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What You Need to Know About Alien Crosstalk Today

![Alien Crosstalk](http// "Alien Crosstalk")

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The industry has been predicting the growth of 10GBASE-T for years, and it’s finally happening. More networks are planning 10G migrations. Why? Due to demand from more advanced devices, users and applications.

But new concerns come into play with this Ethernet standard. Alien crosstalk – the interference caused by wire pairs in one cable inducing noise into other wire pairs in adjacent cables – is the transmission parameter that most significantly impacts 10GBASE-T performance.


## What is Alien Crosstalk?

Alien crosstalk is a combination of alien near-end crosstalk (NEXT) and alien far-end crosstalk (FEXT); the noise source originates from a common mode signal that is converted onto the differential mode signal through some type unbalance on cable and components.


## Why is Alien Crosstalk Bad for Today’s Applications?

In high-speed, high-bandwidth applications – used today to accommodate more users and more devices – alien crosstalk can cause many problems. In a cable bundle, it’s possible that cable pairs in one cable pick up interference from pairs of another cable. The digital signal processors (DSPs) used in [10GBASE-T architectures]( can’t remove unpredictable exterior noise. Noise sensitivity increases at higher frequencies, such as 500 MHz, which is the highest frequency of Category 6A cabling.

This interference isn’t just a nuisance; it has the potential to shut your entire network down – which leads to unplanned downtime, financial losses, a productivity nosedive and unhappy users.


## What Causes Alien Crosstalk?

Alien crosstalk originates from a common mode signal that is converted onto the differential mode signal through some type of unbalance on the cable and components. Category 6A cabling and components are designed and tested to reduce alien crosstalk to a level low enough that it does not interfere with the differential mode signal.

Make sure all components are [Category 6A]( This is especially important to note for patch cords. When high-quality, Category 6 cable is tested, it may pass Category 6A patch cord requirements because only near-end crosstalk and return loss are measured. When these patch cords are bundled and placed in a Category 6A channel, however, the channel fails alien crosstalk requirements. Why? Because Category 6 cable isn’t designed to handle high data-speed requirements.

Don’t over-tighten cable ties. Cable ties that increase tension can force cables together and impact alien crosstalk. When using cabling ties to dress the cabling, make sure the ties are free to rotate after tightening.


## What Do Standards Say About Alien Crosstalk?

[[Poll Goes Here]]Alien crosstalk reduces cabling’s operational bandwidth due to increased channel noise levels; as a result, ANSI/TIA standards state that [Category 6A cabling]( best meets the demands of 10G. (According to current standards, Class E and Category 6 cabling aren’t recommended for new 10GBASE-T installations over 37m.)

Here are a few reasons why Category 6A is the best choice:

- Achieving [10GBASE-T]( over copper requires 500 MHz bandwidth and full duplex transmission, which Category 6A provides
- It must follow stringent ISO/IEC and ANSI/TIA transmission-parameter regulations
- It uses specially designed jackets and cross-webs that physically separate internal twisted pairs from external twisted pairs, ensuring low alien crosstalk
- It provides a guaranteed alien crosstalk margin above minimum TIA-568-C.2 requirements
- Category 6A specifications allow compliant cabling for 10GBASE-T transmission

Belden’s Category 6A cabling solutions provide a simple design without compromising performance or quality, ensuring robust performance and reliable networks. Learn more about our [10GSX cables](, which feature a smaller diameter, a rounder jacket, a smaller bend radius, fewer twists and easy-to-remove barrier tape.

<div style="text-align: center;">[![IoT WP CTA](http// WP CTA_86060.png "IoT WP CTA")](</div>Source: Spine and Leaf (1st) test

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Cabinet Load Ratings: Why They Matter (and Why They’re Changing)

Cabinet Load Ratings

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To make better use of floor space and decrease operating costs, more active gear is being placed inside cabinets and enclosures. As a result, they’re getting wider, deeper and taller. Just a few years ago, most enclosures offered 42 RUs or 45 RUs of space. Today, however, many cabinets offer 48 RUs of space – and can offer as many as 52 RUs (or more).

But as cabinets grow in size to accommodate more active gear, they also get heavier. If cabinets get too heavy, the floor may not be able to support them; the cabinets may also be very difficult to move (rolled from one spot to another, transported for loading and shipping, etc.).

It’s becoming crucial to analyze load ratings (also known as “load capacities”) when selecting enclosures. Here are the load ratings you need to know:

- *Static load rating*: How much weight a cabinet can hold when racks are loaded in the data center
- *Dynamic load rating*: How much weight a cabinet can accommodate when shipped fully loaded (important to note with services like Data Center Ready becoming more popular)
- *Rolling load rating*: How much weight a cabinet can tolerate as it is moved/rolled across the floor

Most enclosures are listed against UL 2416 for static load. Just a few years ago, the average static load rating was approximately 1500 pounds; now, a static load rating of 3000 pounds isn’t unusual. In many cases, dynamic and rolling load ratings will be the same for a cabinet.

