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                                                                    Exhibit 10.8

                                                    235 Littleton Road, Westford
                                                                  EXECUTION COPY

                              AGREEMENT OF SUBLEASE

      THIS AGREEMENT OF SUBLEASE ("Sublease") is made as of the 20th day of
October, 2000, by and between Unisphere Networks, Inc., a Delaware corporation
("Landlord"), having an office at One Executive Drive, Chelmsford, MA 01824 and
Sonus Networks, Inc. ("Tenant"), a Delaware corporation, having an office at 5
Carlisle Road, Westford, MA 01886.

                                     WITNESS

      WHEREAS, by Lease dated as of December 9, 1999, as amended by that certain
Addendum to Lease dated as of June 23, 2000 (the "First Amendment")
(collectively hereinafter the "Prime Lease") by and between 235 Littleton Road
Associates, Inc. ("Prime Landlord") and Unisphere Solutions, Inc., Prime
Landlord leased to Unisphere Solutions, Inc. the premises (as hereinafter
defined) (the "Premises") which is located within the building known by the
street address of 235 Littleton Road, Westford, MA 01886 (the "Building"), which
Premises are more particularly described in the Prime Lease and include 8,418
rentable square feet consisting of Units 1, 3 & 5;

      WHEREAS, Unisphere Solutions, Inc. changed its name to Unisphere Networks,
Inc. (hereinafter referred to as "Landlord");

      WHEREAS, Landlord desires to sublease to Tenant and Tenant desires to
sublease from Landlord the Premises, and Landlord is willing to sublease the
Premises on the terms and conditions hereinafter set forth.

      NOW, THEREFORE, in consideration of the mutual covenants herein contained
and for other good and valuable consideration, the parties agree as follows:

      1. Subleasing of Premises. Subject to the written consent of the Prime
Landlord, Landlord hereby subleases to Tenant and Tenant hereby subleases from
Landlord the Premises, upon and subject to all of the terms, covenants, recitals
and conditions hereinafter set forth.

      2. Term

            a. The term (the "Term") of this Sublease shall commence on February
1, 2001 (the "Commencement Date"), with said Term to expire at midnight on
January 13, 2003 (the "Expiration Date"), unless sooner terminated as
hereinafter provided.

            b. Tenant acknowledges that Landlord is in the process of
constructing a new building into which it intends to relocate its operations
from the Premises. Notwithstanding any other provision of this Sublease to the
contrary, Landlord may deliver the Premises to Tenant at any time from February
1, 2001 to June 30, 2001 upon thirty (30)

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days notice ("Commencement Date Notice") to Tenant, provided that the
Commencement Date shall be extended to such date and the Rent, as hereinafter
defined, shall become payable on the Commencement Date.

            c. Under no circumstances shall Landlord be required to vacate the
Premises if its new building shall not be substantially complete, in Landlord's
sole judgment. In the event that Landlord is unable to deliver the Premises to
Tenant on or before June 30, 2001, then either party may terminate this Sublease
in which case this Sublease shall terminate without further recourse to either
party hereunder and shall be null and void with no further force or effect.
Tenant shall have no right to terminate this Sublease (in the event of
Landlord's failure to deliver the Premises on or before June 30, 2001) unless
Tenant terminates that certain Agreement of Sublease by and between Landlord and
Tenant dated of even date herewith relating to space lease at 5 Carlisle Road,
Westford.

            d. Tenant shall not be required to take delivery of the Premises
unless and until Landlord shall deliver possession of the Premises located at 5
Carlisle Road, Westford, Massachusetts.

            e. Tenant shall have the right to have entry and access to the
Premises commencing on the twentieth day after receipt of the Commencement Date
Notice and Tenant shall not be obligated to pay any rent due hereunder but all
other terms and conditions of this Sublease shall be in full force and effect
upon the date of entry into the Premises by Tenant for any purposes.

      3. Base Rent. During the Term, Tenant shall pay to Landlord, in lawful
money of the United States which at the time shall be legal tender in payment of
all debts and dues, public and private, an annual fixed rent (the "Base Rent")
of $145,210.88 in monthly installments of $12,100.88. All such monthly
installments shall be paid in advance, on the first (1st) day of each month
during the Term, at the office of the Landlord, or such other place as Landlord
may designate, without any setoff or deduction of any kind whatsoever.

      4. Additional Rent.

            (a) Beginning on the Commencement Date, Tenant shall pay, as
Additional Rent one hundred percent (100%) of all additional rent payments for
real estate taxes under Section 6 of the Prime Lease (as such terms are referred
to in the Prime Lease) and one hundred percent (100%) of all payments for the
use of the dumpster under Section 22 of the Prime Lease. Rental and any other
sums due hereunder not paid by the due date shall bear interest of 18% per
annum. All payments shall be made to Landlord at its address set forth in
Section 24 below, or at such other address or addresses as Landlord may from
time to time designate by written notice to Tenant.

            Tenant shall also pay, as Additional Rent, the cost of all utilities
furnished to Tenant on the Premises, including, but not limited to, electricity,
gas, oil, water and sewer.

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Tenant agrees to pay any and all such charges for the Premises to Landlord in
the event any such utilities are not separately metered to Tenant (to the extent
Landlord is assessed such charges by Prime Landlord) or directly to the utility
company if such utilities are separately metered.

            (b) Tenant's obligation to pay Additional Rent hereunder shall be on
account of the period from and after the Commencement Date and shall survive the
Expiration Date or sooner termination of the Term.

            (c) All amounts payable by Tenant to Landlord pursuant to this
Sublease, including, without limitation, Base Rent and Additional Rent, shall be
deemed and constitute rent and, in the event of any non-payment thereof,
Landlord shall have all of the rights and remedies provided herein, in the Prime
Lease or in law or at equity for non-payment of rent.

            (d) Tenant agrees to pay to Landlord Tenant's pro rata share of any
taxes attributable to leasehold improvements, furniture or equipment within the
Premises which are payable by Landlord under the Prime Lease.

      5. Care, Surrender and Restoration of the Premises.

            (a) Without limiting any other provision of this Sublease or the
Prime Lease, Tenant shall take good care of the Premises, suffer no waste or
injury thereto and shall comply with all those laws, orders and regulations
applicable to the Premises, the Building and Tenant's use or manner of use
thereof, which are imposed on Landlord, as tenant under the Prime Lease, in
connection with the Premises and the Building, including without limitation any
rules and regulations promulgated by the Prime Landlord.

