Author: JP

In the mid 1960’s the Bell System companies used the 505A plug, a round connector with four prongs.  We’ve moved to the de facto standard of Registered Jacks.

Common Registered Jacks

Code	Connector	Usage
RJ2MB	50-pin micro ribbon	2–12 telephone lines with make-busy arrangement
RJ11(C/W)	6P2C	For one telephone line (6P4C if power on second pair)
RJ12(C/W)	6P6C	For one telephone line ahead of the key system
RJ13(C/W)	6P4C	For one telephone line behind the key system
RJ14(C/W)	6P4C	For two telephone lines (6P6C if power on third pair)
RJ15C	3-pin weatherproof	For one telephone line
RJ18(C/W)	6P6C	For one telephone line with make-busy arrangement
RJ21X	50-pin micro ribbon	For up to 25 lines
RJ25(C/W)	6P6C	For three telephone lines
RJ26X	50-pin micro ribbon	For multiple data lines, universal
RJ27X	50-pin micro ribbon	For multiple data lines, programmed
RJ31X	8P4C	Allows an alarm system to seize the telephone line to make an outgoing call during an alarm. Jack is placed ahead of all other equipment. (Only 4 conductors are used)
RJ38X	8P4C	Similar to RJ31X, with continuity circuit. If the plug is disconnected from the jack shorting bars allows the phone circuit to continue to the site phones. (Only 4 conductors are used)
RJ41S	8P8C, keyed	For one data line, universal (fixed loop loss and programmed)
RJ45S	8P8C, keyed	For one data line, with programming resistor
RJ48C	8P4C	For four-wire data line (DSX-1)
RJ48S	8P4C, keyed	For four-wire data line (DDS)
RJ48X	8P4C with shorting bar	For four-wire data line (DS1)
RJ49C	8P8C	For ISDN BRI via NT1
RJ61X	8P8C	For four telephone lines
RJ71C	50-pin micro ribbon	12 line series connection using 50-pin connector (with bridging adapter) ahead of customer equipment. Mostly used for call sequencer equipment.

Many of the basic names have suffixes that indicate subtypes:

• C: flush-mount or surface mount
• F: flex-mount
• W: wall-mount
• L: lamp-mount
• S: single-line
• M: multi-line
• X: complex jack

T1 Termination

An RJ-48 plug is often mistaken for RJ-45. On the outside, the two look identical—both are housed in miniature 8-position jacks. The difference is in the wire pairing. RJ-48 connectorIn RJ-48, two of the wires are for transmit, two are for receive, and two are for the drain. The last two wires are reserved for future use

 

 

Three subsets

There are three subsets within RJ-48: RJ-48C, RJ-48X, and RJ-48S. RJ-48C and RJ-48X are very similar, though RJ-48C is more common. Both use lines 1, 2, 4, and 5, and connect T1 lines. RJ-48X connectors, however, have shorting bars. RJ-48S uses lines 1, 2, 7, and 8, and generally connects 56K DDS lines.

Here’s how RJ-48C pinning compares to RJ-48S pinning:

Pin	RJ-48C	RJ-48S
1	Receive ring	Receive data +
2	Receive tip	Receive data –
3	No connection	No connection
4	Transmit ring	No connection
5	Transmit tip	No connection
6	No connection	No connection
7	No connection	Transmit data +
8	No connection	Transmit data –

(*T568B is equivalent to AT&T 258A so for reasons of tradition, it’s likely the wire scheme the telco is going to drop off)

 

DS0 / DDS Termination

The demarcation point (DMARC) is the point at which the public switched telephone network (PSTN)ends and connects with the customer’s on-premises wiring (called Inside Wire or IW.)  Don’t confuse this with a NIU, it’s the same but different.

For residential locations you might have started off with an old Western Electric Company (WECO) lightning protector:

 

After that they went to the carbon and porcelain blocks which were much smaller:

 They got fancy with mounts  & attached them to the side of your house:

Then we come to the modern Network Interface Device, Telephone Network Interface, NID, NI, dmarc:

 

Check out http://catalog.corning.com/CableSystems/en-US/catalog/CategoryBrowser.aspx?cid=network_interface_devices_nids_web

 

What about businesses?  Do they just have 66 of these on the wall, one for each line?

Don’t be crazy,  they use a 66 block / M-Block / B-Block as a type of punchdown block to terminate the line.

They could also have a 110 block:

 

 

http://pre-wire.tripod.com/interfaces_and_protectors.html

http://www.aflglobal.com/Products/Copper-Apparatus/Demarcation.aspx