Document:

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                                                                   EXHIBIT 4.5

                       EXCHANGE NATIONAL BANCSHARES, INC.
                        INCENTIVE STOCK OPTION AGREEMENT

                  THIS AGREEMENT, made and entered into this _____ day of
_______________, ____ (the "Granting Date"), by and between EXCHANGE NATIONAL
BANCSHARES, INC., a Missouri corporation (the "Company"), and
______________________ (the "Optionee").

                  WITNESSETH:

                  WHEREAS, effective as of February 29, 2000, the Company
adopted an Incentive Stock Option Plan (the "Plan") pursuant to which the
Company was authorized to grant from time to time, on or prior to February 28,
2010, options to purchase shares of common stock of the Company ("ENB Common
Stock"), to key employees of the Company or of any of its subsidiaries, such
options to be granted to such persons who are eligible to receive options under
the Plan in such amounts and under such form of agreement as shall be determined
by the Committee pursuant to the Plan; and

                  WHEREAS, the Committee, as defined in the Plan, has determined
that the Optionee is a key employee of the Company or of one of its subsidiaries
and that the Optionee shall be granted an option to purchase shares of ENB
Common Stock on the terms and conditions herein set forth;

                  NOW, THEREFORE, in consideration of the mutual promises and
covenants herein contained and other good and valuable consideration provided by
the Optionee to the Company, the parties hereto do hereby agree as follows:

                  1.   Incorporation of Plan

                       All provisions of this Agreement and the rights of the
Optionee hereunder are subject in all respects to the provisions of the Plan and
the powers of the Committee therein provided.

                  2.   Grant of Option

                       Pursuant to the authorization of the Committee, and
subject to the terms, conditions and provisions contained in the Plan and this
Agreement, the Company hereby grants to the Optionee as a matter of separate
inducement and agreement in connection with the Optionee's employment, but not
in lieu of any salary or other compensation for the Optionee's services, the
right and option (the "Option") to purchase from the Company, at the times and
on the terms and conditions hereinafter set forth, all or part of an aggregate
of ___________ shares of ENB Common Stock at the purchase price of $______ per
share, which is the fair market value, as determined in accordance with Section
7 of the Plan, of ENB Common Stock on the Granting Date. Exercises of this
Option may be honored by issuing authorized and unissued shares of ENB Common
Stock or, at the election of the Company, by transferring shares of ENB Common
Stock which may at the time be held by the Company as treasury shares.

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                  3.   Terms of Option

                       The Option granted hereunder shall be exercisable
from time to time by the Optionee by the giving of written notice of exercise to
the Company in advance of an exercise date hereinafter set forth, specifying the
number of shares to be purchased, and by payment in full of the purchase price
therefor by either (i) cash or certified bank check to the order of the Company,
or (ii) shares of ENB Common Stock having a fair market value equal to the
purchase price on the exercise date and which have then been held by the
Optionee for at least six months (whether by the actual surrender of shares or,
subject to the conditions and limitations contained in the Plan, by the
affirmation and attestation of ownership of shares), subject, however, to the
following restrictions and to the restrictions set forth in the Plan:

                       (a) The Option shall be exercisable within a ten year
period beginning on the Granting Date and only in the following maximum amounts:
(i) none until the expiration of one year from the Granting Date (the waiting
period); (ii) ______ shares after the expiration of one year from the Granting
Date; (iii) _______ shares after the expiration of two years from the Granting
Date; (iv) ______ shares after the expiration of three years from the Granting
Date; (v) ________shares after the expiration of four years from the Granting
Date, and ______ shares after the expiration of five years from the Granting
Date. This Option shall expire ten years after the Granting Date. To the extent
that the Optionee does not purchase part or all of the shares of ENB Common
Stock to which the Optionee is entitled within ten years after Granting Date,
this Option shall expire as to such unpurchased shares. For purposes of this
Agreement, a "year" shall mean a period of 365 days (or 366 in the event of a
leap year) ending on an anniversary of the Granting Date.

                       (b) Notwithstanding the provisions of subparagraph (a) of
paragraph 3 of this Agreement, in the event of a Change in Control of the
Company, as the term "Change in Control" is defined in Section 14 of the Plan,
the Option shall be accelerated in accordance with the terms of Section 14 of
the Plan.

                       (c) The Option shall be exercisable in the manner set
forth above, during the lifetime of the Optionee only by the Optionee and may
not be exercisable by him or her unless at the time of exercise the Optionee is
an employee of the Company or of one of its subsidiaries and shall have been
continuously so employed since the Granting Date, or, if the Optionee's
employment with the Company or any of its subsidiaries shall have terminated,
the Option shall be exercisable only if exercised prior to the expiration of
three months after the date of such termination or prior to ten years after the
Granting Date, whichever shall first occur, and (except as otherwise provided by
subparagraph (b) of this paragraph 3) only to the extent that the Optionee was
entitled to exercise the Option prior to the date of such termination.

