<PAGE>

     As filed with the Securities and Exchange Commission on August 9, 2000.

                                                     Registration No. 333-32206
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                             ----------------------

                                    FORM S-8
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933
                             ----------------------

                              SONUS NETWORKS, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                                    DELAWARE
         (STATE OR OTHER JURISDICTION OF INCORPORATION OR ORGANIZATION)

                                   04-3387074
                      (I.R.S. EMPLOYER IDENTIFICATION NO.)

5 CARLISLE ROAD, WESTFORD, MASSACHUSETTS                   01886
(Address of Principal Executive Offices)                 (Zip Code)

                             ----------------------

                 AMENDED AND RESTATED 1997 STOCK INCENTIVE PLAN
                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            (FULL TITLE OF THE PLAN)
                             ----------------------

                                 HASSAN M. AHMED
                                    President
                           and Chief Executive Officer
                              Sonus Networks, Inc.
                                 5 Carlisle Road
                               Westford, MA 01886
                     (NAME AND ADDRESS OF AGENT FOR SERVICE)

                                 (978) 692-8999
           TELEPHONE NUMBER, INCLUDING AREA CODE, OF AGENT FOR SERVICE
                             ----------------------

                                    Copy to:
                              DAVID L. ENGEL, ESQ.
                             JOHAN V. BRIGHAM, ESQ.
                                BINGHAM DANA LLP
                               150 Federal Street
                           Boston, Massachusetts 02110
                                 (617) 951-8000


<PAGE>

                                      -2-


                         CALCULATION OF REGISTRATION FEE
================================================================================


<TABLE>
<CAPTION>

                                                              Proposed          Proposed
              Title Of                                        Maximum           Maximum
             Securities                     Amount            Offering         Aggregate           Amount Of
               To Be                         To Be           Price Per          Offering          Registration
             Registered                   Registered         Share (1)           Price                Fee
------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------
<S>                                   <C>                  <C>             <C>                 <C>
Common Stock (Par Value $0.001 Per          718,236             $19.55         $14,041,514(1)        $ 4,212.45
Share) issuable under 2000 Employee 
Stock Purchase Plan

Common Stock (Par Value $0.001 Per           50,000(2)          $ 0.02               1,000                 0.30
Share) issuable under 1997 Stock            463,145(2)          $ 0.20              92,629                27.79
Incentive Plan                              241,500(2)          $ 0.48             115,920                34.77
                                            161,250(2)          $ 0.66             106,425                31.93
                                            380,299(2)          $ 2.00             760,598               228.18
                                          1,366,465(2)          $10.00          13,664,650             4,099.40
                                            455,175(2)          $12.00           5,462,100             1,638.63
                                            834,350(2)          $14.00          11,680,900             3,504.27
                                            177,200(2)          $23.00           4,075,600             1,222.68
                                         -------------                         -----------           ----------
Total                                     4,847,620                            $50,001,336           $15,000.40

------------------------------------------------------------------------------------------------------------------
</TABLE>


(1) Based on the maximum exercise price of the shares subject to outstanding 
    options issued under the registrant's 2000 Employee Stock Purchase Plan 
    (the "ESPP"). Pursuant to Rule 457(h)(1), the aggregate offering price 
    and amount of the registration fee has been computed with respect to 
    those shares of the common stock issuable under the ESPP that are being 
    registered hereunder.
(2) Such shares are issuable upon exercise of outstanding options with fixed 
    exercise prices. Pursuant to Rule 457(h)(1), the aggregate offering price 
    and the fee have been computed upon the basis of the price at which the 
    options may be exercised. The offering price per share set forth for such 
    shares is the exercise price per share at which such options are 
    exercisable.



