THIRTEENTH AMENDMENT TO LEASE

         THIS  THIRTEENTH  AMENDMENT  TO  LEASE  (the  "Amendment")  is made and
entered  into this 18th day of  October,  1999,  by and between  LAFP-SF,  Inc.,
successor  in  interest  to  The   Prudential   Insurance   Company  of  America
("Landlord"),  having  an  office  c/o Lowe  Enterprises  Colorado,  Inc.,  1515
Arapahoe  Street,  Tower  III,  Suite  900,  Denver,  Colorado  80202,  and Data
Transmission Network Corporation ("Tenant"), having an office at 9110 West Dodge
Road, Suite 200, Omaha, Nebraska 68114.

                                    Recitals

A.       The  Prudential  Insurance  Company of America and Tenant  entered into
         that  certain  Lease  dated  as  of  May  2,  1995.  Subsequently,  The
         Prudential  Insurance  Company of America  and Tenant  executed a First
         Amendment to Lease dated  September  29,  1995,  a Second  Amendment to
         Lease  dated  January 5, 1996,  and a Third  Amendment  to Lease  dated
         January 5, 1996, and thereafter,  Landlord and Tenant executed a Fourth
         Amendment to Lease dated December 23, 1996, a Fifth  Amendment to Lease
         dated July 7, 1997,  a Sixth  Amendment  to Lease dated July 7, 1997, a
         Seventh  Amendment  to  Lease  dated  September  19,  1997,  an  Eighth
         Amendment to Lease dated September 19, 1997, a Ninth Amendment to Lease
         dated September 19, 1997, a Tenth Amendment to Lease dated December 23,
         1997, an Eleventh Amendment to Lease dated March 31, 1998 and a Twelfth
         Amendment  to Lease dated May 12,  1999.  The lease and all  amendments
         thereto are hereinafter referred to as the "Lease".

B.       Pursuant to the Lease, Tenant occupies Suites #175A, #175B, #100, #101,
         #110, #130,  #200,  #300,  #301,  #310, #315, #320, #325, #340,  #350A,
         #350B, #360, and #362, containing approximately 107,576 rentable square
         feet (the "Current  Premises"0 in the Building  known as Embassy Plaza,
         located at 9110 West Dodge Road, Omaha, Nebraska pursuant to the Lease.

C.       All  capitalized  terms not  defined  herein  shall  have the  meanings
         ascribed to them in the Lease.

         NOW,  THEREFORE,  in consideration of the foregoing  promises and other
good and  valuable  considerations,  the  receipt and  sufficiency  of which are
hereby acknowledged, the parties hereto covenant and agree as follows:

         1. Installation of Generator.  Landlord shall allow Tenant to construct
and install a generator,  diesel tank and related equipment on a pad site within
the Building  Complex as more  particularly  described on the site plan attached
hereto and incorporated  herein by this reference as Exhibit A (the "Pad Site"),
provided that all governmental  authorities having  jurisdiction  thereover have
granted the necessary approvals and/or licenses therefor. Tenant shall construct
and install the generator and related  equipment in strict  accordance  with the
attached plan which has been approved by Landlord.  All construction  work shall

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be supervised  by Tenant and overseen and approved by Landlord,  it being agreed
that Tenant shall bear all responsibility for the completion of the construction
and installation of the generator,  and that Landlord shall in no event bear any
responsibility  therefor.  All costs  incurred in the pursuit and  obtainment of
approvals or licenses, and the costs of construction,  installation, maintenance
and removal of the generator shall be at Tenant's sole expense. Tenant agrees to
indemnify  and hold  Landlord  harmless  from any  damages or losses  whatsoever
occasioned by Landlord as a result of such installation, maintenance or removal.
At the end of the Lease term,  Tenant shall remove the generator and all related
components thereto,  and shall return the Pad Site and any other portions of the
Building  Complex to the condition that existed prior to the installation of the
generator.

         2. Use  Restrictions.  Tenant shall run the  generator  only: i) in the
event that there is a power  failure in the Building and ii) to test the system,
provided  that such  testing  shall occur only on  weekdays  before 7:00 a.m. or
after 7:00 p.m. or after 1:00 p.m. on Saturdays.

         3. Reaffirmation of Lease. Except as herein specifically  provided, the
terms and conditions of the Lease shall  continue in full force and effect.  The
parties  hereto hereby  reaffirm and ratify all covenants,  representations  and
warranties in the Lease as amended by this Amendment.

         4. Binding  Effect.  This Amendment  shall be binding upon and inure to
the benefit of the parties hereto, their successors and assigns.

         IN WITNESS WHEREOF, Landlord and Tenant have executed this Amendment as
of the day and year first above written.

Tenant:                                 Landlord:

Data Transmission Network               LAFP-SF, Inc.
Corporation a Delaware
Corporation

By: /s/ Greg T. Sloma                   By:  Lowe Enterprises Investment
   ------------------------------            Management, Inc.
    Greg T. Sloma                            Its: Authorized Agent

Its:  President and COO                 By:  /s/ Tom Rau
                                             ----------------------------------
                                             Tom Rau
                                        Its: Vice President

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