LAN/WAN Testers Find Bugs in Sophisticated Networks

Real-time communications with anyone, anywhere once was science fiction; font-family: Arial;”>but no more. Via computer networks, businesses can connect employees in a single building, whole sites and even offshore facilities. But the increased number of interactions from everyone to everywhere does not automatically occur error-free. The connections must be carefully planned and tested to eliminate the bugs.

Often, it is often the network engineer who must ensure that communications are smooth, consistent and trouble-free. The testing requires methods and tools to monitor and troubleshoot a complex web of local area networks (LANs) and wide area networks (WANs) and their accompanying switches, routers and bridges.

What instruments are needed to check the integrity of LANs/WANs? A mix of equipment makes the most sense for managers of networks because problems occur at different layers of the protocol stack, said David Skingley, Product Marketing Manager at Fluke. The collection of instruments includes cable testers, traffic generators, personal network managers and protocol analyzers.

The cable tester checks the physical layer during a new installation or while moving or adding to the network, continued Mr. Skingley. For these tasks, you need instruments ranging from a basic connectivity tester to a full-blown certification tool that actively tests the link at 100 MHz. Some units, such as the Fluke DSP-100, are digital cable testers that can identify the location of a crosstalk fault.

LAN cable testing in a facility is specific to the customer’s hardware, said Norm Meritt, Product Marketing Specialist at Tekelec. For unshielded twisted-pair and shielded twisted-pair cables, a simple tone generator and receiver are enough to isolate a cable fault. For testing fiber cables, you need specialized tools such as the optical time domain reflectometer (OTDR).

Light throughput and OTDR tests are recommended for examining LAN/WAN fiber cables, said Ken Ditto, Product Marketing Manager at Tektronix. The light throughput technique shines a light source into the cable and checks the result at the far end of the cable using a detector, such as a power meter. This method measures the optical loss of the cable and determines if enough signal is available to operate properly within the requirements of the system.

OTDR testing provides more comprehensive information regarding optical cables than the light throughput method, continued Mr. Ditto. It measures the events on a fiber cable with respect to distance. OTDRs identify the location of splices, reflections and breaks, and provide qualitative data regarding the length, location and magnitude of each event.

A cable tester is the basic instrument for checking the physical layer of LANs, agreed Peter Luff of Telecommunications Techniques. However, a WAN needs a bit error rate tester to check the network cables at various data rates. It generates a known data pattern and transmits it into another tester at the far end or back to itself via a loopback connector. The received pattern is compared with the transmitted pattern to determine the error rate for the cables.

Other techniques give more than the error count and measure the distribution of errors, added Mr. Luff. Tests of cable conditions for jitter, signal frequency, voltage levels and pulse shape help determine the possible causes by ensuring that they fall within standardized limits.

The traffic generator creates control sequences and data packages so devices within the network are tested under normal and stress conditions. It also performs stimulus/response testing to simultaneously transmit and receive test packets. Traffic generators are important for testing the interoperability of devices in the LAN.

After the physical layer is tested, the link layer is checked, said Mr. Luff (see Figure 1). This procedure checks the ability of the layer to transport a service such as ATM or frame relay. The traffic generator produces bursts of cells or frames and determines whether any cells or frames are dropped by the service. It also stresses individual channels to verify that the contracted service parameters such as throughput, allowable burst rate and minimum error rate are delivered.

Personal network analyzers combine cable test, some protocol analyzer functions and network management functions, said Mr. Skingley. They also contain hardware checks, including network interconnection tests and traffic-generation functions. These hand-held tools test the first three layers of the protocol stack.

Protocol analyzers are more sophisticated instruments used for interpreting network behavior. They provide utilization and peak-performance statistics, protocol information to analyze the traces, and events to verify proper network operation.

Protocol analyzers help interpret network behavior and verify proper operation of the equipment. They provide statistical and decode information and help solve problems that occur in the upper levels of the protocol stack, observed Mr. Skingley. Users must be highly skilled and experienced to operate and interpret the information provided.

The protocol analyzer is called in when there is a service break that requires troubleshooting. Some instruments such as the FIREBERD 500 Internetwork Analyzer nonintrusively capture the flow of packets in both directions to determine protocol violations.

The analyzer catches complex problems, such as end-to-end protocol process breakdowns or router misconfigurations, by viewing encapsulated LAN traffic from a WAN access point. The unit simultaneously monitors the link layer and physical layer, and views LAN and WAN traffic.

A protocol analyzer must be able to connect at any point on a LAN or WAN because problems can occur anywhere on the network. For example, a network could include Ethernet hubs, token rings and FDDI and use protocols such as TCP/IP, Banyan, Novell or DECNet. It may be connected by T1 lines, 56k lines, ATM and frame relay. Interconnecting devices may include routers, bridges and switching hubs. The best tool to test this vast array of equipment is the protocol analyzer because it contains all the measurement capabilities and decode and troubleshooting functions needed to assess the operation of the network components.

