EXHIBIT 1.1 

                                                                  DRAFT 9/16/97



                            ________________ Shares


                          EXCEL SWITCHING CORPORATION

                    COMMON STOCK ($.01 PAR VALUE PER SHARE)



                            UNDERWRITING AGREEMENT


                              ____________, 1997


                       MORGAN STANLEY & CO. INCORPORATED
                             HAMBRECHT & QUIST LLC
                             MONTGOMERY SECURITIES

 
                              _______________, 1997



Morgan Stanley & Co. Incorporated
Hambrecht & Quist LLC
Montgomery Securities
c/o Morgan Stanley & Co.  Incorporated
1585 Broadway
New York, New York 10036

Dear Sirs and Mesdames:

     Excel Switching Corporation, a Massachusetts corporation (the "Company"),
proposes to issue and sell to the several Underwriters named in Schedule II
hereto (the "Underwriters"), an aggregate of _______________ shares of the
common stock, $.01 par value per share, of the Company (the "Firm Shares").

     Robert P. Madonna, a shareholder of the Company (the "Selling
Shareholder"), also proposes to sell to the several Underwriters not more than
an additional _______________ shares of the common stock, $.01 par value per
share, of the Company (the "Additional Shares"), if and to the extent that you,
as Managers of the offering, shall have determined to exercise, on behalf of the
Underwriters, the right to purchase such shares of common stock granted to the
Underwriters in Section 3 hereof.  The Firm Shares and the Additional Shares are
hereinafter collectively referred to as the "Shares." The shares of common
stock, $.01 par value per share, of the Company to be outstanding after giving
effect to the sales contemplated hereby are hereinafter referred to as the
"Common Stock."  The Company and the Selling Shareholder are hereinafter
sometimes collectively referred to as the "Sellers."

     The Company has filed with the Securities and Exchange Commission (the
"Commission") a registration statement, including a prospectus, relating to the
Shares. The registration statement as amended at the time it becomes effective,
including the information (if any) deemed to be part of the registration
statement at the time of effectiveness pursuant to Rule 430A under the
Securities Act of 1933, as amended (the "Securities Act"), is hereinafter
referred to as the "Registration Statement"; the prospectus in the form first
used to confirm sales of Shares is hereinafter referred to as the "Prospectus."
If the Company has filed an abbreviated registration statement to register
additional shares of Common Stock pursuant to Rule 462(b) under the Securities
Act (the "Rule 462 Registration Statement"), then any reference herein to the
term "Registration Statement" shall be deemed to include such Rule 462
Registration Statement.

 
     As part of the offering contemplated by this Agreement, Morgan Stanley &
Co. Incorporated ("Morgan Stanley") has agreed to reserve out of the Shares set
forth opposite its name on Schedule II to this Agreement, up to _____________
shares, for sale to the Company's employees, officers and directors [and other
parties associated with the Company] (collectively, "Participants"), as set
forth in the Prospectus under the heading "Underwriting" (the "Directed Share
Program").  The Shares to be sold by Morgan Stanley pursuant to the Directed
Share Program (the "Directed Shares") will be sold by Morgan Stanley pursuant to
this Agreement at the public offering price.  Any Directed Shares not orally
confirmed for purchase by any Participants by the end of the first business day
after the date on which this Agreement is executed will be offered to the public
by Morgan Stanley as set forth in the Prospectus.

     1.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company represents
          ---------------------------------------------                        
and warrants to and agrees with each of the Underwriters that:

          (a) The Registration Statement has become effective; no stop order
     suspending the effectiveness of the Registration Statement is in effect,
     and no proceedings for such purpose are pending before or threatened by the
     Commission.

          (b) (i) The Registration Statement,  when it became effective,  did
     not contain and,  as amended or supplemented, if applicable,  will not
     contain any untrue statement of a material fact or omit to state a material
     fact required to be stated therein or necessary to make the statements
     therein not misleading, (ii)  the Registration Statement and the Prospectus
     comply and,  as amended or supplemented,  if applicable, will comply in all
     material respects with the Securities Act and the applicable rules and
     regulations of the Commission thereunder and (iii) the Prospectus does not
     contain and, as amended or supplemented, if applicable, will not contain
     any untrue statement of a material fact or omit to state a material fact
     necessary to make the statements therein, in the light of the circumstances
     under which they were made, not misleading, except that the representations
     and warranties set forth in this paragraph 1(b) do not apply to statements
     or omissions in the Registration Statement or the Prospectus based upon
     information relating to any Underwriter furnished to the Company in writing
     by such Underwriter through you expressly for use therein.

          (c) The Company has been duly incorporated, is validly existing as a
     corporation in good standing under the laws of the jurisdiction of its
     incorporation, has the corporate power and authority to own its property
     and to conduct its business as described in the Prospectus and is duly
     qualified to transact business and is in good standing in each jurisdiction
     in which the conduct of its business or its ownership or leasing of
     property requires such qualification, except to the extent that the failure
     to be so qualified or be in good standing 

                                      -2-

 
     would not have a material adverse effect on the Company and its
     subsidiaries, taken as a whole.

          (d) Each subsidiary of the Company has been duly incorporated, is
     validly existing as a corporation in good standing under the laws of the
     jurisdiction of its incorporation, has the corporate power and authority to
     own its property and to conduct its business as described in the Prospectus
     and is duly qualified to transact business and is in good standing in each
     jurisdiction in which the conduct of its business or its ownership or
     leasing of property requires such qualification, except to the extent that
     the failure to be so qualified or be in good standing would not have a
     material adverse effect on the Company and its subsidiaries, taken as a
     whole; all of the issued shares of capital stock of each subsidiary of the
     Company have been duly and validly authorized and issued, are fully paid
     and non-assessable and are owned directly by the Company, free and clear of
     all liens, encumbrances, equities or claims.

          (e) This Agreement has been duly authorized, executed and delivered by
     the Company.

          (f) The authorized capital stock of the Company conforms as to legal
     matters to the description thereof contained in the Prospectus.

          (g) The shares of Common Stock (including the Shares to be sold by the
     Selling Shareholders) outstanding prior to the issuance of the Shares to be
     sold by the Company have been duly authorized and are validly issued, fully
     paid and non-assessable.

          (h) The Shares to be sold by the Company have been duly authorized
     and, when issued and delivered in accordance with the terms of this
     Agreement, will be validly issued, fully paid and non-assessable, and the
     issuance of such Shares will not be subject to any preemptive or similar
     rights.

          (i) The execution and delivery by the Company of, and the performance
     by the Company of its obligations under, this Agreement will not contravene
     any provision of applicable law or the certificate of incorporation or by-
     laws of the Company or any agreement or other instrument binding upon the
     Company or any of its subsidiaries that is material to the Company and its
     subsidiaries, taken as a whole, or any judgment, order or decree of any
     governmental body, agency or court having jurisdiction over the Company or
     any subsidiary, and no consent, approval, authorization or order of, or
     qualification with, any governmental body or agency is required for the
     performance by the Company of its obligations under this Agreement, except
     such as may be required by the securities or Blue Sky laws of the various
     states in connection with the offer and sale of the Shares.

                                      -3-

 
          (j) There has not occurred any material adverse change, or any
     development involving a prospective material adverse change, in the
     condition, financial or otherwise, or in the earnings, business or
     operations of the Company and its subsidiaries, taken as a whole, from that
     set forth in the Prospectus (exclusive of any amendments or supplements
     thereto subsequent to the date of this Agreement).

          (k) There are no legal or governmental proceedings pending or
     threatened to which the Company or any of its subsidiaries is a party or to
     which any of the properties of the Company or any of its subsidiaries is
     subject that are required to be described in the Registration Statement or
     the Prospectus and are not so described or any statutes, regulations,
     contracts or other documents that are required to be described in the
     Registration Statement or the Prospectus or to be filed as exhibits to the
     Registration Statement that are not described or filed as required.

          (l) Each preliminary prospectus filed as part of the registration
     statement as originally filed or as part of any amendment thereto, or filed
     pursuant to Rule 424 under the Securities Act, complied when so filed in
     all material respects with the Securities Act and the applicable rules and
     regulations of the Commission thereunder.

          (m) The Company is not and, after giving effect to the offering and
     sale of the Shares and the application of the proceeds thereof as described
     in the Prospectus, will not be an "investment company" as such term is
     defined in the Investment Company Act of 1940, as amended.

