EXHIBIT 10.1
                           EXCEL SWITCHING CORPORATION

                             1997 STOCK OPTION PLAN


         1. PURPOSE. This 1997 Stock Option Plan (the "Plan") is intended to
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provide incentives: (a) to the officers and other employees of Excel Switching
Corporation (the "Company"), any present or future parent and any present or
future subsidiaries of the Company (collectively, "Related Corporations") by
providing them with opportunities to purchase stock in the Company pursuant to
options granted hereunder which qualify as "incentive stock options" ("ISO" or
"ISOs") under Section 422(b) of the Internal Revenue Code of 1986, as amended
(the "Code"); (b) to directors, officers, employees and consultants of the
Company and Related Corporations by providing them with opportunities to
purchase stock in the Company pursuant to options granted hereunder which do not
qualify as ISOs ("Non-Qualified Option" or "Non-Qualified Options"); (c) to
directors, officers, employees and consultants of the Company and Related
Corporations by providing them with awards of stock in the Company ("Awards");
and (d) to directors, officers, employees and consultants of the Company and
Related Corporations by providing them with opportunities to make direct
purchases of stock in the Company ("Purchases"). Both ISOs and Non-Qualified
Options are referred to hereafter individually as an "Option" and collectively
as "Options". Options, Awards and authorizations to make Purchases are referred
to hereafter collectively as "Stock Rights". As used herein, the terms "parent"
and "subsidiary" mean "parent corporation" and "subsidiary corporation",
respectively, as those terms are defined in Section 424 of the Code.

         2. ADMINISTRATION OF THE PLAN.
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         A. BOARD OR COMMITTEE ADMINISTRATION. The Plan shall be administered by
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      the Board of Directors of the Company (the "Board") or, subject to
      paragraph 2(D) (relating to compliance with Section 162(m) of the Code),
      by a committee appointed by the Board (the "Committee"). Hereinafter, all
      references in this Plan to the "Committee" shall mean the Board if no
      Committee has been appointed. Subject to ratification of the grant or
      authorization of each Stock Right by the Board (if so required by
      applicable state law), and subject to the terms of the Plan, the Committee
      shall have the authority to (i) determine the employees of the Company and
      Related Corporations (from among the class of employees eligible under
      paragraph 3 to receive ISOs) to whom ISOs may be granted, and to determine
      (from among the class of individuals and entities eligible under paragraph
      3 to receive Non-Qualified Options and Awards and to make Purchases) to
      whom Non-Qualified Options, Awards and authorizations to make Purchases
      may be granted; (ii) determine the time or times at which Options or
      Awards may be granted or Purchases made; (iii) determine the exercise
      price per share subject to each Option, which price shall not be less than
      the minimum price specified in paragraph 6, and the purchase price of
      shares subject to each Purchase; (iv) determine whether each Option
      granted shall be an ISO or a Non-Qualified Option; (v) determine (subject
      to paragraph 7) the time or times when each Option shall become
      exercisable and the duration of the exercise period; (vi) extend the
      period during 

 
                                      -2-

      which outstanding Options may be exercised; (vii) determine whether
      restrictions such as repurchase options are to be imposed on shares
      subject to Options, Awards and Purchases and the nature of such
      restrictions, if any, and (viii) interpret the Plan and prescribe and
      rescind rules and regulations relating to it. If the Committee determines
      to issue a Non-Qualified Option, it shall take whatever actions it deems
      necessary, under Section 422 of the Code and the regulations promulgated
      thereunder, to ensure that such Option is not treated as an ISO. The
      interpretation and construction by the Committee of any provisions of the
      Plan or of any Stock Right granted under it shall be final unless
      otherwise determined by the Board. The Committee may from time to time
      adopt such rules and regulations for carrying out the Plan as it may deem
      best. No member of the Board or the Committee shall be liable for any
      action or determination made in good faith with respect to the Plan or any
      Stock Right granted under it.

         B. COMMITTEE ACTION. The Committee may select one of its members as its
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      chairman, and shall hold meetings at such time and places as it may
      determine. Acts by a majority of the Committee, or acts reduced to or
      approved in writing by a majority of the members of the Committee, shall
      be the valid acts of the Committee. From time to time the Board may
      increase the size of the Committee and appoint additional members thereof,
      remove members (with or without cause) and appoint new members in
      substitution therefor, fill vacancies however caused, or remove all
      members of the Committee and thereafter directly administer the Plan.

