This appendix provides further explanation of concepts related to the hub. It also provides information on how to use the hub in your network.
The IEEE 802.3u standard defines two different classes of 100BaseT repeaters, Class I and Class II. Class I repeaters limit a network to having a single repeater. Class II repeaters allow networks to be built with more than one repeater. In addition, Class II repeaters allow longer cable distances in single repeater configurations than do Class I repeaters. The Micro Hubs are Class II repeaters.
Many switches have "built-in" repeaters or plug-in repeater modules. In these devices, the switch is actually attached to a port on the internal repeater. When connecting to a switch, determine if the port is a repeater port or not, and, if so, what type of repeater is present. If it is not a repeater port, the switch is treated as an ordinary end-station. If the port is a Class I repeater port, do not connect the hub or any other repeater to the port. If it is a Class II repeater port, see
"Examples of Micro Hub Wiring Limits" on page B-4" for configuration guidelines.
Micro Hubs are designed to be stacked through the UP and DOWN stacking connectors on the rear panel. Once connected through the stacking connectors, the hubs in a managed stack appear to the rest of the network and to the management interface as a single logical repeater with a maximum of 32 10/100-Mbps ports. shows two examples of a Micro Hub stack: as 1-logical-repeater with a 32-port maximum and as 2-logical repeaters with a 14-port maximum.
Figure A-1 Logical Repeater Configurations for the Micro Hub
You can build networks with two or more Class II repeaters in a single collision domain. With two Class II repeaters, a short cable segment connects the repeaters while maintaining 100-meter Category 5 cable connections to the attached stations. Using more than two repeaters in a single collision domain requires considerably shorter connections to attached stations. shows examples of a 2-stack collision domain with a 62-port maximum and a 2-unit collision domain with a 14-port maximum.
Figure A-2 Collision Domain Examples of for the Micro Hub
The Cisco 1538 series Micro Hubs 10/100 support a 10BaseT network segment and a 100BaseTX network segment. Each hub port can be in either segment, and each segment communicates with the other via an internal bridge as shown in .
Figure A-3 Internal Bridging Feature
The hub supports the autonegotiation of port speed. As a result, when connected to another network device, the Micro Hub determines the highest common speed for both devices for that port and uses it as the default.
The speed of the connected network device determines the speed at which packets are transmitted for a particular port. For example, if the network device is running at 10 Mbps, this connection transmits packets at 10 Mbps. If the network device is running at 100 Mbps, this connection transmits packets at 100 Mbps. You can also configure a given port from the CLI or hub manager to run exclusively at 10 or 100 Mbps.
For example, when two Micro Hubs are connected as shown in , the two hubs will autonegotiate the speed of the connection to 100 Mbps.
Figure A-4 Autonegotiating Speed With Another Micro Hub
Connections From a Switch, Router, or Server
The Micro Hub can provide a connection between a compatible switch, router, or server and PCs or workstations as shown in . To be considered compatible, a switch, router, server, PC, or workstation must support either 10BaseT or 100BaseTX. For example, the Cisco 1548M series Micro Switch 10/100 or any of the Cisco 1700 series routers are compatible devices.
Figure A-5 Desktop Connection From Switch, Router, or Server