SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* SUMMIT PARTNERS L P (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Casa Systems Inc [ CASA ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) X Other (specify below) Manager of GP of 10% owner
	3. Date of Earliest Transaction (Month/Day/Year) 12/19/2017
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	12/19/2017		C		38,592,000	A	(1)	38,592,000(2)	D(3)(4)
Common Stock	12/19/2017		P		250,000(5)	A	$13	38,842,000(6)	D(3)(4)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series C Convertible Preferred Stock	(1)	12/19/2017		C		3,859,200		(1)	(1)	Common Stock	38,592,000(2)	$0(1)	0	D(3)(4)

1. Name and Address of Reporting Person* SUMMIT PARTNERS L P (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* SUMMIT MASTER COMPANY, LLC (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Partners PE VII, L.P. (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Partners PE VII, LLC (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Investors Management, LLC (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Partners Private Equity Fund VII-A, L.P. (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Partners Private Equity Fund VII B L P (Last) (First) (Middle) 222 BERKELEY STREET 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Investors I, LLC (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

1. Name and Address of Reporting Person* Summit Investors I (UK), L.P. (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR (Street) BOSTON MA 02116 (City) (State) (Zip)

Explanation of Responses:

1. The Series C Convertible Preferred Stock automatically converted into common stock of Casa Systems, Inc. (the "Issuer") on a ten-for-one basis upon the closing of the Issuer's initial public offering. The Series C Convertible Preferred Stock had no expiration date.

2. Consists of 24,052,910 shares of common stock issued upon the conversion of Series C Convertible Preferred Stock held by Summit Partners Private Equity Fund VII-A, L.P., 14,446,570 shares of common stock issued upon the conversion of Series C Convertible Preferred Stock held by Summit Partners Private Equity Fund VII-B, L.P., 82,110 shares of common stock issued upon the conversion of Series C Convertible Preferred Stock held by Summit Investors I, LLC and 10,410 shares of common stock issued upon the conversion of Series C Convertible Preferred Stock held by Summit Investors I (UK), L.P.

3. Summit Partners, L.P. is the managing member of Summit Partners PE VII, LLC, which is the general partner of Summit Partners PE VII, L.P., which is the general partner of each of Summit Partners Private Equity Fund VII-A, L.P. and Summit Partners Private Equity Fund VII-B, L.P. Summit Master Company, LLC is the managing member of Summit Investors Management, LLC, which is the manager of Summit Investors I, LLC, and the general partner of Summit Investors I (UK), L.P. Summit Master Company, LLC, as the managing member of Summit Investors Management, LLC, has delegated investment decisions, including voting and dispositive power, to Summit Partners, L.P. and its investment committee responsible for voting and investment decisions with respect to the Issuer.

4. Summit Partners, L.P., through a three-person investment committee responsible for voting and investment decisions with respect to the Issuer, currently comprised of Peter Y. Chung, Bruce R. Evans and Martin J. Mannion, has voting and dispositive power over the shares held by each of these entities and therefore may be deemed to beneficially own such shares. Each of the Summit entities and persons mentioned in this footnote disclaims beneficial ownership of the shares, except for those shares held of record by such entity, and except to the extent of their pecuniary interest therein.

5. Consists of 155,816 shares of common stock purchased by Summit Partners Private Equity Fund VII-A, L.P., 93,585 shares of common stock purchased by Summit Partners Private Equity Fund VII-B, L.P., 532 shares of common stock issued purchased by Summit Investors I, LLC and 67 shares of common stock purchased by Summit Investors I (UK), L.P.

6. Consists of 24,208,726 shares of common stock held by Summit Partners Private Equity Fund VII-A, L.P., 14,540,155 shares of common stock held by Summit Partners Private Equity Fund VII-B, L.P., 82,642 shares of common stock issued held by Summit Investors I, LLC and 10,477 shares of common stock held by Summit Investors I (UK), L.P.

	Summit Partners, L.P., by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member	12/19/2017
	Summit Master Company, LLC, by Robin W. Devereux, Member	12/19/2017
	Summit Partners PE VII, L.P., by Summit Partners PE VII, LLC, its GP, by Summit Partners, L.P., its Manager, Summit Master Company, LLC, by Robin W. Devereux, Member	12/19/2017
	Summit Partners PE VII, LLC, by Summit Partners, L.P., its Manager, Summit Master Company, LLC, by Robin W. Devereux, Membe	12/19/2017
	Summit Investors Management, LLC, by Summit Master Company, LLC, its Managing Member, by Robin W. Devereux, Member	12/19/2017
	Summit Partners Private Equity Fund VII-A, L.P., by Summit Partners PE VII, L.P., its GP, by Summit Partners PE VII, LLC, its GP, by Summit Partners, L.P., its Managing Member, Summit Master Company, LLC, by Robin W. Devereux, Member	12/19/2017
	Summit Partners Private Equity Fund VII-B, L.P., by Summit Partners PE VII, L.P., its GP, by Summit Partners PE VII, LLC, its GP, by Summit Partners, L.P., its Managing Member, Summit Master Company, LLC, by Robin W. Devereux, Member	12/19/2017
	Summit Investors I, LLC, by Summit Investors Management, LLC, its Manager, by Summit Master Company, LLC, its Managing Member, by Robin W. Devereux, Member	12/19/2017
	Summit Investors I (UK), L.P., by Summit Investors Management, LLC, its General Partner, by Summit Master Company, LLC, its Managing Member, by Robin W. Devereux, Member	12/19/2017
	** Signature of Reporting Person	Date
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** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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