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Reference Guide To Fiber Optics |
| Topic: Premises Cabling - UTP Termination | Table of Contents: The FOA Reference Guide To Fiber Optics |
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Premises Cable: UTP Termination
UTP cables are terminated with standard connectors (plugs and jacks) or punchdowns. The plug/jack is often referred to as a "RJ-45", but that is really a telco designation for the "modular 8 pin connector" terminated with a USOC pinout used for telephones. The male connector on the end of a patchcord is called a "plug" and the receptacle on the wall outlet is a "jack." These terminations are called
"IDC" for "insulation-displacement connections," since the wires are held in knife-edge terminations
that slice through the insulation and dig into the copper wire,
forming a tight seal like this.
All
IDC connections require untwisting a small amount of each pair to get
the wires into the contacts. In order to minimize crosstalk and
return loss problems, its necessary to keep the amount of wire in each
pair untwisted and minimize the amount of cable jacket removed. For Cat
5/5e/6/6A cable, the maximum amount of untwisted wire is specified as
0.5" (13 mm) but it's good practice to minimize the amount of untwist
and the length of cable jacket removed.
In structured cabling as specified by TIA-568, there are two possible color codes or pinouts, called T568A and T568B which differ only in which color coded pairs are connected - pair 2 and 3 are reversed. Either work equally well, as long as you don't mix them! If you always use only one version, you're OK, but if you mix A and B in a cable run, you will get crossed pairs! While it makes no difference electrically which one you use, it is not wise to use both in one customer location. Always check to see which scheme has been used and continue using that one in new cabling installation. The cable pairs are color coded as shown:
Each pair consists of a colored wire and a white wire with a matching color stripe. The stripe wire is "tip" and the solid color wire is "ring," referring to the tip of the old 1/4" telephone plug and the ring around the shaft that makes the connections.
Note: Plugs/jacks and punchdowns have different color codes! You cannot mix them up as they will result in wiremap errors - esp. split pairs which cause big problems with high speed transmission.
Jacks: The jacks are then terminated with these layouts, looking into the jack:
Note that the only difference between T568A and T568B is the reversal of pairs 2 and 3 - it's only a color code change.
Another way of looking at it is as a plug and jack:
The color codes are going to look like this on a jack, showing both T568A and T568B termination schemes:
Note: Cat 3 jacks and all plugs are going to
use these color codes shown above.
Remember: Always follow the color codes on the back of the jacks to insure proper connections!
Terminating Jacks
Here is a virtual hands-on tutorial on terminating jacks.Videos on
Plugs: The plugs are terminated by straightening our the
wires in proper order and crimping on a connector. Like we said
before, you MUST keep the twists as close to the plug as possible
to minimize crosstalk. Here is a virtual hands-on tutorial on terminating plugs.Videos onPatchcords: They generally use stranded wire for flexibility but can be made with solid wire for higher performance. Note that plugs may be different for each type of wire, so make sure you have the right type. Crossover Cables: Normal cables that connect a PC/NIC card to a Hub are wired straight through. That is pin 1 is connected to pin 1, pin 2 to pin 2, etc. However, if you are simply connecting two PCs together without a hub, you need to use a crossover cable made by reversing pair 2 and 3 in the cable, the two pairs used for transmisson by Ethernet. The easy way to make a crossover cable is to make one end to T568A color coding and the other end to T568B. Then the pairs will be reversed.
Punchdowns Sometimes there are cross connects using punchdowns in the telecom closet, more common on telephone wires than data. These are called punchdowns because the cable is punched down into the IDC contacts with a special tool, called (surprise!) a punchdown tool. Of course, you MUST keep the twists as close to the punchdown as possible to minimize crosstalk. Punchdowns
come in 4 varieties: 110, 66, Bix and Krone. Most popular for LAN
interconnects is the 110 block. For telephone cables with large pair
counts (25, 50, 100, etc.), the 66 block is the most common. The Bix
and Krone blocks are rarer proprietary designs (Bix from Northern
Telecom, Krone from Krone in Germany) used mostly on the manufacturer's
own installations.
Here is a 110
block as used in LAN interconnects and on UTP jacks. The actual IDC
contacts are in the connecting block that is punched down on the base,
sandwiching one cable, then the second cable is punched down on the top. Here is a virtual hands-on tutorial on terminating 110 blocks.Videos on
66
block as used for POTS (plain old telephone system) telephone systems.
They are designed for interconnecting large pair count cables. There
are four rows of punchdown IDC contacts. One cable is punched down on
the outside row of contacts of each side then the two sides are
connected using the inside rows of contacts. If connections are
directly across, bridging clips can be used. Otherwise, bridging wire
is punched down on the correct contacts on each side to make
connections. Here is a virtual hands-on tutorial on terminating 66 blocks. Videos on
Punchdowns of all types are always
made with the pairs in order with the white/stripe wire (tip)
first, then the solid colored wire (ring).
(This color code is often remembered by BLOG - BLueOrangeGreen and brown is all that's left!) Refer to our online "virtual
hands-on" explanation of the termination processes of Cat
3/5/5E/6 for complete illustrated procedures.
Patch Panels Patch panels offer the most flexibility
in a telecom closet. All incoming wires are terminated to the
back of the patch panel on 110-style punchdowns (again watching
the 1/2 inch limit of untwisting pairs). Then patch cables are
used to interconnect the cables by simply plugging into the proper
jacks. Patch panels can have massive
number of cables, so managing these cables can be quite a task
in itself. It is important to keep all cables neatly bundled
and labeled so they can be moved when necessary. However, it
is also important to maintain the integrity of the cables, preventing
kinking or bending in too small a radius which may adversely
affect frequency performance.
(Note: Cat 6A and Cat 6 cables are physically
larger in diameter than Cat 5e and usually have a separator for
the pairs. The cable construction makes the cable stiffer and
more prone to kinking, requiring a larger bend radius.)
Table of Contents: The FOA Reference Guide To Fiber Optics |
However, Cat 5, 5e and 6
jacks have internal connections that continue the twists as close
to the pins in the jacks as possible to maintain the performance level. Thus the pinout on the
back of the jacks will not usually follow the standard color
code layouts- see the pin sequence in the photo above and the
twists in the internal connections of the jack here!
