Document:

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                                                                    EXHIBIT 10.6
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  CONFIDENTIAL INFORMATION OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.
                       ASTERISKS (*) DENOTE SUCH OMISSIONS.

                                OMNIBUS AGREEMENT

THIS OMNIBUS AGREEMENT is made and entered into as of August 26, 1999 (the
"Effective Date"),

BY AND BETWEEN:

     NORTEL NETWORKS INC., a corporation organized and existing under the laws
     of the State of Delaware, having a place of business at 2221 Lakeside
     Blvd., Richardson, Texas 75082 (hereinafter referred to as "NNI"), on
     behalf of itself, and Nortel Networks Corporation and its other
     Subsidiaries (hereinafter collectively referred to as "Nortel").

AND:

     Avici Systems Inc., a corporation organized and existing under the laws of
     the State of Delaware having a place of business at 101 Billerica Avenue,
     North Billerica, MA 01862 (hereinafter referred to as "Avici").

WHEREAS, in early 1998, to meet anticipated market requirements for terabit
routers, Nortel and Avici entered into a comprehensive relationship
("Relationship"), which:

     (a)  was structured to expedite the time to market for Avici's Terabit
          Switch Router system ("TSR"); and

     (b)  included, among other components, technology collaboration, market
          collaboration and an equity investment by Nortel in Avici as more
          particularly described in the Prior Agreements; and,

WHEREAS, the Parties have agreed to alter salient elements of the Relationship;

NOW, THEREFORE, in consideration of the foregoing and the mutual promises and
covenants hereinafter set forth, the Parties agree as follows:

1.  DEFINITIONS

    1.1.  Capitalized terms used herein without definition have the meanings
          ascribed to them in Appendix I annexed hereto.

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2.  TERMINATION OF AGREEMENTS

    2.1.  Distribution Agreement. The Distribution Agreement is hereby
          terminated by mutual agreement of the Parties. The Distribution
          Agreement shall be of no further force or effect; provided, however,
          that the provisions enumerated in Section 28 of the Distribution
          Agreement shall survive termination of the Distribution Agreement as
          set forth therein.

    2.2.  Technology License Agreement.

          (a)  The Technology License Agreement is hereby terminated by mutual
               agreement of the Parties. The Technology License Agreement shall
               be of no further force or effect; provided, however, that the
               provisions enumerated in Section 18.10 of the Technology License
               Agreement shall survive termination of the Technology License
               Agreement as set forth therein.

          (b)  Notwithstanding Section 2.2(a) of this Agreement or Section 18.10
               of the Technology License Agreement, upon termination of the
               Technology License Agreement Section 18.6 of the Technology
               License Agreement shall terminate and be of no further force or
               effect.

    2.3.  Assistance Agreement.

          (a)  Notwithstanding anything to the contrary in the Assistance
               Agreement or any Activity Description, the Assistance Agreement
               shall terminate by mutual agreement of the Parties only upon the
               termination of the final Activity Description listed in Section
               3.1 of this Agreement, at which time the Assistance Agreement
               shall be of no further force or effect; provided, however, that
               the provisions enumerated in Section 4.11 of the Assistance
               Agreement shall survive termination of the Assistance Agreement
               as set forth therein.

          (b)  Notwithstanding Section 2.3(a) of this Agreement or Section 4.11
               of the Assistance Agreement, upon termination of the Assistance
               Agreement, Sections 4.9 and 6.3 of the Assistance Agreement shall
               terminate and be of no further force or effect.

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3.  PERFORMANCE OF ACTIVITY DESCRIPTIONS, CONFIDENTIAL INFORMATION, AND LICENSES

    3.1.  Performance. For each of the Assistance Activities listed below, and
          subject to the terms and conditions of this Section 3, Nortel and
          Avici shall perform such Assistance Activity in accordance with the
          terms and conditions set out in the associated Activity Description:

          (a)  The Assistance Activity described in Activity Description 98-011
               ("Flute ASIC Part 2");

          (b)  The Assistance Activity described in Activity Description 98-017
               ("EMC Module and Shelf Design Adaptation"), as amended by an
               "Amendment #1 to Activity Description 98-017", dated as of
               July 2, 1999;

          (c)  The Assistance Activity described in Activity Description 98-018
               ("TSR Product Line Management"), provided that Nortel shall be
               able to remove its employee, Gerald de Grace, from this
               Assistance Activity at any time after August 30, 1999; and

          (d)  The Assistance Activity described in Activity Description 98-021
               ("Flute ASIC Part 3").

    3.2.  License Grant With Respect to Nortel Background IPR.  With respect to
          Nortel Background IPR contained in Contracted Work and such other
          assistance as Nortel may have provided Avici in connection with the
          development of Contracted Work (only as such assistance is described
          under the Activity Descriptions), Nortel hereby grants to Avici a non-
          exclusive, worldwide, royalty-free, perpetual, irrevocable and
          transferable license, with the right to sublicense, to use, copy,
          modify, have modified, enhance, improve, display, distribute (directly
          or indirectly), make derivative works of, license and otherwise
          commercially exploit such Nortel Background IPR and Nortel assistance
          solely in connection with the development, manufacture, marketing,
          sale and support of Avici Products.

    3.3.  Confidential Information.  Except as provided in Sections 3.4, 3.5 and
          4.1 of this Agreement, each Party ("Receiving Party") represents and
          warrants that it shall not use the Confidential Information,
          Intellectual Property Rights or Technology of the other Party
          ("Disclosing Party") for any purpose whatsoever, including, without
          limitation, for research or product development purposes, and without
          limiting the generality of the foregoing, each Party represents and
          warrants that it has not incorporated, and shall not incorporate, the
          Confidential Information, Intellectual Property Rights, or Technology
          of the other Party in any of its products or technology. Upon
          completion of each Activity Description listed in Section 3.1 of this
          Agreement,

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          Confidential Information of Disclosing Party that is no longer
          required to be retained for the purposes set forth in Section 4.1 of
          this Agreement shall be returned to Disclosing Party in accordance
          with such Section 4.1.

    3.4.  Notwithstanding anything else in this Agreement or any of the Prior
          Agreements, neither Party shall be bound by any obligations
          restricting disclosure, return, and use set forth in this Agreement or
          any of the Prior Agreements with respect to Confidential Information,
          or any part thereof, which:

       (a)  was known by Receiving Party prior to disclosure, as evidenced by
            its business records;

       (b)  was lawfully in the public domain prior to its disclosure, or
            becomes publicly available other than through a breach of this
            Agreement;

       (c)  was disclosed to Receiving Party by a third party provided such
            third party or any other party from whom such third party receives
            such information is not in breach of any confidentiality obligation
            in respect of such information;

       (d)  is independently developed by Receiving Party, as evidenced by its
            business records; or

       (e)  is disclosed when such disclosure is compelled pursuant to legal,
            judicial, or administrative proceeding, or otherwise required by
            law, subject to Receiving Party giving all reasonable prior notice
            to Disclosing Party to allow it to seek protective or other court
            orders.

  3.5  Subject to Section 3.4, notwithstanding anything else in this Agreement
       or any of the Prior Agreements, nothing in this Agreement or the Prior
       Agreements shall be construed as precluding or preventing Receiving Party
       from accidentally using the Residuals of Disclosing Party's Confidential
       Information for any purpose, including use in the development, testing,
       manufacture, acquisition, marketing and maintenance of Receiving Party's
       products and services, provided that this right with regard to Residuals
       does not represent, and shall in no event be deemed to grant to either
       Party, a license either expressly, by implication, estoppel or otherwise
       under the other Party's patents, copyrights, mask works or other United
       States or foreign intellectual property rights.  This Section 3.5 will
       not be interpreted to prevent a party from making the decision not to
       pursue a particular development path based on knowledge that it would be
       inefficient or uneconomical to do so.

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4.  RETURN OF MATERIALS AND EQUIPMENT

    4.1.  Subject to Section 3.4 of this Agreement, except to the extent
          retention of Confidential Information is required by either Party (a)
          to fulfill its obligations under Section 3.1 hereof, (b) to fulfill
          its obligations under any agreement between the Parties not terminated
          by this Agreement, including without limitation, the EMC Supply
          Agreement dated as of May 5, 1999, (c) to exercise any surviving
          license of Intellectual Property Rights granted pursuant to this
          Agreement, the Assistance Agreement or the Technology License
          Agreement, each Party shall, within four (4) weeks following the
          Effective Date:

          (a)   return to the other Party, or destroy, at the other Party's
                option, all Confidential Information, Intellectual Property
                Rights, and Technology of the other Party in its possession or
                control, and other materials (including any notes, extracts,
                summaries or analyses), whether in written or electronic form,
                that disclose or embody such Confidential Information,
                Intellectual Property Rights, and Technology; and

          (b)   certify in writing its compliance with the foregoing provision.

       Notwithstanding anything in this Section 4.1, each Party may retain one
       copy of the Confidential Information for archival purposes only, which
       copy can only be accessed to resolve disputes.

  4.2  Return of TSR Equipment.  Without limiting the provisions of Section 4.1
       of this Agreement, Nortel shall promptly return all TSR equipment (the
       cost of such return to be borne [CONFIDENTIAL TREATMENT REQUESTED/*/% by
       Avici and [CONFIDENTIAL TREATMENT REQUESTED/*/% by Nortel), other than
       the GST Units, Beta Unit and Demo Unit (each as defined in Section 8 of
       this Agreement), shipped by Avici to Nortel or to a third party at the
       request of Nortel. In consideration of the costs incurred by Avici in
       connection with the return of all such TSR equipment, Nortel will
       transfer all of its right, title and interest in and to the GST Units to
       Avici effective upon the execution of this Agreement. Nortel shall have
       no further right, title or interest in or to the Beta Unit and the GST
       Units following the execution of this Agreement.

5.  COVENANTS

    5.1.  Filing of Restated Certificate of Incorporation. Nortel shall execute
          the Stockholders Consent attached hereto as Appendix II and shall
          further cooperate with Avici to allow

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/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES ACT OF 1933, AS AMENDED.

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          Avici to cause the filing of the Restated Certificate of Incorporation
          with the Secretary of State of the State of Delaware.

    5.2.  Further Assurances.  Each Party agrees to execute and deliver such
          other documents, certificates, agreements and other writings and to
          take such other actions as may be necessary or desirable in order to
          consummate or implement expeditiously the transactions contemplated by
          this Agreement.

    5.3.  INM Agreement.  The parties shall enter into a Nortel INM Agreement
          whereby Nortel will extend its Integrated Network Manager (INM)
          product, such that the product will include interfaces that will allow
          it to manage the Avici TSR. The terms of the agreement shall be no
          less favorable to Avici than the terms Nortel offers to other
          nonaffiliated third parties offering Nortel similarly valued
          consideration in return for similar INM extensions. The functionality
          provided within INM for the TSR shall be no less than that provided
          for the Versalar25000 or Cisco12000 and other similar products, unless
          functionality differences are attributable to differences in the
          features supported by such products. Nortel will provide ongoing INM
          updates, and will make reasonable efforts to promptly update INM as
          Avici provides new TSR MIBs. Avici shall have the right to sell the
          TSR-related loads of INM to its customers. Provided INM is given a
          reasonable amount of time to complete INM-development work relating to
          the TSR, completion of such development must be complete before the
          associated product release of the TSR. Subject to the satisfactory
          completion and delivery of the INM tool to Avici, the cost to Avici
          for the tool will be [CONFIDENTIAL TREATMENT REQUESTED]/*/, provided
          that the minimum payment due from Avici to Nortel shall be
          [CONFIDENTIAL TREATMENT REQUESTED]/*/

    5.4.  Avici hereby grants Nortel, until the sooner of the execution of the
          Nortel INM Agreement or six months from the Effective Date, a non-
          exclusive, worldwide, royalty-free, license in the MIB-information
          relating to the TSR, with the right to distribute (directly or
          indirectly), and license such MIB-information, provided that the MIB
          information is distributed and licensed only in an non-operational
          state and only as part of its INM product. Upon execution of the INM
          Agreement, this license shall terminate. Notwithstanding anything in
          this grant, and without limiting the generality of the foregoing,
          Nortel cannot use the MIB-information except when using the INM
          product to manage the TSR.