         C. GRANT OF STOCK RIGHTS TO BOARD MEMBERS. Stock Rights may be granted
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      to members of the Board. All grants of Stock Rights to members of the
      Board shall in all other respects be made in accordance with the
      provisions of this Plan applicable to other eligible persons. Members of
      the Board who are either (i) eligible for Stock Rights pursuant to the
      Plan or (ii) have been granted Stock Rights may vote on any matters
      affecting the administration of the Plan or the grant of any Stock Rights
      pursuant to the Plan, except that no such member shall act upon the
      granting to himself of Stock Rights, but any such member may be counted in
      determining the existence of a quorum at any meeting of the Board during
      which action is taken with respect to the granting to him of Stock Rights.

         D. PERFORMANCE-BASED COMPENSATION. The Board, in its discretion, may
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      take such action as may be necessary to ensure that Stock Rights granted
      under the Plan qualify as "qualified performance-based compensation"
      within the meaning of Section 162(m) of the Code and applicable
      regulations promulgated thereunder ("Performance-Based Compensation").
      Such action may include, in the Board's discretion, some or all of the
      following (i) if the Board determines that Stock Rights granted under the
      Plan generally shall constitute Performance-Based Compensation, by a
      committee consisting solely of two or more "outside directors (as defined
      in applicable regulations promulgated under Section 162(m) of the Code),
      (ii) if any Non-Qualified Options with an exercise price less than the
      fair market value per share of Common Stock are granted under the Plan and
      the Board determines that such Options should constitute Performance-Based
      Compensation, such options shall be made exercisable only upon the
      attainment of a pre-established, objective performance goal established by
      the Committee, and such grant shall be submitted for, and 

 
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      shall be contingent upon shareholder approval and (iii) Stock Rights
      granted under the Plan may be subject to such other terms and conditions
      as are necessary for compensation recognized in connection with the
      exercise or disposition of such Stock Right or the disposition of Common
      Stock acquired pursuant to such Stock Right, to constitute Performance-
      Based Compensation.

         3. ELIGIBLE EMPLOYEES AND OTHERS. ISOs may be granted only to employees
            -----------------------------
of the Company or any Related Corporation. Non-Qualified Options, Awards and
authorizations to make Purchases may be granted to any director (whether or not
an employee), officer, employee or consultant of the Company or any Related
Corporation. Notwithstanding the foregoing, effective only on and after the date
of the Company's initial public offering, non-employee directors shall no longer
be eligible to participate in this Plan. The Committee may take into
consideration a recipient's individual circumstances in determining whether to
grant an ISO, a Non-Qualified Option or an authorization to make a Purchase.
Granting of any Stock Right to any individual or entity shall neither entitle
that individual or entity to, nor disqualify him from, participation in any
other grant of Stock Rights.

         4. STOCK. The stock subject to Options, Awards and Purchases shall be
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authorized but unissued shares of Common Stock of the Company, par value $.01
per share (the "Common Stock"), or shares of Common Stock reacquired by the
Company in any manner. The aggregate number of shares which may be issued
pursuant to the Plan is 3,000,000 shares, subject to adjustment as provided in
paragraph 13. If any Option granted under the Plan shall expire or terminate for
any reason without having been exercised in full or shall cease for any reason
to be exercisable in whole or in part, the shares subject to such Options shall
again be available for grants of Stock Rights under the Plan.

         The following provision shall be effective only on and after the date
of the initial public offering of shares of Common Stock of the Company pursuant
to the Securities Act of 1933, as amended. If any Option granted under the Plan
shall expire or terminate for any reason without having been exercised in full
or shall cease for any reason to be exercisable in whole or in part or shall be
repurchased by the Company, the shares subject to such Option shall be included
in the determination of the aggregate number of shares of Common Stock deemed to
have been granted to such employee under the Plan.

         5. GRANTING OF STOCK RIGHTS. Stock Rights may be granted under the Plan
            ------------------------
at any time on or after SEPTEMBER 16, 1997 and prior to SEPTEMBER 15, 2007. The
date of grant of a Stock Right under the Plan will be the date specified by the
Committee at the time it grants the Stock Right; provided, however, that such
date shall not be prior to the date on which the Committee acts to approve the
grant.

