Are Network Switches - MN123114 C

Are Network Switches - MN123114 C
Vigitron IP Infrastructure Design
Educational Series
20
YEARS
smission Leadership
Tran
Are Network Switches Really Designed
for IP Video Security?
TEL (+1) 858 - 484 - 5209 • FAX (+1) 858 - 484 - 1205
7810 Trade Street, Suite 100, San Diego, CA 92121, USA • support@vigitron.com • www.vigitron.com
Vigitron IP Infrastructure Design Educational Series
Are Network Switches Really Designed for IP Video Security?
Are Network Switches Really Designed for IP Video Security?
The simple answers is no. As video security migrated to IP, the major concern of video security personal was the
future of their involvements in regards to the system specification and the control. After all, networks are under the
control of IT directors. However, as the transition occurred and the demands of IP video security grew, it became
apparent that database networks do not directly translate into IP video applications. One example of this is the
Power over Ethernet aspect of network switches. Too often, random shut downs will result in technical calls to a
camera manufacturer. If the response is the power source (namely, the switches PoE port), the typical answer is to
read the power specifications which is either 802.3af (15.4 watts) or 802.3at (30 watts) to assure adequate power
is available.
The misinterpretation of the actual port power is the first problem. Just because a switch port is capable of handling
a certain power level does not mean that power is actually available. To further confuse matters, most switch
specifications only provide an overall power figure. In operations, some power must be allocated to the switch
functions with the remaining power divided between the ports. Next is how the switch allocates this power. In
general, it can one of three ways - activate PoE per port, available power is divided equally across all ports, or full
PoE Class 3 power is available to all ports. In the first method, it is unlikely that full PoE class power can be
achieved at any of the ports. In the second method, the required power levels can only be achieved until the PoE
budget or available PoE is exhausted, leaving some ports without any power. The third method is often reserved
for the most expensive switches and provides at least full 802.3af power to all ports with the ability to allocate up to
30 watts to some ports. In network PoE switches, the most expensive components are those providing PoE power.
Simply put, there are no standards for the allocation of PoE power. However, there are other considerations. In
most data applications, the surge power required to turn on the PoE devices or the applications in working PoE
devices is limited. Day/night, LED, autoback focus, and PTZ start-up all require large power surges which can
exceed available port power. In the case of PTZ, when power is applied, the dome goes to a reference zero
position drawing excessive amounts of power. If a system uses a several PoE domes, this can actual result in
damaging a switch’s power supply.
Reading network switch specifications can be confusing. The following is taken from an actual switch specification.
Note how easy it is to misread the specifications and to think that all ports provide 15.4 watts at the same time.
Power over Ethernet
PoE Standard
IEEE 802.3af Power over
Ethernet/PSE
PoE Power Supply
Type
End-Span
PoE Power Output
Per Port 48V DC, 350mA. Max
15.4 watts
Power Pin
Assignment
1/2(+), 3/6(-)
PoE Power Budget
380 Watts
Max. number of
Class 2 PD
24
Max number of
Class 2 PD
24
PoE Power Output
The wording indicates that all ports
are capable of handling 15.4W, but
does not state that all ports provide
15.4W at the same time.
PoE Power Budget
The following is a specification for a
typical Layer 2 network switch. Upon
the first reading, you might believe that
this switch has the ability to provide a
full 15.4W (802.3af) to all 24 ports.
But, look carefully. Here is the
complete switch specification with
regards to power.
Per Port 48V DC, 350mA. Max
15.4 watts
380 Watts
Max. number of
Class 2 PD
24
Max number of
Class 2 PD
24
This is the most interesting specification.
Class 2 is 6.49W and the specification
clearly states that the maximum
number of Class 2 PDs (cameras that
can be powered are 24, but according to
the specification only at Class 2).
The PoE budget is stated as 15.4W,
but there is no indication of the power
required for overheads.
TEL (+1) 858 - 484 - 5209 • FAX (+1) 858 - 484 - 1205
7810 Trade Street, Suite 100, San Diego, CA 92121, USA • support@vigitron.com • www.vigitron.com
Vigitron IP Infrastructure Design Educational Series
Are Network Switches Really Designed for IP Video Security?
In general, the network switches offer no protection other than main power fusing which will render the switch
inoperative. Further, as network PoE switches conform to the safety aspects of 802.3 features, large surges will
shut down PoE to a camera without the ability to restart. In these cases, the switch can be damaged beyond repair
or the individual camera taken offline. Both of these result in lost of recording and costly service calls. As IP
cameras power requirements continue to increase, the ability to provide required PoE of network PoE meeting the
needs of IP video systems will continue to diminish. Too often, a misreading of network switch specifications leads
to the selection of switches that will only assure camera shutdowns or misleading returns of properly working
cameras to their respective manufacturers. System users learn only too late that their selected switches, despite
their “brand names” or reliable operation in data networks, must be replaced or augmented with separate PoE
midspans.
Vigitron’s network switches are uniquely designed for IP cameras featuring the ability to transmit the largest Jumbo
Frames at 100Mbps and are certified with IP megapixel cameras up to 29MP. They are designed with the highest
available PoE budgets, providing the greatest number of ports with available 802.3at (30 watts) and assuring every
port can provide full Class 3, 802.3af (15.4 watts) power. Up to 26 ports versions are available with built-in PoE
protection allow for port polling and delayed PoE application to prevent damage. Vigitron network switches have
the ability to sense connection losses and automatically reconnect avoiding service calls while providing the
industry’s longest warranty.
Suggested Vigitron Product(s):
Vi3010
Vi3026
Vi3326
Vigitron offers free and without obligation Design Center Services staff by trained factory engineers. To access
Vigitron’s Design Center, click here or direct any questions on any Vigitron related subjects to
support@vigitron.com.
Vigitron, Inc.
Office: (858) 484-5209
Email: support@vigitron.com
Vigitron website: www.vigitron.com | Design Center
TEL (+1) 858 - 484 - 5209 • FAX (+1) 858 - 484 - 1205
7810 Trade Street, Suite 100, San Diego, CA 92121, USA • support@vigitron.com • www.vigitron.com
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