Document:

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                                                                    EXHIBIT 10.3

     REGISTRATION RIGHTS AGREEMENT (the "Agreement") made as of September 30,
1997, by and among MIL 3, INCORPORATED (the "Company"), a Delaware corporation;
SUMMIT VENTURES IV, L.P. ("Summit Ventures"), a Delaware limited partnership;
SUMMIT INVESTORS III, L.P. ("Summit Investors"), a Delaware limited partnership;
ALAIN J. COHEN ("A. Cohen"), an individual residing in Washington, D.C.; and
MARC A. COHEN ("M. Cohen"), an individual residing in Washington, D.C. (Summit
Investors and Summit Ventures are each sometimes referred to herein as an
"Investor" and collectively as the "Investors.")

                                  WITNESSETH:

     WHEREAS, the Company and the Investors entered into a Series A Preferred
Stock Purchase Agreement (the "Stock Purchase Agreement") dated as of September
30, 1997 in accordance with which the Investors have acquired a total of 144,640
shares of the Company's Series A Convertible Preferred Stock, par value $.001
per share (the "Series A Preferred Stock"), and

     WHEREAS, the Company desires to grant to each of the Investors, A. Cohen
and M. Cohen certain rights with respect to the registration under the
Securities Act of 1933, as amended (the "Act") of certain shares of the
Company's Common Stock, par value $.01 per share (the "Common Stock"), they may
hold.

     NOW THEREFORE, in consideration of the foregoing and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto, intending legally to be bound hereby, agree as
follows:

     Section 1.  Certain Definitions.  Terms used herein with initial capital
                 -------------------
letters but not defined herein shall have the meanings set forth in the Stock
Purchase Agreement. In addition, as used in this Agreement, the following terms
shall have the following respective meanings:

          "Act" has the meaning set forth in the recitals to this Agreement.

          "Affiliate" means when used with respect to a specified person, a
person who directly or indirectly, through one or more intermediaries, controls,
is controlled by or is under common control with such specified person.  The
term "control" (including the terms "controlling" and "controlled") means the
power to direct or to cause the direction of the management and policies of a
person, whether by virtue of stock ownership, by contract or otherwise.

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          "Applicable Conversion Value" has the meaning set forth in the
Certificate of Incorporation.

          "Certificate of Incorporation" means the Amended and Restated
Certificate of Incorporation dated September 29, 1997, filed by the Company with
the Secretary of State of the State of Delaware to, among other things,
authorize and fix the terms, privileges and preferences of the Series A
Preferred Stock.

          "Commission" means the Securities and Exchange Commission or any other
federal agency at the time administering the Act.

          "Common Stock" has the meaning set forth in the recitals to this
Agreement.

          "Conversion Shares" means shares of Common Stock issuable or issued
upon conversion of the Series A Preferred Stock.

          "Exchange Act" means the Securities Exchange Act of 1934, as amended.

          "Holder" means the person who is then the record owner of Registrable
Securities or Other Registrable Securities.

          "Initiating Holder" has the meaning set forth in Section 2(a).

          "Management Holder" means each of A. Cohen or M. Cohen and his
respective successors or assignees who is a Holder of Other Registrable
Securities.

          "Other Registrable Securities" means (i) shares of Common Stock held
by and at the time issuable to the Management Holders and (ii) all shares of
Common Stock issued in respect of the shares described in clause (i) upon any
stock split, stock dividend, recapitalization or other similar event.  As to any
particular Other Registrable Securities, once issued such securities shall cease
to be Other Registrable Securities when (a) a registration statement with
respect to the sale of such securities shall have become effective under the Act
and such securities shall have been disposed of, or (b) such securities shall
have been distributed to the public pursuant to Rule 144 (or any successor rule)
under the Act or pursuant to Section 4(1) (or any successor provision) of the
Act.

          "Qualified Public Offering" means the closing of a public offering by
the Company pursuant to a registration statement filed and declared effective
under the Act covering the offer and sale of Common Stock in which the aggregate
gross proceeds are over $20 million and in which the price per share equals or
exceeds three times the then Applicable Conversion Value of the Series A
Preferred Stock determined in accordance with the Certificate of Incorporation.

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          "Register," "registered" and "registration" means a registration
effected by preparing and filing a registration statement in compliance with the
Act and applicable rules and regulations thereunder, and the declaration or
ordering by the Commission of the effectiveness of such registration statement.

          "Registrable Securities" means: (i) all of the Conversion Shares held
by and at the time issuable to the Investors, (ii) all other shares of Common
Stock hereafter acquired by either Investor pursuant to the purchase rights
granted by the Shareholders Agreement; and (iii) all shares of Common Stock
issued in respect of the shares described in clauses (i) or (ii) upon any stock
split, stock dividend, recapitalization or other similar event. As to any
particular Registrable Securities, once issued such securities shall cease to be
Registrable Securities when (a) a registration statement with respect to the
sale of such securities shall have been filed and declared effective under the
Act and such securities shall have been disposed of, or (b) such securities
shall have been distributed to the public pursuant to Rule 144 (or any successor
rule) under the Act or pursuant to Section 4(1) (or any successor provision) of
the Act.

          "Registration Expenses" means all expenses incurred by the Company in
accordance with Sections 2 or 3 hereof, including, without limitation, all
registration and filing fees, printing expenses, transfer taxes, fees and
disbursements of counsel for the Company, "Blue-sky" fees and expenses, the
expense of any special audits incident to or required by any such registration,
and reasonable fees and disbursements of one common counsel for each group of
all Selling Shareholders comprised of (i) the Investors (or their respective
successors or assignees) or (ii) the Management Holders (or their respective
successors or assignees).

