Introduction to Data Communications
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40b. Hub's OSI Operating Layer

Hubs are multiport repeaters and as such obey the same rules as repeaters (See previous section OSI Operating Layer). They operate at the OSI Model Physical Layer.

40c. Hub's Segment to Segment Characteristics

To understand the Ethernet segment to segment characteristics of a hub, the first thing to do with Ethernet Hubs is to determine how they operate. Logically, they appear as a Bus Topology and physically as a Star Topology. Looking inside an Ethernet Hub, we can see that it consists of a electronic printed circuit board which doesn't tell us much. If we form a functional drawing, we can clearly see how the Physical and Star Topology appears:

Understanding that inside the Hub is only more repeaters, we can draw the conclusion that all connections attached to a Hub are on the same Segment and have the same Segment Number. It is considered one repeater from any port to any port even though it is indicated as a path of 2 repeaters.

The 5-4-3 Rule for Ethernet Hubs:

Cascaded Hub Network

Cascading Hubs means to connect the Hubs together through the RJ45 ports. One Master Hub (Level 1) is connected to many Level 2 (Slave) Hubs who are masters to Level 3 (slave) Hubs in a hierarchical tree or clustered star. The maximum number of stations in a Cascaded Hub Network is limited to 128.

Introduction to Data Communications
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