            (b) At the expiration or other termination of the Term, Tenant shall
surrender the Premises and all alterations and additions thereto (including any
fixtures, panelling, railings and like installation installed at the Premises at
any time by Tenant, by Prime Landlord or by Landlord) in good order, repair and
condition, ordinary wear and tear and damage by casualty only excepted, first
removing all goods and effects of Tenant and, to the extent specified by
Landlord by notice to Tenant given at least thirty (30) days before such
expiration or termination (but only to the extent required by Prime Landlord
pursuant to the terms of the Prime Lease), all alterations and additions made by
or on behalf of Tenant. Tenant shall repair any damage caused by such removal
and restore the Premises and leave them clean and neat in compliance with the
requirements of Section 5 of this Sublease and Sections 12 and 21 of the Prime
Lease. All property permitted or required to be removed by Tenant upon the
Expiration Date or sooner termination of the Term remaining in the Premises
shall be deemed abandoned and may, at the election of Landlord, either be
retained as Landlord's property or may be removed from the Premises by Landlord,
at Tenant's expense. Any such reasonable expenses shall be paid by Tenant to
Landlord upon demand therefor and shall be deemed Additional Rent, collectible
by Landlord in the same manner and with the same remedies as though said sums
were Base Rent reserved hereunder.

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            (c) Upon the Expiration Date or sooner termination of the Term,
Tenant shall quit and surrender the Premises to Landlord, broom clean, in good
order and condition, ordinary wear and tear and damage by fire and other
casualty excepted, and Tenant shall remove all of its property. If the
Expiration Date or sooner termination of the Term of this Sublease falls on a
Sunday, this Sublease shall expire at noon on the preceding Saturday unless it
be a legal holiday, in which case it shall expire at noon on the preceding
business day. Tenant shall observe and perform the covenants herein stated and
Tenant's obligations hereunder shall survive the Expiration Date or sooner
termination of the Term.

      6. Use. Tenant shall use and occupy the Premises for the purposes
permitted under Section 8 of the Prime Lease, "Office Space", and for no other
purpose.

      7. Subordination to and Incorporation of Terms of Prime Lease.

            (a) This Sublease is in all respects subject and subordinate to the
terms and conditions of the Prime Lease and to the matters to which the Prime
Lease is or shall be subordinate. Except as otherwise expressly provided in this
Sublease, the terms, provisions, covenants, stipulations, conditions, rights,
obligations, remedies and agreements of the Prime Lease are incorporated in this
Sublease by reference and made a part hereof as if herein set forth at length,
and shall, as between Landlord and Tenant (as if they were the Landlord and
Tenant, respectively, under the Prime Lease and as if the Premises being sublet
hereby were the Prime Lease Premises demised under the Prime Lease), constitute
the terms of this Sublease, except to the extent that they do not relate to the
Premises or are inapplicable to, inconsistent with, or modified or eliminated
by, the terms of this Sublease. In particular, it is intended that Tenant shall
not be subject to duplicate monetary obligations to Landlord and Prime Landlord.
To the extent that Tenant is required by this Sublease to make monetary payments
to Landlord (such as for rent, additional rent or upon default), Tenant shall
not be obligated to the Prime Landlord for any such monetary obligations nor to
Landlord for its monetary obligations to the Prime Landlord. Landlord and Tenant
acknowledge and agree that Tenant has reviewed and is familiar with the Prime
Lease and Landlord hereby represents that the copy delivered to Tenant for such
purpose and attached hereto as Exhibit A is a true, correct and complete copy of
such Prime Lease.

            (b) In the event of a default by Landlord, as tenant under the Prime
Lease, resulting in the termination, reentry or dispossession thereunder, Prime
Landlord shall take over all of the right, title and interest of Landlord under
this Sublease and Tenant hereunder shall, at the option of the Prime Landlord,
attorn to and recognize Prime Landlord as Landlord hereunder except that Prime
Landlord shall not (i) be liable for any previous act or omission of Landlord
under this Sublease, (ii) be subject to any offset, not expressly provided for
in this Sublease, which theretofore accrued to Tenant against Landlord, or (iii)
be bound by any previous modification of this Sublease or by any previous
prepayment of more than one month's rent, and shall, promptly upon Prime
Landlord's request, execute and deliver all instruments necessary or appropriate
to confirm such attornment and recognition. Tenant hereby waives all rights
under any present or future law to elect, by reason of the termination of such
Prime Lease, to terminate this Sublease or surrender possession of the Premises.

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      8. Tenant's Obligations. Except as otherwise specifically provided herein,
during the term of this Sublease all acts to be performed and all of the terms,
provisions, covenants, stipulations, conditions, rights, obligations, remedies
and agreements to be observed by and inuring to the benefit of, Landlord, as
tenant under the Prime Lease of the Premises and arising from and after the
Commencement Date, shall be performed, and observed by, and shall inure to the
benefit of, Tenant, and Tenant's obligations shall run to Landlord or the Prime
Landlord as Landlord may determine to be appropriate or required by the
respective interests of Landlord and Prime Landlord. Tenant shall indemnify
Landlord against, and hold Landlord harmless from and against, all costs,
damages, claims, liabilities, liens and expenses (including, but not limited to,
reasonable attorneys' fees and disbursements, court costs and other expenses of
litigation or arbitration) paid, suffered, incurred by or claimed against
Landlord as a result of the nonperformance or nonobservance by Tenant, Tenant's
agents, contractors, employees, invitees or licensees of any such terms,
provisions, covenants, stipulations, conditions, obligations and agreements
contained in the Prime Lease. In furtherance of the foregoing, Tenant shall not
(i) do or permit to be done anything prohibited to Landlord, as tenant under the
Prime Lease, or (ii) take any action or do or permit anything which would result
in any additional cost or other liability to Landlord under the Prime Lease
and/or this Sublease. In the event of any inconsistency between the Prime Lease
and this Sublease, such inconsistency (i) if it relates to obligations of, or
restrictions on, Tenant, shall be resolved in favor of that obligation which is
more onerous to Tenant or that restriction which is more restrictive of Tenant,
as the case may be, or (ii) if it relates to the rights of, or benefits to be
conferred upon, Tenant, shall be resolved in favor of this Sublease.

