Columbia Capital Equity Partners Iv QP L P SC 13G/A Zayo Group Holdings, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

ZAYO GROUP HOLDINGS, INC.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

98919V105

(CUSIP Number)

December 31, 2015

(Date of Event which Requires filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

¨ Rule 13d-1(c)

x Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No.  98919V105 Schedule 13G Page 1 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners IV (QP), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 16,123,989
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 16,123,989
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 16,123,989
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 6.6%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 2 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity PartnersIV (QPCO), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 1,983,854
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 1,983,854
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,983,854
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.8%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 3 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Employee Investors IV, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 122,646
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 122,646
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 122,646
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.1%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 4 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners III (QP), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 237,020
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 237,020
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 237,020
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.1%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 5 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners III (Cayman), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Cayman Islands
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 130,160
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 130,160
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 130,160
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.1%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 6 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners III (AI), L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 13,094
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 13,094
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 13,094
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.0%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 7 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Investors III, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 58,482
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 58,482
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 58,482
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.0%
12	TYPE OF REPORTING PERSON OO

CUSIP No.  98919V105 Schedule 13G Page 8 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Employee Investors III, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 2,316
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 2,316
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,316
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.0%
12	TYPE OF REPORTING PERSON OO

CUSIP No.  98919V105 Schedule 13G Page 9 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners IV, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 18,107,843
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 18,107,843
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 18,107,843
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 7.4%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 10 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital IV, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 18,230,489
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 18,230,489
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 18,230,489
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 7.4%
12	TYPE OF REPORTING PERSON OO

CUSIP No.  98919V105 Schedule 13G Page 11 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital Equity Partners (Cayman) III, Ltd.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Cayman Islands
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 130,160
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 130,160
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 130,160
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.1%
12	TYPE OF REPORTING PERSON CO

CUSIP No.  98919V105 Schedule 13G Page 12 of 22

1	NAMES OF REPORTING PERSONS ColumbiaCapital Equity Partners III, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 441,072
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 441,072
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 441,072
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.2%
12	TYPE OF REPORTING PERSON PN

CUSIP No.  98919V105 Schedule 13G Page 13 of 22

1	NAMES OF REPORTING PERSONS Columbia Capital III, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 441,072
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 441,072
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 441,072
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.2%
12	TYPE OF REPORTING PERSON OO

CUSIP No.  98919V105 Schedule 13G Page 14 of 22

1	NAMES OF REPORTING PERSONS James B. Fleming, Jr.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	CITIZEN OR PLACE OF ORGANIZATION United States
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5	SOLE VOTING POWER 0
		6	SHARED VOTING POWER 18,671,561
		7	SOLE DISPOSITIVE POWER 0
		8	SHARED DISPOSITIVE POWER 18,671,561
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 18,671,561
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES Not Applicable
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 7.6%
12	TYPE OF REPORTING PERSON IN

CUSIP No.  98919V105 Schedule 13G Page 15 of 22

ITEM 1.  (a)	Name of Issuer:
	Zayo Group Holdings, Inc. (the “Issuer”).
(b)	Address of Issuer’s Principal Executive Offices:
	1805 29th Street, Suite 2050 Boulder, CO 80301
ITEM 2.  (a)	Name of Person Filing:
	Each of the following is hereinafter individually referred to as a “Reporting Person” and collectively as the “Reporting Persons.” This statement is filed on behalf of:
	Columbia Capital Equity Partners IV (QP), L.P. Columbia Capital Equity Partners IV (QPCO), L.P. Columbia Capital Employee Investors IV, L.P. Columbia Capital Equity Partners III (QP), L.P. Columbia Capital Equity Partners III (Cayman), L.P. Columbia Capital Equity Partners III (AI), L.P. Columbia Capital Investors III, LLC Columbia Capital Employee Investors III, LLC Columbia Capital Equity Partners IV, L.P. Columbia Capital IV, LLC Columbia Capital Equity Partners (Cayman) III, Ltd. Columbia Capital Equity Partners III, L.P. Columbia Capital III, LLC James B. Fleming, Jr.
(b)	Address of Principal Business Office:
	The business address of each of the Reporting Persons is 204 S. Union Street, Alexandria, VA 22314.

