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of Structured Cabling
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- Cabling Jargon
Here's an overview of
the basic jargon used in cabling and we'll explain more as we
go along.
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- To begin with, what do we
call this whole area of cabling?
- People call it lots of things:
- VDV (for voice/data/video)
- Premises (e.g. indoor)
- data/voice
- low voltage
- limited energy
- teledata
- datacom
- but most call it "structured
cabling" after the "568" standard
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- It's the infrastructure for
telephone and LAN connections in most commercial installations
and even in some modern homes. It's also used for fire alarms,
building management, audio and video.
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- Structured Cabling: An architecture for communications cabling
specified by the EIA/TIA TR42 committee and used as a voluntary
standard by manufacturers to insure interoperability.
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- Standards
- Structured cabling is based
on a number of industry standards - voluntary standards - developed
by manufacturers who want their products to interoperate - work
together. They meet in committees several times a year and decide
on the specifications of their products. These common specs mean
that equipment will work on any cabling system that follows the
standards and most cabling components can be interchanged without
adversely affecting performance.
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- EIA/TIA: Electronics Industry Alliance/Telecommunications
Industry Assn, an industry trade association that creates voluntary
interoperability standards for the products made by member companies.
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- EIA/TIA 568: The main standard document for structured
cabling, usually referred to as simply "568." It is
now on the "B" revision and includes sections for general
specifications (B.1) and individual sections for copper (B.2)
and fiber optics (B.3)
EIA/TIA 569: Covers pathways and spaces. Defines the "telecom
closet" or telecom room as it is now called.
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- EIA/TIA 570: For residential cabling.
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- EIA/TIA 606: cabling system administration (documentation)
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- EIA/TIA 607: Grounding and bonding
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- Standards are not code!
They are voluntary
interoperability specifications. However every installation must
be compliant to local building codes for safety!
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- NEC (National Electrical
Code): written by NFPA
(National Fire Protection Assn.) this code sets standards for
fire protection for construction and is a legal requirement in
most cities.
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- Structured Cabling Architecture
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Structured Cabling Terms:
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- Telecom Closet (TC): The location of the connection between
horizontal cabling to the backbone. Now often called "Telecom
Room" to imply it's usually bigger than a closet!
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- Main Cross-Connect (MXC): The old telco term for the location
of the main electronics in a building. LAN people may call it
the equipment room
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- Intermediate Cross-Connect
(IXC) : A room in between
the TC and MXC where cables are terminated
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- Work Area Outlet: The jack on the wall which is connected
to the desktop computer by a patchcord
Patch Panel: A rack or box where cables are terminated
- usually in 110 punchdowns and interconected with patchcords
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- Horizontal Cabling: The connection from the telecom closet
to the work area outlet (desktop)
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- Backbone Cabling: The cabling that connects all the hubs
in telecom closets or MXCs together
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- Link: The installed cable plant from work area outlet
jack to the patch panel in the telecom closet
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- Channel: The cable plant including the link plus
patchcords on either end to connect the communications hardware
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- Patchcord: A short length of stranded cable with
a RJ-45 plug on either end, used to connect hardware to the link
or to connect cables in a Patch Panel
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- J hook: A hook shaped like the letter J used to suspend
cables
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- Fishtape: Semiflexible rod used to retrieve cables
or pull line
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- Cable
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- The Types Of "Low Voltage"
Cable.
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- UTP: Unshielded twisted pair cable, comprised of 4 twisted
pairs of copper conductors, graded for bandwidth as "Levels"
(from Anixter) or "Categories" (EIA/TIA 568)
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- Category 3,4,5, 5e, 6: Ratings on the bandwidth performance
of UTP cable, derived from Anixter's Levels program. Cat 5e (enhanced)
is rated to 100MHz. Cat 6 standards for UTP at up to 200 MHz
have recently by ratified and Cat 7 is also discussed for the
future, but only in Europe, not the US.
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- A typical Cat 6 cable is shown
below.
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- STP: Shielded twisted pair, specified by IBM for Token
Ring networks
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- Optical Fiber: Both multimode and singlemode fiber
are included as well. See Lennie
Lightwave's Guide to Fiber Optics for more information
on fiber optics.
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- Coax: A type of cable that uses a central conductor,
insulation, outer conductor/shield, and jacket; used for high
frequency communications like CCTV (closed circuit TV)
or CATV (community antenna TV or cable TV). Coax is
not included in 568 but is included in 570 for home use
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- RG-6/RG-59: 75 ohm coax used for video. RG-6 is
the standard for CATV, RG-59 is used on some short CCTV networks.
