FEATURE TEST & MEASUREMENT
How to select the right testers for active network infrastructure
When it comes to network testing, it is not always clear what type of testing device is right for the job. Should you choose a transmission tester? Or a verifier, qualifier or certifier? Tim Widdershoven, global marketing manager for Ideal Networks, offers advice on understanding the functions of the most common types of equipment
A
ll active networks, regardless of set up or application, use Ethernet. To
identify which type of testing equipment you need for this, it is necessary to understand the different layers that define the Ethernet/IP network. There are three distinct layers that categorise the communication functions of a network.
LAYER ONE: CABLE VERIFIER OR CERTIFIER This consists of the physical electrical/optical signalling and cabling components that connect devices on the networks, including horizontal and backbone cabling (fibre optic and copper), Wi-Fi, hubs and repeaters, network interface ports on network devices (e.g. PCs, IP cameras, wireless access points) and electrical or optical signalling between network devices, such as electrical current, light and radio waves. For layer one cabling, a verifier tests whether cable and terminations have been installed correctly. Cable verifiers test the electrical
continuity of the cabling between two specified points to check for shorts, opens, crossed and split pairs. They are an inexpensive and invaluable part of a technician’s kit. Since more than 80 per cent of all network problems can be traced back to a physical cabling fault, cable verifiers should be used to test every link after it is terminated. In addition, where a cable manufacturer warranty is required, a cable certifier is necessary as it uses radio frequencies on the cabling to measure performance to
Layer two
LAYER THREE: DATA TRANSMISSION TESTER WITH IP PACKET GENERATION CAPABILITY This refers to the network layer that provides data transfer between nodes on different networks. This layer encapsulates layer two frames inside of a data packet, adds source and destination IP address to each data packet and assigns an IP address that is unique to each node on its own network. Layer three testers are very similar to
international ISO and TIA standards, providing a pass or fail result.
LAYER TWO: DATA TRANSMISSION TESTER The data link layer, layer two, provides data transfer between two directly connected nodes or two nodes on the same network. Layer two detects and corrects physical layer problems like automatic crossover switching between two Ethernet switches when a crossover cable is not used, provides media access control (MAC), encodes and decodes data frames, performs error checking, discards bad data frames from layer one, and synchronises devices with systems. Layer two testers check the performance of cabling and Ethernet switches by counting frame loss of actual network data, often called a data transmission test. Unlike a layer one qualifier, a layer two data transmission tester is not measuring electrical parameters of the cabling, it is measuring the successful transmission of
Layer one 1 MAY 2017 | ELECTRICAL ENGINEERING 4
data across a cable or through a network.
those for layer two, but check the performance between different networks through routers and layer three switches, by counting packet loss of actual network data. These testers have the ability to generate an IP packet that encapsulates the Ethernet frame. This packet carries an IP address that can be read by layer three switches and network routers, allowing a layer three packet to traverse different networks or different subnets on a single network. These kinds of testers are suitable for use on large-scale networks or to test WANs (Wide Area Networks), measuring bandwidth between different locations across the Internet.
Layer three
Ideal Networks
www.idealnetworks.net
/ ELECTRICALENGINEERING
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