CUSIP No.  98919V105 Schedule 13G Page 16 of 22

(c) Citizenship:

Columbia Capital Equity Partners IV (QP), L.P.	Delaware
Columbia Capital Equity Partners IV (QPCO), L.P.	Delaware
Columbia Capital Employee Investors IV, L.P.	Delaware
Columbia Capital Equity Partners III (QP), L.P.	Delaware
Columbia Capital Equity Partners III (Cayman), L.P.	Cayman Islands
Columbia Capital Equity Partners III (AI), L.P.	Delaware
Columbia Capital Investors III, LLC	Delaware
Columbia Capital Employee Investors III, LLC	Delaware
Columbia Capital Equity Partners IV, L.P.	Delaware
Columbia Capital IV, LLC	Delaware
Columbia Capital Equity Partners (Cayman) III, Ltd.	Cayman Islands
Columbia Capital Equity Partners III, L.P.	Delaware
Columbia Capital III, LLC	Delaware
James B. Fleming, Jr.	United States

(d)	Title of Class of Securities:
	Common stock, $0.001 par value per share (“Common Stock”).
(e)	CUSIP Number:
	98919V105
ITEM 3.
	Not applicable.

CUSIP No.  98919V105 Schedule 13G Page 17 of 22

ITEM 4.	Ownership.
Ownership (a-c)
The ownership information presented below represents beneficial ownership of Common Stock of the Issuer as of December 31, 2015, based upon 244,866,876 shares of the Issuer’s Common Stock outstanding as of November 6, 2015.

Reporting Person	Amount beneficially owned		Percent of class			Sole power to vote or to direct the vote		Shared power to vote or to direct the vote		Sole power to dispose or to direct the disposition of		Shared power to dispose or to direct the disposition of
Columbia Capital Equity Partners IV (QP), L.P.		16,123,989		6.6	%		0		16,123,989		0		16,123,989
Columbia Capital Equity Partners IV (QPCO), L.P.		1,983,854		0.8	%		0		1,983,854		0		1,983,854
Columbia Capital Employee Investors IV, L.P.		122,646		0.1	%		0		122,646		0		122,646
Columbia Capital Equity Partners III (QP), L.P.		237,020		0.1	%		0		237,020		0		237,020
Columbia Capital Equity Partners III (Cayman), L.P.		130,160		0.1	%		0		130,160		0		130,160
Columbia Capital Equity Partners III (AI), L.P.		13,094		0.0	%		0		13,094		0		13,094
Columbia Capital Investors III, LLC		58,482		0.0	%		0		58,482		0		58,482
Columbia Capital Employee Investors III, LLC		2,316		0.0	%		0		2,316		0		2,316
Columbia Capital Equity Partners IV, L.P.		18,107,843		7.4	%		0		18,107,843		0		18,107,843
Columbia Capital IV, LLC		18,230,489		7.4	%		0		18,230,489		0		18,230,489
Columbia Capital Equity Partners (Cayman) III, Ltd.		130,160		0.1	%		0		130,160		0		130,160
Columbia Capital Equity Partners III, L.P.		441,072		0.2	%		0		441,072		0		441,072
Columbia Capital III, LLC		441,072		0.2	%		0		441,072		0		441,072
James B. Fleming, Jr.		18,671,561		7.6	%		0		18,671,561		0		18,671,561

Consists of (i) 16,123,989 shares held of record by Columbia Capital Equity Partners IV (QP), L.P. (“CCEP IV (QP)”); (ii) 1,983,854 shares held of record by Columbia Capital Equity Partners IV (QPCO), L.P. (“CCEP IV (QPCO)”); (iii) 122,646 shares held of record by Columbia Capital Employee Investors IV, L.P. (“CCEI IV”); (iv) 237,020 shares held of record by Columbia Capital Equity Partners III (QP), L.P. (“CCEP III (QP)”); (v) 130,160 shares held of record by Columbia Capital Equity Partners III (Cayman), L.P. (“CCEP III (Cayman)”); (vi) 13,094 shares held of record by Columbia Capital Equity Partners III (AI), L.P. (“CCEP III (AI)”); (vii) 58,482 shares held of record by Columbia Capital Investors III, LLC (“CCI III”); and (viii) 2,316 shares held of record by Columbia Capital Employee Investors III, LLC (“CCEI III”) (collectively, the “Columbia Entities”).

