Smart Building

4 Factors that Impact Network Bandwidth

Ron Tellas

Think about the roads we travel on everyday. What would happen if traffic engineers and urban planners didn’t accounts for the numbers of vehicles traveling on them, road width requirements or the number of lanes required? At a minimum it would be difficult and timely to get to a destination, drivers would experience bottlenecks, delays and accidents.


The same holds true for your network—it’s only as good as the planning that goes into it. Different types of applications require different network bandwidth levels. Each task completed using your network requires bandwidth, with many bits per second traveling across the network. Knowing how much bandwidth each application uses is key to ensuring the functionality, reliability and speed of your network.


The data rate supported by your network bandwidth is typically expressed in “bps” (bits per second) or “Bps” (bytes per second). Network bandwidth determines the network’s capacity to support key business activities and transactions and is impacted by the design principles of the structured cabling system.


As data rates increase so do bandwidth requirements. For speeds of 1 Gbps, Category 5e and Category 6 cabling are sufficient but what about for 10 Gbps? Category 6A cabling addressed bandwidth and external noise requirements however, with 2.5 Gbps and 5 Gbps on the scene, which cabling system is the right one?

Cabling System Considerations

Application Bandwidth vs Cabling Bandwidth

What are users doing on the network—streaming high-definition audio, sending emails, creating and sharing large imaging files or using software to edit hours of video footage? Knowing what applications and the number of bytes per second they each send across the network makes a marked difference. Although it may seem counterintuitive, 500 people sending email all day may not require as much network bandwidth as 50 users streaming and downloading video and conducting videoconferencing calls.


Once applications and bandwidth requirement are defined, the next step is to understand the bandwidth capabilities of the cabling infrastructure. If users are regularly interacting with bandwidth-intensive content, the cabling infrastructure must be designed to support it. Category 6A cabling for example, can handle the performance demands of 10G Ethernet (10GBASE-T) up to 500 MHz over a maximum distance of 100m.


Near-End Crosstalk Concerns for Speeds Above 1 Gbps

Near-end crosstalk (NEXT) is a measure of unwanted signal coupling from one pair to another at the near (closest) end of the cabling. NEXT is measured at the same end of the link/channel where the signal is sourced. Measured in decibels (dB), the higher the NEXT in dB, the greater the cable’s ability to reject crosstalk at its local connection.


Category 6A provides a higher margin above minimum requirements (1 Gbps Ethernet for alien crosstalk parameters and performance of in-channel test parameters above 250 MHz). With higher frequencies required to support 2.5GBASE-T, 5GBASE-T and 10GBASE-T applications, crosstalk between cables—not just within them—is now a concern. NEXT levels may perform okay above 250 MHz however, alien crosstalk will negatively impact cable performance, which is why Category 5e and Category 6 cabling can’t be used for data rates above 1 Gbps without concern.


To control noise and crosstalk at higher frequencies while providing adequate network bandwidth initially required Category 6A cables (with frequencies of 500 MHz) be up to 50% larger than Category 6 cables to accommodate the twists that minimize crosstalk. The larger size limited the number of cables that could be accommodated in cable trays or runways. Newer Category 6A Cables have reduced cable diameter, closer to that of Category 6 cables.


Far-End Crosstalk Concerns for Speeds Above 1 Gbps

Similar to NEXT, far-end crosstalk (FEXT) is also measured within a channel—rather than being measured at the closest end of the cabling, it’s measured at the far end of the channel. FEXT isn’t typically covered on its own as signals decrease in strength over distance and it doesn’t provide very helpful information.


From FEXT however, information such as equal-level far-end crosstalk (ELFEXT) or attenuation-to-crosstalk ratio far-end (ACRF) can be extracted to measure characteristics including power sum ACRF (PSACRF). As with near-end crosstalk, far-end crosstalk between cables at higher frequencies—not just within them—is a concern. Similar to NEXT performance, FEXT levels might be acceptable above 250 MHz however, alien crosstalk will negatively impact cable performance—which is why Category 5e and Category 6 cabling shouldn't be used for data rates above 1 Gbps without performance concerns. 


The same rules apply—Category 6A cabling is designed to better control noise and crosstalk and newer cabling systems have reduced the size issue opening up the opportunity for LANs to improve network bandwidth with Category 6A cable.


Cable Balance for UTP Cables

Improper cable balance can limit your network bandwidth potential. Cable balance isn’t defined for Category 5e or Category 6 UTP cabling. Cable 'balance' ensures cabling systems offer appropriate electromagnetic compatibility (EMC) performance and eliminate interference. Cabling balance is directly related to alien crosstalk. Without proper balance, alien crosstalk will negatively impact cable performance—which is why Category 5e and Category 6 UTP cabling shouldn't be used for data rates above 1 Gbps without performance concerns.


To be well balanced, voltage and current on each conductor of the pair must be equal in magnitude and opposite in phase. To achieve this balance, the cable’s two insulated conductors must be physically identical in terms of diameter, concentricity and dielectric material, and must be uniformly twisted. This requires precise design and manufacturing processes.