Document:

Form of Indemnification Agreement

 Exhibit 10.1 
 INDEMNIFICATION AGREEMENT 
 This Indemnification Agreement (the “Agreement”) dated
as of December     , 2006, by and between Avici Systems Inc., a Delaware corporation (the “Company”), and
                    , a director [and/or officer] of the Company (the “Indemnitee”): 
 WITNESSETH: 
 WHEREAS, the Indemnitee
is presently serving as a director [and/or officer] of the Company, and the Company desires the Indemnitee to continue in such capacity; 
 WHEREAS, highly competent persons have become more reluctant to serve corporations as directors, officers or in other capacities unless they are provided with adequate protection through insurance or adequate indemnification against
inordinate risks of claims and actions against them arising out of their service to and activities on behalf of the corporation; 
 WHEREAS,
it is reasonable, prudent and necessary for the Company contractually to obligate itself to indemnify, and to advance expenses on behalf of, such persons to the fullest extent permitted by applicable law so that they will serve or continue to serve
the Company free from undue concern that they will not be so indemnified; and 
 WHEREAS, the Indemnitee is willing, subject to certain
conditions, including the execution and performance of this Agreement by the Company, to continue in that capacity or in other capacities on behalf of the Company; 
 NOW, THEREFORE, to induce the Indemnitee to continue to serve the Company in various capacities and in consideration of these premises and the mutual agreements set forth in this Agreement, the Company and the
Indemnitee agree as follows: 
 1. Continued Service. The Indemnitee will continue to serve as a director [and/or officer] of the
Company so long as he is duly elected and qualified in accordance with the Company’s restated by-laws (the “By-Laws”) or until he resigns in writing or is removed from office in accordance with applicable law. 
 2. Definitions. For purposes of this Agreement: 
 (a) A “Change in Control” shall be deemed to occur upon the earliest to occur after the date of this Agreement of any of the following events: 
 (i) Acquisition of Stock by Third Party. Any Person is or becomes the Beneficial Owner, directly or indirectly, of securities of
the Company representing twenty percent (20%) or more of the combined voting power of the Company’s then outstanding securities; 

 (ii) Change in Board of Directors. During any 24 month period (not including any
period prior to the execution of this Agreement), individuals who at the beginning of such period constitute the Board, and any new director whose election by the Board or nomination for election by the Company’s stockholders was approved by a
vote of at least two-thirds of the directors then in office, cease for any reason to constitute a least a majority of the members of the Board; 
 (iii) Corporate Transactions. The effective date of a merger of the Company with any other entity, other than a merger which would result in the voting securities of the Company outstanding immediately prior to
such merger continuing to represent (either by remaining outstanding or by being converted into voting securities of the surviving entity) more than 50% of the combined voting power of the voting securities of the surviving entity outstanding
immediately after such merger or consolidation and with the power to elect at least a majority of the board of directors or other governing body of such surviving entity; 
 (iv) Liquidation. The approval by the stockholders of the Company of a complete liquidation of the Company or an agreement for the
sale or disposition by the Company of all or substantially all of the Company’s assets; and 
 (v) Other Events.
There occurs any other event of a nature that would be required to be reported in response to Item 6(e) of Schedule 14A of Regulation 14A (or a response to any similar item on any similar schedule or form) promulgated under the Exchange Act (as
defined below), whether or not the Company is then subject to such reporting requirement. 
 (vi) For purposes of this
Section 2(a), the following terms shall have the following meanings: 
 “Exchange Act” shall mean the Securities
Exchange Act of 1934, as amended. 
 “Person” shall have the meaning as set forth in Sections 13(d) and 14(d) of the Exchange
Act; provided, however, that Person shall exclude (i) the Company, (ii) any trustee or other fiduciary holding securities under an employee benefit plan of the Company, and (iii) any corporation owned, directly or indirectly, by the
stockholders of the Company in substantially the same proportions as their ownership of stock of the Company. 
 “Beneficial
Owner” shall have the meaning given to such term in Rule 13d-3 under the Exchange Act; provided, however, that Beneficial Owner shall exclude any Person otherwise becoming a Beneficial Owner by reason of the stockholders of the Company
approving a merger of the Company with another entity. 

