Cabling for LAN and Premise Architecture

July 31, 2013 at 10:00 AM

 

Diagram of Wiring Closet Rack

It's hard to fathom just how quickly Ethernet technology has grown. Today no modern office building would be functional without premise wiring, or the cabling run throughout the building to connect computers to the LAN.

 

We may be on the verge of a wireless revolution with new technologies like DAS and MESH, but for now you should at least understand the basic architecture of LAN cabling.

 

LAN wiring is often broken into three types: backbone, horizontal runs, and patch cabling, each with its own purpose and requirements. In an especially large building or in a campus of buildings, the backbone is the wiring that connects server locations together and to the Internet through an ISP. Since a large amount of data may be carried back and forth by these cables, they are typically designed for bandwidth, like T1 lines or fiber optic cables (usually multi-fiber lines like breakout or distribution style, or even ribbon fibers).

 

Close Up View of Solid Conductor Category-rated Cable

The horizontal runs are the individual cables coming from the servers to the Work Areas. Work Areas are the points where the cable is terminated in a wall plate or jack so a user can plug their computer or other device into it.

 

It is often deceptive to assume that a single horizontal run will connect to a single computer. More likely than not, it is connected into a local Ethernet switch or wireless access point, and many computers may be connected to that. For this reason, the actual data carried on a single horizontal cable could vary greatly, and if you are planning your LAN architecture, this is the trickiest thing to get right. It can also be the most expensive piece to change if you get it wrong as you may need to fish the cable back out of a wall or conduit to re-arrange it.

 

Horizontal runs are currently most often solid-conductor Category rated copper cable. This is slowly changing over to fiber optic cabling as the price gap between the two narrows and fiber optic technology improves. Note that the horizontal cable may also require special jacket types to comply with building fire codes.

 

Right Angle Ethernet Cable Assembly

The patch cabling in a LAN is often overlooked, but is also very important. In general it is used to connect two devices together in a rack in a server room, or to connect a device to a wall jack where a horizontal cable is terminated. Being exposed (not behind a wall or on a rack ladder) and possibly being moved frequently, a patch cable needs to be robust and flexible.

 

While patch cables are easily available and can be bought relatively cheap, you might want to consider that cheap cables may introduce problems to your LAN. Cheap cables often use substitute materials such as copper clad aluminum or feature low quality plugs not rated for the application. Cheap cables seldom pass the testing required for the network and will degrade your network performance.

 

With more devices requiring power (POE), the cheaper cables often cannot carry the added burden due to undersized conductors and low grade copper. For a single user's computer, the impact of this may be limited, but in a server room low quality cables can have a disastrous effect on the entire LAN. If the cable manufacturer you purchase from has a robust QC process, it will help.

 

Other features to consider are molded right angle connectors to ensure the connector isn't bent to fit into limited space, cable boots to make depressing the connector latch easier, and high-flex construction and oil resistant jackets for demanding environments.

 

L-com stocks components for every facet of your LAN, from Ethernet cables, plugs and jacks, to bulk copper or fiber cable, to active media converters. We also go beyond that, to reliable racks, panels and cable management accessories, lightning and surge protectors, Power-over-Ethernet components and everything for wireless deployment.

 

Choose the Right Cable Jacket Material

July 17, 2013 at 10:00 AM


Plenum, LSZH and More

 

L-com's Plenum rated multiconductor cable

 

For buyers and technicians using signal-grade cabling, much attention is usually given to the connector type, termination process and bulk cable construction. Another aspect not to be forgotten that can be critical to many applications is the cable jacket material.

 

 

What does the jacket do?

 

More than just a color coding cable management technique, the jacket has several important functions. It allows the separate conductors to be organized into a single data line for ease of organizing, or it can even contain several conductors or wires to be broken out at a drop point.

 

The cable jacket also aids tremendously in the cable's flexibility and durability. In covering any shielding within the cable, it can prevent noise that collects on the shield from degrading the signals of other cables nearby, or from draining at inappropriate spots. Finally, the outer jacket is often the last line of defense between the data-carrying conductors and the environment in which the cable is used.

 

 

Fire Code Considerations

 

Comparison of cable jackets burning

Perhaps the most important aspect of a cable's jacket is how that jacket burns in a fire. PVC, the flexible plastic material that makes up most general purpose or residential grade cables is cheap and convenient, but it burns quickly and releases poisonous gas while burning.

 

If cables are run behind the walls of a building or in a vehicle and a fire breaks out, that fire can "leap" from room to room or floor to floor by burning along the cables behind the walls. And if the location where the cables are run is difficult to exit, as in a submarine, ship, airplane or even crowded warehouse, the poisonous smoke would compound the difficulty in dealing with the fire.