          (n) The Company and its subsidiaries (i) are in compliance with any
     and all applicable foreign, federal, state and local laws and regulations
     relating to the protection of human health and safety, the environment or
     hazardous or toxic substances or wastes, pollutants or contaminants
     ("Environmental Laws"), (ii) have received all permits, licenses or other
     approvals required of them under applicable Environmental Laws to conduct
     their respective businesses and (iii) are in compliance with all terms and
     conditions of any such permit, license or approval, except where such
     noncompliance with Environmental Laws, failure to receive required permits,
     licenses or other approvals or failure to comply with the terms and
     conditions of such permits, licenses or approvals would not, singly or in
     the aggregate, have a material adverse effect on the Company and its
     subsidiaries, taken as a whole.  The Company, in its reasonable judgment,
     has concluded that any costs or liabilities associated with Environmental
     Laws (including, without limitation, any capital or operating expenditures
     required for clean-up, closure of properties or compliance with
     Environmental Laws or any permit, license or approval, any related
     constraints on operating activities and any potential

                                      -4-

 
     liabilities to third parties) would not, singly or in the aggregate, have a
     material adverse effect on the Company and its subsidiaries, taken as a
     whole.

          (o) Subsequent to the respective dates as of which information is
     given in the Registration Statement and the Prospectus, (i) the Company and
     its subsidiaries have not incurred any material liability or obligation,
     direct or contingent, nor entered into any material transaction not in the
     ordinary course of business; (ii) the Company has not purchased any of its
     outstanding capital stock, nor declared, paid or otherwise made any
     dividend or distribution of any kind on its capital stock other than
     ordinary and customary dividends; and (iii) there has not been any material
     change in the capital stock, short-term debt or long-term debt of the
     Company and its consolidated subsidiaries, except in each case as would not
     reasonably be expected to result in any material adverse change in the
     condition, financial or otherwise, or in the earnings, business or
     operations of the Company and its subsidiaries, taken as a whole, except as
     described in or contemplated by the Prospectus.

          (p) The Company and its subsidiaries have good and marketable title in
     fee simple to all real property and good and marketable title to all
     personal property owned by them which is material to the business of the
     Company and its subsidiaries, in each case free and clear of all liens,
     encumbrances and defects except such as are described in the Prospectus or
     such as do not materially affect the value of such property and do not
     interfere with the use made and proposed to be made of such property by the
     Company and its subsidiaries; and any real property and buildings held
     under lease by the Company and its subsidiaries are held by them under
     valid, subsisting and enforceable leases or subleases with such exceptions
     as are not material and do not interfere with the use made and proposed to
     be made of such property and buildings by the Company and its subsidiaries,
     in each case except as described in or contemplated by the Prospectus.

          (q) The Company and its subsidiaries own or possess, or can acquire on
     reasonable terms, all material patents, patent rights, licenses,
     inventions, copyrights, know-how (including trade secrets and other
     unpatented and/or unpatentable proprietary or confidential information,
     systems or procedures), trademarks, service marks and trade names currently
     employed by them in connection with the business now operated by them, and
     neither the Company nor any of its subsidiaries has received any notice of
     infringement of or conflict with asserted rights of others with respect to
     any of the foregoing which, singly or in the aggregate, in the Company's
     reasonable judgment, would result in any material adverse change in the
     condition, financial or otherwise, or in the earnings, business or
     operations of the Company and its subsidiaries, taken as a whole.

                                      -5-

 
          (r) No material labor dispute with the employees of the Company or any
     of its subsidiaries exists, except as described in or contemplated by the
     Prospectus, or, to the knowledge of the Company, is imminent; and the
     Company is not aware of any existing, threatened or imminent labor
     disturbance by the employees of any of its principal suppliers,
     manufacturers or contractors that could result in any material adverse
     change in the condition, financial or otherwise, or in the earnings,
     business or operations of the Company and its subsidiaries, taken as a
     whole.

          (s) The Company and each of its subsidiaries are insured by insurers
     of recognized financial responsibility against such losses and risks and in
     such amounts as are customary in the businesses in which they are engaged;
     neither the Company nor any such subsidiary has been refused any insurance
     coverage sought or applied for; and neither the Company nor any such
     subsidiary has any reason to believe that it will not be able to renew its
     existing insurance coverage as and when such coverage expires or to obtain
     similar coverage from similar insurers as may be necessary to continue its
     business at a cost that would not materially and adversely affect the
     condition, financial or otherwise, or the earnings, business or operations
     of the Company and its subsidiaries, taken as a whole, except as described
     in or contemplated by the Prospectus.

          (t) The Company and its subsidiaries possess all certificates,
     authorizations and permits issued by the appropriate federal, state or
     foreign regulatory authorities necessary to conduct their respective
     businesses, and neither the Company nor any such subsidiary has received
     any notice of proceedings relating to the revocation or modification of any
     such certificate, authorization or permit which, singly or in the
     aggregate, if the subject of an unfavorable decision, ruling or finding,
     would result in a material adverse change in the condition, financial or
     otherwise, or in the earnings, business or operations of the Company and
     its subsidiaries, taken as a whole, except as described in or contemplated
     by the Prospectus.

          (u) The Company and each of its subsidiaries maintain a system of
     internal accounting controls sufficient to provide reasonable assurance
     that (i) transactions are executed in accordance with management's general
     or specific authorizations; (ii) transactions are recorded as necessary to
     permit preparation of financial statements in conformity with generally
     accepted accounting principles and to maintain asset accountability; (iii)
     access to assets is permitted only in accordance with management's general
     or specific authorization; and (iv) the recorded accountability for assets
     is compared with the existing assets at reasonable intervals and
     appropriate action is taken with respect to any differences.

                                      -6-

 
          (v) The accountants who have certified or shall certify the financial
     statements filed or to be filed with the Commission as part of the
     Registration Statement and the Prospectus are independent accountants as
     required by the Securities Act.  The consolidated financial statements of
     the Company and its subsidiaries (together with the related notes thereto)
     included in the Registration Statement present fairly the financial
     position and results of operations of the Company and its subsidiaries at
     the respective dates and for the respective periods to which they apply,
     subject to normal year-end adjustments.  Such financial statements have
     been prepared in accordance with generally accepted accounting principles
     consistently applied throughout the periods involved except as otherwise
     stated therein.

          (w) The Shares have been approved for listing on the Nasdaq National
     Market, subject to official notice of issuance.

          (x) Neither the Company nor any of its subsidiaries is in violation of
     any federal or state law or regulation relating to occupational safety and
     health or to the storage, handling or transportation of hazardous or toxic
     materials and the Company and its subsidiaries have received all permits,
     licenses or other approvals required of them under applicable federal and
     state occupational safety and health and environmental laws and regulations
     to conduct their respective businesses, and the Company and each subsidiary
     is in compliance with all terms and conditions of any such permit, license
     or approval, except any such violation of law or regulation, failure to
     receive required permits, licenses or other approvals or failure to comply
     with the terms and conditions of such permits, licenses or approvals which
     would not, singly or in the aggregate, result in a material adverse change
     in the condition, financial or otherwise, or in the earnings, business or
     operations of the Company and its subsidiaries, taken as a whole, except as
     described in or contemplated by the Prospectus.

          (y) There are no contracts, agreements or understandings between the
     Company and any person granting such person the right to require the
     Company to file a registration statement under the Securities Act with
     respect to any securities of the Company or to require the Company to
     include such securities with the Shares registered pursuant to the
     Registration Statement.

          (z) The Company has complied with all provisions of Section 517.075,
     Florida Statutes relating to doing business with the Government of Cuba or
     with any person or affiliate located in Cuba.

     Furthermore, the Company represents and warrants to Morgan Stanley that (i)
the Registration Statement, the Prospectus and any preliminary prospectus
comply, and any further amendments or supplements thereto will comply, with any
applicable laws or regulations of foreign jurisdictions in which the Prospectus
or any preliminary

                                      -7-

 
prospectus, as amended or supplemented, if applicable, are distributed in
connection with the Directed Share Program, and that (ii) no authorization,
approval, consent, license, order, registration or qualification of or with any
government, governmental instrumentality or court, other than such as have been
obtained, is necessary under the securities laws and regulations of foreign
jurisdictions in which the Directed Shares are offered outside the United
States.

     The Company has not offered, or caused the Underwriters to offer, Shares to
any person pursuant to the Directed Share Program with the specific intent to
unlawfully influence (i) a customer or supplier of the Company to alter the
customer's or supplier's level or type of business with the Company, or (ii) a
trade journalist or publication to write or publish favorable information about
the Company or its products.

     2.   REPRESENTATIONS AND WARRANTIES OF THE SELLING SHAREHOLDER.  The
          ---------------------------------------------------------      
Selling Shareholder represents and warrants to and agrees with each of the
Underwriters that:

          (a) This Agreement has been duly authorized, executed and delivered by
     or on behalf of the Selling Shareholder.

