Cisco Systems VIP-4R/4T manual

VIP Port Adapter Functions

The IBM Token Ring specifies a star topology, with all end stations connected through a device called a multistation access unit (MSAU). IEEE 802.5 does not specify any topology, although most implementations are based on a star configuration with end stations attached to a device called a media access unit (MAU). Also, IBM Token Ring specifies twisted-pair cabling, whereas IEEE

802.5does not specify media type. Most Token Ring networks use shielded twisted-pair cabling; however, some networks that operate at 4 Mbps use unshielded twisted-pair cable. Table 1 shows a comparison of the two types.

Table 1 IBM Token Ring and IEEE 802.5 Comparison

Network Type	Data Rates	Stations/ Segment	Topology	Media	Signaling	Access Method	Encoding
IBM Token	4, 16 Mbps	260 shielded twisted-pair	Star	Twisted-pair	Baseband	Token passing	Differential
Ring network		72 unshielded twisted-pair					Manchester
IEEE 802.5	4, 16 Mbps	250	Not	Not	Baseband	Token passing	Differential
network			specified	specified			Manchester

All 4R port adapter interfaces support both 4- and 16-Mbps operation and early token release. The default for all ports is for 4-Mbps operation and early token release disabled. Both states are enabled with configuration commands in Configuration mode.

To enable 16 Mbps, specify the slot/port address and use the configuration command ring-speed 16; to return to 4 Mbps operation, use the command ring-speed 4. To enable and disable early token release, specify the slot/port address and use the configuration command [ no] early token release. For complete descriptions and examples of software commands, refer to the related software configuration documentation.

In the typical Token Ring network shown in Figure 15, lobe cables connect each Token Ring station (4R port adapter interface) to the MSAU (or MAU), and patch cables connect adjacent MSAUs (or MAUs) to form one large ring.

VIP-4R/4T Installation and Configuration 31