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                                                                     EXHIBIT 4.6

           CERTIFICATE OF VOTING POWERS, DESIGNATIONS, PREFERENCES AND
               RELATIVE PARTICIPATING, OPTIONAL OR OTHER SPECIAL
                     RIGHTS AND QUALIFICATIONS, LIMITATIONS
                         AND RESTRICTIONS THEREOF OF THE
                            SERIES B PREFERRED STOCK
                         OF IMPSAT FIBER NETWORKS, INC.

                           --------------------------

                         Pursuant to Section 151 of the
                General Corporation Law of the State of Delaware

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       I, Guillermo Pardo, Secretary of IMPSAT Fiber Networks, Inc. (the
"Corporation"), a corporation organized and existing under and by virtue of the
General Corporation Law of the State of Delaware, in accordance with the
provisions of Section 151 of the General Corporation Law of the State of
Delaware, DO HEREBY CERTIFY:

       That, pursuant to authority conferred upon the Board of Directors by the
Certificate of Incorporation as amended of said Corporation (the "Certificate of
Incorporation"), said Board of Directors, at a meeting duly called and held on
January 12, 2000, adopted a resolution providing for the issuance of 913,957
authorized shares of Series B Preferred Stock, which resolution is as follows:

       RESOLVED, that pursuant to the authority granted to and vested in the
Board of Directors of this Corporation (hereinafter called the "Board of
Directors" or the "Board") in accordance with the provisions of the Certificate
of Incorporation, the Board of Directors hereby creates a series of Preferred
Stock, par value $1.00 per share (the "Preferred Stock"), of the Corporation and
hereby states the designation and number of shares, and fixes the relative
rights, preferences, and limitations thereof as follows:

       Section 1. Designation and Amount. The shares of such series shall be
designated as "Series B Junior Participating Preferred Stock" (the "Series B
Preferred Stock") and the number of shares constituting the Series B Preferred
Stock shall be 913,957. Such number of shares may be increased or decreased by
resolution of the Board of Directors; provided, that no decrease shall reduce
the number of shares of Series B Preferred Stock to a number less than the
number of shares then outstanding plus the number of shares reserved for
issuance upon the exercise of outstanding options, rights or warrants or upon
the conversion of any outstanding securities issued by the Corporation
convertible into Series B Preferred Stock.


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       Section 2. Dividends and Distributions.

              (A) Subject to the rights of the holders of any shares of any
series of Preferred Stock (or any similar stock) ranking prior and superior to
the Series B Preferred Stock with respect to dividends, the holders of shares of
Series B Preferred Stock, in preference to the holders of common stock, $0.01
par value, (the "Common Stock"), of the Corporation, and of any other junior
stock, shall be entitled to receive, when, as and if declared by the Board of
Directors out of funds legally available for the purpose, quarterly dividends
payable in cash on the first day of March, June, September and December in each
year (each such date being referred to herein as a "Quarterly Dividend Payment
Date"), commencing on the first Quarterly Dividend Payment Date after the first
issuance of a share or fraction of a share of Series B Preferred Stock, in an
amount per share (rounded to the nearest cent) equal to the greater of (a) $1 or
(b) subject to the provision for adjustment hereinafter set forth, 100 times the
aggregate per share amount of all cash dividends, and 100 times the aggregate
per share amount (payable in kind) of all non-cash dividends or other
distributions, other than a dividend payable in shares of Common Stock or a
subdivision of the outstanding shares of Common Stock (by reclassification or
otherwise), declared on the Common Stock since the immediately preceding
Quarterly Dividend Payment Date or, with respect to the first Quarterly Dividend
Payment Date, since the first issuance of any share or fraction of a share of
Series B Preferred Stock. In the event the Corporation shall at any time declare
or pay any dividend on the Common Stock payable in shares of Common Stock, or
effect a subdivision or combination or consolidation of the outstanding shares
of Common Stock (by reclassification or otherwise than by payment of a dividend
in shares of Common Stock) into a greater or lesser number of shares of Common
Stock, then in each such case the amount to which holders of shares of Series B
Preferred Stock were entitled immediately-prior to such event under clause (b)
of the preceding sentence shall be adjusted by multiplying such amount by a
fraction, the numerator of which is the number of shares of Common Stock
outstanding immediately after such event and the denominator of which is the
number of shares of Common Stock that were outstanding immediately prior to such
event.