         6. MINIMUM OPTION PRICE; ISO LIMITATIONS.
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         A. PRICE FOR NON-QUALIFIED OPTIONS, AWARDS, AND PURCHASES. Subject to
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      paragraph 2(D) (relating to compliance with Section 162(m) of the Code),
      the exercise price per share specified in the agreement relating to each
      Non-Qualified Option granted and the 

 
                                      -4-

      purchase price per share of stock granted in any Award or authorized as a
      Purchase under the Plan shall in no event be less than the minimum legal
      consideration required therefor under the laws of any jurisdiction in
      which the Company or its successors in interest may be organized.

         B. PRICE FOR ISOS. The exercise price per share specified in the
            --------------
      agreement relating to each ISO granted under the Plan shall not be less
      than the fair market value per share of Common Stock on the date of such
      grant. In the case of an ISO to be granted to an employee owning stock
      possessing more than ten percent (10%) of the total combined voting power
      of all classes of stock of the Company or any Related Corporation, the
      price per share specified in the agreement relating to such ISO shall not
      be less than one hundred ten percent (110%) of the fair market value per
      share of Common Stock on the date of grant. For purposes of determining
      stock ownership under this paragraph, the rules of Section 424(d) of the
      Code shall apply.

         C. $100,000 ANNUAL LIMITATION ON ISO VESTING. Each eligible employee
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      may be granted options treated as ISOs only to the extent that, in the
      aggregate under this Plan and all incentive stock option plans of the
      Company and any Related Corporation, such ISOs do not become exercisable
      for the first time by such employee during any calendar year in a manner
      which would entitle the employee to purchase more than $100,000 in fair
      market value (determined at the time the ISOs were granted) of Common
      Stock in that year. Any options granted to an employee in excess of such
      amount will be granted as Non-Qualified Options, and the Company shall
      issue separate certificates to the optionee with respect to options that
      are Non-Qualified Options and Options that are ISOs.

         D. DETERMINATION OF FAIR MARKET VALUE. If, at the time an Option is
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      granted under the Plan, the Company's Common Stock is publicly traded,
      "fair market value" shall be determined as of the date of grant or, if the
      prices or quotes discussed in this sentence are unavailable for such date,
      the last business day for which such prices or quotes are available prior
      to the date such Option is granted and shall mean (i) the average (on that
      date) of the high and low prices of the Common Stock on the principal
      national securities exchange on which the Common Stock is traded, if the
      Common Stock is then traded on a national securities exchange; or (ii) the
      last reported sale price (on that date) of the Common Stock on the Nasdaq
      National Market, if the Common Stock is not then traded on a national
      securities exchange; or (iii) the average of the closing bid and asked
      prices last quoted (on that date) by an established quotation service for
      over-the-counter securities, if the Common Stock is not reported on the
      Nasdaq National Market. However, if the Common Stock is not publicly
      traded at the time an Option is granted under the Plan, "fair market
      value" shall be deemed to be the fair value of the Common Stock as
      determined by the Committee after taking into consideration all factors
      which it deems appropriate, including, without limitation, recent sale and
      offer prices of the Common Stock in private transactions negotiated at
      arm's length.

 
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         7. OPTION DURATION. Subject to earlier termination as provided in
            ---------------
paragraphs 9 and 10 or in the agreement relating to such Option, each Option
shall expire on the date specified by the Committee, but not more than (i) ten
years and one day from the date of grant in the case of Non-Qualified Options,
(ii) ten years from the date of grant in the case of ISOs generally, and (iii)
five years from the date of grant in the case of ISOs granted to an employee
owning stock possessing more than ten percent (10%) of the total combined voting
power of all classes of stock of the Company or any Related Corporation, as
determined under paragraph 6(B). Subject to earlier termination as provided in
paragraphs 9 and 10, the term of each ISO shall be the term set forth in the
original instrument granting such ISO, except with respect to any part of such
ISO that is converted into a Non-Qualified Option pursuant to paragraph 16.

         8. EXERCISE OF OPTION. Subject to the provisions of paragraphs 9
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through 12, 21 and 22 each Option granted under the Plan shall be exercisable as
follows:

         A. FULL VESTING OR PARTIAL VESTING. The Option shall either be fully
            --------------------------------
      exercisable on the date of grant or shall become exercisable thereafter in
      such installments as the Committee may specify.

         B. FULL VESTING OF INSTALLMENTS. Once an installment becomes
            ----------------------------
      exercisable it shall remain exercisable until expiration or termination of
      the Option, unless otherwise specified by the Committee or as otherwise
      provided in this Plan.

