Epson MFJ-1278B manual New Parameters, Ackprior Onoff

MFJ-1278B MULTI-MODE ADVANCED OPERATION

Enforcing a channel access delay for all stations on the channel for whom the packet that caused the queue was not intended (& who therefore aren't going to ACK it) allows even ACKs from hidden terminals to get back to the expecting station. This clears that traffic from the offered load list. If the packet was indeed copied and ACKed, further retrys of the same information will not be necessary.

New Parameters

There are several new parameters that relate to this modification of the protocol. They are as follows:

ACKPRIOR ONOFF

This enables prioritized acknowledgments if turned on.

If ACKprior is turned off and SLots (see below) is set to 0, this modification of the AX.25 protocol is effectively disabled. The MFJ-1278B will behave like normal AX.25 protocol.

Being independent of each other, the enabling and disabling of slotted channel access and Prioritized acknowledgments are the same. So you could if you wished run normal AX.25 with slotted channel access or the new protocol without slotted channel access.

DEADTIME 0 - 250 (each increment represents 10 milliseconds)

This is the time between when a remote TNC has pressed PTT and when the local TNC can reasonably be expected to detect this fact.

This must be set to a value that accounts for the slowest acceptable station on the channel. It includes the time required for the remote station's radio to come on the air properly after assertion of PTT (TXDelay) and the time required for the local station's squelch (if used) and TNC DCD circuits to allow generation of a "DCD true" signal in the local TNC. Ideally, once the proper value for this timer is ascertained, all stations on the channel will use the same value.

Very preliminary testing done here on VHF indicates that measurements of the above delay times should be multiplied by 1.5 for use as the DEAdtime parameter. We had carefully measured the times for all stations participating in our tests. This gave us a worst case delay total of 210 milliseconds. When we ran the test, we were still getting about a 5 percent collision rate on the acknowledgments. We were required to increase the DEAdtime parameter to 30 (300 milliseconds) to completely eliminate collisions with ACKs.

The current default for this parameter is a ridiculously short 30 milliseconds. This represents