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                                                                    Exhibit 10.1

AMENDED AND RESTATED PROMISSORY NOTE (NO. 1)


$*****                                              Pleasanton, California
------
                                                                 May 13, 2002

         FOR VALUE RECEIVED, OASYS TELECOM, INC., a California corporation
("Borrower"), HEREBY UNCONDITIONALLY PROMISES TO PAY to the order of LARSCOM
INCORPORATED, a Delaware corporation ("Lender"), on the Maturity Date the
principal sum of ***** ($*****), together with accrued interest thereon.

         For the purposes of this Amended and Restated Promissory Note (this
"Note"): (a) the "Maturity Date" shall mean the first to occur of: (i) a
Liquidation Event, or (ii) May 13, 2004; and (b) "Liquidation Event" shall mean
any of the following events to the extent occurring prior to the first
anniversary of this Note: (i) the acquisition of Borrower (or any person
controlling Borrower), directly or indirectly, and whether through, merger,
consolidation, combination, reorganization, stock purchase or otherwise by any
one or more of the Adverse Persons; or (ii) one or more Adverse Persons (whether
or not acting in concert) shall, directly or indirectly, in one or more
transactions, acquire control of Borrower, or any other person controlling
Borrower, or acquire all or substantially all of the assets of Borrower. All
capitalized terms not otherwise defined in this Note shall have the meaning
ascribed to them in that certain Restructuring Agreement between Borrower and
Lender dated as of May 13, 2002 (as amended, restated or otherwise modified from
time to time, the "Restructuring Agreement").

         1. Amendment and Restatement.
            -------------------------

         This Note, together with the Amended and Restated Promissory Note (No.
2) of even date herewith between the parties (the "Additional Note"), constitute
an amendment and restatement of those certain Convertible Promissory Notes dated
September 7, 2001, September 25, 2001, October 26, 2001, December 17, 2001, and
December 27, 2001 respectively (the "Original Notes") issued in favor of Lender
pursuant to that certain Note and Warrant Purchase Agreement dated as of
September 7, 2001, between Borrower and Lender. This Note represents an
amendment and restatement of certain of the obligations represented by the
Original Notes and is not an accord and satisfaction, a novation or an
extinguishment of the obligations represented by the Original Notes, which
obligations have not been repaid but continue as represented by this Note and
the Additional Note.

         2. Interest.
            --------

         The Borrower further promises to pay interest on the outstanding
principal amount of this Note from the date hereof until repayment (whether at
stated maturity, by acceleration or otherwise), at a rate per annum equal at all
times to ***** (*****%). All interest accruing hereunder shall be compounded
annually, commencing on the first anniversary hereof and shall be payable on the
Maturity Date (unless earlier accelerated in accordance with the terms hereof).
All computations of interest shall be made on the basis of a year of 365 or 366
days, as the case may be, for the actual number of days occurring in the period
for which such interest is payable.

         3. Payments.
            --------

Confidential treatment has been requested for portions of this exhibit. The copy
herewith omits the information subject to the confidentially request. Omissions
are designated as *****. A complete version of this exhibit has been filed
separately with the Securities and Exchange Commission.

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         (a) Borrower shall make all payments hereunder for the account of
Lender at Larscom Incorporated, 1845 McCandless Drive, Milpitas, California
95035, Attention: Chief Financial Officer, or to such other address as Lender
shall notify Borrower. All payments shall be in lawful money of the United
States and in same day or immediately available funds not later than 12:00 noon
(Pacific Time) on the date due. Each payment by or on behalf of Borrower shall
be applied: first, to fees, costs, expenses and other amounts (other than
principal and interest), if any, payable under the Restructuring Agreement and
this Note; second, to accrued and unpaid interest; and third, to principal.

         (b) Whenever any payment hereunder shall be stated to be due, or
whenever any interest payment date or any other date specified hereunder would
otherwise occur, on a day other than a Business Day (as defined below), then,
except as otherwise provided herein, such payment shall be made, and such
interest payment date or other date shall occur, on the next succeeding Business
Day, and such extension of time shall in such case be included in the
computation of payment of interest hereunder. For the purposes of this Note,
"Business Day" means a day (i) other than Saturday or Sunday, and (ii) on which
commercial banks are open for business in San Francisco, California.

