Mitel MiVOICE BUSINESS, Инструкция по инженерии

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CAT 3 Wiring
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CAT 3 WIRING PRACTICES
Category 3 (CAT 3) refers to a type of UTP copper cabling that meets specific transmission
characteristics (see CAT3/EIA/TIA-568 wiring standards). CAT 3 also refers to the installation
practices observed when routing these cables as well as the interconnection and end point
termination methods used. The following sections detail further practical issues to be used in
conjunction with the specification.
Although CAT 3 cabling is not recommended for new installations, there may be instances
where CAT 3 is encountered in an existing installation. CAT 3 installations can fall into different
categories with unique pitfalls:
• CAT 3 cabling plant was installed for supporting traditional telephony equipment. This type
of installation will potentially contain a number of CAT 3 violations that did not interfere with
traditional telephony applications but will present problems for data transmission and VoIP.
• CAT 3 cabling plant was originally installed for supporting traditional telephony equipment.
At a later date spare cable runs were inspected and qualified to support 10M Ethernet. Part
of this cabling plant will be CAT 3 compliant and part will not be CAT 3 compliant. An
installation in this category needs to be carefully re-qualified to CAT 3 standards.
• CAT 3 cabling plant was installed to support a LAN technology other than 10M Ethernet,
such as Apple Talk, Token Passing Ring, or a proprietary networking technology. An instal-
lation in this category needs to be carefully qualified to CAT 3 standards.
It is becoming increasingly difficult to find CAT 3 cables and connectors. The cost of CAT 5
components has been reduced so much that it is not cost-effective to install new CAT 3
networks. For new installations, only CAT 5 or better should be considered.
Many network devices now are capable of operating at both 10BaseT and 100BaseT. Devices
will typically select the higher rate. Using CAT 3 introduces extra difficulties with these newer
devices because the connection speed must be restricted to 10BaseT because of the cable
capabilities. Often, the ability to provide this restriction can only be provided through manual
selection, negating the benefits of using Auto-speed configuration. The cable capacity cannot
be accurately determined so the end devices must be configured to inhibit them from selecting
the higher data rates. If there is a mismatch between auto negotiation and manual settings, the
link will default to the lowest setting of 10BaseT half duplex.
COMMON GUIDELINES AND RESTRICTIONS FOR CAT 3
INSTALLATIONS
• IEEE 802.3 hubs/repeaters should not be used in a network that is going to carry VoIP
traffic due to the limited number of conversations and high level of jitter and packet loss
than can be introduced with other devices. Use only Layer 2 switches at the access points.
• Connections between L2 switches must be at 100BaseT or better (using CAT 5 wiring or
better), including connections to the ICP controllers.
• The network infrastructure and capabilities should be considered in a network that still
employs CAT 3 cable. It may not be capable of handling the Packet Per Second rate needed
for a number of voice devices, as well as the bandwidth throughput. If a connection exists
to data devices, such as PCs, the use of VLANs and a priority mechanism is recommended.