EXHIBIT 2.2
                                                                     -----------

       AMENDMENT NO. 1 TO AGREEMENT AND PLAN OF MERGER AND REORGANIZATION

     This Amendment No. 1 (this "AMENDMENT") to the Agreement and Plan of Merger
and Reorganization dated as of April 15, 1999 (the "MERGER AGREEMENT"), by and
among Excel Switching Corporation, a Massachusetts corporation ("PARENT"),
Racepoint Acquisition Corporation, a Delaware corporation and a wholly-owned
subsidiary of Parent ("MERGER SUB"), RAScom, Inc., a Delaware corporation (the
"COMPANY"), those certain shareholders of the Company set forth on the signature
pages thereof (the "COMPANY SHAREHOLDERS"), and Mark B. Galvin as the
"Indemnification Representative identified therein (the "INDEMNIFICATION
REPRESENTATIVE"), is entered into by and among Parent, the Company, those
stockholders of the Company whose signatures appear below and the
Indemnification Representative as of this 7th day of May, 1999.

     WHEREAS, the parties to this Amendment and others have entered into the
Merger Agreement;

     WHEREAS, Section 8.3 of the Merger Agreement provides that the Merger
Agreement may not be amended except by an instrument in writing signed on behalf
of the Company, a majority of the Company Shareholders and Parent;

     WHEREAS, the parties hereto desire to amend the Merger Agreement as set
forth below, and constitute a sufficient percentage of the Company Shareholders
and each other party specified in Section 8.3 of the Merger Agreement required
to take such action;

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereby agree as
follows:

     1.       Amendment of Merger Agreement. The Merger Agreement is hereby
amended by adding, at the end of Section 2.2(b) thereof, the following new
sentence:

                      Without limiting the foregoing, and notwithstanding the
              prior execution of the Escrow Agreement by the parties thereto in
              the form attached as Exhibit B hereto, the Indemnification
              Representative shall be authorized, in his capacity as
              Indemnification Representative and on behalf of the Company
              Shareholders, to enter into such additional agreement with Parent,
              Merger Sub, the Company and the Indemnification Escrow Agent as
              may be reasonably requested by the Indemnification Escrow Agent
              for the purpose of clarifying or more fully setting forth the
              rights and responsibilities of the Indemnification Escrow Agent
              under the Escrow Agreement; provided, that no such additional
              agreement shall have the effect of enlarging the scope of the
              indemnification obligations of the Company Shareholders, extending
              the Escrow Termination Date, as defined in the Escrow Agreement,
              increasing the number of Indemnification Escrow Shares to be
              delivered to the Indemnification Escrow Agent or providing for
              disparate treatment among similarly situated Company Shareholders
              except to the extent already provided for in the Escrow Agreement.



     IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of
the date first written above.



                                 EXCEL SWITCHING CORPORATION

                                 By: /s/ Christopher Stavros
                                     -------------------------------------
                                 Title: Vice President and General Counsel
                                        ----------------------------------


                                 RACEPOINT ACQUISITION CORPORATION

                                 By: /s/ Christopher Stavros
                                     -------------------------------------
                                 Title: Vice President
                                        ----------------------------------


                                 RASCOM, INC.

                                 By: /s/ Mark Galvin
                                     -------------------------------------
                                     Mark Galvin, President


                                 /s/ Mark Galvin
                                 -----------------------------------------
                                 Mark Galvin, as a Company Shareholder
                                 and as Indemnification Representative


                                 CHARLES RIVER PARTNERSHIP VII

                                 By: /s/ Michael Zak
                                     -------------------------------------
                                 Title: General Partner
                                        ----------------------------------



                                 PCC TRANSFER LIMITED PARTNERSHIP

                                 By: /s/ Frank Polestra
                                     -------------------------------------
                                 Title: Manager
                                        ----------------------------------




                                 PIONEER VENTURES LIMITED PARTNERSHIP II

                                 By: /s/ Frank Polestra
                                     -------------------------------------
                                 Title: President
                                        ----------------------------------


                                 HARBOURVEST PARTNERS V -
                                 DIRECT FUND L.P.
                                 One Financial Center
                                 Boston, MA  02109

                                 By: HVP V - Direct Associates L.L.C.
                                 Its: General Partner

                                 By: Harbour Vest Partners, LLC
                                 Its: Managing Member

                                 By: /s/ Ofer Nemerovsky
                                     -------------------------------------
                                 Title: Managing Director
                                        ----------------------------------