 (b) “Corporate Status” describes the status of a person who is or was a
director, officer, employee, agent or fiduciary of the Company or of any other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise that such person is or was serving at the express written request of the
Company. 
 (c) “Disinterested Director” means a director of the Company who is not and was not a party to
the Proceeding in respect of which indemnification is sought by Indemnitee. 
 (d) “Enterprise” shall mean
the Company and any other corporation, partnership, joint venture, trust, employee benefit plan or other enterprise that Indemnitee is or was serving at the express written request of the Company as a director, officer, employee, agent or fiduciary.

 (e) “Expenses” shall include all reasonable attorneys’ fees, retainers, court costs, transcript
costs, fees of experts, witness fees, travel expenses, duplicating costs, printing and binding costs, telephone charges, postage, delivery service fees and all other disbursements or expenses of the types customarily incurred in connection with
prosecuting, defending, preparing to prosecute or defend, investigating, participating, or being or preparing to be a witness in a Proceeding. Expenses also shall include Expenses incurred in connection with any appeal resulting from any Proceeding,
including without limitation the premium, security for, and other costs relating to any cost bond, supersede as bond, or other appeal bond or its equivalent. Expenses, however, shall not include amounts paid in settlement by Indemnitee or the amount
of judgments or fines against Indemnitee. 
 (f) “Independent Counsel” means a law firm, or a member of a law
firm, that is experienced in matters of corporation law and neither presently is, nor in the past five years has been, retained to represent: (i) the Company or Indemnitee in any matter material to either such party (other than with respect to
matters concerning Indemnitee under this Agreement, or of other indemnitees under similar indemnification agreements), or (ii) any other party to the Proceeding giving rise to a claim for indemnification hereunder. 
 (g) “Proceeding” includes any threatened, pending or completed action, suit, arbitration, alternate dispute resolution
mechanism, investigation, inquiry, administrative hearing or any other actual, threatened or completed proceeding, whether brought by or in the right of the Company or otherwise, in which Indemnitee was, is or will be involved as a party or
otherwise, by reason of the fact that Indemnitee is or was an officer or director of the Company, by reason of any action taken by him or her or of any inaction on his or her part while acting as an officer or director of the Company, or by reason
of the fact that he or she is or was serving at the request of the Company as a director, officer, employee, agent or fiduciary of another Enterprise; in each case whether or not he or she is acting or serving in any such capacity at the time any
liability or expense is 