              (B) The Corporation shall declare a dividend or distribution on
the Series B Preferred Stock as provided in paragraph (A) of this Section
immediately after it declares a dividend or distribution on the Common Stock
(other than a dividend payable in shares of Common Stock); provided that, in the
event no dividend or distribution shall have been declared on the Common Stock
during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $1 per share on the
Series B Preferred Stock shall nevertheless be payable on such subsequent
Quarterly Dividend Payment Date.

              (C) Dividends shall begin to accrue and be cumulative on
outstanding shares of Series B Preferred Stock from the Quarterly Dividend
Payment Date next preceding the date of issue of such shares, unless the date of
issue of such shares is prior to the record date for the first Quarterly
Dividend Payment Date, in which case dividends on such shares shall begin to
accrue from the date of issue of such shares, or unless the


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date of issue is a Quarterly Dividend Payment Date or is a date after the record
date for the determination of holders of shares of Series B Preferred Stock
entitled to receive a quarterly dividend and before such Quarterly Dividend
Payment Date, in either of which events such dividends shall begin to accrue and
be cumulative from such Quarterly Dividend Payment Date. Accrued but unpaid
dividends shall not bear interest. Dividends paid on the shares of Series B
Preferred Stock in an amount less than the total amount of such dividends at the
time accrued and payable on such shares shall be allocated pro rata on a
share-by-share basis among all such shares at the time outstanding. The Board of
Directors may fix a record date for the determination of holders of shares of
Series B Preferred Stock entitled to receive payment of a dividend or
distribution declared thereon, which record date shall be not more than 60 days
prior to the date fixed for the payment thereof.

       Section 3. Voting Rights. The holders of shares of Series B Preferred
Stock shall have the following voting rights:

              (A) Subject to the provision for adjustment hereinafter set forth,
each share of Series B Preferred Stock shall entitle the holder thereof to 100
votes on all matters submitted to a vote of the stockholders of the Corporation.
In the event the Corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the number of votes per share to which holders of shares of Series B
Preferred Stock were entitled immediately prior to such event shall be adjusted
by multiplying such number by a fraction, the numerator of which is the number
of shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

              (B) Except as otherwise provided herein, in any other Certificate
of Designations creating a series of Preferred Stock or any similar stock, or by
law, the holders of shares of Series B Preferred Stock and the holders of shares
of Common Stock and any other capital stock of the Corporation having general
voting rights shall vote together as one class on all matters submitted to a
vote of stockholders of the Corporation.

              (C) Except as set forth herein, or as otherwise provided by law,
holders of Series B Preferred Stock shall have no special voting rights and
their consent shall not be required (except to the extent they are entitled to
vote with holders of Common Stock as set forth herein) for taking any corporate
action.

       Section 4. Certain Restrictions.

              (A) Whenever quarterly dividends or other dividends or
distributions payable on the Series B preferred Stock as provided in Section 2
are in arrears, thereafter


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and until all accrued and unpaid dividends and distributions, whether or not
declared, on shares of Series B Preferred Stock outstanding shall have been paid
in full, the Corporation shall not

                     (i) declare or pay dividends, or make any other
distributions, on any shares of stock ranking junior (either as to dividends or
upon liquidation, dissolution or winding up) to the Series B Preferred Stock;

                     (ii) declare or pay dividends, or make any other
distributions, on any shares of stock ranking on a parity (either as to
dividends or upon liquidation, dissolution or winding up) with the Series B
Preferred Stock, except dividends paid ratably on the Series B Preferred Stock
and all such parity stock on which dividends are payable or in arrears in
proportion to the total amounts to which the holders of all such shares are then
entitled;

                     (iii) redeem or purchase or otherwise acquire for
consideration shares of any stock ranking junior (either as to dividends or upon
liquidation, dissolution or winding up) to the Series B Preferred Stock,
provided that the Corporation may at any time redeem, purchase or otherwise
acquire shares of any such junior stock in exchange for shares of any stock of
the Corporation ranking junior (either as to dividends or upon dissolution,
liquidation or winding up) to the Series B Preferred Stock; or

                     (iv) redeem or purchase or otherwise acquire for
consideration any shares of Series B preferred Stock, or any shares of stock
ranking on a parity with the Series B Preferred Stock, except in accordance with
a purchase offer made in writing or by publication (as determined by the Board
of Directors) to all holders of such shares upon such terms as the Board of
Directors, after consideration of the respective annual dividend rates and other
relative rights and preferences of the respective series and classes, shall
determine in good faith will result in fair and equitable treatment among the
respective series or classes.