                       (d) The Option shall be exercisable after the death of
the Optionee only if the Optionee shall at the time of the Optionee's death have
been an employee of the Company or one of its subsidiaries (or shall have been
so employed within three months of the Optionee's death) and shall have been
continuously so employed since the Granting Date, and then (i) only by or on
behalf of such person or persons to whom the Optionee's rights under the Option
shall have been passed by the Optionee's will or by the laws of descent and
distribution, (ii) (except as otherwise provided by subparagraph (b) of this
paragraph 3) only to the extent that

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the Optionee was entitled to exercise such Option prior to the date of the
Optionee's death, and (iii) only if such Option is exercised prior to the
expiration of twelve months after the date of the Optionee's death.

                  4.   Not an Employment Contract

                       Nothing herein contained shall be construed as requiring
the Company or any of its subsidiaries to employ the Optionee for any specific
period.

                  5.   Nonassignability

                       Except as otherwise herein provided, the Option herein
granted and the rights and privileges conferred hereby shall not be transferred,
assigned, pledged or hypothecated in any way (whether by operation of law or
otherwise) and shall not be subject to execution, attachment, or similar
process. Upon any attempt to transfer, assign, pledge, hypothecate or otherwise
dispose of the Option herein granted, or of any right or privilege conferred
hereby, or upon the levy of any attachment or similar process upon the rights
and privileges conferred hereby, contrary to the provisions hereof, this Option
and the rights and privileges conferred hereby shall immediately become null and
void.

                  6.   Adjustments for Stock Dividends, Splits, etc.

                       In the event that, prior to the delivery to the Optionee
by the Company of all the shares of the ENB Common Stock in respect of which
this Option is hereby granted, the Company shall have effected any stock
dividend, stock split, recapitalization, combination or reclassification of
shares or other similar transaction, then to the extent necessary to prevent
dilution or enlargement of the Optionee's rights hereunder:

                       (a)  in the event that a net increase  shall have been
effected in the number of outstanding shares of ENB Common Stock, the number of
shares remaining subject to this Option shall be proportionately increased, and
the cash consideration payable per share shall be proportionately reduced; and

                       (b)  in the event that a net reduction shall have been
effected in the number of outstanding shares of ENB Common Stock, the number of
shares remaining subject to this Option shall be proportionately reduced, and
the cash consideration payable per share shall be proportionately increased.

                  7.   Rights of Optionee

                       The Optionee shall not be, nor shall the Optionee have
any of the rights or privileges of, a shareholder of the Company in respect of
any of the shares issuable upon the exercise of this Option unless and until
certificates representing such shares shall have been issued and delivered;
except that the Company shall supply the Optionee with all financial information
and other reports which the Company furnished its shareholders during the Option
period.

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                  8.   $100,000 Limitation

                       The Option evidenced by this Agreement is intended to be
an incentive stock option. If the Option granted hereby should result in the
Optionee having an Option becoming first exercisable in any calendar year with
respect to stock having a fair market value (determined on the date of grant) in
excess of $100,000, only that portion of the Option which becomes first
exercisable in any calendar year with respect to stock having a fair market
value of $100,000 or less shall be treated as an incentive stock option, and
such part of this Option with respect to stock having a fair market value in
excess of $100,000 shall be treated as a nonqualified stock option the terms of
which are governed by the terms of the Plan.

                  9.   Notice

                       Any notice required to be given under the terms of this
Agreement shall be addressed to the Company in care of its secretary at its
offices at 132 East High Street, Jefferson City, MO 65102, and any notice to be
given to the Optionee shall be addressed to him or her at the address given
beneath the Optionee's signature hereto. Either party hereto may from time to
time change the address to which notices are to be sent to such party by giving
written notice of such change to the other party. Any notice hereunder shall be
deemed to have been duly given if and when addressed as aforesaid, registered
and deposited, postage and registry fee prepaid, in a post office regularly
maintained by the United States Government.

                  10.  Withholding

                       The Optionee agrees to make appropriate arrangements with
the Company for satisfaction of any applicable Federal, state or local income
tax withholding requirements or like requirements, including the payment to the
Company at the time of a "disqualifying disposition" (as defined in the Internal
Revenue Code of 1986, as amended) of stock acquired pursuant to the exercise of
an Option of all such taxes and requirements.

                  11.  Binding Effect

                       This Agreement shall bind, and, except as specifically
provided herein, shall inure to the benefit of the respective heirs, legal
representatives, successors and assigns of the parties hereto.

                  12.  Governing Law

                       This Agreement and the rights of all persons claiming
hereunder shall be construed and determined in accordance with the laws of the
State of Missouri.

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                       IN WITNESS WHEREOF, the Company has caused this Agreement
to be executed by its officers thereunto duly authorized and its corporate seal
to be hereunto affixed, and the Optionee has hereunto set his or her hand as of
the day and year first above written.

                                    EXCHANGE NATIONAL BANCSHARES, INC.