<PAGE>

                                      -3-


                                     PART II

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by Sonus Networks, Inc. (the
"REGISTRANT") with the Securities and Exchange Commission (the "SEC") are hereby
incorporated by reference into this Registration Statement: (1) the Registrant's
prospectus filed pursuant to Rule 424(b)(4) under the Securities Act of 1933, as
amended (the "SECURITIES ACT"); (2) all other reports filed by the Registrant
pursuant to Sections 13(a) or 15(d) of the Exchange Act since December 31, 1999;
and (3) the description of the common stock of the Registrant, $0.001 par value
per share (the "COMMON STOCK"), contained in the Registrant's registration
statement on Form 8-A (file No. 000-30229) filed with the SEC on April 5, 2000,
pursuant to Section 12(g) of the Securities Exchange Act of 1934, as amended
(the "EXCHANGE ACT"), including any amendment or report filed for the purpose of
updating such description.

         In addition, all documents filed pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Exchange Act subsequent to the date of this Registration
Statement and prior to the filing of a post-effective amendment which indicates
that all securities registered hereby have been sold or which deregisters all of
such securities then remaining unsold shall be incorporated by reference into
this Registration Statement as of the filing date of each.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145 of the Delaware General Corporation law empowers a Delaware
corporation to indemnify its officers and directors and certain other persons to
the extent and under the circumstances set forth therein.

         The Fourth Amended and Restated Certificate of Incorporation of the
Registrant and the Amended and Restated By-Laws of the Registrant, as amended to
date, provide for indemnification of officers and directors of the Registrant
and certain other persons against liabilities and expenses incurred by any of
them in certain stated proceedings and under certain stated conditions.

         The Registrant may maintain insurance for the benefit of its directors,
officers, employees, agents and certain other persons, insuring such persons
against any expense, liability, or loss, including liability under the
securities laws.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.




<PAGE>

                                      -4-

ITEM 8.  EXHIBITS.

         The following exhibits are filed as part of this Registration
Statement:

EXHIBIT NO.                                 DESCRIPTION OF DOCUMENTS

         4.1      Form of Fourth Amended and Restated  Certificate of
                  Incorporation of the Registrant,  incorporated by reference
                  to Exhibit No. 3.1 to the Registrant's Registration
                  Statement on Form S-1 (file No. 333-32206), filed on
                  May 22, 2000.

         4.2.     Form of Amended and Restated By-Laws of the Registrant,
                  incorporated by reference to Exhibit No. 3.2 to the
                  Registrant's Registration Statement on Form S-1
                  (file No. 333-32206), filed on May 22, 2000.

         4.3      Amended and Restated 1997 Stock Incentive Plan, incorporated
                  by reference to Exhibit No. 10.2 to the Registrant's
                  Registration Statement on Form S-1 (file No. 333-32206), 
                  filed on May 22, 2000.

         4.4      2000 Employee Stock Purchase Plan, as amended, incorporated
                  by reference to Exhibit No. 10.3 to the Registrant's
                  Registration Statement on Form S-1 (file No. 333-32206),
                  filed on May 22, 2000.

         5        Opinion of company counsel as to the legality of the
                  securities being registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of company counsel (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this
                  Registration Statement).


ITEM 9.  UNDERTAKINGS

         (A) The undersigned registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
                           are being made, a post-effective amendment to this
                           registration statement:

                           (i)      To include any prospectus required by 
                                    Section 10(a)(3) of the Securities Act;

                           (ii)     To reflect in the prospectus any facts or 
                                    events arising after the effective date of 
                                    the registration statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the 
                                    information set forth in the registration
                                    statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of 
                                    securities offered (if the total dollar 
                                    value of securities offered would not 
                                    exceed that which was registered) and any 
                                    deviation from the low or high and of the 
                                    estimated maximum offering range may be 
                                    reflected in the form of prospectus filed 
                                    with the Commission pursuant to Rule 424(b)
                                    if, in the aggregate, the changes in volume 
                                    and price represent no more than 20 percent
                                    change in the maximum aggregate offering 
                                    price set forth in the "Calculation of 
                                    Registration Fee" table in the effective 
                                    registration statement.



