Exhibit 3.1

RESTATED CERTIFICATE OF INCORPORATION

OF

ADTRAN, INC.

(Pursuant to Section 245 of the

General Corporation Law of the State of Delaware)

ADTRAN, INC., a corporation organized and existing under the General Corporation Law of the State of Delaware (the “Corporation”), DOES HEREBY CERTIFY:

1.  The name of the Corporation is ADTRAN, Inc.  The date of filing of the Corporation’s original certificate of incorporation with the Secretary of State of the State of Delaware was November 18, 1985.

2.  This Restated Certificate of Incorporation only restates and integrates and does not further amend the provisions of the certificate of incorporation of the Corporation as heretofore amended or supplemented.  There is no discrepancy between the provisions of this Restated Certificate of Incorporation and the provisions of the certificate of incorporation of the Corporation as heretofore amended or supplemented.  This Restated Certificate of Incorporation has been duly adopted in accordance with the provisions of Section 245 of the General Corporation Law of the State of Delaware.  The text of the certificate of incorporation of the Corporation is hereby integrated and restated to read herein as set forth in full:

FIRST:  The name of the Corporation is ADTRAN, Inc.

SECOND:  The address of its registered office in the State of Delaware is Corporation Trust Center, 1209 Orange Street, Wilmington, New Castle County, Delaware 19801.  The name of its registered agent at such address is The Corporation Trust Company.

THIRD:  The nature of the business or purposes to be conducted or promoted is to engage in any lawful act or activity for which corporations may be organized under the General Corporation Law of Delaware.

FOURTH:  The aggregate number of shares of stock which the corporation shall have the authority to issue is Two Hundred Million (200,000,000) shares of common stock of the par value of One Cent ($.01) per share, all of the same class and constituting a total authorized capital of Two Million ($2,000,000).

FIFTH:  [Reserved]

SIXTH:  In furtherance and not in limitation of the powers conferred by statute, the board of directors is expressly authorized:

To make, alter or repeal the by-laws of the corporation.

To authorize and cause to be executed mortgages and liens upon the real and personal property of the corporation.

To set apart out of any of the funds of the corporation available for dividends a reserve or reserves for any proper purpose and to abolish any such reserve in the manner in which it was created.

By a majority of the whole board, to designate one or more committees, each committee to consist of two or more of the directors of the corporation. The board may designate one or more directors as alternate members of any committee, who may replace any absent or disqualified member at any meeting of the committee. Any such committee, to the extent provided in the resolution or in the by-laws of the corporation, shall have and may exercise the powers of the board of directors in the management of the business and affairs of the corporation, and may authorize the seal of the corporation to be affixed to all papers which may require it; provided, however, the by-laws may provide that in the absence or disqualification of any member of such committee or committees, the member or members thereof present

at any meeting and not disqualified from voting, whether or not he or they constitute a quorum, may unanimously appoint another member of the board of directors to act at the meeting in the place of any such absent or disqualified member.

When and as authorized by the affirmative vote of the holders of a majority of the stock issued and outstanding having voting power given at a stockholders’ meeting duly called upon such notice as is required by statute, or when authorized by the written consent of the holders of a majority of the voting stock issued and outstanding, to sell, lease or exchange all or substantially all of the property and assets of the corporation, including its good will and its corporate franchises, upon such terms and conditions and for such consideration, which may consist in whole or in part of money or property including shares of stock in, and/or other securities of, any other corporation or corporations, as its board of directors shall deem expedient and for the best interests of the corporation.

SEVENTH:  Whenever a compromise or arrangement is proposed between this corporation and its creditors or any class of them and/or between this corporation and its stockholders or any class of them, any court of equitable jurisdiction within the State of Delaware may, on the application in a summary way of this corporation or of any creditor or stockholder thereof or on the application of any receiver or receivers appointed for this corporation under the provisions of section 291 of Title 8 of the Delaware Code or on the application of trustees in dissolution or of any receiver or receivers appointed for this corporation under the provisions of section 279 of Title 8 of the Delaware Code order a meeting of the creditors or class of creditors, and/or of the stockholders or class of stockholders of this corporation, as the case may be, to be summoned in such manner as the said court directs.  If a majority in number representing three‑fourths in value of the creditors or class of creditors, and/or of the stockholders or class of stockholders of this corporation, as the case may be, agree to any compromise or arrangement and to any reorganization of this corporation as consequence of such compromise or arrangement, the said compromise or arrangement and the said reorganization shall, if sanctioned by the court to which the said application has been made, be binding on all the creditors or class of creditors, and/or on all the stockholders or class of stockholders, of this corporation, as the case may be, and also on this corporation.