(CORPORATE SEAL)                    By:     _____________________________
ATTEST:                                     Name:
                                            Title:

--------------------------
Name:
Title:

                                     ------------------------------
                                     Optionee Name:

                                     Address: _____________________

                                              _____________________

                                              _____________________

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                                                                   Exhibit 10.37

                          AGREEMENT AND GENERAL RELEASE

CONSULT WITH A LAWYER BEFORE SIGNING THIS AGREEMENT AND RELEASE. BY SIGNING THIS
AGREEMENT, YOU GIVE UP AND WAIVE IMPORTANT LEGAL RIGHTS.

I, Thomas M. Burkardt, of 2231 Ocean Blvd., Rye, NH 03870, understand and, of my
own free will, enter into this AGREEMENT AND GENERAL RELEASE ("AGREEMENT" or
"Agreement") for the benefit of Unisphere Networks, Inc., a Delaware corporation
with principal offices at Ten Technology Park Drive, Westford, MA 01886, and its
parents, subsidiaries and affiliates,(hereinafter referred to individually and
collectively as the "COMPANY"), and in consideration of the payments and
benefits described herein, agree as follows:

1.       My employment with the COMPANY will be terminated on July 2, 2001 by
         virtue of my resignation of employment as of that date (the
         "Resignation Date"). My last day actively at work with the COMPANY will
         be July 2, 2001. I hereby resign from any corporate office or official
         position which I hold with the COMPANY or any affiliate of the COMPANY
         effective as of the Resignation Date and agree to execute any letters
         of resignation in the form presented by the Company.

2.       I will be paid as part of the consideration for this Agreement, base
         salary continuation payments (in an amount equal to my bi-weekly base
         salary rate in effect on the Resignation Date) on a bi-weekly basis
         (i.e., every two weeks) on the Company's regular payroll periods, less
         applicable federal, state, and local withholding and FICA taxes, during
         the period from the Resignation Date until July 1, 2002 (the "Severance
         Period"). I understand that health and dental insurance benefits, if
         any, will continue through the Resignation Date at the same employee
         contribution rate, at which point coverage will terminate subject to
         continuation under the COBRA law as explained under separate cover. In
         addition to the foregoing, the COMPANY will pay the monthly COBRA
         payment on my behalf for continuation of my group health and dental
         insurance coverage for the period of July 3, 2001 through July 2, 2002,
         provided that I am then eligible and remain eligible for COBRA. I
         understand that these payments are contingent upon return of this
         Agreement, as stated in paragraph 10.
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         The COMPANY acknowledges and agrees that I will receive these salary
         continuation payments regardless of whether or not I become employed or
         self-employed during the Severance Period unless the COMPANY terminates
         these payments under Section 10 hereof.

3.       I hereby agree to act as a consultant to the COMPANY to assist with the
         transition of my responsibilities, including but not limited to
         strategy, market positioning and product development, during the period
         from July 3, 2001 to July 2, 2002 (the "Consultancy Period"). The
         compensation I shall receive for such assistance shall consist of the
         vesting of those incentive stock options and non-qualified stock
         options previously awarded to me under the COMPANY'S 1999 Amended and
         Restated Stock Incentive Plan (the "Plan") which would have vested on
         or before April 1, 2002 had I remained an employee until that date.
         These options shall vest in accordance with the terms of the Plan and
         the terms of my option award(s) with the COMPANY provided, however,
         that such options and any shares issued upon the exercise of such
         options (once vested) shall be subject to the COMPANY's right of first
         refusal to purchase the same if I elect to transfer or otherwise
         dispose thereof, either in whole or in part, to any third party during
         the Consultancy Period. If I elect to transfer or otherwise dispose of
         these shares issued upon the exercise of such options, either in whole
         or in part, to any third party during the Consultancy Period, I shall
         first contact Suzanne M. Zabitchuck, the General Counsel of the
         COMPANY, and advise her in writing of my intention to dispose of the
         same. The COMPANY shall then have ten (10) business days from receipt
         of such notice to purchase these shares, in whole or in part, at the
         original exercise price (exclusive of any taxes which I was required to
         pay upon exercise of those options). If the COMPANY declines to
         purchase such shares, then I shall be entitled to transfer or otherwise
         dispose thereof subject to the terms and conditions on transfer and
         disposition set forth in the Plan, any option award and the lock-up
         agreement.

4.       I hereby acknowledge and agree that nothing in this Agreement shall be
         deemed to affect the restricted stock previously acquired by me from
         the COMPANY, and such restricted stock shall be governed by the terms
         and conditions of the Restricted Stock Agreement Granted under the 1999
         Stock Incentive Plan between me and the COMPANY, dated as of August 1,
         2000, (hereinafter the "Restricted

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         Stock Agreement"), including but not limited to, the Purchase Option
         set forth therein. The parties hereby acknowledge and agree that the
         COMPANY has a Purchase Option to acquire One Hundred Thirty Seven
         Thousand Five Hundred (137,500) restricted shares under the terms of
         the Restricted Stock Agreement. I hereby acknowledge and agree that I
         shall not vest in any restricted shares following my Resignation Date.