<PAGE>

                                      -5-

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the registration
                                    statement or any material change to such
                                    information in the registration statement;

                           PROVIDED, HOWEVER, that paragraphs (1)(i) and (1)(ii)
                           do not apply if the information required to be
                           included in a post-effective amendment by those
                           paragraphs is contained in periodic reports filed
                           with or furnished to the Commission by the registrant
                           pursuant to Section 13 or Section 15(d) of the
                           Exchange Act that are incorporated by reference in
                           the registration statement.

                  (2)      That, for the purpose of determining any liability
                           under the Securities Act, each such post-effective
                           amendment shall be deemed to be a new registration
                           statement relating to the securities offered therein,
                           and the offering of such securities at that time
                           shall be deemed to be the initial BONA FIDE offering
                           thereof.

                  (3)      To remove from registration by means of a
                           post-effective amendment any of the securities being
                           registered which remain unsold at the termination of
                           the offering.

         (B)      The undersigned registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  each filing of the registrant's annual report pursuant to
                  Section 13(a) or Section 15(d) of the Exchange Act (and, where
                  applicable, each filing of an employee benefit plan's annual
                  report pursuant to Section 15(d) of the Exchange Act) that is
                  incorporated by reference in the registration statement shall
                  be deemed to be a new registration statement relating to the
                  securities offered therein, and the offering of such
                  securities at that time shall be deemed to be the initial BONA
                  FIDE offering thereof.

         (C)      Insofar as indemnification for liabilities arising under the 
                  Securities Act may be permitted to directors, officers and
                  controlling persons of the registrant pursuant to the 
                  foregoing provisions, or otherwise, the registrant has been 
                  advised that in the opinion of the Securities and Exchange\
                  Commission such indemnification is against public policy as 
                  expressed in the Securities Act and is, therefore, 
                  unenforceable. In the event that a claim for indemnification 
                  against such liabilities (other than the payment by the 
                  registrant of expenses incurred or paid by a director,
                  officer or controlling person of the registrant in the 
                  successful  defense of any action, suit or proceeding) is 
                  asserted by such director, officer or controlling person in 
                  connection with the securities being registered, the 
                  registrant will, unless in the opinion of its counsel the 
                  matter has been settled by controlling precedent, submit 
                  to a court of appropriate jurisdiction the question whether 
                  such indemnification by it is against public policy as 
                  expressed in the Securities Act and will be governed by the 
                  final adjudication of such issue.





<PAGE>

                                      -6-

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the Town of Westford, Commonwealth of Massachusetts, as of
the 31st day of July 2000.

                                       SONUS NETWORKS, INC.

 
                                       By: 
                                          -------------------------------------
                                          Hassan M. Ahmed
                                          President and Chief Executive Officer



                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoints Hassan M.
Ahmed, Stephen J. Nill, and each of them severally, his true and lawful
attorney-in-fact with the authority to execute in the name of each such person,
and to file with the Securities and Exchange Commission, together with any
exhibits thereto and other documents therewith, any and all amendments
(including without limitation post-effective amendments) to this Registration
Statement on Form S-8 necessary or advisable to enable the Registrant to comply
with the Securities Act of 1933, as amended, and any rules, regulations, and
requirements of the Securities and Exchange Commission in respect thereof, which
amendments may make such other changes in the Registration Statement as the
aforesaid attorney-in-fact executing the same deems appropriate.

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this Registration Statement has been signed by the following persons in the
capacities indicated as of the 31st day of July 2000.



<TABLE>
<CAPTION>

         Signature                                            Title
         ---------                                            -----
<S>                                      <C>

-------------------------                President, Chief Executive Officer and Director (Principal
Hassan M. Ahmed                          Executive Officer)

-------------------------                Vice President of Finance and  Administration  and Chief  Financial
Stephen J. Nill                          Officer (Principal Financial and Accounting Officer)

-------------------------                Chairman of the Board of Directors and Director
Rubin Gruber

-------------------------                Director
Edward T. Anderson

-------------------------                Director
Paul J. Ferri

-------------------------                Director
Paul J. Severino

</TABLE>




<PAGE>


                                  EXHIBIT INDEX


<TABLE>
<CAPTION>

Exhibit No.                                 Description of Documents
-----------                                 ------------------------
<S>               <C> 

         4.1      Form of Fourth Amended and Restated Certificate of Incorporation of the Registrant, incorporated by reference to
                  Exhibit No. 3.1 to the Registrant's Registration Statement on Form S-1 (file No. 333-32206), filed on
                  May 22, 2000.

