Chapter 12

TDR (time domain reflectometer)

A high-end instrument for testing the qualities of a cable. It works by issuing a signal on a cable and measuring the way in which the signal bounces back (or reflects) to the TDR. Many performance testers rely on TDRs.

Network Monitor

A network monitoring program that comes with Windows Server 2003 (as well as with Windows NT and Windows 2000 Server).

giant

A packet that exceeds the medium's maximum packet size. For example, any Ethernet packet that is larger than 1518 bytes is considered a giant.

runt

A packet that is smaller than the medium's minimum packet size. For instance, any Ethernet packet that is smaller than 64 bytes is considered a runt.

OTDR (optical time domain reflectometer)

A performance testing device for use with fiber-optic networks. An OTDR works by issuing a light-based signal on a fiber-optic cable and measuring the way in which the signal bounces back (or reflects) to the OTDR. By measuring the length of time it takes the signal to return, an OTDR can determine the location of a fault.

change management system

A process or program that provides support personnel with a centralized means of documenting changes made to the network.

baseline

A record of how a network operates under normal conditions (including its performance, collision rate, utilization rate, and so on). Baselines are used for comparison when conditions change.

multimeter

A simple instrument that can measure multiple characteristics of an electric circuit, including its resistance and voltage.

tone locator

A small electronic device that emits a tone when it detects electrical activity on a wire pair. When used in conjunction with a tone generator, it can help locate the termination of a wire pair.

tone generator

A small electronic device that issues a signal on a wire pair. When used in conjunction with a tone locator, it can help locate the termination of a wire pair.

protocol analyzer

A software package or hardware-based tool that can capture and analyze data on a network. Protocol analyzers are more sophisticated than network monitoring tools, as they can typically interpret data up to Layer 7 of the OSI Model.

call tracking system

A software program used to document technical problems and how they were resolved (also known as help desk software).

network monitor

A software-based tool that monitors traffic on the network from a server or workstation attached to the network. Network monitors typically can interpret up to Layer 3 of the OSI Model.

spectrum analyzer

A tool that assesses the characteristics (for example, frequency, amplitude, and the effects of interference) of wireless signals.

voltmeter

A device used to measure voltage (or electrical pressure) on an electrical circuit.

supported services list

A document that lists every service and software package supported within an organization, plus the names of first- and second-level support contacts for those services or software packages.

ghost

A frame that is not actually a data frame, but rather an aberration caused by a device misinterpreting stray voltage on the wire. Unlike true data frames, ghosts have no starting delimiter.

cable performance tester

A troubleshooting tool that tests cables for continuity, but can also measure crosstalk, attenuation, and impedance; identify the location of faults; and store or print cable testing results.

local collision

A collision that occurs when two or more stations are transmitting simultaneously. Excessively high collision rates within the network can usually be traced to cable or routing problems.

late collision

A collision that takes place outside the normal window in which collisions are detected and redressed. Late collisions are usually caused by a defective station (such as a card, or transceiver) that is transmitting without first verifying line status or by failure to observe the configuration guidelines for cable length, which results in collisions being recognized too late.

jabber

A device that handles electrical signals improperly, usually affecting the rest of the network. A network analyzer will detect a jabber as a device that is always retransmitting, effectively bringing the network to a halt. A jabber usually results from a bad NIC. Occasionally, it can be caused by outside electrical interference.

cable tester

A device that tests cables for one or more of the following conditions: continuity, segment length, distance to a fault, attenuation along a cable, near-end crosstalk, and termination resistance and impedance. Cable testers may also issue pass/fail ratings for wiring standards or store and print cable testing results.

ohmmeter

A device used to measure resistance in an electrical circuit.

continuity tester

An instrument that tests whether voltage (or light, in the case of fiber-optic cable) issued at one end of a cable can be detected at the opposite end of the cable. A continuity tester can indicate whether the cable will successfully transmit a signal.

fox and hound

Another term for the combination of devices known as a tone generator and a tone locator. The tone locator is considered the hound because it follows the tone generator (the fox).

promiscuous mode

The feature of a network adapter that allows it to pick up all frames that pass over the network—not just those destined for the node served by the card.

site selection

The process of determining optimal locations for access points on a wireless network.

NETMON

Novell's network monitoring NLM. NETMON is included in NetWare 5.x and 6.x.

negative frame sequence check

The result of the CRC (cyclic redundancy check) generated by the originating node not matching the checksum calculated from the data received. It usually indicates noise or transmission problems on the LAN interface or cabling. A high number of (nonmatching) CRCs usually results from excessive collisions or a station transmitting bad data.