    5.5.  Employee Notification. Promptly following the execution of this
          Agreement, each Party shall notify those of its employees who have had
          access to the Confidential Information of the other Party of their
          obligations under this Agreement, including without limitation, the
          obligations set forth in Section 3 hereof.

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/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES ACT OF 1933, AS AMENDED.

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6.  CUSTOMER ISSUES

    6.1.  Systems Integrator. For three (3) months following the Effective Date,
          at the request of GST/NTON, Qwest and any other customer that is
          mutually agreed upon by the Parties ("Customer"), Nortel shall act as
          a Systems Integrator of Avici Products with respect to such Customer.
          In such event,:

          (a)  Customer shall enter into (i) a formal or other binding agreement
               directly with Avici to purchase/license the desired Avici
               Products and (ii) a formal or other binding agreement
               ("Integration Agreement") directly with Nortel that governs
               Nortel's role as a Systems Integrator; and,

          (b)  Provided that Avici consents to the terms of the Integration
               Agreement, which consent shall not be unreasonably withheld,
               Avici shall in good faith cooperate with and assist Nortel in
               meeting Nortel's obligations under the Integration Agreement, and
               any other agreement that is ancillary to the Integration
               Agreement.

7.  PERSONNEL MATTERS

    7.1.  For a period of twelve (12) months following July 1, 1999, neither
          Party (the "Non-Hiring Party") shall:

          (a)  solicit for employment, directly or indirectly, whether as an
               employee, agent, contract worker, independent contractor or any
               individual in a similar capacity, any employee of the other
               Party, provided however, and except as set forth in section
               7.1(b), that this Section 7.1(a) shall not prevent either Party
               from soliciting such other Party's employees if such solicitation
               takes place solely by means of a general solicitation of
               employment, by advertisements, or by engaging firms to conduct
               searches that are not specifically directed towards employees of
               the other Party any employee of the other Party; and,

          (b)  offer employment to, or hire, directly or indirectly, whether as
               an employee, agent, contract worker, independent contractor or in
               any similar capacity, any employee of the other Party with whom
               the Non-Hiring Party has had substantial direct contact prior to
               or after the Effective Date of this Agreement, including the
               employees restricted under Section 7.2 of this Agreement.

    7.2.  No Nortel employee, agent, contract worker, contractor or other
          individual listed on Appendix III hereto shall work on (or consult
          with any individual working on) the design, development, marketing or
          manufacture of high speed internet routers and

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       router switches, or products related thereto for the period of time set
       forth opposite each such individual's name on Appendix III attached
       hereto, except as set forth in Appendix III.

8.  SALE OF TSR EQUIPMENT AND PAYMENT

    8.1.  Sale of TSR Equipment. In connection with the Relationship, Nortel
          confirms that it has purchased [CONFIDENTIAL TREATMENT REQUESTED]/*/
          TSR units from Avici, to be used by GST/NTON (the "GST Units"). Nortel
          shall pay Avici [CONFIDENTIAL TREATMENT REQUESTED]/*/ for the GST
          Units. The GST Units were purchased on an "as is" basis and the sale
          is final and unconditional.

    8.2.  Payment for Beta Unit at Qwest. In connection with the Relationship,
          Nortel and Avici placed one (1) Avici TSR beta test unit (the "Beta
          Unit") at Qwest. Nortel shall pay Avici $[CONFIDENTIAL TREATMENT
          REQUESTED]/*/. All right, title and interest to the Beta Unit shall
          vest exclusively in Avici.

    8.3.  Sale of TSR Demo Unit. In connection with the Avici TSR demonstration
          unit (the "Demo Unit") ordered by Nortel from Avici and shipped to
          Nortel in Q2 1999, Nortel shall pay Avici [CONFIDENTIAL TREATMENT
          REQUESTED]/*/. This sale is final and unconditional, except that (i)
          [CONFIDENTIAL TREATMENT REQUESTED]/*/ and (ii) Nortel shall use the
          Demo Unit solely for the purpose of interoperability testing and for
          no other purpose.

    8.4.  Payment. The amounts owed by Nortel to Avici shall be currently due
          and payable and may, at the option of Nortel, be offset against all
          amounts owed by Avici to Nortel as of the date of this Agreement for
          services provided by Nortel to Avici. Notwithstanding anything to the
          contrary in any agreement executed by and between Nortel and Avici,
          all amounts owed by Avici to Nortel as of the date of this Agreement
          (other than amounts that have been offset pursuant to the preceding
          sentence), shall be payable upon the earlier to occur of thirty (30)
          days following the first closing of the next round of equity financing
          of Avici or ninety days following the date of this Agreement.

9.  RELEASE

    9.1.  In consideration of mutual releases and of other good and valuable
          consideration, the receipt and sufficiency of which are hereby
          acknowledged, and in reliance upon the representations and warranties
          and mutual promises and covenants contained in this Agreement, Avici,
          on behalf of itself and each of its corporate parents, subsidiaries
          and affiliates (individually and collectively, "AVICI RELEASOR")
          generally, unconditionally and irrevocably releases and discharges
          Nortel, and its corporate

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/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES ACT OF 1933, AS AMENDED.

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          parents, subsidiaries and affiliates and all of their respective
          present and former directors, officers, employees, agents, successors,
          assigns, transferees and beneficiaries (individually and collectively,
          "NORTEL RELEASEE") from all actions, causes of action, accounts,
          agreements, bonds, bills, covenants, contracts, controversies, claims,
          damages, demands, debts, dues, extents, executions, judgments,
          liabilities, obligations, promises, predicate acts, reckonings,
          specialties, suits, sums of money, trespasses and variances
          whatsoever, whether known or unknown, in law, admiralty or equity
          which each AVICI RELEASOR ever had, now has, or may at any time or
          from time to time have, arising out of or by reason of any matter,
          cause or thing whatsoever from the beginning of the world to the
          Effective Date, which would not have occurred but for the Relationship
          (collectively, "Actions"), including, without limiting the foregoing,
          any Action arising from or relating to:

          (a)  any negotiation, execution, termination, performance or lack of
               performance under:

               .  any of the Prior Agreements, or

               .  any other written or oral contracts in effect between any
                  AVICI RELEASOR and any NORTEL RELEASEE;

          (b)  Nortel's cessation of the distribution of Avici's products;

          (c)  any NORTEL RELEASEE not offering to acquire control of Avici; and

          (d)  Nortel's cessation of the performance, negotiation, or
               contemplation of any commenced or proposed activity, including
               any Assistance Activity, relating to the Assistance Agreement.

          This Section 9.1 does not apply to any Action that an AVICI RELEASOR
          may have against a NORTEL RELEASEE arising from or relating to:

          (e)  any obligation of Nortel set forth in this Agreement;

          (f)  a material misappropriation or infringement by a NORTEL RELEASEE
               of a material element of Avici Technology and/or Avici's
               Intellectual Property Rights; and

          (g)  the sections that shall survive the termination of each of the
               Distribution Agreement, Technology License Agreement and
               Assistance Agreement, respectively, as set out in Section 2
               hereunder, which sections include without limitation Section 17
               of the Technology License Agreement, Section 17 of the
               Distribution Agreement, and Section 9 of the Assistance
               Agreement.

     9.2. In consideration of mutual releases and of other good and valuable
          consideration, the receipt and sufficiency of which are hereby
          acknowledged, and in reliance upon the representations and warranties
          and mutual promises and covenants contained in this

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          Agreement, NNI, on behalf of itself and each of its corporate parents,
          subsidiaries and affiliates (individually and collectively, a "NORTEL
          RELEASOR") generally, unconditionally and irrevocably releases and
          discharges Avici, and its corporate parents, subsidiaries and
          affiliates and all of their respective present and former directors,
          officers, employees, agents, successors, assigns, transferees and
          beneficiaries (collectively, "AVICI RELEASEE") from all actions,
          causes of action, accounts, agreements, bonds, bills, covenants,
          contracts, controversies, claims, damages, demands, debts, dues,
          extents, executions, judgments, liabilities, obligations, promises,
          predicate acts, reckonings, specialties, suits, sums of money,
          trespasses and variances whatsoever, whether known or unknown, in law,
          admiralty or equity which each NORTEL RELEASOR ever had, now has, or
          may at any time or from time to time have, arising out of or by reason
          of any matter, cause or thing whatsoever from the beginning of the
          world to the Effective Date, which would not have occurred but for the
          Relationship (collectively, "Actions"), including, without limiting
          the foregoing, any Action arising from or relating to:

          (a)  any negotiation, execution, termination, performance or lack of
               performance under:

               .  any of the Prior Agreements, or

               .  any other written or oral contract in effect between any
                  NORTEL RELEASOR and any AVICI RELEASEE.

          This Section 9.2 does not apply to any Action that a NORTEL RELEASOR
          may have against an AVICI RELEASEE arising from or relating to:

          (b)  any obligation of Avici set forth in this Agreement;

          (c)  a material misappropriation or infringement by an AVICI RELEASEE
               of a material element of Nortel Technology and/or Nortel's
               Intellectual Property Rights, except for any Claim by a NORTEL
               RELEASOR for acts occurring before the Effective Date of this
               Agreement with regard to Avici's "Nutcracker" customer support
               testing software, which Claim, if any, is expressly released
               hereunder; and

          (d)  the sections that shall survive the termination of each of the
               Distribution Agreement, Technology License Agreement and
               Assistance Agreement, respectively, as set out in Section 2
               hereunder, which sections include without limitation Section 17
               of the Technology License Agreement, Section 17 of the
               Distribution Agreement, and Section 9 of the Assistance
               Agreement.

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10.  NOTICES

     10.1.  Any and all notices or other information to be provided by one Party
            to another shall be in writing and shall be deemed sufficiently
            given when sent by prepaid registered or certified first-class mail,
            overnight courier, facsimile transmission with confirming receipt,
            or hand delivery to the other Party at the following address:

            If to Nortel:

            Nortel Networks Corp.
            8200 Dixie Road, Suite 100
            Brampton, Ontario L6T 5P6
            Canada
            Fax No.: (905) 863-8261

            Attention: Mergers and Acquisitions Department

            Copy to:

            Nortel Networks Inc.
            200 Athens Way
            Nashville, TN 37228
            Fax No.: (615) 734-4067

            Attention: Legal Department

            If to Avici:

            Avici Systems Inc.
            101 Billerica Avenue
            North Billerica, MA  01862
            Fax No.: (978) 964-2100

            Attention:  President and Chief Executive Officer

            Copy to:

            Testa, Hurwitz & Thibeault, LLP
            125 High Street
            Boston, MA  02110
            Fax No.:  (617) 248-7100

            Attention:  John A. Meltaus, Esq.

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           or such other address as such Party may designate by giving thirty
           (30) days prior written notice.

    10.2.  Such notices shall be deemed to have been received five (5) business
           days after mailing if sent by mail, and the following business day if
           sent by facsimile transmission, overnight courier or delivered by
           hand.

11. GENERAL

    11.1.  No agency, partnership, joint venture or employment relationship is
           or shall be created by virtue of this Agreement.

    11.2.  No Party shall use the name of the other in any advertising, public
           relations or media release without the prior written consent of the
           other Party. The Parties agree that the terms and conditions of this
           Agreement shall be treated as Confidential Information which shall
           not be disclosed to any third party without the prior written consent
           of the non-disclosing Party, provided, however, that each Party may
           disclose the terms and conditions of the Agreement: (i) as required
           by any court or other governmental body; (ii) as otherwise required
           by law; (iii) to legal counsel of the Parties; (iv) in confidence, to
           accountants, banks, investors and other financing sources and their
           advisors; (v) in confidence, in connection with the enforcement of
           this Agreement or rights under this Agreement; or (vi) in confidence,
           in connection with an actual or proposed merger, acquisition, or
           similar transaction.