      9. Landlord's Obligations. Anything contained in this Sublease or in the
Prime Lease to the contrary notwithstanding, Landlord shall have no
responsibility to Tenant for, and shall not be required to provide, any of the
services or make any of the repairs or restorations that Prime Landlord has
agreed to make or provide, or cause to be made or provided, under the Prime
Lease (including, without limitation, those set forth in Sections 11(B)
[Lessor's Obligations], and Section 16 [Indemnification and Liability] thereof),
and Tenant shall rely upon, and look solely to, Prime Landlord for the provision
or making thereof. If Prime Landlord shall default in the performance of any of
its obligations under the Prime Lease, or if Tenant wishes to file a protest or
to dispute any matter or thing, Landlord has the right to protest or dispute as
tenant under the Prime Lease, then Tenant shall advise Landlord of such protest
or dispute (together with all material facts and circumstances pertaining
thereto) and Landlord shall make demand on Prime Landlord and shall employ all
reasonable efforts to cause Prime Landlord to cure such default or resolve such
dispute. Except as may result from a default of Landlord from its obligations
specified in the preceding sentence, Tenant shall not make any claim against
Landlord for any damage which may arise, nor shall Tenant's obligations
hereunder be impaired or abated (except for any abatement provided to and
actually received by Landlord) by reason of (i) the failure of Prime Landlord to
keep, observe or perform its obligations pursuant to the Prime Lease, or (ii)
the acts or omissions of Prime Landlord and each of its agents, contractors,
servants, employees, invitees or licensees.

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      10. Covenants with respect to the Prime Lease. Tenant covenants and agrees
that Tenant shall not do anything that would constitute a default under the
Prime Lease or omit to do anything that Tenant is obligated to do under the
terms of this Sublease so as to cause there to be a default under the Prime
Lease.

      11. Broker. Tenant represents and warrants to Landlord that Tenant has not
dealt with any broker in connection with this Sublease. Tenant shall indemnify
Landlord against, and hold Landlord harmless from, any claim on, or liability
to, any broker or any other party with whom Tenant shall have dealt in
connection with this transaction and Sublease.

      12. Indemnification.

            12.1 Reciprocal Indemnification of Landlord and Tenant.

                  (a) Tenant shall indemnify, defend with competent and
experienced counsel and hold harmless Landlord from and against any and all
damages, liabilities, actions, causes of action, suits, claims, demands, losses,
costs and expenses (including without limitation reasonable attorneys' fees and
disbursements and court costs) to the extent arising from or in connection with
the negligence or willful misconduct of Tenant, its agents, employees,
representatives or contractors.

                  (b) Landlord shall indemnify, defend with competent and
experienced counsel and hold harmless Tenant, its subsidiaries and affiliates
and their respective officers, directors, shareholders and employees, from and
against any and all damages, liabilities, actions, causes of action, suits,
claims, demands, losses, costs and expenses (including without limitation
reasonable attorneys' fees and disbursements and court costs) to the extent
arising from or in connection with the negligence or willful misconduct of
Landlord, its agents, employees, representatives or contractors.

                  (c) The party seeking indemnification under this Section (the
"Indemnified party") shall provide prompt written notice of any third party
claim to the party from whom indemnification is sought (the "Indemnifying
Party"). The Indemnifying Party shall have the right to assume exclusive control
of the defense of such claim or at the option of the Indemnifying Party, to
settle the same. The Indemnified Party agrees to cooperate reasonably with the
Indemnifying Party in connection with the performance of the Indemnifying
Party's obligations under this Section.

                  (d) Notwithstanding anything to the contrary contained in this
Sublease, neither party hereto shall be liable to the other for any indirect,
special, consequential or incidental damages (including without limitation loss
of profits, loss of use or loss of goodwill) regardless of (i) the negligence
(either sole or concurrent) of either party' or (ii) whether either party has
been informed of the possibility of such damages. It is expressly understood and
agreed that damages payable by either party to Prime Landlord shall be deemed to
constitute direct damages of such party. This subparagraph (d) shall not be
applicable to Section 21 of this Sublease.

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            12.2 Indemnification by Tenant of Prime Landlord. Tenant agrees to
defend, save harmless and indemnify Prime Landlord to the same extent as
Landlord is required to do so under the provisions of the Prime Lease including,
but not limited to, Section 16 of the Prime Lease.

            12.3 Survival. The provisions of this Section shall survive the
expiration or earlier termination of this Sublease.

      13. Quiet Enjoyment. Subject to the terms and conditions hereof and as
long as Tenant pays all of the Base Rent and Additional Rent due hereunder and
otherwise performs and observes all of the obligations, terms and conditions
contained herein and in the Prime Lease as herein incorporated, Tenant shall
peaceably and quietly have, hold and enjoy the Premises.

      14. Termination of Prime Lease. If for any reason the term of the Prime
Lease is terminated prior to the Expiration Date of this Sublease, this Sublease
shall thereupon terminate, and Landlord shall not be liable to Tenant by reason
thereof unless such termination is due solely to an event of default on behalf
of Landlord. Notwithstanding the foregoing, if the termination of the Prime
Lease does not result in the termination of this Sublease by reason of Tenant's
attornment to, and recognition of, Prime Landlord as landlord hereunder in
accordance with the provisions of Section 7(b) hereof, Landlord shall not be
liable to Tenant hereunder for damages or otherwise, and Landlord's obligation
to Tenant shall be limited to returning to Tenant a portion of any rent paid in
advance by Tenant, if any, prorated as of the date of such termination.

      15. Modification of Prime Lease. For the purposes hereof, the terms of the
Prime Lease are subject to the following modifications:

            (a) In all provisions of the Prime Lease requiring the approval or
consent of Prime Landlord, Tenant shall be required to obtain the approval or
consent of both Prime Landlord and Landlord. In all provisions of the Prime
Lease requiring that notice be given to Prime Landlord, Tenant shall be required
to give notice to both the Prime Landlord and Landlord.

            (b) The following provisions of the Prime Lease do not apply to
Tenant and are hereby deleted in respect of this Sublease: Sections 3 (Term), 13
(Assignments -- Subleasing) (as between Landlord and Tenant only), 18 (Fire,
Casualty -- Eminent Domain) (but only with respect to any right to terminate the
Prime Lease) and 22 (Other Provisions).

      16. Consents. Landlord's refusal to consent to or approve any matter or
thing, whenever Landlord's consent or approval is required under this Sublease
or under the Prime Lease, as incorporated herein, shall be deemed reasonable if
Prime Landlord has refused or failed to give its consent or approval to such
matter or thing.

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      17. Condition of the Premises; Tenant's Changes.

