Token Ring
This extension of the ring can be used to allow the Token Ring network to connect widely-separated groups of stations in a single ring, or can be used to support greater numbers of users than a single Token Ring stack can accommodate. A Token Ring stack of maximum size will provide for the connection of 120 stations, well below the 250 station maximum of the IEEE 802.5 standard for some cabling types. If a Network Designer faced a situation in which a maximum-size stack had not been able to support all the required connections, the addition of an RI/RO link between the full stack and a new stack would allow the network to support up to another 120 stations.
These RI/RO connections for ring extension are made using specialized PIMs called TPIMs, or Token Ring Port Interface Modules.
Management functionality provided by an intelligent stack base is not distributed to non-intelligent devices that are connected to that base through RI/RO ports.
Design Example
The following example traces the design of a small office network. The network is intended for a newly-formed Health Maintenance Organization (HMO), and consists of a series of related departments, each having nearly equal demands of the network. The Network Designer has examined the needs of the end users and the organization of the stations and facility, and has decided that a single, 16Mbps Token Ring network will offer the necessary performance and reliability to this network. The cabling to be used will be Category 5 UTP cable, and all the cable runs have been determined to be within the limitations of the Token Ring networking technology.
The HMO network will consist of 45 stations: 15 office receptionists, 12 doctors’ offices, 3 pharmacy stations, 3 records stations, 8 accounting and billing stations, and 4 management personnel. None of these stations has any particular importance over others from the point of view of the Network Designer, and there is currently no desire to provide internetworking capabilities or segmentation to the network.
Examining the first networking device selection criteria, the Network Designer, who is familiar with the use of both SNMP and RMON as diagnostic and fault-aversion tools, opts to investigate the short-term cost savings that would be provided by selecting the STHI series of Token Ring concentrators rather than the MicroMMAC-T series of concentrators. The Network Designer eliminates the non-intelligent devices and those devices which provide management functions more extensive than SNMP. The resulting selection field is summarized below.
Token Ring Workgroup Design | 8-5 |
