Telecom Addressing Group
Philadelphia, PA

The present multi-tap protocol is suitable for short innocuous messages but for serious business messaging it is slow and inadequate. Although data-based search protocols are now included with most cellular phones they are designed for selecting and correcting recurrent words in simple messages. They are in adequate for simple business correspondence which generally involve punctuation and special symbols.
Because text-messaging is the fastest growing market in cellular phone usage, but one that totally neglects business text-messaging, a proprietary software protocol for serious text-messaging has been developed that employs a standard cellular phone keypad and permits unambiguous alphanumeric data input. This unique procedure denoted the Input Doublet Protocol allows rapid letter, number, punctuation and special symbol inputs as readily as would a full keyboard. The Input Doublet Protocol provides a fixed number of keystrokes per character and greater speed and convenience for text messaging.
This text-messaging protocol is compared in specifics with the conventional multi-tap protocol in common usage, particularly keystrokes required per character. There are no timing delays involved with the Input Doublet Protocol. Characters are displayed as rapidly as they are keyed.
For example, consider the following text-message sent from a field salesman to the home-office computer or office manager using a standard cellular phone:
While both the multi-tap and Input Doublet Protocols would display exactly the same message multi-tap would require a user with extraordinary patience to endure the timing-delay requirements of this poorly conceived procedure totally unsuitable for serious business messaging with its susceptibility to timing errors. In contrast the Input Doublet Protocol would accommodate this business message as rapidly as the characters are keyed in.
The Input Doublet Protocol is described in detail below.

Text messaging using the standard cellular keypad accounts for the most rapid growth of cellular phone usage. Yet text messaging using the standard multi-tap cellular keypad is a tedious process that is best avoided for serious cellular phone users. Not only do the number of keystokes differ for each letter depending on their position on each key.
Not only is their is no cadence established because the number of keystrokes differ but access to punctuation breaks the messaging stride. Hence there is no learning curve and a veteran text messaging user is only marginally faster in composing a message than a neophyte.
Moreover if the number of keystrokes per letter is delayed this timing error causes the wrong character to be displayed. For example to input the simple word
by multi-tap requires that the 2 key be actuated six times: three times for the letter C, once for the letter A and twice for the letter B. Accordingly
must be entered with the proper delay between groups, and this is a typical example. If the time delay between keystrokes is too short or keying rate too slow only nonsense results.
These timing errors are among the major drawbacks to multi-tap, even with data-based search protocols. The time delay can be almost as long as a second, followed by a beep, a difficulty in business text-messaging, partuclerly with its need for punctuation and special symbols. Consequently multi-tap is so time-consuming that special abbreviations are available to speed up messaging, requiring a data-base.
While there are available in the market dedicated text messaging devices using a full keyboard these are inconvenient for ordinary usage, expensive and generally bulkier than ordinary cellular phones. Their usage is restricted to those engaged in intense text messaging.
Considering conventional cellular phones, the evaluation of text-messaging protocols largely involves the establishment of a paradigm upon which their characteristics can be compared. The four principal criteria are as follows:
The first criteria measures typing rate, though reasonably quantitative, it is still depends highly on degree of skill.
The second criteria (KSPC) is an average over a message and measures the gross efficiency of data input (MacKenzie, 2002). The KSPC his been most widely studied and the easiest criteria to quantize (Hesselgren,Montnemery,Svensson,2003).
The third criteria would depend on establishing a typing cadence, which would be easiest with the same specific KSPC for each of the characters.
The fourth criteria is the principal limitation on input protocols: practicality. Some approaches will probably not prove commercially acceptable to established firms, such as requiring more than a single key to be depressed simultaneously, requiring high degree of ambidexterity, quite difficult while multi-tasking; or requiring a special key to differentiate between characters or the use of a stylus.
Most of the protocols being currently considered by those in the field of phone-human text-messaging interactions are compared below.
With few exceptions these protocols require either a fundamental change in the usual cellular phone configuration or would require a dictionary or data-base to speed up the text-messaging process. The problem with timing error is that a subsequent keystroke, struck too soon, causes an error in the message, slowing the CPS.
Consider now an advanced text messaging protocol using a standard cellular keypad and a fixed specific KSPC for all characters., thereby establishing a cadence and permitting a learning curve without requiring a dictionary or data-base to speed up the text-messaging process.