The equipment of choice is the multiprotocol analyzer, said Norm Meritt, Product Marketing Specialist at Tekelec. This unit generates a load, analyzes data and supports different technology interfaces and protocols. It is used to troubleshoot a network or measure network performance.

As a troubleshooting tool, the multiprotocol analyzer tests the capabilities of the device under test, such as a frame relay access device. This device has a performance rating of 1,000 frames/s on an average 500-byte frame. The test tool must generate this constant load and verify that the throughput is 1,000 frames/s with 500 bytes/frame.

Network Trends

The insatiable demand for bandwidth drives the LAN/WAN market, according to Mr. Skingley. Trends include the microsegmenting of networks with routers, and the addition of switches to increase network throughput.

While helping to increase network capability, the segmented topology adds complexity, which presents a major challenge for maintaining, troubleshooting and repairing the network, continued Mr. Skingley. Switches and routers help isolate network traffic but increase the difficulty of locating a network problem.

Network managers need a tool that provides a picture of the network’s performance. The instrument must help collect critical network parameters and report to central locations where the operation is viewed in real time. For example, the Fluke Enterprise LANMeter offers the Simple Network Management Protocol which queries the information in managed devices providing visibility beyond the attached segment.

A key trend of the LAN/WAN market is the wide-scale connection of these networks into larger internetworks, said Joel Salzburg of Hewlett-Packard. By combining WAN links, LAN links and backbone technologies such as FDDI, ATM, Ethernet and token-ring, network complexity will grow exponentially.

A second trend is the need to move data quickly. Current methods are reaching their limits and other methods such as ATM, switched Ethernet, frame relay and ISDN are needed to keep up with demand. Because each of these technologies has a unique set of strengths and weaknesses, multiple high-speed technologies will be used throughout the internetwork.

For the WAN arena, the lower tariff rates for ISDN have made it economical for a home office or remote office to access an enterprise network, continued Mr. Meritt. What was once costly to provide via a dedicated line is now available on demand through ISDN. Faster throughput is also gained with ISDN because it connects to the Internet at speeds of 64 kb/s.

It is true that the ISDN market has grown tremendously this past year, agreed Ilan Bar, Product Manager for Radcom. ISDN provides a similar service at a much lower price than FT1 and FE1.

Frame relay is another service experiencing explosive growth because it provides more bandwidth at a lower price than the older technologies, said Mr. Bar. Faster CPUs and the need for pathways that can accommodate multimedia and video information are behind this trend.

LAN/WAN Products

Hand-Held Analyzer Monitors

Packet Exchange to File Server

The NETcat™ 2000 Series Testers are PC-controlled hand-held analyzers for diagnosing and troubleshooting Ethernet problems such as slow network response. The analyzers monitor packet exchange between a station and file server, and display the cause of a connection failure. The NETcat 2100 provides a wire map of 10BASE-T cable and detects broken or intermittent wiring, crossed pairs, reversed pairs, opens and shorts. The NETcat 2200 checks UTP, STP and coax cables for conformance to network standards. 2100: $1,795; 2200: $2,995. Datacom Technologies, (206) 355-0590.

Hand-Held Analyzer Provides

ATM Test Capabilities

The OC3/ATM Analyzer with OC3portplus provides ATM service testing, equipment verification and troubleshooting capabilities. It simulates ATM traffic and OAM support. The hand-held instrument combines a full set of physical-layer SONET test capabilities with an ATM test set to isolate and diagnose network problems. It features eight programmable ATM transmit cell streams, CBR, VBR-Burst, VBR-Poisson and PDU-Poisson traffic simulation models. $11,995. DeskNet Systems, (914) 273-6232.

Portable Unit Configurable As

Protocol or Network Analyzer

The PC900/6 is a portable communications test platform with a 486/100-MHz processor. It can be configured with a WAN900 protocol or LAN900 network analyzer for Ethernet and token-ring systems, a DS-3 BERT, ATM and transmission analyzers. The multislot unit offers six full-size ISA slots or five full-size and two PCMCIA-type II slots. It contains an autosensing power supply for applications from 85 VAC to 264 VAC. The standard configuration includes an 850-MB drive, a 16-MB RAM and an active 10.4″ VGA color display. $7,500. Digitech Industries, (203) 797-2676.

LAN Meter Accesses Information

Stored in Information Bases

The 68X Enterprise LANMeter Series tools troubleshoot complex, segmented networks and access information stored in the management information bases and remote monitoring agents via the Simple Network Management Protocol. The meters help sense across a router and determine LAN/WAN link performance. NetBIOS protocols are supported. The segment discovery test analyzes attached segments, giving a list of available SNMP agents. $8,495 to $11,495. Fluke, (800) 44-FLUKE.

Fading Emulator Performs

Tests With 12 Paths

The Multipath MP2600 Fading Emulator offers a 26-MHz bandwidth and emulates one- or two-channel wireless communications between base stations and mobile transceivers. It performs single-channel tests with 12 paths or dual-channel tests with six paths/channel. The instrument allows direct setting of output power levels. Differential path delay, attenuation and Doppler shift are programmable. Rayleigh, Rican, Log-normal, Suzuki and Nakagami distributions are available. It performs forward and reverse links, diversity, interference and duplex testing. $39,800. Noise Com, (201) 261-8797.