    11.3.  No Party shall have the right to delegate any duty or assign any
           right hereunder without the prior written consent of the other Party,
           provided, however, that Avici may assign all of its rights hereunder
           as part of a sale of all or substantially all of the assets of Avici.
           Notwithstanding the foregoing, NNI shall have the right to delegate
           or assign this Agreement or any right hereunder to Nortel Networks
           Corporation or any Subsidiary of Nortel Networks Corporation without
           the consent of Avici. A merger, consolidation or sale of more than
           fifty percent (50%) of the equity securities of Avici shall not be
           deemed to be an assignment for the purposes of this Agreement.

    11.4.  If the performance by a Party of any of its obligations under this
           Agreement shall be interfered with by reason of any circumstances
           beyond the reasonable control of that Party, including without
           limitation, fire, explosion, acts of God, war, revolution, civil

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          commotion, unavailability of supplies or sources of energy, power
          failure, breakdown of machinery, or labor difficulties, including
          without limitation, strikes, slowdowns, picketing or boycotts, then
          that Party shall be excused from such performance for a period equal
          to the delay resulting from the applicable circumstances and such
          additional period as may be reasonably necessary to allow that Party
          to resume its performance. With respect to labor difficulties as
          described above, a Party shall not be obligated to accede to any
          demands being made by employees or other personnel. This provision
          shall not apply to the performance of any payment obligations.

   11.5.  The attached Appendices form part of this Agreement. This Agreement
          may not be amended or modified except in a writing executed by the
          duly authorized representatives of the Parties. Neither Party shall be
          deemed, by any act or omission, to have waived any of its rights or
          remedies hereunder unless such waiver is in writing and signed by the
          waiving Party, and then only to the extent specifically set forth in
          such writing. The waiver by either Party of a breach of any provision
          of this Agreement by the other Party will not operate or be
          interpreted as a waiver of any other or subsequent breach.

   11.6.  In the event that any provision of this Agreement is found to be
          invalid, voidable or unenforceable, the Parties agree that unless such
          provision materially affects the entire intent and purpose of this
          Agreement, such invalidity, voidability or unenforceability shall
          affect neither the validity of this Agreement nor the remaining
          portions herein, and that the provisions in question shall be deemed
          to be replaced with a valid and enforceable provision most closely
          reflecting the intent and purpose of the original provision. In the
          event that any provision of this Agreement is found to be invalid,
          voidable or unenforceable, and such provision materially affects the
          entire intent and purpose of this Agreement, the Parties shall
          negotiate in good faith to enter into a new agreement replacing this
          Agreement. In the event that the Parties are unable to enter into a
          new agreement replacing this Agreement, this Agreement shall
          terminate.

   11.7.  This Agreement and the surviving provisions of the Prior Agreements as
          amended by this Agreement constitute the entire agreement between the
          Parties and supersede all prior written or oral agreements between the
          Parties concerning the subject matter hereof.

   11.8.  This Agreement and all matters related hereto shall be governed by and
          construed in accordance with the laws of the Commonwealth of
          Massachusetts without regard to conflict of laws principles, and the
          Parties consent to personal and exclusive jurisdiction and venue in
          the state and federal courts sitting in Suffolk and Middlesex
          counties, Massachusetts. Process may be served on either Party by
          using the notice provisions of Section 10 above.

                                       13
<PAGE>

    11.9.  Each Party represents and warrants that it has obtained all rights
           and waivers necessary to grant the rights, title and interests
           granted to the other Party under this Agreement.

                                       14
<PAGE>

IN WITNESS WHEREOF, the Parties have executed this Agreement as of the date set
forth above.

Nortel Networks Inc.                      Avici Systems Inc.

/s/ Klaus M. Buechner                     /s/ Surya Panditi
--------------------                      -----------------
Authorized Signature                      Authorized Signature

Klaus M. Buechner,
S.V.P. Corporate Strategy & Alliances     Surya Panditi, President & CEO
-------------------------------------     ------------------------------
Name and Title                            Name and Title

                                       15
<PAGE>

                            APPENDIX I: DEFINITIONS
                            -----------------------

"Activity Description" has the meaning given to that term in the Assistance
Agreement;

"Agreement" means this document, including all Appendices attached hereto and
any amendments as may be, from time to time, mutually agreed in writing and
signed by authorized representatives of the Parties;

"Assistance Activity" has the meaning given to that term in the Assistance
Agreement;

"Assistance Agreement" means the Nortel - Avici Assistance Agreement executed by
and between Nortel and Avici, dated as of January 28, 1998 and terminated
pursuant to the terms and conditions of this Agreement. The Assistance
Agreement, pursuant to Section 2.1 thereof, shall include all Activity
Descriptions executed by and between the Parties, including any such Activity
Descriptions executed pursuant to this Agreement;

"Avici" means Avici Systems Inc. and all of its Subsidiaries;

"Avici Product" means any present or future product which Avici develops,
licenses or sells, and shall include any enhancement, replacement, modification
or evolution of any such Avici Product or any portions thereof;

"Avici Technology" has the meaning given to that term in the Technology License
Agreement;

"Background IPR" has the meaning given to that term in the Assistance Agreement;

"Confidential Information" means any business, marketing, technical, scientific
or other information obtained from any Party which, at the time it is obtained,
is designated as confidential (or like designation), is disclosed in
circumstances of confidence, or would be understood by the Parties, exercising
reasonable business judgment, to be confidential.  Confidential Information
shall include, without limitation, the terms and conditions of this Agreement;

"Contracted Work" has the meaning given to that term in the Assistance
Agreement;

"Distribution Agreement" means the Distribution Agreement executed by and
between Nortel and Avici, dated as of January 28, 1998 and terminated pursuant
to the terms and conditions of this Agreement;

"Effective Date" means the date that this Agreement was made and entered into as
set forth in the first sentence of this Agreement;

                                       16
<PAGE>

"Foreground IPR" has the meaning given to that term in the Assistance Agreement;

"Intellectual Property Rights" means all rights in any invention, discovery,
improvement, utility model, copyright, industrial design or mask work right, and
all rights of whatsoever nature in computer software and data, Confidential
Information, trade secrets or know-how, and all intangible rights or privileges
of a nature similar to any of the foregoing, in every case in any part of the
world and whether or not registered, and shall include all rights in any
applications and granted registrations for any of the foregoing.  Intellectual
Property Rights shall include the subject matter thereof;

"NNI" means Nortel Networks Inc.;

"Nortel Product" means any present or future product which Nortel develops,
licenses or sells, and shall include any enhancement, replacement, modification
or evolution of any such Nortel Product or any portions thereof;

"Party" means either Nortel or Avici; "Parties" means both Nortel and Avici;

"PLM Function" means a function that involves the following activities: (1)
Develop the product strategy, business case, and perform product business
analysis (2) Work with marketing and sales to bring in project values to the
customer value proposition (3) Develop and manage project specifics as it
relates to product portfolio (4) Assist Product Development to develop and
maintain the detailed feature specifications required to satisfy customer needs
(5) Coordination of PLM team support (6) Feed-in and feed-out project
information into the LOB product-line manager (7) Manage cross-Project
dependencies and opportunities (8) Facilitate cross-line-of-business
opportunities and alliances (9) Select field trial and lead customers (10)Work
with Marketing and Sales departments to ensure the lead customer provides
adequate feature coverage (11) Collateral and Pre-Sales Support;

"Prior Agreements" means the Distribution Agreement, Technology License
Agreement, Assistance Agreement, Series C Convertible Preferred Stock Purchase
Agreement dated as of January 28, 1998 by and between Avici and Nortel, EMC
Module Supply Agreement dated as of May 5, 1999 by and between Avici and Nortel,
Series D Convertible Preferred Stock Purchase Agreement dated as of January 28,
1998 by and among Avici, Nortel and the other Purchasers named therein, and the
Third Amended and Restated Investor Rights Agreement dated as of March 31, 1998
by and among Avici, the Investors named therein and the Founders named therein;

"Product Development Work" has the meaning given to that term in the Assistance
Agreement;

"Residuals" means information of a general nature, such as general knowledge,
ideas or concepts,

                                       17
<PAGE>

that is retained in the unaided memories of the Receiving Party's employees
(without reference to any material which is written, stored in magnetic,
electronic or physical form or otherwise fixed), as the result of exposure to
the Disclosing Party's Confidential Information. An employee's memory is unaided
only if the employee has not memorized the Disclosing Party's Confidential
Information for the purpose of retaining and subsequently improperly using or
improperly disclosing it. Residuals shall not include the unique Avici
implementations (as of the date of the completion of the last Activity
Description set forth in Section 3.1 of this Agreement) of the following
technologies:

   (i)    forwarding/packet classification/scheduling technology including:
          .  Avitri - Search Tree Builder;
          .  Forwarding engine implementation;
          .  Scheduler that enables scaling, multi-cast and composite trunking;
             and,
          .  Distributed source routing for internal fabric routing;
          .  Methods for maintaining packet order while performing the lookup
             in parallel on multiple lookup engines;

   (ii)   switch fabric technology including:
          .  toroidal mesh with passive backplane interconnect;
          .  distributed fabric control; and,
          .  the topology, flow control mechanisms, including virtual networks,
             buffer organization, insertion and extraction mechanisms, fabric
             router architecture and logical organization, signaling methods,
             error control methods employed in the Avici routing fabric, packet
             division into flits and wormhole routing;
          .  methods for distributing network timing, as long as such methods do
             not include Technology, Confidential Information, or Intellectual
             Property Rights belonging to Nortel.

   (iii)  quality of service (QOS) technology including:
          .  Unique implementation of RED, WFQ, GPRA/GPRS;
          .  Unique queue management and organization;
          .  Fabric priority and tournament search

   (iv)   composite trunking; and,

   (v)    packet descriptor layer definition and implementation.

"Restated Certificate of Incorporation" means the Restated Certificate of
Incorporation of Avici Systems Inc., which is attached as an exhibit to the
Stockholders Consent;

"Stockholders Consent" means the Avici Systems Inc. Written Consent of
Stockholders in Lieu of a Special Meeting, which is attached to the Agreement as
Appendix II;

                                       18
<PAGE>

"Schedule C Entries" means all the descriptions of technology licensed by Nortel
to Avici under the Technology License Agreement, which descriptions were
executed by the Parties in accordance with section 7.2 of the Technology License
Agreement, prior to the Effective Date;

"Subsidiary" of a Party means any corporation or other legal entity in which
that Party directly or indirectly owns or controls, and continues to own or
control, fifty percent (50%) or more of the voting stock or shares;

"Systems Integrator" means a person, corporation or other legal entity that
plans, coordinates, integrates, manages, schedules, tests, improves and/or
maintains a network, where such network comprises communications and other sorts
of equipment and systems that have been sourced from a plurality of vendors;

"Technology" has the meaning given to that term in the Technology License
Agreement;

"Technology License Agreement" means the Technology License and Agreement
executed by and between Nortel and Avici, dated as of January 28, 1998 and
terminated pursuant to the terms and conditions of this Agreement.  The
Technology License Agreement, pursuant to Section 7.2 thereof, shall include all
Schedule C Entries executed by and between the Parties prior to the Effective
Date; and

"Avici Terabit Router" has the meaning given to that term in the Technology
License Agreement.

                                       19
<PAGE>

                                  APPENDIX II
                                  -----------

                               AVICI SYSTEMS INC.

   Written Consent of Stockholders in Lieu of Special Meeting of Stockholders
   --------------------------------------------------------------------------

                        Effective as of August __, 1999

     The undersigned stockholders of Avici Systems Inc., a Delaware corporation
(the "Corporation"), do hereby adopt, pursuant to Sections 228, 242 and 245 of
the General Corporation Law of the State of Delaware, the following resolutions
by consent and without a meeting:

Restated Certificate of Incorporation

RESOLVED:   That, the Restated Certificate of Incorporation of the
            Corporation in the form attached hereto as Exhibit A (the
            "Certificate of Incorporation") be filed with the Division of
            Corporations, Department of State in the State of Delaware and that
            such Restated Certificate of Incorporation is hereby adopted,
            approved, ratified and confirmed in all respects.

