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■    A passive hub is typically unpowered and makes only physical, electrical connections. Typically, the maximum segment distance of a


particular topology is shortened because the hub takes some power away from the signal strength in order to do its job.

The Multistation Access Unit (MAU)


This Physical layer device is unique to Token Ring networks. Token Ring networks use a physical star topology, yet they use a logical ring topology (discussed later). The central device on an Ethernet star topology network is a hub, but on a Token Ring network, the central device is a Multistation Access Unit (MAU, sometimes called MSAU). The functionality of the MAU is similar to that of a hub, but the MAU provides the data path that creates the logical “ring” in a Token Ring network. The data can travel in an endless loop between stations. MAUs are chained together by connecting the Ring Out port of one MAU to the Ring In port of another and connecting the last Ring Out port to the Ring In of the first MAU in the chain, thus forming a complete loop. In a Token Ring network, you can have up to 33 MAUs chained together. MAUs are shown in Figure 2.11.


FIGURE 2.11 MAUs in a Token Ring network

The Data Link Layer


The Data Link layer is actually made up of two sublayers:


■    The Media Access Control (MAC)


■    The Logical Link Control (LLC)


Figure 2.12 illustrates this arrangement.


FIGURE 2.12 Sublayers of the Data Link layer


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