Connection Priority

Description

The Connection Priority application demonstrates the utilization of the SPARK Wireless Core in scenarios where multiple connections compete for limited network resources by assigning priorities. This application uses a bidirectional communication between a Coordinator and a Node, showcasing how five connections with varying priorities share link capacity.

Behavior

The Connection Priority application’s schedule consists of two timeslots. The first timeslot is used by the Coordinator’s 3 TX connections to transmit to the Node. The second timeslot is used by the Node’s 2 TX connections to transmit to the Coordinator. A transmitted payload always contains the ID of the connection by which it was sent.

The following diagram illustrates the general structure of the schedule used in this application.

Figure 19: Connection Priority application’s schedule.

Both devices transmit different types of payloads at varying generation rates, each destined for different TX connections. The variation in payload generation rates serves to illustrate the impact of connection priority on the packet transmission order.

Table 3: Connection Description

Connection ID	Timeslot	Coordinator mode	Node mode	Payload size (bytes)	Payload rate (pps)	Priority
CID0	0	TX	RX	15	500	High
CID1	0	TX	RX	8	400	Medium
CID2	0	TX	RX	15	500	Low
CID3	1	RX	TX	15	750	High
CID4	1	RX	TX	8	200	Medium

Link Capacity Utilization

The connection with the highest priority can always transmit its data, while the lower priority connections will only transmit data when the higher ones do not require the airtime.

The link capacity for each direction is 1000 packets per seconds (pps). CID0 and CID1 together utilize 90% of the available link capacity, allowing them to transmit 100% of their data. CID2, being the lowest priority, can only utilize the remaining 10% of the link capacity, resulting in a transmission limit of 100 pps. Since CID2 has a payload rate of 500 pps, which is half of the link capacity, 80% of CID2’s payloads will be dropped due to higher priority connections.

In this application, the Coordinator switch SW1 toggles ON or OFF the data generation on CID0. When CID0 is turned OFF, no frame gets enqueued in the high priority connection, thus freeing bandwidth for other connection. The low priority connections, CID1 and CID2, can then transmit at their full rate.

Connections using the second timeslot will be able to transmit at their full rate. CID3, with the highest priority, requires 75% of the link capacity, leaving 25% for CID4. However, since CID4 requires only 20% of the link capacity to achieve full packet rate, there will be a 5% portion of the link that remains unused. Consequently, no packet transmission will be observed for 5% of the timeslot occurences.

Coordinator Device

• The SW1 switch is used to toggle ON or OFF the data generation on CID0. Data generation is enabled by default.

Table 4: Coordinator User Interface Description

Interface	Name	Description
SW1	CID0 Toggle	Enable/Disable data generation on CID0.
SW2	Reset Stats	Reset the TX and RX statistics.
LED0	N/A	N/A
LED1	N/A	N/A
LED2	N/A	N/A

Node Device

Table 5: Node User Interface Description

Interface	Name	Description
SW1	N/A	N/A
SW2	Reset Stats	Reset the TX and RX statistics.
LED0	N/A	N/A
LED1	N/A	N/A
LED2	N/A	N/A

Configuration

Terminal

Host terminal configuration should be as follows:

• Speed (baud): 115200

• Data bits: 8

• Stop bit: 1

• Parity: None

• Flow control: None

The following figure shows the serial interface output of this application.

Figure 20: Connection Priority application serial interface output.

See Statistics for more details on the Wireless Core statistics displayed by the application.