EXHIBIT 10.17

GUARANTY

GUARANTY dated as of December 23, 2006 made by the undersigned (individually, or if more than one, collectively, the “ Guarantor ”) in favor of JPMorgan Chase Bank, N.A., and/or any of its subsidiaries or affiliates (individually or collectively, as the context may require, the “ Bank ”).

PRELIMINARY STATEMENTS :  The Bank has entered, or may from time to time enter, into agreements or arrangements with Avistar Communications Corporation, a Delaware corporation (the “ Borrower ”), providing for credit extensions or financial accommodation to the Borrower of any kind whatsoever including, without limitation, the making of loans, advances or overdrafts, whether or not secured, discount or purchase of notes, securities or other instruments or property, creation of acceptances, issuance or confirmation of letters of credit, guaranties or indemnities, entering into foreign exchange or precious metals contracts or interest rate or currency swap or protection agreements, entering into any other derivative transactions under any ISDA Master Agreement or similar agreements between the Bank and the Borrower, or any other kind of lease, contract or agreement under which the Borrower may be indebted to the Bank in any manner (all of the foregoing agreements or arrangements being the “ Facilities ” and any writing or record evidencing, supporting, securing, or delivered in connection with a Facility, including but not limited to this Guaranty, and including as may subsequently be renewed, extended, amended,  modified, substituted and/or replaced, being a “ Facility Document ”).

THEREFORE , in order to induce the Bank to extend credit or give financial accommodation under the Facilities, the Guarantor agrees (and if more than one, jointly and severally agrees) as follows:

Guaranty of Payments .  For value received and in consideration of the Facilities extended by the Bank the Guarantor unconditionally and irrevocably guarantees to the Bank (a) performance and observance of every agreement and condition contained in any Facility Document to be performed or observed by the Borrower, and (b) payment of all sums now owing or which may in the future be owing by the Borrower under the Facilities, when the same are due and payable, whether on demand, at stated maturity, by acceleration or otherwise, and whether for principal, interest, fees, expenses, indemnification or otherwise (the “ Liabilities ”).  The Liabilities include, without limitation, interest accruing after the commencement of a proceeding under bankruptcy, insolvency or similar laws of any jurisdiction at the rate or rates provided in the Facility Documents.

This Guaranty is a guaranty of payment and performance and not of collection only.  The Bank shall not be required to exhaust any right or remedy or take any action against the Borrower or any other person or entity or any collateral.  The Guarantor agrees that, as between the Guarantor and the Bank, the Liabilities may be declared to be due and payable for the purposes of this Guaranty notwithstanding any stay, injunction or other prohibition which may prevent, delay or vitiate any declaration as regards the Borrower and that in the event of a declaration or attempted declaration, the Liabilities shall immediately become due and payable by the Guarantor for the purposes of this Guaranty.

The Guarantor shall pay the Liabilities by the seventh (7th) day on which commercial banks are not authorized or required to close in New York City (a “Banking Day”) after the Bank’s demand for payment thereof (or if such demand is accompanied by notice from the Bank, or the Bank thereafter delivers notice, that the value of collateral securing the Liabilities is less than the amount of the Liabilities, on the second (2 nd ) Banking Day after delivery of such notice) (the “Due Date”).  Upon the Bank’s making demand for payment of the Liabilities but prior to the Due Date, the Guarantor shall have the right (but not the obligation) to execute and deliver to the Bank a note sale agreement substantially in the form of Exhibit A hereto (the “Loan Sale Agreement”) together with payment of the “Note Purchase Price” (as defined therein) in immediately available funds, whereupon the obligations of the Guarantor hereunder shall terminate (but subject to reinstatement as provided below).

Guaranty Absolute .  The Guarantor guarantees that the Liabilities shall be performed and paid strictly in accordance with the terms of the Facilities.  The liability of the Guarantor under this Guaranty is absolute and unconditional irrespective of:  (a) any change in the amount, time, manner or place

of payment of, or in any other term of, all or any of the Facility Documents or Liabilities, or any other amendment or waiver of or any consent to departure from any of the terms of any Facility Document or Liability; (b) any release or amendment or waiver of, or consent to departure from, any other guaranty or support document, or any exchange, release or non-perfection of any collateral, for all or any of the Facility Documents or Liabilities; (c) any present or future law, regulation or order of any jurisdiction (whether of right or in fact) or of any agency thereof purporting to reduce, amend, restructure or otherwise affect any term of any Facility Document or Liability; (d) without being limited by the foregoing, any lack of validity or enforceability of any Facility Document or Liability; and (e) any other defense, setoff or counterclaim whatsoever (in any case, whether based on contract, tort or any other theory) with respect to the Facility Documents or the transactions contemplated thereby which might constitute a legal or equitable defense available to, or discharge of, the Borrower or a guarantor.

Guaranty Irrevocable .  This Guaranty is a continuing guaranty of all Liabilities now or hereafter existing under the Facilities and shall remain in full force and effect until payment in full of all Liabilities and other amounts payable under this Guaranty and until the Facilities are no longer in effect or, if earlier, when the Guarantor has given the Bank written notice that this Guaranty has been revoked; provided that any notice under this Section shall not release the Guarantor from any Liability, absolute or contingent, existing prior to such notice.  Such notice shall be effective only after the Bank’s actual receipt of the notice at its address set forth below, and the Bank shall have had a reasonable time to act upon such notice at each of its offices or departments responsible for the Facilities.

Reinstatement .  This Guaranty shall continue to be effective or be reinstated, as the case may be, if at any time (i) any payment of any of the Liabilities is rescinded or must otherwise be returned by the Bank on the insolvency, bankruptcy or reorganization of the Borrower or otherwise, all as though the payment had not been made or (ii)  the Loan Sale Agreement  shall be held invalid or unenforceable in whole or in any part..

Subrogation .  The Guarantor shall not exercise any rights against the Borrower which it may acquire by way of subrogation, by any payment made under this Guaranty or otherwise, until all the Liabilities have been paid in full and the Facilities are no longer in effect.  If any amount is paid to the Guarantor on account of subrogation rights under this Guaranty at any time when all the Liabilities have not been paid in full, the amount shall be held in trust for the benefit of the Bank and shall be promptly paid to the Bank to be credited and applied to the Liabilities, whether matured or unmatured or absolute or contingent, in accordance with the terms of the Facilities.

Subordination .  Without limiting the Bank’s rights under any other agreement, any liabilities owed by the Borrower to the Guarantor in connection with any extension of credit or financial accommodation by the Guarantor to or for the account of the Borrower, including but not limited to interest accruing at the agreed contract rate after the commencement of a bankruptcy or similar proceeding, are hereby subordinated to the Liabilities, and such liabilities of the Borrower to the Guarantor, if the Bank so requests, shall be collected, enforced and received by the Guarantor as trustee for the Bank and shall be paid over to the Bank on account of the Liabilities but without reducing or affecting in any manner the liability of the Guarantor under the other provisions of this Guaranty.

Representations and Warranties .  T