          (b) The execution and delivery by the Selling Shareholder of, and the
     performance by such Selling Shareholder of its obligations under, this
     Agreement, the Custody Agreement signed by such Selling Shareholder and
     ____________, as Custodian, relating to the deposit of the Shares to be
     sold by such Selling Shareholder (the "Custody Agreement") and the Power of
     Attorney appointing certain individuals as such Selling Shareholder's
     attorneys-in-fact to the extent set forth therein, relating to the
     transactions contemplated hereby and by the Registration Statement (the
     "Power of Attorney"), will not contravene any provision of applicable law
     or any agreement or other instrument binding upon the Selling Shareholder
     or any judgment, order or decree of any governmental body, agency or court
     having jurisdiction over the Selling Shareholder, and no consent, approval,
     authorization or order of, or qualification with, any governmental body or
     agency is required for the performance by the Selling Shareholder of his
     obligations under this Agreement or the Custody Agreement or Power of
     Attorney of such Selling Shareholder, except such as may be required by the
     securities or Blue Sky laws of the various states in connection with the
     offer and sale of the Shares.

          (c) The Selling Shareholder has, and on the Closing Date will have,
     valid title to the Shares to be sold by the Selling Shareholder and the
     legal right and power, and all authorization and approval required by law,
     to enter into this Agreement, the Custody Agreement and the Power of
     Attorney and to sell, transfer and deliver the Shares to be sold by the
     Selling Shareholder.

                                      -8-

 
          (d) The Shares to be sold by the Selling Shareholder pursuant to this
     Agreement have been duly authorized and are validly issued, fully paid and
     non-assessable.

          (e) The Custody Agreement and the Power of Attorney have been duly
     authorized, executed and delivered by the Selling Shareholder and are valid
     and binding agreements of the Selling Shareholder.

          (f) Delivery of the Shares to be sold by the Selling Shareholder
     pursuant to this Agreement will pass title to such Shares free and clear of
     any security interests, claims, liens, equities and other encumbrances.

          (g) (i) the Registration Statement, when it became effective, did not
     contain and, as amended or supplemented, if applicable, will not contain
     any untrue statement of a material fact or omit to state a material fact
     required to be stated therein or necessary to make the statements therein
     not misleading, (ii) the Registration Statement and the Prospectus comply
     and, as amended or supplemented, if applicable, will comply in all material
     respects with the Securities Act and the applicable rules and regulations
     of the Commission thereunder and (iii) the Prospectus does not contain and,
     as amended or supplemented, if applicable, will not contain any untrue
     statement of a material fact or omit to state a material fact necessary to
     make the statements therein, in the light of the circumstances under which
     they were made, not misleading, except that the representations and
     warranties set forth in this paragraph 2(g) do not apply to statements or
     omissions in the Registration Statement or the Prospectus based upon
     information relating to any Underwriter furnished to the Company in writing
     by such Underwriter through you expressly for use therein.

     3.   AGREEMENTS TO SELL AND PURCHASE.  The Company hereby agrees to sell to
          -------------------------------                                       
the several Underwriters, and each Underwriter, upon the basis of the
representations and warranties herein contained, but subject to the conditions
hereinafter stated, agrees, severally and not jointly, to purchase from the
Company at $______ a share (the "Purchase Price") the number of Firm Shares
(subject to such adjustments to eliminate fractional shares as you may
determine) that bears the same proportion to the number of Firm Shares to be
sold by the Company as the number of Firm Shares set forth in Schedule II hereto
opposite the name of such Underwriter bears to the total number of Firm Shares.

     On the basis of the representations and warranties contained in this
Agreement, and subject to its terms and conditions, the Company and the Selling
Shareholder agree to sell to the Underwriters the Additional Shares, and the
Underwriters shall have a one-time right to purchase, severally and not jointly,
up to ______________ Additional Shares at the Purchase Price.  If you, on behalf
of the Underwriters, elect to exercise such option, you shall so notify the
Company in writing not later than 30 days after the date 

                                      -9-

 
of this Agreement, which notice shall specify the number of Additional Shares to
be purchased by the Underwriters and the date on which such shares are to be
purchased. Such date may be the same as the Closing Date (as defined below) but
not earlier than the Closing Date nor later than ten business days after the
date of such notice. Additional Shares may be purchased as provided in Section 5
hereof solely for the purpose of covering over-allotments made in connection
with the offering of the Firm Shares. If any Additional Shares are to be
purchased, each Underwriter agrees, severally and not jointly, to purchase the
number of Additional Shares (subject to such adjustments to eliminate fractional
shares as you may determine) that bears the same proportion to the total number
of Additional Shares to be purchased as the number of Firm Shares set forth in
Schedule II hereto opposite the name of such Underwriter bears to the total
number of Firm Shares.

     Each Seller hereby agrees that, without the prior written consent of Morgan
Stanley & Co.  Incorporated on behalf of the Underwriters, it will not, during
the period ending 180 days after the date of the Prospectus, (i) offer, pledge,
sell, contract to sell, sell any option or contract to purchase, purchase any
option or contract to sell, grant any option, right or warrant to purchase or
otherwise transfer or dispose of, directly or indirectly, any shares of Common
Stock or any securities convertible into or exercisable or exchangeable for
Common Stock or (ii) enter into any swap or other arrangement that transfers to
another, in whole or in part, any of the economic consequences of ownership of
the Common Stock, whether any such transaction described in clause (i) or (ii)
above is to be settled by delivery of Common Stock or such other securities, in
cash or otherwise.  The foregoing sentence shall not apply to (A) the Shares to
be sold hereunder or (B) the issuance by the Company of shares of Common Stock
upon the exercise of an option or warrant or the conversion of a security
outstanding on the date hereof of which the Underwriters have been advised in
writing.  In addition, each Selling Shareholder agrees that, without the prior
written consent of Morgan Stanley & Co. Incorporated on behalf of the
Underwriters, it will not, during the period ending 180 days after the date of
the Prospectus, make any demand for, or exercise any right with respect to, the
registration of any shares of Common Stock or any security convertible into or
exercisable or exchangeable for Common Stock.

     4.   TERMS OF PUBLIC OFFERING.  The Sellers are advised by you that the
          ------------------------                                          
Underwriters propose to make a public offering of their respective portions of
the Shares as soon after the Registration Statement and this Agreement have
become effective as in your judgment is advisable.  The Sellers are further
advised by you that the Shares are to be offered to the public initially at
$____________ a share (the "Public Offering Price") and to certain dealers
selected by you at a price that represents a concession not in excess of $______
a share under the Public Offering Price, and that any Underwriter may allow, and
such dealers may reallow, a concession, not in excess of $_____ a share, to any
Underwriter or to certain other dealers.

                                      -10-

 
     5.   PAYMENT AND DELIVERY.  Payment for the Firm Shares to be sold by each
          --------------------                                                 
Seller shall be made to such Seller in Federal or other funds immediately
available in New York City against delivery of such Firm Shares for the
respective accounts of the several Underwriters at 10:00 A.M., New York City
time, on ____________ 1997, or at such other time on the same or such other
date, not later than _________, 1997, as shall be designated in writing by you.
The time and date of such payment are hereinafter referred to as the "Closing
Date."  The closing of the offering and sale of the Firm Shares will be held at
the offices of Testa, Hurwitz & Thibeault, LLP, 125 High Street, Boston,
Massachusetts.

     Payment for any Additional Shares shall be made to the Company in Federal
or other funds immediately available in New York City against delivery of such
Additional Shares for the respective accounts of the several Underwriters at
10:00 A.M., New York City time, on the date specified in the notice described in
Section 3 or at such other time on the same or on such other date, in any event
not later than _______, 1997, as shall be designated in writing by you.  The
time and date of such payment are hereinafter referred to as the "Option Closing
Date."  The closing of the offering and sale of the Additional Shares will be
held at the offices of Testa, Hurwitz & Thibeault, LLP, 125 High Street, Boston,
Massachusetts.

     Certificates for the Firm Shares and Additional Shares shall be in
definitive form and registered in such names and in such denominations as you
shall request in writing not later than one full business day prior to the
Closing Date or the Option Closing Date, as the case may be.  The certificates
evidencing the Firm Shares and Additional Shares shall be delivered to you on
the Closing Date or the Option Closing Date, as the case may be, for the
respective accounts of the several Underwriters, with any transfer taxes payable
in connection with the transfer of the Shares to the Underwriters duly paid,
against payment of the Purchase Price therefor.

     6.   CONDITIONS TO THE UNDERWRITERS' OBLIGATIONS.  The obligations of the
          -------------------------------------------                         
Sellers to sell the Shares to the Underwriters and the several obligations of
the Underwriters to purchase and pay for the Shares on the Closing Date are
subject to the condition that the Registration Statement shall have become
effective not later than 4:30 p.m. (New York City time) on the date hereof.