General
-------

RESOLVED:   That the officers of the Corporation hereby are, and each of
            them singly hereby is, authorized to execute and deliver all such
            instruments, make such payments, make all such filings and do all
            such other acts and things as in their opinion, or in the opinion of
            any of them, may be necessary or appropriate in order to carry out
            the intents and purposes of the foregoing resolutions.

     The undersigned further direct that this Consent shall be filed in the
minute books of the Corporation with the minutes of the meetings of the
stockholders.  This written consent may be signed in separate counterparts and
is effective as of the date first written above.

                              By:
                                 -----------------------------------
                                 Print Name of Stockholder:

                                       20
<PAGE>

                                  APPENDIX III
                                  ------------

NORTEL EMPLOYEE                END AND NATURE OF RESTRICTION
--------------------------------------------------------------------------------

[CONFIDENTIAL TREATMENT        March 31, 2000, as set out in section 7.2 except
REQUESTED]/*/                  that [CONFIDENTIAL TREATMENT REQUESTED]/*/ may
                               work on (or consult with any individual working
                               on) any Nortel Product that does not directly
                               compete with the TSR, in a PLM Function.
                               Notwithstanding anything to the contrary in this
                               Agreement, Nortel's Bay RS Product shall not be
                               considered a competing product for the purposes
                               of this restriction.

[CONFIDENTIAL TREATMENT        June 30, 2000
REQUESTED]/*/

[CONFIDENTIAL TREATMENT        March 31, 2000, as set out in section 7.2,
REQUESTED]/*/                  except that [CONFIDENTIAL TREATMENT REQUESTED]/*/
                               may work on (or consult with any individual
                               working on) any Nortel Product created under
                               Nortel's Equinox Project, provided such Nortel
                               Product does not involve interconnect technology
                               based on or related to toroidal mesh or modified
                               toroidal mesh architectures.

[CONFIDENTIAL TREATMENT        March 31, 2000
REQUESTED]/*/

[CONFIDENTIAL TREATMENT        September 30, 1999
REQUESTED]/*/

[CONFIDENTIAL TREATMENT        March 31, 2000, as set out in section 7.2 except
REQUESTED]/*/                  that [CONFIDENTIAL TREATMENT REQUESTED]/*/ may
                               work on (or consult with any individual working
                               on) any Nortel Product created under Nortel's
                               Equinox Project, provided such Nortel Product
                               does not involve interconnect technology based on
                               or related to toroidal mesh or modified toroidal
                               mesh architectures.

[CONFIDENTIAL TREATMENT        June 30, 2000
REQUESTED]/*/

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES ACT OF 1933, AS AMENDED.

                                       21<PAGE>

                                                                    EXHIBIT 10.8
                                                                    ------------

 CONFIDENTIAL INFORMATION OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
     EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.
                      ASTERISKS (*) DENOTE SUCH OMISSIONS.

                  CONFIDENTIAL AND PROPRIETARY INFORMATION OF
                  --------------------------------------------
                               AVICI SYSTEMS INC.
                               ------------------
                          EMC MODULE SUPPLY AGREEMENT

THIS EMC MODULE SUPPLY AGREEMENT (the "Agreement") is made effective as of the -
5th day of May, 1999 (the "Effective Date") by and between Nortel Networks Inc.
("Nortel"), a Delaware corporation, having a place of business at 5555 Windward
Parkway, Alpharetta, Georgia, 30201-3895, and Avici Systems Inc., a Delaware
corporation, having a place of business at 101 Billerica Avenue, North
Billerica, MA 01862 (hereinafter "Avici").

                              W I T N E S S E T H:

WHEREAS, Avici desires to have Nortel manufacture and assemble certain Products
(as hereinafter defined) for use in Avici's Terabit Router (as described in the
Technology License Agreement (as hereinafter defined)) pursuant to one or more
Purchase Orders (as hereinafter defined) issued by Avici in accordance with this
Agreement.

WHEREAS, Nortel desires to manufacture and assemble such Products for Avici
hereunder;

NOW, THEREFORE, Avici and Nortel, in consideration of the mutual premises
contained herein and for other good an valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, agree as follows:

                            SECTION 1:  DEFINITIONS

Capitalized terms used in this Agreement and not otherwise defined herein shall
have the meanings set forth below:

     "ACTIVITY DESCRIPTION" shall mean Activity Description No. 98-017, EMC
     Module and Shelf Design Adaptation, entered into by the parties hereto,
     dated September 28, 1998, an addendum to the Assistance Agreement.

<PAGE>

     "AFFILIATE" of Nortel shall mean, Nortel Networks Corporation, any entity
     of which Nortel directly or indirectly owns or controls at least 50% of the
     voting securities, and any entity of which Nortel Networks Corporation
     directly or indirectly either owns or controls at least 50% of the voting
     securities.

     "ASSISTANCE AGREEMENT" shall mean the Nortel-Avici Assistance Agreement
     entered into by the parties hereto, dated as of January 28, 1998.

     "DAYS" shall mean calendar days, unless otherwise specified, provided that
     if a deadline falls on a Saturday, Sunday, or holiday, it shall be extended
     until the following regular business day.

     "DELIVERY" shall mean Nortel's delivery of Products, FOB Nortel's North
     American manufacturing facility, distribution center or approved supplier.

     "DELIVERY DATE" shall mean the date of Delivery of Products.

     "ESCROW MATERIALS" shall mean the design documentation for tooling
     necessary to manufacture the OC-192 and X-Core Components of the Products
     described in Schedule C.001000 6, Section 3.2 and 3.3.

     "EVENTS OF RELEASE" shall mean the events listed in Section 16.2.

     "PRICE" shall mean the amount payable for Products or Services, exclusive
     of any commissions, bonds, levees, insurance, taxes, delivery charges and
     other similar amounts.  All Prices and other amounts in this Agreement
     shall be construed to be in U.S. dollars ($U.S.).

     "PRODUCTS" shall mean any one of:  (1) circuit pack EMC enclosure piece
     part sets: (II) EMC enclosure shelf assemblies (two (2) types); (III)
     backplace EMC gasket hardware kits; and (IV) assembly of the faceplate
     portion of circuit pack EMC enclosure piece part

<PAGE>

     sets, to be delivered as a kit of parts, as such products are more fully
     described in the Activity Description, to be manufactured by Nortel
     pursuant to this Agreement. Delivery quantities will be defined by means of
     Purchase Orders issued under this Agreement.

     "PURCHASE ORDER" shall mean an order to purchase a specific quantity of a
     Product submitted by Avici and accepted by Nortel in accordance with this
     Agreement, which refers to the type and volume and timing of Products to be
     manufactured and purchased; price terms; schedule Delivery Dates (unless
     submitted on open Delivery terms); and "sold to," and "ship to" addresses.
     The terms of this Agreement take precedence over any preprinted terms on a
     Purchase Order acknowledgement, confirmation, or invoice and any
     inconsistent terms in a Purchase Order unless expressly accepted by Nortel.

     "SERVICES" shall mean the repair services described in Section 12.

     "SCHEDULE C.00100 6" shall mean Schedule C.00100 6 entered into by the
     parties hereto, dated as of September 30, 1998, a schedule to the
     Technology License and Agreement.

     "SPECIFICATIONS" shall mean the description of the Products, performance
     and test requirements, and in-process and final test criteria, attached
     hereto as Schedule A.  Upon completion of the activity described in the
     Activity Description the parties shall amend the Specifications to conform
     to the results of such activity, to take effect as of the next
     manufacturing cycle of the Product after the date of such amendment.  Any
     changes to the Specifications must be in writing and signed by authorized
     representatives of the parties hereto.

     "TECHNOLOGY LICENSE AND AGREEMENT" shall mean the Technology License and
     Agreement entered into by the parties hereto, dated as of January 29, 1998.

<PAGE>

                           SECTION 2:  SCOPE OF WORK

2.1  SCOPE

     Nortel and Avici acknowledge and agree that this Agreement is an "EMC
     Supply Agreement" as defined in Schedule C.00100 6, Section 6, Grant B.
     Nortel agrees to perform for Avici the tasks and Services described
     hereafter, with respect to the Products described in this Agreement and
     according to the terms and conditions set forth herein, as modified from
     time to time by mutual agreement, in writing, signed by both parties, under
     the specific supervision of the technical coordinator by Avici.

2.2  MANUFACTURING OF PRODUCTS

     Nortel shall manufacture and shall coordinate with such of its Affiliates
     or subcontractors as necessary, and Avici shall order the manufacture of,
     Products by Nortel, in accordance with the terms and conditions of this
     Agreement.  Nortel shall deliver to Avici's specified location only that
     quantity of Products specified in Avici's Purchase Orders at the Prices set
     forth herein.  All applicable transportation and insurance costs incurred
     by Nortel in connection with the Delivery of the Products to Avici shall be
     for the account of Avici.

2.3  MANUFACTURING SCHEDULING

     Nortel shall coordinate the manufacturing scheduling and pre-process
     material planning with regard to the Products to be manufactured with all
     necessary Affiliates and subcontractors and shall manage the overall
     production plan and Deliveries thereunder in accordance with the Product
     forecasts provided by Avici in accordance with Section 4.3 and the Delivery
     Dates set forth in the Purchase Orders in accordance with Section 4.1.

2.4  QUALITY ASSURANCE

     Nortel shall build and inspect the Products in accordance with the
     Specifications.  Inspection data will be maintained by Nortel for at least
     two (2) years from the date of such inspection and will be available for
     inspection by Avici during normal business hours upon reasonable notice.

2.5  REPAIRS
     Nortel shall manage the Product repair process in accordance with Section
     12 of this Agreement.

<PAGE>

2.6  TOOLING

     Avici grants to Nortel a license to use or have used, and Avici shall
     deliver to Nortel, the Specific EMC Tooling (as defined in Schedule C.00100
     6, Section 3.3(b)) without charge, to manufacture Products.

                     SECTION 3:  PRICING AND PAYMENT TERMS

3.1  PRICING OF PRODUCTS AND SERVICES

     Prices for each Product and Service to be paid by Avici for Services
     performed and Product(s) delivered under this Agreement are as follows:

     (i)   Schedule B contains a Price schedule for Products for the initial
           term of this Agreement. [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days
           prior to the close of the first term, at Avici's option in accordance
           with Section 15, the parties shall enter into good faith negotiation
           with the intent to reach agreement on second term pricing in
           accordance with Schedule C.00100 6, Section 6, Grant B, paragraph
           (d).

     (ii)  Subject to any non-renewal notice provided pursuant to section 15.1,
           thereafter, for each subsequent term, [CONFIDENTIAL TREATMENT
           REQUESTED]/*/ Days prior to the close of the previous term, the
           parties shall enter into good faith negotiations for subsequent-term
           pricing.

     (iii) Such price negotiation opportunities shall not apply to the
           intellectual property rights buy-out prices set out in
           Schedule C.00100 6.

     (iv)  Subsequent term pricing changes, if any, shall not be effective until
           set out in writing, signed by both parties, and attached to this
           Agreement as an amendment to Schedule B.

3.2  PAYMENT

     Payment terms are as follows:

     (i)   Net [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days from the date of
           Nortel's Invoice to Avici;

     (ii)  Intentionally deleted;

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

     (iii) Avici shall pay Nortel in accordance with the above payment terms the
           full amount due under each invoice, less amounts for shortages and/or
           non-conforming Products or Services;

     (iv)  If Avici fails to pay any amount when due, Avici shall pay a late
           payment charge equal to one percent (1%) per month (twelve (12%) per
           annum) or the maximum rate permitted by applicable law, whichever is
           lesser, calculated daily from the due date, on such unpaid amounts,
           together with all costs and expenses, including reasonable attorney's
           fees, incurred by Nortel in collecting such overdue amounts;

     (v)   If Avici disputes any invoice rendered, Avici shall so notify
           Nortel and the parties will use their best efforts to resolve
           such dispute expeditiously. Provided that Avici so notifies Nortel of
           a disputed invoice and there is a good-faith basis for such dispute,
           the time for paying the portion of the invoice in dispute shall be
           extended by a period of time equal to the time between Nortel's
           receipt of such notice from Avici and [CONFIDENTIAL TREATMENT
           REQUESTED]/*/ Days after resolution of such dispute. Avici shall pay
           for nondisputed items in accordance with the terms of this Agreement.