5.       I will receive a payment equal to accrued and unused vacation as of
         July 2, 2001, less applicable federal, state, and local withholding and
         FICA taxes. This payment is not contingent upon the execution and
         return of this Agreement and will be paid with the next regular payroll
         period following the Resignation Date.

6.       I hereby acknowledge and agree that, in accordance with the terms of
         the Company's 1999 Amended and Restated Stock Incentive Plan (the
         "Plan"), all unvested options previously awarded to me under that Plan
         shall be cancelled and forfeited by me on July 2, 2001 except those
         options which would have vested during the period from July 3, 2001 to
         and including April 1, 2002, as set forth in Paragraph 3 hereof. All
         options which were vested as of the Resignation Date and any options
         which shall subsequently vest in accordance with the terms of Paragraph
         3 hereof must be exercised by me no later than October 1, 2002.

7.       In the event that the current lock-up letter to the COMPANY in
         connection with its potential initial public offering expires prior to
         such offering, I agree to execute the form of lock-up agreement then
         provided to me by the COMPANY provided, however, that the terms of such
         lock-up letter shall be no more restrictive than the terms of the
         lock-up executed by the then executive officers of the COMPANY.

8.       During the Severance Period and the Consultancy Period, I agree not to,
         directly or indirectly:

         -        acquire or agree, offer, seek or propose to acquire, or cause
                  to be acquired, ownership of any of the COMPANY'S assets or
                  business or any voting securities issued by the COMPANY, or
                  any other rights or options to acquire such ownership
                  (including from a third party),

         -        seek or propose to influence (otherwise than in my role as a
                  consultant to the COMPANY as set forth in Section 3 hereof
                  provided, however, that my actions in that regard

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         are limited to internal dialogue only with the COMPANY's management) or
         control the COMPANY'S management or policies, or

         -        enter into any discussions, negotiations, arrangements or
                  understandings with any third party with respect to any of the
                  foregoing.

         The restrictions contained in this paragraph shall not be applicable to
         purchases solely for investment purposes aggregating less than 5% of
         the COMPANY'S outstanding voting securities or to the exercise of any
         option granted to me under the terms of the COMPANY'S 1999 Amended and
         Restated Stock Incentive Plan.

9.       I understand that, except as provided in Paragraphs 2, 3, 5 and 6 of
         this AGREEMENT, after the Resignation Date, I will have no further
         rights to any other compensation or benefits from the COMPANY or any of
         its parents, subsidiaries or affiliates, including, but not limited to,
         any rights to or under any salary, bonus, compensation, milestone,
         incentive, retention or stock option plans of the COMPANY or its
         parents, subsidiaries, or affiliates, or vacation, severance, pension,
         medical, dental, life, short term disability, long term disability or
         other insurance or benefits of any kind, including, but not limited to,
         any rights or benefits set forth in the Employment Agreement between
         Castle Networks, Inc. and me, dated as of March 7, 1999 (hereinafter
         the "Employment Agreement").

10.      I understand the COMPANY will not be required to provide the payments
         and benefits set forth in Paragraphs 2, 3 and 6 of this AGREEMENT
         unless and until I sign this AGREEMENT and this AGREEMENT becomes
         effective pursuant to Paragraph 24 hereof. I further understand and
         agree that in the event that I breach any of the terms and conditions
         set forth in this Agreement, the COMPANY shall provide me with written
         notice of such breach and shall, following ten (10) days from the date
         of such notice, unless prohibited by an order from an arbitrator in
         accordance with the terms of Section 26 hereof, be entitled to
         terminate all future payments and benefits due and owing to me under
         this Agreement, including, but not limited to forfeiture of any further
         vesting of any then unvested options, which shall be in addition to any
         other relief and damages which may be available to the COMPANY under
         applicable law or in equity. The parties hereto further agree that,
         during this ten day

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         notice period, the parties shall attempt to resolve any dispute in a
         mutually agreeable manner but nothing herein shall preclude the COMPANY
         from terminating the future payments and benefits due hereunder upon
         the expiration of said notice period if the parties fail to mutually
         agree upon a resolution, absent an order from the arbitrator as
         specified in the immediately preceding sentence.

11.      I understand that this AGREEMENT does not constitute an admission by
         the COMPANY or myself of any (a) violation of any statute, law or
         regulation; (b) breach of contract, actual or implied, including but
         not limited to my Employment Agreement; or (c) commission of any tort.

