As more companies realize that linking data-processing facilities—particularly their PCs—can increase profitability, new networks are being installed daily. At the same time, many existing networks plagued by data-traffic congestion require bandwidth expansion while others are being extended to cover larger service areas. All these new and expanded network installations need more interconnecting cables and equipment—all of which must be checked out with, hopefully, easy-to-use test equipment.
Cable and Fiber Testing
Twisted-pair cables provide the least expensive, practical interconnection media for carrying local area network (LAN) data traffic. The telecommunications industry has developed standards identifying physical and performance characteristics for various types of twisted pairs. While five categories of performance levels originally were defined, only two are used today: Cat 3, supporting data rates to 10 Mb/s; and Cat 5, supporting 100 Mb/s and 155 Mb/s data rates.
Installation and test criteria for Cat 5 twisted-pair cables have been defined by the Telecommunications Industry Association (TIA) in Standard TIA 568A TSB-67. Most LAN cable testers provide pass/fail indications regarding wiremap, near-end crosstalk (NEXT) and attenuation conformance with TIA 568A TSB-67. However, not many offer cable- grading capability, a feature desirable for two reasons, according to Jim Bordyn, director of marketing at Datacom Technologies:
Users want to know whether a link barely passes minimum test limits or whether there is a substantial margin (headroom) between the actual cable performance and the specification limits, especially for tests concerning NEXT.
Enhanced Cat 5 cable now offers superior crosstalk performance as verifiable by the more rigorous power-sum NEXT test defined in TIA 568A TSB-67. These cables typically cost 20% more than regular Cat 5 cables, and users want to prove that they are getting their money’s worth.
Although Cat 5 cables are becoming more popular for carrying ATM 155 Mb/s traffic, only a few cable testers cover more than the industry-standard range of 1 MHz to 100 MHz. “However, the ATM Forum, a cross-industry group of more than 300 users and network equipment suppliers, has confirmed that the physical-layer requirements for ATM 155 Mb/s are met with regular Category-5 cabling and components as defined by EIA/TIA 568A and tested per TSB-67,” commented Mr. Bordyn.
High data-rate transmission often is accomplished via fiber-optic cables which are commonly tested and characterized with optical time-domain reflectometers (OTDR). OTDRs not only perform loss and distance-to-fault measurements on individual fibers, but also evaluate the integrity of splices or impediments due to improper terminations.
While earlier OTDRs were difficult to use, new models contain built-in intelligence and feature software-controlled multimode operation. For instance, the Tektronix TekRanger 2 uses IntelliTrace to automatically acquire information about a given fiber-optic cable, according to John Breeden, product marketing manager of optical cable test products at Tektronix.
Many electroconductive cable testers now perform some non-OTDR-based fiber-optic cable tests. This ancillary capability usually is provided through an optional external adapter that connects between the fiber and the cable tester.
“Frequently, these adapters are battery-powered modules that attach to the tester with a test cord, creating a dangling box that can get in the way,” warned Mr. Bordyn of Datacom Technologies. To avoid this problem, the LANcat Vx cable tester provides space for a plug-in module that performs optic power and loss measurements.
Transmission and Service-Quality Testing
While testing interconnecting cables or wireless links poses the initial challenge, verifying the operational performance of the message-processing or message-forwarding equipment is an even more complex endeavor. All equipment involved in the network communications links must be checked, preferably from a single location, to determine that:
It can route traffic to the desired end-points.
The transmission fidelity is adequate.
The quality of service is acceptable.
Checking the physical traffic-routing capabilities of LANs once was easy. As long as the cabling terminations for all token ring- or Ethernet-connected terminals were correct, the physical routing was fixed, and tracing faults to specific locations was straightforward. But this no longer is the case for joined LAN/WANs (wide area networks) or virtual LANs (VLANs) where two or more LANs are interconnected via switches, such as Asynchronous Transfer Mode (ATM) links or high-speed frame relay.
“The ability to see what is occurring at each switch port and to determine which VLAN a port belongs to is essential in today’s switched environments,” said David Skingley, product marketing manager at Fluke. “Internal switch functionality information usually is proprietary; however, a license agreement allows Fluke to use proprietary protocol details employed in the Cisco Catalyst 5000 series of switches to offer the LANMeter SwitchWizard™ option. Using Signaling Network Management Protocol (SNMP) and Remote Network Monitoring Specification (RMON) capabilities, you can ‘see’ across bridges and routers, and inside switches.”
Of course, evaluating protocol-embedded routing capabilities requires the use of protocol analyzers which, in conjunction with BERTs, determine transmission fidelity. Equipped with added features, transmission-quality analyzers also can help evaluate service quality.
Determining the quality of service a network provides entails a variety of checks. Service quality may encompass attributes, such as the time required to initiate data transmission, the delay between sending and receiving data, acceptable traffic rates, blocking probability, and system availability.
“Service providers must specify and test not only the ‘pipe’ (transmission quality), but also the service on the pipe (service quality),” commented Steve Greer, product line manager at Telecommunications Techniques. “Fortunately, test equipment is available that merges these two requirements into one instrument.”
