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                                                                     Exhibit 4.5

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS
AMENDED, OR ANY STATE SECURITIES LAWSDefault UserFinancial Printing GroupTHESE
SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS AMENDED,
OR ANY STATE SECURITIES LAWS.  THEY MAY NOT 8E SOLD, OFFERED FOR SALE, PLEDGED,
OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT RELATED
THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL) REASONABLY
SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAWS.

WARRANT AGREEMENT

To Purchase Shares of the Series C Preferred Stock of

CHORUM TECHNOLOGIES INC.

Dated as of September 22, 1998 (the "Effective Date")

WHEREAS, CHORUM TECHNOLOGIES INC., a Delaware corporation (the "Company"), has
entered into a Master Lease Agreement dated as of September 22, 1998, Equipment
Schedule No. VL-1 and VL-2 dated as of September 22, 1998, and related Summary
Equipment Schedules (collectively, the "Leases") with Comdisco, Inc., a Delaware
corporation (the "Warrantholder"); and

WHEREAS, the Company desires to grant to Warrantholder in consideration for such
Leases, the right to purchase shares of its Series C Preferred Stock;

NOW, THEREFORE, in consideration of the Warrantholder executing and delivering
such Leases and in consideration of mutual covenants and agreements contained
herein, the Company and Warrantholder agree as follows:

1.  GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

For value received, the Company hereby grants to the Warrantholder, and the
Warrantholder is entitled, upon the terms and subject to the conditions
hereinafter set forth, to subscribe for and purchase from the Company that
number of fully paid and nonassessable shares of the Company's Series C
Preferred Stock ("Preferred Stock") equal to $87,500 ("Aggregate Purchase
Price") divided by the Exercise Price ("Exercise Price").  The Exercise Price
shall equal to the sum of $1.50 per share (the "Last Round Price") plus the
product of (a) the difference between the price per share of the next round of
equity financing (the "Next Round") and the Last Round Price, multiplied by (b)
the fraction resulting from dividing (x) the number of days from June 3,1998, to
the date of execution of the Leases, by (y) the number of days from June 3, 1998
to the date of closing of the Next Round; provided however, if the Next Round
has not closed by June 1, 1999, then the Exercise Price shall be equal to $1.50
per share.  The number and purchase price of such shares are subject to
adjustment as provided in Section 8 hereof.
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2.  TERM OF THE WARRANT AGREEMENT.

Except as otherwise provided for herein, the tern of this Warrant Agreement and
the right to purchase Preferred Stock as granted herein shall commence on the
earlier of (A) the closing of the Next Round or (B) June 1, 1999 and shall be
exercisable for a period of (i) seven (7) years from the Effective Date or (ii)
three (3) years from the effective date of the Company's initial public
offering, whichever is shorter.  Notwithstanding the term of this Warrant
Agreement fixed pursuant to preceding sentence, the right to purchase Preferred
Stock a granted herein shall expire, if not previously exercised, immediately
upon (i) a merger or consolidation of the Company with or into any other
corporation or corporations, unless the shareholders of the Company immediately
prior to any such transaction are holders of a majority of the voting securities
of the surviving corporation or acquiring corporation immediately thereafter and
hold such securities in substantially similar proportions as prior to such
transaction (and for purposes of this calculation equity securities which any
shareholder of the Company owned immediately prior to such merger or
consolidation as shareholder of another party to the transaction shall be
disregarded), or (ii) a sale or other transfer of all or substantially all of
the assets of the Company or any series of related transactions resulting in the
sale or other transfer of all or substantially all of the assets of the Company
("Termination Event").

The Company shall notify the Warrantholder if the Termination Event is proposed
no later than the date such notice is provided to the Company's stockholders of
such Termination Event.  Such notice shall also contain such details of the
proposed Termination Event as are reasonable in the circumstances.  If such
closing does not take place, the Company shall promptly notify the Warrantholder
that such proposed transaction has been terminated, and the Warrantholder may
rescind any exercise of its purchase rights promptly after such notice of
termination of the proposed transaction.  In the event of such recession, this
Warrant Agreement shall continue to be exercisable on the same terms and
conditions contained herein.

If all of the Company's outstanding Preferred Stock is converted into shares of
Common Stock, then this Warrant shall automatically become exercisable for that
number of shares of Common Stock equal to the number of shares of Common Stock
that would have been received if this Warrant had been exercised in full and the
shares of Preferred Stock received thereupon had been simultaneously converted
into shares of Common Stock immediately prior to such event, and the Exercise
Price shall be automatically adjusted to equal the amount obtained by dividing
(i) the aggregate Exercise Price of the shares of Preferred Stock for this which
this Warrant was exercisable immediately prior to such conversion, by (ii) the
number of shares of Common Stock for which this Warrant is exercisable
immediately after such conversion.

3.  EXERCISE OF THE PURCHASE RIGHTS.

The purchase rights set forth in this Warrant Agreement are exercisable by the
Warrantholder, in whole or in part, at any time, or from time to time, prior to
the expiration of the term set forth in Section 2 above, by tendering to the
Company at its principal office a notice of exercise in the form attached hereto
as Exhibit I (the "Notice of Exercise"), duly completed and executed.  Promptly
upon receipt of the Notice of Exercise and the payment of the purchase price in
accordance with the terms set forth below, and in no event later than twenty-one
(21) days thereafter, the Company shall issue to the Warrantholder a certificate
for the number of shares of Preferred Stock purchased and shall execute the
acknowledgment of exercise in the form

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attached hereto as Exhibit II (the "Acknowledgment of Exercise") indicating the
number of shares which remain subject to future purchases, if any.

The Exercise Price may be paid at the Warrantholder's election either (i) by
cash or check, or (ii) by surrender of Warrants ("Net Issuance") as determined
below.  If the Warrantholder elects the Net Issuance method, the Company will
issue Preferred Stock in accordance with the following formula:

X = Y(A-B)/A

Where: X =  the number of shares of Preferred Stock to be issued to the
Warrantholder.

Y =  the number of shares of Preferred Stock requested to be exercised under
this Warrant Agreement.

A =  the fair market value of one (1) share of Preferred Stock at the time the
net issuance election is made.

B =  the Exercise Price.

For purposes of the above calculation, current fair market value of Preferred
Stock shall mean with respect to each share of Preferred Stock:

(i)    if the exercise is in connection with an initial public offering of the
Company's Common Stock, and if the Company's Registration Statement relating to
such public offering has been declared effective by the SEC, then the fair
market value per share shall be the product of (x) the initial "Price to Public"
specified in the final prospectus with respect to the offering and (y) the
number of shares of Common Stock into which each share of Preferred Stock is
convertible at the time of such exercise;

(ii)   if this Warrant is exercised after, and not in connection with the
Company's initial public offering, and:

(a)    if traded on a securities exchange, the fair market value shall be deemed
to be the average of the closing prices over a twenty-one (21) day period ending
three days before the day the current fair market value of the securities is
being determined; or

(b)    if actively traded over-the-counter, the fair market value shall be
deemed to be the average of the closing bid and asked prices quoted on the
NASDAQ system (or similar system) over the twenty-one (21) day period ending
three days before the day the current fair market value of the securities is
being determined;

(iii)  if at any time the Common Stock is not listed on any securities exchange
or quoted in the NASDAQ System or the over-the-counter market, the current fair
market value of Preferred Stock shall be the product of (x) the highest price
per share which the Company could obtain from a willing buyer (not a current
employee or director) for shares of Common Stock sold by the Company, from
authorized but unissued shares, as determined in good faith by its Board of
Directors and (y) the number of shares of Common Stock into which each share of
Preferred

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Stock is convertible at the time of such exercise or such earlier time as all
outstanding share of the Company's Preferred Stock convert into shares of Common
Stock, unless the Company shall become subject to a merger, acquisition or other
consolidation pursuant to which the Company is not the surviving party, in which
case the fair market value of Preferred Stock shall be deemed to be the value
received by the holders of the Company's Preferred Stock on a common equivalent
basis pursuant to such merger or acquisition.

Upon partial exercise by either cash or Net Issuance, the Company shall promptly
issue an amended Warrant Agreement representing the remaining number of shares
purchasable hereunder.  All other terms and conditions of such amended Warrant
Agreement shall be identical to those contained herein, including, but not
limited to the Effective Date hereof.