          "Restricted Securities" has the meaning set forth in Rule 144 under
the Act.

          "Selling Expenses" means all (i) underwriting discounts and selling
commissions applicable to the sale of Registrable Securities and Other
Registrable Securities and (ii) fees of counsel (other than one common counsel
for each group of Selling Shareholders comprised of (a) the Investors (or their
respective successors or assignees) or (b) the Management Holders (or their
respective successors or assignees)).

          "Selling Shareholder" means each person selling Common Stock in
accordance with the registration rights contemplated by this Agreement.

          "Series A Preferred Stock" has the meaning set forth in the recitals
to this Agreement.

          "Stock Purchase Agreement" has the meaning set forth in the recitals
to this Agreement.

          "Underwriter" means the representative of the underwriter(s) selected
to underwrite an offering of securities in accordance with this Agreement.

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     Section 2.  Demand Registration.
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          (a)  If on any two occasions after the date of the Company's first
     Qualified Public Offering, the Company shall receive from any of (x) the
     Investors, (y) A. Cohen or (z) M. Cohen a written request (in any such
     case, the Holder(s) providing such request is hereinafter sometimes
     referred to as an "Initiating Holder(s)") that the Company effect the
     registration of Registrable Securities or Other Registrable Securities, as
     the case may be, representing at least twenty-five percent (25%) of the
     Registrable Securities or Other Registrable Securities, as the case may be,
     then held by and issuable to (1) the Investors (or their successors or
     assignees) if the Initiating Holder is an Investor (or a successor or
     assignee of an Investor), (2) A. Cohen (or his successors or assignees) if
     the Initiating Holder is A. Cohen (or his successors or assignees), or (3)
     M. Cohen (or his successors or assignees) if the Initiating Holder is M.
     Cohen (or his successors or assignees) (or any lesser percentage if the
     reasonably anticipated aggregate price to the public of the Registrable
     Securities or Other Registrable Securities, as applicable, to be included
     in such registration by such Holder would exceed $5,000,000) in connection
     with a firm commitment underwriting by a nationally recognized Underwriter
     selected by such Initiating Holder(s) and reasonably acceptable to the
     Company, the Company shall:

               (i)   promptly (and in no event less than 30 days before the
          anticipated filing date of such registration statement) give written
          notice of the proposed registration to all other Holders; and

               (ii)  as soon as practicable, use all of its commercially
          reasonable best efforts to effect such registration as may be so
          requested and as would permit or facilitate the sale and distribution
          of such portion of such Registrable Securities or Other Registrable
          Securities, as applicable, as are specified in such request, together
          with such portion of the Registrable Securities and Other Registrable
          Securities of Holders joining in such request as are specified in a
          written request by such Holder(s) given within 30 days after receipt
          of such written notice from the Company.

          (b)  The right of any Holder to registration pursuant to this Section
     2 shall be conditioned upon such Holder's participation, and the inclusion
     of such Holder's Registrable Securities or Other Registrable Securities, in
     the underwriting (unless otherwise mutually agreed by such Holder, the
     Underwriter and a majority in interest of the Initiating Holder(s) to the
     extent provided herein. A Holder may elect to include in such underwriting
     all or a part of the Registrable Securities or Other Registrable Securities
     it holds.

          (c)  The Company shall, together with all Holders of Registrable
     Securities and of Other Registrable Securities proposing to distribute
     their securities through such

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     underwriting, enter into an underwriting agreement in customary form with
     the Underwriter.

          (d)  Notwithstanding any other provision of this Section 2, if the
     Underwriter advises the Initiating Holder(s) in writing that the inclusion
     in the subject registration statement of Registrable Securities or Other
     Registrable Securities held by Holders other than Initiating Holder(s)
     would limit the number of Registrable Securities or Other Registrable
     Securities sought to be included by the Initiating Holder(s) or reduce the
     offering price thereof, then the Registrable Securities and Other
     Registrable Securities held by Holders other than Initiating Holder(s)
     shall be excluded from such registration to the extent so required by such
     limitation (such exclusion to be in the order of priority specified in
     Section 3(d). No Registrable Securities or Other Registrable Securities so
     excluded from the underwriting by reason of the Underwriter's above
     marketing limitation shall be included in such registration. If any Holder
     of Registrable Securities or Other Registrable Securities disapproves of
     the terms of the underwriting, such person may elect to withdraw therefrom
     by written notice to the Company, the Underwriter and the Initiating
     Holder(s) The securities so withdrawn shall also be withdrawn from
     registration. If the Underwriter has not limited the number of Registrable
     Securities and Other Registrable Securities to be underwritten, the Company
     may include its securities for its own account in such registration if the
     Underwriter so agrees and if the number of Registrable Securities and Other
     Registrable Securities which would otherwise have been included in such
     registration and underwriting will not thereby be limited.

          (e)  No registration initiated by any of the Initiating Holders
     hereunder shall count as a registration under this Section 2 unless and
     until the Company has incurred expenses equal to at least $20,000 related
     to the preparation of such registration.