EIGHTH:  Meetings of stockholders may be held within or without the State of Delaware, as the by-laws may provide.  The Books of the corporation may be kept (subject to any provision contained in the statutes) outside the State of Delaware at such place or places as may be designated from time to time by the board of directors or in the by-laws of the corporation. Elections of directors need not be by written ballot unless the by-laws of the corporation shall so provide.

NINTH:  Any corporate action upon which a vote of stockholders is required or permitted may be taken with the written consent of stockholders having not less than a majority of all of the stock entitled to vote upon the action if a meeting were held; provided that in no case shall the written consent be by holders having less than the minimum percentage of the vote required by statute for the proposed corporate action and provided that prompt notice be given to all stockholders of the taking of corporate action without a meeting and by less than unanimous written consent.

TENTH:  The Corporation reserves the right at any time and from time to time to amend, alter, change or repeal any provisions contained in this Certificate of Incorporation; and other provisions authorized by the laws of the State of Delaware at the time in force may be added or inserted, in the manner now or hereafter prescribed by law; and all rights, preferences and privileges of whatsoever nature conferred upon stockholders, directors or any other person whomsoever by and pursuant to this Certificate of Incorporation in its present form or as hereafter amended are granted subject to the right reserved in this Article.

ELEVENTH:  (a) No person shall be personally liable to the Corporation or its stockholders for monetary damages for breach of fiduciary duty as a director; provided, however, that the foregoing shall not eliminate or limit the liability of a director (i) for any breach of the director’s duty of loyalty to the Corporation or its stockholders, (ii) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (iii) under Section 174 of the General Corporation Law of the State of Delaware or (iv) for any transaction from which the director derived an improper personal benefit.  If the General Corporation Law of the State of Delaware is subsequently amended to further eliminate or

limit the liability of a director, then a director of the Corporation, in addition to the circumstances in which a director is not personally liable as set forth in the preceding sentence, shall not be liable to the fullest extent permitted by the amended General Corporation Law of the State of Delaware.  For purposes of this Article ELEVENTH, “fiduciary duty as a director” also shall include any fiduciary duty arising out of serving at the Corporation’s request as a director of another corporation, partnership, joint venture or other enterprise, and “personal liability to the Corporation or its stockholders” also shall include any liability to such other corporation, partnership, joint venture, trust or other enterprise, and any liability to the Corporation in its capacity as a security holder, joint venturer, partner, beneficiary, creditor or investor of or in any such other corporation, partnership, joint venture, trust or other enterprise.

(b)Any repeal or modification of Section (a) of this Article ELEVENTH by the stockholders of the Corporation shall not adversely affect any right or protection of a director of the Corporation existing at the time of such repeal or modification.