4.    RESERVATION OF SHARES.

(a)   Authorization and Reservation of Shares. The Company currently has an
insufficient number of unissued authorized shares of Series C Preferred Stock to
provide for the complete exercise of the rights to purchase Series C Preferred
Stock as herein provided. The Company shall use its best efforts to amend its
Charter (as defined below) to authorize a sufficient additional number of shares
of its Series C Preferred Stock to provide for the complete exercise of the
rights to purchase Series C Preferred Stock as herein provided upon the earlier
of (A) the closing of the Next Round or (B) June 1, 1999.

(b)   Registration or Listing. If any shares of Preferred Stock required to be
reserved hereunder require registration with or approval of any governmental
authority under any Federal or State law (other than any registration under the
Securities Act of 1933, as amended ("1933 Act"), as then in effect, or any
similar Federal statute then enforced, or any state securities law, required by
reason of any transfer involved in such conversion), or listing on any domestic
securities exchange, before such shares may be issued upon conversion, the
Company will, at its expense and as expeditiously as possible, use its best
efforts to cause such shares to be duly registered, listed or approved for
listing on such domestic securities exchange, as the case may be.

5.    NO FRACTIONAL SHARES OR SCRIP.

No fractional shares or scrip representing fractional shares shall be issued
upon the exercise of the Warrant, but in lieu of such fractional shares the
Company shall make a cash payment therefor upon the basis of the Exercise Price
then in effect.

6.    NO RIGHTS AS SHAREHOLDER.

This Warrant Agreement does not entitle the Warrantholder to any voting rights
or other rights as a shareholder of the Company prior to the exercise of the
Warrant.

7.    WARRANTHOLDER REGISTRY.

The Company shall maintain a registry showing the name and address of the
registered holder of this Warrant Agreement.

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8.    ADJUSTMENT RIGHTS.

The purchase price per share and the number of shares of Preferred Stock
purchasable hereunder are subject to adjustment, as follows:

(a)   Merger and Sale of Assets. If at any time there shall be a capital
reorganization of the shares of the Company's stock (other than a combination,
reclassification, exchange or subdivision of shares otherwise provided for
herein), or a merger or consolidation of the Company with or into another
corporation whether or not the Company is the surviving corporation other than a
Termination Event, as defined in Section 2 hereof, or the sale of all or
substantially all of the Company's properties and assets to any other person
other than a Termination Event (hereinafter referred to as a "Merger Event"),
then, as a part of such Merger Event, lawful provision shall be made so that the
Warrantholder shall thereafter be entitled to receive, upon exercise of the
Warrant, the number of shares of preferred stock or other securities of the
successor corporation resulting from such Merger Event, equivalent in value to
that which would have been issuable if Warrantholder had exercised this Warrant
immediately prior to the Merger Event. In any such case, appropriate adjustment
(as determined in good faith by the Company's Board of Directors) shall be made
in the application of the provisions of this Warrant Agreement with respect to
the rights and interest of the Warrantholder after the Merger Event to the end
that the provisions of this Warrant Agreement (including adjustments of the
Exercise Price and number of shares of Preferred Stock purchasable) shall be
applicable to the greatest extent possible.

(b)   Reclassification of Shares. If the Company at any time shall, by
combination, reclassification, exchange or subdivision of securities or
otherwise, change any of the securities as to which purchase rights under this
Warrant Agreement exist into the same or a different number of securities of any
other class or classes, this Warrant Agreement shall thereafter represent the
right to acquire such number and kind of securities as would have been issuable
as the result of such change with respect to the securities which were subject
to the purchase rights under this Warrant Agreement immediately prior to such
combination, reclassification, exchange, subdivision or other change.

(c)   Subdivision or Combination of Shares. If the Company at any time shall
combine or subdivide its Preferred Stock, the Exercise Price shall be
proportionately decreased in the case of a subdivision, or proportionately
increased in the case of a combination.

(d)   Stock Dividends. If the Company at any time shall pay a dividend payable
in, or make any other distribution (except any distribution specifically
provided for in the foregoing subsections (a) or (b)) of the Company's Preferred
Stock, then the Exercise Price shall be adjusted, from and after the record date
of such dividend or distribution, to that price determined by multiplying the
Exercise Price in effect immediately prior to such record date by a fraction (i)
the numerator of which shall be the total number of all shares of the Company's
Preferred Stock outstanding immediately prior to such dividend or distribution,
and (ii) the denominator of which shall be the total number of all shares of the
Company's Preferred Stock outstanding immediately after such dividend or
distribution. The Warrantholder shall thereafter be entitled to purchase, at the
Exercise Price resulting from such adjustment, the number of shares of Preferred
Stock (calculated to the nearest whole share) obtained by multiplying the
Exercise Price in effect immediately prior to such adjustment by the number of
shares of Preferred Stock issuable upon

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the exercise hereof immediately prior to such adjustment and dividing the
product thereof by the Exercise Price resulting from such adjustment.

(e)   Antidilution Rights. Antidilution rights applicable to the Preferred Stock
purchasable hereunder are as set forth in the Company's Certificate of
Incorporation, as amended through the Effective Date, a true and complete copy
of which is attached hereto as Exhibit ___ (the "Charter"). The Company shall
promptly provide the Warrantholder with any restatement, amendment, modification
or waiver of the Charter. The Preferred Stock purchasable hereunder shall have
the benefit of the same antidilution rights applicable to such Preferred Stock
as designated in the Company's Charter, and the Company shall provide
Warrantholder with all notices and information at the time and to the extent it
is required to do so to the holders of the Preferred Stock.

(f)   Notice of Adjustments. If: (i) the Company shall declare any dividend or
distribution upon its stock, whether in cash, property, stock or other
securities; (ii) the Company shall offer for subscription prorata to the holders
of any class of its Preferred or other convertible stock on the basis of their
ownership thereof any additional shares of stock of any class or other rights;
(iii) there shall be any Merger Event; (iv) there shall be an initial public
offering; or (v) there shall be any voluntary dissolution, liquidation or
winding up of the Company; then, in connection with each such event, the Company
shall send to the Warrantholder: (A) prior written notice no later than the date
that such notice is provided to the Company's shareholders of the date on which
the books of the Company shall close or a record shall be taken for such
dividend, distribution, subscription rights (specifying the date on which the
holders of Preferred Stock shall be entitled thereto) or for determining rights
to vote in respect of such Merger Event, dissolution, liquidation or winding up;
(B) in the case of any such Merger Event, dissolution, liquidation or winding
up, prior written notice no later than the date that such notice is provided to
the Company's shareholders of the date when the same shall take place (and
specifying the date on which the holders of Preferred Stock shall be entitled to
exchange their Preferred Stock for securities or other property deliverable upon
such Merger Event, dissolution, liquidation or winding up); and (C) in the case
of a public offering, the Company shall give the Warrantholder prior written
notice no later than the date that such notice is provided to the Company's
shareholders.

Each such written notice shall set forth, in reasonable detail, (i) the event
requiring the adjustment, (ii) the amount of the adjustment, (iii) the method by
which such adjustment was calculated, (iv) the Exercise Price, and (v) the
number of shares subject to purchase hereunder after giving effect to such
adjustment, and shall be given by first class mail, postage prepaid, addressed
to the Warrantholder, at the address as shown on the books of the Company.

(g)   Timely Notice. Failure to timely provide such notice required by
subsection (f) above shall entitle Warrantholder to retain. The benefit of the
applicable notice period notwithstanding anything to the contrary contained in
any insufficient notice received by Warrantholder. The notice period shall begin
on the date Warrantholder actually receives a written notice containing all the
information specified above.

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9.    REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

(a)   Reservation of Preferred Stock. The Preferred Stock issuable upon exercise
of the Warrantholder's rights, when issued in accordance with the provisions of
this Warrant Agreement, will be validly issued, fully paid and non-assessable,
and will be free of any taxes, liens, charges or encumbrances of any nature
whatsoever; provided, however, that the Preferred Stock issuable pursuant to
this Warrant Agreement may be subject to restrictions on transfer under state
and/or Federal securities laws. The Company has made available to the
Warrantholder true, correct and complete copies of its Charter and Bylaws, as
amended. The issuance of certificates for shares of Preferred Stock upon
exercise of the Warrant Agreement shall be made without charge to the
Warrantholder for any issuance tax in respect thereof, or other cost incurred by
the Company in connection with such exercise and the related issuance of shares
of Preferred Stock. The Company shall not be required to pay any tax which may
be payable in respect of any transfer involved and the issuance and delivery of
any certificate in a name other than that of the Warrantholder.

