The length of signal PDUs transmitted from ASTi systems is constantly varying, automatically controlled by Model Builder. Model Builder is designed to maximize packet transmission speed and typically the software does not buffer enough audio samples to completely fill an ethernet payload before transmitting a packet. This means that Signal PDU lengths are usually significantly less than the 1500 byte MTU of standard IP link layer frames. Also, the packet length is typically lower for multicast-by-exercise vs single-group multicast and broadcast.

In ASTi systems, the DIS packet length is not directly adjustable by the user. But the Single and Multiple PDUs / Packet setting will effect the transmitted PDU packet length. DACSs running Model Builder 4.09-series software default to single PDUs per packet, which minimizes packet length and maximizes transfer rate, at a small cost of increased bandwidth consumption. Setting DACS to operate in multiple PDUs per packet mode will increase packet length, while slightly decreasing bandwidth consumption.

Note: the single - multiple PDUs per packet setting only effects transmission. ASTi systems will automatically receive either type of packet format.

To determine whether a DACs is operating in the Single or Multiple PDUs / Packet mode, go to: DIS Options Window and look at the PDUs/Pkt field (top right):

Should you desire to change the single / multiple PDUs per packet setting, use the configuration file command:

DIS:SINGLE_PDUS=<Mode>

... where <Mode> is ON or OFF.

Command Notes:
In single PDU mode the DIS driver will only allow a single PDU per Ethernet packet. This mode exists to force compatibility with other manufacturers products that will only accept single PDU/Ethernet packets. With this mode disabled (Off) the DACS will transmit multiple PDUs in a single Ethernet packet when this is appropriate (i.e., when there is more than one active transmitter in the DACS). This mode makes marginally better use of the available bandwidth.

The default value (MB 4.09 and later) is:

DIS:SINGLE_PDUS=ON.