**Exhibit 4.5.7**

SIXTH SUPPLEMENTAL INDENTURE 

SIXTH SUPPLEMENTAL INDENTURE (this“Supplemental Indenture”) dated as of October 15, 2010, among PAETEC Holding Corp., a Delaware corporation (the “Issuer”), Cairo Acquisition Corp., a subsidiary of the Issuer (the “NewGuarantor”), and The Bank of New York Mellon (formerly known as The Bank of New York), as trustee under the indenture referred to below (the “Trustee”). 

**RECITALS**

**WHEREAS,** the Issuer and certain of its Subsidiary Guarantors have heretofore executed and delivered to the Trustee an Indenture,dated as of July 10, 2007 (as supplemented by the First Supplemental Indenture, the Second Supplemental Indenture, the Third Supplemental Indenture and the Fourth Supplemental Indenture referred to below, the “Indenture”),providing for an initial issuance of an aggregate principal amount of $300,000,000 of the Issuer’s 9.5% Senior Notes due 2015 (the “Notes”) and Subsidiary Guarantees of the Notes by the Subsidiary Guarantors, and the Issuer andother Subsidiary Guarantors have heretofore executed and delivered to the Trustee a First Supplemental Indenture, dated as of September 25, 2007 (the “First Supplemental Indenture”), a Second Supplemental Indenture, dated as ofFebruary 8, 2008 (the “Second Supplemental Indenture”), a Third Supplemental Indenture, dated as of December 18, 2009 (the “Third Supplemental Indenture”), a Fourth Supplemental Indenture, dated as ofApril 23, 2010 (the “Fourth Supplemental Indenture”), and a Fifth Supplemental Indenture, dated as of June 22, 2010 (the “Fifth Supplemental Indenture”), each providing for Subsidiary Guarantees of theNotes by the Subsidiaries party thereto; 

**WHEREAS,**Sections 4.19 and 10.03 of the Indenture provide thatthe Issuer is required to use commercially reasonable efforts to cause its current and future Restricted Subsidiaries that are eligible to be Subsidiary Guarantors under the definition thereof in the Indenture to execute and deliver to the Trustee asupplemental indenture pursuant to which such Restricted Subsidiaries shall, jointly and severally with the other Subsidiary Guarantors, fully and unconditionally guarantee the payment and performance of the Notes and the other obligations set forthin Section 10.01 of the Indenture, subject to Article Ten of the Indenture; 

**WHEREAS,** the NewGuarantor is a Restricted Subsidiary and is eligible to guarantee the Notes; 

**WHEREAS,** this Supplemental Indentureexecuted pursuant to Sections 4.19 and 10.03 of the Indenture shall evidence the Subsidiary Guarantee of the New Guarantor set forth in Section 10.01 of the Indenture; 

**WHEREAS,** pursuant to Section 4.19, Section 9.01 and Section 10.03 of the Indenture, theTrustee, the Issuer and the New Guarantor are authorized to execute and deliver this Supplemental Indenture and the New Guarantor is authorized to execute and deliver the Subsidiary Guarantee; 

**WHEREAS,**all acts and requirements necessary to make this Supplemental Indenture the legal, valid and binding obligation of theIssuer and the New Guarantor have been done; 

**NOW THEREFORE,** in consideration of the foregoing and for other good andvaluable consideration, the receipt of which is hereby acknowledged, the parties mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows: 

1. Capitalized Terms. Capitalized terms used in this Supplemental Indenture (including the recitals hereto) without definitionshall have the meanings set forth in the Indenture. 

2. Agreement to Guarantee. Subject to Article Ten of the Indenture, the NewGuarantor hereby agrees, jointly and severally with the other Subsidiary Guarantors, to guarantee fully and unconditionally to each Holder of a Note and to the Trustee and its successors and assigns the payment and performance of the Notes and theother obligations set forth in Section 10.01 of the Indenture and to be bound by all other applicable provisions of the Indenture and the Notes. The New Guarantor acknowledges and agrees, pursuant to Section 10.03 of theIndenture, that, upon its execution and delivery of this Supplemental Indenture, the New Guarantor shall be deemed to be a Subsidiary Guarantor for all purposes of the Indenture (including, without limitation, for purposes of Article Tenthereof). 

3. Ratification of Indenture; Supplemental Indenture Part of Indenture. Except as expressly amended hereby,the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder ofNotes heretofore or hereafter authenticated and delivered shall be bound hereby. 

4. Trustee’s Disclaimer. TheTrustee makes no representation or warranty as to the validity or sufficiency of this Supplemental Indenture. The recitals and the statements herein are deemed to be those of the Issuer and the New Guarantor and not of the Trustee. 

5. Governing Law. **THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY THE LAWS OF THE STATE OF NEW YORK. THE ISSUER, THE NEWGUARANTOR AND THE TRUSTEE AGREE TO SUBMIT TO THE JURISDICTION OF THE COURTS OF THE STATE OF NEW YORK IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS SECOND SUPPLEMENTAL INDENTURE.**

6. Successors. All agreements of the New Guarantor in this Supplemental Indenture shall bind its successors. 

7. Counterparts. This Supplemental Indenture may be executed in two or more counterparts, all of which shall be considered one andthe same agreement. 

8. Effect of Headings. The Section headings herein are for convenience only and shall not affectthe construction thereof. 

9. Conflict with the Trust Indenture Act. If any provision of this Supplemental Indenturelimits, qualifies or conflicts with any provision of the Trust Indenture Act of 1939 (the “TIA”) that is required under the TIA to be part of and govern any provision of this Supplemental Indenture, the provision of the TIA shallcontrol. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the provision of the TIA shall be deemed to apply to the Indenture as so modified or to be excluded by thisSupplemental Indenture. 

   

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be dulyexecuted as of the date first written above. 

 
**The New Guarantor****Cairo Acquisition Corp.**By: 
/s/ Mary K. O’Connell
Name: Mary K. O’ConnellTitle: Senior Vice President, General Counsel and Secretary**The Issuer****PAETEC Holding Corp.**By: 
/s/ Mary K. O’Connell
Name: Mary K. O’ConnellTitle: Senior Vice President, General Counsel and Secretary
   
**The Trustee**The Bank of New York MellonBy: 
/s/ Thomas J. Provenzano
Name: Thomas J. ProvenzanoTitle: Vice President