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

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.

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:

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:

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:

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.