         (c) All payments hereunder shall be made unconditionally in full
without deduction, setoff, counterclaim or other defense.

         4. Prepayments.
            -----------

         This Note may be prepaid by the Borrower, in whole but not in part, at
any time, on or after November 13, 2002, (the "Prepayment Period"), without
penalty or premium, by the payment to Lender of an amount equal to $***** (the
"Prepayment Amount"). Payment of the Prepayment Amount in accordance with this
Section 4 shall be a full and complete discharge of all amounts owing in respect
of this Note and shall constitute a complete discharge thereof. In the event
that the Borrower shall have prepaid the entire amount of this Note in
accordance with this Section 4, the Lender will promptly deliver the original
Note to the Borrower and, in the event that this Note and the Additional Note
shall have been fully paid or prepaid, that certain Intellectual Property
Security Agreement between the parties of even date herewith shall terminate and
the security interest granted thereunder shall be deemed to be released.
Notwithstanding the foregoing, the Borrower shall not be entitled to prepay this
Note at any time during the Prepayment Period so long as: (i) any Event of
Default pursuant to Section 8(b) or 8(d) remains outstanding, or (ii) or any
Liquidation Event shall have occurred.

         5. Highest Lawful Rate.
            -------------------

         In the event that, contrary to the intent of Lender and Borrower,
Borrower pays interest under this Note and it is determined that such interest
rate was in excess of the then legal maximum rate, then that portion of the
interest payment representing an amount in excess of the then legal maximum rate
shall be deemed a payment of principal and applied against the principal then
due under this Note.

         6. Covenants.
            ---------

         Until the termination of this Note and the indefeasible payment in
accordance with the terms hereof, Borrower shall promptly notify the Lender of
the occurrence of any Event of Default (as defined below) of which the Borrower
has knowledge or becomes aware, by a statement of the president or chief
executive officer or chief financial officer of the Borrower setting forth
details of such Event of Default and the action that the Borrower proposes to
take with respect thereto.

         7. Representations and Warranties.
            ------------------------------

         Borrower represents and warrants to Lender that:


***** Confidential treatment has been requested for the redacted portions. The
confidential redacted portions have been filed separately with the Securities
and Exchange Commission.

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         (a) Borrower is a corporation duly organized, validly existing and in
good standing under the law of the jurisdiction of its incorporation and has all
requisite corporate power and authority to execute, deliver and perform its
obligations under the Restructuring Agreement and this Note (collectively, the
"Note Documents").

         (b) The execution, delivery and performance by Borrower of the Note
Documents have been duly authorized by all necessary corporate action of
Borrower, and the Note Documents constitute the legal, valid and binding
obligations of Borrower, enforceable against Borrower in accordance with their
terms, except as limited by applicable bankruptcy, insolvency, reorganization,
moratorium or other laws of general application relating to the rights of
creditors generally or the effect of equitable principles which limit the
availability of equitable remedies.

         (c) No authorization, consent, approval, license, exemption of, or
filing or registration with, any governmental authority or agency, or approval
or consent of any other person or entity, is required for the due execution,
delivery or performance by Borrower of the Note Documents.

         (d) None of the documents or materials relating to the Borrower and its
subsidiaries provided to the Lender in connection with the Note Documents
contains any untrue statement of material fact or omits to state any fact
necessary in order to make the statements contained therein not materially
misleading.