         C. PARTIAL EXERCISE. Each Option or installment may be exercised at any
            ----------------
      time or from time to time, in whole or in part, for up to the total number
      of shares with respect to which it is then exercisable.

         D. ACCELERATION OF VESTING. Subject to any accounting considerations
            -----------------------
      with respect to "Accounting for Business Combinations" pursuant to
      Accounting Principles Board Opinion No. 16, The Committee shall have the
      right to accelerate the date of exercise of any installment of any Option;
      provided that the Committee shall not accelerate the exercise date of any
      installment of any Option granted to any employee as an ISO (and not
      previously converted into a Non-Qualified Option pursuant to paragraph 16)
      if such acceleration would violate the annual vesting limitation contained
      in Section 422(d) of the Code, as described in paragraph 6(C).

         9. TERMINATION OF EMPLOYMENT. Unless otherwise specified in the
            --------------------------
Agreement relating to such ISO, if an ISO Optionee ceases to be employed by the
Company and all Related Corporations other than by reason of death or disability
as defined in paragraph 10, no further installments of his ISOs shall become
exercisable, and his ISOs shall terminate after the passage of ninety (90) days
from the date of termination of his employment, but in no event later than on
their specified expiration dates, except to the extent that such ISOs (or
unexercised installments thereof) have been converted into Non-Qualified Options
pursuant to paragraph 16. Employment shall be considered as continuing
uninterrupted during any bona fide leave of absence (such as those attributable
to illness, military obligations or governmental service) provided that the
period of such leave does not exceed ninety (90) days or, if longer, any period

 
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during which such Optionee's right to reemployment is guaranteed by statute or
by contract. A bona fide leave of absence with the written approval of the
Committee shall not be considered an interruption of employment under the Plan,
provided that such written approval contractually obligates the Company or any
Related Corporation to continue the employment of the Optionee after the
approved period of absence. ISOs granted under the Plan shall not be affected by
any change of employment within or among the Company and Related Corporations,
so long as the Optionee continues to be an employee of the Company or any
Related Corporation. Nothing in the Plan shall be deemed to give any grantee of
any Stock Right the right to be retained in employment or other service by the
Company or any Related Corporation for any period of time.

         10. DEATH; DISABILITY.
             -----------------

         A. DEATH. If an ISO Optionee ceases to be employed by the Company and
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      all Related Corporations by reason of his or her death, any ISO owned by
      such Optionee may be exercised, to the extent of the number of shares with
      respect to which he or she could have exercised it on the date of his or
      her death, by the estate, personal representative or beneficiary who has
      acquired the ISO by will or by the laws of descent and distribution, at
      any time prior to the earlier of (i) the specified expiration date of the
      ISO or (ii) 180 days from the date of the Optionee's death.

         B. DISABILITY. If an ISO Optionee ceases to be employed by the Company
            ----------
      and all Related Corporations by reason of his or her disability, such
      Optionee shall have the right to exercise any ISO held by him or her on
      the date of termination of employment, to the extent of the number of
      shares with respect to which he or she could have exercised it on that
      date, until the earlier of (i) the specified expiration date of the ISO or
      (ii) 180 days from the date of the termination of the Optionee's
      employment. For the purposes of the Plan, the term "disability" shall mean
      "permanent and total disability" as defined in Section 22(e)(3) of the
      Code or successor statute.

         11. ASSIGNABILITY. No Option shall be assignable or transferable by the
             -------------
Optionee except by will or by the laws of descent and distribution or in case of
Non-Qualified Options only, pursuant to a valid domestic relations order, and
during the lifetime of the Optionee each Option shall be exercisable only by him
or her.

         12. TERMS AND CONDITIONS OF OPTIONS. Options shall be evidenced by
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instruments (which need not be identical) in such forms as the Committee may
from time to time approve. Such instruments shall conform to the terms and
conditions set forth in paragraphs 6 through 11 hereof and may contain such
other provisions as the Committee deems advisable which are not inconsistent
with the Plan, including restrictions applicable to shares of Common Stock
issuable upon exercise of Options. In granting any Non-Qualified Option, the
Committee may specify that such Non-Qualified Option shall be subject to the
restrictions set forth herein with respect to ISOs, or to such other termination
and cancellation provisions as the Committee may determine. The Committee may
from time to time confer authority and responsibility on one or more of its own
members and/or one or more officers of the Company to execute and deliver such

 
                                      -7-

instruments. The proper officers of the Company are authorized and directed to
take any and all action necessary or advisable from time to time to carry out
the terms of such instruments.