         4.2.     Form of Amended and Restated By-Laws of the Registrant, incorporated by reference to Exhibit No. 3.2 to the
                  Registrant's Registration Statement on Form S-1 (file No. 333-32206), filed on May 22, 2000.

         4.3      Amended and Restated 1997 Stock  Incentive Plan, incorporated by reference to Exhibit No. 10.2 to the Registrant's
                  Registration Statement on Form S-1 (file No. 333-32206), filed on May 22, 2000.

         4.4      2000 Employee Stock Purchase Plan, as amended, incorporated by reference to Exhibit No. 10.3 to the Registrant's
                  Registration Statement on Form S-1 (file No. 333-32206), filed on May 22, 2000.

         5        Opinion of company counsel as to the legality of the securities registered.

         23.1     Consent of Arthur Andersen LLP, independent accountants.

         23.2     Consent of company counsel (included in Exhibit 5).

         24       Power of Attorney (included on the signature page of this Registration Statement).


</TABLE>






<PAGE>

                                                                  EXHIBIT 5


                                         August 9, 2000


Sonus Networks, Inc.
5 Carlisle Road
Westford, MA 01886

     RE: REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

     I have acted as counsel for Sonus Networks, Inc., a Delaware corporation 
(the "COMPANY"), in connection with the preparation of the Company's 
Registration Statement on Form S-8 proposed to be filed with the Securities 
and Exchange Commission on or about August 9, 2000 (the "REGISTRATION 
STATEMENT").

     The Registration Statement covers the registration of 4,847,620 shares 
of common stock, $0.001 par value per share, of the Company (the "SHARES"), 
which are issuable by the Company pursuant to its 1997 Stock Incentive Plan 
or 2000 Employee Stock Purchase Plan (the "PLANS").

     I have reviewed the corporate proceedings of the Company with respect to 
the authorization of the Plans and the issuance of the Shares thereunder. I 
have also examined and relied upon originals or copies of such corporate 
records, instruments, agreements or other documents of the Company, and an 
opinion of Bingham Dana LLP relating to the same subject matter, as I have 
deemed necessary or appropriate as a basis for the opinions hereinafter 
expressed. In my examination, I have assumed the genuineness of all 
signatures,
 the conformity to the originals of all documents reviewed by me 
as copies, the authenticity and completeness of all original documents 
reviewed by me in original or copy form and the legal competence of each 
individual executing any document.

     This opinion is limited solely to the Delaware General Corporation Law, 
as applied by courts located in Delaware, the applicable provisions of the 
Delaware Constitution and the reported judicial decisions interpreting those 
laws.

     Based upon and subject to the foregoing, I am of the opinion that the 
Shares, when issued and delivered upon the exercise of options or awards 
pursuant to the Plans and against the payment of the purchase price therefor, 
as specified in such Plans or documents governing such awards, will be 
validly issued, fully paid and non-assessable.

     We hereby consent to the filing of this opinion as an exhibit to the 
Registration Statement.


                                             Very truly yours,


                                             /s/ MELINDA BROWN

                                             MELINDA BROWN




<PAGE>



                                                       EXHIBIT 23.1




                              [ARTHUR ANDERSEN LETTERHEAD]


                        CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


     As independent public accountants, we hereby consent to the use of our 
report dated March 10, 2000 (and to all references to our Firm) included in 
or made a part of this Registration Statement.


/s/ Arthur Andersen LLP

Arthur Andersen LLP


Boston, Massachusetts
August 9, 2000