(b) Due Authority. Subject to the Company obtaining the necessary approvals for
the amendment of the Company's Certificate of Incorporation to authorize a
sufficient additional number of shares of its Series C Preferred Stock, the
execution and delivery by the Company of this Warrant Agreement and the
performance of all obligations of the Company hereunder, including the issuance
to Warrantholder of the right to acquire the shares of Preferred Stock, have
been duly authorized by all necessary corporate action on the part of the
Company, and the Leases and this Warrant Agreement are not inconsistent with the
Company's Charter or Bylaws, to the Company's knowledge, do not contravene any
law or governmental rule, regulation or order applicable to it, do not and will
not contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument to which it is a party or by which it is
bound, and the Leases and this Warrant Agreement constitute legal, valid and
binding agreements of the Company, enforceable in accordance with their
respective terms, except as limited by applicable bankruptcy, insolvency,
reorganization, moratorium and other laws of general application affecting
enforcement of creditor's rights generally and as limited by laws relating to
the availability of specific performance, injunctive relief or other equitable
remedies.

(c)   Consents and Approvals. No consent or approval of, giving of notice to,
registration with, or taking of any other action in respect of any state,
Federal or other governmental authority or agency is required with respect to
the execution, delivery and performance by the Company of its obligations under
this Warrant Agreement, except for any filing of notices pursuant to Regulation
D under the 1933 Act and any filing required by applicable state securities law,
which filings will be effective by the time required thereby.

(d)   Issued Securities. All issued and outstanding shares of Common Stock,
Preferred Stock or any other securities of the Company have been duly authorized
and validly issued and are fully paid and nonassessable. All outstanding shares
of Common Stock, Preferred Stock and any other securities were issued in full
compliance with all Federal and state securities laws. In addition the
authorized capital of the Company consists of:

      (i)   Preferred Stock.  Ten million (10,000,000) shares of Preferred Stock
(the "Preferred Stock"), of which three million seven hundred twenty thousand
(3,720,000) shares have been designated as Series A Preferred Stock, all of
which are issued and outstanding, two

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million one hundred twenty thousand seven hundred fifty-three (2,120,753) shares
have been designated Series B Preferred Stock (the "Series B Preferred Stock"),
two million seventy thousand seven hundred fifty-three (2,070,753) of which are
issued and outstanding, and three million two hundred ninety-four thousand one
hundred forty-one (3,294,141) shares have been designated Series C Preferred
Stock (the "Series C Preferred Stock"), three million two hundred forty-four
thousand one hundred seventy (3,244,170) of which are issued and outstanding.

      (ii)   Common Stock.  Twenty million (20,000,000) shares of Common Stock
("Common Stock"), of which ________ shares are issued and outstanding.

      (iii)  Except for (A) the conversion privileges of the Series A, Series B
and Series C Preferred Stock, (B) the rights provided in Section 2.4 of the
Rights Agreement (as defined below), and (C) currently outstanding options to
purchase __________ shares of the Company's Common Stock, there are not
outstanding any options, warrants, rights (including conversion or preemptive
rights) or agreements for the purchase or acquisition from the Company of any
shares of its capital stock.  The Company has reserved __________ shares of its
Common Stock for purchase upon exercise of options to be granted in the future
under the Company's 1997 Stock Plan.

(e)   Other Commitments to Register Securities. Except as set forth in this
Warrant Agreement and in that certain Amended and Restated Investors Rights
Agreement (the "Rights Agreement") dated as of June 3, 1998 by and between the
Company and the Founders and the Investors (as defined therein), the Company is
not, pursuant to the terms of any other agreement currently in existence, under
any obligation to register under the 1933 Act any of its presently outstanding
securities or any of its securities which may hereafter be issued.

(f)   Exempt Transaction. Subject to the accuracy of the Warrantholder's
representations in Section 10 hereof, the issuance of the Preferred Stock upon
exercise of this Warrant will constitute a transaction exempt from (i) the
registration requirements of Section 5 of the 1933 Act, in reliance upon Section
4(2) thereof, and (ii) the qualification requirements of the applicable state
securities laws.

10.   REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

This Warrant Agreement has been entered into by the Company in reliance upon the
following representations and covenants of the Warrantholder:

(a)   Investment Purpose. The right to acquire Preferred Stock or the Preferred
Stock issuable upon exercise of the Warrantholder's rights contained herein or
Common Stock issuable upon conversion thereof will be acquired for investment
and not with a view to the sale or distribution of any part thereof, and the
Warrantholder has no present intention of selling or engaging in any public
distribution of the same except pursuant to a registration or exemption.

(b)   Private Issue. The Warrantholder understands (i) that the Preferred Stock
issuable upon exercise of this Warrant (or Common Stock issuable upon conversion
thereof) is not registered under the 1933 Act or qualified under applicable
state securities laws on the ground that the issuance contemplated by this
Warrant Agreement will be exempt from the registration and

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qualifications requirements thereof, and (ii) that the Company's reliance on
such exemption is predicated on the representations set forth in this Section
10.

(c)   Disposition of Warrantholder's Rights. In no event will the Warrantholder
make a disposition of any of its rights to acquire Preferred Stock or Preferred
Stock issuable upon exercise of such rights (or Common Stock issuable upon
conversion thereof) unless and until (i) it shall have notified the Company of
the proposed disposition, and (ii) if requested by the Company, it shall have
furnished the Company with an opinion of counsel (which counsel may either be
inside or outside counsel to the Warrantholder) satisfactory to the Company and
its counsel to the effect that (A) appropriate action necessary for compliance
with the 1933 Act has been taken, or (B) an exemption from the registration
requirements of the 1933 Act is available. Notwithstanding the foregoing, the
restrictions imposed upon the transferability of any of its rights to acquire
Preferred Stock or Preferred Stock issuable on the exercise of such rights (or
Common Stock issuable upon conversion thereof) do not apply to transfers from
the beneficial owner of any of the aforementioned securities to its nominee or
from such nominee to its beneficial owner, and shall terminate as to any
particular share of Preferred Stock when (1) such security shall have been
effectively registered under the 1933 Act and sold by the holder thereof in
accordance with such registration or (2) such security shall have been sold
without registration in compliance with Rule 144 under the 1933 Act, or (3) a
letter shall have been issued to the Warrantholder at its request by the staff
of the Securities and Exchange Commission or a ruling shall have been issued to
the Warrantholder at its request by such Commission stating that no action shall
be recommended by such staff or taken by such Commission, as the case may be, if
such security is transferred without registration under the 1933 Act in
accordance with the conditions set forth in such letter or ruling and such
letter or ruling specifies that no subsequent restrictions on transfer are
required. Whenever the restrictions imposed hereunder shall terminate, as
hereinabove provided, the Warrantholder or holder of a share of Preferred Stock
then outstanding (or Common Stock issuable upon conversion thereof) as to which
such restrictions have terminated shall be entitled to receive from the Company,
without expense to such holder, one or more new certificates for the Warrant or
for such shares of Preferred Stock (or Common Stock issuable upon conversion
thereof) not bearing any restrictive legend.

(d)   Financial Risk. The Warrantholder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment, and has the ability to bear the economic risks of its
investment.

(e)   Risk of No Registration. The Warrantholder understands that if the Company
does not register with the Securities and Exchange Commission pursuant to
Section 12 of the 1934 Act (the "1934 Act"), or file reports pursuant to Section
15(d), of the 1934 Act, or if a registration statement covering the securities
under the 1933 Act is not in effect when it desires to sell (i) the rights to
purchase Preferred Stock pursuant to this Warrant Agreement, or (ii) the
Preferred Stock issuable upon exercise of the right to purchase (or Common Stock
issuable upon conversion thereof) it may be required to hold such securities for
an indefinite period. The Warrantholder also understands that any sale of its
rights of the Warrantholder to purchase Preferred Stock or Preferred Stock (or
Common Stock issuable upon conversion thereof) which might be made by it in
reliance upon Rule 144 under the 1933 Act may be made only in accordance with
the terms and conditions of that Rule.

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(f)   Accredited Investor. Warrantholder is an "accredited investor" within the
meaning of the Securities and Exchange Rule 501 of Regulation D, as presently in
effect.

