Token Ring Design Rules

 


All Token Ring networks must be properly planned before the initial installation or before making changes to an existing installation. The design rules vary depending on the speed, cabling type, and type of MSAUs used in the network.

This page contains the design rules for both UTP and STP Token Ring networks.


Network Design Procedure

Every Token Ring network design, regardless of cable type, has certain common steps which must be followed to ensure that it will work. Basically, the process consists of knowing how many MSAUs are going to be required, how many wiring closets they will be installed into, and what the longest lobe length needed will be.

The first step in designing a Token Ring network is to obtain or create a drawing of the physical layout of the area the network will be installed into. This drawing should show the location of each device which is to be connected to the network, and should be drawn to scale so distances can be accurately estimated.

The second step is to decide on a network speed, cable type, and whether or not to use active or passive MSAUs. Generally, it is best to use active MSAUs, as these units amplify the signal and help create a more reliable network with a guaranteed lobe length. Passive units can also be used, however the distance which can be achieved with them will vary depending on the overall layout of the network.

The third step in the design process is to take the total number of devices the network will support and divide it by the number of ports per MSAU. The result is the number of MSAUs required to implement the design. For example, a 42 node network built with eight-port MSAUs will require six MSAUs.

The fourth step requires that we refer to the drawing we obtained from the first step of this design process. The designer must now make a decision as to where to physically locate the MSAUs and whether to located all of them in a central location or to distribute them around the building to create shorter lobe lengths and therefore use less cable. Either approach is acceptable at this stage. Draw a box on the drawing where each wiring closet will be located and count how many wiring closets the network will need. This number is called the Number of Wiring Closets and is used as one variable in verification of the design.

The fifth step in designing the network is to draw lines representing cables to connect the wiring closets together. Once all of the wiring closets are interconnected, estimate the length of each cable run between them. Also, estimate the longest lobe length the resulting layout will require.

The network is now designed and the design needs to be validated to ensure it will work properly. Add together the length of all cable runs which are interconnecting the wiring closets, and subtract the shortest one. Do not count any patch cords connecting Ring In to Ring Out on the MSAUs inside the wiring closets, only the cable runs between the closets. The resulting number is called the Adjusted Ring Length, or ARL for short.

At this stage, consult the table below which matches the speed and cable type selected for the network, and in the table use the number which matches the number of MSAUs and wiring closets used in the network. This number represents the sum of the ARL and longest lobe length the design can support using passive MSAUs, or the maximum ARL allowed with active MSAUs. If there is no number shown for the combination of cable type, speed, number of MSAUs, and number of closets the design needs, then the design is invalid.

Assuming a value was obtained from the table, subtract the ARL from it. The result is the maximum allowed lobe length using passive MSAUs. Regardless of MSAU type, if this number is negative, then the network design is invalid and will not work.

If the result of the above step is a positive number and the network is using passive MSAUs, this number denotes the maximum lobe length the design can support. Make certain that the longest lobe length needed in the design does not exceed this distance. This step can be disregarded if the network is using active MSAUs.

Oftentimes, an invalid design can be fixed by using various devices to extend the ring or to split a network into multiple smaller rings. The most common ways are explained on our Advanced Token Ring page.


Network Design Tables

4 Mbps Token Ring Over Type 1 & 2 Cable
Multiple Wiring Closet Distances in Feet
NUMBER OF WIRING CLOSETS
MSAUs 2 3 4 5 6 7 8 9 10 11 12
2 1192
3 1163 1148
4 1135 1120 1104
5 1106 1091 1076 1061
6 1078 1062 1047 1032 1017
7 1049 1034 1019 1004 989 974
8 1020 1005 990 975 960 945 930
9 992 977 962 947 932 916 901 886
10 963 948 933 918 903 888 873 858 843
11 935 920 905 890 874 859 844 829 814 799
12 906 891 876 861 846 831 816 801 786 770 755
13 878 863 848 833 817 802 787 772 757 742 727
14 849 834 819 804 789 774 759 744 729 713 698
15 821 806 791 775 760 745 730 715 700 685 670
16 792 777 762 747 732 717 702 687 671 656 641
17 764 749 733 718 703 688 673 658 643 628 613
18 735 720 705 690 675 660 645 629 614 599 584
19 707 691 676 661 646 631 616 601 586 571 556
20 678 663 648 633 618 603 587 572 557 542 527
21 649 634 619 604 589 574 559 544 529 514 499
22 621 606 591 576 561 545 530 515 500 485 470
23 592 577 562 547 532 517 502 487 472 457 441
24 564 549 534 519 503 488 473 458 443 428 413
25 532 520 505 490 475 640 445 430 415 399 384
26 505 492 477 461 446 431 416 401 386 371 356
27 476 463 448 433 418 403 388 373 357 342 327

Note: If using Type 6 or Type 9 cable instead of Type 1 or Type 2, divide the number found in the table for your configuration by 1.33. If using Type 8 cable, divide the number found in the table for your configuration by 2.

