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                                                                 EXHIBIT 10.11.3

                             UNCONDITIONAL GUARANTY

         For and in consideration of the loan by COMERICA BANK-CALIFORNIA
("Bank") to AVISTAR COMMUNICATIONS CORPORATION ("Borrower"), pursuant to a Loan
and Security Agreement by and between Bank and Borrower dated as of February 27,
2002, as amended from time to time, including without limitation by that certain
First Amendment to Loan and Security Agreement dated as of December 16, 2002
(collectively, the "Loan Agreement"), the undersigned guarantor ( "Guarantor")
hereby unconditionally and irrevocably guarantees the prompt and complete
payment of all amounts that Borrower owes to Bank and performance by Borrower of
the Loan Agreement in strict accordance with its terms (collectively, the
"Borrower Obligations").

         1.       If Borrower does not perform the Borrower Obligations in
strict accordance with the Loan Agreement, Guarantor shall immediately upon
demand pay all amounts owing to Bank thereunder (including, without limitation,
all principal, interest, and fees).

         2.       If there is more than one guarantor, the obligations hereunder
and under any other guaranty relating exclusively to the Borrower Obligations
(the "Guaranteed Obligations") are joint and several, and whether or not there
is more than one guarantor, the obligations hereunder are independent of the
Borrower Obligations and the obligations of any other person or entity, and a
separate action or actions may be brought and prosecuted against Guarantor
whether action is brought against Borrower or any other guarantor or whether
Borrower or any other guarantor be joined in any such action or actions. The
Borrower Obligations and the Guaranteed Obligations shall hereinafter be
referred to collectively as the "Obligations". Guarantor waives the benefit of
any statute of limitations affecting its liability hereunder or the enforcement
thereof, to the extent permitted by law. Guarantor's liability under this
Guaranty is not conditioned or contingent upon the genuineness, validity,
regularity or enforceability of the Loan Agreement.

         3.       Guarantor authorizes Bank, without notice or demand and
without affecting its liability hereunder, from time to time to (a) renew,
extend, or otherwise change the terms of the Loan Agreement or any part thereof;
(b) take and hold security for the payment of this Guaranty, any other guaranty
or the Loan Agreement, and exchange, enforce, waive and release any such
security; and (c) apply such security and direct the order or manner of sale
thereof as Bank in its sole discretion may determine.

         4.       Guarantor waives any right to require Bank to (a) proceed
against Borrower, any guarantor or any other person; (b) proceed against or
exhaust any security held from Borrower or any other guarantor; or (c) pursue
any other remedy in Bank's power whatsoever. Bank may, at its election, exercise
or decline or fail to exercise any right or remedy it may have against Borrower
or any other guarantor or any security held by Bank, including without
limitation the right to foreclose upon any such security by judicial or
nonjudicial sale, without affecting or impairing in any way the liability of
Guarantor hereunder. Guarantor waives any defense arising by reason of any
disability or other defense of Borrower or by reason of the cessation from any
cause whatsoever of the liability of Borrower or any other guarantor. Guarantor
waives any setoff, defense or counterclaim that Borrower may have against Bank.
Guarantor waives any defense arising out of the absence, impairment or loss of
any right of reimbursement or subrogation or any other rights against Borrower
or any other guarantor. Until all of the obligations under the Loan Agreement
have been satisfied in full, (i) Guarantor shall have no right of subrogation or
reimbursement, contribution or other rights against Borrower, (ii) Guarantor
waives any right to enforce any remedy that Bank now has or may hereafter have
against Borrower, and (iii) Guarantor waives all rights to participate in any
security now or hereafter held by Bank. Bank acknowledges and agrees that, once
all of Borrower's obligations to Bank under the Loan Agreement have been
satisfied in full, Guarantor shall have full rights of subrogation against
Borrower. Guarantor waives all presentments, demands for performance, notices of
nonperformance, protests, notices of protest, notices of dishonor, and notices
of acceptance of this Guaranty and of the existence, creation, or incurring of
new or additional indebtedness. Guarantor assumes the responsibility for being
and keeping itself informed of the financial condition of Borrower and of all
other circumstances bearing upon the risk of nonpayment of any indebtedness or
nonperformance of any obligation of Borrower, warrants to Bank that it will keep
so informed, and agrees that absent a request for particular information by
Guarantor, Bank shall have no duty to advise Guarantor of information known to
Bank regarding such condition or any such circumstances. Guarantor waives the
benefits of California Civil Code sections 2809, 2810, 2819, 2845, 2850, 2899
and 3433. Until all of the obligations under the Loan Agreement have been
satisfied in full and Bank has no further obligation to make credit extensions
to Borrower, Guarantor waives the benefits of California Civil Code sections
2847, 2848, and 2849.

         5.       Guarantor acknowledges that, to the extent Guarantor has or
may have certain rights of subrogation or reimbursement against Borrower or any
other guarantor, those rights may be impaired or destroyed if Bank elects to
proceed against any real property security of Borrower or any other guarantor by
non-judicial foreclosure. That impairment or destruction could, under certain
judicial cases and based on equitable principles of estoppel, give rise to a
defense by a Guarantor against its obligations under this Guaranty. Guarantor
waives that defense and any others arising from Bank's election to pursue
non-judicial foreclosure to the fullest extent permissible under applicable law.

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         6.       Without limiting the generality of Section 5 of this Guaranty,
Guarantor waives all rights and defenses that Guarantor may have because all or
a portion of the Obligations are secured by real property in which Borrower or
another guarantor has an interest and which has been pledged to secure all or a
portion of the Obligations. This means, among other things, that:

                  a.       Bank may collect from Guarantor without first
foreclosing on any real or personal property collateral pledged by Borrower or
any other guarantor.

                  b.       If Bank forecloses on any real property collateral
pledged by Borrower or any guarantor:

                           i.       The amount of the Borrower Obligations that
Guarantor has agreed to guarantee under this Guaranty may be reduced only by the
price for which that collateral is sold at the foreclosure sale, even if the
collateral is worth more than the sale price.