This proprietary approach to text messaging denoted the Input Doublet Protocol (IDP) is a software solution using the standard cellular keypad, allowing the user a comfortable transition to IDP. The IDP neither requires different numbers of keystrokes for each letter, nor is it susceptible to timing errors. Because IDP is not menu driven no dictionary or database is required.
The closest approach to IDP is Two-Key described above. Two-Key was originally considered promising because it permitted a fixed KSPC (Butts & Cockburn) , similarly to IDP but Two-Key cannot accommodate special symbols.
According to the IDP two keystrokes alone are required for each character whether letter, number, or punctuation (KSPC=2) to create a unique identifier:position doublet as shown below. The KSPC is essentially constant for all characters, allowing a cadence to be established to attain a higher CPS.
The identifier-position doublet is the basic unit of the IDP. The standard cellular phone uses twelve keys to specify the desired characters. The doublets permit the cellular keypad shown below to emulate a full keyboard. Each doublet specifies a single letter, number or symbol.
For example character a is located on key 2 in sequence position 1 as shown above. It is specified simply as doublet a1.
Character c is likewise located on key 2 but in sequence position 3. Hence it is specified simply as doublet c3.
Similarly n is located on key 6 in sequence position 2. Hence it is specified simply as doublet n2.
Using this protocol with just two keystrokes letter q can be identified as doublet q2
and z as doublet z4.
The actuation sequence for the doublets is shown in below.
The most important feature of the IDP is that the same number of keystrokes are required for each letter: a doublet allowing a rapid cadence to be established. Equally important, the sequence positions follows from the letters chosen. Thus 3 always follows c, 2 always follows n, 2 always follows q and 4 always follows z. Hence, the letters are mnemonics leading to the sequence positions. Accordingly, when key stroking the letter c is recalled as c3.
Hence a learning curve is established.

There are four identifier keys available not associated with keypad letters: '0', '1', '*' and '#'. Because there are twelve possible position keys, therefore 48 separate doublets are available to the IDP.
Using '0' key as the identifier the IDP can readily accommodate numerals.
For punctuation the '#' and the '1' keys can be used as identifiers.
Of course these doublets would ostensibly require memorization and therefore would be less often used, if at all, and probably of no consequence to most users. They would be important however for business and technical text messaging.
When used as doublets the identifier keys can act as function keys as shown.
For example, inputting ## displays all of the punctuation marks but with a significant difference than is now practiced using multi-tap. At present the punctuation marks are displayed and by scrolling the required mark is chosen, a procedure that is time consuming and interrupts the text messaging procedure and cadence. The #* doublet would display special keys such as ¥ or £ and other monetary symbols which are important for international business transactions for rapid unambiguous transmission, for example, of stock or commodity prices using a standard cellular phone.
With the IDP the associated doublet is displayed with each punctuation mark, which can then be directly entered. Hence, actuating the doublet ## or #* could display punctuation or special symbols. Evidently with usage the most common symbols would be recalled without the display. Again there is a distinct learning curve established.
For example the number $86,400 has seven characters, two of which are special symbol: '$' and ','. This would require the seven doublets 14 08 06 #2 04 00 00. The number 3.1416 has six characters and would require the six doublets 03 #3 01 04 01 06.

To compare the IDP with the conventional text-messaging protocol a sample message will be analyzed.
The message comprises 111 alphanumeric characters; 3 punctuation marks; 3 special symbols; and 21 spaces, all of which must be keyed in and displayed.
Using the conventional multi-tap text-messaging protocol the required keystrokes are as follows:
Scrolling is required for special symbols. For this conventional multi-tap message KSPC=2.24.
Using the IDP the required keystrokes are as follows:
For this IDP message KSPC=2.00.
The KSPC for the IDP is almost 15% more efficient than the multi-tap protocol. Moreover scrolling time is not counted with the conventional protocol, which would significantly decrease the multi-tap CPS count.

The IDP as described herein is superior in terms of convenience in learning and usage compared to other proposed approaches. The IDP requires no more than reprogramming text messaging mode of standard cellular phones. Accordingly, the IDP
The IDP is a very powerful proprietary means of using the telephone keypad for alphanumeric data input by emulating a full keyboard by use of doublets, eliminating the possibility of timing errors. The IDP would be comfortably used by present multi-tap users and can be programmed as a switchable option on cellular phones in text messaging mode. It is the serious users who would most appreciate the convenience of the IDP.


MacKenzie, I. S., & Soukoreff, R. W. (2002). Text entry for mobile computing: Models and methods, theory and practice. Human-Computer Interaction, 17, p 147

Butts L. & Cockburn A. (2005) Human-Computer interaction Lab. Canterbury University. New Zealand

Wigdor D. & Balakrishnan (2003) Using tilt for text input to mobile phones, Proc. UIST, ACM Press.

Dunlop, M. D. & Crossan, A. (2000), Predictive entry methods for mobile phones, Personal Technologies p. 134

ISO/IEC 9995-8 (1994) Information systems. Keyboard layouts for text and office systems (Part 8).

James, C. L. & Reischel, K. M. (2001), Text input for mobile devices: comparing model prediction to actual performance, Proc. of CHI2001, ACM, New York, p365

Silfverberg, M., MacKenzie, I. S. & Korhonen, P. (2000), Predicting text entry speed on mobile phones,
Proc of CHI2000, ACM, New York,p 9

Moishe Garfinkle, PhD
Telecom Addressing Group
Philadelphia, PA

(215) 235-5042