Exhibit 5.1

	53rd at Third
	885 Third Avenue
	New York, New York 10022-4834
	Tel: +1.212.906.1200 Fax: +1.212.751.4864
	www.lw.com
	FIRM / AFFILIATE OFFICES
	Beijing	Moscow
	Boston	Munich
August 6, 2018	Brussels	New York
	Century City	Orange County
	Chicago	Paris
	Dubai	Riyadh
	Düsseldorf	Rome
	Frankfurt	San Diego
	Hamburg	San Francisco
	Hong Kong	Seoul
	Houston	Shanghai
	London	Silicon Valley
	Los Angeles	Singapore
	Madrid	Tokyo
	Milan	Washington, D.C.

Ribbon Communications Inc.

4 Technology Park Drive

Westford, Massachusetts 01886

Re:Registration Statement on Form S-8; 329,479 shares of common stock, par value $0.0001 per share, of Ribbon Communications Inc.

Ladies and Gentlemen:

We have acted as special counsel to Ribbon Communications Inc., a Delaware corporation (the “Company”), in connection with the registration by the Company of 329,479 shares of its common stock, $0.0001 par value per share (the “Shares”), issuable under the Edgewater Networks, Inc. Amended and Restated 2002 Stock Option Plan (the “Plan”).  The Shares are included in a registration statement on Form S-8 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on August 6, 2018 (the “Registration Statement”).  This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or the related prospectus, other than as expressly stated herein with respect to the issue of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter.  With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters.  In our examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, and the conformity to authentic original documents of all documents submitted to us as copies. We are opining herein only as to the General Corporation Law of the State of Delaware (the “DGCL”) and we express no opinion with respect to any other laws.

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, when the Shares shall have been duly registered on the books of the transfer agent and registrar therefor in the name or on behalf of the holders and have been issued by the Company for legal consideration (not less than par value) in the circumstances contemplated by the Plan, assuming that the individual grants or awards under the Plan have been duly authorized by all necessary corporate action and duly granted or awarded and exercised in accordance with the requirements of law and the Plan (and the agreements and awards duly adopted thereunder and in accordance therewith), the issue of the Shares will have been duly authorized by all necessary corporate action of the Company, and the Shares will be validly issued, fully paid and nonassessable.  In rendering the foregoing opinion, we have assumed that the Company will comply with all applicable notice requirements regarding uncertificated shares in the DGCL.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act.  We consent to your filing this opinion as an exhibit to the Registration Statement.  In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Latham & Watkins LLP

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