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                                                                    Exhibit 10.1

                                 PROMISSORY NOTE


$286,000                                             October 26, 2000
                                               North Andover, Massachusetts


     FOR VALUE RECEIVED, the undersigned, Interspeed, Inc., a Delaware
corporation (the "Borrower"), hereby promises to pay to the order of Brooktrout,
Inc., the principal sum of TWO HUNDRED EIGHTY-SIX THOUSAND DOLLARS ($286,000),
together with interest on the unpaid principal balance from time to time
outstanding from the date hereof and until the entire principal balance is paid
in full, at a variable rate equal to the current prime rate per annum of Silicon
Valley Bank (the "Prime Rate"), so long as payment is made before the Maturity
Date specified below, and (b) five percent (5%) per annum in excess of the Prime
Rate for any period that any such amount remains unpaid (i) after the Maturity
Date or (ii) upon the occurrence and during the continuance of any Default (as
defined herein), but in either event, not greater than the highest rate
permitted by applicable law. Any interest accruing hereunder that remains unpaid
at the Maturity Date and the end of each calendar month thereafter shall be
added to principal and shall thereafter bear interest as provided herein.

     The entire principal balance hereof and all interest thereon shall be due
and payable in full on the earlier of demand or on November 30, 2000 (the
"Maturity Date"), provided that, upon the occurrence of a Default, the entire
principal balance and all accrued interest shall become immediately due and
payable in full. Notwithstanding the foregoing, the Borrower shall be required
to pay in full the entire principal balance hereof and all accrued interest
immediately upon the closing by Borrower of the proposed $2,500,000 secured
revolving credit facility with Brooktrout, Inc.

     Principal, interest and all other amounts due under this Promissory Note
shall be payable to the original holder of this Promissory Note at its principal
offices, 250 First Avenue, Suite 300, Needham, MA 02494-2814, or at such other
address as the then holder of this Promissory Note (the "Holder") has from time
to time designated in writing to the Borrower.

     The occurrence of any of the following events shall constitute a "Default"
hereunder: (i) commencement of proceedings under the Bankruptcy Code or any
insolvency or similar law by the Borrower; (ii) commencement of any such
proceedings against the Borrower which are not dismissed within 60 days after
commencement; (iii) the appointment of a trustee, receiver, custodian,
liquidator or other similar official with respect to the Borrower or any
substantial part of the Borrower's property; or (iv) an assignment for the
benefit of creditors of the Borrower.

     The Borrower hereby waives presentment, demand, notice, protest and other
demands and notices in connection with the delivery, acceptance or enforcement
of this Promissory Note.

     No delay or omission on the part of the Holder in exercising any right
hereunder shall operate as a waiver of such right or of any other right under
this Promissory Note, and a waiver, delay or


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omission on any one occasion shall not be construed as a bar to or waiver of any
such right on any future occasion.

     If the Holder is required to commence legal proceedings or incur any other
cost to collect amounts due and payable, Borrower shall be liable to pay or
reimburse the Holder for all reasonable costs and expenses incurred in
connection with the collection of such amounts and any such legal proceedings.

     This Promissory Note shall be deemed to be under seal, and all rights and
obligations hereunder shall be governed by the laws of the Commonwealth of
Massachusetts.


                                             INTERSPEED, INC.


                                             By: /s/ Rajeev Agarwal
                                                 ------------------
                                                 Rajeev Agarwal, President


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