            (a) Tenant represents it has made a thorough examination of the
Premises and it is familiar with the condition thereof. Tenant acknowledges that
it enters into this Sublease without any representation or warranties by
Landlord except as set forth in this Lease, or anyone acting or purporting to
act on behalf of Landlord, as to the present or future conditions of the
Premises or the appurtenances thereto or any improvements therein or of the
Building. It is further agreed that Tenant does and will accept the Premises "as
is" in their present condition and Landlord has no obligation to perform any
work therein.

            (b) Notwithstanding anything to the contrary contained in the Prime
Lease, Tenant shall not make any changes to the Premises whatsoever, including,
without limitation, structural or non-structural changes, without the prior
written consent of Landlord which consent shall not be unreasonably withheld,
conditioned or delayed but subject to prior consent of Prime Landlord in
accordance with the Prime Lease. All structural and/or non-structural changes
shall be subject to the Construction Specifications attached hereto as Exhibit
B.

      18. Assignment and Subletting.

            (a) Tenant, for itself, its successors and assigns, expressly
covenants that it shall not assign, whether by operation of law or otherwise,
mortgage or pledge or otherwise transfer or encumber this Sublease, or sublet
all or any part of the Premises without obtaining the prior written consent of
Landlord which consent may be given or withheld in Landlord's sole discretion.
Notwithstanding the foregoing, Landlord's consent shall not be unreasonably
withheld with respect to assignments or transfers to Affiliated Entities.
Affiliated Entities shall mean (i) a subsidiary of Tenant, (ii) a corporation or
other entity into or with which Tenant has merged or consolidated or to which
substantially all of Tenant's stock or assets are transferred, or (iii) any
corporation or other entity which controls, is controlled by, or is under common
control with Tenant.

            Notwithstanding the foregoing, provided there is no default
continuing beyond any applicable notice and/or cure period, Landlord also
agrees, upon the written request of Tenant, to not unreasonably withhold its
consent to a sub-sublease of the Premises by Tenant, provided and on the
condition that: (i) such sub-sublease including the subtenant shall be subject
to Prime Landlord's prior approval, which approval shall be governed by the
terms of the Prime Lease; (ii) such subtenant shall be of a business reputation
reasonably acceptable to Landlord; (iii) such subtenant shall have a financial
net worth, determined by generally acceptable accounting principles,
satisfactory to Landlord (and Tenant shall supply financial information and
documentation regarding such financial status to Landlord thirty (30) days prior
to the execution of any new sub-sublease); (iv) the terms of such new
sub-sublease shall be on the same or better terms as this Sublease (or if any
term may be less favorable to Landlord, the inclusion of such change in the new
sub-sublease shall be subject to Landlord's sole discretion); (v) the new
sub-sublease shall be unconditionally guaranteed by Tenant, which form of
guaranty shall be satisfactory to Landlord; (vi) Tenant shall reimburse Landlord
for its reasonable out-of-pocket expenses, including reasonable

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attorney's fees, incurred in connection with such surrender and sub-sublease and
Tenant shall be solely responsible for any leasing commissions, improvements
allowances or other expenses relating to the proposed sub-sublease; (vii) Tenant
shall not be in default hereunder; (viii) Tenant shall pay to Landlord 50% of
all rents received in connection with such sub-sublease in excess of the rents
set forth herein; and (ix) the new sub-sublease shall be in the form of this
Sublease. Any obligations of Tenant to reimburse Landlord hereunder shall
survive the surrender of the Sublease.

            (b) If Tenant requests Landlord's consent to a sublease as set forth
above, Tenant, together with such request for consent, shall provide Landlord
with the name of the proposed transferee and the nature of the business of the
proposed transferee, the term, use, rental rate and all other material terms and
conditions of the proposed transfer, including, without limitation, a copy of
the proposed sub-sublease or other contractual documents and evidence
satisfactory to Landlord that the proposed transferee is financially
responsible.

            With respect to any sub-sublease of fifty (50%) percent or more of
the Premises, Landlord may have the right to recapture the Premises if Tenant
proposes to sub-sublease the Premises to a third party after the one year
anniversary of the Commencement Date. Landlord must exercise (or forego) its
recapture rights within fifteen (15) days of its receipt of Tenant's
sublease/assignment notice. In order to effectuate its recapture rights,
Landlord may terminate, at its election, the sublease with respect to the entire
Premises or with respect to that portion of the Premises described in the
sub-sublease and Tenant shall have no further obligations (except as otherwise
specifically set forth in this Sublease) with respect to that portion of the
Premises which are recaptured (and there shall be a pro rata reduction in Rent
and the Security Deposit based upon the rentable square footage of the
recaptured portion of the Premises relative to the rentable square footage of
Premises prior to recapture), except as specifically set forth herein, and
Tenant shall at its expense erect, if necessary, a demising wall to separate the
remainder of the Premises from that portion of the Premises which is being
recaptured and to take such other steps as shall be necessary to make the
portion of the Premises that is not being recaptured into a self-contained,
lawfully demisable rental unit.

            (c) In the event Landlord is requested to consent to an assignment
of this Sublease or a subletting of the Premises, Tenant shall pay all costs and
expenses in connection with such assignment or subletting, including, without
limitation, any reasonable attorneys' fees of Landlord in connection with its
review of the assignment or subletting documents, any cost of renovating,
altering or decorating the Premises for a new occupancy (if Tenant desires to do
the same) and any leasing brokerage fees payable.

            (d) The listing of any name other than that of Tenant, whether on
the doors of the Premises or on the Building directory, or otherwise, shall not
operate to vest any right or interest in this Sublease or in the Premises or be
deemed to be the written consent of Landlord mentioned in this Section, it being
expressly understood that any such listing is a privilege extended by Landlord
revocable at will by written notice to Tenant.

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                                     - 10 -


            (e) If this Sublease is assigned, or if the Premises or any part
thereof is sublet or occupied by anybody other than Tenant, Landlord may at any
time and from time to time, collect rent and other charges from the assignees,
subtenants or occupants, and apply the net amount collected to the Base Rent and
other charges herein reserved, but no such assignment, sublease or collection
shall be deemed a waiver of this covenant, or the acceptance of the assignee,
Tenant or occupant as a Landlord, or a release of Tenant from the further
performance of covenants on the part of Tenant herein contained, including
without limitation, Tenant's obligation to pay the Base Rent and other charges,
or a release of the Security Deposit (as hereinafter defined). The consent by
Landlord to an assignment or subletting or occupancy shall not in any way be
construed to relieve Tenant from obtaining the express consent in writing of
Landlord to any further assignment or subletting or occupancy.

