Curs PC si internet cap 8.5 Planning Structured Cabling: Horizontal and Backbone Cabling

8.5 Planning Structured Cabling: Horizontal and Backbone Cabling 8.5.1 Catchment area problems Instructor Note The purpose of this target indicator is to introduce what happens in larger buildings. Unlike the prior example for choosing a wiring closet, many buildings will require cable runs greater than 100meters. This necessitates the use of repeaters, or multi-port repeaters called hubs, and the use of IDFs. Emphasize to the students that these requirements are a matter of both technology (the network will not work properly if the rules are violated) and standards (networks must be built according to various standards). If the 100 m catchment area of a simple star topology wiring closet cannot provide enough coverage for all the devices that need to be networked, the star topology can be extended by using repeaters. Their purpose is to avoid the problem of signal attenuation, and are called hubs. Generally speaking, when repeaters, or hubs, are used in this manner, they are located in additional wiring closets called IDFs, and are linked by networking media to a central hub located in another wiring closet called the MDF. TIA/EIA-568-A specifies the use of one of the following types of networking media:100 ohm UTP (four pair) 150 ohm STP-A (two pair) 2 fiber (duplex) 62.5/125 optical fiber multimode optical fiber The TIA/EIA recommends the use of CAT 5 UTP for horizontal cabling, when an Ethernet LAN uses a simple star topology. Web Links Cabling Glossary Industry Standards for Structured Cabling 8.5 Planning Structured Cabling: Horizontal and Backbone Cabling 8.5.3 Example of where you would use multiple wiring closets Instructor Note The situation of multiple buildings -- a campus LAN -- is introduced. As with the multi-story building, an extended star topology is used. Another example of a LAN that would probably require more than one wiring closet would be a multi-building campus. The main figure illustrates locations where backbone and horizontal cabling have been placed, in an Ethernet LAN, in just such a multi-building campus. It shows an MDF in the center of the campus. In this instance, the POP is located inside the MDF. The backbone cabling (red lines) runs from the MDF to each of the IDFs. The IDFs (yellow boxes) are located in each of the campus buildings. In addition, the main building has an IDF, as well as an MDF, so that all computers fall within the catchment area. Horizontal cabling, running from the IDFs and MDFs to the work areas, is represented by the blue lines. Web Links Cabling Glossary Industry Standards for Structured Cabling 8.5 Planning Structured Cabling: Horizontal and Backbone Cabling 8.5.6 TIA/EIA-568-A requirements for backbone cabling 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. In such instances, the IDF that connects to the work areas is called the horizontal cross-connect, and 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. Web Links Cabling Glossary Industry Standards for Structured Cabling 8.5 Planning Structured Cabling: Horizontal and Backbone Cabling 8.5.7 Maximum distances for backbone cabling Instructor Note The maximum backbone lengths for single-mode optical fiber (3000m), multimode optical fiber (2500m), and UTP (90m) are presented. Note the 3km distance of optical fiber allows it to be used, in an Ethernet extended star topology, in a area greater than many high school and junior college campuses. On the other extreme, note that the use of UTP as a backbone cable has severe length restrictions. As you have already learned, the maximum distances for cabling runs varies from one type of cable to another. For backbone cabling, the maximum distance for cabling runs can also be impacted by how the backbone cabling is to be used. To understand what this means, assume that a decision has been made to use single-mode fiber-optic cable for the backbone cabling. If the networking media is to be used to connect the HCC to the MCC, as described above, then the maximum distance for the backbone cabling run would be 3,000 m. If the backbone cabling is to be used to connect the HCC to an ICC, and the ICC to the MCC, then the maximum distance of 3,000 m must be split between the two sections of backbone cabling. When this occurs, the maximum distance for the backbone cabling run between the HCC and the ICC is 500 m. The maximum distance for the backbone cabling run between the ICC and the MCC is 2,500 m. The Figure lists TIA/EIA-568-A specifications for maximum distances for backbone cabling runs for each type of networking media. Web Links Cabling Glossary Industry Standards for Structured Cabling