Columbia Capital Equity Partners IV, L.P. (“CCEP IV”) is the general partner of CCEP IV (QP) and CCEP IV (QPCO). Columbia Capital IV, LLC (“CC IV”) is the general partner of CCEP IV and CCEI IV. CC IV has sole voting and investment power over the shares held directly and indirectly by the entities of which it is the general partner as described above. James B. Fleming, Jr. controls CC IV, and as a result, he exercises voting and investment control over all the shares held by CCEP IV (QP), CCEP IV (QPCO) and CCEI IV. The general partner of CCEP III (Cayman) is Columbia Capital Equity Partners (Cayman) III, Ltd. Columbia Capital Equity Partners III, L.P. (“CCEP III”) is the sole stockholder of Columbia Capital Equity Partners (Cayman) III, Ltd. and is also the managing member of CCI III and CCEI III. CCEP III is also the general partner of CCEP III (QP) and CCEP III (AI). The general partner of CCEP III is Columbia Capital III, LLC (“CCIII”). Mr. Fleming controls CCIII, and as a result, he exercises voting and investment control over all the shares held by CCEP III (QP), CCEP III (AI), CCEP III (Cayman), CCI III and CCEI III. Each of the foregoing entities and Mr. Fleming disclaims beneficial ownership of the shares held of record by the Columbia Entities.

CUSIP No.  98919V105 Schedule 13G Page 18 of 22

ITEM 5.	Ownership of Five Percent or Less of a Class.
	Not applicable.
ITEM 6.	Ownership of More Than Five Percent on Behalf of Another Person.
	Not applicable.
ITEM 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person.
	Not applicable.
ITEM 8.	Identification and Classification of Members of the Group.
	Not applicable.
ITEM 9.	Notice of Dissolution of Group.
	Not applicable.
ITEM 10.	Certifications.
	Not applicable.

CUSIP No.  98919V105 Schedule 13G Page 19 of 22

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: February 12, 2016

COLUMBIA CAPITAL EQUITY PARTNERS IV (QP), L.P.
By:	Columbia Capital Equity Partners IV, L.P., its general partner
By:	Columbia Capital IV, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS IV (QPCO), L.P.
By:	Columbia Capital Equity Partners IV, L.P., its general partner
By:	Columbia Capital IV, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EMPLOYEE INVESTORS IV, L.P.
By:	Columbia Capital IV, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS III (QP), L.P.
By:	Columbia Capital Equity Partners III, L.P., its general partner
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President

CUSIP No.  98919V105 Schedule 13G Page 20 of 22

COLUMBIA CAPITAL EQUITY PARTNERS III (CAYMAN), L.P.
By: Columbia Capital Equity Partners (Cayman) III, Ltd., its general partner
By: Columbia Capital Equity Partners III, L.P., its sole shareholder
By: Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS III (AI), L.P.
By:	Columbia Capital Equity Partners III, L.P., its general partner
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL INVESTORS III, LLC
By: Columbia Capital Equity Partners III, L.P., its managing member
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EMPLOYEE INVESTORS III, LLC
By: Columbia Capital Equity Partners III, L.P., its managing member
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS  IV, L.P.
By:	Columbia Capital IV, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President

CUSIP No.  98919V105 Schedule 13G Page 21 of 22

COLUMBIA CAPITAL IV, LLC
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS (CAYMAN) III, LTD.
By: Columbia Capital Equity Partners III, L.P., its sole shareholder
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL EQUITY PARTNERS III, L.P.
By:	Columbia Capital III, LLC, its general partner
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
COLUMBIA CAPITAL III, LLC
By:	/s/ Donald A. Doering
Name:	Donald A. Doering
Title:	Executive Vice President
JAMES B. FLEMING, JR.
By:	/s/ James B. Fleming, Jr.

CUSIP No.  98919V105 Schedule 13G Page 22 of 22

LIST OF EXHIBITS

Exhibit No.	Description
99	Joint Filing Agreement (incorporated by reference to Exhibit 99 to the Schedule 13G filed by the Reporting Persons on February 12, 2015)