          (f)  The Company shall not be required to effect any registration
     under this Section 2 if (i) the Company is, at the time at which it
     receives any such request by an Initiating Holder, conducting or, has
     before receipt of such request, notified the Holders that it had planned,
     within 60 days of receipt by the Company of such request, to conduct an
     offering of its securities and the Company reasonably believes that such
     offering would be adversely affected by the requested registration, (ii)
     such request is received by the Company within six months after the
     effective date of the registration statement relating to the Company's
     first Qualified Public Offering, (iii) such request is received by the
     Company within three months after the effective date of any other
     registration statement relating to the Company's securities, (iv) the
     filing of the registration statement would require the Company to furnish
     audited financial statements customarily prepared at the end of its fiscal
     year other than in respect of such fiscal year, or (v) the filing of the
     registration statement would require the Company to furnish unaudited
     financial statements customarily prepared at the end of its fiscal quarters
     other than in respect of its regularly reported interim quarterly periods.

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     Section 3.  "Piggy-Back" Registrations.
                  -------------------------

          (a)  If, at any time after the date of the Company's first Qualified
     Public Offering, the Company shall determine to register any of its
     securities, either for its own account or for the account of a security
     holder or holders (including an Initiating Holder) exercising its
     registration rights, other than a registration relating solely to employee
     benefit plans, or a registration on any registration form which does not
     permit secondary sales, or a registration relating solely to a Commission
     Rule 145 transaction, or a registration that does not include substantially
     the same information as would be required to be included in a registration
     statement covering the sale of Registrable Securities or Other Registrable
     Securities, the Company will:

               (i)  promptly (and in no event less than 30 days before the
          anticipated filing date of such registration statement) give to each
          Holder of Registrable Securities and Other Registrable Securities
          written notice thereof, which shall include the number of shares the
          Company or other security holder proposes to register and, if known,
          the name of Underwriter selected by the Company (if the registration
          is for the account of the Company) or by such other person initiating
          such registration and reasonably acceptable to the Company; and

               (ii) use all of its commercially reasonable best efforts to
          include in such registration all the Registrable Securities and Other
          Registrable Securities specified in a written request or requests made
          by any Holder within 30 days after the date of delivery of the written
          notice from the Company described in clause i) above.

          (b)  The right of any Holder to registration pursuant to this Section
     3 shall be conditioned upon such Holder's participation, and the inclusion
     of such Holder's Registrable Securities or Other Registrable Securities, in
     the underwriting (unless otherwise agreed by the Company, a majority in
     interest of the person(s) initiating such registration, and the
     Underwriter).

          (c)  All Holders proposing to distribute their securities through such
     underwriting shall (together with the Company and any other shareholders
     distributing their securities through such underwriting) enter into an
     underwriting agreement in customary form with the Underwriter. The Company
     shall use all of its commercially reasonable best efforts to cause the
     Underwriter of such proposed underwritten offering to permit the
     Registrable Securities and Other Registrable Securities requested to be
     included in the registration statement for such offering to be included on
     the same terms and conditions as any similar securities of the Company
     included therein.

          (d)  Notwithstanding any other provision of this Section 3, if the
     Underwriter advises the Company that the inclusion of Registrable
     Securities and/or Other Registrable Securities in the subject registration
     statement would limit the number of securities

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     originally determined to be included therein or would reduce the offering
     price thereof, then the Underwriter may require a limitation on the number
     of shares offered pursuant to such registration statement, as follows:

                    (i)  Any securities of the Company held by officers and
          directors of the Company (other than Registrable Securities or Other
          Registrable Securities) shall be excluded from such registration and
          underwriting to the extent required by such limitation: and

                    (ii) if a limitation on the number of shares is still
          required, then:

                         (a)  if the registration is for the account of the
               Company, Registrable Securities and Other Registrable Securities
               shall be excluded from such registration and underwriting to the
               extent required by such limitation, in proportion, as nearly as
               practicable, to the respective amount of Registrable Securities
               and Other Registrable Securities which had been requested to be
               included in such registration, prior to limiting the inclusion of
               the securities of the Company for the account of the Company; and

                         (b)  if the registration is at the request of an
               Initiating Holder(s) of  Registrable Securities and does not
               include shares to be sold by the Company (except pursuant to the
               last sentence of this Section 3),  Registrable Securities and
               Other Registrable Securities of each other Holder shall be
               excluded to the extent required by such limitation, in
               proportion, as nearly as practicable, to the amount of
               Registrable Securities and Other Registrable Securities which had
               been requested to be included in such registration in accordance
               with this Section 3; and

                         (c)  if the registration is at the request of an
               Initiating Holder(s) of Other Registrable Securities and does not
               include shares to be sold by the Company (except pursuant to the
               last sentence of this Section 3), Registrable Securities and
               Other Registrable Securities of each other Holder shall be
               excluded to the extent required by such limitation, in
               proportion, as nearly as practicable, to the amount of
               Registrable Securities and Other Registrable Securities which had
               been requested to be included in such registration in accordance
               with this Section 3.

          (e)  If any Holder of Registrable Securities, Other Registrable
     Securities or any officer or director disapproves of the terms of any such
     underwriting, such person may, prior to effectiveness of the registration,
     elect to withdraw therefrom by written notice to the Company and the
     Underwriter.  Any securities excluded or withdrawn from such underwriting
     shall be withdrawn from such registration.

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          (f)  If the registration is for the account of a person other than the
     Company and the Underwriter has not limited the number of Registrable
     Securities and Other Registrable Securities requested to be registered
     under this Section 3, the Company may include its securities for its own
     account in such registration if the Underwriter so agrees and if the number
     of Registrable Securities and Other Registrable Securities which would
     otherwise have been included in such registration and underwriting will not
     thereby be limited.

