EXHIBIT "B" to be made a part of a Ninth  Amendment  To Lease  between  LAFP-SF,
INC.  (Landlord),  and DATA TRANSMISSION NETWORK CORPORATION  (Tenant),  dated ,
1997 (Page 1 of 2)



                        TENANT IMPROVEMENTS WORK SCHEDULE



                                    ARTICLE I
                       Landlord's Construction Obligations

     Landlord  shall have no  construction  obligations  under  this  Amendment.
Tenant  accepts the Option  Space in an "as is"  condition,  with all faults and
with the understanding that it shall be responsible for any and all improvements
required for its occupancy and use in accordance with Article II of this Exhibit
"B".



                                   ARTICLE II
                       Construction of Tenant Improvements

     Tenant  shall  have the right to place  partitions  and  fixtures  and make
improvements  or other  alterations  in the Option Space in accordance  with the
provisions of Paragraph 9 of the Lease.  Landlord  shall provide Tenant a tenant
finish  allowance of up to One Hundred  Twenty-One  Thousand,  Seven Hundred and
Twenty-Eight Dollars and No Cents ($121,728.00) to be applied toward the cost of
any such tenant-provided improvements as follows:

     1. The tenant finish allowance shall be paid in periodic installments,  not
more frequently than once per month,  equal to the total of the  contractor's or
consultant's  invoice  amounts  for  improvements  made  to  the  Option  Space,
excluding   any   furnishings   or  business   equipment   (such  as  computers,
satellite/microwave  dish, office  equipment,  etc.), as submitted by Tenant and
verified to Landlord's  reasonable  satisfaction;  provided,  however, that such
payments  will be made only if Tenant is not then in Default  under the terms of
this Lease and invoices are  accompanied  by lien waivers in the amount equal to
that of the  invoices.  The  tenant  finish  allowance  shall be  allocated  and
distributed subject to the provisions of this Exhibit "B" as follows:

  January 1, 1998 - December 31, 1998                      Up To $121,728.00


     2. Upon the earlier of the end date  identified in the allocation  schedule
specified  in  Paragraph  1  above,  or  the  satisfaction  of  all  obligations
associated  with the  tenant  improvements  covered  under  this  Article II and
receipt of the  associated  lien waivers for the work,  the Tenant shall forfeit
any unused  portion of the allowance.  Any requests for payment  received by the
Landlord after the above  specified end date, will be returned to the Tenant and
will be the obligation and sole responsibility of the Tenant.


     3. In addition to the provisions set forth in Paragraph 9 of the Lease,
Tenant's  contractor shall (and its contract shall so provide):

         (a)  conduct  its  work  in  such a  manner  so as not to  unreasonably
              interfere with other tenants in the Building, Building operations,
              or any other  construction  occurring on or in the Building or the
              Premises;

         (b)  execute  a set  of and  comply  with  all  rules  and  regulations
              relating to the  construction  activities in or on the Building as
              may be reasonably promulgated from time to time by Landlord or its
              agents;

         (c)  maintain such insurance  (such as general  liability and workman's
              compensation)  and bonds (such as performance  and  completion) in
              force and effect as may be reasonably  requested by Landlord or as
              required by  applicable  law (but in any event said bonds shall be
              in amounts  equal to the full value or cost of the work being done
              by the Tenant contractor);


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<PAGE>

EXHIBIT "B" to be made a part of a Ninth  Amendment  To Lease  between  LAFP-SF,
INC.  (Landlord),  and DATA TRANSMISSION NETWORK CORPORATION  (Tenant),  dated ,
1997. (Page 2 of 2)



         (d)  be  responsible  for reaching an agreement  with  Landlord and its
              agents as to the terms and  conditions  for all  contractor  items
              relating to the conducting of its work,  including but not limited
              to, those matters relating to hoisting,  systems interfacing,  use
              of  temporary  utilities,  storage  of  materials,   placement  of
              dumpsters,  access  to the  Premises  and  the  Building,  and the
              purchase and return of Building standard materials.

         (e)  Upon  completion  of any tenant  improvements,  Tenant shall
              promptly  furnish  Landlord  with sworn  owner's and  contractors'
              statements  and full and final  waivers of lien covering all labor
              and  materials  included in such  improvements.  Tenant  shall not
              permit any  mechanic's  lien to be filed against the Building,  or
              any part thereof,  arising out of any  improvement  performed,  or
              alleged to have been performed,  by or on behalf of Tenant. If any
              such lien is filed,  Tenant shall within ten (10) days  thereafter
              have such lien released of record or deliver to Landlord a bond in
              form,  amount,  and issued by a surety  satisfactory  to Landlord,
              indemnifying  Landlord against all costs and liabilities resulting
              from  such  lien  and the  foreclosure  or  attempted  foreclosure
              thereof.  If  Tenant  fails to have such  lien so  released  or to
              deliver such bond to Landlord, Landlord, without investigating the
              validity of such lien,  may pay or discharge the same;  and Tenant
              shall  reimburse  Landlord  upon  demand for the amount so paid by
              Landlord, including Landlord's expenses and attorney's fees.

     4. Landlord shall have the right to approve all  subcontractors  to be used
by the Tenant's contractor, which approval shall not be unreasonably withheld as
long as such subcontractors satisfy the requirements of this Article II.


     5.  Tenant  shall  indemnify  and  hold  harmless  Landlord,   its  agents,
contractors (including Building Contractor), and any mortgagee of Landlord, from
and against  any and all losses,  damages,  costs  (including  costs of suit and
attorneys' fees), liabilities, or causes of action for injury to or death of any
person,  for damage to any property,  and for mechanic's  materialmen's or other
liens or  claims  arising  out of or in  connection  with  the work  done by the
Tenant's    contractor   (and   Tenant's    contractor's    subcontractors   and
sub-subcontractors) under its contract with Tenant.


     6. The failure by Tenant,  after receiving  written  notice,  to materially
comply with any of the provisions of Article II of this Exhibit shall constitute
a Default  by Tenant  under the terms of the Lease and  Landlord  shall have the
benefit of all remedies  provided for in the Lease,  except  Tenant shall have a
thirty (30) day right to cure Default upon receipt of written notice .


     7. Upon  completion  of the Tenant  Improvements,  Tenant shall  deliver to
Landlord  two (2)  copies of the "as  built"  plans and  specifications  for the
Tenant  Improvements  completed  under Article II of this Exhibit  within thirty
(30) days of completing the same.


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