Installation checkout and maintenance often take place in tight quarters, so portability, lightweight, and multifunctionality are highly valued test-equipment attributes. As a result, the demand is high for comprehensive multifunctional test tools available from a single platform.
The instruments fall into two main categories: those that perform multiple types of tests and those that solve problems pertaining to operating in multitechnology environments.
Equipment such as the Fluke Enterprise LANMeter Test Tool typifies the first category. “Experience indicates that most network-related problems occur in the bottom three layers of the protocol stack,” said Fluke’s Mr. Skingley. “We combined the troubleshooting features of cable testers, protocol analyzers, and network management systems into a single, portable product.”
An example of the second type of multifunctionality is the multitechnology Radcom PrismLite Protocol Analyzer which accepts up to 20 interface modules and supports more than 200 protocols. “As ATM and other new technologies are integrated into existing networks, single-technology analyzers are just not enough,” said Jacob Cazes, product marketing manager at Radcom. “Interconnection between technologies is the source of most networking problems. To solve these problems quickly and efficiently, field service engineers and network managers need a tool to test several technologies at the same time.”
Some test systems offer both types of multifunctionality, such as the T-BERD 950 from Telecommunications Techniques. It interfaces with multiple services, such as ISDN, frame relay, and DDS local loops. It contains a dual display which allows simultaneous viewing of configuration data and monitoring of results.
Many test instruments from Telecommunications Techniques provide simultaneous transmission and protocol test results which are particularly helpful for instances where a service- related problem can be correlated to a physical-layer problem. The simultaneous- results approach produces quicker and more concise problem resolutions.
Providing multiple simultaneous analysis and display capabilities also is valuable when evaluating interoperability of connected networks using different technologies, such as in LAN/WAN, VLAN, or LAN/ATM/LAN configurations. Resolution and prevention of interoperability conflicts are becoming paramount endeavors as existing networks expand to deal with increasing traffic demands.
“With the advent of Internet/Intranet applications for enterprise networks, most large campus and backbone networks are being bombarded by bandwidth demands that the original legacy network designs cannot support,” commented Joe Zeto, broadband products manger at Tekelec. “The solution is to link legacy systems onto new technologies like ATM and high-speed frame relay.
“But installation and maintenance of these combined networks may not be without problems. Fortunately, by using systems containing emulation and simulation capabilities, network installation engineers can validate new technologies, protocols, applications, and performance prior to implementation,” Mr. Zeto concluded.
Network Test Equipment
Laser Sources Feature
The Model 262A and 262C Dual Wavelength Laser Sources provide calibrated outputs in the 1,310-nm and 1,550-nm ranges. Both outputs are available from a single port, obviating the need to disconnect/reconnect when switching between lasers. A universal connector interface accommodates industry-standard fiber-optic connectors via a line of screw-on/screw-off adapters. Typical applications include connector-loss and continuity testing and evaluating single-mode fiber-optic links. Both units are splash-resistant and feature auto shutoff. The 262C offers an APC UCI interface. RIFOCS
Cable and Antenna Analyzer
Rejects External Interference
Two models added to the Site Master™ SWR/Return Loss Analyzer line offer segmented coverage from 5 MHz to 3,300 MHz. The units measure SWR, return loss, and distance-to-fault on analog and digital RF transmission lines. They also provide wattmeter features. The models reject external RFI, allowing them to test at live sites and in dense RF environments. Site Master isolates transmission faults using frequency-domain reflectometry which locates RF faults, not just DC open- or short-circuit conditions. Anritsu Wiltron, (408) 776-8300.
Cable Tester Measures
Power-Sum Near-End Crosstalk
The LANcat V Series 3.20 Category 5 Cable Testers include direct power-sum near-end crosstalk (NEXT)-measurement and cable-grading capabilities. Assessment of power-sum NEXT ensures that installed cabling supports parallel high data-rate transmission. The hand-held tester performs automated certification of LAN cable for conformance with cabling and network standards including TIA 568A TSB-67 Category 5, ISO 11801 Class D, AS/NZS 3080 Class D, ATM 155 Mb/s, Fast Ethernet, TP-PMD, 10BASE-T, and token ring. Datacom Technologies, (206) 355-0590.
New Mini-OTDR Version
Offers Higher Performance
The new TFS3031 TekRanger® 2 Mini-OTDR offers enhanced IntelliTrace™ measurement capabilities traceable to NIST standards. IntelliTrace software automatically adjusts and optimizes acquisition parameters. TekRanger 2 features extended dynamic and measurement ranges, improvements in dead-zone performance, and compatibility with Tektronix’ new Windows-based FMTAP™ 3.0 documentation and analysis software. A new high-dynamic-range option for single-mode systems detects fiber ends up to 200 km away at 1,550 nm. Tektronix, (800) 426-2200, press 3, code 1015.
Protocol Analyzers Offer
Web-Enabled Access Feature
The HP Internet Advisor helps you test, troubleshoot, maintain, and manage local-area, wide-area, and high-speed networks, including switched, full-duplex Fast Ethernet, Gigabit Ethernet, ATM, and FDDI. With new web-enabled management capabilities, you can access and control many of the instrument’s functions remotely with any Java™-enabled Web browser. The instrument also provides a five-minute health check so you can see the status of the network at a glance. Hewlett-Packard, (800) 452-4844, ext. 5348.
