Exhibit 10.21

Separation Agreement and General Release

     This Separation Agreement and General Release (hereinafter “Agreement”) is
entered into by and between Advanced Switching Communications, Inc. (referred to
as “the Company”) and Larry Kraft (referred to as “Employee”), who are
collectively referred to herein as the “Parties.”

     WHEREAS, the Parties now desire and agree to forever sever their employment
relationship and to fully and finally resolve any and all existing or potential
issues, claims, causes of action, grievances and disputes without any admission
of liability or finding or admission that any of Employee’s rights, under any
statute, claim or otherwise, were in any way violated. In consideration of the
mutual promises contained herein, and other good and valuable consideration as
hereinafter recited, the receipt and adequacy of which is hereby acknowledged,
the Parties, intending to be legally bound, agree as follows:

     1.     Employee notified the Company of his intent to resign on January 18,
2002 (the “Notification Date”) and that his resignation from the Company would
be effective on February 1, 2002 (the “Resignation Date”). From the Notification
Date through the Resignation Date, Employee agrees to provide transitional
services as they may be reasonably requested by the Company. Employee’s
employment at the Company will end on the Resignation Date. Employee recognizes
that for purposes of the continuation coverage requirements of group health
plans under the Consolidated Omnibus Budget Reconciliation Act of 1985 (COBRA),
as amended, and the group health provisions of any applicable state or local
law, a “qualifying event” occurs on Employee’s Resignation Date.

     2.     In exchange for the promises made by Employee herein and if Employee
executes and does not revoke this Agreement, the Company agrees to pay to
Employee an amount equal to Employee’s base pay (i.e., Employee’s monthly
salary) that Employee would have earned from February 2, 2002, to July 31, 2002
(the “Guaranteed Severance Period”), less all lawful deductions, which shall be
paid to Employee in accordance with the Company’s normal payroll schedule over
the period. The Company agrees to begin making the Guaranteed Severance payments
to Employee within fourteen (14) days after the “Effective Date,” as defined in
paragraph 15.

     3.     Employee agrees that on or before the Resignation Date, he will
surrender to the Company every item and every document in Employee’s possession
or control that is the Company’s property (including but not limited to keys,
records, computers, peripherals, computer files and disks, notes, memoranda,
models, inventory and equipment) or contains Company information, in whatever
form. Employee acknowledges and stipulates that all of the Company’s electronic
and telephonic communication systems, computers and other business equipment
including, but not limited to, computer systems, data bases, phone mail, modems,
e-mail, Internet access, Web sites, fax machines, techniques, processes,
formulas, mask works, source codes,

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programs, semiconductor chips, processors, memories, disc drives, tape heads,
computer terminals, keyboards, storage devices, printers and optical character
recognition devices, and any and all components, devices, techniques or
circuitry incorporated in any of the above and similar business devices (herein
collectively referred to as “Electronic Equipment” ), are the sole property of
the Company, and that any information transmitted by, received from, or stored
in such Electronic Equipment is also the Company’s property. Employee agrees
that, after his separation of employment from the Company, he shall not,
directly or indirectly, for himself or for any other person or entity, use,
access, copy, or retrieve, or attempt to use, access, copy, or retrieve, any of
the Company’s Electronic Equipment or any information on the Company’s
Electronic Equipment.

     4.     All reference requests from Employee’s prospective employers shall
be made in writing addressed to the attention of Laurie Foglesong, Director of
Human Resources. In response to such requests, the Department of Human Resources
will provide to prospective employers Employee’s dates of employment and job
title. The Department of Human Resources will not provide any additional
information to prospective employers regarding Employee’s employment without
Employee’s written consent.

     5.     The parties acknowledge that Employee’s entitlement to stock options
of the Company is governed by one or more stock option agreements (the “Option
Agreements”). The procedures and time restrictions for the exercise of vested
options are set forth in the Option Agreements. All unvested options previously
granted to Employee shall expire and terminate on the Resignation Date.

     6.     Employee agrees that he is not otherwise entitled to the severance
payments from the Company described in Paragraph 2 above during the Guaranteed
Severance Period. Employee understands that by signing this Agreement, he is
electing to receive those payments under the terms set forth in this Agreement.

     7.     As of the date Employee signs this Agreement, Employee represents
that he has been paid for all hours worked through the date of his signature and
has not suffered any on-the-job injury as of the date of his signature for which
he has not already filed a claim. As a part of this Agreement, the Company
agrees that all vacation pay, commissions, or overtime pay (if applicable) that
he is owed will be paid on February 15, 2002.

     8.     Employee agrees that, in consideration of the additional severance
payments described in paragraph 2 herein, he will, and hereby does, forever and
irrevocably release and discharge the Company, and its past, present and future,
affiliates, parents, subsidiaries, divisions, predecessors, purchasers, assigns,
representatives and successors, and its and their officers, directors,
employees, independent contractors, agents, (herein collectively referred to as
the “Releasees”) from any and all claims, causes of action, damages, defenses,
promises, judgments, and liabilities, known or unknown, whatsoever which he now
has, has had, or may have, whether the same be at law, in equity, or mixed, in
any way arising from or relating to any act, occurrence, or

