<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM ASCEND
COMMUNICATIONS, INC. AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<RESTATED>
<MULTIPLIER> 1,000

<S>                             <C>                     <C>                    <C>
<PERIOD-TYPE>                   YEAR                   YEAR                    YEAR
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1996            DEC-31-1995
<PERIOD-START>                             JAN-01-1997             JAN-01-1996            JAN-01-1995
<PERIOD-END>                               DEC-31-1997             DEC-31-1996            DEC-31-1995
<CASH>                                         240,817                 312,369                202,524
<SECURITIES>                                   335,822                 208,872                147,478
<RECEIVABLES>                                  245,483                 187,726                 52,350
<ALLOWANCES>                                    11,300                   2,632                  1,202
<INVENTORY>                                     99,637                  68,544                 34,513
<CURRENT-ASSETS>                               914,587                 807,341                402,517
<PP&E>                                         173,428                 105,809                 36,101
<DEPRECIATION>                                  59,077                  32,763                 12,013
<TOTAL-ASSETS>                               1,137,894                 922,127                481,873
<CURRENT-LIABILITIES>                          168,638                 154,894                 70,580
<BONDS>                                              0                       0                      0
<PREFERRED-MANDATORY>                                0                       0                      0
<PREFERRED>                                          0                       0                      0
<COMMON>                                           191                     182                    172
<OTHER-SE>                                     969,065                 767,051                411,121
<TOTAL-LIABILITY-AND-EQUITY>                 1,137,894                 922,127                481,783
<SALES>                                      1,167,352                 890,273                287,438
<TOTAL-REVENUES>                             1,167,352                 890,273                287,438
<CGS>                                          413,570                 311,745                101,859
<TOTAL-COSTS>                                  413,570                 311,745                101,859
<OTHER-EXPENSES>                               821,763                 293,710                108,201
<LOSS-PROVISION>                                     0                       0                      0
<INTEREST-EXPENSE>                                   0                       0                      0
<INCOME-PRETAX>                               (44,952)                 302,004                 85,738
<INCOME-TAX>                                    79,422                 118,114                 32,793
<INCOME-CONTINUING>                          (124,374)                 183,890                 52,945
<DISCONTINUED>                                       0                       0                      0
<EXTRAORDINARY>                                      0                       0                      0
<CHANGES>                                            0                       0                      0
<NET-INCOME>                                 (124,374)                 183,890                 52,945
<EPS-PRIMARY>                                    (.66)                    1.03                    .33
<EPS-DILUTED>                                    (.66)                     .94                    .30


</TABLE>