Information Technology Reference
In-Depth Information
on the low-end networking devices. However, as network speeds increase, and as the
costs of networking equipment decrease, it will become more sensible to use moni-
toring devices to determine the health of the wiring system.
Physical Cable Monitoring
Physical monitoring of installed LAN wiring presents some very special problems.
Most of the simple ways that can be used require that the monitoring be performed
by the connected LAN devices (such as 10/100 BaseT or Token-Ring hubs). The hub
monitors the condition of the link and reports it by indicator lights on the front
panel of the hub, or by sending messages to a remote monitoring station. These
devices and their capabilities are specific to the type of LAN you are using.
All 10BaseT, 100BaseTX, and 1000BaseT Ethernet twisted pair systems pro-
vide a positive indication of link operation. A continuous link signal is built into the
physical layer protocol, that indicates both link status and link speed. Standard
10/100/1000BaseT systems actually only evaluate the integrity of the received signal
from the other end of the link, but enhanced systems can indicate integrity of the
complete link (local and remote ends) and report the link status to a remote moni-
toring system.
A Token-Ring multi-station access unit (MSAU), in contrast, uses DC connec-
tivity on the link to set or reset a sensitive relay in the MSAU. Even a simple MSAU
can easily provide an LED indicator on the front panel to indicate link condition.
Intelligent MSAUs are able to report the status of any lobe to a remote monitor. Of
course, the indication shows more than just the integrity of the cable, because the
workstation operation is also a factor in lobe status. Nevertheless, this is an effec-
tive means of physical monitoring.
Remote Cable System Monitoring
Another type of direct cable monitoring system pays no attention to the LAN pro-
tocol, but has custom electronics that is designed to indicate the integrity of a con-
nection. These monitored patching systems can provide connectivity monitoring
with virtually any type of LAN. The way this works is that these systems use pairs
on the cable that are unused by the LAN to indicate connectivity, and in some cases,
even the cable map—where each patch cord terminates. For example, 10BaseT,
100BaseTX, and Token-Ring use only two of the pairs on the cable. The other two
are available for other purposes such as connectivity monitoring. While this does
not truly indicate that the two network pairs are connected, it certainly will indicate
whether a patch cable is connected or disconnected.