         13. ADJUSTMENTS. Upon the occurrence of any of the following events, an
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Optionee's rights with respect to Options granted to him hereunder shall be
adjusted as hereinafter provided, unless otherwise specifically provided in the
written agreement between the Optionee and the Company relating to such Option:

         A. STOCK DIVIDENDS AND STOCK SPLITS. If the shares of Common Stock
            --------------------------------
      shall be subdivided or combined into a greater or smaller number of shares
      or if the Company shall issue any shares of Common Stock as a stock
      dividend on its outstanding Common Stock, the number of shares of Common
      Stock deliverable upon the exercise of Options shall be appropriately
      increased or decreased proportionately, and appropriate adjustments shall
      be made in the purchase price per share to reflect such subdivision,
      combination or stock dividend.

         B. CONSOLIDATIONS OR MERGERS. If the Company is to be consolidated with
            -------------------------
      or acquired by another entity in a merger or other reorganization in which
      the holders of the outstanding voting stock of the Company immediately
      preceding the consummation of such event, shall, immediately following
      such event, hold as a group, less than a majority of the voting securities
      of the surviving or successor entity, or in the event of a sale of all or
      substantially all of the Company's assets or otherwise (an "Acquisition"),
      the Committee or the board of directors of any entity assuming the
      obligations of the Company hereunder (the "Successor Board"), shall, as to
      outstanding Options, take one or more of the following actions: (i) make
      appropriate provision for the continuation of such Options by substituting
      on an equitable basis for the shares then subject to such Options the
      consideration payable with respect to the outstanding shares of Common
      Stock in connection with the Acquisition; or (ii) make appropriate
      provision for the continuation of such Options by substituting on an
      equitable basis for the shares then subject to such Options any equity
      securities of the successor corporation or such other securities as the
      Successor Board deems appropriate, the fair market value of which shall
      not materially exceed the fair market value of the shares of Common Stock
      subject to such Options immediately preceding the Acquisition; or (iii)
      upon written notice to the Optionees, provide that all Options must be
      exercised, to the extent then exercisable, within a specified number of
      days of the date of such notice, at the end of which period the Options
      shall terminate; or (iv) terminate all Options in exchange for a cash
      payment equal to the excess of the fair market value of the shares subject
      to such Options (to the extent then exercisable) over the exercise price
      thereof; or (v) accelerate the date of exercise of such Options or of any
      installment of any such Options; or (vi) terminate all Options in exchange
      for the right to participate in any stock option or other employee benefit
      plan of any successor corporation. The foregoing actions are subject in
      all instances to the approval of the Board of Directors and any accounting
      considerations for any acquisition which is treated as a "pooling of
      interests" transaction pursuant to the Accounting Principles Board (APB)
      Opinion No. 16, if any discretionary action by the Board of Directors
      would otherwise violate the accounting rules for treatment of the
      Acquisition as a "pooling of interests" under APB No. 16.

 
                                      -8-

         C. RECAPITALIZATION OR REORGANIZATION. In the event of a
            ----------------------------------
      recapitalization or reorganization of the Company (other than a
      transaction described in subparagraph B above) pursuant to which
      securities of the Company or of another corporation are issued with
      respect to the outstanding shares of Common Stock, an Optionee upon
      exercising an Option shall be entitled to receive for the purchase price
      paid upon such exercise the securities he or she would have received if he
      or she had exercised his or her Option prior to such recapitalization or
      reorganization.

         D. MODIFICATION OF ISOS. Notwithstanding the foregoing, any adjustments
            --------------------
      made pursuant to subparagraphs A, B or C with respect to ISOs shall be
      made only after the Committee, after consulting with counsel for the
      Company, determines whether such adjustments would constitute a
      "modification" of such ISOs (as that term is defined in Section 424 of the
      Code) or would cause any adverse tax consequences for the holders of such
      ISOs. If the Committee determines that such adjustments made with respect
      to ISOs would constitute a modification of such ISOs, or would cause
      adverse tax consequences to the holders, it may refrain from making such
      adjustments.

         E. DISSOLUTION OR LIQUIDATION. In the event of the proposed dissolution
            --------------------------
      or liquidation of the Company, each Option will terminate immediately
      prior to the consummation of such proposed action or at such other time
      and subject to such other conditions as shall be determined by the
      Committee.