     Section 4.  Market Stand-Off Agreement.
                 --------------------------

          (a)  To the extent not inconsistent with applicable law, each Holder
     (and each officer and director of the Company, if any) whose securities are
     included in a registration statement in accordance with this Agreement,
     agrees not to effect any public sale or distribution of the issue being
     registered or a similar security of the Company, including a sale pursuant
     to Rule 144 under the Act, during the 60 day period beginning on the
     effective date of such registration statement (except as part of such
     registration), if and to the extent requested by the Company in the case of
     the non-underwritten public offering or if and to the extent requested by
     the Underwriter in the case of an underwritten public offering.

          (b)  The Company agrees, if requested by the Underwriter for an
     offering of Registrable Securities or Other Registrable Securities (or
     other securities of the Company), (i) not to effect any public sale or
     distribution of its equity securities or securities convertible into or
     exchangeable or exercisable for any of such securities during the 120 day
     period beginning on the effective date of such registration statement,
     except as part of such underwritten offering and except pursuant to
     registrations on Form S-4 or S-8 or any successor or similar forms thereto,
     and (ii) to use all of its commercially reasonable best efforts to cause
     each holder (other than a Holder) of its equity securities or any
     securities convertible into or exchangeable or exercisable for any of such
     securities to agree not to effect any such public sale or distribution of
     such securities during such periods.

          (c)  Each Holder agrees that any market stand-off period required by
     the Underwriter of any offering in which such Holder is participating shall
     supersede this Section 4.

     Section 5.  Expenses of Registration.  All Registration Expenses incurred
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in connection with any registration, qualification or compliance pursuant to
Sections 2 or 3 shall be paid by the Company.  All Selling Expenses incurred in
connection with any such registration, qualification or compliance shall be
borne by the holders of the securities registered, pro rata on the basis of the
                                                   --- ----
number of their shares so registered.

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     Section 6.  Registration on Form S-3.  From and after the date of the first
                 ------------------------
effective registration statement on Form S-1 filed by the Company, the Company
shall use all of its commercially reasonable best efforts to qualify for
registration on Form S-3 or any comparable or successor form; and to that end
the Company shall register (whether or not required by law to do so) the Common
Stock as a class under the Exchange Act following the effective date of the
first registration of any securities of the Company on Form S-1 or any
comparable or successor form.

     Section 7.  Registration Procedures.  In the case of each registration
                 -----------------------
effected by the Company pursuant to this Agreement, the Company will keep each
Holder of Registrable Securities or Other Registrable Securities included in
such registration advised in writing as to the initiation of such registration
and as to the completion thereof.  At its expense, the Company will do the
following for the benefit of such Holders:

          (a)  keep such registration effective for a period of 120 days or
     until the Holders have completed the distribution described in the
     registration statement relating thereto, whichever first occurs, and amend
     or supplement such registration statement and the prospectus contained
     therein from time to time to the extent necessary to comply with the Act
     and applicable state securities laws;

          (b)  use all of its commercially reasonable best efforts to register
     or qualify the Registrable Securities or Other Registrable Securities
     covered by such registration under the applicable securities or "Blue-sky"
     laws of such jurisdictions as the Selling Shareholders may reasonably
     request; provided, however, that the Company shall not be obligated to
              --------  -------
     qualify to do business in any jurisdiction where it is not then so
     qualified or otherwise required to be so qualified or to take any action
     which would subject it to the service of process in suits other than those
     arising out of such registration;

          (c)  furnish such number of prospectuses and other documents incident
     thereto as any such  Holder from time to time may reasonably request;

          (d)  in connection with any underwritten offering pursuant to a
     registration statement filed pursuant to Section 2 hereof, enter into any
     underwriting agreement reasonably necessary to effect the offer and sale of
     Common Stock, provided, however, that such underwriting agreement contains
                   --------  -------
     customary underwriting provisions and is entered into by the Holders whose
     securities are included therein and provided further, however, that if the
                                         -------- -------  -------
     Underwriter so requests, the underwriting agreement will contain customary
     contribution provisions on the part of the Company;

          (e)  to the extent then permitted under applicable professional
     guidelines and standards, obtain a comfort letter from the Company's
     independent public accountants in customary form and covering such matters
     of the type customarily covered by comfort letters and an opinion from the
     Company's counsel in customary form and covering such

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     matters of the type customarily covered in a public issuance of securities,
     in each case addressed to the Holders whose securities are included in the
     subject registration statement, and provide copies thereof to such Holders;
     and

          (f)  permit counsel to the Selling Shareholders whose expenses are
     being paid pursuant to this Agreement to inspect and copy such of the
     Company's corporate documents as he may reasonably request.

