Sun Microsystems 6U manual Defining an Additional Delay Before Transmitting a Packet

If your network has systems that use longer IPG (the sum of ipg1 and ipg2), and if those systems seem to be slow when accessing the network, increase the values of ipg1 and ipg2 to match the longer IPGs of the other systems.

Defining an Additional Delay Before Transmitting a Packet

The adapter’s PFEX ASIC supports a programmable mode called local area network controller for Ethernet (LANCE) mode, which is set with the lance_mode parameter.

When a driver receives a packet with lance_mode enabled (the default), it adds an additional time delay before transmitting the packet. This delay, set by the ipg0 parameter, is in addition to the delay set by the ipg1 and ipg2 parameters. The additional ipg0 delay helps to reduce collisions.

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. Systems that have lance_mode enabled might not have enough time to transmit a large number of back-to-back packets on the network.

You can add an additional delay by setting the ipg0 parameter to a value from 0 to 31, which is the nibble time delay. Note that nibble time is the time it takes to transfer four bits on the link. If the link speed is 10 Mbps, nibble time is equal to 400 ns. If the link speed is 100 Mbps, the nibble time is equal to 40 ns.

For example, if the link speed is 10 Mbps, and you set ipg0 to 20, multiply 20 by 400 ns to get 8000 ns. If the link speed is 100 Mbps, and you set ipg0 to 30, you would multiply 30 by 40 ns to get 1200 ns.

TABLE B-4defines the lance_mode and ipg0 parameters.

TABLE B-4Parameters Defining lance_mode and ipg0

Parameter	Values	Description
lance_mode	0	0	= lance_mode disabled
	1	1	= lance_mode enabled (default)
ipg0	0 to 31	Additional media byte time delay before
		transmitting a packet (after receiving a
		packet)

Note –The default value of ipg0 is 16, which is 6.4 microseconds for 10 Mbps and 0.64 microseconds for 100 Mbps.

Appendix B Configuring the Sun Quad FastEthernet Device Driver Parameters 61