Tip and Ring in Telecommunications
What is tip and ring?
Tip and ring are slang words referring to the wires that comprise telephone circuitry. In the earlier mechanical phone models, the plug is composed of electrical contacts – one located at the tip and the other on top of it known as the ring (LISCO RDSL Support, 2008). The tip is the electrically positive wire while the ring is the electrically negative wire (tech-FAQ.com, 2008).
Low amounts of voltage passes through one of the wires and is sufficient to make the phone ring. During the widespread use of switchboards by telephone operators, the tip and ring is also used to manually connect two different lines on the board. Static heard over the line by the operator when he inserts the tip into the line jack is an indicator that the particular line is busy. The tip and ring are the sending and receiving medium for signals to and from a phone unit.
Telephones work by using electricity to transmit sound from one phone to another. Because the tip and ring wires serves as both transmitter and receiver – receives the incoming signal and routes it to the earpiece and transmits the microphone signal or output downstream of the phone line, the telephone is referred to as a duplex apparatus. The tip and ring also supply DC current needed for the telephone electronics to work, AC current in order to trigger the ringer and a full duplex balanced bi-directional audio path (Klinger, 2002).
A balanced voice path on the tip and ring wires means that signals can travel long distances even without being shielded and is possible by the use of common mode rejection to eliminate interference generated on the two wires (Klinger, 2002). A two-wire to four-wire hybrid circuit is required for sending and receiving as it transforms the tip and ring into distinct transmit and receive sound paths (Klinger, 2002). However, hybrid circuits have mostly been replaced by integrated circuits.
Telephone Wires, Plugs, Jacks and Network Interface Device
Telephone wiring today consists of two or more strands of copper wire which are inter-twined in pairs where each pair constitutes one phone line (Gregory, 2004). Wires are twisted together in pairs to eliminate the possibility of multiple lines interfering with one other. In most telephone models today, wires have four strands or two pairs and permit the installation of two phone lines.
In a four-strand wiring, one phone line is made up of green and red wires to make the Christmas pair while black and yellow wires compose the Halloween pair or second phone line (Gregory, 2004). Telephone wiring can also come in six strands, eight strands or higher for use when three or more lines are needed. A third line is made up of blue and white wires. Green, black and blue are the tip wires while red, yellow and white are the ring wires. However, this color coding scheme is increasingly being replaced by other schemes associated with the use of newer UTP wiring technology or Category 5 UTP which carry more bandwidth (LANshack.com, 2008). These wires have one dominant color, have stripes as secondary colors and attach to pins. If the main color is white and the stripes are green then the wire color is white/green. In the diagram above, T refers to tip and R refers to ring.
Plugs, Jacks and Network Interface
Commonly used types of modular plugs or the male ends in telephone circuitry are the RJ-11 and the RJ-14 where the first employs two wires and is therefore a one-line plug and the second employs four wires and is a two-line plug (Gregory, 2004). Phone lines connect to a Central office (CO) line or Plain Old Telephone Service (POTS) line which links to the switching device of the telephone company and enables an individual subscriber to connect with others.
The CO line terminates in a box called the network interface device screwed outside the house or office and has modular test jacks from which to check if the line is live as well as terminal strips where internal wiring can be attached to (Gregory, 2004). After deciding on what topology the internal wiring would be, e.g. star topology, the POTS line’s tip wire is attached to the modular jack’s tip wire and the POTS line’s ring wire is attached to the modular jack’s ring wire. The colors of tip and ring wires serve as a guide and correct attachment should be observed to avoid reversing the polarity of the wires. The phone is then plugged to the jack or the female receptacle located on the wall and a dial tone should be expected.
The status of a telephone line differs according to what the subscriber as well as the telephone company (TELCO) does to the phone. The central office (CO) directs varying DC and AC voltages to the dual wire or tip and ring telephone circuit in the course of the different phases of making a call. When the phone is in idle mode, a -48(±6) Vdc in series with 500 watts to 2,500 watts is applied to the ring wire by the CO and at the same time, the tip line is terminated to ground with 0 watts to 710 watts (Solid State Optronics, 2008).
It is also worthy to note that on the average, there is a maximum of 1,300 watts external line resistance along the line from the CO to the end user. In the event that the phone receiver is removed from its hook, the CO switches to the dialing mode, applies a dial tone, a DC level of -43 to -79 volts in series with 200 watts (±50 watts) on ring wire and terminating the tip wire with the same electricity level as in ground state (Solid State Optronics, 2008).
After the call is answered and the subscribers are connected or during the talk phase, the DC voltage and ground state of the ring and tip wires respectively become steady and unchanged although the TELCO, based on its judgment, may transpose the polarity of the DC voltage directed to the ring wire. In order for the phone to ring, the TELCO directs 89(±2) Vrms at 20Hz atop the usual 48 Vdc bias (Solid State Optronics, 2008).
With regards to the DC signal, the AC ringing signal is applied to the “ring” lead and the standard specification for phone rings is a two-second burst after every 6 seconds (Solid State Optronics, 2008). When the telephone circuit is being tested for functioning, varying AC and DC test signals are directed by the TELCO over the connection to ascertain that the system is operational (Solid State Optronics, 2008). A diagram of the telephone circuit is provided below in the diagram below:
The Telephone Line Circuit
Tip and Ring and the Modem Circuit
An application of the tip and ring can also be observed in the conventional modem circuitry as illustrated below (Solid State Optronics, 2008):
The input consists of a regular and commonly used outlet which contains one lead for the tip and one for the ring. From the tip and ring is a Surge Protection device which functions to avert possible damages to the remaining components of the circuit in the event that temporary changes in the amount of current occur such as when lightning strikes or power crosses (Solid State Optronics, 2008).
The purpose of the Ring Detect device is to operate as a sensor providing signals to the modem when a ring signal is perceived by the CO. The ring signal is characterized as high voltage AC, is typically 48V DC applied on the CO DC battery and is transmitted with a frequency about 15.3 to 68.0Hz, has an RMS voltage of 40 to 150 volts and a specification of two second rings after every four seconds of silence (Solid State Optronics, 2008). The ring detection device is attached to modem’s input port and it is where ring signals are authenticated.
Meanwhile, the Hook Switch device triggers the connection of the tip and ring wires and like the Ring Detect, it is connected to a control unit (Solid State Optronics, 2008). This device is set off by either the modem or the subscriber when he makes a call or answers one when the phone unit rings. The on-hook or “line open” and off-hook or “line closed” states of the phone circuit are managed by the hook switch device through connecting with the modem (Solid State Optronics, 2008).
List of References
Gregory, H. (2004). The Basics of Telephone Wiring. Retrieved 26 October 2008 from http://telecom.hellodirect.com/docs/Tutorials/TelWiringBasics.1.040401.asp.
Klinger, J. (2002). Phone Line Basics – Revisited. Retrieved 26 October 2008 from http://www.jkaudio.com/article_10.htm.
LANshack.com (2008). How to Wire a Phone Jack. Retrieved 26 October 2008 from http://www.lanshack.com/wire_phone_jack.aspx.
LISCO RDSL Support (2008). Glossary: Tip and Ring. Retrieved 26 October 2008 from http://www.lisco.com/support/Reach/glossary.htm
Solid State Optronics (2008). Introduction to Telecommunications. Retrieved 26 October 2008 from http://www.ssousa.com/appnote015.asp.
Tech-FAQ.com (2008). How Do I Install Telephone Wiring?. Retrieved 26 October 2008 from http://www.tech-faq.com/telephone-wiring.shtml.