AMENDMENT TO RIGHTS AGREEMENT 


  
           This AMENDMENT (this "Amendment") is being entered into as of
 August 3, 1998 between Stratus Computer, Inc., a Massachusetts corporation
 (the "Company"), and BankBoston, N.A., as rights agent (the "Rights
 Agent"). 

           The Company and The First National Bank of Boston are parties to
 a Rights Agreement dated as of December 4, 1990 (the "Rights Agreement"). 
 Pursuant to Section 27 of the Rights Agreement, the Company and the Rights
 Agent may, prior to the Distribution Date (as defined therein), amend any
 provision of the Rights Agreement (other than certain specifically
 enumerated provisions) without the approval of any holders of certificates
 representing the common stock of the Company.  The Company now desires to
 amend the Rights Agreement as set forth in this Amendment.   
  
           NOW THEREFORE, in consideration of the premises and the mutual
 agreement herein set forth, the parties hereby agree as follows: 
  
           1.   AMENDMENT OF SECTION 1(a).  Section 1(a) of the Rights
 Agreement is hereby amended to add the following sentence at the end
 thereof:
  
           "Notwithstanding anything in this Rights Agreement to the
           contrary, neither Ascend nor any of its existing or future
           Affiliates or Associates shall be deemed to be an Acquiring
           Person solely by virtue of (i) the execution of the Merger
           Agreement, (ii) the acquisition of Common Stock or other capital
           stock of the Company pursuant to the Merger Agreement or the
           consummation of the Merger, or (iii) the consummation of the
           other transactions contemplated by the Merger Agreement." 
  
           2.   AMENDMENT OF SECTION 1(v).  Section 1(v) of the Rights
 Agreement is hereby amended to add the following proviso at the end
 thereof:
  
           "; provided, however, that no Triggering Event shall result
           solely by virtue of (i) the execution of the Merger Agreement,
           (ii) the acquisition of Common Stock or other capital stock of
           the Company pursuant to the Merger Agreement or the consummation
           of the Merger or (iii) the consummation of the other transactions
           contemplated by the Merger Agreement." 
  
           3.   AMENDMENT OF SECTION 1.  Section 1 of the Rights Agreement
 is hereby further amended to add the following subparagraphs at the end
 thereof:
  
                (w)  "Ascend" shall mean Ascend Communications, Inc., a
           Delaware corporation. 
  
                (x)  "Merger" shall have the meaning set forth in the Merger
           Agreement. 
  
                (y)  "Merger Agreement" shall have the meaning set forth in
           Section 35 hereof. 
  
                (z)  "Merger Subsidiary" shall have the meaning set forth in
           Section 35 hereof. 
  
           4.   AMENDMENT OF SECTION 3(a).  Section 3(a) of the Rights
 Agreement is hereby amended to add the following sentence at the end
 thereof:
  
           "Notwithstanding anything in this Rights Agreement to the
           contrary, a Distribution Date shall not be deemed to have
           occurred solely by virtue of (i) the execution of the Merger
           Agreement, (ii) the acquisition of Common Stock or other capital
           stock of the Company pursuant to the Merger Agreement or the
           consummation of the Merger or (iii) the consummation of the other
           transactions contemplated by the Merger Agreement." 
  
           5.   AMENDMENT OF SECTION 7(a).  Section 7(a) of the Rights
 Agreement is amended to add the following sentence at the end thereof:
  
           "Notwithstanding anything in this Rights Agreement to the
           contrary,  none of (i) the execution of the Merger Agreement,
           (ii) the acquisition of Common Stock or other capital stock of
           the Company pursuant to the Merger Agreement or the consummation
           of the Merger or (iii) the consummation of the other transactions
           contemplated by the Merger Agreement shall be deemed to be events
           that cause the Rights to become exercisable pursuant to the
           provisions of this Section 7 or otherwise." 
  
           6.   AMENDMENT OF SECTION 11.  Section 11 of the Rights Agreement
 is amended to add the following sentence after the first sentence of said
 Section:
  
           "Notwithstanding anything in this Rights Agreement to the
           contrary,  none of (i) the execution of the Merger Agreement,
           (ii) the acquisition of Common Stock or other capital stock of
           the Company pursuant to the Merger Agreement or the consummation
           of the Merger or (iii) the consummation of the other transactions
           contemplated in the Merger Agreement shall be deemed to be events
           of the type described in this Section 11 or to cause the Rights
           to be adjusted or to become exercisable in accordance with this
           Section 11." 
  
           7.   AMENDMENT OF SECTION 13(d).  Section 13(d) of the Rights
 Agreement is amended to add the following sentence at the end thereof:
  
           "Notwithstanding anything in this Rights Agreement to the
           contrary,  none of (i) the execution of the Merger Agreement,
           (ii) the acquisition of Common Stock or other capital stock of
           the Company pursuant to the Merger Agreement or the consummation
           of the Merger or (iii) the consummation of the other transactions
           contemplated in the Merger Agreement shall be deemed to be events
           of the type described in this Section 13 or to cause the Rights
           to be adjusted or to become exercisable in accordance with this
           Section 13." 
  
           8.   ADDITION OF SECTION 35.  The Rights Agreement is hereby
 modified, supplemented and amended to add the following new Section 35:
  
           "Section 35.  Merger With Wildcard Merger Corporation 
  
                The Company, Ascend and Wildcard Merger Corporation,  a
           Delaware corporation and a wholly owned subsidiary of Ascend
           ("Merger Subsidiary"), have entered into an Agreement and Plan of
           Merger, dated as of August 3, 1998 as it may be amended from time
           to time (the "Merger Agreement"), pursuant to which Merger
           Subsidiary shall merge with and into the Company. 
           Notwithstanding anything in this Rights Agreement to the
           contrary, if the Merger Agreement shall be terminated for any
           reason, then (a) the last sentence of Section 1(a) hereof shall
           be deemed repealed and deleted without any further action on the
           part of the Company or the Rights Agent and (b) the proviso at
           the end of Section 1(v) hereof shall be deemed repealed and
           deleted without any further action on the part of the Company or
           the Rights Agent." 
  
           9.   EFFECTIVENESS.  This Amendment shall be deemed effective as
 of the date first written above, as if executed on such date.  Except as
 amended hereby, the Rights Agreement shall remain in full force and effect
 and shall be otherwise unaffected hereby.
  
           10.  MISCELLANEOUS.  This Amendment shall be deemed to be a
 contract made under the laws of the Commonwealth of Massachusetts and for
 all purposes shall be governed by and construed in accordance with the laws
 of the Commonwealth of Massachusetts applicable to contracts to be made and
 performed entirely within the Commonwealth of Massachusetts without giving
 effect to the principles of conflict of laws thereof.  This Amendment may
 be executed in any number of counterparts,  each of such counterparts shall
 for all purposes be deemed to be an original, and all such counterparts
 shall together constitute but one and the same instrument.  If any
 provision, covenant or restriction of this Agreement is held by a court of
 competent jurisdiction or other authority to be invalid, illegal or
 unenforceable, the remainder of the terms, provisions, covenants and
 restrictions of this Amendment shall remain in full force and effect and
 shall in no way be affected, impaired or invalidated.
  
           EXECUTED under seal as of the date first set forth above. 
  
 Attest:                       STRATUS COMPUTER, INC. 
  
  
 /s/ Eileen Casal              By: /s/ Maurice L. Castonguay
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 Attest:                       RIGHTS AGENT:  BANKBOSTON, N.A. 
  
  
 /s/ Paul Lyons                By: /s/ Tyler Haynes
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