     The several obligations of the Underwriters are subject to the following
further conditions:

          (a) Subsequent to the execution and delivery of this Agreement and
     prior to the Closing Date:

               (i) if any of the Company's securities are rated by any
          "nationally recognized statistical rating organization," as such term
          is defined for purposes of Rule 436(g)(2) under the Securities Act,
          there shall not have

                                      -11-

 
          occurred any downgrading, nor shall any notice have been given of any
          intended or potential downgrading or of any review for a possible
          change that does not indicate the direction of the possible change, in
          the rating accorded any such securities; and

               (ii) there shall not have occurred any change, or any development
          involving a prospective change, in the condition, financial or
          otherwise, or in the earnings, business or operations of the Company
          and its subsidiaries, taken as a whole, from that set forth in the
          Prospectus (exclusive of any amendments or supplements thereto
          subsequent to the date of this Agreement) that, in your judgment, is
          material and adverse and that makes it, in your judgment,
          impracticable to market the Shares on the terms and in the manner
          contemplated in the Prospectus.

          (b) The Underwriters shall have received on the Closing Date a
     certificate, dated the Closing Date and signed by an executive officer of
     the Company, to the effect set forth in clause (a) (i) above and to the
     effect that the representations and warranties of the Company contained in
     this Agreement are true and correct as of the Closing Date and that the
     Company has complied with all of the agreements and satisfied all of the
     conditions on its part to be performed or satisfied hereunder on or before
     the Closing Date.

          The officer signing and delivering such certificate may rely upon the
     best of his or her knowledge as to proceedings threatened.

          (c) The Underwriters shall have received on the Closing Date an
     opinion of Testa, Hurwitz & Thibeault, LLP, outside counsel for the
     Company, dated the Closing Date, to the effect that:

               (i) the Company has been duly incorporated, is validly existing
          as a corporation in good standing under the laws of the jurisdiction
          of its incorporation, has the corporate power and authority to own its
          property and to conduct its business as described in the Prospectus
          and is duly qualified to transact business and is in good standing in
          _________, ________ and _________, which are the only jurisdictions in
          which the Company maintains an office or owns or leases property;

               (ii)  each subsidiary of the Company has been duly incorporated,
          is validly existing as a corporation in good standing under the laws
          of the jurisdiction of its incorporation, has the corporate power and
          authority to own its property and to conduct its business as described
          in the Prospectus and is duly qualified, in the case of _____, in
          _____, ______ and _____, and in the case of _____, in _____, ________
          and _______, which are the only

                                      -12-

 
          jurisdictions in which such subsidiary maintains an office or owns or
          leases property;

               (iii) the authorized capital stock of the Company conforms in all
          material respects as to legal matters to the description thereof
          contained in the Prospectus under the caption "Description of Capital
          Stock" and the Shares have been duly authorized for quotation on the
          Nasdaq National Market.

               (iv)  the shares of Common Stock (including the Shares to be sold
          by the Selling Shareholders) outstanding prior to the issuance of the
          Shares to be sold by the Company have been duly authorized and are
          validly issued, fully paid and non-assessable;

               (v) all of the issued shares of capital stock of each subsidiary
          of the Company have been duly and validly authorized and issued, are
          fully paid and non-assessable and are owned directly by the Company,
          free and clear of all liens, encumbrances, equities or claims;

               (vi)  the Shares to be sold by the Company have been duly
          authorized and, when issued and delivered in accordance with the terms
          of this Agreement, will be validly issued, fully paid and non-
          assessable, and the issuance of such Shares will not be subject to any
          preemptive or similar rights under the Massachusetts Business
          Corporation Law or, to such counsel's knowledge, similar rights
          granted by contract;

               (vii)  this Agreement has been duly authorized, executed and
          delivered by the Company;

               (viii) the execution and delivery by the Company of, and the
          performance by the Company of its obligations under, this Agreement
          will not contravene any provision of applicable law (except that such
          counsel need express no opinion as to state securities or blue sky
          laws) or the articles of organization or by-laws of the Company or, to
          the best of such counsel's knowledge, any agreement or other
          instrument binding upon the Company or any of its subsidiaries that is
          material to the Company and its subsidiaries, taken as a whole, or, to
          the best of such counsel's knowledge, any judgment, order or decree of
          any governmental body, agency or court having jurisdiction over the
          Company or any subsidiary, and no consent, approval, authorization or
          order of, or qualification with, any governmental body or agency is
          required for the performance by the Company of its obligations under
          this Agreement, except that counsel need express no opinion as to
          state securities or blue sky laws;

                                      -13-

 
               (ix) no shares of Common Stock are required pursuant to any
          agreement or other right to be registered under the Registration
          Statement, and no person has the right to require such registration,
          except such rights that have either been satisfied or validly waived;
   
               (x) the statements (A) in the Prospectus under the captions "Risk
          Factors -- Shares Eligible for Future Sale," "Risk Factors --
          Potential Adverse Effects of Anti-Takeover Provisions; Availability of
          Preferred Stock for Issuance," "Management -- Stock Plans,"
          "Description of Capital Stock," "Shares Eligible for Future Sale" and
          the first, second, third and fifth paragraphs of the "Underwriters"
          and (B) in the Registration Statement in Items 14 and 15, in each case
          insofar as such statements constitute summaries of the legal matters,
          documents or proceedings referred to therein, fairly present the
          information called for with respect to such legal matters, documents
          and proceedings and fairly summarize the matters referred to therein;
    
               (xi)  after due inquiry, such counsel does not know of any legal
          or governmental proceedings pending or threatened to which the Company
          or any of its subsidiaries is a party or to which any of the
          properties of the Company or any of its subsidiaries is subject that
          are required to be described in the Registration Statement or the
          Prospectus and are not so described or of any statutes, regulations,
          contracts or other documents that are required to be described in the
          Registration Statement or the Prospectus or to be filed as exhibits to
          the Registration Statement that are not described or filed as
          required;

               (xii) the Company is not and, after giving effect to the offering
          and sale of the Shares and the application of the proceeds thereof as
          described in the Prospectus, will not be an "investment company" as
          such term is defined in the Investment Company Act of 1940, as
          amended; and

               (xiii)  such counsel (A) is of the opinion that the Registration
          Statement and Prospectus (except for financial statements and
          schedules and other financial and statistical data included therein as
          to which such counsel need not express any opinion) comply as to form
          in all material respects with the Securities Act and the applicable
          rules and regulations of the Commission thereunder, (B) has no reason
          to believe that (except for financial statements and schedules and
          other financial and statistical data as to which such counsel need not
          express any belief) the Registration Statement and the prospectus
          included therein at the time the Registration Statement became
          effective contained any untrue statement of a material fact or omitted
          to state a material fact required to be stated therein or necessary to
          make the statements therein not misleading and (C) has no reason to
          believe that (except for financial statements and schedules and

                                      -14-

 
          other financial and statistical data as to which such counsel need not
          express any belief) the Prospectus contains any untrue statement of a
          material fact or omits to state a material fact necessary in order to
          make the statements therein, in the light of the circumstances under
          which they were made, not misleading.

          (d) If the option granted pursuant to the second paragraph of Section
     3 hereof is exercised, the Underwriters shall have received on the Closing
     Date an opinion of Testa, Hurwitz & Thibeault, LLP, counsel for the Selling
     Shareholder, dated the Closing Date, to the effect that:

               (i) this Agreement has been duly authorized, executed and
          delivered by or on behalf of the Selling Shareholder;

               (ii)  the execution and delivery by the Selling Shareholder of,
          and the performance by the Selling Shareholder of his obligations
          under, this Agreement and the Custody Agreement and Power of Attorney
          of such Selling Shareholder will not contravene any provision of
          applicable law or, to the best of such counsel's knowledge, any
          agreement or other instrument binding upon the Selling Shareholder or,
          to the best of such counsel's knowledge, any judgment, order or decree
          of any governmental body, agency or court having jurisdiction over the
          Selling Shareholder, and no consent, approval, authorization or order
          of, or qualification with, any governmental body or agency is required
          for the performance by the Selling Shareholder of his obligations
          under this Agreement or the Custody Agreement or Power of Attorney of
          such Selling Shareholder, except such as may be required by the
          securities or Blue Sky laws of the various states in connection with
          offer and sale of the Shares;

               (iii) the Selling Shareholder is the record owner of the Shares
          to be sold by him and he has the legal right and power, and all
          authorization and approval required by law, to enter into this
          Agreement and the Custody Agreement and Power of Attorney of such
          Selling Shareholder and to sell, transfer and deliver the Shares to be
          sold by him;

               (iv)  the Custody Agreement and the Power of Attorney of the
          Selling Shareholder have been duly authorized, executed and delivered
          by the Selling Shareholder and are valid and binding agreements of the
          Selling Shareholder; and

               (v) each Underwriter that is a "bona fide purchaser" within the
          meaning of Article 8 of the Massachusetts Uniform Commercial Code (the
          "Code") will acquire, upon payment for the Shares as provided in this

                                      -15-

 
          Agreement, its interest in the Shares, free of any adverse claim, as
          defined in the Code.