         F. ISSUANCES OF SECURITIES. Except as expressly provided herein, no
            -----------------------
      issuance by the Company of shares of stock of any class, or securities
      convertible into shares of stock of any class, shall affect, and no
      adjustment by reason thereof shall be made with respect to, the number or
      price of shares subject to Options. No adjustments shall be made for
      dividends paid in cash or in property other than securities of the
      Company.

         G. FRACTIONAL SHARES. No fractional shares shall be issued under the
            -----------------
      Plan and the Optionee shall receive from the Company cash in lieu of such
      fractional shares.

         H. ADJUSTMENTS. Upon the happening of any of the foregoing events
            -----------
      described in subparagraphs A, B or C above, the class and aggregate number
      of shares set forth in paragraph 4 hereof that are subject to Stock Rights
      which previously have been or subsequently may be granted under the Plan
      shall also be appropriately adjusted to reflect the events described in
      such subparagraphs. The Committee or the Successor Board shall determine
      the specific adjustments to be made under this paragraph 13 and, subject
      to paragraph 2, its determination shall be conclusive.

If any person or entity owning restricted Common Stock obtained by exercise of a
Stock Right made hereunder receives shares or securities or cash in connection
with a corporate transaction described in subparagraphs A, B or C above as a
result of owning such restricted Common Stock, such shares or securities or cash
shall be subject to all of the conditions and restrictions 

 
                                      -9-

applicable to the restricted Common Stock with respect to which such shares or
securities or cash were issued, unless otherwise determined by the Committee or
the Successor Board.

         14. MEANS OF EXERCISING STOCK RIGHTS. A Stock Right (or any part or
             --------------------------------
installment thereof) shall be exercised by giving written notice to the Company
at its principal office address. Such notice shall identify the Stock Right
being exercised and specify the number of shares as to which such Stock Right is
being exercised, accompanied by full payment of the purchase price therefor
either (a) in United States dollars in cash or by check, or (b) at the
discretion of the Committee, through delivery of shares of Common Stock having a
fair market value equal as of the date of the exercise to the cash exercise
price of the Stock Right, or (c) at the discretion of the Committee, by delivery
of the grantee's personal recourse note bearing interest payable not less than
annually at no less than 100% of the lowest applicable Federal rate, as defined
in Section 1274(d) of the Code, or (d) at the discretion of the Committee and
consistent with applicable law, through the delivery of an assignment to the
Company of a sufficient amount of the proceeds from the sale of the Common Stock
acquired upon exercise of the Option and an authorization to the broker or
selling agent to pay that amount to the Company, which sale shall be at the
participant's direction at the time of exercise, or (e) at the discretion of the
Committee, by any combination of (a), (b), (c) and (d) above. If the Committee
exercises its discretion to permit payment of the exercise price of an ISO by
means of the methods set forth in clauses (b), (c), (d) or (e) of the preceding
sentence, such discretion shall be exercised in writing at the time of the grant
of the ISO in question. The holder of a Stock Right shall not have the rights of
a shareholder with respect to the shares covered by his Stock Right until the
date of issuance of a stock certificate to him for such shares. Except as
expressly provided above in paragraph 13 with respect to changes in
capitalization and stock dividends, no adjustment shall be made for dividends or
similar rights for which the record date is before the date such stock
certificate is issued.

         15. TERM AND AMENDMENT OF PLAN. This Plan was adopted by the Board as
             --------------------------
of SEPTEMBER 16, 1997, subject (with respect to the validation of ISOs granted
under the Plan) to approval of the Plan by the stockholders of the Company at
the next Meeting of Stockholders or, in lieu thereof, by unanimous written
consent. If the approval of stockholders is not obtained by SEPTEMBER 16, 1998,
any grants of Options under the Plan made prior to that date will be rescinded.
The Plan shall expire at the end of the day on SEPTEMBER 15, 2007 (except as to
Options outstanding on that date). Subject to the provisions of paragraph 5
above, Stock Rights may be granted under the Plan prior to the date of
stockholder approval of the Plan. The Board may terminate or amend the Plan in
any respect at any time, except that, without the approval of the stockholders
obtained within 12 months before or after the Board adopts a resolution
authorizing any of the following actions: (a) the total number of shares that
may be issued under the Plan may not be increased (except by adjustment pursuant
to paragraph 13); (b) the benefits accruing to participants under the Plan may
not be materially increased; (c) the requirements as to eligibility for
participation in the Plan may not be materially modified; (d) the provisions of
paragraph 3 regarding eligibility for grants of ISOs may not be modified; (e)
the provisions of paragraph 6(B) regarding the exercise price at which shares
may be offered pursuant to ISOs may not be modified (except by adjustment
pursuant to paragraph 13); (f) the expiration date of the Plan may not be
extended; and (g) the

