How to Choose a Suitable Network Switch
There are bunch of different network peripherals out there for options. How do you use them efficiently to ensure your equipments reach the maximum performance in every operating environment?
The popularization of IP surveillance systems means an increasing number of new projects are now completely IP-based. All available image monitoring and traffic processing capabilities are also assessed as well to optimize performance. However, these assessments often encounter black boxes in different types of IT devices, and the data of which often provides critical information on device capabilities. Here we examine the commonly heard of "Backbone Full Wired-Speed" and "PoE Capability" to see how these functions should be defined.
Non-blocking and wired-speed both refer to the performance of the Ethernet switch. With a 24 port 10/100/1000 switch, if each port is 2G in full duplex mode, then 24 ports means the device is 48G. When this volume of data is passed through the switch, the switch performance can be categorized as non-blocking or wired speed. If the switch is connected to another switch, or to a server that uses network storage or transfers, then non-blocking is essential. Yet, how this is accomplished is up to the vendor's switch design. The user can only rely on the data provided by the vendor. Otherwise, the user must test the switch's capability using tools such as Spirent TestCenter SmartBits. It is not possible to derive the switch’s capability from just the port configuration. Let us now use the Spirent TestCenter to test EtherWAN's EX78822 and see how the report shows that it is "full wired-speed".
As shown figure 1, we connected all of the cables and set up data transfers between pairs of RJ45 ports (check the option for“Bidirectional”). Full duplex transfers of different packs were also carried out at the same time. If the test showed that the device supports "full wired-speed", then the numbers for "Aggregated Throughput" and "Aggregated Theoretical Max" in the following graphs should match. As the ports were paired for testing, actual throughput should be 3000 Mbps x 2 = 6000 Mbps (6 Gbps).
The specifications for the EtherWAN EX78822 used here was 10-port 10/100 BASE (8 x PoE) with a 2-port Gigabit Ethernet Switch (10 x 100 Mbps + 2 x 1000 Mbps) = 3000 Mbps. Under full duplex mode, the operating bandwidth should be 3000 Mbps x 2 = 6000 Mbps. Our calculations were consistent with the actual test results, so this switch supports full wired-speed. While it is not that easy to obtain the necessary testing equipment to carry out the experiment when we put these devices into service, we can still ask the vendor to provide test reports shown as figure 2 that back up their claims.
Now, we are going to discuss PoE capabilities in following section. PoE is a convenient and cost-efficient power solution for IP surveillance systems. System integrators or users no longer need to attach an extra power cable to each IP camera in a different location. Here, we will show the important facts to be considered when choosing a suitable PoE switch to make your IP surveillance system more effective and efficient.
Most PoE switches come in two types off-the-shelf: “guarantee per port” operation and “total power budget” operation.
Guarantee per port:
This type of PoE switch provides a lot more flexibility to users when planning and expanding their IP surveillance system. PoE switches that act as power source equipment (PSE) should successfully feed sufficient power to connected powered devices (PD) after retrieving the power consumption information of each IP camera and comparing the data to the total number of connected IP cameras. When each port is guaranteed a full power design in compliance with either IEEE802.3af or IEEE802.3at, the switch is effectively plug-and-play. No sophisticated engineering effort is needed.
Total Power Budget:
This PoE switch operates as a “total power budget”, but users need to consider a number of points when selecting this type of system. For instance, features like pan–tilt–zoom, cooling fans, heaters or infrared illuminators may require extra power. If the total power consumption is over the total power budget of the PoE switch, it may cause the entire system to malfunction. Users should accurately measure the total power of all devices to effectively avoid errors from occurring in the field. After power issues are settled, users should also consider environmental conditions when selecting PoE switches.
When an IP surveillance system is planned, users may perform a simple test, under room temperature, by connecting the IP cameras to all PoE ports on the switch. Users should let the system run for a few days to see if it is operating stably. If it is, users are highly recommended to test the system again under a full workload and various operating temperatures. Occasionally, instability will occur under long periods with a high workload or in rapidly fluctuating temperatures. A good PoE switch should be able to withstand functional and environmental challenges.
PSE Conformance Testing is performed in EtherWAN quality assurance labs. The test suite analyzes up to 115 test parameters depending upon the capabilities of the PSE. These parameters are measured in 23 distinct tests that cover over 95 percent of the PSE PICS (conformance check list items) in the IEEE 802.3at/af specifications.
The following figure 3 shows the environmental testing standard of EtherWAN’s switches with PoE/PD load to simulate a full workload. Passing conditions should ensure the switch can operate continuously under low and high temperatures without any data transmission errors.
Reviewing product specifications is only a basic step of the PoE switch decision making process. Making the right decision requires comprehensive testing report to ensure that the networking product is designed with high quality engineering. Once you work with a networking partner who delivers such quality, you will always be able to count on them for the success of your surveillance system.