Instructor Note   Three more acronyms -- MCC (Main Cross Connect), ICC (Intermediate Cross Connect), and HCC (horizontal cross connect) -- are introduced in the context of the TIA/EIA-568-A standards.

The topology that is used when more than one wiring closet is required is the extended star topology. Because more complex equipment is located at the most central point in an extended star topology, sometimes it is referred to as a hierarchical star topology.

In the extended star topology, there are two ways in which an IDF can be connected to the MDF. In the first, each IDF can be connected directly to the main distribution facility. In this case, because the IDF is where the horizontal cabling connects to a patch panel in the wiring closet, whose backbone cabling then connects to the hub in the MDF, the IDF is sometimes referred to as the horizontal cross-connect (HCC). The MDF is sometimes referred to as the main cross-connect (MCC) because it connects the backbone cabling of the LAN to the Internet.

A second method of connecting an IDF to the central hub uses a "first" IDF interconnected to a "second" IDF. The "second" IDF is then connected to the MDF. The IDF that connects to the work areas is called the horizontal cross-connect. The IDF which connects the horizontal cross-connect to the MDF is called the intermediate cross-connect (ICC). Note that no work areas or horizontal wiring connects to the intermediate cross-connect when this type of hierarchical star topology is used.

When the second type of connection occurs, TIA/EIA-568-A specifies that no more than one ICC can be passed through to reach the MCC.

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