          (e) The Underwriters shall have received on the Closing Date an
     opinion of Cesari and McKenna LLP, patent counsel for the Company, dated
     the Closing Date, covering the matters referred to in Exhibit A hereto.

          (f) The Underwriters shall have received on the Closing Date an
     opinion of Hale and Dorr LLP, counsel for the Underwriters, dated the
     Closing Date, covering the matters referred to in subparagraphs (vi),
     (vii), (x) (but only as to the statements in the Prospectus under
     "Description of Capital Stock" and "Underwriters") and (xiii) of paragraph
     (c) above.

          With respect to the first two clauses of subparagraph (v) of paragraph
     (c) above, Testa, Hurwitz & Thibeault, LLP, may rely upon an opinion of
     local counsel to any subsidiary of the Company in giving such opinion,
     provided that (A) counsel for the subsidiary is satisfactory to your
     --------                                                            
     counsel, (B) a copy of each opinion so relied upon is delivered to you and
     is in form and substance satisfactory to your counsel, and (C) Testa,
     Hurwitz & Thibeault, LLP, shall state in their opinion that they are
     justified in relying on each such other opinion.  With respect to
     subparagraph (xiii) of paragraph (c) above, Testa, Hurwitz & Thibeault,
     LLP, and Hale and Dorr LLP may state that their opinion and belief are
     based upon their participation in the preparation of the Registration
     Statement and Prospectus and any amendments or supplements thereto and
     review and discussion of the contents thereof, but are without independent
     check or verification, except as specified.

          The opinions of Testa, Hurwitz & Thibeault, LLP, described in
     paragraphs (c) and (d) above shall be rendered to the Underwriters at the
     request of the Company or the Selling Shareholder, as the case may be, and
     shall so state therein.

          (g) The Underwriters shall have received, on each of the date hereof
     and the Closing Date, a letter dated the date hereof or the Closing Date,
     as the case may be, in form and substance satisfactory to the Underwriters,
     from Arthur Andersen LLP, independent public accountants, containing
     statements and information of the type ordinarily included in accountants'
     "comfort letters" to underwriters with respect to the financial statements
     and certain financial information contained in the Registration Statement
     and the Prospectus; provided that the letter delivered on the Closing Date
                         --------                                              
     shall use a "cut-off date" not earlier than the date hereof.

          (h) The "lock-up" agreements, each substantially in the form of
     Exhibit B hereto, between you and certain shareholders, officers and
     directors of the

                                      -16-

 
     Company relating to sales and certain other dispositions of shares of
     Common Stock or certain other securities, delivered to you on or before the
     date hereof, shall be in full force and effect on the Closing Date.

     The several obligations of the Underwriters to purchase Additional Shares
hereunder are subject to the delivery to you on the Option Closing Date of such
documents as you may reasonably request with respect to the good standing of the
Company, the due authorization and issuance of the Additional Shares and other
matters related to the issuance of the Additional Shares.

     7.   COVENANTS OF THE COMPANY.  In further consideration of the agreements
          ------------------------                                             
of the Underwriters herein contained, the Company covenants with each
Underwriter as follows:

          (a) To furnish to you, without charge, four signed copies of the
     Registration Statement (including exhibits thereto) and for delivery to
     each other Underwriter a conformed copy of the Registration Statement
     (without exhibits thereto) and to furnish to you in New York City, without
     charge, prior to 10:00 A.M.  New York City time on the business day next
     succeeding the date of this Agreement and during the period mentioned in
     paragraph (c) below, as many copies of the Prospectus and any supplements
     and amendments thereto or to the Registration Statement as you may
     reasonably request.

          (b) Before amending or supplementing the Registration Statement or the
     Prospectus, to furnish to you a copy of each such proposed amendment or
     supplement and not to file any such proposed amendment or supplement to
     which you reasonably object, and to file with the Commission within the
     applicable period specified in Rule 424(b) under the Securities Act any
     prospectus required to be filed pursuant to such Rule.

          (c) If, during such period after the first date of the public offering
     of the Shares as in the opinion of counsel for the Underwriters the
     Prospectus is required by law to be delivered in connection with sales by
     an Underwriter or dealer, any event shall occur or condition exist as a
     result of which it is necessary to amend or supplement the Prospectus in
     order to make the statements therein, in the light of the circumstances
     when the Prospectus is delivered to a purchaser, not misleading, or if, in
     the opinion of counsel for the Underwriters, it is necessary to amend or
     supplement the Prospectus to comply with applicable law, forthwith to
     prepare, file with the Commission and furnish, at its own expense, to the
     Underwriters and to the dealers (whose names and addresses you will furnish
     to the Company) to which Shares may have been sold by you on behalf of the
     Underwriters and to any other dealers upon request, either amendments or
     supplements to the Prospectus so that the statements in the Prospectus as
     so amended or supplemented will not, in the light of the circumstances when
     the

                                      -17-

 
     Prospectus is delivered to a purchaser, be misleading or so that the
     Prospectus, as amended or supplemented, will comply with law.

          (d) To aid your counsel in qualifying the Shares for offer and sale
     under the securities or Blue Sky laws of such jurisdictions as you shall
     reasonably request.

          (e) To make generally available to the Company's security holders and
     to you as soon as practicable an earning statement covering the twelve-
     month period ending _________, 1998 that satisfies the provisions of
     Section 11(a) of the Securities Act and the rules and regulations of the
     Commission thereunder.

          (f) Whether or not the transactions contemplated in this Agreement are
     consummated or this Agreement is terminated, to pay or cause to be paid all
     expenses incident to the performance of its and the Selling Shareholder's
     obligations under this Agreement, including: (i) the fees, disbursements
     and expenses of the Company's counsel, the Company's accountants and
     counsel for the Selling Shareholder in connection with the registration and
     delivery of the Shares under the Securities Act and all other fees or
     expenses in connection with the preparation and filing of the Registration
     Statement, any preliminary prospectus, the Prospectus and amendments and
     supplements to any of the foregoing, including all printing costs
     associated therewith, and the mailing and delivering of copies thereof to
     the Underwriters and dealers, in the quantities hereinabove specified, (ii)
     all costs and expenses related to the transfer and delivery of the Shares
     to the Underwriters, including any transfer or other taxes payable thereon,
     (iii) the cost of printing or producing any Blue Sky or Legal Investment
     memorandum in connection with the offer and sale of the Shares under state
     securities laws and all expenses in connection with the qualification of
     the Shares for offer and sale under state securities laws as provided in
     Section 7(d) hereof, including filing fees and the reasonable fees and
     disbursements of counsel for the Underwriters in connection with such
     qualification and in connection with the Blue Sky or Legal Investment
     memorandum, (iv) all filing fees and disbursements of counsel to the
     Underwriters incurred in connection with the review and qualification of
     the offering of the Shares by the National Association of Securities
     Dealers, Inc., (v) all fees and expenses in connection with the preparation
     and filing of the registration statement on Form 8-A relating to the Common
     Stock and all costs and expenses incident to listing the Shares on the
     Nasdaq National Market, (vi) the cost of printing certificates representing
     the Shares, (vii) the costs and charges of any transfer agent, registrar or
     depositary, (viii) the costs and expenses of the Company relating to
     investor presentations on any "road show" undertaken in connection with the
     marketing of the offering of the Shares, including, without limitation,
     expenses associated with the production of road show slides and graphics,
     fees and expenses of any consultants engaged in connection with the road
     show presentations with the prior approval of the 

                                      -18-

 
     Company, travel and lodging expenses of the representatives and officers of
     the Company and any such consultants, and the cost of any aircraft
     chartered in connection with the road show, and (ix) all other costs and
     expenses incident to the performance of the obligations of the Company
     hereunder for which provision is not otherwise made in this Section. It is
     understood, however, that except as provided in this Section, Section 9
     entitled "Indemnity and Contribution," and the last paragraph of Section 11
     below, the Underwriters will pay all of their costs and expenses, including
     fees and disbursements of their counsel, stock transfer taxes payable on
     resale of any of the Shares by them and any advertising expenses connected
     with any offers they may make.