 incurred for which indemnification can be provided under this Agreement; including those pending on or
before the date of this Agreement, but excluding those initiated by an Indemnitee pursuant to Section 5 of this Agreement to enforce his or her rights under this Agreement. 
 3. Indemnity of Indemnitee. The Company hereby agrees to hold harmless and indemnify Indemnitee to the fullest extent permitted by law, as such
may be amended from time to time. 
 (a) Proceedings Other Than Proceedings by or in the Right of the Company.
Indemnitee shall be entitled to the rights of indemnification provided in this Section 3(a) if, by reason of his Corporate Status, the Indemnitee is, or is threatened to be made, a party to or participant in any Proceeding other than a
Proceeding by or in the right of the Company. Pursuant to this Section 3(a), Indemnitee shall be indemnified against all Expenses, judgments, penalties, fines and amounts paid in settlement actually and reasonably incurred by him, or on his
behalf, in connection with such Proceeding or any claim, issue or matter therein, if the Indemnitee acted in good faith and in a manner the Indemnitee reasonably believed to be in or not opposed to the best interests of the Company, and with respect
to any criminal Proceeding, had no reasonable cause to believe the Indemnitee’s conduct was unlawful. 
 (b)
Proceedings by or in the Right of the Company. Indemnitee shall be entitled to the rights of indemnification provided in this Section 3(b) if, by reason of his Corporate Status, the Indemnitee is, or is threatened to be made, a party to
or participant in any Proceeding brought by or in the right of the Company. Pursuant to this Section 3(b), Indemnitee shall be indemnified against all Expenses actually and reasonably incurred by the Indemnitee, or on the Indemnitee’s
behalf, in connection with such Proceeding if the Indemnitee acted in good faith and in a manner the Indemnitee reasonably believed to be in or not opposed to the best interests of the Company; provided, however, if applicable law so provides, no
indemnification against such Expenses shall be made in respect of any claim, issue or matter in such Proceeding as to which Indemnitee shall have been adjudged to be liable to the Company unless and to the extent that the Court of Chancery of the
State of Delaware shall determine that such indemnification may be made. 
 (c) Indemnification for Expenses of a Party Who
is Wholly or Partly Successful. Notwithstanding any other provision of this Agreement, to the extent that Indemnitee is, by reason of his Corporate Status, a party to and is successful, on the merits or otherwise, in any Proceeding, he shall be
indemnified to the maximum extent permitted by law, as such may be amended from time to time, against all Expenses actually and reasonably incurred by him or on his behalf in connection therewith. If Indemnitee is not wholly successful in such
Proceeding but is successful, on the merits or otherwise, as to one or more but less than all claims, issues or matters in such Proceeding, the Company shall indemnify Indemnitee against all Expenses actually and reasonably incurred by him or on his

 behalf in connection with each successfully resolved claim, issue or matter. For purposes of this Section
and without limitation, the termination of any claim, issue or matter in such a Proceeding by dismissal, with or without prejudice, shall be deemed to be a successful result as to such claim, issue or matter 
 4. Advancement of Expenses. Notwithstanding any other provision of this Agreement, the Company shall advance all reasonable Expenses incurred by
or on behalf of Indemnitee in connection with any Proceeding by reason of Indemnitee’s Corporate Status within thirty (30) days after the receipt by the Company of a statement or statements from Indemnitee requesting such advance or
advances from time to time, whether prior to or after final disposition of such Proceeding. Such statement or statements shall reasonably evidence the Expenses incurred by Indemnitee and shall include or be preceded or accompanied by an undertaking
by or on behalf of Indemnitee to repay any Expenses advanced if it shall ultimately be determined that Indemnitee is not entitled to be indemnified against such Expenses. Any advances and undertakings to repay pursuant to this Section 4
shall be unsecured and interest free. 
 5. Procedures and Presumptions for Determination of Entitlement to Indemnification. It is the
intent of this Agreement to secure for Indemnitee rights of indemnity that are as favorable as may be permitted under the Delaware General Corporation Law and public policy of the State of Delaware. Accordingly, the parties agree that the following
procedures and presumptions shall apply in the event of any question as to whether Indemnitee is entitled to indemnification under this Agreement: 
 (a) To obtain indemnification under this Agreement, Indemnitee shall submit to the Company a written request, including therein or therewith such documentation and information as is reasonably available to Indemnitee
and is reasonably necessary to determine whether and to what extent the Indemnitee is entitled to indemnification. The Secretary of the Company shall, promptly upon receipt of such a request for indemnification, advise the Board of Directors in
writing that Indemnitee has requested indemnification. 
 (b) Upon written request by Indemnitee for indemnification, a
determination, if required by applicable law, with respect to Indemnitee’s entitlement thereto shall be made by one of the following four methods at the election of the Company’s Board of Directors: (1) by a majority vote of the
Disinterested Directors, even though less than a quorum, (2) by a committee of Disinterested Directors designated by a majority vote of the Disinterested Directors, even though less than a quorum, (3) if there are no Disinterested
Directors, if the Disinterested Directors so direct or if there has been a Change in Control, by Independent Counsel in a written opinion to the Board of Directors, a copy of which shall be delivered to the Indemnitee or (4) if so directed by
the Board of Directors, by the stockholders of the Company. 
 (c) If the determination of entitlement to indemnification is
to be made by Independent Counsel pursuant to Section 5(b) hereof, the Independent Counsel shall be selected by the Company’s Board of Directors. Indemnitee may, within 

