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                                                                  Exhibit 10.31

                                    ADDENDUM
                                       TO
                             STOCK OPTION AGREEMENT

                  The following provisions are hereby incorporated into, and are
hereby made a part of, that certain Stock Option Agreement dated 2~ (the "Option
Agreement") by and between ACT Networks, Inc. (the "Corporation") and 1~
("Optionee") evidencing the stock option granted on such date to Optionee under
the terms of the Corporation's 1997 Non-Executive Officer Stock Option/Stock
Issuance Plan, and such provisions shall be effective immediately. All
capitalized terms in this Addendum, to the extent not otherwise defined herein,
shall have the meanings assigned to them in the Option Agreement.

                        INVOLUNTARY TERMINATION FOLLOWING
                                CHANGE IN CONTROL

                  1. The exercisability of the option shall not accelerate upon
the occurrence of a Change in Control, and the option shall, over Optionee's
continued period of Service after the Change in Control, continue to become
exercisable for the Option Shares in accordance with the provisions of the
Option Agreement. However, immediately upon an Involuntary Termination of
Optionee's Service within eighteen (18) months following the Change in Control,
the exercisability of this option, to the extent the option is at the time
outstanding but not otherwise fully exercisable, shall automatically accelerate
so that the option shall immediately become fully exercisable for all the Option
Shares at the time subject to the option and may be exercised for any or all of
those shares as fully vested shares of Common Stock at any time prior to the
earlier of (i) the Expiration Date or (ii) the expiration of the one (1)-year
period measured from the date of the Involuntary Termination.

                  2. For purposes of this Addendum, a CHANGE IN CONTROL shall be
deemed to occur in the event of a change in ownership or control of the
Corporation effected through either of the following transactions:

                  (i)  the acquisition, directly or indirectly, by any person or
         related group of persons (other than the Corporation or a person that
         directly or indirectly controls, is controlled by, or is under common
         control with, the Corporation) of beneficial ownership (within the
         meaning of Rule 13d-3 of the Securities Exchange Act of 1934, as
         amended) of securities possessing more than fifty percent (50%) of the
         total combined voting power of the Corporation's outstanding securities
         pursuant to a tender or exchange offer made directly to the
         Corporation's stockholders, or
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                  (ii) a change in the composition of the Board over a period of
         thirty-six (36) consecutive months or less such that a majority of the
         Board members ceases by reason of one or more contested elections for
         Board membership, to be comprised of individuals who either (A) have
         been Board members continuously since the beginning of such period or
         (B) have been elected or nominated for election as Board members during
         such period by at least a majority of the Board members described in
         clause (A) who were still in office at the time such election or
         nomination was approved by the Board.

                  3. The provisions of Paragraph 1 of this Addendum shall govern
the period for which the option is to remain exercisable following the
Involuntary Termination of Optionee's Service within eighteen (18) months after
the Change in Control and shall supersede any provisions to the contrary in the
Option Agreement.

                  IN WITNESS WHEREOF, ACT Networks, Inc. has caused this 
Addendum to be executed by its duly-authorized officer, and Optionee has
executed this Addendum, all as of the Effective Date specified below.

                                       ACT NETWORKS, INC.

                                       By: ____________________________________

                                       Title: _________________________________


                                       ________________________________________
                                       1~, OPTIONEE


EFFECTIVE DATE:_______________ , 199__


                                       2.