          (g) Not to file with the Commission any registration statement on Form
     S-8 relating to its Common Stock prior to 180 days after the date of the
     Prospectus.

          (h) That in connection with the Directed Share Program, the Company
     will ensure that the Directed Shares will be restricted to the extent
     required by the National Association of Securities Dealers, Inc. (the
     "NASD") or the NASD rules from sale, transfer, assignment, pledge or
     hypothecation for a period of three months following the date of the
     effectiveness of the Registration Statement. Morgan Stanley will notify the
     Company as to which Participants will need to be so restricted.  At the
     request of Morgan Stanley, the Company will direct the transfer agent to
     place stop transfer restrictions upon such securities for such period of
     time.

          (i) To pay all fees and disbursements of counsel incurred by the
     Underwriters in connection with the Directed Share Program and stamp
     duties, similar taxes or duties or other taxes, if any, incurred by the
     Underwriters in connection with the Directed Share Program.

     Furthermore, the Company covenants with Morgan Stanley that the Company
will comply with all applicable securities and other applicable laws, rules and
regulations in each foreign jurisdiction in which the Directed Shares are
offered in connection with the Directed Share Program.
 
     The provisions of this Section shall not supersede or otherwise affect any
agreement that the Sellers may otherwise have for the allocation of such
expenses among themselves.

     8.   Expenses of the Selling Shareholder.  The Selling Shareholder agrees
          -----------------------------------                                 
to pay or cause to be paid all taxes, if any, on the transfer and sale of the
Shares being sold by the Selling Shareholder.

                                      -19-

 
     9.   Indemnity and Contribution.
          -------------------------- 

          (a) The Company and the Selling Shareholder, jointly and severally,
     agree to indemnify and hold harmless each Underwriter and each person, if
     any, who controls any Underwriter within the meaning of either Section 15
     of the Securities Act or Section 20 of the Securities Exchange Act of 1934,
     as amended (the "Exchange Act"), from and against any and all losses,
     claims, damages and liabilities (including, without limitation, any legal
     or other expenses reasonably incurred in connection with defending or
     investigating any such action or claim) caused by any untrue statement or
     alleged untrue statement of a material fact contained in the Registration
     Statement or any amendment thereof, any preliminary prospectus or the
     Prospectus (as amended or supplemented if the Company shall have furnished
     any amendments or supplements thereto), or caused by 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, except
     insofar as such losses, claims, damages or liabilities are caused by any
     such untrue statement or omission or alleged untrue statement or omission
     based upon information relating to any Underwriter furnished to the Company
     in writing by such Underwriter through you expressly for use therein.

          The Company agrees to indemnify and hold harmless Morgan Stanley and
     each person, if any, who controls Morgan Stanley within the meaning of
     either Section 15 of the Securities Act or Section 20 of the Exchange Act
     ("Morgan Stanley Entities"), from and against any and all losses, claims,
     damages and liabilities (including, without limitation, any legal or other
     expenses reasonably incurred in connection with defending or investigating
     any such action or claim) (i) caused by any untrue statement or alleged
     untrue statement of a material fact contained in the prospectus wrapper
     material prepared by or with the consent of the Company for distribution in
     foreign jurisdictions in connection with the Directed Share Program
     attached to the Prospectus or any preliminary prospectus, or caused by any
     omission or alleged omission to state therein a material fact required to
     be stated therein or necessary to make the statements therein, when
     considered in conjunction with the Prospectus or any applicable preliminary
     prospectus, not misleading; (ii) caused by the failure of any Participant
     to pay for and accept delivery of the shares which, immediately following
     the effectiveness of the Registration Statement, were subject to a properly
     confirmed agreement to purchase; or (iii) related to, arising out of, or in
     connection with the Directed Share Program, provided that, the Company
     shall not be responsible under this subparagraph (iii) for any losses,
     claim, damages or liabilities (or expenses relating thereto) that are
     finally judicially determined to have resulted from the bad faith or gross
     negligence of Morgan Stanley Entities.

                                      -20-

 
          (b) The Selling Shareholder agrees to indemnify and hold harmless the
     Company, its directors, its officers who sign the Registration Statement
     and each person, if any, who controls the Company within the meaning of
     either Section 15 of the Securities Act or Section 20 of the Exchange Act,
     from and against any and all losses, claims, damages and liabilities
     (including, without limitation, any legal or other expenses reasonably
     incurred in connection with defending or investigating any such action or
     claim) caused by any untrue statement or alleged untrue statement of a
     material fact contained in the Registration Statement or any amendment
     thereof, any preliminary prospectus or the Prospectus (as amended or
     supplemented if the Company shall have furnished any amendments or
     supplements thereto), or caused by 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, but only with reference to
     information relating to the Selling Shareholder furnished in writing by or
     on behalf of the Selling Shareholder expressly for use in the Registration
     Statement, any preliminary prospectus, the Prospectus or any amendments or
     supplements thereto.

          (c) Each Underwriter agrees, severally and not jointly, to indemnify
     and hold harmless the Company, the Selling Shareholder, the directors of
     the Company, the officers of the Company who sign the Registration
     Statement and each person, if any, who controls the Company within the
     meaning of either Section 15 of the Securities Act or Section 20 of the
     Exchange Act from and against any and all losses, claims, damages and
     liabilities (including, without limitation, any legal or other expenses
     reasonably incurred in connection with defending or investigating any such
     action or claim) caused by any untrue statement or alleged untrue statement
     of a material fact contained in the Registration Statement or any amendment
     thereof, any preliminary prospectus or the Prospectus (as amended or
     supplemented if the Company shall have furnished any amendments or
     supplements thereto), or caused by 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, but only with reference to
     information relating to such Underwriter furnished to the Company in
     writing by such Underwriter through you expressly for use in the
     Registration Statement, any preliminary prospectus, the Prospectus or any
     amendments or supplements thereto.

          (d) The aggregate liability of the Selling Shareholder under the
     representations and warranties contained in Section 2(g) hereof and for
     indemnification under Section 9(a) shall in no event exceed the lesser of
     (i) the net proceeds received by the Selling Shareholder from the
     Underwriters in the offering of the Shares and (ii) that proportion of the
     total of such losses, claims, damages and liabilities equal to the
     proportion of the Shares being sold by such Selling Shareholder to the
     total Shares being sold hereunder.

                                      -21-

 
          (e) In case any proceeding (including any governmental investigation)
     shall be instituted involving any person in respect of which indemnity may
     be sought pursuant to paragraph (a), (b) or (c) of this Section 9, such
     person (the "indemnified party") shall promptly notify the person against
     whom such indemnity may be sought (the "indemnifying party") in writing and
     the indemnifying party, upon request of the indemnified party, shall retain
     counsel reasonably satisfactory to the indemnified party to represent the
     indemnified party and any others the indemnifying party may designate in
     such proceeding and shall pay the fees and disbursements of such counsel
     related to such proceeding.  In any such proceeding, any indemnified party
     shall have the right to retain its own counsel, but the fees and expenses
     of such counsel shall be at the expense of such indemnified party unless
     (i) the indemnifying party and the indemnified party shall have mutually
     agreed to the retention of such counsel or (ii) the named parties to any
     such proceeding (including any impleaded parties) include both the
     indemnifying party and the indemnified party and representation of both
     parties by the same counsel would be inappropriate due to actual or
     potential differing interests between them.  It is understood that the
     indemnifying party shall not, in respect of the legal expenses of any
     indemnified party in connection with any proceeding or related proceedings
     in the same jurisdiction, be liable for (i) the fees and expenses of more
     than one separate firm (in addition to any local counsel) for all
     Underwriters and all persons, if any, who control any Underwriter within
     the meaning of either Section 15 of the Securities Act or Section 20 of the
     Exchange Act, (ii) the fees and expenses of more than one separate firm (in
     addition to any local counsel) for the Company, its directors, its officers
     who sign the Registration Statement and each person, if any, who controls
     the Company within the meaning of either such Section and (iii) the fees
     and expenses of more than one separate firm (in addition to any local
     counsel) for the Selling Shareholder, and that all such fees and expenses
     shall be reimbursed as they are incurred.  In the case of any such separate
     firm for the Underwriters and such control persons of any Underwriters,
     such firm shall be designated in writing by Morgan Stanley & Co.
     Incorporated.  In the case of any such separate firm for the Company, and
     such directors, officers and control persons of the Company, such firm
     shall be designated in writing by the Company.  In the case of any such
     separate firm for the Selling Shareholder, such firm shall be designated in
     writing by the persons named as attorneys-in-fact for the Selling
     Shareholder under the Power of Attorney.  The indemnifying party shall not
     be liable for any settlement of any

                                      -22-

 
     proceeding effected without its written consent, but if settled with such
     consent or if there be a final judgment for the plaintiff, the indemnifying
     party agrees to indemnify the indemnified party from and against any loss
     or liability by reason of such settlement or judgment. Notwithstanding the
     foregoing sentence, if at any time an indemnified party shall have
     requested an indemnifying party to reimburse the indemnified party for fees
     and expenses of counsel as contemplated by the second and third sentences
     of this paragraph, the indemnifying party agrees that it shall be liable
     for any settlement of any proceeding effected without its written consent
     if (i) such settlement is entered into more than 30 days after receipt by
     such indemnifying party of the aforesaid request and (ii) such indemnifying
     party shall not have reimbursed the indemnified party in accordance with
     such request prior to the date of such settlement. No indemnifying party
     shall, without the prior written consent of the indemnified party, effect
     any settlement of any pending or threatened proceeding in respect of which
     any indemnified party is or could have been a party and indemnity could
     have been sought hereunder by such indemnified party, unless such
     settlement includes an unconditional release of such indemnified party from
     all liability on claims that are the subject matter of such proceeding.

