Exhibit 4.1
                                                                     -----------

                       $300,000 NEGOTIABLE PROMISSORY NOTE
                       -----------------------------------

                                                              December 30, 2003
                                                              -----------------


         For value received, on December 29, 2005, General DataComm Industries,
Inc, having an office at 6 Rubber Avenue, Naugatuck CT 06770 ("Payor"), promises
to pay to the order of Howard S. Modlin, having an office at 445 Park Avenue,
15th floor, New York, New York 10022 ("Payee"), with interest at the rate of 10%
per annum on the unpaid balance thereof from December 30, 2003, the principal
sum of $300,000 in lawful money of the United States of America. This Note may
be prepaid at any time without penalty or premium. Interest which accrues during
each calendar month shall be paid on the first day of the following calendar
month during the term of this Note except the first interest payment shall be
made May 1, 2004.

         1.       Payment of this Note is unconditional and shall be made
without defense, counterclaim or offset, any defense to be asserted in a
separate suit. If payment is not made at maturity or upon the occurrence of a
Default, then interest shall accrue from such date until paid in full at the
rate of 12% per annum or the maximum permitted by law, whichever is less. This
Note is secured by a security agreement dated this date.

            2.    (a) At the option of the Payee or holder the principal amount
of this Note may be converted in whole or in part into Common Stock of the Payor
at the conversion price of $2.12 per share by written notice designating the
amount thereof being converted in minimum multiples of $10,000 principal amount
or integral multiples thereof. The Payee or holder acknowledges any shares of
Common Stock issued on conversion will not be registered under the Securities
Act of 1933, as amended and must be held for investment without a view to
distribution and the certificates for such shares shall bear a restrictive
legend therefor. The Payor shall issue a replacement note for this Note in the
event of any conversion for the remaining balance thereof

                  (b) (a) If additional shares of Common Stock are issued by the
Payor pursuant to a stock split or stock dividend in excess of 5% in any one
fiscal year of the Payor, the number of shares of Common Stock then issuable on
conversion shall be increased proportionately with no increase in the principal
amount of this Note being converted. In the event that the shares of common
stock of the Payor are reduced at any time by a combination of shares, the
number of shares of common stock then issuable on conversion herein shall be
reduced proportionately with no reduction in the principal amount of this Note
being converted. If the Payor shall be reorganized, consolidated or merged with
another corporation, or if all or substantially all of the assets of the Payor
shall be sold or exchanged, the Payee shall, at the time of issuance of the
stock under such a corporate event, be entitled to receive upon the conversion
of this Note, the same number and kind of shares of stock or the same amount of
property, cash or securities as he would have been entitled to receive upon the

                                        3
<PAGE>

happening of any such corporate event as if he had been, immediately prior to
such event, the holder of the number of shares receivable on conversion of this
Note.

           3.     The term "Default" as used herein shall mean the failure of
Payor to pay the principal or interest on this Note when due or the failure of
Payor to perform any other obligation (including the obligations under
Paragraphs 2(a) or (b) when required, or the security agreement securing this
Note or if an Event of Default exists under the Payor's Loan and Security
Agreement with Ableco Finance LLC and such indebtedness is accelerated.

           4.     Payor agrees to pay all costs and expenses of collection,
including reasonable attorney's fees, in the event of acceleration of this Note
by Payee or holder following Default.

           5.     Presentation for payment, notice of dishonor, protest and
notice of protest are hereby waived.

           6.     This Note shall be governed by the laws of the State of
Connecticut. The Payor of this Note hereby submits to the exclusive jurisdiction
of the courts of general jurisdiction of the State of Connecticut , and hereby
waives, and agrees not to assert, as a defense in any action, suit or proceeding
for the interpretation or enforcement of this Note, that it is not subject
thereto or that such action, suit or proceeding may not be brought or it is not
maintainable in such courts, or that this Note may not be enforced in or by such
courts, or that the suit, action or proceeding is brought in an inconvenient
forum, or that the venue of the suit, action or proceeding is improper. Service
of process with respect thereto may be made upon Payor by mailing a copy thereof
by registered or certified mail, postage prepaid, to such party at its address
as provided above.


                                       GENERAL DATACOMM INDUSTRIES, INC.

                                       BY: /s/ WILLIAM G. HENRY
                                           -------------------------------------
                                           William G. Henry
                                           Title: Vice President, Finance
                                           and Administration

                                        4