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transaction before the date of this Agreement, including without limitation his
employment and separation of employment from the Company and any and all tax
related liabilities that may result from this Agreement. Employee expressly
acknowledges that this General Release includes, but is not limited to,
Employee’s intent to release the Company from tort and contract claims, wrongful
discharge claims, statutory claims, compensation claims, and claims of
discrimination or harassment based on age, race, color, sex, religion, handicap,
disability, national origin, ancestry, citizenship, marital status, retaliation
or any claim under Title VII of the Civil Rights Acts of 1964 and 1991 as
amended (42 U.S.C. §§ 2000e et seq.), Employee Retirement Income Security Act
(29 U.S.C. §§ 1001 et seq.), the Consolidated Omnibus Budget Reconciliation Act
of 1985 (29 U.S.C. §§ 1161 et seq.), the Americans With Disabilities Act (42
U.S.C. §§ 12101 et seq.), the Rehabilitation Act of 1973 (29 U.S.C. §§ 701 et
seq.), the Family and Medical Leave Act (29 U.S.C. §§ 2601 et seq.), the Worker
Adjustment and Retraining Notification Act (29 U.S.C. §§ 2101 et seq), and any
other federal, state or local law prohibiting employment discrimination or
relating to the employment relationship. This release does not include any
claims that cannot be waived by law. It is agreed and understood that this
release is a GENERAL RELEASE to be construed in the broadest possible manner
consistent with applicable law.

     9.     Employee agrees not to make or file any legal claims of any kind
against the Company or any of the Releasees in any federal, state or municipal
court, administrative agency or other tribunal concerning any claim that he/she
has released in this Agreement. Employee further agrees that no legal claims
have already been made or filed by or on behalf of Employee regarding any claims
that have been released by this Agreement. Employee further agrees and covenants
not to assist or encourage others in making or filing any legal claims of any
kind in any federal, state or municipal court against the Company or any of the
Releasees. If any administrative agency or other group files a legal claim of
any kind on Employee’s behalf against the Company or any of the Releasees
concerning any claim that Employee has released in this Agreement, Employee
waives any right to monetary recovery.

     10.     Employee agrees that the additional severance payments provided for
in this Agreement shall not be construed as an admission of any wrongdoing or
liability on the part of the Company and that any such wrongdoing or liability
is expressly denied. Employee represents that he has not assigned or transferred
to any person or entity any claim against the Company and that any such claim is
not assignable or transferable. The Parties agree that this Agreement shall be
governed by Virginia law, and that the state and/or federal courts in Virginia
shall have sole and exclusive jurisdiction and venue to hear any dispute
concerning this Agreement. If any terms of the provisions of this Agreement are
found null, void or inoperative, for any reason, the remaining provisions will
remain in full force and effect. The language of all parts of this Agreement
shall in all cases be construed as a whole, according to its fair meaning, and
not strictly for or against either of the Parties.

     11.     The Parties agree that this Agreement contains and comprises the
entire agreement and understanding of the Parties, that there are no additional
promises or terms

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of the Agreement among the Parties other than those contained herein, and that
this Agreement shall not be modified except in a writing signed by each of the
Parties hereto.

     This Agreement cancels and supersedes any prior employment agreements or
arrangements that Employee may have entered into with the Company or any of the
Releasees, except that the terms of paragraphs 6 and 7 of Employee’s Key
Employee Employment Agreement and the Option Agreement(s) (to the extent
applicable for vested options) entered into by Employee and Company shall remain
and continue in effect in accordance with the terms thereof.

     12.     Employee agrees that he will not disclose or cause to be disclosed
any negative, adverse or derogatory comments or information about the Company,
about any product or service provided by the Company, or about the Company’s
prospects for the future, except as required by law. Furthermore, Employee
hereby represents to the Company that he has made no such communication to any
public official, to any person associated with the media, or to any other person
or entity. Employee acknowledges that the Company relies upon this
representation in agreeing to enter into this Agreement.

     13.     Employee represents that he has read this Agreement, that he
understands all of its terms, that in executing this Agreement he does not rely
and has not relied upon any representation or statements made by any of the
Company’s agents, representatives, or attorneys with regard to the subject
matter, basis, or effect of the Agreement, and that he enters into this
Agreement voluntarily, of his own free will, without any duress and with
knowledge of its meaning and effect. Employee acknowledges that he has had a
reasonable amount of time in which to consult an attorney prior to executing the
Agreement, if he so chooses.

     14.     Employee understands that he/she has seven (7) days from the date
of his/her receipt of this Agreement, which was January 18, 2002, to sign it,
and that he/she may unilaterally waive this period at his/her election.
Employee’s signature on this Agreement constitutes an express waiver of the
seven (7) day period if affixed prior to the expiration of that period. By
signing this Agreement, Employee expressly acknowledges that his/her decision to
sign this Agreement was knowing and voluntary and of his/her own free will. The
Parties agree that any revisions or modifications to this Agreement, whether
material or immaterial, will not and did not restart this time period.

     15.     This Agreement shall become effective on the date on which the
Employee signs it and delivers it to Sherry Rhodes or Laurie Foglesong.

     16.     Employee also acknowledges that the Company may require him to
provide assistance to the Company in the investigation and/or defense of
potential or actual claims, charges or legal actions against the Company and
agrees to provide the requested assistance, which may include, but is not
limited to, interview(s), affidavit(s) and/or in person testimony. Employee
acknowledges that such requests may come during and/or after his Guaranteed
Severance Period and agrees to provide the assistance as and when required on a
reasonable basis. If Employee no longer resides in the Washington, D.C.
metropolitan area when his assistance is required and it is necessary

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that he be present in the metropolitan area to provide that assistance, the
Company will pay his reasonable travel and related expenses for such period as
his presence is required and will compensate him on a reasonable basis for his
time spent rendering such assistance.

     IN WITNESS WHEREOF, the parties have duly executed this Agreement as of the
day and year first written above.

      Employee Signature/Printed Name   Date     /s/ Lawrence A. Kraft   1/24/02

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    Lawrence A. Kraft         For: Advanced Switching Communications, Inc.  
Date     /s/ Sherry L. Rhodes   1/24/02

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    Sherry L. Rhodes     VP, General Counsel
& Secretary    

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