Epson MFJ-1278B manual Radio Baud Rate, Wait time = Dwait * 10 + r * Txdelay

MFJ-1278B MULTI-MODE ADVANCED OPERATION

The wait time is set by the command DWAIT, which specifies 40 ms intervals. If no digipeating is being done by anyone in the local area, this parameter can be set to 0, but in any event it should be set to the same value by all members of a local packet group.

In order to avoid unnecessary packet retries, the MFJ-1278B implements a collision- avoidance strategy which applies to all packets except those being digipeated. On the second and subsequent transmissions of a particular packet, the MFJ-1278B waits an additional random time after detecting a clear channel before beginning transmission. This prevents re- peated collisions of transmissions by the same two stations. The random time is a multiple (0-15) of the TXDELAY time.

The interval, in milliseconds, between the MFJ-1278B detecting carrier-drop and beginning to transmit is

Wait time = DWAIT * 10

for the first transmission of a packet. For subsequent transmissions of the same packet the interval is

Wait time = DWAIT * 10 + ( r * TXDELAY ) * 10

where r is a random number from 0 to 15. Thus, if your MFJ-1278B is forced to re-transmit packets, you will occasionally hear a fairly long delay before transmission begins.

Multiple packets may be transmitted before waiting for an acknowledgment. This permits more efficient channel use when large amounts of data are being transferred. The maximum number of packets which the MFJ-1278B will send before waiting for acknowledgment is specified by the command MAXFRAME. This does not mean that the MFJ-1278B will wait until several packets have been entered before transmitting. MAXFRAME in combination with the command PACLEN, which sets the maximum number of characters in a packet, determines how much information can be sent in a single transmission. The best combination for efficient data transfer is determined partly by the channel quality and partly by the rate at which the terminal can process data. For a 1200 baud terminal data rate, you should start with a combination that produces about 300 characters outstanding at one time.

Radio Baud Rate

The radio data transmission rate is software selectable for 300 baud and 1200 baud. External modem (if installed) can also be selected thru software command.

Note that there is no relationship between terminal baud rate and radio baud rate. In order to communicate with another packet station you must use the same radio baud rates. The length of time required to send a given amount of information increases as the baud rate decreases.