#SCS, #Structured cabling system
Structured cabling system.
Ensuring high bandwidth of the transmission path is the most important issue in the design and installation of technical security systems.
It is especially relevant if it is necessary to solve the problem of video signal transmission, because video surveillance systems are highly informative systems, the volume of information and data transmitted in them is much higher than, for example, in a security and fire alarm system.
Experts know: if the transmission path does not provide the necessary network bandwidth, all talk about the nuances of the operation of high-quality video equipment can turn into, in essentially, into an empty sound.
More and more often, facing such a problem, customers, when installing complex security systems, turn not just to equipment suppliers, but to organizations that build structured cabling systems (SCS) to connect video surveillance systems on their basis.
There are many examples of companies that initially specialized in creating SCS, successfully entering the market of technical security systems.
There is another good reason for these notes: not long ago, a new international standard for SCS was released.
I consider it necessary to dwell in more detail on the issues of constructing structured cabling systems for security systems.
Perhaps this will initiate a discussion of technical solutions proposed in this area.
SCS is a low-current telecommunications cabling system that services all engineering systems located in a building.
SCS must meet the following necessary requirements:
- have a standardized structure and topology;
use only standardized components (cables, distribution devices, connectors, etc.); - ensure standardized electromagnetic parameters (attenuation, bandwidth, etc.) of communication lines organized with its help;
- be managed (administered) by standardized methods.
A structured cabling system is a hierarchical cabling system of a building or group of buildings, divided into structural subsystems.
A structured cabling system consists of:
— a set of cables (copper and/or optical);
— patch panels;
— patch cords;
— cable connectors;
— modular jacks;
— information sockets (IS);
— auxiliary equipment.
All of the listed elements are integrated into a single system and operated according to certain rules.
All SCS must be built according to uniform rules, have the same means of switching and connecting equipment, and ensure pre-known parameters of the data transmission environment.
Recently, the concept of building a cable system has begun to take shape, i.e. a device made from components of a standardized series, built according to the modular principle, with pre-set characteristics that ensure the operability of equipment connected to the SCS.
Surprisingly, these ideas, long accepted and implemented, in particular, in mechanical engineering (standard series of threaded connections, bearings, etc.), have only now begun to gain ground in the field of telecommunications [2].
History of the issue
The beginning of the 50s of the last century is the date of birth of the first telephone networks.
In the 80s, the first cable solutions appeared: IBM connected its mainframes using 93-ohm RG-62 coaxial cable using a star topology.
The first cabling solutions were introduced by the largest manufacturers of computer and telephone equipment and were based on closed technologies.
Many developments pursued exclusively private goals and objectives of a specific organization.
The emerging market for local area networks suffered from a chronic lack of uniformity, which was inevitable due to the changing structure of the industry.
1987 — TR41.8 committee (Electronic Industries Association) began developing a standard for cables placed inside buildings.
1989 – Underwriters Laboratories, a research organization, and Anixter developed a new classification for twisted pair cables.
1991 – ANSI/EIA/TIA-568 specification published. Developers – Electronic Industry Association (EIA) and Telecommunications Industries Association (TIA).
In fairness, it must be acknowledged that for quite a long time even law-abiding Western companies ignored the recommendations of standards committees. This was partly the reason why the quality of services provided on the market declined.
Failure to comply with the requirements for installation and placement of SCS, its termination and testing was a fairly common occurrence.
In connection with this, the problem of improving the qualifications of industry employees became acute. And the revision of the standards themselves soon became an urgent need. Serious institutes with an excellent reputation appeared: TIA and CBM.
These institutes have been active in raising awareness of the prevailing standards and providing appropriate training to those who seek it.
1995 – two main normative and technical documents describing SCS as a technical object are adopted. These are the American standard TIA/EIA-568-A and the international standard ISO/IEC 11801.
Despite the fact that both main documents describe the same technical object, they have quite serious conceptual differences, considering SCS from different positions, and largely complement each other.
The second generation TIA-568-A (Commercial Building Telecommunications Cabling Standard) differed significantly from the previous document in that the use of coaxial cable was not recommended for the construction of newly created SCS and at the same time the use of single-mode fiber-optic cables in trunk subsystems was permitted.