11.   TRANSFERS.

Subject to the terms and conditions contained in Section 10 hereof, this Warrant
Agreement and all rights hereunder are transferable in whole or in part by the
Warrantholder and any successor transferee, provided, however, in no event shall
the number of transfers of the rights and interests in all of the Warrants
exceed three (3) transfers and in all events shall the transferee be subject to
the obligations hereunder.  The transfer shall be recorded on the books of the
Company upon receipt by the Company of a notice of transfer in the form attached
hereto as Exhibit III (the "Transfer Notice"), at its principal offices and the
payment to the Company of all transfer taxes and other governmental charges
imposed on such transfer.

12.   MARKET STANDOFF.

Warrantholder hereby agrees that, during the period of duration specified by the
Company and an underwriter of Common Stock or other securities of the Company,
following the effective date of a registration statement of the Company filed
under the Act, it shall not, to the extent requested by the Company and such
underwriter, directly or indirectly sell, offer to sell, contract to sell
(including, without limitation, any short sale), grant any option to purchase or
otherwise transfer or dispose of (other than to donees who agree to be similarly
bound) any securities of the Company held by it immediately prior to the
effective date of such registration statement, except Common Stock included in
such registration; provided, however, that:

(a)   such agreement shall be applicable only to the first such registration
statement of the Company that covers Common Stock (or other securities) to be
sold on its behalf to the public in an underwritten offering;

(b)   all officers and directors of the Company and all other persons with
registration rights (whether or not pursuant to this Agreement) enter into
similar agreements; and

(c)   such market stand-off time period shall not exceed one hundred eighty
(180) days.

In order to enforce the foregoing covenant, the Company may impose stop-transfer
instructions with respect to the Company's securities held by the Warrantholder
(and the shares or securities of every other person subject to the foregoing
restriction) until the end of such period.

13.   MISCELLANEOUS.

(a)   Effective Date. The provisions of this Warrant Agreement shall be
construed and shall be given effect in all respects as if it had been executed
and delivered by the Company on the date hereof. This Warrant Agreement shall be
binding upon any successors or assigns of the Company and Warrantholder.

(b)   Attorney's Fees. In any litigation, arbitration or court proceeding
between the Company and the Warrantholder relating hereto, the prevailing party
shall be entitled to attorneys' fees and expenses and all costs of proceedings
incurred in enforcing this Warrant Agreement.

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(c)   Governing Law. This Warrant Agreement shall be governed by and construed
for all purposes under and in accordance with the laws of the State of Texas.

(d)   Counterparts. This Warrant Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

(e)   Notices. Any notice required or permitted hereunder shall be given in
writing and shall be deemed effectively given upon personal delivery, facsimile
transmission (provided that the original is sent by personal delivery or mail as
hereinafter set forth) or seven (7) days after deposit in the United States
mail, by registered or certified mail, addressed (i) to the Warrantholder at
6111 North River Road, Rosemont, Illinois 60018, Attention: Venture Lease
Administration, cc: Legal Department, Attention: General Counsel, (and/or, if by
facsimile, (847) 518-5465 and (847) 518-5088) and (ii) to the Company at 1155
East Collins Blvd. Richardson, TX 75081, Attention: Chief Financial Officer
(and/or if by facsimile, (972) 238-1477 or at such other address as any such
party may subsequently designate by written notice to the other party.

(f)   Remedies. In the event of any default hereunder, the non-defaulting party
may proceed to protect and enforce its rights either by suit in equity and/or by
action at law, including but not limited to an action for damages as a result of
any such default, and/or an action for specific performance for any default
where Warrantholder will not have an adequate remedy at law and where damages
will not be readily ascertainable. The Company expressly agrees that it shall
not oppose an application by the Warrantholder or any other person entitled to
the benefit of this Agreement requiring specific performance of any or all
provisions hereof or enjoining the Company from continuing to commit any such
breach of this Warrant Agreement.

(g)   No Impairment of Rights. The Company will not, by amendment of its Charter
or through any other means, avoid or seek to avoid the observance or performance
of any of the terms of this Warrant, but will at all times in good faith assist
in the carrying out of all such terms and in the taking of all such actions as
may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment. The foregoing notwithstanding, the Company
shall not be deemed to have impaired the Warrantholder's rights hereunder if it
amends its Charter, or the holders of the Preferred Stock waive rights
thereunder or if the holders of Preferred Stock elect to convert all outstanding
shares of the Company into Common Stock, in a manner that does not affect the
Warrantholder in a manner different from the effect that such amendments or
waivers or election have on the rights of the holders of the Preferred Stock.

(h)   Survival. The representations, warranties, covenants and conditions of the
respective parties contained herein or made pursuant to this Warrant Agreement
shall survive the execution and delivery of this Warrant Agreement.

(i)   Severability. In the event any one or more of the provisions of this
Warrant Agreement shall for any reason be held invalid, illegal or
unenforceable, the remaining provisions of this Warrant Agreement shall be
unimpaired, and the invalid, illegal or unenforceable provision shall be
replaced by a mutually acceptable valid, legal and enforceable provision, which
comes closest to the intention of the parties underlying the invalid, illegal or
unenforceable provision.

                                       11
<PAGE>

(j)   Amendments. Any provision of this Warrant Agreement may be amended or
waived by a written instrument signed by the Company and by the Warrantholder.

(k)   Additional Documents. The Company, upon execution of this Warrant
Agreement, shall provide the Warrantholder with certified resolutions with
respect to the representations, warranties and covenants set forth in
subparagraphs (a) through (d), (e) and (f) of Section 9 above.

IN WITNESS WHEREOF, the parties hereto have caused this Warrant Agreement to be
executed by its officers thereunto duly authorized as of the Effective Date.

Company:  CHORUM TECHNOLOGIES INC.

By:      /s/ Scott Grout
   ---------------------------

Title:  President and CEO

Warrantholder:  COMDISCO, INC.

By:
   ---------------------------

Title:________________________

                                       12
<PAGE>

EXHIBIT I

NOTICE OF EXERCISE

To:_______________________

(1)  The undersigned Warrantholder hereby elects to purchase ____ shares of the
Series ____ Preferred Stock of ___________________, pursuant to the terms of the
Warrant Agreement dated the ____ day of _____________________, ______  (the
"Warrant  Agreement") between ________________________________ and the
Warrantholder, and tenders herewith payment of the purchase price for such
shares in full, together with all applicable transfer taxes, if any.

(2)  In exercising its rights to purchase the Series _____ Preferred Stock of
_________________________, the undersigned hereby confirms and acknowledges the
investment representations and warranties made in Section 10 of the Warrant
Agreement.

(3)  Please issue a certificate or certificates representing said shares of
Series ___ Preferred Stock in the name of the undersigned or in such other name
as is specified below.

_____________________________
(Name)

_____________________________
(Address)

WARRANTHOLDER: COMDISCO, INC.

By:_____________________________

Title:__________________________

Date:___________________________

                                       13
<PAGE>

EXHIBIT II

ACKNOWLEDGMENT OF EXERCISE

     The undersigned ____________________, hereby acknowledge receipt of the
"Notice of Exercise" from Comdisco, Inc., to purchase _______ shares of the
Series ______ Preferred Stock of _______________________, pursuant to the terms
of the Warrant Agreement, and further acknowledges that ________ shares remain
subject to purchase under the terms of the Warrant Agreement.

Company:

By:_____________________________

Title:__________________________

Date:___________________________

                                       14
<PAGE>

EXHIBIT III

TRANSFER NOTICE

(To transfer or assign the foregoing Warrant Agreement execute this form and
supply required information.  Do not use this form to purchase shares.)

FOR VALUE RECEIVED, the foregoing Warrant Agreement and all rights evidenced
thereby are hereby transferred and assigned to

_______________________________________________
(Please Print)

whose address is ______________________________

_______________________________________________

Dated:_________________________________________

Holder's Signature:____________________________

Holder's Address:______________________________

_______________________________________________

Signature Guaranteed:__________________________

Transferee hereby agrees to be bound by the terms and conditions of this Warrant
Agreement

Acknowledged and Agreed:

By:_____________________________

Title:__________________________

Date:___________________________

NOTE:  The signature to this Transfer Notice must correspond with the name as it
       appears on the face of the Warrant Agreement, without alteration or
       enlargement or any change whatever.  Officers of corporations and those
       acting in a fiduciary or other representative capacity should file proper
       evidence of authority to assign the foregoing Warrant Agreement.