 
                                      -10-

Board may not take any action which would cause the Plan to fail to comply with
Rule 16b-3. Except as otherwise provided in this paragraph 15, in no event may
action of the Board or stockholders alter or impair the rights of a grantee,
without his consent, under any Stock Right previously granted to him.

         16. CONVERSION OF ISOS INTO NON-QUALIFIED OPTIONS; TERMINATION OF ISOS.
             ------------------------------------------------------------------
Subject to paragraph 13(D), without the prior written consent of the holder of
an ISO, the Committee shall not alter the terms of such ISO (including the means
of exercising such ISO) if such alteration would constitute a modification
(within the meaning of Section 424(h)(3) of the Code). The Committee, at the
written request or with the written consent of any Optionee, may in its
discretion take such actions as may be necessary to convert such Optionee's ISOs
(or any installments or portions of installments thereof) that have not been
exercised on the date of conversion into Non-Qualified Options at any time prior
to the expiration of such ISOs, regardless of whether the Optionee is an
employee of the Company or a Related Corporation at the time of such conversion.
Such actions may include, but shall not be limited to, extending the exercise
period or reducing the exercise price of the appropriate installments of such
ISOs. At the time of such conversion, the Committee (with the consent of the
Optionee) may impose such conditions on the exercise of the resulting
Non-Qualified Options as the Committee in its discretion may determine, provided
that such conditions shall not be inconsistent with this Plan. Nothing in the
Plan shall be deemed to give any Optionee the right to have such Optionee's ISOs
converted into Non-Qualified Options, and no such conversion shall occur until
and unless the Committee takes appropriate action. Upon the taking of such
action, the Company shall issue separate certificates to the Optionee with
respect to Options that are Non-Qualified Options and Options that are ISOs.

         17. APPLICATION OF FUNDS. The proceeds received by the Company from the
             --------------------
sale of shares pursuant to Options granted and Purchases authorized under the
Plan shall be used for general corporate purposes.

         18. GOVERNMENTAL REGULATION. The Company's obligation to sell and
             -----------------------
deliver shares of the Common Stock under this Plan is subject to the approval of
any governmental authority required in connection with the authorization,
issuance or sale of such shares.

         19. WITHHOLDING OF ADDITIONAL INCOME TAXES. Upon the exercise of a
             --------------------------------------
Non-Qualified Option, the grant of an Award, the making of a Purchase of Common
Stock for less than its fair market value, the making of a Disqualifying
Disposition (as defined in paragraph 20), the making of a distribution or other
payment with respect to such stock or securities, or the vesting or transfer of
restricted Common Stock acquired on the exercise of a Stock Right hereunder, the
Company may withhold income and/or employment taxes in respect of amounts that
constitute compensation includible in gross income, or otherwise treated by law
as wages for withholding for income or employment tax purposes. The Committee in
its discretion may condition (i) the exercise of an Option, (ii) the grant of an
Award, (iii) the making of a Purchase of Common Stock for less than its fair
market value, or (iv) the vesting or transferability of restricted Common Stock
acquired by exercising a Stock Right, on the grantee's making satisfactory
arrangement for such withholding. Such arrangement may include payment 

 
                                      -11-

by the grantee in cash or by check of the amount of the withholding taxes or, at
the discretion of the Company, by the grantee's delivery of previously held
shares of Common Stock or the withholding from the shares of Common Stock
otherwise deliverable upon exercise of Option shares having an aggregate fair
market value equal to the amount of such withholding taxes. The use of any
method of payment other than by cash or check in some cases may require or cause
additional withholding obligations.

         20. NOTICE TO COMPANY OF DISQUALIFYING DISPOSITION. By accepting an ISO
             ----------------------------------------------
granted under the Plan, each ISO Optionee thereby agrees to notify the Company
in writing immediately after such Optionee makes a Disqualifying Disposition of
any Common Stock acquired pursuant to the exercise of an ISO. Generally, a
Disqualifying Disposition is any disposition (including any sale) of such Common
Stock occurring on or before the later of the date (a) two years after the date
the employee was granted the ISO, or (b) one year after the date the employee
acquired Common Stock by exercising the ISO.