12.      In consideration for the payments and benefits set forth in Paragraphs
         2, 3 and 6 of this AGREEMENT, I do, on behalf of myself, my legal
         representatives, heirs, executors, administrators, successors and
         assigns, agree and promise not to sue and to forever release the
         COMPANY, its affiliates, parents, subsidiaries, and divisions and their
         respective predecessors, successors and assigns and their current and
         former directors, representatives, agents, employees, officers and
         shareholders, both individually and in their official capacities, (the
         "Releasees") from any and all claims, actions, causes of action, suits,
         demands, liabilities, complaints, contracts, agreements, promises and
         charges of every kind, nature and description, whenever they arose and
         whether in law or in equity, which may by law be waived including, but
         not limited to, claims related to my employment, the compensation,
         benefits, terms and conditions of my employment, the compensation,
         benefits, terms and conditions of my Employment Agreement, or the
         cessation of my employment as well as any application for re-employment
         that has been made prior to this date with the COMPANY. This release
         includes but is not limited to any claim, charge or action arising
         under any federal, state or local discrimination statute, which
         include, but are not limited to, Title VII of the Civil Rights Act of
         1964 and 1991, The Age Discrimination in Employment Act, the
         Rehabilitation Act of 1973, the Older Workers Benefit Protection Act,
         the Massachusetts Fair Employment Practices Act, the Fair Labor
         Standards Act, the Americans with Disabilities Act, the Occupational
         Health and Safety Act, the Family and Medical Leave Act, and the
         National Labor Relations Act. This release also includes any other
         federal, state, county, city or local law, statute, ordinance,
         regulation, public policy, contract or tort law

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         having any bearing whatsoever on the terms and conditions of my
         employment or the cessation of that employment, including, but not
         limited to, those laws relating to discrimination on the basis of age,
         sex, race, national origin, religion, marital status, sexual
         orientation or payment of wages, or under any other theory of law or
         contract, including but not limited to, fraud, wrongful termination or
         intentional or negligent infliction of emotional or mental distress,
         libel or slander. I intend to waive and release any rights I may have
         under these and other laws which I ever had, now have or shall have as
         of the date of this Agreement, but I do not intend to nor am I waiving
         any rights or claims that may arise after the date I sign this
         AGREEMENT, or that may arise from the Company's breach of this
         AGREEMENT.

13.      I understand and acknowledge that the payments and benefits set forth
         under this AGREEMENT completely satisfy any obligations which the
         COMPANY may have towards me under the Employment Agreement and the
         Plan.

14.      I understand and acknowledge that any and all obligations owed to me
         under the terms of any merger agreement or any milestone, incentive or
         retention plans associated with the acquisition of Castle Networks,
         Inc. by the COMPANY, or any of its parents, subsidiaries or affiliates,
         have previously been fulfilled and that I have no further rights to any
         other compensation or benefits from the COMPANY or any of its parents,
         subsidiaries or affiliates thereunder.

15.      In light of the consideration and benefits set forth in Paragraphs 2, 3
         and 6 of this Agreement, I further agree to amend the terms of the
         Non-Competition and Non-Solicitation Agreement between me and Castle
         Networks, Inc, dated as of March 7, 1999 (hereinafter the
         "Non-Competition and Non-Solicitation Agreement"), as follows:

         a.       Section 1/Term shall be amended as follows: This Agreement
                  shall be for a term commencing on the Closing Date (as defined
                  in the Merger Agreement) and ending on January 1, 2003, the
                  date which is eighteen months following July 2, 2001, which is
                  the date on which the Employee shall cease to be an employee
                  of the Company and its affiliates (the "Restricted Period").
                  Nothing in this Agreement shall confer on the Employee any
                  right to continue in the employ of the Company or its
                  affiliates.

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         b.       Section 2.2/Non-Solicitation shall be amended as follows:
                  During the Restricted Period, the Employee shall not, without
                  the Company's prior written consent, directly or indirectly,
                  (i) solicit or encourage to leave the employment or other
                  service of the Company, or any of its affiliates, any employee
                  or independent contractor thereof or (ii) hire (on behalf of
                  the Employee or any other person or entity) any employee or
                  independent contractor who is employed or engaged by the
                  Company at the time of the Employee's termination of
                  employment, or at any time within the 6 month period which
                  precedes such termination, or who has left the employment or
                  other service of the Company or any of its affiliates within
                  the six-month period which precedes such hiring. From the date
                  hereof through the end of the Restricted Period, the Employee
                  will not, whether for his own account or for the account of
                  any other person, firm, corporation of other business
                  organization, intentionally interfere with the Company's or
                  any of their affiliates' relationship with, or endeavor to
                  entice away from the Company or any of their affiliates, any
                  person who during the Term is or was a customer or client of
                  the Company or any of its affiliates.

         The COMPANY hereby acknowledges and agrees that it interprets the term
         "the Business" as used in Section 2.1 of the Non-Competition and
         Non-Solicitation Agreement, as amended herein, to refer to the
         development, manufacture, marketing or sale of any product that is
         competitive with any product developed, manufactured, marketed or sold,
         or under development (as evidenced by a written development plan) while
         I was employed by the COMPANY, including but not limited to Unisphere
         Networks, Inc. and Castle Networks, Inc., through and including July 2,
         2001, the Resignation Date.

