<PAGE>


                           SUB-LEASE - RAD-BYNET GROUP
                                   March 1999

Concluded on March___1999 between the Company RAD Data Communications Ltd.
(hereinafter : "the Lessor") and the Company RADVision Ltd. (hereinafter : "the
Lessee"), as follows :

1.       "The Premises" - an area of 292 square metres on Level A in Stage B in
         the building situate at 24 Raoul Wallenberg Road Tel Aviv, as marked on
         the diagram in ANNEX A together with 32 parking bays.

2.       The Lessor leases the Premises under a sub-lease from the Company Bay
         Networks (Israel) Ltd. (hereinafter : "Bay") which leases the Premises
         from Vitalgo Textile Enterprises Ltd. (hereinafter : "the Owner").

3.       Bay and the Owner have given approval to the Lessor for the lease of
         the Premises to the Lessee, subject to the agreements between Bay and
         the Owner and between Bay and the Lessor (hereinafter : "the Principal
         Lease Agreements"). The Principle Lease Agreements are attached hereto
         as ANNEX C.

4.       Subject to the provisions of the Principal Lease Agreements and of this
         Agreement, the Lessee leases the Premises from the Lessor under a
         sub-lease with effect from 18th March 1999 (hereinafter : "the Date of
         Commencement of the Lease") until 30th September 2000 (hereinafter :
         "the Lease Period"). Notwithstanding all the foregoing, should this be
         required by the Owner and/or by Bay, the Lessor shall have the right to
         give notice of termination of the lease to the Lessee prior to the
         expiration of the Lease Period at such time as it shall be required so
         to do by the Owner and/or by Bay. The Lessee shall not be entitled to
         any consideration and/or compensation of any kind arising from the
         termination of the Agreement for any reason. The provisions of this
         paragraph are fundamental provisions and constitute the basis for the
         entering into of contractual arrangements under this Agreement.

         Should the Lessor also continue to lease the Premises from Bay and/or
         from the Owner after 30th September 2000, an option shall be granted to
         the Lessee to extend the Lease Period and for the lease of the Premises
         by the Lessor for the entire duration of the Lessee's further Lease
         Period from Bay and/or the Owner (hereinafter : "the Further Lease
         Period"), subject however to all the provisions of this Agreement, to
         the Principal Lease Agreements, including the amendments thereto, if
         any, and such agreements for the renewal of the lease relating to the


<PAGE>


         Premises as shall, if at all, be entered into between the Lessor and
         Bay and/or the Owner.

5.       The Lessee accepts the Premises in their present condition, "As Is", in
         clean and good condition, meeting its needs (hereinafter : "the Basic
         Condition of the Premises").

6.       Should the Lessee request alterations to be effected to the Premises in
         a departure from the Basic Condition of the Premises, the Lessor shall
         effect the same in accordance with such specification and plans as
         shall be approved in advance and in writing by the Lessor and which
         shall be attached as ANNEX B to this Agreement. Upon the termination of
         this Agreement for any reason, should the Owner and/or Bay require
         this, the Lessee shall be obliged to restore the Premises to the Basic
         Condition of the Premises. For the sake of clarity, the Lessee shall
         not be required to reinstate the former condition and to remove those
         alterations which had been made as set forth in the diagram attached to
         letter from Mr. Yehuda Kashti dated 17th March 1999, attached to this
         Agreement as ANNEX E. After the alterations have been effected, as set
         out above, the Lessee shall not effect any further alteration to the
         premises (hereinafter : "the Further Changes") without the prior
         written consent of the Lessor.

7.       The monthly rental shall be as follows :

         7.1      A sum in new Israeli shekels equal to US $ 18.5 per square
                  metre. A sum in new Israeli shekels equal to US $ 120 for each
                  covered parking bay.

                  Should during the Further Lease Period the rental which the
                  Lessor pays to Bay and/or to the Owner increase, the rental
                  payable by the Lessee to the Lessor as set forth above shall
                  be increased in the same proportion.

                  The aforesaid rental shall be translated into new Israeli
                  shekels at the representative rate of exchange of the dollar
                  as at 18th March 1999, from which date it shall be linked to
                  the Consumer Price Index as is know on the date of each and
                  every actual payment.