Option Facilitates Viewing
Across Virtual LANs
The new SwitchWizard™ Option (Version 7.5) for the Enterprise LANMeter allows network maintainers to see across virtual local area networks (VLANs) that include Cisco Catalyst™ 5000 Series switches. New information includes slot and port number displays and indications of the VLAN-number of accessed ports. The Enterprise LANMeters troubleshoot complex, segmented networks and access information available from management information bases and remote monitoring agents. Fluke, (800) 44-FLUKE.
Coaxial LAN Test Accessory
Kits Simplify Diagnostics
Two new kits provide accessories for coaxial cable LAN troubleshooting, installation, and repair. The 6201 is a multipurpose kit; the 6202 is designed for Fluke LAN testers. The kits include two 50-W BNC cables; two BNC male to Grabber® breakouts with Minigrabber® and Mini-gator test clips; BNC termination plugs for 50-, 75-, and 100-WW impedances, and eight BNC and Type N adapters. ITT Pomona Electronics, (909) 469-2900. impedances; Type N termination plugs for 50- and 75-
Modular Tester Targets
Digital Wireless Networks
The T-BERD® 2207 is a modular, battery-powered, hand-held test instrument for installing and maintaining digital wireless networks. It performs physical-layer testing and dual-receiver in-service monitoring of T1 circuit connections and 64-kb/s channels within a T1. The module also accesses the compressed subchannels of PCS 1900 digital networks. An application-oriented, graphical user interface simplifies test configurations and minimizes training requirements. Applications are accessed through a touch screen. Telecommunications Techniques, (800) 638-2049.
Hand-Held Protocol Analyzers
Perform Multiple Functions
The HCT2000 and HCT6000 are hand-held field service analyzers that perform multiple functions and weigh only two pounds each. The HCT2000 performs BERT up to 64 kB and offers interfaces for RS232, V.24, and V.35. The HCT6000 carries out BERT up to 2 MB and provides interfaces for RS449 (V.36), RS530, and X.21. Both analyzers include decodes for async/sync, HDLC, SDLC, X.25, and DDCMP. The HCT6000 also has frame relay, SNA, TCP/IP, SLIP, and PPP decode capabilities. Data can be downloaded into a PC for analysis. Digitech, (215) 362-0800.
ISDN Tester Analyzes Problems
And Graphics Aid Resolution
The portable Network Probe Total Network Tester is used for installing, monitoring, and troubleshooting ISDN lines. It performs automatic interface detection, interpretation, and setup. U terminal, S/T terminal, and NT1 emulation is provided. Features include Q.921/Q.931 interpretation, passive S/T and U interface monitoring, LT layer-one emulation, and B-channel protocol analysis. Provisioning tests include BERT, data, voice, and D packet calls, and multiterminal ID Nx64 384k data calls. A built-in Test Wizard escorts you through each test. Network Communications, (800) 451-1984.
Transmission Line Test Set
Checks Voice and Data Circuits
The Telesense 2500 Telecommunication Test Set evaluates and isolates malfunctions on voice, ISDN, ADSL, HDSL, and DDS two-wire or four-wire circuits. It performs tests at frequencies from 20 kHz to 200 kHz and measures levels from -60 dBm to +10 dBm at frequencies up to 200 kHz. Noise measurements may be performed with C, E, or F filters, each with true rms detection. The unit is lightweight, passes the 4’ drop test, and includes DMM capabilities. American Reliance, (818) 303-6688.
Test Set Suited for Checking
LAN Cabling, Premises Wiring
The Model DXB66 Cable Tester conducts performance evaluations and termination verification of premises cabling and patch cords used in local area networks. The unit verifies pairing in accordance with the EIA/TIA568 standard and tests for shield continuity. Coaxial cabling commonly used in broadband networks such as Ethernet 10BASE-2 also can be tested. L-com, (800) 343-1455.
Protocol Analyzer Supports
The portable PrismLite Protocol Analyzer accommodates multiple technologies via 20 selectable interface modules and supports 200 protocols. As many as three different medias may be analyzed, such as WAN, LAN, and ATM (up to 2 at a time), with a common time-stamp of 1-µs resolution. Two ports are available for each technology, up to a total of six ports. The system consists of a real-time unit connected to a PC and employs an MS-Windows 3.1/95/NT user interface. Radcom Equipment, (201) 529-2020.
Failures in Network
With the new User-Definable Interface Tool for the Chameleon Open Protocol Analyzer, network operators can achieve seamless transitions among technologies. The tool offers quick custom configuration capabilities meeting ATM, high-speed frame relay, and Fast Ethernet requirements. Pre-built load generation, protocol decode, and monitoring, filtering, analysis, and conformance checking suites are included. The Chameleon Open System may be used for diagnostic testing and validating LAN and WAN performance and conformance parameters. Tekelec, (818) 880-5656.
Copyright 1997 Nelson Publishing Inc.