16 Mbps Token Ring Over Type 1 & 2 Cable
Multiple Wiring Closet Distances in Feet
NUMBER OF WIRING CLOSETS
MSAUs 2 3 4 5 6 7 8 9 10
2 530
3 509 492
4 487 471 454
5 465 449 432 416
6 443 427 411 394 378
7 422 405 389 372 356 340
8 400 383 367 350 344 318 301
9 378 361 345 329 312 296 279 263
10 356 340 323 307 290 274 258 241 225
11 334 318 301 285 269 252 236 219 203
12 312 296 279 263 247 230 214 197 181
13 270 253 236 220 204 188 171 155 138
14 227 211 194 178 161 145 129 112 96
15 184 168 152 135 119 102 86 69 53
16 142 125 109 92 76 60 43 27 10
17 99 83 66 50 33 17
18 56 40 24

Note: If using Type 6 or Type 9 cable instead of Type 1 or Type 2, divide the number found in the table for your configuration by 1.33. If using Type 8 cable, divide the number found in the table for your configuration by 2.

4 Mbps Token Ring Over UTP
Multiple Wiring Closet Distances in Feet
NUMBER OF WIRING CLOSETS
MSAUs 1 2 3 4
1 730
2 711 678
3 692 659 642
4 673 640 623 606
5 654 621 604 587
6 635 602 585 568
7 616 583 566 549
8 597 564 547 530
9 578 545 528 511
10 559 526 509 492
16 Mbps Token Ring Over UTP
Multiple Wiring Closet Distances in Feet
NUMBER OF WIRING CLOSETS
MSAUs 1 2 3
1 180
2 148 128
3 116 96 76
4 84 64
5 52

Examples

In this section, we will analyze two Token Ring networks. One network will meet all design criteria, and the second one will not. This exercise should clarify the design procedure enumerated above.

Figure One
Sample Token Ring Network

Example One

Figure One above shows a Token Ring network planned for Fictional Company. This drawing is the type which must be generated for every Token Ring layout, and shows the number of MSAUs, Wiring Closets, number of nodes, length of each intercloset cable run, and the longest lobe length in the entire network.

This ring needs to be calculated to determine if it is a valid design. In the figure, we can see that there are three wiring closets and four MSAUs. The cable runs between the wiring closets are 45. 55, and 25 feet. Add these together and subtract the shortest one to determine the ARL of the network. In this case it is:

ARL = (25 + 45 + 55 - 25) = 100 feet

Let us assume that the network cabling is Type 1, the MSAUs are passive, and the speed is 16 Mbps. The tables above show a maximum allowable ring size of 471 feet. Since the MSAUs are passive, we then subtract the ARL from the maximum allowable ring length to establish the longest allowable lobe length. In this case it is:

Max - ARL = Lobe
471 - 100 = 371

The maximum lobe length allowed for this network will be 371 feet. Since the design laid out in the diagram shows that the maximum lobe length actually used in this network is 45 feet, and we are allowed to go 371 feet, the network design is valid and should work with no problems whatsoever.


Example Two

Let us look at the same network, except we will change the cable type to UTP. The speed will remain at 16 Mbps, and we will still use passive MSAUs. Our ARL remains unchanged at 100 feet, but referring to the table for 16 Mbps UTP networks shows that we can not have a combination of four MSAUs, three wiring closets, UTP cable and 16 Mbps operation. In other words, the network design will not work with UTP.

When we have an invalid design, we must change it. In this case, the easiest solution would be to put all of the MSAUs in one wiring closet. That would allow a maximum ring length of 84 feet per the table. Since all of the MSAUs are in one closet, our ARL is zero. Recalculating with this combination shows that our longest allowable lobe length will be:

84 - 0 = 84 feet

The building in Figure One is roughly 50 feet by 40 feet in size, so it should not be a problem for us to find a place which is within 84 feet of all nodes and install the MSAUs there. Actually, it would be an excellent idea to use an active MSAU in this network to boost the signal on the lobe ports and allow a distance of 300 feet per run to the nodes. Since cable is rarely pulled in a straight line from MSAU to the workstation, all runs are somewhat longer than they may appear at first glance, usually by about 10%. Therefore, active MSAUs will give additional "insurance" that the network will operate without problems.