It’s also critical to note that static, dynamic and rolling load ratings are *not* the same as a cabinet’s seismic rating. Seismic ratings indicate how much protection the rack-mount equipment in a cabinet will receive during an earthquake. (We’ll cover this topic in an upcoming blog post.)

While a cabinet’s width, depth and height can influence load ratings, there are other factors to consider as well.


## Cabinet Construction

There are two main enclosure types: fully welded enclosures and enclosures with bolted-together components. A bolted design allows cabinets to be shipped flat, saving shipping costs. Typically, however, fully welded enclosures have higher load ratings; they can adequately support more weight from active gear.

Corner post geometry and the steel gauge (thickness) used to construct corner posts and mounting rails can also influence a cabinet’s load rating.


## Casters

Before a cabinet is shipped, it is often loaded with switches, servers and everything else needed. Then, it is tested and commissioned. Once testing is complete, the cabinet is shipped to the end-user. To get the enclosure into a truck, however, it needs to be rolled – and then rolled again once it arrives at its destination.

Moving an enclosure across the floor doesn’t just require an adequate rolling load rating – it also requires the correct casters. Heavy-duty casters make a world of difference in accommodating a heavier rolling load rating, as well as withstanding rolling movement. There’s a significant load-rating difference (up to 1000 pounds or more) between a cabinet with regular-capacity casters and a cabinet with high-capacity casters.


## Built-In Levelers

Levelers don’t impact a cabinet’s static, rolling or dynamic load rating – but they can make it much easier to safely move a cabinet. For best performance of active gear, enclosures need to be level. Built-in levelers underneath enclosures allow installers to move cabinets and level them once they’re in place.

A few years ago, cabinets were leveled before equipment was placed inside – which made it more difficult to move the cabinet and ensure that everything remained level. Today, however, built-in levelers allow you to install equipment inside beforehand and level the enclosures once the cabinets are loaded.


## Vibration

Vibration doesn’t directly influence load ratings, either, but the ability of a cabinet to withstand vibration and shocks when being moved – without distortion – is an important factor.

Many times, special shock-absorbent pallets are used to insulate active gears mounted in the enclosure to offer protection during transportation.


## Belden

Belden’s X Series enclosures – XHM and XHS – have a static load rating of 3000 pounds. They seamlessly integrate power distribution, airflow containment and management, networking connectivity and cable management. They are shipped fully assembled and configured to your exact specifications, with several options for doors, side panels, passive chimneys or active AEHC units and PDU mounting.

Learn more about the data center solutions available from Belden to help maximize space, save time, speed up deployment, reduce downtime and save costs here.


Advances in Multi-Fiber Connectivity WP CTA
Advances in Multi-Fiber Connectivity WP CTA Source: Spine and Leaf (1st) test

HDBaseT: Is it Convergence?


Bending Loss: A Risk Associated with Reusing Installed Fiber Cable

[![Fiber Bending Loss](http// "Fiber Bending Loss")](http//

Thanks to its ultra-high data transmission capacity, ultra-low loss and installation flexibility, glass optical fiber is the most power-efficient data transmission media available today. Optical fiber cables have been deployed worldwide to connect people and “[things](” together.

According to [CRU’s Optical Fibre and Cable Monitor](, last year, the global optical cable demand reached 318 million kilometers in the first three quarters of 2016.

As we mentioned in a [previous blog](, two types of optical fiber are available for different network environments and link distances:

- Multimode fiber (MMF) for short-reach links up to a few hundred meters, mainly used in data centers environments
- Singlemode fiber (SMF) for long-reach links, such as in LANs, access networks, metro/transport networks and hyperscale data centers

![Multimode Fiber](http// "Multimode Fiber")

Fiber cables are typically installed and owned by internet service providers or internet content providers (including cloud service providers), or enterprise IT departments. People commonly believe that fiber cable has unbounded bandwidth capacity and can last forever; however, with the recent [data traffic boom]( – cloud services, over-the-top content delivery and [Internet of Things (IoT)]( – some old fiber infrastructure has hit its capacity limit and needs to be upgraded.

This blog is the first of three in a series where we will walk you through the risks of reusing installed fiber cable, and help you understand how fiber cable infrastructure performance and quality could impact your business operations.

## Macrobending and Bend-Insensitive Fiber

Optical fiber cables are recognized as the superior data transmission media over long distances. The optical fiber is a waveguide that confines light within the fiber core, which is bounded by the cladding material that prevents light from escaping.