     (vi)  All payments hereunder shall be made in U.S. dollars ($U.S.).

3.3  INVOICING

     Nortel may invoice for Products upon Delivery of such Products or
     completion of Services, as applicable, pursuant to Purchase Orders.
     Invoices shall be dated no earlier than the Delivery Date for such Products
     and shall identify and show separately quantities of Products, unit prices,
     total amount for each item, applicable sales or use taxes, discounts where
     applicable, estimated shipping charges, if applicable, and total amount
     due.

3.4  TAXES

     Avici shall be responsible for sales, use, or custom taxes or duties
     resulting from the manufacture and sale or Delivery of Products in
     accordance with the Purchase Orders.  Avici shall provide tax exemption
     numbers, if applicable, for such purchases.

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.
<PAGE>

                          SECTION 4:  PURCHASE ORDERS

4.1  PURCHASE ORDERS

     Subject to its buy-out rights as set out in Schedule C.00100 6, Avici will
     provide to Nortel Purchase Order(s) on a quarterly basis for the following
     quarter, no later than [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days prior to
     the commencement of Delivery for such quarter, unless otherwise agreed by
     the parties, in accordance with the forecast to be provided by Avici to
     Nortel in accordance with Section 4.3. During the initial 18-month term of
     the Agreement, and notwithstanding Section 5, Avici shall purchase no less
     than [CONFIDENTIAL TREATMENT REQUESTED]/*/ circuit pack EMC enclosure piece
     part sets.

     4.1.1  In the event the Agreement is extended for a second 18-month
            term, Avici shall, during such second term, notwithstanding Section
            5, purchase no less than [CONFIDENTIAL TREATMENT REQUESTED]/*/
            circuit pack EMC enclosure piece part sets.

     4.1.2  In the event of a conflict between the terms and conditions of
            a Purchase Order and terms and conditions of this Agreement, this
            Agreement shall govern unless otherwise mutually agreed.

     4.1.3  All Purchase Orders submitted by Avici to Nortel pursuant to
            this Agreement shall reference this Agreement.

     4.1.4  The parties acknowledge and agree that the units of circuit
            pack EMC enclosure piece part sets purchased by Avici from Nortel
            pursuant to Avici Purchase Order No. 981492, dated April 1, 1999,
            shall be credited towards the [CONFIDENTIAL TREATMENT REQUESTED]/*/
            unit minimum purchase amount described in the opening paragraph of
            this Section 4.1, and that Nortel shall credit the aggregate
            difference between the price for the circuit pack EMC enclosure
            piece part sets purchased pursuant to Purchase Order No. 981492 and
            the Price for circuit pack EMC enclosure piece part sets against
            payments owned by Avici in respect of circuit pack EMC enclosure
            piece part sets purchased hereunder.

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

4.2  ACCEPTANCE OF PURCHASE ORDERS

     Nortel shall accept all Purchase Orders conforming to the requirements of
     this Agreement delivered via facsimile (and confirmed by telephone
     conversation) to the address and addressee of Nortel set forth in Section
     17.6. Any Purchase Order not rejected within [CONFIDENTIAL TREATMENT
     REQUESTED]/*/ business days of receipt by Nortel shall be deemed accepted.
     Failure by Nortel to accept a conforming Purchase Order shall be considered
     a material breach of this Agreement, provided Avici is not in material
     breach thereof.

     4.2.1  Nortel will maintain raw material inventory in stock and tooling on
            hand sufficient to meet Avici orders and requirements.

     4.2.2  Notwithstanding any provision in this Agreement to the contrary,
            Nortel's supply of Products shall be limited to the capability, tool
            life and/or quantity of the tools provided to Nortel by Avici
            pursuant to Section 2.5.

     4.2.3  Avici will reimburse Nortel [CONFIDENTIAL TREATMENT REQUESTED]/*/
            percent ([CONFIDENTIAL TREATMENT REQUESTED]/*/%) of the cost of
            finished goods inventory per month maintained by Nortel at Avici's
            request.

4.3  PRODUCT FORECASTS

     Avici shall provide Nortel with written 12-month forecasts by calendar
     quarter of all Purchase Orders in respect of Products Avici expects to
     place on Nortel, not later than [CONFIDENTIAL TREATMENT REQUESTED]/*/
     months prior to the 12-month period covered thereby. Avici shall update
     such forecasts every [CONFIDENTIAL TREATMENT REQUESTED]/*/ months and
     report to Nortel any significant changes in the forecasts. Such forecasts
     shall not be binding purchase obligations upon Avici. Firm purchase and
     sale commitments shall be made through Purchase Orders issued by Avici and
     accepted by Nortel.

              SECTION 5: PURCHASE ORDER RESCHEDULING/CANCELLATIONS

5.1  RESCHEDULING

     5.1.1  Avici may, by written notice received by Nortel [CONFIDENTIAL
            TREATMENT REQUESTED]/*/ Days, or less, prior to the Delivery Date,
            at no charge, reschedule the Delivery of ordered Products, provided
            that such rescheduled Delivery Date shall not be later than
            [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days from the original
            Delivery Date, and provided such rescheduled Delivery

---------------------
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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

            Date shall not exceed the then current term of this Agreement. The
            Delivery Date for a particular Purchase Order may only be
            rescheduled once pursuant to this Section 5.1.1.

     5.1.2  Subsequent rescheduling [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days,
            or less, prior to the Delivery Date will be subject to an additional
            fee of [CONFIDENTIAL TREATMENT REQUESTED]/*/ percent ([CONFIDENTIAL
            TREATMENT REQUESTED]/*/%) of Nortel's Product Price.

     5.1.3  Purchase orders may be rescheduled greater than [CONFIDENTIAL
            TREATMENT REQUESTED]/*/ days but less than [CONFIDENTIAL TREATMENT
            REQUESTED]/*/ days prior to the Delivery Date at no charge, provided
            the rescheduled Delivery Date shall not be later than [CONFIDENTIAL
            TREATMENT REQUESTED]/*/ Days from the original Delivery Date.

     5.1.4  Purchase Orders may be re-scheduled more than [CONFIDENTIAL
            TREATMENT REQUESTED]/*/ Days prior to the Delivery Date at no
            charge, provided such rescheduled Delivery Date shall not exceed the
            then current term of this Agreement.

     5.1.5  There shall be no rescheduling charge applied to expedited
            deliveries.

5.2  CANCELLATION CHARGES

     5.2.1  Avici may cancel all or a portion of a Purchase Order already
            accepted by Nortel by providing Nortel with a written notice of
            cancellation and by paying to Nortel a fee equal to:

     [CONFIDENTIAL TREATMENT REQUESTED]/*/

     [CONFIDENTIAL TREATMENT REQUESTED]/*/

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/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

     [CONFIDENTIAL TREATMENT REQUESTED]/*/

     5.2.2  In no event shall the cancellation charges set forth in this Section
            5.2 exceed [CONFIDENTIAL TREATMENT REQUESTED]/*/.

     5.2.3  Nortel will provide Avici with documentation adequate to support its
            claim for cancellation charges.  Components and completed work and
            work-in-process that are paid for by Avici pursuant to such
            cancellation charges shall be Avici's property subject to the terms
            herein and shall be held or Delivered to Avici as Avici may
            reasonably request. Notwithstanding the foregoing, Avici shall have
            no obligation to pay cancellation charges if the cancellation is
            occasioned by the failure of Nortel to perform its material
            obligations under this Agreement unless Nortel's failure is the
            result of Avici's failure to perform its material obligations
            hereunder.

5.3  Notwithstanding any provision in this Agreement or Avici Purchase Order No.
     981492, dated April 1, 1999, to the contrary, Avici covenants and agrees
     that Avici may not cancel or reschedule (unless mutually agreed) all or any
     part of Avici Purchase Order No. 981492, dated April 1, 1999, for any
     reason.

                      SECTION 6:  SHIPPING/DELIVERY/TITLE

6.1  FOB TERMS

     All Deliveries of Products covered under this Agreement shall be made FOB
     Nortel's North American manufacturing facility, distribution center or
     approved supplier, freight collect.  Such Delivery shall constitute
     delivery to Avici.  As of the moment a Product is delivered to Avici, Avici
     accepts all risk of loss, mishandling, breakage, and other damages relating
     thereto. Avici shall use is best efforts to specify the carrier at least
     [CONFIDENTIAL TREATMENT REQUESTED]/*/ business Days prior to the Delivery
     Date and shall be responsible for paying such carrier.

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

     In the event Avici does not so specify the carrier, Nortel shall select a
     carrier and Deliver the Products as described above, in a reasonably
     economical manner, freight prepaid by Nortel and charged to Avici in the
     applicable invoice. If Products are designated for export, Avici is
     responsible for assuring compliance with applicable export laws, and Avici
     will provide Nortel with instructions for the handling of such export
     shipments and shall reimburse Nortel for all costs associated therewith.

6.2  SHIPPING

     Intentionally deleted.

6.3  PACKING

     All products shipped hereunder shall be packed by Nortel, at no additional
     charge to Avici, in containers adequate to prevent damage during shipping,
     handling and storage.

6.4  DELIVERY IN INSTALLMENTS

     Nortel may fill a Purchase Order in installments, but only in mutually
     agreeable partial quantities and at mutually agreeable intervals.  Nortel
     may not ship incomplete Products at any time, unless pre-approved by Avici.

6.5  TITLE

     Title to Products will pass to Avici upon Delivery.  Avici grants to Nortel
     a first priority security interest in the Products.  Nortel may perfect
     such interest, and Avici shall assist Nortel, as reasonably necessary, to
     do so.  Nortel may retain such interest until Avici has paid Nortel in full
     for the Products.  Prior to payment in full for such Products, Avici shall
     not cause or permit the Products, or any portion thereof, to be sold,
     leased or subjected to a lien or other encumbrance.  Nothing contained in
     this Section 6.5 shall be construed so as to vary the provisions contained
     in the Activity Description or Schedule C.00100 6, as applicable, related
     to ownership and licensing of, or other obligations related to, the
     intellectual property, and rights therein, incorporated into Products.

6.6  LATE DELIVERY

     (a)    Nortel shall Deliver the Products and perform Services ordered by
            Avici by the Delivery Date mutually agreed to by the parties.  All
            scheduled Delivery Dates of Products or performance of Services are
            firm, and time shall be of the essence.

<PAGE>

     (b)    Nortel's Delivery obligations pursuant to Section 6 are subject to
            the condition that the Delivery Dates specified in Purchase Orders
            shall comply with minimum [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days
            lead time, unless Nortel expressly agrees to shorter intervals.

     (c)    Unless otherwise instructed by Avici, Nortel shall for all Purchase
            Orders placed hereunder: (i) ship complete orders, (ii) ship to the
            location designated in the Purchase Order; (iii) ensure that all
            subordinate documents bear Avici's Purchase Order Number; (iv)
            enclose a packing memorandum; (v) mark Avici's Purchase Order number
            on all packages and shipping papers; and (vi) not Deliver earlier
            than [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days before the Delivery
            Dates specified in the applicable Purchase Order unless otherwise
            mutually agreed.

     (d)    Nortel shall immediately notify Avici of any anticipated late
            Deliveries and any impending plant or facility shutdowns for any
            reason, including vacation, tool repair, labor difficulties or
            governmental order, which may adversely impact the scheduled
            Delivery Dates. In the event that Nortel is delinquent on delivering
            a Product to Avici for reasons other than those attributable to
            Avici or in accordance with Section 17.11, Nortel shall deliver such
            Product to Avici in the most expeditious manner possible and the
            payment of premium transportation cots associated with the shipment
            of the Product shall be at Nortel's expense.

     (e)    The rights and obligations of the parties under this Section 6.6
            shall not apply to the extent that any delay in delivering a Product
            is caused by a relevant delay in performance by Avici of its
            obligations under this Agreement.

