**Exhibit 10.51**
**EXTENSION AND AMENDMENT OF AGREEMENT**
     This Extension and Amendment is dated as of February 8, 2004 betweenTollgrade Communications, Inc., having an address at 493 Nixon Road, Cheswick,PA 15024 (the “Corporation”) and Samuel C. Knoch, an individual residing in theCommonwealth of Pennsylvania and an employee of the Corporation (the“Executive”).
     **WHEREAS**, the Corporation and the Executive entered into an Agreement madeas of February 9, 2000, which provides for compensation to the Executive upontermination of employment under certain circumstances related to a change incontrol of the Corporation (the “Agreement”);
     **WHEREAS**, the initial term of the Agreement is stated to continue for aperiod of four (4) years, and the Agreement provides further that uponexpiration, the Corporation shall, in its sole discretion, determine whetherthe Agreement shall be renewed upon such terms as the Corporation deemsadvisable;
     **WHEREAS**, the Board of Directors of the Corporation have determined that itis in the best interests of the Corporation to renew the Agreement, extendingits term for an additional period of four (4) years, provided that theAgreement is amended as set forth herein to include a covenant againstcompetition;
     **WHEREAS,**the Executive desires to extend the Agreement, as amended hereby,in order to obtain the benefits described in the Agreement in the event theExecutive’s employment is terminated under the circumstances described in theAgreement.
     **NOW THEREFORE**, in consideration of the premises contained herein and forother good and valuable consideration, the parties agree as follows:
     **1. Extension of Agreement.**The term of the Agreement is hereby extendedthrough February 8, 2008. Upon expiration of the term, as so extended, theCorporation shall, in its sole discretion, determine whether the Agreementshall be renewed upon such terms as it deems advisable.
     **2. Amendment of Agreement.**A new Section 11 is hereby added to theAgreement to read in its entirety as set forth on Exhibit A attached hereto.
     **3. No Other Modifications.**Except as modified by this Extension andAmendment, the provisions of the Agreement shall remain in full force andeffect.
     **4. Miscellaneous.**This Extension and Amendment will be governed in allrespects by the laws of the Commonwealth of Pennsylvania without reference toany choice of law provisions. This Extension and Amendment may be executed inany number of counterparts and by the different parties hereto on separatecounterparts, each of which, when so executed, shall be deemed an original, butall such counterparts shall constitute but one and the same instrument.
     **IN WITNESS WHEREOF,**the parties have hereunto set their hands the datefirst above
 

 

written.     **TOLLGRADE COMMUNICATIONS, INC.** **EXECUTIVE**     By: /s/ Jennifer M. Reinke /s/ Samuel C. Knoch    Name: Jennifer M. Reinke Samuel C. Knoch    Title: Assistant Secretary      
 

 

**Exhibit A**
     **11. Noncompetition.**The Executive covenants and agrees that if theExecutive receives payment under Section 4(b)(ii) of this Agreement, thenduring the Restricted Period, the Executive shall not in the United States ofAmerica, directly or indirectly, whether as principal or as agent, officer,director, employee, consultant, shareholder or otherwise alone or inassociation with any other person, corporation or other entity, engage orparticipate in, be connected with, lend credit or money to, furnishconsultation or advice or permit the Executive’s name to used in connectionwith, any Competing Business. For purposes of this Agreement, the term“Restricted Period” shall mean a number of years following the termination ofExecutive’s employment with the Corporation equal to the number calculatedpursuant to Section 4(b)(ii)(A) of this Agreement, plus any amount of timeduring such period during which the Executive is in violation of thisprovision. For purposes of this Agreement, the term “Competing Business” shallmean any person, corporation or other entity engaged in the business of sellingor attempting to sell any product or service which competes with (a) productsor services sold by the Corporation within the two (2) years prior totermination of the Executive’s employment or (b) new products of theCorporation with respect to which the Corporation had allocated engineeringresources at the date of the Executive’s termination to develop such newproducts.