In connection with the rapid development of information technologies, the need to transmit ever larger flows of information, in September 2002 the second edition of the ISO/IEC IS 11801:2002(E) standard was published, which introduced new parameters and clarified the values of traditional parameters of components and paths based on twisted pairs to ensure the transmission of information flows in the horizontal subsystem of Gigabit Ethernet network interfaces and similar ones.
From 2002 to the present, the development of information technologies has not followed the path of a sharp increase in the volume of transmitted information flows, as was predicted, but along the path of improving the technological capabilities of the networks themselves. In this regard, in 2008, a new edition of the ISO/IEC IS 11801:2008(E) standard was adopted.
This standard is a very voluminous and serious document describing all the features of the construction and design of SCS.
Unfortunately, in Russia today, the national SCS standard is missing from the GOST R 34 «Information Technology» standards group. Therefore, Russian designers, developers, suppliers, installers, and owners of SCS are forced to base their work on international standards.
Components of SCS
If SCS is designed and installed correctly, it can serve for 25 years or more and is thus a capital system.
SCS is serviced in the same way as any capital system: regular inspections and checks, called testing and certification of the system for compliance with the standards of a certain class. Preventive maintenance of this system, scheduled maintenance, switching, etc. are possible.
Only certified specialists have the right to build and provide guarantees for a structured cabling system.
To be able to classify and certify a structured cabling system, it is necessary to know that the electromagnetic characteristics of the SCS are defined by the ISO/IEC 11801:2008 (E) standard for certain configurations: channel and fixed line.
A permanent link is a passive section of the SCS between two directly connected points (interfaces) of connection to it, through which a signal can be transmitted. That is, a permanent link is a permanent cable and connectors at its ends (Fig. 1).
A permanent link is designed to test the performance characteristics of a permanent component of cable wiring.
The concept of Permanent Link is introduced to define a test configuration that characterizes the parameters of the fixed part of the cable system as accurately as possible.
The Permanent Link configuration requires that the contributions of the connecting cables used to access the line under test are excluded from the measurement results.
Therefore, the limiting test values for Permanent Link differ from the values for Link by an amount attributed to the tester's connecting cables according to an a priori estimate. The total length of a Permanent Link line can be up to 90 m.
A fixed line does not include cords used to connect the transmitting and receiving devices, nor any patch cords.
A channel is a passive path capable of transmitting a signal from end to end, connecting any two active units of electronic equipment, for example, a workstation and a LAN switch (Fig. 2).
A channel, according to the ISO/IEC 11801:2008(E) standard, is a path for interaction between active network equipment.
The concept was introduced in 1999.
The channel includes a fixed SCS line and various cords used for connection.
The channel as an object of measurements – such a model was introduced to achieve a better approximation of the final configuration of the user system.
The standard describes two fundamentally different measurement objects: a permanent link and a channel. The document provides the relevant standards for both objects. If there are special requirements, a selective or continuous check of the channel or permanent link parameters can be performed at the acceptance testing stage.
The channel model is convenient to work with during the current operation of the SCS when searching for and troubleshooting.
The performance limits for symmetrical cables are strictly defined by the components on the basis of which the channel is created (ISO/IEC 11801:2008(E)). For maximum values, this is 90 m of single-core copper cable, 10 m of various cords and 4 joints (1 joint is a plug and socket connected together).
For class F, only 2 joints are allowed in the current version of the standard.
As is known, active switches, video recorders and other similar equipment impose different requirements on the information transmission channels for frequency bandwidth. Therefore, electrical channels and lines are divided into six classes: A, B, C, D, E, F. Channels and lines of the specified classes provide guaranteed support for the corresponding classes and all lower classes.
The components that make up a structured cabling system (cables, connectors, plugs, sockets) are also classified in the ISO/IEC 11801:2008(E) standard by the bandwidth of the frequencies they pass through, and different requirements are also imposed on the quality of installation.
Application classes
Class A: lines specified up to 100 kHz for voice and low-speed data transmission – video signal transmission.
Class B: lines specified up to 1 MHz for medium-speed data transmission – transmission rate of 1 Mbit/s.
Class C: Lines specified up to 16 MHz for high-speed data transfer – transfer rate of 10 Mbps.