                                       15<PAGE>

                                                                     EXHIBIT 4.6

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS
AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE,
PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT
RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL)
REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES
LAWS.

                               WARRANT AGREEMENT

             To Purchase Shares of the Series C Preferred Stock of

                           CHORUM TECHNOLOGIES INC.

              Dated as of January 22, 1999 (the "Effective Date")

WHEREAS, CHORUM TECHNOLOGIES INC., a Delaware corporation (the "Company") has
entered into a Master Lease Agreement dated as of September 22, 1998, Equipment
Schedule No. VL-3 and VL-4 dated as of January 22, 1999, and related Summary
Equipment Schedules (collectively, the "Leases") with Comdisco, Inc., a Delaware
corporation (the "Warrantholder"); and

WHEREAS, the Company desires to grant to Warrantholder in consideration for such
Leases, the right to purchase shares of its Series C Preferred Stock;

NOW, THEREFORE, in consideration of the Warrantholder executing and delivering
such Leases and in consideration of mutual covenants and agreements contained
herein, the Company and Warrantholder agree as follows:

1.       GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

The Company hereby grants to the Warrantholder, and the Warrantholder is
entitled, upon the terms and subject to the conditions hereinafter set forth, to
subscribe to and purchase from the Company 58,824 fully paid and non-assessable
shares of the Company's Series C Preferred Stock ("Preferred Stock") at a
purchase price of $4.25 per share (the "Exercise Price"). The number and
purchase price of such shares are subject to adjustment as provided in Section 8
hereof.
<PAGE>

2.       TERM OF THE WARRANT AGREEMENT.

Except as otherwise provided for herein, the term of this Warrant Agreement and
the right to purchase Preferred Stock as granted herein shall commence on the
Effective Date and shall be exercisable for a period of (i) seven (7) years or
(ii) three (3) years from the effective date of the Company's initial public
offering, whichever is shorter. Notwithstanding the term of this Warrant
Agreement fixed pursuant to preceding sentence, the right to purchase Preferred
Stock a granted herein shall expire, if not previously exercised, immediately
upon (i) a merger or consolidation of the Company with or into any other
corporation or corporations, unless the shareholders of the Company immediately
prior to any such transaction are holders of a majority of the voting securities
of the surviving corporation or acquiring corporation immediately thereafter and
hold such securities in substantially similar proportions as prior to such
transaction (and for purposes of this calculation equity securities which any
shareholder of the Company owned immediately prior to such merger or
consolidation as shareholder of another party to the transaction shall be
disregarded), or (ii) a sale or other transfer of all or substantially all of
the assets of the Company or any series of related transactions resulting in the
sale or other transfer of all or substantially all of the assets of the Company
("Termination Event").

The Company shall notify the Warrantholder if the Termination Event is proposed
no later than the date such notice is provided to the Company's stockholders of
such Termination Event. Such notice shall also contain such details of the
proposed Termination Event as are reasonable in the circumstances. If such
closing does not take place, the Company shall promptly notify the Warrantholder
that such proposed transaction has been terminated, and the Warrantholder may
rescind any exercise of its purchase rights promptly after such notice of
termination of the proposed transaction. In the event of such recession, this
Warrant Agreement shall continue to be exercisable on the same terms and
conditions contained herein.

If all of the Company's outstanding Preferred Stock is converted into shares of
Common Stock then this Warrant shall automatically become exercisable for that
number of shares of Common Stock equal to the number of shares of Common Stock
that would have been received if this Warrant had been exercised in full and the
shares of Preferred Stock received thereupon had been simultaneously converted
into shares of Common Stock immediately prior to such event, and the Exercise
Price shall be automatically adjusted to equal the amount obtained by dividing
(i) the aggregate Exercise Price of the shares of Preferred Stock for this which
this Warrant was exercisable immediately prior to such conversion, by (ii) the
number of shares of Common Stock for which this Warrant is exercisable
immediately after such conversion.

3.       EXERCISE OF THE PURCHASE RIGHTS.

The purchase rights set forth in this Warrant Agreement are exercisable by the
Warrantholder, in whole or in part, at any time, or from time to time, prior to
the expiration of the term set forth in Section 2 above, by tendering to the
Company at its principal office a notice of exercise in the form attached hereto
as Exhibit I (the "Notice of Exercise"), duly completed and executed. Promptly
upon receipt of the Notice of Exercise and the payment of the purchase price in
accordance with the terms set forth below, and in no event later than twenty-one
(21) days thereafter, the Company shall issue to the Warrantholder a certificate
for the number of shares of Preferred Stock purchased and shall execute the
acknowledgment of exercise in the form

                                       2
<PAGE>

attached hereto as Exhibit II (the "Acknowledgment of Exercise") indicating the
number of shares which remain subject to future purchases, if any.

The Exercise Price may be paid at the Warrantholder's election either (i) by
cash or check, or (ii) by surrender of Warrants ("Net Issuance") as determined
below. If the Warrantholder elects the Net Issuance method, the Company will
issue Preferred Stock in accordance with the following formula:

X = Y(A-B)
    ------
      A

Where: X = the number of shares of Preferred Stock to be issued to the
Warrantholder.

Y = the number of shares of Preferred Stock requested to be exercised under this
Warrant Agreement.

A = the fair market value of one (1) share of Preferred Stock at the time the
net issuance election is made.

B = the Exercise Price.

For purposes of the above calculation, current fair market value of Preferred
Stock shall mean with respect to each share of Preferred Stock:

(i)      if the exercise is in connection with an initial public offering of the
Company's Common Stock, and if the Company's Registration Statement relating to
such public offering has been declared effective by the SEC, then the fair
market value per share shall be the product of (x) the initial "Price to Public"
specified in the final prospectus with respect to the offering and (y) the
number of shares of Common Stock into which each share of Preferred Stock is
convertible at the time of such exercise;

(ii)     if this Warrant is exercised after, and not in connection with the
Company's initial public offering, and:

(a)      if traded on a securities exchange, the fair market value shall be
deemed to be the average of the closing prices over a twenty-one (21) day period
ending three days before the day the current fair market value of the securities
is being determined; or

(b)      if actively traded over-the-counter, the fair market value shall be
deemed to be the average of the closing bid and asked prices quoted on the
NASDAQ system (or similar system) over the twenty-one (21) day period ending
three days before the day the current fair market value of the securities is
being determined;

(iii)    if at any time the Common Stock is not listed on any securities
exchange or quoted in the NASDAQ System or the over-the-counter market, the
current fair market value of Preferred Stock shall be the product of (x) the
highest price per share which the Company could obtain

                                       3
<PAGE>

from a willing buyer (not a current employee or director) for shares of Common
Stock sold by the Company, from authorized but unissued shares, as determined in
good faith by its Board of Directors and (y) the number of shares of Common
Stock into which each share of Preferred Stock is convertible at the time of
such exercise or such earlier time as all outstanding share of the Company's
Preferred Stock convert into shares of Common Stock; unless the Company shall
become subject to a merger, acquisition or other consolidation pursuant to which
the Company is not the surviving party, in which case the fair market value of
Preferred Stock shall be deemed to be the value received by the holders of the
Company's Preferred Stock on a common equivalent basis pursuant to such merger
or acquisition.

Upon partial exercise by either cash or Net Issuance, the Company shall promptly
issue an amended Warrant Agreement representing the remaining number of shares
purchasable hereunder. All other terms and conditions of such amended Warrant
Agreement shall be identical to those contained herein, including, but not
limited to the Effective Date hereof.

4.       RESERVATION OF SHARES.

(a)      Authorization and Reservation of Shares. The Company currently has an
insufficient number of unissued authorized shares of Series C Preferred Stock to
provide for the complete exercise of the rights to purchase Series C Preferred
Stock as herein provided. The Company shall use its best efforts to amend its
Charter (as defined below) to authorize a sufficient additional number of shares
of its Series C Preferred Stock to provide for the complete exercise of the
rights to purchase Series C Preferred Stock as herein provided upon the earlier
of (A) the closing of the Next Round or (B) June 1, 1999.