     Section 8.  Indemnification.
                 ---------------

          (a)  The Company will, and hereby does, indemnify each Holder of
     Registrable Securities and/or Other Registrable Securities, each of its
     officers, directors and partners, and each person controlling such Holder
     within the meaning of the Act, with respect to which registration,
     qualification or compliance has been effected pursuant to this Agreement,
     and each underwriter, if any, and each person who controls such underwriter
     within the meaning of the Act, against all claims, losses, damages and
     liabilities (or actions in respect thereof) arising out of or based on any
     untrue statement (or alleged untrue statement) of a material fact contained
     in any prospectus, offering circular or other document (including any
     related registration statement, notification or the like) incident to any
     such registration, qualification or compliance, or based on any omission
     (or alleged omission) to state therein a material fact required to be
     stated therein or necessary to make the statements therein not misleading,
     or any violation by the Company of the Act or the Exchange Act or the
     securities act of any state or any rule or regulation thereunder applicable
     to the Company and relating to action or inaction required of the Company
     in connection with any such registration, qualification or compliance, and
     will reimburse each such Holder, each of its officers, directors and
     partners, and each person controlling such Holder, each such underwriter
     and each person who controls any such underwriter, for any legal and any
     other expenses reasonably incurred in connection with investigating and
     defending any such claim, loss, damage, liability or action, whether or not
     resulting in any liability, provided, however, that the Company will not be
                                 --------  -------
     liable in any such case to the extent that any such claim, loss, damage,
     liability or expense arises out of or is based on any untrue statement (or
     alleged untrue statement) or omission (or alleged omission) based upon
     written information furnished to the Company by such Holder or underwriter
     and stated to be specifically for use therein.

          (b)  Each Holder will, if Registrable Securities or Other Registrable
     Securities held by him are included in such registration, qualification or
     compliance, indemnify the Company, each of its directors and officers and
     each underwriter, if any, of the Company's securities covered by such a
     registration statement, each person who controls the Company or such
     underwriter within the meaning of the Act and the rules and regulations
     thereunder, each other person whose securities are included in such
     registration  and each of their officers, directors and partners, and each
     person controlling such other person, against all claims, losses, damages
     and liabilities (or actions in respect thereof) arising out

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     of or based on any untrue statement (or alleged untrue statement) of a
     material fact contained in any such registration statement, prospectus,
     offering circular or other document, or any omission (or alleged omission)
     to state therein a material fact required to be stated therein or necessary
     to make the statements therein not misleading, and will reimburse the
     Company, each such other person and such other person's directors,
     officers, partners, underwriters or control persons for any legal or any
     other expenses reasonably incurred in connection with investigating or
     defending any such claim, loss, damage, liability or action, whether or not
     resulting in liability, in each case to the extent, but only to the extent,
     that such untrue statement (or alleged untrue statement) or omission (or
     alleged omission) is made in such registration statement, prospectus,
     offering circular or other document in reliance upon and in conformity with
     written information furnished to the Company by such Holder and stated to
     be specifically for use therein, provided, however, the liability of each
                                      --------  -------
     Holder shall not exceed the lesser of (A) that proportion of the total of
     such losses,  claims, damages or liabilities indemnified against equal to
     the proportion of the total number of Registrable Securities or Other
     Registrable Securities , as applicable, sold by such Holder through such
     registration, to the total number of the Company's securities included in
     such registration, or (B) the aggregate proceeds (net of discounts)
     received by such Holder upon the sale of the Registrable Securities or
     Other Registrable Securities as applicable.

          (c)  Each person entitled to indemnification under this Section 8 (the
     "Indemnified Person") shall give notice to the person required to provide
     indemnification (the "Indemnifying Person") promptly after such Indemnified
     Person has actual knowledge of any claim as to which indemnity may be
     sought, but the failure of any Indemnified Person to give such notice shall
     not relieve the Indemnifying Person of its obligations under this Section 8
     (except and to the extent the Indemnifying Person has been prejudiced as a
     consequence thereof).  The Indemnifying Person will be entitled to
     participate in, and to the extent that it may elect by written notice
     delivered to the Indemnified Person promptly after receiving the aforesaid
     notice from such Indemnified Person, at its expense to assume, the defense
     of any such claim or any litigation resulting therefrom, with counsel
     reasonably satisfactory to such Indemnified Person, provided that the
                                                         --------
     Indemnified Person may participate in such defense at its expense,
     notwithstanding the assumption of such defense by the Indemnifying Person,
     and provided, further, that if the defendants in any such action shall
         --------  -------
     include both the Indemnified Person and the Indemnifying Person and the
     Indemnified Person shall have reasonably concluded that there may be legal
     defenses available to it and/or other Indemnified Persons which are
     different from or additional to those available to the Indemnifying Person,
     the Indemnified Person or Persons shall have the right to select separate
     counsel to assert such legal defenses and to otherwise participate in the
     defense of such action on behalf of such Indemnified Person or Persons and
     the fees and expenses of such counsel shall be paid by the Indemnifying
     Person, and provided, further, however, that the Company shall not be
                 --------  -------  -------
     responsible for paying the fees of more than one counsel for each of (x)
     all Investors and their successors or assigns who may be Indemnified
     Persons and (y) each of the Management Holders and their respective

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     successors or assigns who may be Indemnified Persons.  No Indemnifying
     Person, in the defense of any such claim or litigation shall, except with
     the consent of each Indemnified Person, consent to entry of any judgment or
     enter into any settlement which does not include as an unconditional term
     thereof the giving by the claimant or plaintiff to such Indemnified Person
     of a release from all liability in respect to such claim or litigation.
     Each Indemnified Person shall (i) furnish such information regarding itself
     or the claim in question as an Indemnifying Person may reasonably request
     in writing and as shall be reasonably required in connection with defense
     of such claim and litigation resulting therefrom and (ii) reasonably assist
     the Indemnifying Person in any such defense, provided that the Indemnified
                                                  --------
     Person shall not be required to expend its funds in connection with such
     assistance.

          (d)  Neither the Company nor any Holder shall be required to effect
     any registration under Section 2 or Section 3 of this Agreement pursuant to
     which it would be required to execute an underwriting agreement which
     imposes indemnification or contribution obligations on the Company more
     onerous than those imposed hereunder.