            (f) Notwithstanding the immediately preceding sentences, any steps
taken by Landlord or Tenant in this regard shall be subject to all terms and
conditions of the Prime Lease.

            (g) Landlord reserves the right to transfer and assign its interest
in and to this Sublease to any entity or person who shall succeed to Landlord's
interest in and to the Prime Lease.

            (h) Consent by Landlord to any assignment, transfer or subletting to
any party shall not be construed as a waiver or release of Tenant from the terms
of any covenant or its primary responsibility under this Sublease, nor shall
consent to one assignment, transfer or sublease to any person, partnership, firm
or corporation be deemed to be a consent to any subsequent assignment, transfer
or subletting to another person, partnership, firm or corporation; Tenant shall
remain directly and primarily liable and any such sublessee or assignee agrees
directly with Landlord by written instrument reasonably satisfactory to Landlord
to be bound by all of the obligations of Tenant.

      19. Insurance.

            (a) Tenant agrees to maintain all insurance coverages specified in
and in accordance with Section 17 of the Prime Lease (including without
limitation commercial general liability and property damage insurance, casualty
insurance and, in addition, statutory workers' compensation insurance). All such
insurance shall be underwritten by a company or companies licensed to do
insurance business in the Commonwealth of Massachusetts by the Department of
Insurance and in good standing, and shall be written on an "occurrence basis."
All such insurance policies shall name Landlord and Prime Landlord as additional
insureds thereunder and, in addition, shall name as additional insureds the
holders of any mortgage of the Building, or the property on which the building
is located (the "Property"), of which Tenant is notified in writing, as their
respective interests may appear. Tenant shall furnish Landlord receipts
evidencing payment of the premiums for such insurance (if requested by Landlord)
and shall deposit with Landlord certificates for such insurance no later than
the Rent Commencement Date and at least fifteen (15) days before each insurance
renewal date thereof, bearing the endorsement that the polices will not

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be canceled nor will coverages be reduced until after ten (10) days' prior
written notice to both Landlord and Prime Landlord of such proposed action.
Tenant shall pay all premiums and charges for such insurance, and if Tenant
shall fail to obtain such insurance, Landlord may, but shall not be obligated
to, obtain the same, in which event the amount of the premium paid shall be paid
by Tenant to Landlord upon Landlord's demand therefor, shall be deemed
Additional Rent and shall be collectible by Landlord in the same manner and with
the same remedies as though said sums were Additional Rent reserved hereunder.

            (b) Tenant acknowledges that Landlord will not carry any insurance
in favor of Tenant, and that neither Prime Landlord nor Landlord will carry
insurance on Tenant's furniture and/or furnishings or any fixtures or equipment,
improvements or appurtenances of Tenant in or about the Premises.

      20. Waiver of Subrogation.

            (a) Any casualty insurance carried by the Tenant with respect to the
Premises, the Building or the Property, or property therein or occurrences
thereon shall include a clause or endorsement denying to the insurer rights of
subrogation against the other party to the extent rights have been waived by the
insured prior to occurrence of injury or loss, provided that such clause or
endorsement is obtainable without payment of an additional premium. If such
clause or endorsement is obtainable upon payment of an additional premium,
notice thereof shall be given to the Landlord and the Landlord may request the
Tenant to obtain it and shall reimburse the Tenant for the cost of such
additional premium.

            (b) Each party, notwithstanding any provisions of this Sublease to
the contrary, hereby waives any rights of recovery against the other for injury
or loss due to hazards covered by such insurance to the extent such party's
policy permits such waivers of subrogation and then only with respect to sums
which are collectible thereunder. Landlord shall be afforded the protection of
this provision notwithstanding any right which Tenant may have to self insure.

      21. End of Term. If Tenant shall remain in possession of the Premises or
any part thereof after the expiration or prior termination of the Term hereof,
as the same may be extended, the parties agree that no such holding over by
Tenant shall operate to extend or renew this Sublease, and that any such holding
over shall cause Tenant to become a month-to-month tenant and Tenant shall be
obligated to pay monthly installment of Base Rent and Additional Rent in an
amount equal to one hundred fifty percent (150%) times the sum of the
installment of Base Rent and Additional Rent payable during the last full
calendar month of the Lease Term, and such tenancy shall otherwise be subject to
all the terms, conditions, covenants and agreements of this Sublease. Tenant
further agrees to pay to Landlord all direct, indirect and consequential
damages, costs and expenses incurred by Landlord as a result of such holding
over, including without limitation, any costs and expenses that Prime Landlord
charges to Landlord on account thereof and Tenant agrees to indemnify Landlord
against, and hold Landlord harmless from, any damage, loss, claim,

<PAGE>
                                     - 12 -


liability or expenses, including without limitation, reasonable attorneys' fees
arising out of such holding over.

      22. Default.

            (a) In the event that Tenant shall default in the payment of Base
Rent, Additional Rent or any other charge payable hereunder within five (5) days
after written notice, or shall default in the performance or observance of any
of the terms, conditions and covenants of this Sublease within twenty (20) days
after written notice, or, if not curable within said twenty-day period, Tenant
does not commence to cure said default within said twenty-day period and
diligently prosecute the same to completion, and provided that there exists no
event of default under the Prime Lease, Landlord, in addition to and not in
limitation of any rights otherwise available to it, shall have the same rights
and remedies with respect to such default as are provided to Prime Landlord
under the Prime Lease with respect to defaults by Landlord as tenant thereunder,
with the same force and effect as though all such provisions relating to any
such default or defaults were set forth herein in their entirety, and Tenant
shall have all of the obligations of the tenant under the Prime Lease with
respect to such default or defaults.

            Notwithstanding anything to the contrary as contained herein the
parties acknowledge that there is not a grace period under the Prime Lease for
non-monetary default, and accordingly, should Prime Landlord notify Landlord of
a default with respect to non-monetary matters, the twenty (20) day period set
forth above shall automatically be revoked.

            (b) In the event of a default by Tenant in the performance of any of
its non-monetary obligations hereunder, including those under the Prime Lease,
Landlord may, at its option, and without waiving any other remedies for such
default herein or at law or by incorporation by reference of the Prime Lease
provided, at any time thereafter, give written notice to Tenant that if such
default is not cured, or the cure not commenced, within twenty (20) days after
notice, and if so commenced is not thereafter pursued diligently to completion,
Landlord may cure such default for the account of Tenant, and any amount paid or
incurred by Landlord in so doing shall be deemed paid or incurred for the
account of Tenant and Tenant agrees promptly to reimburse Landlord therefor and
save Landlord harmless therefrom; provided, however, that Landlord may cure any
such default as aforesaid prior to the expiration of any waiting period if
reasonably necessary to protect Landlord's interest under the Prime Lease or to
prevent injury or damage to persons or property.

