7.5.1 Structured cabling

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In the previous chapter shows the schematic illustration of the principles of operation of local networks. Can be seen devices LAN environment such as servers, PCs users and display their connection via Ethernet network infrastructure. As in the last decade of rapid development of the Internet has led to a drastic increase required by the nature and tasks of the network equipment, and the number of equipment, improvisations and half-solutions in connecting local networks of certain factors out of space. In addition to telephone and computer systems, along with other installations of this group, is creating a real mess of cables, and the whole system has become more expensive, immense, inflexible and highly susceptible to failures. Respect systematically by current requirements imposed, it is essential that they do not happen the situation illustrated by the left side of Figure 7.5.2b. Therefore, the recommendations were introduced to interconnect all the principles of STRUCTURED CABLING that provides quality network infrastructure dedicate multiple high-performance Internet, video, data storage, telephone communication and more. Structured cabling design includes two main groups of equipment in LAN:

Although basically the term refers to the passive cabling equipment, the design of passive equipment can not be realized without considering quality demands in terms of active equipment. Both of these segments must be carefully matched to current and future customer requirements. The following figure shows the cross-section of the building and deployment of basic infrastructure. First, it can be seen as switching between floors are network cabinets for active equipment (wiring closet - rack), which is the size, except meter size is expressed in the number of basic components embedded (Rack Unit 1U = 1 3/4"), so switching cabinet of 42U has the capacity, which would correspond to the amount of the closet about 200 cm. Within cabinets are installed the required active equipment (router, firewall, switch ...), passive equipment (patch panel) with built-in connectors for connecting UTP and FO cables of building, cables for connecting active equipment with connectors on panels (patch cord) supervisory measuring equipment, uninterruptible power source for devices (UPS) and everything else that is necessary.

 Scheme of structured cabling
Figure* 7.5.2 Design of LAN in case of a building. ( +/- )

Structured cabling is a single system or multiple subsystems in one or more buildings that can be interconnected in a common functional unit. Whether it is a system or subsystem principle is the same as shown in Figure 7.5.2. Thus, the first layer of the OSI model and not an innocent project. It is a common structured cabling divided in two basic groups with subgroups, as described further.

MDA is connected to all the HDA vertical cabling (backbone), which is essentially a very fast communication, usually implemented using optical media (FO). MDA is the hub of all communications systems. For MDA associated access point setting (ER - CARNet as a service provider, T-Com ...), managed and system administration and server resources are also the backbone. From the HDA containing all active equipment that serves users horizontal cabling (usually UTP) allows the user to access the system. If the system is larger, the more buildings, like the campus, the structure is the same except that the dispersed tree with even an intermediate zone. New MDA and ER are some other system.

 Zones of cabling
Figure 7.5.3 Topological scheme of structured cabling.

The basic scheme of topological spaces and cabling to the example shown in Figure 7.5.2 is shown in Figure 7.5.3, where the hierarchical importance of the particular areas from the top to the bottom of the image. Simpler scheme for less demanding system would unify the ER and MDA in an environment where one would have all joined the HDA. This new unit was then part of the computer space and has the role of 'excessive' MDA. Operations Center joins support. The number of spaces is reduced to two. The extended scheme displayed image meant to add another secondary ER of an existing primary ER space, and an additional vertical cabling to him from the MDA and its turnover significant HDA. Thus, the individual would be HDA approached from two directions (MDA and secondary ER). Number of space increases, the scheme would have a topological interlocking elements (mesh). Significantly expanded scheme would feature one campus cabling in which is possible to realize more related structure shown in Figure 7.5.3 through unified access I / O space. Merging of individual I / O space to access I / O space is done then specialized networking equipment specifically for this purpose, as the switches for the acceptance of the whole traffic (CORE switch) and switches traffic to the distribution of the areas (DISTRIBUTION switch). These CORE devices are usually connected to the principle of 'mesh' topology and generally know how to arrange transport its processing in the third layer (Network) of the OSI model. It is common for I / O devices and MDA data processing on the third layer of the OSI model, and for HDA devices (ACCESS switch) processing the data on the second layer (Data Link) of the OSI model because the traffic above them is mainly directed. Accordingly, network equipment must be connected as shown below.

 Physical network topology
Figure 7.5.4 Topological scheme connection of network devices.

ER (FIREWALL + ROUTER + CORE switch) and MDA (DISTRIBUTION switch) network devices are connected with each other and switches that belong to these groups are not the same peculiarities as switches for the HDA environment (ACCESS switch) that are not connected to each other and serve customers across EDA connection places (RJ45 outlet). The role of a firewall is in an era of increasing clutter on the Internet and misuse of certain services is becoming increasingly important, and almost every serious company ga used to separate the internal traffic from the Internet through the NAT mechanism. Figure 7.5.4 represents the PHYSICAL topology of the network, if the network devices support the distribution of traffic using VLAN (Virtual Local Area Network) technology in order to get traffic in distributed mutually independent internal network so that computers can be shown to belong to different virtual networks, regardless of which port of switch are connected, then the LOGICAL topology of the network obtained that describes the distribution of traffic through the physical resources. So, sort of a pattern displayed similar but more complex logical relationships of mutual respect.

The essence of structured cabling is the use of a single cable system for all installations that transmit any message - information as speech, image, data as digital signals through a single type of connector - RJ45. The wall outlet for users can be connected to a computer, printer, digital phone or some similar device by the technology, and work with it detects the corresponding active network equipment (switch, for example) with which the device is connected. Without intervention, the entire network cabling system can be configured in a completely different way, according to user needs. This allows the design of active network equipment designed for quick and easy switching as needed. When the user changes the physical location of the work, a network administrator will be done logical switching at the appropriate equipment and active users will have a new workplace condition that he had before.