              (B) The Corporation shall not permit any subsidiary of the
Corporation to purchase or otherwise acquire for consideration any shares of
stock of the Corporation unless the Corporation could, under paragraph (A) of
this Section 4, purchase or otherwise acquire such shares at such time and in
such manner.

       Section 5. Reacquired Shares. Any shares of Series B Preferred Stock
purchased or otherwise acquired by the Corporation in any manner whatsoever
shall be retired and cancelled promptly after the acquisition thereof. All such
shares shall upon their cancellation become authorized but unissued shares of
Preferred Stock and may be reissued as part of a new series of Preferred Stock
subject to the conditions and restrictions on issuance set forth herein, in the
Certificate of Incorporation, or in any other Certificate of Designations
creating a series of Preferred Stock or any similar stock or as otherwise
required by law.


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       Section 6. Liquidation, Dissolution or Winding Up. Upon any liquidation,
dissolution or winding up of the Corporation, no distribution shall be made (1)
to the holders of shares of stock ranking junior (dither as to dividends or upon
liquidation, dissolution or winding up) to the Series B Preferred Stock unless,
prior thereto, the holders of shares of Series B Preferred Stock shall have
received $100 per share, plus an amount equal to accrued and unpaid dividends
and distributions thereon, whether or not declared, to the date of such payment,
provided that the holders of shares of Series B Preferred Stock shall be
entitled to receive an aggregate amount per share, subject to the provision for
adjustment hereinafter set forth, equal to 100 times the aggregate amount to be
distributed per share to holders of shares of Common Stock, or (2) to the
holders of shares of stock ranking on a parity (either as to dividends or upon
liquidation, dissolution or winding up) with the Series B Preferred Stock,
except distributions made ratably on the Series B Preferred Stock and all such
parity stock in proportion to the total amounts to which the holders of all such
shares are entitled upon such liquidation, dissolution or winding up. In the
event the Corporation shall at any time declare or pay any dividend on the
Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the aggregate amount to which holders of shares of Series B Preferred
Stock were entitled immediately prior to such event under the proviso in clause
(1) of the preceding sentence shall be adjusted by multiplying such amount by a
fraction the numerator of which is the number of shares of Common Stock
outstanding immediately after such event and the denominator of which is the
number of shares of Common Stock that were outstanding immediately prior to such
event.

       Section 7. Consolidation, Merger, etc. In case the Corporation shall
enter into any consolidation, merger, combination or other transaction in which
the shares of Common Stock are exchanged for or changed into other stock or
securities, cash and/or any other property, then in any such case each share of
Series B Preferred Stock shall at the same time be similarly exchanged or
changed into an amount per share, subject to the provision for adjustment
hereinafter set forth, equal to 100 times the aggregate amount of stock,
securities, cash and/or any other property (payable in kind), as the case may
be, into which or for which each share of Common Stock is changed or exchanged.
In the event the Corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision or
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the amount set forth in the preceding sentence with respect to the
exchange or change of shares of Series B Preferred Stock shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.


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       Section 8. No Redemption. The shares of Series B Preferred Stock shall
not be redeemable.

       Section 9. Rank. The Series B Preferred Stock shall rank, with respect to
the payment of dividends and the distribution of assets, junior to all series of
any other class of the Corporation's Preferred Stock.

       Section 10. Amendment. The Certificate of Incorporation of the
Corporation shall not be amended in any manner which would materially alter or
change the powers, preferences or special rights of the Series B Preferred Stock
so as to affect them adversely without the affirmative vote of the holders of at
least two-thirds of the outstanding shares of Series B Preferred Stock, voting
together as a single class.

       Section 11. Limitations. Except as may otherwise be required by law, the
shares of Series B Preferred Stock shall not have any powers, preferences or
relative, participating, optional or other special rights other than those
specifically set forth in this resolution (as such resolution may be amended
from time to time) or otherwise in the Certificate of Incorporation of the
Corporation.

       IN WITNESS WHEREOF, this Certificate of Designations is executed on
behalf of the Corporation by its President and attested by its Secretary this
6th day of June, 2000.

                                          IMPSAT FIBER NETWORKS, INC.

                                          By:
                                               ---------------------------------
                                               Guillermo Pardo
                                               Secretary