         7.2      In addition to the rental and to the payments set forth above,
                  the Lessee shall be responsible for the payments set forth in
                  paragraphs 9 and 10 hereunder.


<PAGE>


8.       The rental, including value added tax, shall be paid quarterly for
         three (3) months in advance, on the first day of each calendar month,
         or on the first business day next following the first day of the month
         if this day is a Sabbath or Holiday. The first payment shall be on 15th
         April 1999 for the months 18th March - to June 30 1999, and with effect
         from the second payment on the first day of the month commencing on
         each annual quarter.

9.       The Lessee shall be responsible for all the on-going payments
         associated with the use of the Premises during the Lease Period,
         including municipal assessment rates, accounts for water, electricity,
         gas, telephone (including the cost of the extensions and the
         installation thereof), maintenance and air conditioning. Debiting shall
         be effected in the manner ordinarily applied by the RAD-Bynet Group
         from time to time (as the Lessor shall determine).

10.      The Lessee undertakes to enter into a management agreement with the
         Management Company of the building in the form attached to this
         Agreement as ANNEX D, and to sign any revision or addendum thereto, and
         it shall be obliged to comply with all its obligations in accordance
         with that agreement. Failure to sign an agreement with the Management
         Company or any breach of the agreement between the Lessee and the
         Management Company shall be regarded as a breach of this Agreement on
         the part of the Lessee, and it is expressly recorded that non payment
         of the management and maintenance fee to the Lessor or to the
         Management Company as required and on the due date thereof shall be
         deemed to be a fundamental breach of this Agreement on the part of the
         Lessee. Furthermore, it is recorded that the cleaning of the interior
         of the Premises is optional and is not comprised within the services
         which the Lessee shall receive from the Lessor or from the Management
         Company.

11.      A delay of 3 or more months in any payment due by the Lessee under this
         Agreement shall constitute a fundamental breach of this Agreement by
         the Lessee and shall confer upon the Lessor the right to evict the
         Lessee forthwith. Without prejudice to the Lessor's right to evict the
         Lessee as aforesaid - this shall accord the Lessor the right to enforce
         such payment against the Lessee and inasmuch that the Lessee may have
         failed to effect such payment on due date thereof, the Lessee shall
         also be liable to pay the Lessor arrears interest on the amount so in
         arrears at the Libor rate applicable at such time plus 3% per month to
         date of actual payment. The receipt of the interest by the Lessor shall
         be in addition to its rights under this Agreement and under any law and
         the receipt thereof shall not be and shall not be considered as a
         waiver of any rights accorded to it in pursuance of this Agreement or
         under any law.


<PAGE>


12.      Upon the expiration of the Lease Period or termination thereof as
         defined in paragraph 2 above, as the case may be, the Lessee undertakes
         to restore the Premises and the appurtenances therein to the same
         condition as they had been received after effecting the alterations to
         the Basic Condition of the Premises and prior to carrying out any
         Further Alterations (if any), including re-painting and cleaning as set
         forth in paragraph 3 above, save for normal wear and tear resulting
         from ordinary and reasonable use or deterioration caused to the
         Premises during the Lease Period, notwithstanding ordinary and
         reasonable use by the Lessee or by a person on its behalf or under its
         authority, or as a result of VIS MAJOR.

13.      The Lessee shall be liable for damage caused as a result of the lease
         and the use of the Premises by it and/or by its agents and/or by its
         invitees and/or any person on its behalf. The Lessee shall repair any
         damage as aforesaid in accordance with the Lessor's requirements.

14.      The Lessee is an insured within the framework of the insurance held by
         the RAD-Bynet Group and shall remain such an insured for the entire
         Lease Period as shall be customarily applied by the Group from time to
         time.