         8. Events of Default.
            -----------------

         The occurrence of any one or more of the following events shall
constitute an "Event of Default" hereunder:

         (a) Borrower shall fail to pay any principal or other amount payable
under any Note Document when due; or

         (b) Borrower shall fail to perform any of its other covenants,
obligations or agreements contained in (i) any Note Document, or (ii) Section
3.1 or 7.3 of the License Agreement dated as of May 13, 2002 between the
Borrower and Lender (as amended, restated or otherwise modified from time to
time, the "License Agreement"), or (iii) Section 9 or 10 of the Supply Agreement
dated as of May 13, 2002 between the Borrower and Lender (as amended, restated
or otherwise modified from time to time, the "Supply Agreement"); and in any
such case such failure shall continue for thirty (30) days after the date on
which Borrower receives notice of such failure; or

         (c) Any representation, warranty, certificate, or other statement
(financial or otherwise) made or furnished by or on behalf of Borrower in
writing to Lender in connection with any Note Document shall have been false or
incorrect, in any material respect, when made or deemed made; or

         (d) Any Note Document or the License Agreement shall cease to be, or
shall be asserted by anyone in the context of any bankruptcy proceeding or
assignment for the benefit of creditors not to be, a legal, valid and binding
obligation of Borrower, enforceable in accordance with its terms; provided,
however, that any such default shall be considered to have been cured in the
event that it shall have been finally determined by a court of competent
jurisdiction that such assertion is unsuccessful and the Note Document or
License Agreement (as applicable) is valid and subsisting.

                  Upon the occurrence and during the continuation of any Event
of Default: (a) the Lender may, at any time, declare all unpaid amounts owing or
payable under the Note Documents to be immediately due and payable without
presentment, demand, protest or any other notice of any kind, all of which are
hereby expressly waived by Borrower; and (b) the Lender may exercise all rights
and remedies available to Lender under the Note Documents, applicable law or
otherwise, without presentment, demand, protest or any other notice of any kind,
all of which are hereby expressly waived by Borrower. The rights and remedies
under the Note Documents are cumulative and not exclusive of any rights,
remedies, powers and privileges that may otherwise be available to the Lender.

                  This Note is secured by that certain Intellectual Property
Security Agreement dated as of even date herewith between Borrower and Lender.

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         9. Costs and Expenses.
            ------------------

         Borrower agrees to pay on demand all costs and expenses of Lender, and
the reasonable fees and disbursements of counsel, in connection with (i) any
amendments, modifications or waivers of the terms of the Note Documents
requested or initiated by Borrower, and (ii) the enforcement or attempted
enforcement of, and preservation of any rights or interests under the Note
Documents, including in any out-of-court workout or other refinancing or
restructuring or in any bankruptcy case. Any amounts payable to Lender pursuant
to this Section 9 if not paid upon demand shall bear interest from the date of
such demand until paid in full at the rate of ten percent (10%) per annum.

         10. Severance.
             ---------

         Whenever possible, each provision of the Note shall be interpreted in
such manner as to be effective and valid under all applicable laws and
regulations. If, however, any provision of this Note shall be prohibited by or
invalid under any such law or regulation in any jurisdiction, it shall, as to
such jurisdiction, be deemed modified to conform to the minimum requirements of
such law or regulation, or, if for any reason it is not deemed so modified, it
shall be ineffective and invalid only to the extent of such prohibition or
invalidity without affecting the remaining provisions of this Note, or the
validity or effectiveness of such provision in any other jurisdiction.

         11. No Waiver.
             ---------

         Any term, covenant, agreement or condition of this Note may be amended
or waived if such amendment or waiver is in writing and is signed by Borrower
and Lender. No failure or delay by Lender in exercising any right or remedy
under any Note Document shall operate as a waiver thereof or of any other right
or remedy nor shall any single or partial exercise of any such right or remedy
preclude any other further exercise thereof or of any other right or remedy. The
acceptance at any time by Lender of any past-due amount hereunder shall not be
deemed to be a waiver of the right to require prompt payment when due of any
other amounts then or thereafter due and payable. Unless otherwise specified in
such waiver or consent, a waiver or consent given hereunder shall be effective
only in the specific instance and for the specific purpose for which given.