     Section 9.  Information from Holders.  Each Holder of Registrable
                 ------------------------
Securities and Other Registrable Securities included in any registration shall
furnish to the Company such information regarding such Holder and the
distribution proposed by such Holder as the Company may reasonably request in
writing and as shall be reasonably required in connection with any registration,
qualification or compliance referred to in this Agreement or otherwise required
by applicable state or federal securities laws.

     Section 10.  Limitations on Registration Rights.  The Company shall not
                  ----------------------------------
enter into any agreement with any person who has after the date of this
Agreement acquired any newly issued securities of the Company which agreement
gives such person (a) the right to require the Company, upon any registration of
any of its securities, to include, among the securities which the Company is
then registering, such securities owned by such person, unless under the terms
of such agreement, such person may include such securities in any such
registration only to the extent that the inclusion of its securities will not
limit the number of Registrable Securities or Other Registrable Securities
sought to be included by the Holders of Registrable Securities or Other
Registrable Securities or reduce the offering price thereof; or (b) the right to
require the Company to initiate any registration of any securities of the
Company on terms more favorable than provided to the Investors hereunder.

     Section 11.  Exception to Registration.  The Company shall not be required
                  --------------------------
to effect a registration under this Agreement of Registrable Securities or Other
Registrable Securities if and to the extent in the written opinion of counsel
for the Company, which counsel and the opinion so rendered shall be reasonably
acceptable to the Holders of Registrable Securities or Other Registrable
Securities, as applicable, or pursuant to no-action letter obtained by the
Company from the Commission, such Holder may sell without registration under the
Act all Registrable Securities or Other Registrable Securities for which it
requested registration (a) under the provisions of the

                                       12
<PAGE>

Act; or (b) in the relevant three month period in accordance with the volume
limitations of Rule 144; and/or (c) in accordance with Rule 144A; provided,
                                                                  --------
however, that this Section 11 shall not apply to sales made under Rule 144(k) or
-------
any successor rule promulgated by the Commission until after the first
registration under the Act filed by the Company for an offering of its
securities to the public.

     Section 12.  Rule 144 Reporting.  With a view to making available the
                  ------------------
benefits of certain rules and regulations of the Commission which may permit the
sale of Restricted Securities to the public without registration, the Company
agrees to:

          (a)  make and keep public information available as those terms are
     understood and defined in Rule 144 under the Act, at all times from and
     after 90 days following the effective date of the first registration under
     the Act filed by the Company for an offering of its securities to the
     general public;

          (b)  use all of its commercially reasonable best efforts to file with
     the Commission in a timely manner all reports and other documents required
     of the Company under the Act and the Exchange Act at any time after it has
     become subject to such reporting requirements; and

          (c)  so long as any Holder (or its successors or assignees) owns any
     Restricted Securities, furnish to such Holder forthwith upon request a
     written statement by the Company as to its compliance with the reporting
     requirements of Rule 144 (at any time from and after 90 days following the
     effective date of the first registration statement filed by the Company for
     an offering of its securities to the general public), and of the Act and
     Exchange Act (at any time after it has become subject to such reporting
     requirements), a copy of the most recent annual or quarterly report of the
     Company, and such other reports and documents so filed as any Holder (or
     its successors or assignees) may reasonably request in availing itself of
     any rule or regulation of the Commission allowing the sale of any such
     securities without registration.

     Section 13.  Listing Application.  If Common Stock of the Company shall be
                  -------------------
listed on a national securities exchange or on the NASDAQ National Market System
(or NASDAQ SmallCap Market, as applicable), the Company shall, at its expense,
include in its listing application all of the Registrable Securities and Other
Registrable Securities.

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

          (a)  Amendments and Waivers. Amendments or additions to this Agreement
               ----------------------
     may be made, agreements with any decision of the Company may be made, and
     compliance with any term, covenant, agreement, condition or provision set
     forth herein may be omitted or waived (either generally or in a particular
     instance and either retroactively or prospectively) upon the written
     consent of each of (i) the Company, (ii)

                                       13
<PAGE>

     each of the Management Holders and (ii) the Holders of a majority of the
     Registrable Securities. Prompt notice of any such amendment or waiver shall
     be given to each party to this Agreement who did not consent thereto.

          (b) Notices.  All notices, requests, consents, reports and demands
              -------
     shall be in writing and shall be hand delivered, or mailed, postage
     prepaid, to the Company at the address set forth below, and to the
     Investors and the Management Holders at the addresses set forth on Schedule
                                                                        --------
     A and B hereto, or to such other address as may be furnished in writing to
     -     -
     the other parties hereto:

          The Company:

               MIL 3, Incorporated
               3400 International Drive, N.W.
               Washington, D.C. 20008
               Attn:  Marc A. Cohen, Chairman of
                      the Board of and Chief Executive
                      Officer

          with copy to:

               Verner, Liipfert, Bernhard, McPherson
                & Hand, Chartered
               Suite 700
               901 15th Street, N.W.
               Washington, D.C. 20005
               Attn: Harold I. Freilich, Esquire

          The Investors:

               The address set forth opposite the Investor's name on Schedule B
                                                                     ----------
               attached hereto.

          with copy to:

               Hutchins, Wheeler & Dittmar
               A Professional Corporation
               101 Federal Street
               Boston, MA  02120
               Attention:  James Westra, Esquire

                                       14
<PAGE>

          The Management Holders:

               The address set forth opposite each Management Holders' name on
               Schedule A hereto.
               ----------

     Notices given in accordance with the foregoing shall be deemed received (i)
     upon receipt, if hand delivered, and (ii) five business days after
     deposited in the U.S. mail, if sent by mail.