15.      The Lessee shall not be entitled to transfer any part of its rights in
         and to the Premises.

16.      Should the level of the holdings of Yehuda Zisapel and Zohar Zisapel
         decline, directly or indirectly below 25% of the issued share capital
         of the Lessee, and this as a guarantee for the fulfilment of all the
         obligations of the Lessee under this Agreement, the Lessee shall
         deposit with the Lessor, immediately upon receipt of the Lessor's
         initial request, and to its order, an autonomous unconditional,
         transferable bank guarantee, capable of foreclosure in its entirely or
         in stages at any time without attributing any reason therefor; in an
         amount in new Israeli shekels equal to 6 months rental, including
         management fees, calculated at the rate applicable at the time of the
         issue of such bank guarantee. The guarantee shall be linked to the
         Consumer Price Index. The guarantee shall be valid for the entire Lease
         Period then remaining at the time of receipt of the Lessor's initial
         request, plus 3 months, and the validity thereof shall be renewed from
         time to time, one month prior to the date on which such validity is due
         to lapse, up to the expiration of the Option Period plus 3 months after
         the expiration of such Option Period. The guarantee shall be duly
         stamped and all costs involved in the issue thereof shall be due solely
         be the Lessee.


<PAGE>


17.      Remarks :

         ---------------------------------------------------------
         ---------------------------------------------------------
         ---------------------------------------------------------

                 RAD                                     RADVISION LTD.

      --------------------------------                   ------------------
      RAD Data Communications Ltd.                       RADVision Ltd.


<PAGE>


                                    ANNEX A

[This Exhibit consists of a two dimensional floor plan for the leased
premises (an area of 292 square meters on Level A in Stage B, together with
32 parking bays) at 24 Raoul Wallenberg Street Tel Aviv Israel. The floor
plan shows a cross sectional view of room divisions within the premises.]

<PAGE>


                                   ANNEX B

Works to be performed at the leased premises at 24 Raoul Walenberg Street Tel
Aviv Israel--

                                     [NONE]


<PAGE>


                                     ANNEX C

1) Summary of lease agreement between Bay Networks (Israel ) 1996 Ltd. and
Vitalgo Textile Industries Ltd. - translated from Hebrew original

<TABLE>
<S>               <C>

Date of Lease:    June 11, 1996

Landlord:         Vitalgo Textile Industries Ltd.

Tenant:           Bay Networks (Israel) 1996 Ltd..

Premises:         24 Raoul Wallenberg Street, Tel Aviv Israel.

Square Meters:    2112 sq meters and 76 parking spaces.

Permitted Use:    Industry and data communications.

Term:             2 initial years and option to extend the lease to additional
                  3 years, (each extension one year )

                  (a) Scheduled commencement date: October 6, 1996.
                  (b) Scheduled expiration date:   October 5, 1998.

Security Deposit:          $132,000 in bank guarantee.
</TABLE>

2) Summary of lease agreement between Bay Networks Ltd. and RAD Data
Communications Ltd, - translated from Hebrew original

<TABLE>
<S>               <C>

Date of Lease:    March 10, 1999

Landlord:         Bay Networks (Israel) 1996 Ltd.

Tenant:           RAD Data Communications Ltd...

Premises:         24 Raoul Wallenberg Street, Tel Aviv Israel.

Square Meters:    1056 sq meters and 32 parking spaces.

Permitted Use:    development, marketing and manufacturing of data
                  communications products.

Term:             18.5 months.

                  (a) Scheduled commencement date: March 18, 1999
                  (b) Scheduled expiration date:   September 30, 2000.
</TABLE>

Rent - $18.50 per square meter, i.e. $19,536 per month. and $120 per parking
space, i.e. $3840.

Security Deposit:          $61,000 in bank guarantee.


<PAGE>


                                     ANNEX D

           Summary of Management Agreement--translated from Hebrew original

Management Company:   Ariel Properties--ZIV towers Management Ltd.

Building-  24 Raoul Wallenberg Street Tel Aviv Israel.

Services:  Providing maintenance services to the shared area in the building.

Fees:      Each tenant will pay the pro rata of its share in the shared areas,
           according to actual costs paid by the management company plus 10%
           (provided such costs are reasonable and as customary in similar
           buildings). Such fees will be paid quarterly.


<PAGE>


                                   ANNEX E

Summary of letter from Landlord addressed to the Registrant - translated from
Hebrew original

         After performing the changes as detailed in the two dimensional floor
plan attached to the landlord's letter, Registrant will not be required to
restore the premises to their previous condition.