In networks with less than five switches, each switch can productively poll all the other switches in the network. In larger networks, each switch does not poll every other switch. But which switches must each switch poll? The term polling patterns describes the relationships between switches in multisite BSR applications.

Do not use the following polling patterns:

• Mutual polling: As much as possible, 2 switches must not poll each other. This is difficult in small networks, but in large networks mutual polling can and must be minimized.

• Polling chains: For example, if switch A polls B and C, B polls C and D, this is a polling chain.

You can experiment with polling patterns appropriate for your network and applications, if you are not constrained by the physical structure of the network. The following table provides a template for creating polling patterns for applications of up to 12 switches. In the majority of situations, the patterns produce results that are close to optimal. To use the following table, first assign a number from 1 to x to each switch in your application. Next, find the column that matches the number of switches in your application. As you read the column, see which switches each switch in the application must poll.

Switch	Must poll the specific switches shown in the column for your network size
	5	6	7	8	9	10	11	12
1	2,4,5	2,4,5	2,4,6	2,4,7	2,4,6	2,4,7	2,4,8,10	2,4,8,9
2	3,5,1	3,5,6	3,5,7	3,5,8	3,5,7	3,5,8	3,5,9,11	3,5,9,10
3	4,1,2	4,6,1	4,6,1	4,6,1	4,6,8	4,6,9	4,6,10,1	4,6,10,11
4	5,2,3	5,1,2	5,7,2	5,7,2	5,7,9	5,7,10	5,7,11,2	5,7,11,12
5	1,3,4	6,2,3	6,1,3	6,8,3	6,8,1	6,8,1	6,8,1,3	6,8,12,1
6		1,3,4	7,2,4	7,1,4	7,9,2	7,9,2	7,9,2,4	7,9,1,2
7			1,3,5	8,2,5	8,1,3	8,10,3	8,10,3,5	8,10,2,3
8				1,3,6	9,2,4	9,1,4	9,11,4,6	9,11,3,4
9					1,3,5	10,2,5	10,1,5,7	10,12,4,5
10						1,3,6	11,2,6,8	11,1,5,6
11							1,3,7,9	12,2,6,7
12								1,3,7,8

In applications of more than 12 switches, the following table provides the formulae you must figure out the optimal polling pattern.

Number of switches in application	Switch to poll
13 or 16	i + 1, i + 3, i + 7, i +11
14 or 19	i + 1, i + 3, i + 7, i + 9
15	i + 1, i + 3, i + 7, i + 10
17 or 20	i + 1, i + 3, i + 7, i + 12
18	i + 1, i + 3, i + 7, i + 13
21-23	i + 1, i + 3, i + 7, i + 15, i + 17
24	i + 1, i + 3, i + 7, i + 15, i + 19
25	i + 1, i + 3, i + 7, i + 15, i + 20

To use one of the formulae, first assign a number from 1 to x to each switch in your application. Then, in the left-hand column of the table, find the number of switches in your application. The corresponding formula in the right-hand column is the one you must use.

In the formulae, i is the number of the switch for which you are calculating a polling pattern. To calculate the polling patterns in an application with 16 switches, the formula to use is: i + 1, i + 3, i + 7, i +11

As shown in the first row of the table. Here are the actual results of this formulae for the first 5 switches in this 16-switch application. The numbers wrap, that is, start over at 1, after you have polled the last switch in the network: switch 5 polls switch 16 as its fourth poll and then the polling pattern for switch 6 has switch 1 in the fourth position.

Switch number	Switch to poll
1	2 ,4, 8, 12
2	3, 5, 9, 13
3	4, 6 ,10, 14
4	5, 7, 11, 15
5	6, 8, 12, 16
6	7, 9, 13, 1
7	8, 10, 14, 2