Network Testing and Fault Management

1. Network Testing and Fault Management

2. In order to manage a communications facility,we have to perform three separate functions: Testing • to establish baseline operational levels • for analysis of fault conditions as they occur Monitoring • periodic analysis of the data flow to identify faults and communications bottlenecks, etc Control • to remotely configure communications deviceseg, bridges, routers, etc • to react to fault conditions FIT2018 (c) Monash University

3. It may seem obvious that we need to test a facility that is non-functional (ie. if your network is down, you are under pressure to remedy the situation). • The need to analyse the current operation of an apparently working network (ie establish baseline) is not as obvious • Control of network components becomes an issue where the network is of a significant complexity or has remote components FIT2018 (c) Monash University

4. Network Testing: Systems and equipment Breakout box BERT (Bit Error Rate Tester)

5. FIT2018 (c) Monash University

6. Testing Devices At the simplest level, there are devices available to test serial communications hardware - Breakout Box A unit that is inserted in the path of an RS-232C (V.24) connection. It consists of LEDs (light emitting diodes) that indicate the condition of the receive, transmit and control lines of a serial connection The LEDs indicate the presence of a valid voltage level on the relevant wires. This unit is easily and cheaply manufactured and therefore is quite affordable for most situations. It is often seen as a useful toolkit item for the technician. FIT2018 (c) Monash University

7. The presence, or absence, of a voltage is readily observed at common data rates. However, as the speed increases, the length of time at which the indication can be observed decreases and limits the device's usefulness. Data Analyser / BERT More complex test units can test for, and report on conditions that are generated by the units themselves. Bit Error Rate Testers generate predefined (or stored) sequences of characters or frames that can be displayed on suitable DTE equipment. Alternatively, the units can be supplied with their own storage and display facilities. FIT2018 (c) Monash University

8. Network Testing: Systems and equipment Cable Scanner

9. At the lowest level of a network (the cable), there are many problems that may appear. • While copper cable provides a cheap and capable transport medium, it also brings with it some inherent problems which are compounded by the data rates, connectors and other network equipment being used. • Cables can be experience intermittent noise injection problems due to some minor damage. • The cable can be suffering from an open or short circuit FIT2018 (c) Monash University

10. Twisted pair installations using existing or new wiring must be tested for the performance of the wire pairs that will be used for the transmission of 10Mbps (or 100Mbps or even 1Gbps) of data. • The problem of gaining access to the cable for fault location just adds to our problems. • A suitable test device for the problems outlined above is a cable testing device(sometimes called a cable scanner). • This is usually supplied with interfaces for the common media that need to be tested. • It is capable of performing noise immunity tests, open or short circuit location and other lower-level hardware related functions. FIT2018 (c) Monash University

11. The open or short circuit location is performed with the implementation of a time-domain reflectometer (TDR, similar to radar) circuit within the unit. • Wikipedia http://en.wikipedia.org/wiki/Time-domain_reflectometer • Some sophisticated units can also provide printed reports and offer remote (dial-up) operation. • There are similar units that can test fibre-optic cables. FIT2018 (c) Monash University

12. Any conductors placed close together have impedance. A TDR looks for a change in impedance. Cable damage, water ingress, variation of cable type, improper installation, and even manufacturing flaws, can all cause impedance changes. A TDR sends electrical pulses down the cable and samples the reflected energy. Any impedance change will cause some energy to reflect back toward the TDR and will be displayed. How much the impedance changes determines the amplitude of the reflection. FIT2018 (c) Monash University

13. Cable TestersConnectivity • Verify cable OK • Detect basic faults • Fluke microScanner http://www.flukenetworks.com/us/Cabling/Residential+and+Basic+Testing/MicroScanner+Pro/Overview.htm • Fluke LinkRunner http://www.flukenetworks.com/us/LAN/Handheld+Testers/LinkRunner/Overview.htm FIT2018 (c) Monash University

14. Cable TestersQualification • Fluke CableIQQualification tester Overview: http://www.flukenetworks.com/us/LAN/Handheld+Testers/CableIQ/Overview.htm FIT2018 (c) Monash University

15. Cable TestersCertification • Precision instruments that test for compliance with TIA wiring standards • Fluke DTX CableAnalyzer Overview: http://www.flukenetworks.com/us/Cabling/Copper+Cabling/DTX+Cable+Analyzer/Overview.htm FIT2018 (c) Monash University

16. Cable TestersIn-Line scanner • Scanner with 2 interfaces • Positioned between network devices • simple Protocol Analyser Fluke NetTool inLine network tester Overview: http://www.flukenetworks.com/us/LAN/Handheld+Testers/NetTool/Overview.htm FIT2018 (c) Monash University

17. Why monitor network traffic? • To be aware of current network state • To find faults quickly • To develop a measure of what is normal • the network “baseline” or quiescent level • What are metrics of network health? • Error rate, Collision rate (?) • Throughput or bandwidth utilisation • Packet size • Protocol distribution and behaviour FIT2018 (c) Monash University

18. Why monitor network traffic?eg effect of Packet size on Throughput FIT2018 (c) Monash University

19. Network Monitoring: Systems and equipment Specialised Network Analysers

20. Some problems that occur over networks can not be detected by the use of media testing equipment. On an Ethernet some problems may be caused by excess collisions, media, hardware, or software fault conditions and may occur intermittently. Network devices can fail outright, or may be just not performing to specification, bringing other network components down with them (eg. a jabbering Ethernet card will swamp a subnet). Periodic recording of LAN traffic for long enough to register all conditions on the net, will allow off-line examination of the data to look for alarm conditions indicating problems or failures or for potential problem eg. excessive loading on bridge, router, etc. FIT2018 (c) Monash University

21. Alternatively, the LAN segments may be examined in real-time in order to counter a major problem (eg. security, severe loading problems). The device that is employed in this fashion is a protocol analyser (sometimes called a sniffer). They can be a dedicated piece of hardware, a dedicated computer, or a normal workstation with the recording process operating in the background. Some units are designed to support a single protocol, while others can trap and interpret a range of protocols. FIT2018 (c) Monash University

22. Many of the more sophisticated units use multitasking operating systems (eg. UNIX) and have adapters that have on-board microprocessors to support the analysis function. They may be preprogrammed to detect common fault scenarios In an Ethernet environment, where packets are addressed to individual adapter cards, only those adapters that can be configured to accept all packets (called promiscuous mode) are able to be used in the analyser. FIT2018 (c) Monash University

23. Circa 1995 FIT2018 (c) Monash University

24. Fluke EtherScope II Network Assistant Overview:http://www.flukenetworks.com/us/LAN/Handheld+Testers/EtherScope/Overview.htm FIT2018 (c) Monash University

25. Software protocol analysers Modern PCs are now fast enough to run network analysis programs such as: • Ethereal (recently morphed into wireshark) • Etherpeek and Airopeek from WildPackets • Agilent Internet Advisor (software version) FIT2018 (c) Monash University

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