            (c) In addition to any other event of default under this Sublease or
the Prime Lease, it shall be an event of default under this Sublease, without
any notice or cure period, if Tenant shall be in default under that certain
Agreement of Sublease between Landlord and Tenant dated October 20, 2000
relating to space located at 5 Carlisle Road, Westford, MA continuing beyond any
applicable notice and/or cure period.

<PAGE>
                                     - 13 -


      23. Destruction, Fire and other Casualty. If the whole or any part of the
Premises or the Building shall be damaged by fire or other casualty and the
Prime Lease is not terminated on account thereof by either Landlord or Prime
Landlord in accordance with the terms thereof this Sublease shall remain in full
force and effect and Base Rent and Additional Rent, shall not abate except to
the extent Base Rent and Additional Rent for the Premises shall abate under the
terms of the Prime Lease.

      Notwithstanding the foregoing, if and only to the extent Landlord has an
opportunity under Section 18 of the Prime Lease to terminate the Prime Lease
with respect to the Premises ("Casualty Termination Option"), Landlord shall
within ten (10) days of such Casualty Termination Option notify Tenant whether
Landlord has elected to terminate or not terminate the Prime Lease. If Landlord
has decided not to terminate the Prime Lease under Section 18 of the Prime Lease
with respect to the Premises, Tenant may decide, notwithstanding such decision,
that it elects to terminate the Sublease provided (i) there is no default
hereunder, and (ii) Tenant informs Landlord within five (5) business days of
receipt of such Casualty Termination Option from Landlord that it elects to
terminate the Sublease which event the Sublease shall terminate in accordance
with Section 18 of the Prime Lease. If Tenant fails to satisfy all of the
foregoing conditions, Tenant shall be deemed to have waived any rights set forth
herein. All times set forth herein are of the essence.

      24. Notices.

            (a) Whenever, by the terms of this Sublease, notice, demand or other
communication shall or may be given to either party, the same shall be in
writing and addressed as follows:

                   If to Landlord:   Unisphere Networks, Inc.
                                     One Executive Drive
                                     Chelmsford, MA 01824
                                           Attn: Suzanne M. Zabitchuck
                                                 General Counsel

                   with a copy to:
                                     Gadsby Hannah LLP
                                     225 Franklin Street
                                     Boston, MA 02110
                                           Attn: Cynthia B. Keliher, Esq.

                   If to Tenant:     Sonus Networks, Inc.
                                     5 Carlisle Road
                                     Westford, MA 01886
                                     Attn: Stephen J. Nill, Vice President of
                                           Finance and CFO

or to such other address or addresses as shall from time to time be designated
by written notice by either party to the other as herein provided. All notices
shall be sent by registered

<PAGE>
                                     - 14 -


or certified mail, postage prepaid and return receipt requested, or by Federal
Express or other comparable courier providing proof of delivery, and shall be
deemed duly given and received (i) if mailed, on the third business day
following the mailing thereof, or (ii) if sent by courier, the date of its
receipt (or, if such day is not a business day, the next succeeding business
day). Landlord and Tenant each promptly shall deliver to the other copies of all
notices, requests, demands or other communications which relate to the Premises
or the use or occupancy thereof after receipt of the same from Prime Landlord or
others.

            (b) Each party hereunder shall promptly furnish the other with
copies of all notices under the Prime Lease or this Sublease with respect to the
Premises which such party shall receive from Prime Landlord under the Prime
Lease.

      25. Sublease Conditional Upon Certain Consents. Landlord and Tenant each
acknowledge and agree that this Sublease is subject to Landlord's obtaining the
unconditional consent of Prime Landlord in accordance with the terms of the
Prime Lease, and that if such consent shall not be obtained within forty-five
(45) days of the date hereof, then this Sublease shall be deemed cancelled and
terminated and neither of the parties hereto shall have any liability to the
other.

      26. Security Deposit. Tenant concurrently with the execution of this
Sublease has deposited with Landlord a deposit (the "Security Deposit") in the
amount of Twelve Thousand One Hundred 88/100 Dollars ($12,100.88) to be held by
Landlord without interest as security for the faithful performance and
observance by Tenant of the terms, conditions and provisions of this Sublease,
including without limitation the surrender of possession of the Premises to
Landlord as herein provided. Landlord shall not be required to maintain the
Security Deposit in a separate account. It is agreed that in the event Tenant
defaults in respect of any of the terms, provisions and conditions of this
Sublease, including, but not limited to, the payment of Base Rent and Additional
Rent, Landlord may apply or retain the whole or any part of the Security Deposit
to the extent required for the payment of any Base Rent and Additional Rent or
any other sum as to which Tenant is in default or for any sum which Landlord may
expend or may be required to expend by reason of Tenant's default in respect of
any of the terms, covenants and conditions of this Sublease, including but not
limited to, any damages or deficiency in the reletting of the Premises, whether
such damages or deficiency accrue or accrues before or after summary proceedings
or other reentry by Landlord. The Security Deposit is not to be used or applied
by Tenant as a substitute for rent due any month, but may be so applied by
Landlord at any time at Landlord's option. The use, application or retention of
the Security Deposit, or any portion thereof, by Landlord shall not prevent
Landlord from exercising any other right or remedy provided by this Sublease or
by law and shall not operate as a limitation on any recovery to which Landlord
may otherwise be entitled. If Landlord applies or retains any part of the
Security Deposit, Tenant, upon written demand therefor by Landlord, shall
deposit cash with Landlord in such amount so that Landlord shall have the full
deposit on hand at all times during the Term. If Tenant shall fully and
faithfully comply with all of the terms, provisions, covenants and conditions of
this Sublease, the balance of the Security Deposit, if any, shall be returned to
Tenant within thirty (30) days after the Expiration Date and after the delivery
of the entire possession of the Premises to Landlord.

<PAGE>
                                     - 15 -


      27. Payment of the First Month's Base Rent. Tenant shall pay to Landlord
the first monthly installment of the applicable Base Rent upon execution of this
Sublease.