Hand-Held Unit Tests

Physical Layer Nonintrusively

The LANMaster™ 100 and the LANMaster 100RS Data Clamp with an RS-232 interface are hand-held LAN traffic monitors. They provide nonintrusive test for active networks, and diagnose and identify network, application or end-user problems. Compatible with UTP, STP and coaxial cables, the products clip on top of network cables to provide a readout of bandwidth utilization. Inductive sensors work with Ethernet and token-ring networks. Network activity is logged and recorded from 12 min to 24 h. LanMaster 100: $749; LanMaster 100RS: $899. Harris, (805) 987-9511.

Analyzer Software Detects

Frame Relay Problems

The Frame Relay Troubleshooter Software complements the company’s WAN/LAN analyzer to provide an expert system for detecting problems on frame relays. It helps managers identify and analyze traffic problems over WANs and helps field service engineers monitor frame relay lines to locate the distribution, type and source of erroneous frames. The software identifies frames with incorrect values in 14 different frames, including DLCI, EA1, EA2, PVC length and protocol discriminator. $1,995. RADCOM, (201) 529-2020.

OTDR Automatically

Adjusts Parameters

The TekRanger™ TFS3031 mini-OTDR tests fiber-optic networks and adjusts acquisition parameters such as pulse width and number of averages as it automatically analyzes a fiber link. It measures small and closely spaced events over long distances. Near-in events are captured superior for testing from 5 m to 100 km. $8,900. Tektronix, (800) 426-2200.

Instrument Tests LAN/WAN

And Broadband Networks

The Chameleon Open provides simultaneous full bandwidth testing of applications and LAN/WAN and broadband networks. It supports multiple LAN and WAN interfaces connected to different mediums, and traces user applications as they transition through network segments. Application modules for ATM, SMDS, frame relay, X.25, ISDN PRI, Ethernet, token-ring and FDDI testing are available. Starting at $22,000. Tekelec, (818) 880-5656.

Wideband System Tests

Wireless Equipment

The TAS 4500 FLEX/Wideband™ RF Channel Emulator provides a 15-MHz signal-processing bandwidth to test wireless equipment and services such as cellular telephony, personal communications, digital audio/video broadcast and wireless LANs. The propagation model includes as many as 12 paths. Each path performs fading, propagation delay, log-normal shadowing and attenuation functions. The system provides active terrain emulation and a Windows-based software program to control test functions. $37,950. Telecom Analysis Systems, (908) 544-8700.

Instrument Provides Test Sets

For ATM, DS3 and SONET

The DS3 ATM option for the T-BERD 310 Communications Analyzer performs ATM switch and network facilities tune-up and maintenance for DS3 and SONET networks. The DS3 ATM option provides in-service and out-of-service testing for ATM switches and network facilities by generating and analyzing cells at DS3 rates. It checks QoS parameters including cell loss, cell misinsertion and round trip delay. Search and preview modes help look for network problems by automatically identifying active channels. Analyzer: from $9,995; DS3 option: from $4,995. Telecommunications Techniques, (301) 353-1550.

Analyzer Package Tests

Devices and Connections

The DA-30C Internetwork Analyzer equipped with the HSSI/Multi-WAN Analysis Package tests devices, services and internetworks. It monitors and analyzes WANs, LAN-to-WAN and WAN-to-public-network devices. The instrument contains a plug-in board and a software package running under the company’s DA-3X for Windows interface program. The full duplex analyzer generates simulated traffic, monitors reception at a full line rate, tests two networks simultaneously and monitors both sides of an internetworking device. It performs seven-level protocol analysis on WANs and simulates bit-oriented protocols. From $25,000. Wandel & Goltermann, (919) 941-5730.

Instrument Views Network

Events by Protocol Category

The HP Internet Advisor for LAN Series provides monitoring and analysis for Ethernet, FDDI and token-ring networks. The HP J2522B is the Ethernet version, HP J2523B is for the Ethernet/token-ring network and the HP J2524A is the FDDI analyzer. The series offers graphical presentations of network health with real-time parameter summaries. An expert commentator feature allows access to an information base for solving network problems. Network stack decodes show all fields of all major protocols, including Novell, TCP/IP, AppleTalk, Banyan, OSI and DECnet. HP J2522B: $16,000; HP J2523B: $21,000; HP J2524A: $22,000. Hewlett-Packard, (800) 452-4844 x1334.


Figure 1


Layer 7 Application Interface with network users


Layer 6 Presentation Format conversion


Layer 5 Session Connections for application programs


Layer 4 Transport Error-free, end-to-end delivery


Layer 3 Network Internetwork addressing and routing


Layer 2 Data Link Local addressing and error detection


Layer 1 Physical Signaling and interfaces



Copyright 1996 Nelson Publishing Inc.

May 1996


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