 10 days after such written notice of selection shall have been given, deliver to the Company, as the case
may be, a written objection to such selection; provided, however, that such objection may be asserted only on the ground that the Independent Counsel so selected does not meet the requirements of Independent Counsel, and the objection
shall set forth with particularity the factual basis of such assertion. If a written objection is made and substantiated, the Independent Counsel selected may not serve as Independent Counsel unless and until such objection is withdrawn or a court
has determined that such objection is without merit. 
 (d) In making a determination with respect to entitlement to
indemnification hereunder, the person or persons or entity making such determination shall presume that Indemnitee is entitled to indemnification under this Agreement. Anyone seeking to overcome this presumption shall have the burden of proof and
the burden of persuasion by clear and convincing evidence. 
 (e) Indemnitee shall be deemed to have acted in good faith if
Indemnitee’s action is based on the records or books of account of the Enterprise, the advice of legal counsel for the Enterprise, or information or records given or reports made to the Enterprise by an independent certified public accountant
or by an appraiser or other expert selected with reasonable care by the Enterprise. In addition, the knowledge and/or actions, or failure to act, of any director, officer, agent or employee of the Enterprise shall not be imputed to Indemnitee for
purposes of determining the right to indemnification under this Agreement. Anyone seeking to overcome this presumption shall have the burden of proof and the burden of persuasion by clear and convincing evidence. 
 (f) If the person, persons or entity empowered or selected under Section 5 to determine whether Indemnitee is entitled to
indemnification shall not have made a determination within 60 days after receipt by the Company of the request therefor, the Indemnitee shall be entitled to such indemnification absent (i) a misstatement by Indemnitee of a material fact, or an
omission of a material fact necessary to make Indemnitee’s statement not materially misleading, in connection with the request for indemnification, or (ii) a prohibition of such indemnification under applicable law; provided,
however, that such 60-day period may be extended for a reasonable time, not to exceed an additional 30 days. 
 (g)
Indemnitee shall cooperate with the person, persons or entity making such determination with respect to Indemnitee’s entitlement to indemnification, including providing to such person, persons or entity upon reasonable advance request any
documentation or information that is not privileged or otherwise protected from disclosure and that is reasonably available to Indemnitee and reasonably necessary to such determination. Any costs or expenses (including attorneys’ fees and
disbursements) incurred by Indemnitee in so cooperating with the person, persons or entity making such determination shall be borne by the Company (irrespective of the determination as to Indemnitee’s entitlement to indemnification) and the
Company hereby indemnifies and agrees to hold Indemnitee harmless therefrom. 

 (h) The Company acknowledges that a settlement or other disposition short of final
judgment may be successful if it permits a party to avoid expense, delay, distraction, disruption and uncertainty. In the event that any action, claim or proceeding to which Indemnitee is a party is resolved in any manner other than by adverse
judgment against Indemnitee (including, without limitation, settlement of such action, claim or proceeding with or without payment of money or other consideration) it shall be presumed that Indemnitee has been successful on the merits or otherwise
in such action, suit or proceeding. Anyone seeking to overcome this presumption shall have the burden of proof and the burden of persuasion by clear and convincing evidence. 
 (i) The termination of any Proceeding or of any claim, issue or matter therein, by judgment, order, settlement or conviction, or upon a
plea of nolo contendere or its equivalent, shall not (except as otherwise expressly provided in this Agreement) of itself adversely affect the right of Indemnitee to indemnification or create a presumption that Indemnitee did not act in good faith
and in a manner that he or she reasonably believed to be in or not opposed to the best interests of the Company or, with respect to any criminal Proceeding, that Indemnitee had reasonable cause to believe that his or her conduct was unlawful.