(b)      Registration or Listing. If any shares of Preferred Stock required to
be reserved hereunder require registration with or approval of any governmental
authority under any Federal or State law (other than any registration under the
Securities Act of 1933, as amended ("1933 Act"), as then in effect, or any
similar Federal statute then enforced, or any state securities law, required by
reason of any transfer involved in such conversion), or listing on any domestic
securities exchange, before such shares may be issued upon conversion, the
Company will, at its expense and as expeditiously as possible, use its best
efforts to cause such shares to be duly registered, listed or approved for
listing on such domestic securities exchange, as the case may be.

5.       NO FRACTIONAL SHARES OR SCRIP.

No fractional shares or scrip representing fractional shares shall be issued
upon the exercise of the Warrant, but in lieu of such fractional shares the
Company shall make a cash payment therefor upon the basis of the Exercise Price
then in effect.

6.       NO RIGHTS AS SHAREHOLDER.

This Warrant Agreement does not entitle the Warrantholder to any voting rights
or other rights as a shareholder of the Company prior to the exercise of the
Warrant.

                                       4
<PAGE>

7.       WARRANTHOLDER REGISTRY.

The Company shall maintain a registry showing the name and address of the
registered holder of this Warrant Agreement.

8.       ADJUSTMENT RIGHTS.

The purchase price per share and the number of shares of Preferred Stock
purchasable hereunder are subject to adjustment, as follows:

(a)      Merger and Sale of Assets. If at any time there shall be a capital
reorganization of the shares of the Company's stock (other than a combination,
reclassification, exchange or subdivision of shares otherwise provided for
herein), or a merger or consolidation of the Company with or into another
corporation whether or not the Company is the surviving corporation other than a
Termination Event, as defined in Section 2 hereof, or the sale of all or
substantially all of the Company's properties and assets to any other person
other than a Termination Event (hereinafter referred to as a "Merger Event"),
then, as a part of such Merger Event, lawful provision shall be made so that the
Warrantholder shall thereafter be entitled to receive, upon exercise of the
Warrant, the number of shares of preferred stock or other securities of the
successor corporation resulting from such Merger Event, equivalent in value to
that which would have been issuable if Warrantholder had exercised this Warrant
immediately prior to the Merger Event. In any such case, appropriate adjustment
(as determined in good faith by the Company's Board of Directors) shall be made
in the application of the provisions of this Warrant Agreement with respect to
the rights and interest of the Warrantholder after the Merger Event to the end
that the provisions of this Warrant Agreement (including adjustments of the
Exercise Price and number of shares of Preferred Stock purchasable) shall be
applicable to the greatest extent possible.

(b)      Reclassification of Shares. If the Company at any time shall, by
combination, reclassification, exchange or subdivision of securities or
otherwise, change any of the securities as to which purchase rights under this
Warrant Agreement exist into the same or a different number of securities of any
other class or classes, this Warrant Agreement shall thereafter represent the
right to acquire such number and kind of securities as would have been issuable
as the result of such change with respect to the securities which were subject
to the purchase rights under this Warrant Agreement immediately prior to such
combination, reclassification, exchange, subdivision or other change.

(c)      Subdivision or Combination of Shares. If the Company at any time shall
combine or subdivide its Preferred Stock, the Exercise Price shall be
proportionately decreased in the case of a subdivision, or proportionately
increased in the case of a combination.

(d)      Stock Dividends. If the Company at any time shall pay a dividend
payable in, or make any other distribution (except any distribution specifically
provided for in the foregoing subsections (a) or (b)) of the Company's Preferred
Stock, then the Exercise Price shall be adjusted, from and after the record date
of such dividend or distribution, to that price determined by multiplying the
Exercise Price in effect immediately prior to such record date by a fraction (i)
the numerator of which shall be the total number of all shares of the Company's
Preferred Stock

                                       5
<PAGE>

outstanding immediately prior to such dividend or distribution, and (ii) the
denominator of which shall be the total number of all shares of the Company's
Preferred Stock outstanding immediately after such dividend or distribution. The
Warrantholder shall thereafter be entitled to purchase, at the Exercise Price
resulting from such adjustment, the number of shares of Preferred Stock
(calculated to the nearest whole share) obtained by multiplying the Exercise
Price in effect immediately prior to such adjustment by the number of shares of
Preferred Stock issuable upon the exercise hereof immediately prior to such
adjustment and dividing the product thereof by the Exercise Price resulting from
such adjustment.

(e)       Antidilution Rights. Antidilution rights applicable to the Preferred
Stock purchasable hereunder are as set forth in the Company's Certificate of
Incorporation, as amended through the Effective Date, a true and complete copy
of which is attached hereto as Exhibit (the "Charter"). The Company shall
promptly provide the Warrantholder with any restatement, amendment, modification
or waiver of the Charter. The Preferred Stock purchasable hereunder shall have
the benefit of the same antidilution rights applicable to such Preferred Stock
as designated in the Company's Charter, and the Company shall provide
Warrantholder with all notices and information at the time and to the extent it
is required to do so to the holders of the Preferred Stock.

(g)       Notice of Adjustments. If: (i) the Company shall declare any dividend
or distribution upon its stock, whether in cash, property, stock or other
securities; (ii) the Company shall offer for subscription prorata to the holders
of any class of its Preferred or other convertible stock on the basis of their
ownership thereof any additional shares of stock of any class or other rights;
(iii) there shall be any Merger Event; (iv) there shall be an initial public
offering; or (v) there shall be any voluntary dissolution, liquidation or
winding up of the Company; then, in connection with each such event, the Company
shall send to the Warrantholder: (A) prior written notice no later than the date
that such notice is provided to the Company's shareholders of the date on which
the books of the Company shall close or a record shall be taken for such
dividend, distribution, subscription rights (specifying the date on which the
holders of Preferred Stock shall be entitled thereto) or for determining rights
to vote in respect of such Merger Event, dissolution, liquidation or winding up;
(B) in the case of any such Merger Event, dissolution, liquidation or winding
up, prior written notice no later than the date that such notice is provided to
the Company's shareholders of the date when the same shall take place (and
specifying the date on which the holders of Preferred Stock shall be entitled to
exchange their Preferred Stock for securities or other property deliverable upon
such Merger Event, dissolution, liquidation or winding up); and (C) in the case
of a public offering, the Company shall give the Warrantholder prior written
notice no later than the date that such notice is provided to the Company's
shareholders.

Each such written notice shall set forth, in reasonable detail, (i) the event
requiring the adjustment, (ii) the amount of the adjustment, (iii) the method by
which such adjustment was calculated, (iv) the Exercise Price, and (v) the
number of shares subject to purchase hereunder after giving effect to such
adjustment, and shall be given by first class mail, postage prepaid, addressed
to the Warrantholder, at the address as shown on the books of the Company.

                                       6
<PAGE>

(h)       Timely Notice. Failure to timely provide such notice required by
subsection (g) above shall entitle Warrantholder to retain the benefit of the
applicable notice period notwithstanding anything to the contrary contained in
any insufficient notice received by Warrantholder. The notice period shall begin
on the date Warrantholder actually receives a written notice containing all the
information specified above.

9.        REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

(a)       Reservation of Preferred Stock. The Preferred Stock issuable upon
exercise of the Warrantholder's rights, when issued in accordance with the
provisions of this Warrant Agreement, will be validly issued, fully paid and
non-assessable, and will be free of any taxes, liens, charges or encumbrances of
any nature whatsoever; provided, however, that the Preferred Stock issuable
pursuant to this Warrant Agreement may be subject to restrictions on transfer
under state and/or Federal securities laws. The Company has made available to
the Warrantholder true, correct and complete copies of its Charter and Bylaws,
as amended. The issuance of certificates for shares of Preferred Stock upon
exercise of the Warrant Agreement shall be made without charge to the
Warrantholder for any issuance tax in respect thereof, or other cost incurred by
the Company in connection with such exercise and the related issuance of shares
of Preferred Stock. The Company shall not be required to pay any tax which may
be payable in respect of any transfer involved and the issuance and delivery of
any certificate in a name other than that of the Warrantholder.