Class D: Lines specified up to 100 MHz for ultra-high-speed data transfer – transfer rate of 100 Mbps – 1 GGbps.
Class E: Lines specified up to 250 MHz for ultra-high-speed data transfer with speeds up to 1 GGbps.
Class F: Lines specified up to 600 MHz for ultra-high-speed data transfer with speeds of 1 GGbps – 10 GGbps.
That is, if we choose high-quality video surveillance cameras that form high-resolution frames, and therefore with a large volume, high-quality video recorders or switches that transmit the received image in live video mode to the network, which will also take up a considerable amount of traffic, and organize the transmission via a cable system that is obviously of a lower class or incorrectly designed, then the image quality will be irretrievably lost, and the live video mode will not be achieved either.
Therefore, the investment in equipment will not justify itself.
In addition to the frequency range, the ISO/IEC:2008(E) standard sets clear requirements for the parameters of channels and fixed lines based on both twisted pairs and fiber-optic cables. For twisted pair systems, channels of classes D, E, F must have a wave impedance of 100 Ohm, for classes A, B, C the preferred value is 100 Ohm, but a value of 150 Ohm is also acceptable. Also stratified are parameters such as return loss, insertion loss, structural return loss, near-end immunity (NEXT), total near-end crosstalk loss (PSNEXT), far-end crosstalk loss (FEXT) and its total value (PSFEXT), near-end attenuation-to-crosstalk ratio (ACR), total near-end crosstalk loss-normalized (PSARC), far-end crosstalk loss-normalized (ELFEXT), total far-end crosstalk loss-normalized (PSELFEXT), signal delay (PD), and delay skew (DS).
Using cable structure parameters is also inevitable during the installation of a video surveillance system. The installer needs to calculate the location of the power source and the camera.
According to the international standard ISO/IEC11801, Category 5 (Class D) 100 MHz twisted pair with a data transfer rate of 1 GGb/s has a resistance of no more than 20 Ohm per 100 m (in reality, about 2 Ohm per 100 m). No more than 6 V of voltage drops over 300 m of twisted pair. Therefore, the power supply can be connected at a distance of about 300 m from the camera.
For more accurate calculations, it is necessary to test the structured cabling system.
It is advisable to say a few words about the SCS based on fiber-optic cables. The main standardized parameters of fiber-optic communication lines are the numerical aperture (NA), attenuation (A), and the broadband coefficient (K).
In lines using optical cable for high-speed and ultra-high-speed data transmission, bandwidth is not considered as a limiting factor.
The numerical value specified in the class name defines the minimum channel length in meters at which the channel of this class is guaranteed to support the corresponding application if the channel is created in accordance with the requirements of the standard:
OF-300 class: from 300 m.
OF-500 class: from 500 m.
OF-2000 class: from 2 km.
The OF-2000 class supports applications including Gigabit Ethernet 1000Base-LX protocol over OS1 single-mode fiber up to 2000 m at IL 4.56 dB in the 1310 nm window.
OF-500 class supports Gigabit Ethernet 1000Base-LX application over OM1, OM2, and OM3 multimode fiber up to 500 m at IL 2.35 dB in the 1300 nm window.
The channel length increase from 550 to 2000 m in the 1300 nm window is achieved by improving the refractive profile.
The standard specifies the bandwidth (bandwidth coefficient) for laser input of at least 2000 MHz x km in the 850 nm window for OM3 fibers.
Therefore, the choice of transmission equipment, such as active switches, for transmitting a video signal must be made either taking into account the existing SCS at the facility, or taking into account the territorial extent of the facility and the rules for designing a structured cabling system on fiber-optic communication lines.
In conclusion, it is necessary to pay attention to the following fact.
The only company that conducts research on the SCS market in all countries of the world is the independent consulting company BSRIA – Building Services Research & Information Association, based in the UK.
According to the official BSRIA report on the copper SCS market in Russia for 2007, Eurolan SCS ranks 3rd with a market share of 8.7%, behind only Typo Electronics (10.8%) and Systimax Solution (16.9%).
LITERATURE
Networks and Communication Systems, No. 6, May 5, 2008, p. 11. Samarsky P. A. Fundamentals of Structured Cable Systems. Moscow: 2005.