          Notwithstanding anything contained herein to the contrary, if
     indemnity may be sought pursuant to the last paragraph of Section 9(a)
     hereof in respect of such action or proceeding, then in addition to such
     separate firm for the indemnified parties, the indemnifying party shall be
     liable for the reasonable fees and expenses of not more than one separate
     firm (in addition to local counsel) for Morgan Stanley for the defense of
     any losses, claims, damages and liabilities arising out of the Directed
     Share Program, and all persons, if any, who control Morgan Stanley within
     the meaning of either Section 15 of the Act or Section 20 of the Exchange
     Act.

          (f) To the extent the indemnification provided for in paragraph (a),
     (b) or (c) of this Section 9 is unavailable to an indemnified party or
     insufficient in respect of any losses, claims, damages or liabilities
     referred to therein, then each indemnifying party under such paragraph, in
     lieu of indemnifying such indemnified party thereunder, shall contribute to
     the amount paid or payable by such indemnified party as a result of such
     losses, claims, damages or liabilities (i) in such proportion as is
     appropriate to reflect the relative benefits received by the indemnifying
     party or parties on the one hand and the indemnified party or parties on
     the other hand from the offering of the Shares or (ii) if the allocation
     provided by clause (i) above is not permitted by applicable law, in such
     proportion as is appropriate to reflect not only the relative benefits
     referred to in clause (i) above but also the relative fault of the
     indemnifying party or parties on the one hand and of the indemnified party
     or parties on the other hand in connection with the statements or omissions
     that resulted in such losses, claims, damages or liabilities, as well as
     any other relevant equitable considerations.  The relative benefits
     received by the Sellers on the one hand and the Underwriters on the other
     hand in connection with the offering of the Shares shall be deemed to be in
     the same respective proportions as the net proceeds from the offering of
     the Shares (before deducting expenses) received by each Seller and the
     total underwriting discounts and commissions received by the Underwriters,
     in each case as set forth in the table on the cover of the Prospectus, bear
     to the aggregate Public Offering Price of the Shares.  The relative fault
     of the Sellers on the one hand and the Underwriters on the other hand shall
     be determined by reference to,

                                      -23-

 
     among other things, whether the untrue or alleged untrue statement of a
     material fact or the omission or alleged omission to state a material fact
     relates to information supplied by the Sellers or by the Underwriters and
     the parties' relative intent, knowledge, access to information and
     opportunity to correct or prevent such statement or omission. The
     Underwriters' respective obligations to contribute pursuant to this Section
     9 are several in proportion to the respective number of Shares they have
     purchased hereunder, and not joint.

          (g) The Sellers and the Underwriters agree that it would not be just
     or equitable if contribution pursuant to this Section 9 were determined by
     pro rata allocation (even if the Underwriters were treated as one entity
     --------                                                                
     for such purpose) or by any other method of allocation that does not take
     account of the equitable considerations referred to in paragraph (f) of
     this Section 9.  The amount paid or payable by an indemnified party as a
     result of the losses, claims, damages and liabilities referred to in the
     immediately preceding paragraph shall be deemed to include, subject to the
     limitations set forth above, any legal or other expenses reasonably
     incurred by such indemnified party in connection with investigating or
     defending any such action or claim.  Notwithstanding the provisions of this
     Section 9, no Underwriter shall be required to contribute any amount in
     excess of the amount by which the total price at which the Shares
     underwritten by it and distributed to the public were offered to the public
     exceeds the amount of any damages that such Underwriter has otherwise been
     required to pay by reason of such untrue or alleged untrue statement or
     omission or alleged omission.  No person guilty of fraudulent
     misrepresentation (within the meaning of Section 11(f) of the Securities
     Act) shall be entitled to contribution from any person who was not guilty
     of such fraudulent misrepresentation.  The remedies provided for in this
     Section 9 are not exclusive and shall not limit any rights or remedies
     which may otherwise be available to any indemnified party at law or in
     equity.

          (h) The indemnity and contribution provisions contained in this
     Section 9 and the representations, warranties and other statements of the
     Company and the Selling Shareholders contained in this Agreement shall
     remain operative and in full force and effect regardless of (i) any
     termination of this Agreement, (ii) any investigation made by or on behalf
     of any Underwriter or any person controlling any Underwriter, any Selling
     Shareholder or any person controlling any Selling Shareholder, or the
     Company, its officers or directors or any person controlling the Company
     and (iii) acceptance of and payment for any of the Shares.

     10.  TERMINATION.  This Agreement shall be subject to termination by notice
          -----------                                                           
given by you to the Company, if (a) after the execution and delivery of this
Agreement and prior to the Closing Date (i) trading generally shall have been
suspended or materially limited on or by, as the case may be, any of the New
York Stock Exchange, the American Stock Exchange, the National Association of
Securities Dealers, Inc., the Chicago Board of Options Exchange, the Chicago
Mercantile Exchange or the Chicago

                                      -24-

 
Board of Trade, (ii) trading of any securities of the Company shall have been
suspended on any exchange or in any over-the-counter market, (iii) a general
moratorium on commercial banking activities in New York shall have been declared
by either Federal or New York State authorities or (iv) there shall have
occurred any outbreak or escalation of hostilities or any change in financial
markets or any calamity or crisis that, in your judgment, is material and
adverse and (b) in the case of any of the events specified in clauses (a) (i)
through (iv), such event, singly or together with any other such event, makes
it, in your judgment, impracticable to market the Shares on the terms and in the
manner contemplated in the Prospectus.

     11.  EFFECTIVENESS; DEFAULTING UNDERWRITERS.  This Agreement shall become
          --------------------------------------                              
effective upon the execution and delivery hereof by the parties hereto.

     If, on the Closing Date or the Option Closing Date, as the case may be, any
one or more of the Underwriters shall fail or refuse to purchase Shares that it
has or they have agreed to purchase hereunder on such date, and the aggregate
number of Shares which such defaulting Underwriter or Underwriters agreed but
failed or refused to purchase is not more than one-tenth of the aggregate number
of the Shares to be purchased on such date, the other Underwriters shall be
obligated severally in the proportions that the number of Firm Shares set forth
opposite their respective names in Schedule II bears to the aggregate number of
Firm Shares set forth opposite the names of all such non-defaulting
Underwriters, or in such other proportions as you may specify, to purchase the
Shares which such defaulting Underwriter or Underwriters agreed but failed or
refused to purchase on such date; provided that in no event shall the number of
                                  --------                                     
Shares that any Underwriter has agreed to purchase pursuant to this Agreement be
increased pursuant to this Section 11 by an amount in excess of one-ninth of
such number of Shares without the written consent of such Underwriter.  If, on
the Closing Date, any Underwriter or Underwriters shall fail or refuse to
purchase Firm Shares and the aggregate number of Firm Shares with respect to
which such default occurs is more than one-tenth of the aggregate number of Firm
Shares to be purchased, and arrangements satisfactory to you, the Company and
the Selling Shareholders for the purchase of such Firm Shares are not made
within 36 hours after such default, this Agreement shall terminate without
liability on the part of any non-defaulting Underwriter, the Company or the
Selling Shareholders.  In any such case either you or the relevant Sellers shall
have the right to postpone the Closing Date, but in no event for longer than
seven days, in order that the required changes, if any, in the Registration
Statement and in the Prospectus or in any other documents or arrangements may be
effected.  If, on the Option Closing Date, any Underwriter or Underwriters shall
fail or refuse to purchase Additional Shares and the aggregate number of
Additional Shares with respect to which such default occurs is more than one-
tenth of the aggregate number of Additional Shares to be purchased, the non-
defaulting Underwriters shall have the option to (i) terminate their obligation
hereunder to purchase Additional Shares or (ii) purchase not less than the
number of Additional Shares that such non-defaulting Underwriters would have
been obligated to purchase in the absence of such default.

