Since telecom/network wiring is becoming so prevalent in facilities, what can be done to prevent complete shutdown in case of a disaster?
The loss of elements that support the transport of information (voice, data, image, and other signals) from one location to another can devastate operations at a facility. Therefore, you should develop a disaster recovery plan in case such a catastrophe occurs. Even though this plan may be well thought out, bringing back a downed network will not be a simple task. What cables are still intact? Can rerouting accomplish anything? Can critical segments be remapped? These and many other questions must be answered in great detail and as quickly as possible after a disaster occurs.
Suggested design alternatives
Before we discuss restoration procedures, let's look at some system design concepts that could be used in conjunction with setting up our disaster plan.
Alternate telephone service facility. Since the telephone service facility (where outside telephone network cables come into a building) is subject to damage from a variety of causes, an alternate entrance facility capable of handling part of the external telecommunications network is recommended. This service facility should be in a different part of the building. Thus, if the communication link to the telephone central office(s) is lost at the first entrance facility, some circuits will still be available at the alternate location.
Additionally, if a roof space is available, you may want to modify your existing system to accommodate satellite and microwave systems, which could be used to bypass the underground conduit service entirely.
Seismic design. If your area has even a small potential for seismic activity, the conduit and pathway systems should be designed to survive a credible event. Seismic and vibration restraints (springs, bracing, and aircraft cable) should be added to the structural support elements to keep cable systems and equipment in place.
You should segment entrance conduit runs to eliminate the possibility of a long conduit acting as a battering ram during seismic activity. This can be accomplished by using flexible couplings at some conduit joints to provide freedom of movement. Also, wall and slab penetrations should be designed to permit conduit movement independent of the building.
Use trapeze hangers and two-plane bracing to support overhead ladder racks or cable trays. House telecom/local area network equipment in seismic-rated cabinets.
Parallel backbones and telecom closets. Another design alternative is the use of two telecom closets per floor along with two smaller-pair-count parallel backbone cables rather than one large pair count cable. The chance of a single backbone cable being damaged is greater than the chance that two backbone cables would be damaged at the same time. Each of these cables should have separate routes or shafts so that if one riser shaft is damaged, the other can be used to pull in new backbone cable.
Spare capacity. Spare capacity for future growth normally is not designed into a telecom infrastructure. However, since cable costs are such a small part of the total installation costs, this is an excellent way of providing spare media should temporary connections be needed.
Fire stops. Make sure that all wall and floor penetrations for cables and conduits have fire stopping materials installed. This will help prevent the spread of fire and smoke. While floor slab openings are generally fire-stopped when sleeves are installed in a new facility, this practice is often omitted when additional penetrations are made in an existing facility.
Record keeping. Document and keep up-to-date your cable plant. A good cable plant administration system makes it easy to identify both damaged and undamaged cables, thereby eliminating the difficult task of identifying cables under a time constraint. Also, record keeping makes it easy to assign spare capacity as replacement for damaged circuits.
Security. Access to network components should be controlled. This may range from locks and remote monitoring to guards and access codes. Where feasible, cable should be routed through secure parts of a building; outside cables should be buried to limit access. Manholes, handholes, pull boxes, and pedestals located outside should have strong, tamper-proof locking mechanisms.
Testing and restoring a network
Unless complete plant destruction occurs, there will be parts of a cable plant that are still functional. A visual inspection of wiring closets and wall plates can help you determine the condition of cable ends. With this information, you can decide what to test. This also will help in determining what sections of the cable plant to repair first. Also, you should compare the cable plant records with notes made during this inspection. This information can be used in making estimates about damage and preparing for cable evaluation.
Obviously, your first priority is to test the cables and separate the usable from the damaged. This can be done with hand-held testing equipment. Several types of compact reasonably priced test tools are available for copper cable evaluation.
An intelligent loopback plug and a signal injector are two devices used to identify conductors in a multiple cable run.
The signal injector does just what its name implies: inject tones onto telephone and/or copper data lines. Usually 3 distinct tones are generated so that several test devices can be used on the same line without creating confusion. An inductive tracer, or probe, is the used to identify the tone in the specific wire, usually from a distance of within 12 in. of the wire without piercing the wire's insulation. The main benefit is that the tone can be traced through dry wall, wood, or other nonmetallic surfaces.