 (j) The knowledge and/or actions, or failure to act, of any director, officer, employee, agent, trustee or fiduciary of the
Enterprise shall not be imputed to Indemnitee for purposes of determining the right to indemnification hereunder. 
 6. Remedies of
Indemnitee. 
 (a) In the event that (i) a determination is made pursuant to Section 5 of this Agreement
that Indemnitee is not entitled to indemnification under this Agreement, (ii) advancement of Expenses is not timely made pursuant to Section 4 of this Agreement, (iii) payment of indemnification is not made pursuant to this
Agreement within 10 days after receipt by the Company of a written request therefor or (iv) payment of indemnification is not made within 10 days after a determination has been made that Indemnitee is entitled to indemnification or such
determination is deemed to have been made pursuant to Section 5 of this Agreement, Indemnitee shall be entitled to an adjudication in an appropriate court of the State of Delaware, or in any other court of competent jurisdiction, of
Indemnitee’s entitlement to such indemnification. Indemnitee shall commence such proceeding seeking an adjudication within 180 days following the date on which Indemnitee first has the right to commence such proceeding pursuant to this
Section 6(a). The Company shall not oppose Indemnitee’s right to seek any such adjudication. 
 (b) In the
event that a determination shall have been made pursuant to Section 5(b) of this Agreement that Indemnitee is not entitled to indemnification, any judicial proceeding commenced pursuant to this Section 6 shall be conducted in
all respects as a de novo trial on the merits. 

 (c) If a determination shall have been made pursuant to Section 5(b) of this
Agreement that Indemnitee is entitled to indemnification, the Company shall be bound by such determination in any judicial proceeding commenced pursuant to this Section 6, absent (i) a misstatement by Indemnitee of a material fact,
or an omission of a material fact necessary to make Indemnitee’s misstatement not materially misleading in connection with the application for indemnification, or (ii) a prohibition of such indemnification under applicable law. 

(d) In the event that Indemnitee, pursuant to this Section 6, seeks a judicial adjudication of his or her rights under, or
to recover damages for breach of, this Agreement, or to recover under any directors’ and officers’ liability insurance policies maintained by the Company, the Company shall pay on his or her behalf, in advance, any and all Expenses
actually and reasonably incurred by him or her in such judicial adjudication, regardless of whether Indemnitee ultimately is determined to be entitled to such indemnification, advancement of expenses or insurance recovery. 
 (e) The Company shall be precluded from asserting in any judicial proceeding commenced pursuant to this Section 6 that the
procedures and presumptions of this Agreement are not valid, binding and enforceable and shall stipulate in any such court that the Company is bound by all the provisions of this Agreement. 
 (f) Notwithstanding anything in this Agreement to the contrary, no determination as to entitlement to indemnification under this Agreement
shall be required to be made prior to the final disposition of the Proceeding. 
 7. Non-Exclusivity; Survival of Rights; Insurance;
Subrogation. 
 (a) The rights of indemnification as provided by this Agreement shall not be deemed exclusive of any other
rights to which Indemnitee may at any time be entitled under applicable law, the certificate of incorporation of the Company, the Certificate of Incorporation, any agreement, a vote of stockholders, a resolution of directors or otherwise. No
amendment, alteration or repeal of this Agreement or of any provision hereof shall limit or restrict any right of Indemnitee under this Agreement in respect of any action taken or omitted by such Indemnitee in his or her Corporate Status prior to
such amendment, alteration or repeal. To the extent that a change in the Delaware General Corporation Law, whether by statute or judicial decision, permits greater indemnification than would be afforded currently under the Certificate of
Incorporation and this Agreement, it is the intent of the parties hereto that Indemnitee shall enjoy by this Agreement the greater benefits so afforded by such change. No right or remedy herein conferred is intended to be exclusive of any other
right or remedy, and every other right and remedy shall be cumulative and 

