EXHIBIT 2.2


                              AMENDMENT NO. 1 TO

                             AMENDED AND RESTATED

                         AGREEMENT AND PLAN OF MERGER

     This Amendment No. 1 (this "Amendment") to that certain Amended and
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Restated Agreement and Plan of Merger, dated as of August 4, 1999 (the "Merger
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Agreement") by and among CAIS Internet, Inc., a Delaware corporation ("CAIS"),
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CIAM Corp., a California corporation (the "Company"), and Atcom, Inc., a
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California corporation ("Atcom"), is made as of September 1, 1999.  Unless
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otherwise defined herein, capitalized terms used herein shall have the same
meanings as those set forth in the Merger Agreement.

     WHEREAS the parties hereto desire to amend the Merger Agreement as provided
below.

     NOW, THEREFORE, in consideration of the mutual promises herein contained,
the parties, intending to be legally bound, agree as follows:

     1.   Amendment to Section 2.10 of the Merger Agreement.  Section 2.10(b) of
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the Merger Agreement is hereby amended to read in full as follows:

          Notwithstanding the provisions of subsection (a) above, if any holder
          of Dissenting Shares shall effectively withdraw or lose (through the
          failure to perfect or otherwise) such holder's dissenters' rights
          under the CGCL, then, as of the Effective Time or the occurrence of
          such event, such holder's shares shall automatically be converted into
          and represent only the right to receive shares of CAIS Common Stock
          upon surrender of the applicable Certificate(s) in accordance with
          Sections 2.2 and 2.3 hereof.

     2.   Governing Law.  This Amendment shall be construed in accordance with
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and governed by the laws of the State of California without regard to choice of
law principals.

     3.   Counterparts.  This Agreement may be executed in any number of
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counterparts, each of which shall be deemed an original but all of which shall
constitute one and the same instrument.

     4.   Effect of Amendment.  Except as expressly provided in this Amendment,
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the Merger Agreement shall remain unmodified and in full force and effect.


     IN WITNESS WHEREOF, the undersigned have executed this Amendment to be duly
executed, all as of the day and year first above written.

CAIS INTERNET, INC.                         CIAM CORP.

By: /s/ Ulysses G. Auger, II                By: /s/ Ulysses G. Auger, II
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Title: Chief Executive Officer              Title: Chief Executive Officer
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       and President                               and President
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ATCOM, INC.

By: /s/ Wendell S. Nye
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Title: President & CEO
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