         12. Successors and Assigns.
             ----------------------

         The Note Documents shall be binding upon and inure to the benefit of
Borrower, Lender, and their respective successors and permitted assigns. Either
party may at any time assign or otherwise transfer to any other person or entity
all or part of its rights or obligations under the Note Documents in connection
with an acquisition of all or substantially all of its assets or businesses or
acquisition of a controlling interest in its equity securities or in connection
with a merger, consolidation, reorganization or other like transaction. Except
as provided herein, neither party may assign or transfer any of its rights or
obligations under the Note Documents without the prior written consent of the
other party, which consent shall not to be unreasonably withheld (and any
purported assignment without such consent shall be void).


         13. No Benefit.
             ----------

         Nothing expressed in or to be implied from this Note is intended to
give, or shall be construed to give, any person or entity other than the parties
hereto and their permitted successors and assigns hereunder any benefit or legal
or equitable right, remedy or claim under or by virtue of this Note or under or
by virtue of any provision herein.

         14. Miscellaneous.
             -------------

         (a) The words "hereof," "herein," "hereunder" and similar words refer
to this Note as a whole and not to any particular provision of this Note.

         (b) Borrower hereby waives presentment, demand, protest, notice of
dishonor and all other notices, except as expressly provided herein, any release
or discharge arising from any extension of time, discharge of a prior party, or
other cause of release or discharge other than indefeasible payment in
accordance with the terms hereof.

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         15. Notices.
             -------

         (a) All notices and other communications provided for hereunder shall,
unless otherwise stated herein, be in writing (including by facsimile and
electronic mail) and mailed, sent or delivered to the respective parties hereto
as follows (or at or to such other address as shall be designated by any party
in a written notice to the other parties hereto):

If to Lender:         Larscom Incorporated
                      1845 McCandless Drive
                      Milpitas, CA  95035
                      Facsimile: (408) 956-0998
                      Attention: Chief Financial Officer

With a copy to:       Brobeck, Phleger & Harrison LLP
                      2000 University Avenue
                      East Palo Alto, CA  94303
                      Facsimile: (650) 331-8100
                      Attention: Jonathan P. Shanberge, Esq.

If to Borrower:       Oasys Telecom, Inc.
                      7060 Koll Center Parkway, Suite 340
                      Pleasanton, CA  94566
                      Facsimile: 925) 462-3338
                      Attention: Gerard Miille
                                 President and Chief Executive Officer


         (b) All such notices and communications shall be effective (i) if
delivered by hand, upon delivery; (ii) if sent by mail, upon the earlier of the
date of receipt or five Business Days after deposit in the mail, first class (or
air mail, with respect to communications to be sent to or from the United
States), postage prepaid; (iii) if sent by overnight courier, one day after
deposit with a nationally recognized and reputable overnight courier, specifying
next day delivery, with written verification of receipt, and postage prepaid;
and (iv) if sent by facsimile or electronic mail, when sent.

         16. Law and Jurisdiction.
             --------------------

         (a) This Note shall be construed in accordance with and governed by the
laws of the State of California, excluding conflict of law principles. Each
party hereby consents to the institution and resolution of any action or
proceeding of any kind or nature with respect to or arising out of this Note and
the other Note Documents in the state and federal courts located within Santa
Clara county or the Northern District, respectively, of the State of California.

         (b) The Borrower and Lender hereby agree to waive their respective
rights to a trial by jury of any claim or cause of action based upon or arising
out of or related to the Note Documents or the transactions contemplated thereby
in any action, proceeding or other litigation of any type brought by any of the
parties against any other party. The Borrower and Lender hereby agree that any
such claim or cause of action shall be tried by a court trial without a jury.
Without in any way limiting the foregoing, the Borrower and Lender further agree
that their respective right to a trial by jury is waived by operation of this
section as to any action, counterclaim or other proceeding that seeks, in whole
or in part, to challenge the validity or enforceability of this Note, the other
Note Documents or any provision hereof or thereof.

[Remainder of page intentionally left blank]

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         IN WITNESS WHEREOF, the undersigned duly authorized officer of Borrower
has executed this Note as of the date first set forth above.

                                    "BORROWER"

                                    OASYS TELECOM, INC.



                                    By: /s/ Gerard Miille

                                    Name: Gerard Miille

                                    Title: President and Chief Executive Officer