                                      -25-

 
Any action taken under this paragraph shall not relieve any defaulting
Underwriter from liability in respect of any default of such Underwriter under
this Agreement.

     If this Agreement shall be terminated by the Underwriters, or any of them,
because of any failure or refusal on the part of any Seller to comply with the
terms or to fulfill any of the conditions of this Agreement, or if for any
reason any Seller shall be unable to perform its obligations under this
Agreement, the Sellers will reimburse the Underwriters or such Underwriters as
have so terminated this Agreement with respect to themselves, severally, for all
out-of-pocket expenses (including the fees and disbursements of their counsel)
reasonably incurred by such Underwriters in connection with this Agreement or
the offering contemplated hereunder.

     12.  COUNTERPARTS.  This Agreement may be signed in two or more
          ------------                                              
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

     13.  APPLICABLE LAW.  This Agreement shall be governed by and construed in
          --------------                                                       
accordance with the internal laws of the State of New York.

     14.  HEADINGS.  The headings of the sections of this Agreement have been
          --------                                                           
inserted for convenience of reference only and shall not be deemed a part of
this Agreement.





                            [BLANK PAGE IN ORIGINAL]

                                      -26-

 
                              Very truly yours,

                              EXCEL SWITCHING CORPORATION


                              By______________________________________
                                    Name:
                                    Title:

                              The Selling Shareholder


                              _________________________________________
                                    Robert P. Madonna



Accepted as of the date hereof

Morgan Stanley & Co. Incorporated
Hambrecht & Quist LLC
Montgomery Securities

Acting severally on behalf of
 themselves and the several
 Underwriters named herein.

     By Morgan Stanley & Co.
        Incorporated


     By __________________________
        Name:
        Title:

                                      -27-

 
                                   SCHEDULE I



                                    Number of Additional
                                    Shares to be Sold
                                    --------------------
                               
Robert P. Madonna
 
                                    ----------------
        Total.....................
                                    ================


                                      -28-

 
                                  SCHEDULE II




                                       
                                       Number of Firm
                                       Shares To Be
            Underwriter                Purchased
            -----------                ---------
 
                                  
Morgan Stanley & Co. Incorporated

Hambrecht & Quist LLC

Montgomery Securities

[NAMES OF OTHER UNDERWRITERS]
 
 
 
 
                                       ------------
              Total.................
                                       ============


                                      -29-

 
                                                   Exhibit A
                                                   ---------


                    MATTERS TO BE COVERED IN THE OPINION OF
                              CESARI AND MCKENNA LLP


     Such counsel are familiar with the technology used by the Company and its
subsidiaries in their businesses and the manner of its use thereof and have read
the Registration Statement and the Prospectus, including particularly the
portions of the Registration Statement and the Prospectus referring to
trademarks, trade names, patents, mask works, copyrights, licenses, trade
secrets or other intellectual property rights and:

          (i) such counsel have no reason to believe that the Registration
     Statement or the Prospectus (A) contains any untrue statement of a material
     fact with respect to trademarks, trade names, patents, mask works,
     copyrights, licenses, trade secrets or other intellectual property rights
     owned or used by the Company or any of its subsidiaries, or the manner of
     its use thereof, or any allegation on the part of any person that the
     Company or any of its subsidiaries is infringing any trademarks, trade
     names, patent rights, mask works, copyrights, licenses, trade secrets or
     other intellectual property rights of any such person or (B) omits to state
     any material fact relating to trademarks, trade names, patents, mask works,
     copyrights, licenses, trade secrets or other intellectual property rights
     owned or used by the Company or any of its subsidiaries, or the manner of
     its use thereof, or any allegation of which such counsel have knowledge,
     that is required to be stated in the Registration Statement or the
     Prospectus or is necessary to make the statements therein not misleading;

          (ii) to the best of such counsel's knowledge and except as set forth
     in the Prospectus under the captions "Risk Factors-Dependence on
     Proprietary Rights" and "Business-Intellectual Property," there are no
     legal or governmental proceedings pending relating to trademarks, trade
     names, patent rights, mask works, copyrights, licenses, trade secrets or
     other intellectual property rights of the Company or any of its
     subsidiaries, and to the best of such counsel's knowledge no such
     proceedings are threatened or contemplated by governmental authorities or
     others;

          (iii)  the Company and its subsidiaries duly and properly hold the
     patents, and have duly and properly filed the patent applications, listed
     in the Prospectus under the caption "Business-Intellectual Property";

          (iv) such counsel do not know of any contracts or other documents
     relating to the Company's or any of its subsidiaries' trademarks, trade
     names, patents, mask works, copyrights, licenses, trade secrets or other
     intellectual property rights of a character required to be filed as an
     exhibit to the Registration

 
     Statement or required to be described in the Registration Statement or the
     Prospectus that are not filed or described as required;
   
          (v) to the best of such counsel's knowledge, neither the Company nor
     any of its subsidiaries (A) is infringing or otherwise violating any
     patents, mask works, copyrights, licenses, trade secrets or other
     intellectual property rights of others or (B) has received any allegation
     or notice of infringement or other violation of any trademark or trade
     name, and to the best of such counsel's knowledge there are no
     infringements by others of any of the Company's or any of its subsidiaries'
     trademarks, trade names, patents, mask works, copyrights, licenses, trade
     secrets or other intellectual property rights which in the judgment of such
     counsel could affect materially the use thereof by the Company of any of
     its subsidiaries; and
    

          (vi) to the best of such counsel's knowledge, the Company or one of
     its subsidiaries owns or possesses sufficient licenses or other rights to
     use all patents, mask works, copyrights, licenses, trade secrets or other
     intellectual property rights necessary to conduct the business now being or
     proposed to be conducted by the Company and its subsidiaries as described
     in the Prospectus.
    

                                      -2-

 
                                                                       Exhibit B
                                                                       ---------



                            [FORM OF LOCK-UP LETTER]
                             ---------------------- 


                                                   ______________, 1997

Morgan Stanley & Co. Incorporated
Montgomery Securities
Hambrecht & Quist LLC
c/o Morgan Stanley & Co. Incorporated
1585 Broadway
New York, NY  10036

Dear Sirs and Mesdames:

     The undersigned understands that Morgan Stanley & Co. Incorporated ("Morgan
Stanley") proposes to enter into an Underwriting Agreement (the "Underwriting
Agreement") with Excel Switching Corporation, a Massachusetts corporation (the
"Company"), providing for the public offering (the "Public Offering") by the
several Underwriters, including Morgan Stanley (the "Underwriters"), of 
4,500,000 shares (the "Shares") of the Common Stock, $.01 par value per share
of the Company (the "Common Stock").

     To induce the Underwriters that may participate in the Public Offering to
continue their efforts in connection with the Public Offering, the undersigned
hereby agrees that, without the prior written consent of Morgan Stanley on
behalf of the Underwriters, it will not, during the period commencing on the
date hereof and ending 180 days after the date of the final prospectus relating
to the Public Offering (the "Prospectus"), (1) offer, pledge, sell, contract to
sell, sell any option or contract to purchase, purchase any option or contract
to sell, grant any option, right or warrant to purchase, or otherwise transfer
or dispose of, directly or indirectly, any shares of Common Stock or any
securities convertible into or exercisable or exchangeable for Common Stock
(provided that such shares or securities are either now owned by the undersigned
or are hereafter acquired prior to or in connection with the Public Offering),
or (2) enter into any swap or other arrangement that transfers to another, in
whole or in part, any of the economic consequences of ownership of the Common
Stock, whether any such transaction described in clause (1) or (2) above is to
be settled by delivery of Common Stock or such other securities, in cash or
otherwise. The foregoing sentence shall not apply to the sale of any Shares to
the Underwriters pursuant to the Underwriting Agreement.  In addition, the
undersigned agrees that, without the prior written consent of Morgan Stanley on
behalf of the Underwriters, it will not, during the

 
period commencing on the date hereof and ending 180 days after the date of the
Prospectus, make any demand for or exercise any right with respect to, the
registration of any shares of Common Stock or any security convertible into or
exercisable or exchangeable for Common Stock.

     Whether or not the Public Offering actually occurs depends on a number of
factors, including market conditions. Any Public Offering will only be made
pursuant to an Underwriting Agreement, the terms of which are subject to
negotiation between the Company and the Underwriters.


                              Very truly yours,


                              ---------------------------------
                              (Name)

                              ---------------------------------
                              (Address)


                                      -2-