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- RG-58: 50 ohm coax used for "Thinnet" Ethernet.
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- HFC: Hybrid fiber-coax CATV network combines coax and
optical fiber
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- Terminations
- The connectors for UTP are also
standard - used on every cable for Cat 3, 5, 5e, 6, but must
be rated for the same performance level, e.g. Cat 6 hardware
on Cat 6 cable.
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- RJ-45: The popular name of the modular 8 pin connector
used with UTP cable in structured cabling systems.
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- Jack: The receptacle for a RJ-45 Plug.
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- Plug: The connector put on the end of UTP cable.
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- Punchdown: A connecting block that terminates two
cables directly. 110 blocks are most popular for LANs, 66 blocks
for telco, but some installers use BIX or Krone.
Below - 66 blocks on the left, 110 blocks on the right:
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- Testing
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- After installing the cables,
they must be tested. Every cable, including Cat 3 for telephones,
must be tested for wiremap, but cable certifiers will test for
all the parameters listed below.
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- Wiremap: All eight wires must be connected to
the correct pins, and the test is called a wiremap test.
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- Length: The length must be less than 90 m for
the permanent link and less than 100 m for the channel
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- Attenuation: The reduction in signal strength due
to loss in the cable.
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- NEXT: Near End Cross Talk, or the signal coupled from
one pair to another in UTP cable.
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- ACR: Attenuation to crosstalk ratio, a measure of how
much more signal than noise exists in the link, by comparing
the attenuated signal from one pair at the receiver to the crosstalk
induced in the same pair
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- Return Loss: Reflection from an impedance mismatch
in a copper cable
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- ELFEXT: Equal level far end crosstalk; crosstalk at the
far end with signals of equal level being transmitted.
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- Propagation Delay: The time it takes a signal to go down
the cable.
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- DC Loop Resistance: The DC resistance of the cable in ohms.
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- Delay Skew: The maximum difference of propagation
time in all pairs of a cable.
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- Power Sum Next: Near end crosstalk tested with all pairs
but one energized to find the total amount of crosstalk caused
by simultaneous use of all pairs for communication
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- Power Sum ElFEXT: ELFEXT for the sum of the other 3 pairs
on the 4th pair.
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- PSACR: PowerSum ACR
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- Then There's The Electronics
That Makes It All Work Over The Cabling As A Network:
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- Hub: The electronic box that connects to all the horizontal
cables which are them connected by backbone cabling, enabling
any PC to talk to any other
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- Switch: A device like a hub but connects any two devices
directly, allowing multiple connections simultaneously
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- Bridge: A device that connects two or more sets
of network wires
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- Router: A smart switch that connects to the outside
world
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- Ethernet:: A 10, 100 or 1000 Megabit per second
local area network (LAN) that is by far the most popular LAN
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- 10Base-T: 10 MB/s Base Band Transmission, 100 meters
max, segment length on Cat 3, or better twisted pair cable
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- 100Base-TX: 100 MB/s Base Band Transmission, 100
meters max, segment length on Cat 5, twisted-pair cable, also
referred to as Fast Ethernet
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- 1000Base-T: Gigabit Ethernet on Cat 5e UTP
- All versions of Ethernet
also have fiber optic connection standards.
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- Power over Ethernet: The IEEE 802.3 Ethernet committee added
provisions for powering devices off the spare pairs in a 4-pair
UTP cable. Since Ethernet up to 100Base-TX uses only pairs 2
and 3, pairs 1 and 4 are available to provide power. Pair 1 (pins
4/5) is the + conductor, pari 4 (pins 7/8) is the - conductor.
Almost 13 watts of power are available, adequate for powering
local swithches or hubs that can serve several users locally
from one UTP cable, thus saving cabling costs.
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- Wireless Is NOT Wireless
- Most LANs today include wireless
access points. Wireless is by no means wireless, as it requires
wiring to connect it to the network. It merely replaces patchcords
with a wireless link to allow roaming within a limited area.
Wireless requires many access points connected (over wire or
fiber) into the backbone.
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- Test Equipment and Tools:
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- Digital multimeter: A simple tester that measures if the
cable is shorted and whether or not it is open
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- Wire Mapper: Checks each wire to make sure they are
terminated in the correct order
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- Cable Certification Tester: Tests everything, wiremap, length, attenuation
and crosstalk in one connection, gives you a pass/fail result
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- TDR: Time domain reflectometer, a testing device used
for copper cable that operates like radar to find length, shorts
or opens, and impedance mismatches
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