Frequently Asked Questions about LAN Cabling and Cable Sharing in Converged Networks
Balanced twisted-pair copper cabling plays a key role in providing a migration path to fully IP-enabled building automation systems and uniquely features the ability to remotely power work area devices using Power over Ethernet (or PoE) technology. The cabling media selection process involves understanding the benefits that higher performing solutions, such as category 6A/class EA and category 7A/class FA cabling, can provide in terms of future-proofing, added flexibility to accommodate new applications, and improved heat dissipation. Advanced strategies such as using Siemon TERA™ category 7A/class FA cabling systems to support multiple applications under one sheath can provide additional cost and pathway space savings benefits. Answers to the most common media selection questions can be found below.
Figure1: LAN Cabling Connections
How does LAN cabling integrate with BAS devices in a converged network? In a converged cabling system, balanced twisted-pair copper cabling is used to interface between BAS software and IP-enabled BAS devices with modular RJ-45 interfaces or controllers that communicate with multiple BAS devices. Figure 1 depicts structured LAN cabling connections, represented by blue lines, from a BAS server to an IP-enabled camera and a controller in a basic converged cabling example. The cabling from the controller to the BAS devices, represented by green lines, is typically application dependent low voltage wiring (e.g. two 18 AWG conductors). In some cases, non‑IP BAS devices can accommodate both LAN cabling and low voltage cabling connections. When the option is available, the use of LAN cabling for non-IP BAS device connections is always recommended to facilitate future migration to a fully IP‑based building automation system. Note that a Standards-compliant structured cabling topology includes one or two patch panels in the telecommunications room, an equipment outlet in the work area, and an optional horizontal connection point located in a zone box to facilitate BAS device adds, moves, and changes. For simplicity, these connection points are not shown in Figure 1.
What is zoned cabling? Structured cabling featuring optional consolidation points, consisting of BAS outlets in a zone box enclosure is recommended for converged networks because this topology supports more efficient moves, adds and changes. The availability of spare ports enables the rapid addition of new services, and the fewest disruptions due to moves, adds, and changes. A zoned cabling design consists of horizontal cables run from the horizontal cross‑connect or interconnect in the telecommunications room to connections within the zone box enclosure, which may be located in a raised floor, in the ceiling, furniture or wall mounted. Solid cables are then connected from the zone box to the rear of work area outlets and BAS devices are connected via a patch cord to the work area outlets.
Figure 2: Multiple BAS Applications Served from HCPs in a Zone Box
Figure 2 shows Siemon category 6A/class EA and TERA category 7A/class FA cabling extending from a zone box enclosure to multiple applications in a BAS coverage area.
How can Siemon TERA™ category 7A/class FA cabling systems enhance a converged network? Class FA is the only grade of LAN cabling that is fully-characterized over the entire frequency spectrum over which broadband video is transmitted. This bandwidth makes Siemon TERA category 7A/class FA cabling ideal for HDTV applications supported by inexpensive video baluns. In addition, the cable sharing feature of TERA category 7A/class FA cabling systems can improve the overall efficiency of a converged BAS network by reducing the number of unused pairs, optimizing pathway space, and delivering media cost savings opportunities. Example applications that are suitable for cable sharing are shown in Table 1. Note that the number of pairs required for a BAS controller is application dependent. Consult with your BAS controller manufacturer to determine if cable sharing can be part of your controller cabling strategy.
Do Standards allow cable sharing? Yes! Cable sharing is recognized in TIA TSB-190 (“Guidelines on Shared Pathways and Shared Sheaths”), ISO/IEC 11801: 2002, 2nd edition (“Information technology - Generic cabling for customer premises”), and ISO/IEC 15018 (“Information technology – Generic cabling for homes”). All of these Standards provide examples of applications commonly deployed in a shared sheath environment and discuss how cabling noise affects whether multiple applications or appearances of the same application can coexist in one 4-pair cable channel. Because of its fully shielded construction, the signals on individual category 7A pairs are fully isolated from each other and multiple applications or appearances of the same application transmitting on just one or two pairs may be run over a TERA category 7A/class FA channel without concern for interference.
Is PoE compatible with cable sharing? Yes! In PoE and PoE Plus applications, power may be injected into the channel by an end-span device, such as a switch, located at one end of the cabling channel or by a mid‑span device, such as a powered patch panel, from within a segment of the cabling channel. Typically, end-span devices inject power over the two 10/100BASE-T data-carrying pairs in accordance with IEEE 802.3 Alternative A, while mid-span devices inject power over the two non-data carrying pairs in accordance with IEEE 802.3 Alternative B. Cable sharing is definitely an option for 2-pair 10/100BASE-T PoE and PoE applications that employ Alternative A for power delivery. In fact, category 7A/class FA media is so robust, that two Alternative A sourced PoE applications (12.95 W maximum power delivered to the each powered device) can be supported over one TERA channel!
What is the recommended cabling practice to enable future migration to IPTV? IPTV offers viewers a high-definition television experience over 4-pair LAN cabling. IPTV signals are transmitted via IP packets to a set-top box that decodes the packets and sends the image to a television. IPTV is a secure, closed system with content that is managed by a service provider (or by an end-user that centrally manages in-house IPTV equipment) and eliminates the need for coaxial cabling. If support of IPTV is a future goal but the service is not yet available, then the recommended practice is to deploy one 4-pair 10Gb/s-ready cable to each television. In the interim, video baluns are used to convert the existing coaxial broadband signal to a balanced twisted-pair signal. Note that, although only one twisted-pair is required to transmit HDTV signals in a video balun based solution, cable sharing is not part of the recommended interim strategy since four twisted-pairs will ultimately be required to support IPTV.