      28. Signage. Any signage contemplated by the Tenant shall be subject the
consent of the Prime Landlord. Landlord shall have no obligation or
responsibility to remove any signage which exists at the Premises as of the
Commencement Date.

      29. Landlord's Representations. Landlord hereby represents and warrants
that (i) the Prime Lease is in full force and effect, (ii) the Prime Lease
attached hereto as Exhibit A is the complete Prime Lease and that, except for
the Addendum to Lease dated June 23, 2000, the Prime Lease has not been amended
or modified; (iii) to the best of Landlord's knowledge, there are no existing
setoffs, defenses or counterclaims against the Prime Landlord with respect to
the payment of rent reserved under the Prime Lease or any performance of other
terms, conditions or covenants of the Prime Lease on the part of the Tenant
under the Prime Lease to be performed; and (iv) there exists no defaults or
breaches of Prime Landlord's or Tenant's obligations under the Prime Lease nor,
to the best of Landlord's knowledge, any event which with the giving of notice
or passage of time, or both, would constitute a default under the Prime Lease.

      30. Miscellaneous.

            (a) This Sublease may not be extended, renewed, terminated, or
otherwise modified except by an instrument in writing signed by the party
against whom enforcement of any such modification is sought.

            (b) It is understood and agreed that all understandings and
agreements heretofore had between the parties hereto are merged in this
Sublease, which alone fully and completely expresses their agreement, and that
the same is entered into after full investigation, neither party relying upon
any statement, representation or warranty made by the other not embodied in this
Sublease.

            (c) The paragraph headings appearing herein are for purposes of
convenience only and are not deemed to be a part of this Sublease.

            (d) The provisions of this Sublease shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts
without regard to principles of conflicts of laws. Landlord and Tenant agree to
submit to jurisdiction in the Commonwealth of Massachusetts with respect to any
dispute under or arising out of this Sublease and agree that any such dispute
shall be brought either in the courts of the Commonwealth of Massachusetts or in
the applicable federal district court located in Massachusetts.

            (e) If any provision of this Sublease or the application thereof to
any person or circumstance shall to any extent be invalid or unenforceable, the
remainder of this Sublease, or the application of such provision to persons or
circumstance other than those as

<PAGE>
                                     - 16 -


to which it is invalid or unenforceable, shall not be affected thereby, and each
provision of this Sublease shall be valid and enforced to the fullest extent
permitted by law.

            (f) This Sublease may be executed in counterparts each of which
shall be deemed an original and all of which together shall constitute one and
the same document.

            (g) This Sublease (or any notice hereof) shall not be recorded.

            (h) Landlord and Tenant hereby each waive trail by jury in any
action, proceeding or counterclaim brought by either against the other, on or in
respect of any matter whatsoever arising out of or in any way connected with
this Sublease, the relationship of Landlord and Tenant or Tenant's use or
occupancy of the Premises.

            (i) This Sublease includes and incorporates all Exhibits referred to
hereby and attached hereto.

                      [SIGNATURES APPEAR ON THE NEXT PAGE]

<PAGE>
                                     - 17 -


      IN WITNESS WHEREOF, this Agreement of Sublease has been duly executed as
of the day and year first above written.

                                     LANDLORD:
                                     UNISPHERE NETWORKS, INC.


                                     By: /s/ John J. Connolly
                                         --------------------------------
                                     Name: John J. Connolly
                                           ------------------------------
                                     Title: V.P. Finance & CFO.
                                            -----------------------------

                                     TENANT:
                                     SONUS NETWORKS, INC.


                                     By: /s/ S. J. Nill
                                         --------------------------------
                                     Name: S. J. Nill
                                           ------------------------------
                                     Title: VP & CFO
                                            -----------------------------

<PAGE>
                                     - 18 -


                                    EXHIBIT A
                                   Prime Lease

                                 Attached hereto

<PAGE>
                                     - 19 -


                                    EXHIBIT B
                          TENANT IMPROVEMENTS AGREEMENT

      This Tenant Improvements Agreement (the "Agreement") is attached to and
made a part of the Sublease. The capitalized terms used in this Agreement that
are defined in the Sublease shall have the same meanings as provided in the
Sublease.

1.    General

      This Agreement sets forth the terms and conditions governing Tenant's
construction of improvements to be installed in the Premises (the "Tenant
Improvements").

2.    Intentionally Omitted.

3.    Design and Schedule.

      3.1   Tenant Plans for Tenant Improvements.

            (a)   Space Plan: The "Space Plan" as used herein shall mean a plan
                  containing, among other things, a partition layout, door
                  location and, if appropriate, some furniture located in key
                  spaces within the Premises.

            (b)   Construction Drawings and Specifications: The "Construction
                  Drawings and Specifications" as used herein shall mean the
                  construction working drawings, the mechanical, electrical and
                  other technical specifications, and the finishing details,
                  including wall finishes and colors and technical and
                  mechanical equipment installation, if any, all of which
                  details the installation of the Tenant Improvements in the
                  Premises. The Construction Drawings shall be signed by
                  Tenant's Representative:

                  (i)   be compatible with the Building shell, and with the
                        design, construction and equipment of the Building;

                  (ii)  comply with all applicable laws, codes and ordinances
                        including the Americans With Disabilities Act, and the
                        rules and regulations of all governmental authorities
                        having jurisdiction;

                  (iii) comply with all applicable insurance regulations and the
                        requirements of the Board of Underwriters for a fire
                        resistant Class A building; and

<PAGE>
                                     - 20 -


                  (iv)  include locations of all Tenant Improvements including
                        complete dimensions.

      3.2   Approvals by Landlord. The Space Plan and all Construction Drawings
            and Specifications for the Tenant Improvements shall be subject to
            Landlord's prior written approval, which shall not be unreasonably
            withheld or delayed, except that Landlord shall have complete
            discretion with regard to granting or withholding approval of
            Construction Drawings and Specifications to the extent they impact
            the Building's structure or systems, affect future marketability of
            the Building or would be visible from the common facilities or
            exterior of the Building. Any changes, additions or modifications
            that Tenant desires to make to the Tenant Plans shall also be
            subject to Landlord's prior written approval, which shall not be
            unreasonably withheld or delayed except as provided above for
            Building structure, system or appearance impact.