                              SECTION 7:  QUALITY
7.1  QUALITY ASSURANCE

     Prior to first production start, Nortel and Avici shall engage in good
     faith negotiations to develop a mutually satisfactory quality plan, which
     plan shall include failure root cause analysis and a corrective action plan
     which meets the requirements of ISO 9001 or 9002, whichever is applicable.
     This plan shall be set out in a separate document.

     Nortel agrees that all Deliveries of Products shall be verified for
     compliance with the Specifications for each Product(s).

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
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PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

     Further, the parties agree that regular quality reviews will be held no
     less frequently than on a quarterly basis at such time and place as
     mutually agreed to by the parties.  Reasons for such meetings may include,
     but shall not be limited to:

     (a)  Review of quality acceptance criteria;

     (b)  Quality performance and receiving inspection results;

     (c)  Corrective action results/change control; and

     (d)  Field problem reviews and regulatory impacts.

     In addition, Nortel will:

     (a)  Respond in a timely manner to Avici's quality related corrective
          action requests as a result of non-conformance to the quality plan;

     (b)  Allow inspections of Nortel Product manufacturing facilities and
          periodic quality audits by Avici to determine Product conformance to
          quality criteria described in the Specifications; and

     (c) Manufacture Products in compliance with applicable Specifications.

7.2  INSPECTION AND ACCEPTANCE

     Avici shall notify Nortel in writing of particular deficiencies in Products
     that do not conform to the Specifications that Avici has knowledge of, from
     time to time. Products will be deemed accepted by Avici if a notice of
     deficiency is not received by Nortel via facsimile (and confirmed by
     telephone conversation) to the address and addressee of Nortel set forth in
     Section 17.6 within [CONFIDENTIAL TREATMENT REQUESTED]/*/ days after
     Delivery of the Products. Such unaccepted non-conforming Products shall be
     returned to Nortel at Nortel's expense for repair or replacement, at
     Nortel's option and expense, as soon as commercially possible but no later
     than thirty (30) Days after receipt of such non-conforming Product.
     Nortel's responsibility for deficiencies discovered after the close of the
     [CONFIDENTIAL TREATMENT REQUESTED]/*/day inspection period, but prior to
     the close of the warranty period as set out in Section 11, shall be as
     provided for under the warranty provisions of this Agreement.

7.3  MANUFACTURING PLANT INSPECTION

     Nortel will allow Avici into its facility manufacturing Products pursuant
     to this Agreement, at which any of the Products may be inspected upon
     reasonable prior written notice as long as any such inspection will not
     unduly interfere with Nortel's operations.  Avici and its employees shall
     comply with all Nortel rules and procedures when in or on Nortel's
     premises.

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

                                   SECTION 8:
     Intentionally deleted.

                    SECTION 9:  QUARTERLY OPERATIONS REVIEWS
9.1   Reviews

      Avici and Nortel will review quarterly the performance of each party
      hereunder.  Such review shall include items such as Product Delivery,
      Product forecasts, Product performance, quality and cost.

                       SECTION 10: Intentionally deleted.

                             SECTION 11:  WARRANTY
11.1  NORTEL'S WARRANTY

      Nortel warrants that the Products manufactured hereunder, under normal use
      and service, will be free from defects in material and workmanship, and
      will perform substantially in accordance with the applicable
      Specifications, for a period of [CONFIDENTIAL TREATMENT REQUESTED]/*/ from
      Delivery (the "Warranty Period"); provided, however, that Nortel shall
      have no liability for any defects as a result of design or Specification
      flaws. This warranty shall not apply to items normally consumed in
      operation, such as lamps and fuses. Nortel's sole obligation and Avici's
      exclusive remedy under this warranty is limited to the replacement or
      repair, at Nortel's option and expense, of the defective Products.
      Replacement Products may be new or reconditioned to perform as new at
      Nortel's option. The foregoing warranty does not apply: (i) if the defect
      arises from mishandling; abuse; improper storage; improper performance of
      installation, other service or maintenance other than by Nortel; misuse
      (including, without limitation, any use of the Product beyond the
      environmental parameters set forth in the applicable Specifications);
      damage by fire, explosion, power failure, power surge or other power
      irregularity (beyond such parameters which are set forth in the applicable
      Specifications); or (ii) if any repair or

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OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

      modification (or attempted repair or modification) of the Product is made
      other than by Nortel unless that repair or modification (or attempted
      repair or modification) of the Product made by any party other than Nortel
      has been specifically authorized in writing by Nortel. In the event a
      repair is required as a result of (i) or (ii) above, Nortel will repair
      the Product and Avici will pay to Nortel expenses incurred by Nortel in
      connection therewith, in accordance with Nortel's then current standard
      rates therefor. Turnaround time for warranty repair or replacement shall
      be no greater than [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days. Repair or
      replacement Products furnished by Nortel during the Warranty Period shall
      be warranted for a period of [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days or
      the remainder of the original Warranty Period, whichever is longer. The
      aforementioned warranties shall inure to Avici, its successors and
      assigns. Nortel warrants that the Products delivered to Avici are free and
      clear of all liens and encumbrances. Notwithstanding the foregoing, the
      warranty applicable to components supplied to Nortel by a third party and
      forming a part of a Product shall be the warranty provided by such third
      party supplier.

11.2  Y2K WARRANTIES

      Nortel warrants that any software or systems of Nortel used by Nortel in
      the supply of Products shall: (i) process date and time related data
      without causing processing interruptions, abnormal terminations, or
      changes in performance characteristics; and (ii) shall process and
      manipulate all date and time related functions correctly.

11.3  NORTEL'S DUTIES

      Nortel shall maintain such inspection logs for Products Delivered as
      Nortel would create in the normal course, for a period of twenty-four (24)
      months after such inspection and shall make such information available to
      Avici on request. In the event Avici root cause analysis of field failures
      of its Terabit Router reasonably indicate that non-conformance of Products
      to the Specifications and/or defects in material and workmanship are the
      cause of the failures, Nortel shall provide reasonable assistance to Avici
      in performing root cause analysis of such Products and make such
      information available to Avici on request.

11.4  CONFORMING PRODUCTS

      For Products that are returned to Nortel by Avici for repair or
      replacement pursuant to Section 11.1 and are found by Nortel to conform to
      the applicable Specifications, Avici shall pay Nortel for all costs it has
      incurred in connection with the handling and testing of the Products as
      well as shipping charges and duties.

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

11.5  DISCLAIMER

      THE FOREGOING WARRANTIES AND REMEDIES CONSTITUTE THE ONLY WARRANTIES,
      GUARANTEES OR CONDITIONS WITH RESPECT TO PRODUCTS AND SERVICES AND ARE
      AVICI'S EXCLUSIVE REMEDIES IN THE EVENT SUCH WARRANTIES ARE BREACHED. SUCH
      WARRANTIES ARE IN LIEU OF ALL OTHER WARRANTIES, GUARANTEES OR CONDITIONS,
      WRITTEN OR ORAL, STATUTORY, EXPRESS OR IMPLIED, INCLUDING WITHOUT
      LIMITATION, ANY WARRANTY WITH RESPECT TO ANY OTHER SERVICES PROVIDED BY
      NORTEL HEREUNDER OR OTHERWISE, AND ANY WARRANTY OF MERCHANTABILITY,
      FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. NORTEL SHALL NOT BE
      RESOPNSIBILE FOR ANY WARRANTY OFFERED BY AVICI TO ANY CUSTOMER(S) OF
      AVICI. IN NO EVENT SHAL NORTEL BE LIABLE FOR ANY INCIDENTAL, INDIRECT,
      SPECIAL OR CONSEQUENTIAL DAMAGES RELATING TO BREACH OF WARRANTY.

                              SECTION 12:  REPAIRS

12.1  Nortel agrees to provide repair Services during the period described in
      Section 12.4 for the Products it manufactures.  Repair Services for items
      supplied to Nortel by third parties will be subject to any agreement
      between Nortel and such third party.

12.2  REPAIRS UNDER WARRANTY

      Nortel is responsible for the cost of repairs, including return shipment
      costs from Nortel to Avici, in respect of Product repair pursuant to
      Section 11.1. Avici shall be responsible for shipment costs to Nortel from
      Avici for such Products.

12.3  REPAIRS OUT OF WARRANTY

      The Price to Avici for out-of-warranty repairs shall be at Nortel's
      standard rate therefor at such time. Turnaround time for such repairs
      shall be [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days. Invoices for out-of-
      warranty repairs shall be paid by Avici within [CONFIDENTIAL TREATMENT
      REQUESTED]/*/ Days of the date of invoice for the cost of such repairs.

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

12.4  TIME LIMITATIONS

      Nortel must retain repair capabilities for each Product for a period of
      [CONFIDENTIAL TREATMENT REQUESTED]/*/ years from the date such Product was
      last manufactured by Nortel, provided, in the event Avici transfers the
      manufacture of such Product to a third party, to the extent permitted in
      Schedule C.00100 6, the obligation imposed upon Nortel in this Section
      shall terminate as of such date.

12.5  OUT-OF-WARRANTY REPLACEMENTS

      During the period described in Section 12.4, in the event that any Product
      is beyond repair, it shall, at Avici's option, be returned to Avici as is
      at Avici's expense. If, during the period described in Section 12.4, the
      Warranty Period for such Product has expired and, in such case, should
      Avici request a replacement Product, the applicable price for such
      replacement will be the full cost of the Product, plus all transportation
      costs, at such time.

12.6  PRODUCT RETURNS

      Avici shall be responsible for the return of the Products to Nortel,
      subject to Section 12.2, replaced under Section 12.5. In the event that
      Nortel ships a replacement Product pursuant to Section 12.5 prior to
      receiving the Product being returned, Nortel must receive the returned
      Product within [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days of shipping the
      replacement. If Nortel has not received the returned Product within such
      [CONFIDENTIAL TREATMENT REQUESTED]/*/ Days, Nortel shall be entitled to
      invoice Avici for the returned Product.

                      SECTION 13:  LIMITATION OF LIABILITY
13.1  EXCLUSION OF CERTAIN DAMAGES

      WITH THE EXCEPTION OF VIOLATIONS OF SECTION 14 BELOW, IN NO EVENT SHALL
      EITHER PARTY BE LIABLE FOR INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
      DAMAGES, LOSS OF PROFITS, LOSS OF USE, OR DATA OR INTERRUPTION OF
      BUSINSES, WHETHER SUCH ALLEGED DAMAGES ARE LABELED IN TORT, CONTRACT, OR
      INDEMNITY, EVEN IF SUCH PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
      DAMAGES. WITH THE EXCEPTION OF VIOLATIONS OF SECTION 14 BELOW, IN NO EVENT
      SHAL NORTEL BE LIABLE FOR DAMAGES FOR ANY CAUSE WHATSOEVER, INCLUDING BUT
      NOT LIMITED TO BREACH OF CONTRACT (INCLUDING FUNDAMENTAL BREACH), TORT
      (INCLUDING NEGLIGENCE), INDEMNITY OR OTHERWISE, IN AN AMOUNT IN EXCESS OF,
      IN THE AGGREGATE, THE PAYMENTS RECEIVED BY NORTEL FROM AVICI PURSUANT TO
      THIS AGREEMENT TO THE DATE OF SUCH LIABILITY, OR ONE HUNDRED THOUSAND
      DOLLARS (US $100,000.00), WHICHEVER IS GREATER.

      WITH THE EXCEPTION OF VIOLATIONS OF SECTION 14 BELOW, IN NO EVENT SHALL
      AVICI BE LIABLE FOR DAMAGES FOR ANY CAUSE WHATSOEVER, INCLUDING BUT NOT
      LIMITED TO BREACH OF CONTRACT (INCLUDING FUNDAMENTAL BREACH), TORT
      (INCLUDING NEGLIGENCE),

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

      INDEMNITY OR OTHERWISE, IN AN AMOUNT IN EXCESS OF, IN THE AGGREGATE, THE
      PAYMENTS RECEIVED BY NORTEL FROM AVICI PURSUANT TO THIS AGREEMENT TO THE
      DATE OF SUCH LIABILITY, OR [CONFIDENTIAL TREATMENT REQUESTED]/*/ DOLLARS
      (US $[CONFIDENTIAL TREATMENT REQUESTED]/*/ ), WHICHEVER IS GREATER.