         I acknowledge and agree that nothing in this AGREEMENT shall be deemed
         to reduce in any way the obligations I have under any non-competition
         agreement which applies to me, including, but not limited, the terms
         and conditions set forth in the Non-Competition and Non-Solicitation
         Agreement, except as such Non-Competition and Non-Solicitation
         Agreement is amended above in this Section 15. I hereby confirm the
         terms, conditions and restrictions set forth in the Non-Competition and
         Non-Solicitation Agreement, as amended herein, and acknowledge

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         and agree that the terms thereof shall survive the termination of my
         employment as set forth therein.

         The COMPANY hereby acknowledged and agrees that I currently am a
         Director of Wavesmith and Kenetic and am a member of the advisory board
         of Vividon. The COMPANY further acknowledges and agrees that I may
         retain these positions and the COMPANY will not claim that the mere
         fact that I hold these positions is a violation of the Non-Competition
         and Non-Solicitation Agreement, as amended herein, even if those
         entities compete with the COMPANY, provided, however, that nothing
         herein shall reduce or diminish in any manner the terms and conditions
         of the Non-Competition and Non-Solicitation Agreement, as amended
         herein, and the Employee Patent and Secrecy Agreement with Castle
         Networks, Inc., dated as of March 9, 1999 (hereinafter the "Employee
         Patent and Secrecy Agreement"). For avoidance of doubt, the COMPANY
         will not claim that I am in violation of the Non-Competition and
         Non-Solicitation Agreement, as amended herein, by virtue of the fact
         that I serve as a director or advisory board member of these
         organizations but nothing herein will preclude the COMPANY from
         pursuing a claim under the Non-Competition and Non-Solicitation
         Agreement, as amended herein, or the Employee Patent and Secrecy
         Agreement in the event that I otherwise violate the terms thereof,
         including by way of example but not by limitation, disclosing
         confidential information regarding the COMPANY to one of these
         entities.

16.      I acknowledge and agree that nothing in this AGREEMENT shall be deemed
         to reduce in any way the obligations I have under any employee patent
         and secrecy agreement or confidentiality agreements which apply to me,
         including, but not limited, the terms and conditions set forth in: (i)
         the Employee Patent and Secrecy Agreement with Castle Networks, Inc.,
         dated as of March 9, 1999 (hereinafter the "Employee Patent and Secrecy
         Agreement"); and (ii) the Non-Competition and Non-Solicitation, except
         as such Non-Competition and Non-Solicitation Agreement is amended
         pursuant to Section 15 herein. I hereby confirm the terms, conditions
         and restrictions set forth in the Employee Patent and Secrecy Agreement
         and the Non-Competition and Non-Solicitation Agreement, as amended
         herein, and acknowledge and agree that the terms thereof shall survive
         the termination of my employment as set forth therein.

17.      I agree to strictly maintain the confidentiality of the terms of this
         AGREEMENT and shall not disclose any

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         information relating thereto to any individual other than my immediate
         family members, legal counsel and tax advisor.

18.      I agree not to disparage the reputation of the Company, its products
         and services, including its current and former officers, directors,
         employees and agents, at any time now or in the future. In addition to
         the foregoing, I agree that in the event that I am contacted by any
         person, including any person associated, directly or indirectly, with
         any customer of the Company, any investment banking firm, any
         securities analyst, the press, any publication or trade journal, or any
         industry association, I will decline to comment other than to confirm
         that I have resigned from the COMPANY and continue to act as a
         consultant thereto through July 2, 2002. In all other respects, I shall
         make no statements or comments other than comments which are clearly of
         a positive nature regarding the Company, its products and services,
         including without limitation, its current and former officers,
         directors and employees. Notwithstanding the foregoing, I shall be free
         to make private comments regarding the Company to the members of my
         immediate family and to my attorneys. In addition, I shall be entitled
         to respond truthfully if I am compelled by legal process to testify in
         any legal or governmental proceeding.

         The Company agrees not to issue a formal written press release
         regarding my resignation from the Company unless I review and approve
         thereof. In addition, James Dolce and Eve Aretakis (the "Named
         Executives") shall, during the course of his/her employment with the
         COMPANY, refrain from making any disparaging comments to any third
         party regarding my reputation and shall confirm to any third party that
         I resigned as an officer of the COMPANY for personal reasons and that I
         continue to act as a consultant thereto through July 2, 2002. The Named
         Executives shall be entitled to respond truthfully if compelled by
         legal process to testify in any legal or governmental proceeding.
         Notwithstanding the foregoing, nothing herein shall restrict in any
         manner any comments by the Named Executives to, or discussions between,
         any of the Named Executives with each other or with any employee or any
         officer of the Company or with the Company's Board of Directors,
         attorneys or advisors. I hereby acknowledge and agree that nothing in
         this Section 18 shall create any personal liability on behalf of the
         Named Executives and that any claim I may

                                       9
<PAGE>   10
         have for their compliance with the terms of this Section 18 shall be
         exclusively against the COMPANY.

