Cat 6a cabling, do you really need it for IP Video?

In security, modern IP video CCTV camera systems inevitably involve support from the IT/Data Communications departments now, and we often get asked about “how much” bandwidth is needed and what cabling types we need for the cameras, switches, and servers.  Often our advice is in conflict with the IT corporate standards, and we end up explaining the practical use for video in security.  This article attempts to discuss in layman’s terms the differences in the cabling types, and how they relate to IP video security.  The actual physics behind the IEEE 802-series specifications are complicated and beyond the scope of this document (fair warning: that rabbit hole goes deep).

In order to understand the basic question, some explanation is needed on the different types Ethernet cabling, and their capabilities and limitations. It’s mostly about increasing the frequency capabilities of the cable.  Cat 5e is built to meet the specification requirements of up to 100 MHz, Cat 6 takes the spec to 250 MHz, and Cat 6a takes it all the way up to 500 MHz. The main difference between these cabling standards is the amount of insulation for the conductors and the rate of twist, although there is also a slight increase in the gauge size for Cat 6 also.   The net effect of these modifications is to reduce crosstalk, attenuation, and EMI.  This can also have the effect of reducing propagation delay and delay skew, which can be measured in millisecond increases in transmission times in some cases.  Delay is known in all types of transmission media, even fiber optics, and is the amount of time that passes between the transmission of a signal and when it is received at the other end of the data link.  In collision based networks like Ethernet using TCP/IP, minimizing propagation delay and skew can have an increased effect on the efficiency of the network and the net amount of data that can be transmitted upon any given network.  Dropped packets mean re-transmission, and bandwidth gets eaten up by repeating data information that’s already been sent (at least) once before.

Cabling Standard Limitations

Cable Type Max Distance Max Data Rate
Cat 5e 100 Meters 1 Gbps
Cat 6 50 Meters 10 Gbps
Cat 6a 100 Meters 10 Gpbs

 

Cat 6 was the first entry into copper based 10Gpbs data transmission at a commercial scale. The problem with Cat 6 is that after 50 meters the data rate is essentially 1Gpbs, or no better than Cat 5e.   Cat 6a was later introduced and will do the full data rate of 10Gbps for the full rated distance for Ethernet (100 meters).  However, Cat 6a cabling is significantly larger in diameter than Cat 5e and has a stiffer jacket, making cable installation more difficult.  It’s also more expensive, about 33% more expensive than Cat 5e.

But do you really need 10Gbps at the edge device?  Probably not for most applications.  Even current high resolution cameras would not be able to fully utilize a 10Gpbs network, never mind that the server hardware on the other end processing a couple dozen full rate video streams would be overwhelmed.  Currently, high resolution 3 megapixel (MP) cameras are widely available on the commercial market.  At 30 frames per second (fps) and at full resolution, it would consume a maximum data rate of 15,000 kilobits per second (Kbps), or 15 Mbps, and more likely it would consume quite less.  In most security applications, resolution and data rates are throttled not because of bandwidth limitations as much as for storage limitations on the server.  Exceptions to that would be the gaming industry and congested high speed traffic areas such as toll booths.  But for most of our applications, we typically find 2MP cameras at 10fps a reasonable compromise that consumes less bandwidth (and disk space) while still providing adequate video information for surveillance, response, and investigation.

Common Camera Resolution and Bitrates

Resolution (MP)
Pixels Frame Rate (fps)
Bitrate (Mbps)
1.0 1280 x 720 30 6
2.0 1920 x 1080 30 10
3.0 2048 x 1536 30 15

 

Even at full resolution and frame rate, you could theoretically put eighty-three (83) 3MP cameras (1250 Mbps/15 Mbps) on one 10GBase-T network cable. Of course in reality it would be considerably less, but you get the idea.

So where is 10Gpbs Ethernet really needed?  For now, backbones.  Those connections from network switch to network switch that are relaying end device connectivity to other devices, clients, or servers.  Often these are fiber optic links, but more and more they are being made available as copper links and using Cat 6a.

So what do we recommend?  Given the additional cost and current technical capabilities of IP cameras, we typically recommend Cat 5e cabling as sufficient for all IP video cameras where the 100m distance limitation is held and special conditions that require fiber optic cable or special media converters don’t apply.  There are also some technical concerns on the terminations and number of cycles for insertion/reinsertion that can come into play due to the cable’s rigidity.  Cat 5e is readily available, inexpensive, reliable, easy to work with, and more than capable of the task at hand.

Still, if the objective is to “future proof” your installation, Cat 6a is among the latest and greatest and should ensure that even 100 MP cameras of the future would be handled without re-cabling.

 

Posted in: Security Technology

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