      WITH THE EXCEPTION OF VIOLATIONS OF SECTION 14 BELOW, IN NO EVENT SHALL
      AVICI BE LIABLE FOR DAMAGES FOR ANY CAUSE WHATSOEVER, INCLUDING BUT NOT
      LIMITED TO BREACH OF CONTRACT (INCLUDING FUNDAMENTAL BREACH), TORT
      (INCLUDING NEGLIGENCE), INDEMNITY OR OTHERWISE, IN AN AMOUNT IN EXCESS OF,
      IN THE AGGREGATE, THE PAYMENTS OWED TO NORTEL BY AVICI PURSUANT TO THIS
      AGREEMENT TO THE DATE OF SUCH LIABILITY, OR [CONFIDENTIAL TREATMENT
      REQUESTED]/*/ DOLLARS (US $[CONFIDENTIAL TREATMENT REQUESTED]/*/),
      WHICHEVER IS GREATER.

                       SECTION 14:  INTELLECTUAL PROPERTY
                     RIGHTS AND CONFIDENTIALITY PROVISIONS

14.1  The rights and obligations of Nortel and Avici related to the Products and
      Services shall be subject to Schedule C.00100 6, Section 6, Grant B and C,
      as applicable.

14.2  All technical information, specifications, drawings, documentation and
      "know-how" of every kind and description whatsoever disclosed in writing
      and identified as confidential by either party to the other under this
      Agreement (the "Information"), except insofar as it may be in the public
      domain or be established to have been independently developed and so
      documented by the other party or obtained by any person not in breach of
      any confidentiality obligations to the disclosing party, is the exclusive
      property of the disclosing party. The recipient party, except as
      specifically authorized in writing by the disclosing party, or as
      permitted hereunder, shall treat and protect the Information as
      confidential, shall not reproduce the Information except to the extent
      reasonably required for the performance of this Agreement, shall not
      divulge the Information in whole or in part to any third parties (except
      for, in the case of Nortel, Nortel Affiliates, subcontractors

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

      and suppliers), and shall use the Information only for purposes necessary
      for the performance of this Agreement or as may be required for the use of
      the Products and/or Services provided hereunder. This obligation shall
      survive the termination of this Agreement for a period of [CONFIDENTIAL
      TREATMENT REQUESTED]/*/ years. Each party shall disclose the Information
      only to those of its employees or agents (including, in the case of
      Nortel, those of its Affiliates, subcontractors and suppliers) who shall
      have a "need-to-know" the Information for the purposes described herein
      after first making such employees or agents aware of the confidentiality
      obligations set forth above.

                       SECTION 15:  TERM AND TERMINATION
15.1  TERM

      This Agreement shall become effective on the Effective Date and shall
      remain in effect for a period of eighteen (18) months, at the conclusion
      of which, at Avici's option, subject to agreement by the parties with
      regard to second term pricing and provided Avici does not exercise buy-out
      options pursuant to Schedule C.00100 6, the Agreement may be renewed for a
      second 18-month term. Subject to Section 15.2, the Agreement shall be
      self-renewing thereafter for successive one (1) year renewal periods
      unless either party notifies the other in writing of its intent to not
      renew the Agreement and such notice is received at least ninety (90) Days
      prior to the end of the then current term, all such period(s) being
      referred to herein as "term," unless and until terminated in accordance
      with this Agreement.

15.2  TERMINATION OF AGREEMENT

      (a)  This Agreement may not be terminated by either party earlier than
           eighteen (18) months after the Effective Date, other than for
           material breach as set out in (b) below.

      (b)  This Agreement may be terminated at any time upon the occurrence of
           any one or more of the following events of default:

           (i)   By either party if the other party defaults in the performance
                 of any material requirement or obligation under this Agreement,
                 and such default is not cured within (a) in the case of an
                 issue requiring initiation of a new production cycle to cure
                 such default, forty-five (45) Days after written

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OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

                 notice of such default is sent to such party or (b) in the case
                 of any other issue, thirty (30) Days after written notice of
                 such default is sent to such party (in either (a) or (b), the
                 "Cure Period"). This Agreement shall not, however, terminate if
                 the other party has cured the breach prior to the expiration of
                 the Cure Period or, if such breach cannot be cured within such
                 Cure Period, the other party has initiated actions to cure such
                 breach within such Cure Period, and thereafter cures such
                 breach as soon as reasonably practicable;

          (ii)   By either party if the other party defaults in the performance
                 of any material requirement or obligation under Schedule
                 C.00100 6, and such default is not cured within forty-five (45)
                 days after written notice of such default is sent to such
                 party;

          (iii)  By Nortel if Avici fails to make (in full) any payment required
                 by this Agreement to Nortel on the date due, and fails to cure
                 such default within forty-five (45) Days after written notice
                 of such default is sent to Avici; or

          (iv)   By either party if the other party ceases to do business, makes
                 a composition or assignment for the benefit of its creditors,
                 makes a general arrangement with its creditors concerning any
                 extension or forgiveness of any of its secured debt, becomes
                 bankrupt or insolvent, suffers or seeks the appointment of a
                 receiver to the whole or any material part of its business,
                 takes any action to liquidate or wind up the whole or any
                 material part of its business, is found subject to any
                 provisions of any bankruptcy code concerning involuntary
                 bankruptcy or similar proceeding, or suffers a material adverse
                 change in its financial position such that payments hereunder
                 may be affected or delayed by a creditor or administrator of
                 the business of the other party.

      (c)  Either party may terminate this Agreement for convenience on a ninety
           (90)-Day prior written notice to the other party.  In the event Avici
           so terminates for convenience, Avici shall reimburse Nortel for the
           actual costs incurred in connection with the Agreement work to the
           date of such termination.  The amount of such actual costs shall be
           comprised of [CONFIDENTIAL TREATMENT REQUESTED]/*/

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

           [CONFIDENTIAL TREATMENT REQUESTED]/*/

      (d)  Termination for convenience by Avici, or termination by Nortel
           pursuant to (b) above, during the first term is subject to
           reimbursement by Avici of Nortel's $[CONFIDENTIAL TREATMENT
           REQUESTED]/*/ unrecovered sunk costs in respect of the Activity
           Description less $[CONFIDENTIAL TREATMENT REQUESTED]/*/ per circuit
           pack EMC enclosure piece part set Delivered to date. Termination for
           convenience by Avici, or termination by Nortel pursuant to (b) above
           during the second term is subject to reimbursement by Avici of
           Nortel's $[CONFIDENTIAL TREATMENT REQUESTED]/*/ unrecovered sunk
           costs in respect of the Activity Description less $[CONFIDENTIAL
           TREATMENT REQUESTED]/*/ per circuit pack EMC enclosure piece part set
           Delivered to date during such second term.

      (e)  Termination for convenience by Nortel during the first term will
           result in Nortel's forfeiture of any remaining portion of such
           $[CONFIDENTIAL TREATMENT REQUESTED]/*/ sunk costs. Termination for
           convenience by Nortel during the second term will result in Nortel's
           forfeiture of any remaining portion of such $[CONFIDENTIAL TREATMENT
           REQUESTED]/*/ sunk costs.

      (f)  In the event of failure to reach agreement after good faith
           negotiations with regard to subsequent-term pricing at the conclusion
           of a given term, the Agreement terminates as of the end of the then-
           current term.

      (g)  In addition, in the event Nortel terminates for convenience, Avici
           shall have the right within ninety (90) Days of receipt of such
           notice to

           (i)   place a Purchase Order(s) for Products which Avici shall deem
                 necessary for support of its own products for three (3) months.
                 The number of units ordered under this subsection shall not be
                 greater than the monthly average of units ordered during the
                 six (6) months prior to Avici's receipt of notice of
                 termination. The Delivery of such Products shall be in
                 accordance with Section 4.1 above, but no later than ninety
                 (90) Days of the date of such termination; and

           (ii)  at Nortel's discretion, Nortel will I) provide on-going supply
                 of re-used parts or make available information necessary for
                 Avici to permit the fabrication of the tools to fabricate the
                 necessary part or II) Avici shall have access to the Escrowed
                 Materials in accordance with Section 16.

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

     (h)  In the event the Agreement is not renewed for a second eighteen (18)
          month term for any reason (other than termination of convenience by
          Nortel), Avici shall pay Nortel $[CONFIDENTIAL TREATMENT REQUESTED]/*/
          in respect of Nortel's unrecovered sunk costs and (g)(ii) shall apply.

15.3  PAYMENT OBLIGATIONS

     No termination or expiry of this Agreement shall release Avici from any
     obligation to pay Nortel any amount that has accrued or become payable at
     or prior to the date of termination or expiry.

                  SECTION 16:  ESCROW AND MANUFACTURING RIGHTS

16.1  Escrow

     Nortel shall deposit the Escrow Materials for the Products with an escrow
     agent to be mutually agreed upon by the parties.  The Escrow Materials
     shall be in machine-readable or hard copy form, as appropriate, suitable
     for reproduction and use by Avici.  During this term of this Agreement,
     Nortel shall keep the Escrow Materials current by promptly depositing
     updates that correspond to any Escrow Materials.

16.2  EVENTS OF RELEASE
     Events of Release are as follows:
     (a)  A material breach of this Agreement by Nortel, including, without
          limitation, a consistent and material failure or refusal, or an
          intentional refusal at any time when Avici is not in material breach
          of this Agreement, to provide Products as required pursuant to this
          Agreement for any reasons within control of Nortel, where such failure
          or refusal has been the subject of a notice in writing to Nortel that
          its continued failure or refusal would cause Avici to invoke its
          rights under this Section 16 forty-five (45) Days after the receipt by
          Nortel of such notice;
     (b)  An intentional refusal to accept a conforming Purchase Order from
          Avici, where such refusal has been the subject of a notice in writing
          to Nortel that its continued refusal

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

          would cause Avici to invoke its rights under this Section 16 forty-
          five (45) Days after the recipient by Nortel of such notice of breach
          under Section 15.2(i)(a), or thirty (30) Days after the receipt by
          Nortel of such notice of breach under Section 15.2(i)(b);
     (c)  Nortel makes an assignment, or enters into an arrangement with or for
          the general benefit of its creditors, or files a notice of intention
          to make a proposal under any applicable bankruptcy or other similar
          laws, is subject to the appointment of a trustee, custodian, receiver,
          or receiver manager of itself or of any substantial part of its
          assets, or otherwise ceases to carry on normal business operation.

16.3   RELEASE

16.3.1  If Avici reasonably believes that an Event of Release has occurred, and
     wishes to have the Escrow Materials released, it shall provide written
     notice of the occurrence of an Event of Release to the escrow agent.  Upon
     receipt of such notice, the escrow agent shall release the Escrow Materials
     to Avici, and provide notice of such release to Nortel.  If Nortel wishes
     to dispute the occurrence of an Event of Release, it shall provide written
     notice of its objection to Avici within thirty (30) Days of the date or
     receipt of the escrow agent's notice.

16.4  LICENSE
     (a)  The use of Escrow Materials shall be subject to Schedule C.00100 6,
          Section 6, Grant C.

16.5  LIQUIDATED DAMAGES

     In the event Avici obtains release of the Escrow Materials and it is
     subsequently proven by Nortel that an Event of Release did not occur: (I)
     Avici shall pay to Nortel an amount equal to $[CONFIDENTIAL TREATMENT
     REQUESTED]/*/ (and an additional amount for Nortel's reasonable attorney's
     fees), which amount represents Nortel's liquidated damages resulting from
     such action by Avici; (II) Avici shall forthwith return all Escrow
     Materials to the escrow agent, or destroy all such Escrow Materials and
     certify to Nortel that all such Escrow Materials have been destroyed; and
     (III) the license granted by Nortel to Avici pursuant to Section 16.4 shall
     terminate immediately.