19.      The Company acknowledges that it has provided certain indemnification
         coverage to me as an officer of Unisphere Networks, Inc. pursuant to
         the Certificate of Incorporation thereof filed with the Delaware
         Secretary of State on January 12, 1999 and that I shall continue to be
         subject to such indemnification for my actions taken prior to the date
         hereof as Executive Vice President and Chief Operating Officer.

20.      This AGREEMENT shall be governed by and construed in accordance with
         the laws of the Commonwealth of Massachusetts without regard to
         principles of conflicts of law.

21.      The terms and provisions of this AGREEMENT are severable. If one or
         more provisions or terms of this AGREEMENT shall be ruled
         unenforceable, the COMPANY may elect to enforce the remainder of this
         AGREEMENT.

22.      I understand that this AGREEMENT may not affect the rights and
         responsibilities of the Equal Employment Opportunity Commission
         ("Commission") to enforce the Age Discrimination in Employment Act
         ("ADEA") or be used to justify interfering with the protected right of
         an employee to file a charge under the ADEA or participate in an
         investigation or proceeding conducted by the Commission under the ADEA.
         I further understand that this AGREEMENT may not affect the rights and
         responsibilities of the Massachusetts Commission Against Discrimination
         ("MCAD") to enforce the laws of the Commonwealth of Massachusetts
         prohibiting discrimination in employment or be used to justify
         interfering with the protected right of an employee to file a charge
         under such laws or participate in an investigation or proceeding
         conducted by the MCAD under those laws.

23.      I was given a copy of this AGREEMENT on or before the Resignation Date.
         I have had an opportunity to consult an attorney before signing it and
         was given a period of at least twenty-one (21) days or until July 23,
         2001 to consider this AGREEMENT. In the event that I sign this
         Agreement within less than twenty-one (21) days of receipt, I
         acknowledge that I did so voluntarily and with knowledge of the
         opportunity to consider this Agreement for the entire twenty-one (21)
         day period. I acknowledge that in signing this AGREEMENT I have relied
         only on the promises

                                       10
<PAGE>   11
         written in this AGREEMENT and not on any other promise made by the
         COMPANY.

24.      I have seven (7) days to revoke this AGREEMENT after I sign it by
         sending written notice to the Company addressed as follows: Unisphere
         Networks, Inc., Ten Technology Park Drive, Westford, MA 01886,
         Attention: Ann Laporte, Director of Human Resources, which notice must
         be postmarked within seven (7) days of my execution hereof. If the
         seventh day is a Saturday, Sunday or legal holiday in Massachusetts,
         then the revocation period shall not expire until the next following
         day which is not a Saturday, Sunday or legal holiday. This AGREEMENT
         will not become effective or enforceable until ten (10) days after the
         COMPANY has received my signed copy of this AGREEMENT (the "Effective
         Date") provided the revocation period expires without my having
         exercised the right to revoke. No payments will be made hereunder until
         the revocation period has expired without exercise and the Agreement
         becomes effective as set forth herein.

25.      This AGREEMENT may not be modified or changed orally. Any modifications
         or amendments must be in writing and signed by the parties hereto. The
         parties agree that this Agreement represents the entire agreement of
         the parties and supersedes all prior communications, agreements or
         understandings, either oral or written, if any, regarding the same,
         provided, however, that the terms and conditions of the Employee Patent
         and Secrecy Agreement, the Non-Competition and Non-Solicitation
         Agreement, as amended herein, the Restricted Stock Agreement, the
         Pledge Agreement with the COMPANY dated as of August 1, 2000, the
         Promissory Note with the COMPANY dated as of August 1, 2000, and the
         Joint Escrow Instructions with the COMPANY dated as of August 1, 2000,
         shall survive in accordance with the terms thereof.

26.      Any and all disputes, complaints, controversies, claims and grievances
         (excluding those specifically excepted herein) arising under, out of,
         in connection with, or in any manner related to this AGREEMENT or the
         relation of the parties hereunder shall be submitted to final and
         binding arbitration to be conducted by the American Arbitration
         Association in accordance with its Rules applicable to these types of
         disputes, complaints, claims or grievances, by one neutral and
         impartial arbitrator acceptable to me and the COMPANY. If such an
         arbitrator has not been selected by me and the COMPANY within 60 days
         after AAA first provides a list of