          (c)  Entire Agreement.  This Agreement and the Schedules referred to
               ----------------
     herein constitute the entire agreement of the parties with respect to the
     matters contemplated herein.  This Agreement and such Schedules supersede
     any and all prior understandings as to the subject matter of this
     Agreement.

          (d)  Equitable Relief.  The Company recognizes and agrees that the
               ----------------
     Holders of Registrable Securities and Other Registrable Securities shall
     not have an adequate remedy at law if the Company fails to comply with the
     provisions of this Agreement, and that damages will not be readily
     ascertainable, and the Company expressly agrees that in the event of such
     failure any such Holder shall be entitled to seek specific performance of
     the Company's obligations hereunder and that the Company will not oppose an
     application seeking such specific performance.

          (e)  Binding Effect; Assignment.  This Agreement shall be binding upon
               --------------------------
     and inure to the benefit of the successors and assigns of the respective
     parties hereto, provided, however, that each such successor and assign
                     --------  -------
     first executes and delivers to the other parties hereto a counterpart of
     this Agreement.

          (f)  General; Definitions.  The headings contained in this Agreement
               --------------------
     are for reference purposes only and shall not in any way affect the meaning
     or interpretation of this Agreement.  In this Agreement the singular
     includes the plural, the plural the singular, and the use of any gender
     includes the neuter, masculine and feminine genders.

          (g)  Severability.  If any provision of this Agreement shall be found
               ------------
     by any court of competent jurisdiction to be invalid or unenforceable, the
     parties hereby waive such provision to the extent that it is found to be
     invalid or unenforceable.  Such provision shall, to the maximum extent
     allowable by law, be modified by such court so that it becomes enforceable,
     and, as modified, shall be enforced as any other provision hereof, with all
     the other provisions hereof continuing in full force and effect.

          (h)  Counterparts.  This Agreement may be executed in multiple
               ------------
     counterparts, each of which together shall constitute an original but all
     of which together shall constitute but one and the same instrument.

                                       15
<PAGE>

          (i)  Governing Law.  This Agreement shall be deemed a contract made
               -------------
     under the laws of the State of New York and together with the rights and
     obligations of the parties hereunder, shall be construed under and governed
     by the laws of such State.

          (j)  Third Party Beneficiaries. This Agreement is made for the benefit
               -------------------------
     of the parties hereto and their successors or assigns, and, except as
     contemplated in Section 8, shall not confer any rights or benefits on any
     person not a party hereto.

                        [Signatures on following page]

                                       16
<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Registration Rights
Agreement to be duly executed as of the date first above written.

                   /s/ Alain J. Cohen
                 ------------------------------------
                 Alain J. Cohen

                   /s/ Marc A. Cohen
                 ------------------------------------
                 Marc A. Cohen

                 MIL 3, INCORPORATED

                 By:   /s/Marc A. Cohen
                   ----------------------------------
                    Name:  Marc A. Cohen
                    Its:  Chairman

                 SUMMIT VENTURES IV, L.P.

                    By:  Summit Partners IV, L.P.
                    Its:  General Partner

                          By:   Stamps, Woodsum & Co. IV
                          Its:   General Partner

                          By:   /s/ Bruce R. Evans
                              ------------------------------
                              General Partner

                 SUMMIT INVESTORS III, L.P.

                    By:  /s/ Bruce R. Evans
                        -----------------------------
                    Its: General Partner
<PAGE>

                                  SCHEDULE A
                                  ----------

Management Holders
------------------

Marc A. Cohen, Chairman of the Board and
 Chief Executive Officer
     MIL 3, Incorporated
     3400 International Drive, N.W.
     Washington, D.C. 20008

Alain J. Cohen, President
     MIL 3, Incorporated
     3400 International Drive, N.W.
     Washington, D.C. 20008
<PAGE>

                                  SCHEDULE B
                                  ----------

Investors
---------

Summit Investors III, L.P.
c/o Summit Partners
600 Atlantic Avenue
Suite 2800
Boston, MA 02210
Attn: Bruce R. Evans

Summit Ventures IV, L.P.
c/o Summit Partners
600 Atlantic Avenue
Suite 2800
Boston, MA 02210
Attn: Bruce R. Evans<PAGE>

                                                                    EXHIBIT 10.4

     STOCK REPURCHASE AGREEMENT dated as of September 30, 1997, by and between
MIL 3, INCORPORATED (the "Company"), a Delaware corporation, and MARC A. COHEN
(the "Shareholder"), an individual residing in the District of Columbia.

                                  WITNESSETH:

     WHEREAS,  Summit Ventures IV, L.P. and Summit Investors III, L.P. (together
the "Investors") and the Company have entered into a Series A Preferred Stock
Purchase Agreement (the "Series A Purchase Agreement") contemplating the sale by
the Company to the Investors of a total of 144,640 shares of the Company's newly
authorized Series A Preferred Stock (the "Series A Preferred Stock"), at a price
of $48.40 per share; and

     WHEREAS, the Shareholder desires to sell to the Company, and the Company
desires to repurchase from the Shareholder, 20,833 shares (the "Common Shares")
of the Company's common stock, par value $.01 per share, owned by the
Shareholder, at a price of $48.40 per Common Share, or an aggregate of
$1,008,317 (the "Repurchase Price").