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

                              SECTION 17:  GENERAL

17.1   Severability

     In the event that any provision of this Agreement is found to be invalid,
     voidable or unenforceable, the parties agree that unless such provision
     materially affects the entire intent and purpose of this Agreement, such
     invalidity, voidability or unenforceability shall affect neither the
     validity of this Agreement nor the remaining portion herein, and that the
     provision in question shall be deemed to be replaced with a valid and
     enforceable provision most closely reflecting the intent and purpose of the
     original provision.

17.2   SURVIVAL

     Notwithstanding any termination or expiry of this Agreement, the provisions
     of Sections 1 (Definitions). 3 (Pricing and Payment Terms), 5 (Purchase
     Order Rescheduling/Cancellation), 6.5 (Title), 11 (Warranty), 12 (Repairs),
     13 (Limitation of Liability), 14 (Intellectual Property Rights and
     Confidentiality Provisions), 15 (Term and Termination) and all consequent
     rights, obligations and liabilities shall survive the termination or the
     expiry of this Agreement.

17.3  ASSIGNMENT

     Neither party shall assign its rights or delegates its duties under this
     Agreement without the prior written consent of the other, provided that
     Avici may assign all of its rights hereunder as part of a sale of
     substantially all of the assets of Avici and Nortel may assign all of its
     obligations hereunder as part of a sale of substantially all of the assets
     of Nortel or its Affiliates used in fulfilling such obligations, subject to
     the terms hereof.  Notwithstanding the foregoing, Nortel shall have the
     right to delegate or assign this Agreement to any Affiliate subject to the
     consent of Avici, which consent shall not be unreasonably withheld.  Nortel
     may subcontract any of its obligations hereunder without Avici's consent.

<PAGE>

17.4   WAIVER

     The failure of either party to enforce at any time or for any period of
     time any of the provisions of this Agreement shall not constitute a waiver
     of such provisions or the right of either party to enforce each and every
     provision.

17.5  GOVERNING LAW

     The rights and obligations arising under the Agreement shall be governed by
     and construed in accordance with the laws of the Commonwealth of
     Massachusetts and the federal laws of the United States applicable therein,
     without regard to its conflicts of law rules.

17.6  NOTICES
     (a)  Any and all notices or other information required to be given by one
          of the parties to the other shall be deemed sufficiently given when
          forwarded by prepaid registered mail, overnight delivery service,
          cable, telegrams, facsimile, telex or hand-delivery to the other party
          at the following address:

     AVICI
     -----
     Avici Systems, Inc.
     101 Billerica Ave., Building 6
     North Billerica, MA
     01862
     Attention:  President and Chief Executive Officer

     NORTEL
     ------
     Northern Telecom Limited
     NSPaN Marketing Operations
     10 Brewer Hunt Way
     Kanata, Ontario, Canada
     K2K 2B5
     Attn:  Marketing Operations Manager
     P:  613-765-5989
     F:  613-763-9431

<PAGE>

     With a copy of all legal notices to:
     Northern Telecom Limited
     8200 Dixie Road, Suite 100
     Brampton, Ontario
     L6T 5P6
     Attention:  Secretary
     Copy to:  Law Department

     and such notices shall be deemed to have been received five (5) business
     Days after mailing if forwarded by mail, and the following business Day if
     forwarded by telegram, telex, overnight service, facsimile or hand-
     delivery.

     (b) The aforementioned address of either party may be changed at any time
     by giving fifteen (15) business Days prior notice to the other party in
     accordance with the foregoing.

     (c) In the event of a generally prevailing labor dispute or other situation
     which will delay or impede the giving of notice by any such means, the
     notice shall be given by such specified mode as will be most reliable and
     expeditious and least affected by such dispute or situation.

17.7  EXPORT COMPLIANCE

     The rights and obligations of the parties may be subject to United States
     and Canadian laws and regulations governing the license and delivery of
     technology abroad by persons subject to the jurisdiction of the United
     States and Canada, including the Export Administration Act of 1979, as
     amended, and the Export Administration regulations issued by the U.S.
     Department of Commerce, International Trade Administration, Office of
     Export Administration.  Each party shall not, directly or indirectly,
     export, reexport, or transmit technology, software, components, or
     products, in such manner as to violate such laws and regulations in effect
     from time to time to the extent that such laws are applicable to a party.

17.8  NAFTA

     17.8.1  Both parties shall perform all administrative actions required to
     qualify each Product sold under this Agreement for preferential treatment
     under the rules of any

<PAGE>

     applicable trade treaty, including, without limitation, the North American
     Free Trade Agreement ("NAFTA"). If a Product qualifies under NAFTA, the
     parties shall prepare and distribute a NAFTA Certificate of Origin, and any
     other documents required. The parties shall respond to requests from the
     other party for information regarding any NAFTA Certificates of Origin and
     assist each other in resolving any eligibility issues.

     17.8.2  If a NAFTA Certificate of Origin is prepared for each shipment,
     each party shall:  (a) retain the original NAFTA Certificates of Origin
     with appropriate backup documentation, (b) attach a copy of the NAFTA
     Certificate of Origin to the customs/shipping documents for the qualifying
     component or Product, and (c) mark the customs/shipping documents with the
     legend:  "Copy of NAFTA Certificate of Origin attached."  If a blanket
     NAFTA Certificate of Origin is prepared, the parties shall:  (a) retain the
     original NAFTA Certificate of Origin with appropriate backup documentation,
     (b) mark the customs/shipping documents for the qualifying component or
     Product with the legend:  "Copy of blanket NAFTA Certificate of Origin on
     file at Nortel's customs office in Milton, Ontario, Canada."  and (c) mail
     copies of the NAFTA Certificate of Origin to the other party.

17.9.  U.N. CONVENTION CONTRACTS

     The parties agree that the U.N. Convention on Contracts for the
     International Sale of Goods (Vienna, 1980) and the 1974 Convention on the
     Limitation Period in the International Sale of Goods (the "1974
     Convention") and the Protocol amending the 1974 Convention, done at Vienna
     April 11, 1980, shall not apply to this Agreement nor to any dispute or
     transaction arising out of this Agreement.

17.10 PUBLICITY

     Prior to the publication or use by a party hereto of any advertising, sale
     promotions, press releases or other publicity matters relating to the
     Products or this Agreement in which the names or logo of other party is
     mentioned or can be reasonably inferred, the party shall obtain the prior
     written consent of the other party.  Such consent shall not be unreasonably
     withheld.  Terms, conditions, and general terms of this Agreement shall be

<PAGE>

     held in confidence by both parties and only disclosed as may be agreed to
     by both parties or as may be required to meet securities disclosure or
     export permit requirements or as may be otherwise required by applicable
     law.  Neither party shall make public statements or issue publicity or
     media releases with regard to this Agreement or the relationship between
     the parties without the prior written approval of the other party, except
     as may be otherwise required by law or stock exchange regulations.  Nothing
     herein shall prevent a party from disclosing the terms of this Agreement to
     potential investors (other than to any of the entities listed in Schedule C
     by Avici, except as necessary pursuant to a bona fide offer by such a party
     to purchase all or substantially all of the assets or shares of Avici) as
     reasonably required by such potential investors to evaluate a potential
     investment in, or purchase of assets of, such party, provided that such
     potential investor agrees in writing to keep such information in confidence
     and to use such information solely for purposes of evaluating the business
     and financial condition of such party.

17.11  FORCE MAJEURE

     Nortel shall not be responsible or liable to Avici for any delay or failure
     to perform hereunder if such delay or failure results from fire, explosion,
     labor dispute, earthquake, casualty or accident, lack or failure of
     transportation facilities, epidemic, flood, drought, or by reason of war,
     declared or undeclared, revolution, civil commotion, the act of a public
     enemy, blockade or embargo, act of God, any inability to obtain any
     requisite license, permit or authorization, or by reason of law,
     proclamation, regulation, ordinance, demand, or requirement of any
     government or by reason of any other cause whatsoever, whether similar or
     dissimilar to those enumerated, beyond the reasonable control of Nortel.
     With respect to labor disputes as described above, Nortel shall not be
     obligated to accede to any demands being made by employees or other
     personnel.  All such causes will delay Nortel's performance hereunder for a
     period equal to the delay resulting from any such causes and such
     additional period as may be reasonably necessary to allow Nortel to resume
     its obligations.

<PAGE>

17.12  ENTIRE AGREEMENT

     This Agreement and Schedules thereto set forth the entire agreement and
     understanding between the parties and supersede and cancel all previous
     negotiations, agreements, commitments and writings in respect of the
     subject matter hereof (except for the Activity Description, Schedule
     C.00100 6 and Avici Purchase Order No. 981492, dated April 1, 1999) and
     there are no understandings representations, conditions, warranties,
     express or implied, statutory or otherwise made or assumed by the parties,
     other than those expressly contained in this Agreement.  Neither party
     shall be bound by any term, clause, provision or conditions save as
     expressly provided herein or as duly set forth on or subsequent to the date
     of this Agreement in writing signed by duly authorized officers of the
     parties.

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement
attested by the hands of their duly authorized representative on dates indicated
below.
AVICI SYSTEMS INC.  NORTEL NETWORKS INC.

By: /S/ [Authorized Officer]          By:/s/Naser Partovi
                                         ----------------

                                    Naser Partovi
                                    -------------
Name (Print or Type)                Name (Print or Type)

Title:                                Title:V.P. Emerging Markets & Technologies
                                            ------------------------------------

Date:                                 Date:

                                  SCHEDULE A

                                 SPECIFICATIONS

          See Avici Module and Shelf File description attached hereto.

<PAGE>

                                   SCHEDULE A

AVICI MODULE AND SHELF FILE DEFINITION
--------------------------------------

The stocklists below define the Nortel drawing numbers, with their vintage
control Stream and Issue, for the Avici TSR Module and Shelf design.

[CONFIDENTIAL TREATMENT REQUESTED]/*/

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

[CONFIDENTIAL TREATMENT REQUESTED]/*/

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

                                   SCHEDULE B
                                     PRICES

<TABLE>
<CAPTION>
Product                                                                   Price Per Product
<C>        <S>                                                       <C>

       1.  Circuit Pack EMC Enclosure Piece Part Set                 $[CONFIDENTIAL TREATMENT REQUESTED]/*/

       2.  Assembly of Face Plate Portion of Circuit Pack EMC        a maximum of $[CONFIDENTIAL TREATMENT REQUESTED]/*/
           Enclosure Piece Part Set                                  for the first [CONFIDENTIAL TREATMENT REQUESTED]/*/ units*** a
                                                                     maximum of $[CONFIDENTIAL TREATMENT REQUESTED]/*/
                                                                     thereafter****
       3.  EMC Enclosure Shelf Assemblies(2 types)*                  $[CONFIDENTIAL TREATMENT REQUESTED]/*/
       4.  Backplane EMC Gasket Hardware Kit**                       $[CONFIDENTIAL TREATMENT REQUESTED]/*/
</TABLE>

*Must be ordered in lots of [CONFIDENTIAL TREATMENT REQUESTED]/*/ units

**Must be ordered in lots of [CONFIDENTIAL TREATMENT REQUESTED]/*/ units

***Such [CONFIDENTIAL TREATMENT REQUESTED]/*/ units does not include the units
ordered under Avici Purchase Order No. 981492, dated April 1, 1999, for which
Avici shall pay the charges set out in such purchase order

****Avici shall be charged, via the applicable invoice,
[CONFIDENTIAL TREATMENT REQUESTED]/*/

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

<PAGE>

                                   SCHEDULE C

[CONFIDENTIAL TREATMENT REQUESTED]/*/

11.  Subsidiaries and affiliates (including parent corporations) of the
     foregoing

---------------------
/*/ [CONFIDENTIAL TREATMENT REQUESTED] INDICATES MATERIAL THAT HAS BEEN
OMITTED AND FOR WHICH CONFIDENTIAL TREATMENT HAS BEEN REQUESTED. ALL SUCH
OMITTED MATERIAL HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
PURSUANT TO RULE 406 PROMULGATED UNDER THE SECURITIES EXCHANGE ACT OF 1933,
AS AMENDED.

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