Network Fundamentals for the Security Installer

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As more and more network devices produced more data traffic, networks had to handle more bandwidth and data switches were created to address this need. A data switch acts similar to that of a video multiplexer by switching the full bandwidth from one source to another, but the switch makes the source selection quickly and automatically. The connections can be from any port to port because all of the ports are bi-directional. A data switch can handle more traffic than a hub since the connection is at the full bandwidth of the switch. Current production switches typically have 100Mb/s or even 1Gb/s bandwidth specifications.

Switches with modifiable parameters are known as managed switches, while units without configurable parameters are known as unmanaged switches. Initially, managed switches had a serial communications port that enabled configuration of the parameters via a terminal or PC. Yet, going from switch to switch to modify configurations was time consuming and as a result, switches today are generally configured over a network connection. The serial port connection is called out-of-band control, while a network connection is known as in-band control.

As the need to interconnect more equipment grew, IT couldn’t connect everything to a single switch, so they chain-linked multiple switches. This resulted in a design using a core switch and edge switch(above). The core switch, which is at the heart of a larger network, provides very high bandwidth specifications in the 10 to 100’s of Gb/s with a large number of ports to connect other switches and devices, such as servers. Edge switches are typically deployed in closets throughout the building to meet the 300-foot maximum distance of an Ethernet connection.





PoE gets the job done

A new enhancement to switches is the implementation of the 802.3af standard, known to the industry as Power over Ethernet (PoE). The standard enables the UTP to carry data and power to a device at the edge of the network. Many new IP video cameras today are powered by PoE connections. The digital data is carried on wires 1,2 and 3,6 while power is carried on wires 4,5 and 7,8.

The process for an 802.3af compliant connection is more complex than what one might think. When the standard was being developed, significant concern was expressed about non-powered devices connecting to a powered port and the potential device damage that could occur. As a result of these concerns, a power-up process was developed that protects non-powered devices from potential damage. PoE is also limited in the total amount of power that can be supplied. The 802.3af standard provides for a maximum of 350 mA at a voltage of 44VDC. This equals a maximum of 15.4 watts of power. In actual operation due to circuit constraints the usable power is only approximately 12.95 watts. There is a new IEEE standard under consideration that would increase the amount of power available via PoE to 25 watts, however the maximum power amount is a cause of concern by UTP cable manufactures due to cable heating at higher power levels.

PoE can be implemented by either installing a switch which has PoE capabilities or by placing a midspan injector into the data stream. In either case the total amount of power available to the end devices is limited to the capacity of the switch or injector, i.e., if a 24-port switch has all ports connected to devices using the full 15 watts per port then the switch would need to be able to supply a total of 360 watts of power. Many PoE switches are only capable of supplying 200 watts. With a 200-watt power supply, the switch could power a maximum of 13 ports.

Some power injectors that are not 802.3af compliant have been manufactured. Depending on the system design 802.3af compliance may not be needed. These devices serve a need but use non-standard voltages and are capable of supplying non-compliant power levels. When using these devices be sure to allow for the heating effect on cables and properly identify the device so that there is no possibility of confusing them with 802.3af compliant devices.


In a nutshell

Many diverse systems are utilizing networks to share information, both within a single application as well as between multiple specifications requiring the same information. Systems are now sharing network bandwidth with lighting controls, security cameras and access control systems and while these systems can clearly coexist on the same physical network, the bandwidth required, system responsibility, possible regulatory requirements (HIPPA, Sarbanes-Oxley, PCI) and data security concerns can be quite different. The use of parallel networks creates a physical network for a specified set of applications, allowing IT personnel to better manage the regulatory environment from both the network side and in providing the facilities department with the necessary tools.