Exhibit 99.7

                ANNEX C TO AMENDMENT NO. 1 TO THE MERGER AGREEMENT

                                VOTING AGREEMENT


Cogent Communications Group, Inc.
1015 31st Street, N.W.
Washington, D.C. 20007

Allied Riser Communications Corporation
1700 Pacific Avenue, Suite 400
Dallas, TX 75201


Ladies and Gentlemen:

     The undersigned, _________________________________, is a beneficial owner
of, or has the right to vote, the number of shares set forth on Schedule I
hereto (the "Shares") of Allied Riser Communications Corporation, a Delaware
corporation (the "Company"), and wishes to facilitate the merger of August
Caesar Merger Sub, Inc., a Delaware corporation ("Merger Sub"), which is a
wholly-owned subsidiary of Cogent Communications Group, Inc., a Delaware
corporation ("Cogent"), with and into the Company, pursuant to that certain
Agreement and Plan of Merger by and among the Company, Cogent and Merger Sub,
dated as of August 28, 2001 and amended as of October ____, 2001 (the
"Agreement" and such merger, the "Merger"). The undersigned recognizes that the
Merger will be of benefit to the undersigned, and that adoption of the Merger
Agreement by stockholders of the Company at a meeting of Company stockholders
(the "Company Stockholders Meeting") is a condition to the consummation of the
Merger and hereby executes and delivers this Voting Agreement pursuant to
Section 5.17 of the Agreement. All capitalized terms used and not defined herein
shall have the meanings assigned to them in the Agreement.

     In consideration of the foregoing and in order to induce Cogent to act in
connection with the Merger, the undersigned hereby agrees, for the benefit of
the Company and of Cogent, to (i) attend the Company Stockholders Meeting, in
person or by proxy, or by written consent in lieu of a stockholders meeting, as
applicable, and (ii) vote (or cause to be voted) all Shares -- and any
additional voting securities of the Company beneficial ownership of which may be
acquired by the undersigned (whether by purchase or otherwise) after the date of
this Voting Agreement -- in favor of adoption of the Agreement and approval of
the Merger and any other matters necessary to consummate the transactions
contemplated in the Agreement in order to effectuate the Merger. The above
agreement to vote shall apply also to any adjournment or adjournments of the
Company Stockholders Meeting.

     From and after the date hereof through the earlier of the Effective Time of
the Merger or the termination of the Agreement, the undersigned hereby agrees
not to sell, transfer, pledge, encumber or otherwise dispose of any Shares or
any voting interest in such Shares (collectively, "Transfer"). Any such Transfer
shall be null and void, and such transferee shall have no rights as a
stockholder of the Company. To the extent inconsistent with the foregoing
provisions of this Voting Agreement, the undersigned hereby revokes any and all
proxies granted




by him with respect to the Shares, and further agrees to execute and deliver
such additional instruments and other documents and to take such further actions
as may be necessary or appropriate to effectuate, carry out, and comply with all
of its obligations hereunder. Without limiting the generality of the foregoing,
the undersigned shall not enter into any agreement or arrangement (or alter,
amend or terminate any existing agreement or arrangement) if such action would
impair its ability to effectuate, carry out, or comply with all the terms of
this Voting Agreement.

     The undersigned represents and warrants that: (i) the undersigned has full
power and authority to enter into the agreements set forth herein; (ii) this
Voting Agreement has been duly executed and delivered and constitutes a valid
and binding obligation of the undersigned, enforceable against the undersigned
in accordance with its terms; and (iii) the Shares set forth on Schedule I
hereto are the only voting securities, or voting rights in capital stock of the
Company, owned (beneficially or of record) by the undersigned as of the date
hereof.

     This Voting Agreement shall be binding upon and shall inure to the benefit
of and be enforceable by the undersigned and its respective successors and
assigns. The undersigned agrees that irreparable damage would occur if any
provision of this Voting Agreement were not performed in accordance with the
terms hereof and that Cogent and/or the Company shall be entitled to an
injunction or injunctions to prevent breaches of this Voting Agreement or to
enforce specifically the performance of the terms and provisions hereof in any
federal court located in the State of Delaware or any Delaware state court, in
addition to any other remedy to which it is entitled at law or in equity. In the
event that the Agreement is terminated in accordance with its terms or is
amended in a manner that is material, this Voting Agreement shall automatically
terminate and be of no further force or effect. Upon such termination, except
for any rights Cogent or the Company may have in respect of any breach by the
undersigned of its obligations hereunder, there shall be no further obligation
or liability hereunder.



                                        Very truly yours,



                                        _________________________________

                                        dated this ____ day of __________, 2001.