                           ii.      Bank may collect from Guarantor even if
Bank, by foreclosing on the real property collateral has destroyed any right
Guarantor may have to collect from the Borrower or another guarantor.

         The foregoing is an unconditional and irrevocable waiver of any rights
and defenses Guarantor may have because all or a portion of the Guaranteed
Obligations are secured by real property in which Borrower or another guarantor
has an interest and which has been pledged to secure all or a portion of the
Obligations. These rights and defenses include, but are not limited to, any
rights or defenses based upon Section 580a, 580b, 580d, or 726 of the California
Code of Civil Procedure. The waivers in this Section 6 shall not apply if
Guarantor's obligations under this Guaranty are directly secured by real
property owned by Guarantor.

         7.       If Borrower becomes insolvent or is adjudicated bankrupt or
files a petition for reorganization, arrangement, composition or similar relief
under any present or future provision of the United States Bankruptcy Code, or
if such a petition is filed against Borrower, and in any such proceeding some or
all of any indebtedness or obligations under the Agreements are terminated or
rejected or any obligation of Borrower is modified or abrogated, or if
Borrower's obligations are otherwise avoided for any reason, Guarantor agrees
that Guarantor's liability hereunder shall not thereby be affected or modified
and such liability shall continue in full force and effect as if no such action
or proceeding had occurred. This Guaranty shall continue to be effective or be
reinstated, as the case may be, if any payment must be returned by Bank upon the
insolvency, bankruptcy or reorganization of Borrower, Guarantor, any other
guarantor, or otherwise, as though such payment had not been made.

         8.       Any indebtedness of Borrower now or hereafter held by
Guarantor is hereby subordinated to any indebtedness of Borrower to Bank; and
such indebtedness of Borrower to Guarantor shall be collected, enforced and
received by Guarantor as trustee for Bank and be paid over to Bank on account of
the indebtedness of Borrower to Bank but without reducing or affecting in any
manner the liability of Guarantor under the other provisions of this Guaranty.

         9.       Upon Bank's request, Guarantor agrees to complete and sign a
personal financial statement on Bank's form. Guarantor agrees to pay reasonable
attorneys' fees and all other costs and expenses which may be incurred by Bank
in the enforcement of this Guaranty. No terms or provisions of this Guaranty may
be changed, waived, revoked or amended without Bank's prior written consent.
Should any provision of this Guaranty be determined by a court of competent
jurisdiction to be unenforceable, all of the other provisions shall remain
effective. This Guaranty, together with any agreements (including without
limitation any security agreements or any pledge agreements) executed in
connection with this Guaranty, embodies the entire agreement among the parties
hereto with

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respect to the matters set forth herein, and supersedes all prior agreements
among the parties with respect to the matters set forth herein. No course of
prior dealing among the parties, no usage of trade, and no parol or extrinsic
evidence of any nature shall be used to supplement, modify or vary any of the
terms hereof. There are no conditions to the full effectiveness of this
Guaranty. Bank may assign this Guaranty without in any way affecting Guarantors'
liability under it. This Guaranty shall inure to the benefit of Bank and its
successors and assigns. This Guaranty is in addition to the guaranties of any
other guarantors and any and all other guaranties of Borrower's indebtedness or
liabilities to Bank.

         10.      This Guaranty shall be governed by the laws of the State of
California, without regard to conflicts of laws principles. EACH GUARANTOR
WAIVES ANY RIGHT TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR
ARISING OUT OF THIS GUARANTY OR ANY TRANSACTION CONTEMPLATED THEREIN, INCLUDING
CLAIMS BASED ON CONTRACT, TORT, BREACH OF DUTY AND ALL OTHER COMMON LAW OR
STATUTORY BASES. Each Guarantor submits to the exclusive jurisdiction of the
state and federal courts located in the County of Santa Clara, State of
California.

         11.      Guarantor shall not create, incur, assume or suffer to exist
any Lien (as defined in the Loan Agreement) with respect to any property pledged
in support of this Guaranty, including without limitation the real property
commonly known as [***], if applicable. Bank shall have a right from time to
time hereafter to appraise such real property at Borrower's expense with results
satisfactory to Bank, provided that such appraisals will be conducted no more
often than once every twelve (12) months unless an Event of Default (as defined
in the Loan Agreement) has occurred and is continuing.

         IN WITNESS WHEREOF, the undersigned Guarantor has executed this
Guaranty as of December 16, 2002.

                                          /s/ Gerald J. Burnett
                                          --------------------------------------
                                          Gerald Burnett, an individual

*** Confidential Treatment requested pursuant to a request for confidential
treatment filed with the Securities and Exchange Commission. The omitted
portions have been filed separately with the Commission.

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STATE OF CALIFORNIA                   )
                                      )   ss.
COUNTY OF ____________________________)

         On ___________________, 20__, before me, the undersigned, a Notary
Public in and for said State, personally appeared _____________________________
______________________________, personally known to me (or proved to me on the
basis of satisfactory evidence) to be the person(s) whose name(s) is/are
subscribed to the within instrument and acknowledged to me that he/she/they
executed the same in his/her/their authorized capacity(ies), and that by
his/her/their signature(s) on the instrument the person(s), or the entity upon
behalf of which the person(s) acted, executed the instrument.

         WITNESS my hand and official seal.

                                              __________________________________
                                              NOTARY PUBLIC

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