# Understanding RU Sizing

The following table shows how to find the appropriate value to specify for the RUSIZES parameter. For the formula RUSIZES=X‘abab’, the first ab pair applies to the secondary logical unit (SLU). The second ab pair applies to the primary logical unit (PLU). The table shows the values for a and b. The number of bytes is found where the a column and the b column intersect in the table.

For example, the bold a and b numbers in the table indicate how it is used to determine the RUSIZES=87F8 for SNA connections. Because the primary LU is able to receive 3,840 bytes, the secondary LU can send 3,840 bytes at a time (the intersection of F and 8). The primary LU can send 1,024 bytes at a time because the secondary LU is able to receive 1,024 bytes (the intersection of 8 and 7).

a | ||||||||
---|---|---|---|---|---|---|---|---|

b | 8 | 9 | A(10) | B(11) | C(12) | D(13) | E(14) | F(15) |

0 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |

1 | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 |

2 | 32 | 36 | 40 | 44 | 48 | 52 | 56 | 60 |

3 | 64 | 72 | 80 | 88 | 96 | 104 | 112 | 120 |

4 | 128 | 144 | 160 | 176 | 192 | 208 | 224 | 240 |

5 | 256 | 288 | 320 | 352 | 384 | 416 | 448 | 480 |

6 | 512 | 576 | 640 | 704 | 768 | 832 | 896 | 960 |

7 | 1,024 | 1,152 | 1,280 | 1,408 | 1,536 | 1,664 | 1,792 | 1,920 |

8 | 2,048 | 2,304 | 2,560 | 2,816 | 3,072 | 3,328 | 3,584 | 3,840 |

9 | 4,096 | 4,608 | 5,120 | 5,632 | 6,144 | 6,656 | 7,168 | 7,680 |

A(10) | 8,192 | 9,216 | 10,240 | 11,264 | 12,288 | 13,312 | 14,336 | 15,360 |

B(11) | 16,384 | 18,432 | 20,480 | 22,528 | 24,576 | 26,624 | 28,672 | 30,720 |

C(12) | 32,768 | 36,864 | 40,960 | 45,056 | 49,152 | 53,248 | 57,344 | 61,440 |

D(13) | 65,536 | 73,728 | 81,920 | 90,112 | 98,304 | 106,496 | 114,688 | 122,880 |

E(14) | 131,072 | 147,456 | 163,840 | 180,224 | 196,608 | 212,992 | 229,376 | 245,760 |

F(15) | 262,144 | 294,912 | 327,680 | 360,448 | 393,216 | 425,984 | 458,752 | 491,520 |

The table is derived from the following calculations:

The RUSIZE of ab means RUSIZE equals a x (2 **b). The b of each ab pair is used as an exponent of base two. The resulting value is multiplied by a to get the RUSIZE for that logical unit.

Using the same example, RUSIZES=87F8, the SLU and PLU values are determined as follows.

if RUSIZES=X‘87F8’ then
the SLU RUSIZE is 87 which indicates 8 x 2**7 = 8 x 128 = 1024 (8 times 2 to the 7th power) the PLU RUSIZE is F8 which indicates F x 2**8 = 15 x 2**8 = 15 x 256 = 3840 (15 times 2 to the 8th power) |