This type of wire tracing test equipment is capable of checking for line polarity, continuity and ringing current in telephone lines and is also suited for twisted pair cable, multi-conductor cable, speaker wire, coaxial cable, alarm cable, and local area network (LAN) cable.
Handheld cable and network analyzers can do performance tests (Category 3, 4, or 5) to ensure that the network cable passes traffic properly. Most handheld testers support battery-powered printers; thus, testing can be done even if building power is not available.
In many locations, fiberoptic network restoration must also be considered. The equipment most often used to do an end-to-end test is a loss test set (test light source and a power meter). It's available as a piece of integrated equipment or as two separate components. The first step in fiber restoration is to locate the damage. Measure the system power level with a power meter and if the level is below that specified for the fiber, use an optical time domain reflectometer (OTDR). An OTDR transmits pulsed light signals down the fiber, providing component loss and reflectance information.
Although an OTDR can be used for troubleshooting, it has inherent limitations. It has dead zones or blind spots following reflective events. Event dead zones refer to the minimum distance from the start of the fiber where a reflective event can be distinguished.
Another handheld tool, the visual fault locator, is useful within OTDR dead zones. The fault locater is a visible light source semiconductor diode with a wavelength of 650 nanometers; it emits a red beam down the fiber. For breaks and significant fault points, the light is visible through a 3-mm coated jacket.
Using EIA/TIA standards
EIA/TIA 568, Commercial Building Telecommunications Wiring Standard, and 569, Commercial Building Standard for Telecommunications Pathways and Spaces, are used as the basis for voice/data design so that a structured cabling system can be developed. EIA/TIA-606,The Administration Standard for the Telecommunications Infrastructure of Commercial Buildings, is recommended as the basis for documentation. This standard tells us how to label and document the elements of the 568 and the 569 standards, such as the media (copper twisted pair, fiber, etc.), the pathways, and the spaces in the building containing the equipment.
TERMS TO KNOW
Attenuation: Deterioration of the strength of signals as they pass through a transmission medium (e.g. through cables, outlets, connecting hardware, patch panels, etc.).
Backbone: A term referring to certain cabling segments used to provide connectivity over long distances within buildings as well as between buildings in a campus. It also refers to certain network architectures used to connect multiple sub networks to one another.
EIA/TIA-568, Commercial Building Telecommunications Wiring Standard.
EIA/TIA-569, Commercial Building Standard for Telecommunications Pathways and Spaces.
TIA/EIA-606, Administration Standard for Telecommunications Infrastructure of Commercial Buildings.
Order copies of the standards from:
Global Engineering Documents, 156 Inverness Way East, Englewood, Colo. 80112-5704. Phones: 1-800-624-3974, 1-303-792-2181; Fax 1-303-397-2633. EIA Engineering Publications Office, 2001 Pennsylvania Ave. N.W., Washington, D.C. 20006. Phone: 1-202-457-4963.
* "The EIA/TIA 568 Cabling Standard," October 1993 issue. "What To Know About EIA/TIA 606," December 1993 issue. "What To Know About EIA/TIA 569," February 1994 issue.
Cost: A set of these articles cost $14.95. Order No. 2208. Orders are taken via facsimile machines only. To order by fax dial 800-234-5709. (Have a credit card and your fax number ready when you dial by fax.)
* EC&M's Voice/Data Engineering/Installation Guide, May 1993 issue.
Cost: Guide cost $14.95. Order No. 2218. Orders are taken via facsimile machines only. To order by fax dial 800-234-5709. (Have a credit card and your fax number ready when you dial by fax.)
* EC&M's Voice/Data Engineering/Installation Guide, May 1994 issue. Cost: Guide cost $14.95. Order No. 2228. Orders are taken via facsimile machines only. To order by fax dial 800-234-5709. (Have a credit card and your fax number ready when you dial by fax.)
* EC&M's Voice/Data Engineering/Installation Guide, May 1995 issue.
Cost: Guide cost $14.95. Order No. 2238. Orders are taken via facsimile machines only. To order by fax dial 800-234-5709. (Have a credit card and your fax number ready when you dial by fax.)