     NOW, THEREFORE, in consideration of the foregoing and the mutual promises
set forth herein, the parties hereto, intending legally to be bound hereby,
agree as follows:

     1.  Notice of Repurchase.  Not later than one business day following
         ---------------------
consummation by the Company of the sale of the Series A Preferred Stock to the
Investors in accordance with the Series A Purchase Agreement (the "Series A
Closing"), the Company shall provide written notice (the "Tender Notice") to the
Shareholder of the date (the "Closing Date") on which the Company will
repurchase the Common Shares.

     2.  Closing.
         --------

          (a)  Following receipt by the Shareholder of the Tender Notice, the
Shareholder shall, on or before the Closing Date, deliver to the Company at its
offices specified in Section 5 below, one or more certificates evidencing the
Common Shares, accompanied by one or more undated stock transfers duly executed
in blank by the Shareholder.

          (b)  Subject to (i) consummation of the Series A Closing  and (ii)
compliance by the Shareholder with the terms and conditions herein, on the
Closing Date, the Company shall repurchase the Common Shares for the Repurchase
Price, which shall be paid by check drawn in the name of the Shareholder.

     3.  Representations.  The Shareholder represents and warrants that (a) he
         ----------------
is the sole and exclusive legal and beneficial owner of the Common Shares, free
and clear of all liens, claims and encumbrances (collectively, the "Liens"),
other than any such Lien that may exist in favor of the Company, (b) he has full
right, power and authority to sell, transfer and convey the Common
<PAGE>

Shares to the Company as contemplated hereby, and (c) he is familiar with the
business and affairs of the Company and has had an opportunity to ask questions
of, and receive answers from, the Company's management concerning the terms and
conditions of this Agreement, the Series A Purchase Agreement, and the Company.

     4.   Survival; Limitation of Liability.  The Shareholder's representations
          ----------------------------------
and warranties in Section 3 shall survive the execution and delivery of this
Agreement and the closing of the sale and repurchase of the Common Shares
contemplated hereby, and shall terminate on the first anniversary of the Closing
Date. Notwithstanding anything to the contrary herein, the liability of the
Shareholder for any breach of his representations and warranties shall not
exceed the Repurchase Price.

     5.   Notices.  All notices or other communications required or permitted to
          --------
be delivered hereunder shall be in writing signed by the party giving the notice
and sent by express delivery service, or regular or certified mail, addressed as
follows:

               If to the Company:

                    MIL 3, Incorporated
                    3400 International Drive, N.W.
                    Washington, D.C. 20008
                    Attn:  Marc A. Cohen, Chairman
                      and Chief Executive Officer

               If to the Shareholder:

                    Marc A. Cohen
                    c/o MIL 3, Incorporated
                    3400 International Drive, N.W.
                    Washington, D.C. 20008
                    Attn:  Marc J. Cohen, Chairman
                      and Chief Executive Officer

     Notices given in accordance with the foregoing shall be deemed received (i)
upon receipt, if hand delivered, and (ii) five business days after deposited in
the U.S. mail, if sent by mail.

     6.   Entire Agreement. This Agreement shall constitute the entire agreement
          ----------------
of the parties with respect to the matters contemplated herein. This Agreement
supersedes any and all prior understandings as to the subject matter of this
Agreement.

     7.   Amendments, Waivers and Consents.  Any provision in this Agreement to
          --------------------------------
the contrary notwithstanding, changes in or additions to this Agreement may be
made, and compliance

                                       2
<PAGE>

with any covenant or provision herein may be omitted or waived, only by a
writing signed by the parties.

     8.   Binding Effect; Assignment.  This Agreement shall be binding upon and
          --------------------------
inure to the benefit of the successors and assigns of the parties hereto.

     9.   General; Definitions. The headings contained in this Agreement are for
          --------------------
reference purposes only and shall not in any way affect the meaning or
interpretation of this Agreement. In this Agreement the singular includes the
plural, the plural the singular, and the masculine gender includes the neuter,
masculine and feminine genders.

     10.  Severability.  If any provision of this Agreement shall be found by
          ------------
any court of competent jurisdiction to be invalid or unenforceable, the parties
hereby waive such provision to the extent that it is found to be invalid or
unenforceable.  Such provision shall, to the maximum extent allowable by law, be
modified by such court so that it becomes enforceable, and, as modified, shall
be enforced as any other provision hereof, with all the other provisions hereof
continuing in full force and effect.

     11.  Counterparts.  This Agreement may be executed in counterparts, each of
          ------------
which shall be considered an original and both of which together shall
constitute one and the same instrument.

     12.  Governing Law.  This Agreement shall be deemed a contract made under
          -------------
the laws of the State of New York and together with the rights and obligations
of the parties hereunder, shall be construed under and governed by the laws of
such State.

     13.  Third Party Beneficiaries. This Agreement is made for the benefit of
          -------------------------
the parties hereto and shall not confer any rights or benefits on any person not
a party hereto.

                           [Signatures on next page]

                                       3
<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed and delivered as of the date for first above written.

                               MIL 3, INCORPORATED

                                By:  /s/   Alain Cohen
                                     -----------------------------
                                     Name:  Alain Cohen
                                     Title: President

                                     /s/   Marc A. Cohen
                                   -------------------------------
                                   MARC A. COHEN

                                       4

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