4.    Construction of Tenant Improvements. Following Landlord's and Landlord's
      final approval of the Tenant Plans and Tenant obtaining permits, Tenant
      shall commence and diligently proceed with the construction of the Tenant
      Improvements. Landlord and Tenant acknowledge that Tenant shall hire a
      contractor mutually acceptable to Prime Landlord, Landlord and Tenant (in
      their reasonable discretion) to complete the Tenant Improvements. The
      Tenant Improvements shall be conducted with due diligence, in a good and
      workmanlike manner befitting a first class office building, and in
      accordance with the Tenant Plans and all applicable laws, codes,
      ordinances and rules and regulations of all governmental authorities
      having jurisdiction.

      Tenant hereby agrees to indemnify Landlord and Landlord and hold Landlord
      and Landlord harmless from any and all claims for personal or bodily
      injury and property damage that may arise from the performance of the
      Tenant Improvements, whether resulting from the negligence or willful
      misconduct of its general contractors, subcontractors or otherwise. Tenant
      and its contractors and subcontractors shall execute such additional
      documents as Landlord deems reasonably appropriate to evidence said
      indemnity.

      Notwithstanding the foregoing, Tenant shall not commence the Tenant
      Improvements until the following is provided:

      (a)   Insurance. Prior to construction, Tenant shall provide Landlord with
            an original certificate of All-Risk Builder's Risk Insurance (the
            "Builder's Risk Insurance Policy"), subject to Landlord's reasonable
            approval, in the minimum amount of the replacement cost of the
            Tenant Improvements issued by a company or companies acceptable to
            Landlord and authorized to do business in the Commonwealth of
            Massachusetts, covering the Premises (including the Premises), with
            premiums prepaid, and which names the Landlord as an additional
            insured. Said policy shall insure the Tenant Improvements and all
            materials and supplies for the Tenant Improvements

<PAGE>
                                     - 21 -


            stored on the Premises (or at any other sites and including the
            Premises) against loss or damage by fire and the risks and hazards
            insured against by the standard form of extended coverage, and
            against vandalism and malicious mischief, and such other risks and
            hazards as Landlord may reasonably request. Said insurance coverage
            shall be for 100% of replacement cost, including architectural fees.
            The Builder's Risk Insurance Policy shall contain a provision that
            the insurance company waive the rights of recovery or subrogation
            against Landlord, its agents, servants, invitees, employees,
            co-tenants, co-venturers, affiliate companies, and their insurers.

      (b)   Governmental Permits. Building permits and other appropriate permits
            and licenses from the appropriate agency or office of any
            governmental or regulatory body having jurisdiction over the
            Premises and which are required for the construction of the Tenant
            Improvements.

      (c)   Additional Insurance. Additional insurance in the form of and
            meeting the requirements as Landlord and Prime Landlord may
            determine in their reasonable discretion provided it is commercially
            reasonable under the circumstances..

5.    Change Orders. If Tenant requests any change or addition to or subtraction
      from the Tenant Improvements ("Change Order") after Tenant's and
      Landlord's approval of the final and complete Construction Drawings and
      Specifications for the Tenant Improvements, Landlord shall respond to
      Tenant's request for consent as soon as possible, but in no event later
      than five (5) working days after being made. Any changes, additions or
      modifications that Tenant desires to make to the Tenant Plans shall not be
      unreasonably withheld, except that Landlord shall have complete discretion
      with regard to granting or withholding approval for Building structure,
      system or appearance as provided in Section 3.2 above.

6.    Cooperation With Other Tenants. Tenant shall promptly remove from the
      common facilities any of Tenant's vehicles, equipment, materials, supplies
      or other property deposited in the common facilities during the
      construction of the Tenant Improvements. Further, Tenant shall at no time
      disrupt or allow disruption to any existing Landlord's parking vehicles
      and pedestrian access, nor allow disruptions of mechanical, electrical,
      telephone and plumbing services. In addition, Tenant shall not interrupt
      the normal business operation of any other tenant at the Building or on
      the Lot.

7.    Inspection by Landlord. Landlord shall have the right to inspect the
      Tenant Improvements at all reasonable times. Landlord's failure to inspect
      the Tenant Improvements shall in no event constitute a waiver of any of
      Landlord's rights hereunder nor shall Landlord's inspection of the Tenant
      Improvements constitute the Landlord's approval of same.

<PAGE>
                                     - 22 -


8.    Removal of Specialized Tenant Improvements. Portions of the Tenant
      Improvements, if any, as reasonably determined by Landlord to be
      specialized improvements shall, at the election of Landlord, either be
      removed by Tenant at its expense before the expiration of the Term or
      shall remain in the Premises and be surrendered therewith at the
      expiration date or earlier termination of this Sublease as the property of
      Landlord without disturbance, molestation or injury. If Landlord requires
      the removal of all or part of said specialized Tenant Improvements,
      Landlord shall so notify Tenant at the time that Landlord renders its
      approval to the Space Plan and Construction Drawings pursuant to Section
      3.2 above, and Tenant, at the expiration or earlier termination of the
      Sublease, at its expense, shall repair any damage to the Premises or the
      Building caused by such removal and restore the Premises to its condition
      prior to the installation of such specialized Tenant Improvements. If
      Tenant fails to remove said specialized Tenant Improvements that Tenant is
      required to remove hereunder, then Landlord may (but shall not be
      obligated to) remove the same and the cost of such removal, repair and
      restoration, together with any and all damages which Landlord may suffer
      and sustain by reason of the failure of Tenant to remove the same, shall
      be charged to Tenant and paid upon demand.

9.    Completion of Tenant Improvements. Tenant shall notify Landlord in writing
      when the Tenant Improvements have been substantially completed. Landlord
      shall thereupon have the opportunity to inspect the Premises in order to
      determine if the Premises has been substantially completed in accordance
      with the Tenant Plans. If the Tenant Improvements has not been
      substantially completed in accordance with the Tenant Plans, Landlord
      shall immediately following inspection, provide Tenant with written
      notification of the items deemed incorrect or incomplete. Tenant shall
      forthwith proceed to correct the incorrect or incomplete items.
      Notwithstanding anything to the contrary, the Tenant Improvements shall
      not be considered suitable for review by Landlord until all designated or
      required governmental inspections, permits and certifications necessary
      for the Tenant Improvements, including, but not limited to a temporary or
      final certificate of occupancy, have been made, given and/or posted.

10.   Consent of Landlord. Tenant shall be solely responsible for obtaining the
      consent of Prime Landlord to the construction of the Tenant Improvements
      pursuant to the terms and conditions of the Prime Lease prior to any
      construction therein and immediately upon receipt shall deliver a copy of
      such consent to Landlord.