 in addition to every other right and remedy given hereunder or now or hereafter existing at law or in
equity or otherwise. The assertion or employment of any right or remedy hereunder, or otherwise, shall not prevent the concurrent assertion or employment of any other right or remedy. 
 (b) To the extent that the Company maintains an insurance policy or policies providing liability insurance for directors, officers,
employees, or agents or fiduciaries of the Company or Enterprise that such person serves at the request of the Company, Indemnitee shall be covered by such policy or policies in accordance with its or their terms to the maximum extent of the
coverage available for any director, officer, employee, agent or fiduciary under such policy or policies. The Company shall take all necessary or desirable action to cause such insurers to pay, on behalf of the Indemnitee, all amounts payable as a
result of such proceeding in accordance with the terms of such policies. 
 (c) In the event of any payment under this
Agreement, the Company shall be subrogated to the extent of such payment to all of the rights of recovery of Indemnitee, who shall execute all papers required and take all action necessary to secure such rights, including execution of such documents
as are necessary to enable the Company to bring suit to enforce such rights. 
 (d) The Company shall not be liable under this
Agreement to make any payment of amounts otherwise indemnifiable hereunder if and to the extent that Indemnitee has otherwise actually received such payment under any insurance policy, contract, agreement or otherwise. 
 (e) The Company’s obligation to indemnify or advance Expenses hereunder to Indemnitee who is or was serving at the request of the
Company as a director, officer, employee or agent of any Enterprise shall be reduced by any amount Indemnitee has actually received as indemnification or advancement of expenses from such Enterprise. 
 8. Exception to Right of Indemnification. Notwithstanding any provision in this Agreement, the Company shall not be obligated under this Agreement
to make any indemnity in connection with any claim made against Indemnitee: 
 (a) for an accounting of profits made from the
purchase and sale (or sale and purchase) by Indemnitee of securities of the Company within the meaning of Section 16(b) of the Securities Exchange Act of 1934, as amended, or similar provisions of state statutory law or common law; or

 (b) in connection with any Proceeding (or any part of any Proceeding) initiated by Indemnitee, including any Proceeding (or
any part of any Proceeding) initiated by Indemnitee against the Company or its directors, officers, employees or other indemnitees, unless (i) the Board of Directors of the Company authorized the Proceeding (or any part of any Proceeding) prior
to its initiation or (ii) the Company provides the indemnification, in its sole discretion, pursuant to the powers vested in the Company under applicable law. 

 9. Duration of Agreement. All agreements and obligations of the Company contained herein shall
continue so long as Indemnitee shall be subject to any Proceeding (or any proceeding commenced under Section 6 hereof) by reason of his or her Corporate Status, whether or not he or she is acting or serving in any such capacity at the
time any liability or expense is incurred for which indemnification can be provided under this Agreement. This Agreement shall be binding upon and inure to the benefit of and be enforceable by the parties hereto and their respective successors
(including any direct or indirect successor by purchase, merger, consolidation or otherwise to all or substantially all of the business or assets of the Company), assigns, spouses, heirs, executors and personal and legal representatives. 

10. Enforcement. 
 (a) The Company expressly confirms and agrees that it has entered into this Agreement and assumes the obligations imposed on it hereby in order to induce Indemnitee to serve as an officer or director of the Company, and the Company
acknowledges that Indemnitee is relying upon this Agreement in serving as an officer or director of the Company. 
 (b) This
Agreement constitutes the entire agreement between the parties hereto with respect to the subject matter hereof and supersedes all prior agreements and understandings, oral, written and implied, between the parties hereto with respect to the subject
matter hereof. 
 11. Severability. The invalidity of unenforceability of any provision hereof shall in no way affect the validity or
enforceability of any other provision. Without limiting the generality of the foregoing, this Agreement is intended to confer upon Indemnitee indemnification rights to the fullest extent permitted by applicable laws. In the event any provision
hereof conflicts with any applicable law, such provision shall be deemed modified, consistent with the aforementioned intent, to the extent necessary to resolve such conflict. 
 12. Modification and Waiver. No supplement, modification, termination or amendment of this Agreement shall be binding unless executed in writing
by both of the parties hereto. No waiver of any of the provisions of this Agreement shall be deemed or shall constitute a waiver of any other provisions hereof (whether or not similar) nor shall such waiver constitute a continuing waiver.