TWELFTH:  (a) Each person who was or is made a party or is threatened to be made a party to or is involved in any action, suit or proceeding, whether civil, criminal, administrative or investigative (hereinafter a “proceeding”), by reason of the fact that he or she, or a person of whom he or she is the legal representative, is or was a director or officer of the Corporation or is or was serving at the request of the Corporation as a director or officer of another corporation or of a partnership, joint venture, trust or other enterprise, including service with respect to employee benefit plans, whether the basis of such proceeding is alleged action in an official capacity as a director or officer or in any other capacity while serving as a director or officer shall be indemnified and held harmless by the Corporation to the fullest extent authorized by the General Corporation Law of the State of Delaware, as the same exists or may hereafter be amended (but, in the case of any such amendment, only to the extent that such amendment permits the Corporation to provide broader indemnification rights than said law permitted the Corporation to provide prior to such amendment), against all expense, liability and loss (including attorneys’ fees, judgments, fines, ERISA excise taxes or penalties and amounts to be paid in settlement) reasonably incurred or suffered by such person in connection therewith, and such indemnification shall continue as to a person who has ceased to be a director or officer and shall inure to the benefit of his or her heirs, executors and administrators; provided, however, that except as provided in Section (b) of this Article TWELFTH with respect to proceedings seeking to enforce rights to indemnification, the Corporation shall indemnify any such person seeking indemnification in connection with a proceeding (or part thereof) initiated by such person only if such proceeding (or part thereof) was authorized by the Board of Directors of the Corporation.  Further, the Corporation also may indemnify and hold harmless employees and agents of the Corporation to the fullest extent authorized by the General Corporation Law of the State of Delaware, as the same exists or may hereafter be amended (but, in the case of any such amendment, only to the extent such amendment permits the Corporation to provide broader indemnification rights than said law permitted the Corporation to provide prior to such amendment), and such discretionary authority to indemnify employees and agents of the Corporation shall be vested in, and may be exercised by, the Board of Directors of the Corporation; provided, however, that the Board of Directors of the Corporation shall have no discretionary authority relative to the indemnification of an employee or agent of the Corporation where the General Corporation Law of the State of Delaware specifically provides that indemnification is mandatory.  The right to indemnification conferred in this Article relative to directors and officers of the Corporation shall be a contract right and shall include the right to be paid by the Corporation the expenses incurred in defending any such proceeding in advance of its final disposition; provided, however, that, if the General Corporation Law of the State of Delaware requires, the payment of such expenses incurred by a director or officer in his or her capacity as a director or officer (and not in any other capacity in which service was or is rendered by such person while a director or officer, including, without limitation, service to an employee benefit plan) in advance of the final disposition of a proceeding shall be made only upon delivery to the Corporation of an undertaking, by or on behalf of such director or officer, to repay all amounts so advanced if it shall ultimately be determined that such director or officer is not entitled to be indemnified under this Article TWELFTH or otherwise.

(b)If a claim relative to which a director, officer, employee or agent is entitled to be mandatorily indemnified under Section (a) of this Article TWELFTH is not paid in full by the Corporation within ninety days after a written claim has been received by the Corporation, the claimant may at any time thereafter bring suit against the Corporation to recover the unpaid amount of the claim and, if successful in

whole or in part, the claimant also shall be entitled to be paid the expense of prosecuting such claim.  It shall be a defense to any such action (other than an action brought to enforce a claim for expenses incurred in defending any proceeding in advance of its final disposition where the required undertaking, if any is required, has been tendered to the Corporation) that the claimant has not met the standards of conduct which make it permissible under the General Corporation Law of the State of Delaware for the Corporation to indemnify the claimant for the amount claimed, but the burden of proving such defense shall be on the Corporation.  Neither the failure of the Corporation (including its Board of Directors, independent legal counsel or stockholders) to have made a determination prior to the commencement of such action that indemnification of the claimant is proper in the circumstances because he or she has met the applicable standard of conduct set forth in the General Corporation Law of the State of Delaware, nor an actual determination by the Corporation (including its Board of Directors, independent legal counsel or stockholders) that the claimant has not met such applicable standard of conduct shall be a defense to the action or create a presumption that the claimant has not met the applicable standard of conduct.

(c)The right to indemnification and the payment of expenses incurred in defending a proceeding in advance of its final disposition conferred in this Article TWELFTH shall not be exclusive of any other right which any person may have or hereafter acquire under any statute, provision of the Certificate of Incorporation, bylaws, agreement, vote of stockholders or disinterested directors or otherwise.

(d)The Corporation may maintain insurance, at its expense, to protect itself and any director, officer, employee or agent of the Corporation or another corporation, partnership, joint venture, trust or other enterprise against any expense, liability or loss, whether or not the Corporation would have the power to indemnify such person against such expense, liability or loss under the General Corporation Law of the State of Delaware.

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IN WITNESS WHEREOF, the Corporation has caused this Restated Certificate of Incorporation to be executed by its duly authorized officer on this 12th day of May, 2021.