         21. NO EXERCISE OF OPTION IF ENGAGEMENT OR EMPLOYMENT TERMINATED FOR
             ----------------------------------------------------------------
CAUSE. If the employment of the Optionee is terminated for "Cause," this option
- -----
shall terminate on the date of such termination and the Option shall thereupon
not be exercisable to any extent whatsoever. "Cause" is conduct, as determined
by the Board of Directors, involving one or more of the following: (i) gross
misconduct by the employee which is materially injurious to the Company; or (ii)
the commission of an act of embezzlement, fraud or deliberate disregard of the
rules or policies of the Company which results in material economic loss, damage
or injury to the Company; or (iii) the unauthorized disclosure of any trade
secret or confidential information of the Company or any third party who has a
business relationship with the Company or the violation of any noncompetition
covenant or assignment of inventions obligation with the Company; or (iv) the
commission of an act which induces any customer or prospective customer of the
Company to break a contract with the Company or to decline to do business with
the Company; or (v) the conviction of the employee of a felony involving any
financial impropriety or which would materially interfere with the employee's
ability to perform his or her services or otherwise be injurious to the Company;
or (vi) the failure of the employee to perform in a material respect his or her
employment obligations without proper cause. In making such determination, the
Board shall act fairly and in utmost good faith. For the purposes of this
Section 21, termination of employment shall be deemed to occur when the employee
receives notice that his employment is terminated.

         22. ACCELERATION AND VESTING OF OPTION FOR BUSINESS COMBINATIONS. Upon
             ------------------------------------------------------------
any merger, consolidation, sale of all (or substantially all) of the assets of
the Company, or other business combination involving the sale or transfer of all
(or substantially all) of the capital stock or assets of the Company in which
the Company is not the surviving entity, or, if it is the surviving entity, does
not survive as an operating going concern in substantially the same line of
business (an "Acquisition"), then the remaining unvested portions of any Option
outstanding to any Optionee shall, immediately prior to the consummation of any
of the foregoing events, become vested and immediately exercisable by the
Optionee according to the following formula and dependent upon the length of the
Optionee's continuous months of employment or engagement by the Company prior to
the consummation of the Acquisition, provided, however, 
                                     -----------------

 
                                      -12-

that this Section shall not apply to any reincorporation of the Company in a
different State pursuant to a migratory merger:

         For an ISO Optionee:

         (i) If the Optionee has been employed by the Company for 36 months or
more, then the remaining unvested portion of any Option held by such Optionee
shall become fully vested and exercisable.

         (ii) If the Optionee has been employed by the Company for more than 30
but less than 36 months, then 80% of the remaining unvested portion of any
Option held by such Optionee shall become fully vested and exercisable.

         (iii) If the Optionee has been employed by the Company for more than 24
but less than 30 months, then 50% of the remaining unvested portion of any
Option held by such Optionee shall become fully vested and exercisable.

         (iv) If the Optionee has been employed by the Company for more than 18
but less than 24 months, then 40% of the remaining unvested portion of any
Option held by such Optionee shall become fully vested and exercisable.

         (v) If the Optionee has been employed by the Company for more than 12
but less than 18 months, then 30% of the remaining unvested portion of any
Option held by such Optionee shall become fully vested and exercisable.

         (vi) If the Optionee has been employed by the Company for more than 6
but less than 12 months, then 20% of the remaining unvested portion of any
Option held by such Optionee shall become fully vested and exercisable.

         (vii) If the Optionee has been employed by the Company for more than 1
but less than 6 months, then 10% of the remaining unvested portion of any Option
held by such Optionee shall become fully vested and exercisable.

         For a Non-Qualified Option Optionee, the remaining unvested portion of
any Option held by such Optionee shall become fully vested and exercisable.

         23. GOVERNING LAW; CONSTRUCTION. The validity and construction of the
             ---------------------------
Plan and the instruments evidencing Stock Rights shall be governed by the laws
of the Commonwealth of Massachusetts or the laws of any jurisdiction in which
the Company or its successors in interest may be organized. In construing this
Plan, the singular shall include the plural and the masculine gender shall
include the feminine and neuter, unless the context otherwise requires.