Exhibit 23.1



                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


      As independent public accountants, we hereby consent to the incorporation
by reference in this registration statement of our reports dated January 26,
1999 included in Excel Switching Corporation's Form 10-K for the year ended
December 31, 1998 and to all references to our Firm included in this
registration statement.


                                                     /s/ Arthur Andersen LLP
                                                     --------------------------
                                                     ARTHUR ANDERSEN LLP



Boston, Massachusetts
May 24, 1999