Glossary 19" rack system, networking

Rack Spaces

Metal structure based on at least 2 vertical sheets called Rack uprights on which networking equipment such as servers, switches, hubs, routers, patch panels and PBXs are fixed with screws or placed on special guides. The aforementioned equipment, in fact, are not only produced in desktop version but also to be rack-mounted. The vertical distance of the holes of such a structure is equal to 1.75 inches (4.445 cm) and is called a rack unit (Rack Unit, RU or U). Network equipment is measured vertically with this unit. For example, rack servers can occupy one, two or more rack units (1U, 2U...) in height, while in width they generally occupy 19" (48.26 cm). Racks are used in many contexts, such as server farms. For the safety of the devices, the racks are enclosed in special cabinets (rack cabinets) usually equipped with a key. © M.D.W.

Rack Units

Rack is a standard hardware installation system, consisting of a modular rack-based structure that is 19 inches (482.6 mm) wide and 1.75 inches (44.5 mm) high. The rack unit is the only constant point of all rack cabinets that then differ by:

  • number of rack units

  • cabinet depth

  • number and type of rack posts (usually 4 for floor cabinets 2 in built-in cabinets)

  • type of doors, walls and finishes.

Rack cabinets are widely used in the industrial, telecommunications and IT fields, they serve to contain servers, switches, switchboards and other equipment in an orderly and easily accessible way. In this way, in the event of a failure or when you decide to update a component, the replacement of the part or its maintenance can be carried out quickly and cleanly and safely. © M.D.W.

 Floor rack cabinets

Floor rack cabinets are used in different areas of which the two main ones are server rack installation and networking. © M.D.W.

Server rack cabinets are characterized by:
  • 1000 mm deep

  • perforated steel front and rear door and high heat exchange with the thermum

  • rollover system

Rack cabinets for networking are characterized by:

  • less depth 800 or 600 mm

higher IP rating, the front door is made of shatterproof glass and the rear door is made of closed steel, cable access is protected by combs and sponges that prevent dust from entering

Built-in rack cabinets

Wall rack cabinets are used for networking applications. They are designed to contain PBXs, routers, switches and patch panels. Ordered and collected inside a cabinet, these peripherals are more protected and easily manageable both at the time of installation and subsequently during maintenance. © M.D.W.
These cabinets are characterized by:

  • shallower depth, generally less than 600 mm

  • only two rack posts (weight of networking devices does not require 4-point fixings)

the glass front door is often the only access to the cabinet even if there are more complex versions with removable sides and "double section" or possibility to open the back of the cabinet. © M.D.W.


Wiring standards

De jure and de facto standards help manage multiprotocol enterprise networks. The most important standardization bodies for computer networks are: CCITT, ITU, ISO, ANSI and IEEE.
Of particular impact is the OSI (Open System Interconnection), an ISO project dating back to the late 70s, which is proposed as a reference model for networks. It presents a 7-layer approach, with a series of protocols that are inserted at various levels. Layers 1 (Physical layer) and 2 (Data Link layer) are now standard, while for the other 5 there are protocols that have existed for some time and standards struggle to impose themselves.

Cabling consists of physical systems (cables, connectors, switches, support infrastructures) that allow you to create a network of computers, typically within a building or a group of buildings.
The electrical characteristics and lengths of the cables and connectors used influence the types of local networks that can be implemented.
Among the first examples of wiring we can mention the first ethernet networks (called 10Base5, thick cable), consisting of large copper coaxial cables, to which the computers had to be connected by drilling the outer sheath until they reached the internal connector. These wiring harnesses had a bus topology.

Structured cabling

Modern office buildings have structured cabling systems to support the implementation of different types of local networks, including for example the telephone network. The systems are based on category 5 or higher cables and RJ-45 connectors. The cables have a maximum length of 90 m, to which 10 m must be added for trade-in cables. This constraint is dictated by the characteristics of the Ethernet network.
For each station to be served, one or more cables are laid in special ducts in the walls, false ceilings or floors of the building, until you reach a floor distribution cabinet (in the jargon of structured cabling, Floor Distributor or FD), usually it is a standard 19-inch rack, which can accommodate both permuters that active devices.
These cables are attested on the one hand in a permutation panel in the cabinet, on the other in a wall or floor plate near the user workstation. By connecting one trade-in cable from the computer to the wall socket, and another from the permutator to a network device (such as a hub or switch), an electrical connection is created that allows the computer to be connected to the network.
If the size of the building does not allow to serve all the utilities with a single FD, the various FD are connected to a building cabinet (Building Distributor, BD), through copper and / or fiber optic cables, also attested in permutators.
Similarly, the different buildings of a campus are connected to a campus permutation cabinet, or Campus Distributor, CD.
The rooms that house the distribution cabinets should have adequate characteristics for power supply (better if protected by an uninterruptible power supply), air conditioning, access control (they are privileged places for intrusions or to cause network malfunctions). ©

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