Structured cabling is defined star-topology network performance. In addition to satisfying the allowed distance connectivity and all the described demands and long-term planned activities, needs, and increase the number of users, the basic principles of structured cabling must meet can be defined with the following three points:

A power supply cables (110/220V~)? Various consumers of electrical energy required for their work energy lines through which the current flows and creates an electromagnetic field, a source of electromagnetic interference by UTP cables (EMI - Electromagnetic Interference). Yet somehow tolerable when it comes to the creation of a new building, but when the old building with the already implemented computer network with UTP tiles along the walls, come 'trained electricians' from 'successful entrepreneurial firms' mount additional lines for a consumer with no 'pardon' will in UTP channel and set the power line. To EMI to network infrastructure reduced to acceptable levels, between the energy and computer wire distribution must be some acceptable distance that would have been roughly the following table.

Mounted the energy cable Minimum distance
(Attention, minimum safe distance is ...)
Power of EMI source < 2 KVA 2-5 KVA > 5 KVA
Unprotected power lines or electrical equipment
nearby without a grounded metal casing
127 mm 305 mm 610 mm
Unprotected power lines or electrical equipment
nearby with a grounded metal casing
64 mm 152 mm 305 mm
Shielded and grounded power lines or electrical
equipment with a grounded metal enclosure
no significance
separate canals
76 mm 192 mm
Electric motor and transformer no referrals no referrals 1220 mm

Maybe somewhere in Croatia there are standards that describe this. The author of this text above information is taken from the manual of the company 'Pressac Structured Cabling Systems' for structured cabling, which, among other things, contains the information on eliminating defects caused by various reasons (e.g. excessive attenuation along the cable) as well as descriptions of specific standards, and holding the recommendations 'The European standard for generic cabling systems recommendations' for wired and optical communication. Naturally, Fiber is very resistant to EMI, but is very susceptible to mechanical damage (kneading, sharply twisting or bending), poor connectivity for fiber connector, as well as dirty connectors. So setting optic seeking 'softer' handling and proper maintenance of connectors during use. Attenuation in any type of communication line is a very important factor. For various categories of UTP cables are described in great detail the criteria that made cable must meet in order to achieve the declared 'range' (typically 100 m). SM and MM optical communication are very different according to the characteristics of optical fiber and light source. But attenuation and range communication line are a special topic that may not belong to 'IT Alphabet'.

Briefly: Structured cabling is a cable network system for multiple purposes, as a unique system or a set of interconnected subsystems. General settings that should be respected in the design are:

  • Versatility - the network does not get smaller and simpler, but more universal.
  • Variety - the network should include video, telephony and IT.
  • Provisions - designed more than current needs, in accordance with the projected growth.
  • Reliability - using proven high quality cables, components and devices.
  • Saturation - enough points of connection to the user's needs.
  • Functionality - one must not ignore the appearance and neatness regarding maintenance.
  • Documentation - thoroughly describe and document of the network infrastructure.

Structured cabling reduces the possibility of errors in the most sensitive part of the networking system - in the cable infrastructure. Wireless networks are just one wonderful characteristics that improves the efficiency of the network, but it can never replace the role of structured cabling facilities, campuses, bank or other institution. Imposes only one question: how to explain to the authorities stated worthwhile investment and that means a competent and trained personnel?

Perhaps not the place to quote a dedicated network system Storage Area Network - SAN, networks, or subnets for data storage and server system usually interconnected optical technology and for this purpose designed switches (multilayer switches of the OSI model) optical modules, ensuring high functionality, scalability and flexibility. Network of this type can be used in the design of clusters or networks of clusters and super-computers. According to the scheme shown in Figure 7.5.3 above would represent an additional rectangle in the computer area, SAN is connected to the MDA, or as a separate area accessible via I / O space, or directly as part of MDA, and the principles of cabling backbones.


When everything is good planning in the cables of passive equipment and at the end of active equipment is put into operation, usually due to GROUNDING problems arise. It is not to be trusted but the vast majority of buildings have NULL-GROUND junction in the outlet of power supply installation that is generally sloppy grounded. Even sadder when this situation is found in new buildings. The result is that the mass contact in the sockets, which are connected to different phases does the same potential and it is the most common cause of damage to the electronic devices, which results when a device wants to connect with a signal cable which is shielded and thus connecting the unit ground. The moment you connect the unit has come to an electric discharge to balance the potential of 'grounding' and the damage is almost certain.

The correct way to solve this problem is to 'trimming' of the entire grounding system in the building. If it is not possible to use technologies that by their nature have no capacity to conduct electricity. For example, if you need to connect devices in two adjacent rooms, each room devices will be powered from a single outlet, and signal connections between the rooms will be realized optic cables. It is not uncommon, especially in older buildings, when you look into connectivity workstations some bank branches with their corresponding server, the signal between the workstation and the server transmits over MM fiber optic cable, that is, network interface cards have optical connectors, although the distance between devices associated not great. This solution does not approach for increasing the speed of data flow, but for the sake of safety and to increase the reliability of the grounding sloppily executed.

So, when equipping a newly constructed facility, particularly if it is a building or institution or institution of very significant public interest (faculty, judiciary, electricity, tax authorities, health, police ...), about all this is very much to consider. Everything has to be very well planned. And if you are planning to networking at the regional level or the state, then a multi-year program of networking types: '.... for all institutions and home users in urban areas to enable optical communication, and where it is not possible to provide fast ADSL communication, and thus economize monitor water and energy usage, delivering video content, availability, variety of services as well as settling accounts electronically for any kind of commitments and consumption, availability of educational textbooks and related services and activities ....' has its own justification and should be encouraged (in principle the Australian Government) because you educated coherent, cheaper and more efficient society. Utopia?


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