![Macrobending]( "Macrobending")
*Source: IBM*

Compared to copper cable, optical fiber cable has a much smaller cross-section diameter to support flexible cable routing and installation, especially for high-density I/O. Nevertheless, strict fiber cable installation rules have to be followed because light can leak out of the fiber core through the cladding when bent or wrapped. Bending loss occurs when a fiber cable bend is tighter than its maximum bend tolerance; bending loss is due to physical bends that are large in relation to the diameter of the cable. As the bend tightens, more light is lost. This phenomenon is referred to as “fiber macrobending.”

![Macrobending 2]( "Macrobending 2")

TIA 568.3-D specifies the minimum bend radius for fiber cable installation to avoid excessive “light leakage” or bending loss:

*Cables with four or fewer fibers intended for Cabling Subsystem 1 shall support a minimum bend radius of 25 mm (1 in) when not subject to tensile load. Cables with four or fewer fibers intended to be pulled through pathways during installation shall support a minimum bend radius of 50 mm (2 in) under a pull load of 220 N (50 lbf). All other inside plant cables shall support a minimum bend radius of 10 times the cable outside diameter or less when not subject to tensile load, and 20 times the cable outside diameter or less when subject to tensile loading up to the cable’s rated limit.*

## Macrobending Hurdles in New Use Cases

In many new practical use cases, fiber cables are required to be installed with even smaller bend radii, which could lead to bending loss:

1. In access networks, optical fiber is installed closer to subscribers; therefore, smaller bend radius is required to support high-density, flexible fiber installation and routing.
2. In data center networks, more and denser fiber cables are installed to support ever-growing bandwidth requirements in limited space; therefore, hassle-free fiber cable installation with higher bend tolerance is increasingly important to reduce bending loss and speed up data center deployment and upgrades.

![Bent and Pinched Fiber]( "Bent and Pinched Fiber")

![Fiber Slack Loop]( "Fiber Slack Loop")

*Source: Anixter*

Legacy fiber cable, although optimized for low-attenuation data transmission, is subject to excessive transmission loss; it was not optimized to support sharp bends and can suffer from bending loss. Accidental fiber loss can happen on a daily basis if care is not taken:

- *Sharp bend*: severe 90-degree bend can induce high link loss of up to 0.4 dB to 0.5 dB
- *Pinched cable*: pinching standard fiber jumper can lead to an attenuation of 3 dB to 4 dB
- *Fiber slack loop*: a tight pulling tension on the fiber jumper can cause an attenuation of >5 dB

## Fibers with Enhanced Macrobend Loss Performance: Bend-Insensitive Fibers

Recently, bend-insensitive SMF and MMF (BI-SMF and BI-MMF) products have been introduced to the market to meet the needs of tighter fiber-bend tolerance to avoid bending loss. Optical fiber manufacturers used a refractive index “trench” in the fiber structure – a ring of lower refractive index material – to reflect lost light back into the core of the fiber.

Industry standards have also been developed to specify the bend-radius tolerance of BI-SMF and BI-MMF.

- BI-MMF: ISO/IEC 60793-2-10 provides specifications for A1a.1b, A1a.2b, A1a.3b and A1a.3W that support two turns of 15mm bending radius with <0.1 dB loss at 850nm, and two turns of 7.5mm bending radius with <0.2 dB at 850 nm. *(BI-MMF cables are only optimized for 850nm but not for 1300nm. While the bend loss at 850nm is as described above, the results at 1300nm are not much different than with standard 50µm MMF.)*
- BI-SMF: ISO/IEC 60793-2-50 provides specifications for B6 singlemode fibers that can support minimum bending radius of 10mm, 7.5mm and 5mm. The same recommendation has also been made in the ITU-T G.657 standard document. *(G.657.A1 and G.657.A2 are fully compliant with traditional SMF standard G.652.D with lower fiber transmission loss; G.657.B2 and G.657.B3 are compatible with G.652.D with smaller minimum bending radii, but the transmission loss is slightly higher.)*

Using bend-insensitive fiber cable will minimize the risks of fiber bending loss, and reduce accidental system downtime by considerably improving link robustness and overall performance.

Given the installation and maintenance advantages, considering BI-MMF and BI-SMF for system upgrades or new fiber cable deployment is highly recommended.

Belden offers BI-MMF and BI-SMF [fiber products]( that are faster, easier and better to use. Our fiber connectivity solutions reduce complexity, increase flexibility and streamline installation.

<div style="text-align: center;">[![Advances in Multi-Fiber Connectivity WP CTA]( in Multi-Fiber Connectivity WP CTA_86060.png "Advances in Multi-Fiber Connectivity WP CTA")](</div>

Source: Spine and Leaf (1st) test