tantivy
join:2007-03-17
Palo Alto, CA
 ·SONIC.NET
2 edits | reply to Killa200
Re: New home office setup. Please comment on feasability
said by Killa200  :the harder to work with comments are because its a thicker, tighter twisted cable. Also while cat6 uses the rj-45 connector, its not the same as a rj-45 crimp end you would use on cat 5 / 5e as cat6 has thicker gauge wiring in the bundle. Actually none of them are "RJ45" despite what all the IT folks say.. (and this is a pet peeve of mine)
RJ45 (and all other RJxx designations) defines a specific connector, wired in a specific manner, as specified for a specific telephone service. The designations are part of the Universal Service Ordering Codes, which were set up so that the telco's were all on the same page following the breakup of the Bell System. (It might have been earlier than that, but somewhere around that time).
The idea is that the customer can order the same service,anywhere in the country (or for that manner, North America), and know that a device that is specified to connect to a POTS circuit terminated on a RJ11C jack will work with any POTS circuit terminated on a RJ11C jack anywhere in the country.
Ethernet (and Token Ring) do not have RJ designations, because they are not telephone services. The original RJ designations were defined in 47 CFR 68.502. (aka: FCC regulations part 68.502), but are now administered by one of the other standards bodies.
It so happens that RJ45 specifies a 8 position 8 contact keyed modular jack, similar to , but not compatible with the unkeyed 8p8c jack used for ethernet. The wiring pattern is different, requiring only 2 pairs, using pins 4/5, and 7/8. At the wall jack, pins 7/8 are terminated with a resistor, with the value derived from a chart based on the measured loop loss from that jack to the central office. The function is to tell the 2 wire leased line modem what transmit level to set. A properly wired 2 pair RJ45 cable will have connectors that will not physically fit into an ethernet jack (because of the key), and lacks electrical continuity on pins 1/2, 3/6, which are the ones used for 10baseT and 100baseT.
There are multiple RJ designations using the same physical connector, wired in different patterns, which may or may not be electrically compatible with each other.
6p6c - RJ11, Rj12, Rj13, RJ14, RJ25, RJ17 (and others)
8p8c (keyed) - RJ45, Rj47, RJ48 (and others)
8p8c (unkeyed) - RJ61, 10baseT/100baseT, Token Ring, EIA/TIA 568A/B (and others)
For instance, RJ11, RJ12, RJ13, and RJ14 all use the same basic jack (6p6c). RJ11 uses only pins 3/4 for a POTS line. RJ14 uses 3/4, and 2/5 for 2 POTS lines. RJ12 and RJ13 use 3/4 for a POTS line, and 2/5 for A-lead control (basically a contact closure). If you plug a phone wired for RJ12/RJ13 into a jack wired for RJ14, you will short out the second POTS line whenever the phone is taken off-hook. The only difference between RJ12 and RJ13 is which side of the key equipment the POTS line is sourced from.
The IT folks somewhere along the line, saw the 8p8c jacks used in their intended application (probably a leased line modem), and made the assumption that the connectors carried the designation, when in fact the designation defines both physical connector, and wiring.
The same thing happened with "DB-9" connectors, where somebody assumed that the 9 pin D-sub connector carried the same DB-25 designation as it's 25 pin brother.. (it doesn't) The 9 pin D-sub is actually a DE-9, since it uses a size E shell, and contains 9 pins. The common sizes are DA-15, DB-25, DC-37, DD-50, and DE-9, but there are other variations such DB-13W3 (Sun Monitors), etc.
See the ITT Canon catalog if you don't believe me. They were the original manufacturer. My hardcopy dates to 1971, and I have seen earlier editions. They all agree with the current pdf.
It's kind of like calling all bleach "Clorox", all photocopiers "Xerox", and all cola "Coke".
But anyway.. Cat6 is a waste.. it is larger (23 awg instead of 24 awg), the pairs are bonded, making it a pain to terminate, and it's generally a royal PITA. Use cat5e, and be happy, unless you are planning on running 10gigE. |