                                       11
<PAGE>   12
         eligible arbitrators, or within thirty days after the occurrence of a
         vacancy, one neutral and impartial arbitrator shall be selected and
         appointed by the American Arbitration Association, in accordance with
         its Rules. Unless otherwise required under applicable law, the
         arbitration proceedings shall be conducted in Boston, Massachusetts or
         a city mutually agreed to by the parties, and the procedural rules of
         the place of arbitration shall apply. Arbitration proceedings hereunder
         may be commenced by written notice from either party hereto to the
         other party. Such proceedings and evidence shall be confidential. The
         arbitrator shall have the power and the authority to make such
         decisions and awards as he/she shall deem appropriate, including
         granting compensatory damages and costs to the prevailing party
         (including fees of the arbitrator, but excluding punitive, exemplary,
         consequential or special damages, and attorneys' fees), and the
         granting or issuance of such mandatory directions, prohibitions,
         orders, restraints and other injunctions (other than any of the
         foregoing that would reestablish the employment relationship formerly
         existing between the COMPANY and myself) that he/she may deem necessary
         or advisable directed to or against any of the parties, including a
         direction or order requiring specific performance of any covenant,
         agreement or provision of this AGREEMENT as a result of a breach or
         threatened breach thereof. The cost of such arbitration shall be borne
         by the COMPANY except that each party shall bear its own cost of
         attorneys' fees and expenses. Any decision and award of the arbitrator
         shall be final, binding and conclusive upon all of the parties hereto
         and said decision and award may be entered as a final judgment in any
         court of competent jurisdiction. It is expressly agreed that
         arbitration as provided herein shall be the exclusive means for
         determination of all matters as above provided and neither of the
         parties hereto shall institute any action or proceeding in any court of
         law or equity, state or federal, other than respecting enforcement of
         the arbitrator's award hereunder. The foregoing sentence shall be a
         bona fide defense in any action or proceeding instituted contrary to
         this AGREEMENT. Notwithstanding the foregoing, nothing contained herein
         shall prevent or restrain in any manner either party from instituting
         an action or claim in any court, or such other forum as may be
         appropriate to enforce the terms of any employee patent and secrecy
         agreement, (or similar agreement relating to the COMPANY's confidential
         or proprietary business information or trade secrets) to protect the
         COMPANY's proprietary or confidential business information or trade
         secrets, to enforce or protect

                                       12
<PAGE>   13
         the COMPANY's patent, copyright, trademark, trade name or trade dress
         rights, to redress claims for product disparagement or trade libel, or
         to protect the COMPANY's reasonable business expectations or relations
         with third parties, or to enforce the terms of any non-competition
         agreement. To the extent this paragraph sets forth different
         procedures, or remedies, or provides the arbitrator different powers
         than are set forth in the Rules of the American Arbitration
         Association, the terms of this paragraph shall take precedence.

REMAINDER OF PAGE INTENTIONALLY LEFT BLANK

                                       13
<PAGE>   14
I HAVE BEEN ADVISED THAT I HAVE TWENTY-ONE (21) DAYS TO CONSIDER THIS AGREEMENT
AND I HAVE BEEN ADVISED IN WRITING TO CONSULT WITH AN ATTORNEY PRIOR TO
EXECUTION OF THIS AGREEMENT. I FURTHER UNDERSTAND THAT I MAY REVOKE THIS
AGREEMENT FOR A PERIOD OF SEVEN (7) DAYS FOLLOWING THE DAY I EXECUTE THE
AGREEMENT AND SAID AGREEMENT SHALL NOT BECOME EFFECTIVE OR ENFORCEABLE UNTIL THE
REVOCATION PERIOD HAS EXPIRED. I UNDERSTAND THAT THIS AGREEMENT WILL BE A
BINDING LEGAL DOCUMENT AND THAT MY SIGNATURE WILL COMMIT ME TO ITS TERMS. I HAVE
READ THIS AGREEMENT, AND I UNDERSTAND ALL OF ITS TERMS. HAVING ELECTED TO
EXECUTE THIS AGREEMENT, TO FULFILL THE PROMISES SET FORTH HEREIN, AND TO RECEIVE
THEREBY THE SUMS AND BENEFITS AS SET FORTH HEREIN, I FREELY AND KNOWINGLY, AND
AFTER DUE CONSIDERATION, VOLUNTARILY ENTER INTO THIS AGREEMENT INTENDING TO
WAIVE, SETTLE AND RELEASE ALL CLAIMS I HAVE, HAD OR MIGHT HAVE AGAINST THE
COMPANY.

                                              /s/ Thomas M. Burkardt
                                              ---------------------------
                                              Thomas M. Burkardt
                                              Date: July 2, 2001

COMMONWEALTH OF MASSACHUSETTS       )
                                   :ss
COUNTY OF ESSEX                     )

On this 2ND day of JULY, 2001 before me personally came Thomas M. Burkardt to me
known and known to be the individual who executed the foregoing AGREEMENT AND
GENERAL RELEASE before me and duly acknowledged to me that he executed the same
as his free act and deed.

                                           /s/ Lisa M. Falcone
                                          --------------------------------------
                                           Notary Public
                                           My Commission Expires:

                                       14
<PAGE>   15
                                           Unisphere Networks, Inc.

                                          BY: /s/ James A. Dolce, Jr.
                                             -----------------------------------

                                          Date: July 3, 2001
                                               ---------------------------------

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