the media byte time delay.
TABLE 4 Read-Write Interpacket Gap Parameter Values and Descriptions
Parameter Values
(Byte-time) Description
ipg1 0, 255 ipg1 = 8 (default at initialization)
ipg2 0, 255 ipg2 = 4 (default at initialization)