(b)       Due Authority. Subject to the Company obtaining the necessary
approvals for the amendment of the Company's Certificate of Incorporation to
authorize a sufficient additional number of shares of its Series C Preferred
Stock, the execution and delivery by the Company of this Warrant Agreement and
the performance of all obligations of the Company hereunder, including the
issuance to Warrantholder of the right to acquire the shares of Preferred Stock,
have been duly authorized by all necessary corporate action on the part of the
Company, and the Leases and this Warrant Agreement are not inconsistent with the
Company's Charter or Bylaws, to the Company's knowledge, do not contravene any
law or governmental rule, regulation or order applicable to it, do not and will
not contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument to which it is a party or by which it is
bound, and the Leases and this Warrant Agreement constitute legal, valid and
binding agreements of the Company, enforceable in accordance with their
respective terms, except as limited by applicable bankruptcy, insolvency,
reorganization, moratorium and other laws of general application affecting
enforcement of creditor's rights generally and (ii) as limited by laws relating
to the availability of specific performance, injunctive relief or other
equitable remedies.

(c)       Consents and Approvals. No consent or approval of, giving of notice
to, registration with, or taking of any other action in respect of any state,
Federal or other governmental authority or agency is required with respect to
the execution, delivery and performance by the Company of its obligations under
this Warrant Agreement, except for any filing of notices pursuant to Regulation
D under the 1933 Act and any filing required by applicable state securities law,
which filings will be effective by the time required thereby.

                                       7
<PAGE>

(d)       Issued Securities. All issued and outstanding shares of Common Stock,
Preferred Stock or any other securities of the Company have been duly authorized
and validly issued and are fully paid and nonassessable. All outstanding shares
of Common Stock, Preferred Stock and any other securities were issued in full
compliance with all Federal and state securities laws. In addition the
authorized capital of the Company consists of:

(i)       Preferred Stock. Ten million (10,000,000) shares of Preferred Stock
(the "Preferred Stock"), of which three million seven hundred twenty thousand
(3,720,000) shares have been designated as Series A Preferred Stock, all of
which are issued and outstanding, two million seventy thousand seven hundred
fifty three (2,070,753) shares have been designated Series B-1 Preferred Stock
(the "Series B-1 Preferred Stock"), all of which are issued and outstanding,
three million two hundred ninety four thousand one hundred forty one (3,294,141)
shares have been designated Series B-2 Preferred Stock (the "Series B-2
Preferred Stock"), three million two hundred forty-four thousand one hundred
seventy (3,244,170) of which are issued and outstanding and four million two
hundred thousand (4,200,000) shares have been designated Series C Preferred
Stock (the "Series C Preferred Stock"), four million thirty-two thousand eight
hundred eighty-eight (4,032,888) of which were issued or outstanding immediately
prior to the Closing.

(ii)      Common Stock. Twenty million (20,000,000) shares of Common Stock
("Common Stock"), of which one million three hundred eighty-three thousand eight
hundred seventy-three (1,383,873) shares are issued and outstanding.

(iii)     Except for (A) the conversion privileges of the Series A, Series B-1,
Series B-2 and Series C Preferred Stock, (B) the rights provided m Section 2.4
of the Rights Agreement (as defined below), and (C) currently outstanding
options to purchase four hundred sixty-six thousand four hundred fifty (466,450)
shares of the Company's Common Stock, there are not outstanding any options,
warrants, rights (including conversion or preemptive rights) or agreements for
the purchase or acquisition from the Company of any shares of its capital stock.
The Company has reserved seven hundred eighteen thousand two hundred forty
(718,240) shares of its Common Stock for purchase upon exercise of options to be
granted in the future under the Company's 1997 Stock Plan.

(e)       Other Commitments to Register Securities. Except as set forth in this
Warrant Agreement and in that certain Amended and Restated Investors Rights
Agreement (the "Rights Agreement") dated as of November 4, 1998 by and between
the Company and the Founders and the Investors (as defined therein), the Company
is not, pursuant to the terms of any other agreement currently in existence,
under any obligation to register under the 1933 Act any of its presently
outstanding securities or any of its securities which may hereafter be issued.

(f)       Exempt Transaction. Subject to the accuracy of the Warrantholder's
representations in Section 10 hereof, the issuance of the Preferred Stock upon
exercise of this Warrant will constitute a transaction exempt from (i) the
registration requirements of Section 5 of the 1933 Act, in reliance upon Section
4(2) thereof, and (ii) the qualification requirements of the applicable state
securities laws.

                                       8
<PAGE>

10.       REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

This Warrant Agreement has been entered into by the Company in reliance upon the
following representations and covenants of the Warrantholder:

(a)       Investment Purpose. The right to acquire Preferred Stock or the
Preferred Stock issuable upon exercise of the Warrantholder's rights contained
herein or Common Stock issuable upon conversion thereof will be acquired for
investment and not with a view to the sale or distribution of any part thereof,
and the Warrantholder has no present intention of selling or engaging in any
public distribution of the same except pursuant to a registration or exemption.

(b)       Private Issue. The Warrantholder understands (i) that the Preferred
Stock issuable upon exercise of this Warrant (or Common Stock issuable upon
conversion thereof) is not registered under the 1933 Act or qualified under
applicable state securities laws on the ground that the issuance contemplated by
this Warrant Agreement will be exempt from the registration and qualifications
requirements thereof, and (ii) that the Company's reliance on such exemption is
predicated on the representations set forth in this Section 10.

(c)       Disposition of Warrantholder's Rights. In no event will the
Warrantholder make a disposition of any of its rights to acquire Preferred Stock
or Preferred Stock issuable upon exercise of such rights (or Common Stock
issuable upon conversion thereof) unless and until (i) it shall have notified
the Company of the proposed disposition, and (ii) if requested by the Company,
it shall have furnished the Company with an opinion of counsel (which counsel
may either be inside or outside counsel to the Warrantholder) satisfactory to
the Company and its counsel to the effect that (A) appropriate action necessary
for compliance with the 1933 Act has been taken, or (B) an exemption from the
registration requirements of the 1933 Act is available. Notwithstanding the
foregoing, the restrictions imposed upon the transferability of any of its
rights to acquire Preferred Stock or Preferred Stock issuable on the exercise of
such rights (or Common Stock issuable upon conversion thereof) do not apply to
transfers from the beneficial owner of any of the aforementioned securities to
its nominee or from such nominee to its beneficial owner, and shall terminate as
to any particular share of Preferred Stock when (1) such security shall have
been effectively registered under the 1933 Act and sold by the holder thereof in
accordance with such registration or (2) such security shall have been sold
without registration in compliance with Rule 144 under the 1933 Act, or (3) a
letter shall have been issued to the Warrantholder at its request by the staff
of the Securities and Exchange Commission or a ruling shall have been issued to
the Warrantholder at its request by such Commission stating that no action shall
be recommended by such staff or taken by such Commission, as the case may be, if
such security is transferred without registration under the 1933 Act in
accordance with the conditions set forth in such letter or ruling and such
letter or ruling specifies that no subsequent restrictions on transfer are
required. Whenever the restrictions imposed hereunder shall terminate, as
hereinabove provided, the Warrantholder or holder of a share of Preferred Stock
then outstanding (or Common Stock issuable upon conversion thereof) as to which
such restrictions have terminated shall be entitled to receive from the Company,
without expense to such holder, one or more new certificates for the Warrant or
for such shares of Preferred Stock (or Common Stock issuable upon conversion
thereof) not bearing any restrictive legend.

                                       9
<PAGE>

(d)       Financial Risk. The Warrantholder has such knowledge and experience in
financial and business matters as to be capable of evaluating the merits and
risks of its investment, and has the ability to bear the economic risks of its
investment.

(e)       Risk of No Registration. The Warrantholder understands that if the
Company does not register with the Securities and Exchange Commission pursuant
to Section 12 of the 1934 Act (the "1934 Act"), or file reports pursuant to
Section 15(d), of the 1934 Act, or if a registration statement covering the
securities under the 1933 Act is not in effect when it desires to sell (i) the
rights to purchase Preferred Stock pursuant to this Warrant Agreement, or (ii)
the Preferred Stock issuable upon exercise of the right to purchase (or Common
Stock issuable upon conversion thereof) it may be required to hold such
securities for an indefinite period. The Warrantholder also understands that any
sale of its rights of the Warrantholder to purchase Preferred Stock or Preferred
Stock (or Common Stock issuable upon conversion thereof) which might be made by
it in reliance upon Rule 144 under the 1933 Act may be made only in accordance
with the terms and conditions of that Rule.