 

Because of this, many cables are given flammability compliance codes to help technicians from buying or using inappropriate cables. But, differences in measurement techniques and designations can make the process very confusing. In general, though, there are two "types" or classes of jacket materials other than PVC.

 

 

Plenum for Fire Retardation and Self-Extinguishing

 

In many large buildings, the duct work between rooms and floors is also the raceway for much of the building's data cabling. This space is often called the building's "plenum", and so the types of cables run in these environments are often called Plenum rated cables or just Plenum cables.

 

Plenum materials must be self-extinguishing, meaning that after they start burning and then the external fire or heat source is removed, the material must stop burning. This prevents the cables from "carrying" the fire to another location in the building and re-igniting unexpectedly. Sometimes Plenum cables are referred to as CL2P, OFNP, or CMP. Plenum cables are known to be more expensive than PVC, but in cases where a fire code requires plenum the cost must be factored into the overall installation job.

 

 

Low Smoke, Zero Halogen (LSZH) for Sealed or Mobile Locations

 

Jacket materials that have been designed to release very little smoke and no poisonous gas when burned are often called LSZH. These are typically reserved for special applications where the occupants near the cables may not be able to escape or ventilate the room in the instance of a fire. Again, this occurs frequently in military and aerospace applications.

 

 

Special Jacket Considerations

 

In addition to the above designations for particular fire codes, jackets may have other features useful in niche applications. UV resistance is important in applications where the cable may be exposed to strong sunlight for long periods. UV light can weaken and eventually destroy many PVC compounds over time. Or, oil resistance may be needed in many factory automation apllications as the petroleum-based compound could dissolve if immersed in oil. High-flex or hi-flex cables often use a special jacket that will not crack and split when the cables are flexed over and over again.

 

If you're looking for industry's largest selection of off-the-shelf Plenum, LSZH and other special-jacketed cable and cable assemblies, stop in at L-com's online configurator or contact customer service to get a quote started. We can custom manufacture cables with the jacket type you need.

 

Low Loss Coaxial Cable for Wireless Applications

June 26, 2013 at 10:00 AM

 

Closeup of Low Loss Coaxial Cable Stripped to Show Components

Even in a wireless network, cables and wires are still used to connect components together (access points to amplifiers, amplifiers to antennas, etc). Each component needs cabling to interact.

 

If you are a wireless engineer and need to interconnect components, chances are you are using low loss coaxial cabling. While 50 Ohm RG-style coax is sometimes used, the attenuation is usually too much for any length over just a few feet. This is where low loss coaxial cable comes in.

 

 

Coaxial Cable and RG-Style Coax

 

All coaxial cable works the same way: the signal is run over two "axes" (thus the name). Coaxial technology is one of the oldest signal cabling types, and is still used today for a specific reason: it is robust and can carry a signal very well over a long distance. In general, the thicker the cable, the less "loss" or attenuation of signal there is over the length of the cable.

 

The original standards for coaxial cable were set forth by the US military. These cables used the term "RG" (for "Radio Guide" or "Radio Government") followed by a number to designate the standard. This worked well at the time, but as technology became more and more utilized in commercial and non-military applications, the restrictions of the standard became less rigid (to the point where RG316, for instance, may have very different properties today depending on who manufactures it).

 

 

Times Microwave LMR® Cables

 

No matter who makes the RG-style cables, they have one fundamental problem: the signal degrades over the length of the cable until it is no longer useable. For shorter use in labs or machine-to-machine applications, this is not a problem. But in wireless applications, the signal integrity up until it is broadcast through the antenna is critical.

 

For that reason, Times Microwave Systems developed a low loss version of coax that it branded as its LMR® series coax. The newly-engineered solution offered far lower loss and better RF shielding, making them a much better choice for wireless systems than the RG styles.

 

Outside of Times Microwave Systems' product (the term LMR® refers specifically to Times Microwave Systems product and is trademarked for their use), several other companies now offer low-loss coaxial cables. These generally follow a similar naming convention as what Times Microwave Systems uses: a three-digit "series" number that refers to both the thickness of the cable and the low loss properties.

 

For instance, 100-series low loss coax is thinner and has greater loss than 200-series, which is thinner and has greater loss than 400-series, etc.

Diagram of most common low-loss coaxial cables

Note that with thicker cable factors such as cable weight and flexibility must be considered. However, there are now ultra-flex versions of thicker series like the 400-series that offer similar loss characteristics but are far more flexible.

 

Quick note: L-com has been manufacturing high-quality coaxial cables and components for over thirty years.
 
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