(f)       Accredited Investor. Warrantholder is an "accredited investor" within
the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

11.      TRANSFERS.

Subject to the terms and conditions contained in Section 10 hereof, this Warrant
Agreement and all rights hereunder are transferable in whole or in part by the
Warrantholder and any successor transferee, provided, however, in no event shall
the number of transfers of the rights and interests in all of the Warrants
exceed three (3) transfers and in all events shall the transferee be subject to
the obligations hereunder. The transfer shall be recorded on the books of the
Company upon receipt by the Company of a notice of transfer in the form attached
hereto as Exhibit III (the "Transfer Notice"), at its principal offices and the
payment to the Company of all transfer taxes and other governmental charges
imposed on such transfer.

12.      MARKET STANDOFF.

Warrantholder hereby agrees that, during the period of duration specified by the
Company and an underwriter of Common Stock or other securities of the Company,
following the effective date of a registration statement of the Company filed
under the Act, it shall not, to the extent requested by the Company and such
underwriter, directly or indirectly sell, offer to sell, contract to sell
(including, without limitation, any short sale), grant any option to purchase or
otherwise transfer or dispose of (other than to donees who agree to be similarly
bound) any securities of the Company held by it immediately prior to the
effective date of such registration statement, except Common Stock included in
such registration; provided, however, that:

(a)       such agreement shall be applicable only to the first such registration
statement of the Company that covers Common Stock (or other securities) to be
sold on its behalf to the public in an underwritten offering;

                                      10
<PAGE>

(b)       all officers and directors of the Company and all other persons with
registration rights (whether or not pursuant to this Agreement) enter into
similar agreements; and

(c)       such market stand-off time period shall not exceed one hundred eighty
(180) days.

In order to enforce the foregoing covenant, the Company may impose stop-transfer
instructions with respect to the Company's securities held by the Warrantholder
(and the shares or securities of every other person subject to the foregoing
restriction) until the end of such period.

13.       MISCELLANEOUS.

(a)       Effective Date. The provisions of this Warrant Agreement shall be
construed and shall be given effect in all respects as if it had been executed
and delivered by the Company on the date hereof. This Warrant Agreement shall be
binding upon any successors or assigns of the Company and Warrantholder.

(b)       Attorney's Fees. In any litigation, arbitration or court proceeding
between the Company and the Warrantholder relating hereto, the prevailing party
shall be entitled to attorneys' fees and expenses and all costs of proceedings
incurred in enforcing this Warrant Agreement.

(c)       Governing Law. This Warrant Agreement shall be governed by and
construed for all purposes under and in accordance with the laws of the State of
Texas.

(d)       Counterparts. This Warrant Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

(e)       Notices. Any notice required or permitted hereunder shall be given in
writing and shall be deemed effectively given upon personal delivery, facsimile
transmission (provided that the original is sent by personal delivery or mail as
hereinafter set forth) or seven (7) days after deposit in the United States
mail, by registered or certified mail, addressed (i) to the Warrantholder at
6111 North River Road, Rosemont, Illinois 60018, Attention: Venture Lease
Administration, cc: Legal Department, Attention.: General Counsel, (and/or, if
by facsimile, (847)518-5465 and (847)518-5088) and (ii) to the Company at 1155
East Collins Blvd. Richardson, TX 75081, Attention: Chief Financial Officer
(and/or if by facsimile, (972)238-1477 or at such other address as any such
party may subsequently designate by written notice to the other party.

(f)       Remedies. In the event of any default hereunder, the non-defaulting
party may proceed to protect and enforce its rights either by suit in equity
and/or by action at law, including but not limited to an action for damages as a
result of any such default, and/or an action for specific performance for any
default where Warrantholder will not have an adequate remedy at law and where
damages will not be readily ascertainable. The Company expressly agrees that it
shall not oppose an application by the Warrantholder or any other person
entitled to the benefit of this Agreement requiring specific performance of any
or all provisions hereof or enjoining the Company from continuing to commit any
such breach of this Warrant Agreement.

                                      11
<PAGE>

(g)       No Impairment of Rights. The Company will not, by amendment of its
Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
actions as may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment. . The foregoing notwithstanding, the Company
shall not be deemed to have impaired the Warrantholder's rights hereunder if it
amends its Charter, or the holders of the Preferred Stock waive rights
thereunder or if the holders of Preferred Stock elect to convert all outstanding
shares of the Company into Common Stock, in a manner that does not affect the
Warrantholder in a manner different from the effect that such amendments or
waivers or election have on the rights of the holders of the Preferred Stock.

(h)       Survival. The representations, warranties, covenants and conditions of
the respective parties contained herein or made pursuant to this Warrant
Agreement shall survive the execution and delivery of this Warrant Agreement.

(i)       Severability. In the event any one or more of the provisions of this
Warrant Agreement shall for any reason be held invalid, illegal or
unenforceable, the remaining provisions of this Warrant Agreement shall be
unimpaired, and the invalid, illegal or unenforceable provision shall be
replaced by a mutually acceptable valid, legal and enforceable provision, which
comes closest to the intention of the parties underlying the invalid, illegal or
unenforceable provision.

(j)       Amendments. Any provision of this Warrant Agreement may be amended or
waived by a written instrument signed by the Company and by the Warrantholder.

(k)       Additional Documents. The Company, upon execution of this Warrant
Agreement, shall provide the Warrantholder with certified resolutions with
respect to the representations, warranties and covenants set forth in
subparagraphs (a) through (d), (e) and (f) of Section 9 above.

IN WITNESS WHEREOF, the parties hereto have caused this Warrant Agreement to be
executed by its officers thereunto duly authorized as of the Effective Date.

Company:  CHORUM TECHNOLOGIES INC.

By:               /s/ Scott Grout
        ------------------------------------

Title:   President & CEO
        ------------------------------------

Warrantholder: COMDISCO, I C.

By:               /s/ Jill C. Hanses
        ------------------------------------

Title:   Senior Vice President
        ------------------------------------

                                      12
<PAGE>

EXHIBIT I

NOTICE OF EXERCISE

To:
         ____________________________________________

(1) The undersigned Warrantholder hereby elects to purchase ____ shares of the
Series ____ Preferred Stock of ___________________, pursuant to the terms of the
Warrant Agreement dated the ____ day of __________________, 20___ (the "Warrant
Agreement") between ________________________________ and the Warrantholder, and
tenders herewith payment of the purchase price for such shares in full, together
with all applicable transfer taxes, if any.

(2)  In exercising its rights to purchase the Series _____ Preferred Stock of
_________________________, the undersigned hereby confirms and acknowledges the
investment representations and warranties made in Section 10 of the Warrant
Agreement.

(3) Please issue a certificate or certificates representing said shares of
Series Preferred Stock in the name of the undersigned or in such other name as
is specified below.

____________________________________________
(Name)

____________________________________________
(Address)

Warrantholder:  COMDISCO, INC.

By:
     _______________________________________

Title:
        ____________________________________

Date:
       _____________________________________

                                      13
<PAGE>

EXHIBIT II

ACKNOWLEDGMENT OF EXERCISE

         The undersigned ______________, hereby acknowledge receipt of the
"Notice of Exercise" from Comdisco, Inc., to purchase _______ shares of the
Series ______ Preferred Stock of _______________________, pursuant to the terms
of the Warrant Agreement, and further acknowledges that ________ shares remain
subject to purchase under the terms of the Warrant Agreement.

Company:

By:
     _______________________________________

Title:
        ____________________________________

Date:
       _____________________________________

                                      14
<PAGE>

EXHIBIT III

TRANSFER NOTICE

(To transfer or assign the foregoing Warrant Agreement execute this form and
supply required information. Do not use this form to purchase shares.)

FOR VALUE RECEIVED, the foregoing Warrant Agreement and all rights evidenced
thereby are hereby transferred and assigned to

______________________________________________________________
(Please Print)

whose address is
                 _____________________________________________

______________________________________________________________

Dated: _______________________________________________________

Holder's Signature: __________________________________________

Holder's Address: ____________________________________________

______________________________________________________________

Signature Guaranteed: ________________________________________

Transferee hereby agrees to be bound by the terms and conditions of this Warrant
Agreement

Acknowledged and Agreed:

By:
     ________________________________________________

Title:
        _____________________________________________

Date:
       ______________________________________________

NOTE: The signature to this Transfer Notice must correspond with the name as it
appears on the face of the Warrant Agreement, without alteration or enlargement
or any change whatever. Officers of corporations and those acting in a fiduciary
or other representative capacity should file proper evidence of authority to
assign the foregoing Warrant Agreement.

                                      15

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