 13. Notice By Indemnitee. Indemnitee agrees promptly to notify the Company in writing upon being served with or otherwise receiving
any summons, citation, subpoena, complaint, indictment, information or other document relating to any Proceeding or matter which may be subject to indemnification covered hereunder. The failure to so notify the Company shall not relieve the Company
of any obligation which it may have to Indemnitee under this Agreement or otherwise unless and only to the extent that such failure or delay materially prejudices the Company. 

 14. Notices. All notices and other communications given or made pursuant to this Agreement shall
be in writing and shall be deemed effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so
confirmed, then on the next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) day after deposit with a nationally recognized
overnight courier, specifying next day delivery, with written verification of receipt. All communications shall be sent to the Company and the Indemnitee at their respective address as set forth on the signature page hereto or to such other address
as may have been furnished to Indemnitee by the Company or to the Company by Indemnitee, as the case may be. 
 15. Counterparts. This
Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same Agreement. This Agreement may also be executed and delivered by facsimile signature and in
two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. 
 16. Headings. The headings of the paragraphs of this Agreement are inserted for convenience only and shall not be deemed to constitute part of this Agreement or to affect the construction thereof. 
 17. Governing Law. This Agreement and the legal relations among the parties shall be governed by, and construed and enforced in accordance with,
the laws of the State of Delaware, without regard to its conflict of laws rules. 

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

			
	AVICI SYSTEMS INC.
		
	By:	 	  

	Name:	 	
	Title:	 	
	
	Avici Systems Inc.
	101 Billerica Avenue
	North Billerica, MA 01862
	Attention: Secretary
	
	INDEMNITEE
	
	  

	Name:	 	
	
	Address:Fifth Amendment to the Rights Agreement

 Exhibit 4.6 
 FIFTH AMENDMENT 
 to the 
 RIGHTS AGREEMENT 
 between 
 REDBACK NETWORKS INC. 
 and 
 U.S. STOCK TRANSFER CORPORATION 
 This Fifth Amendment (this “Amendment”) to the Rights Agreement
is made and entered into as of December 19, 2006 between REDBACK NETWORKS INC., a Delaware corporation (the “Company”), and U.S. STOCK TRANSFER CORPORATION, as Rights Agent (the “Rights Agent”). 
 B A C K G R O U N D 
 WHEREAS, the Company
and the Rights Agent entered into a Rights Agreement dated as of June 12, 2001, which was amended on May 21, 2002, October 2, 2003, January 5, 2004 and May 9, 2006 (the “Rights Agreement”); 
 WHEREAS, Section 27 of the Rights Agreement provides that, in certain circumstances, the Company may supplement or amend the Rights Agreement
without the approval of any holders of Rights; 
 WHEREAS, the Company desires to modify the terms of the Rights Agreement in certain
respects as set forth herein, and in connection therewith, is entering into this Amendment and directing the Rights Agent to enter into this Amendment. 
 NOW, THEREFORE, for good and valuable consideration, the receipt and adequacy of which are hereby acknowledged, the parties hereto agree as follows: 
 1. Effect of Amendment. Except as and to the extent expressly provided by this Amendment, the Rights Agreement and the exhibits thereto, shall be
and remain in full force and effect in all respects. In the event of a conflict or inconsistency between this Amendment and the Rights Agreement and the exhibits thereto, the provisions of this Amendment shall govern. 
 2. Capitalized Terms. All capitalized, undefined terms used in this Amendment shall have the meanings assigned thereto in the Rights Agreement.

 3. Amendment to Section 1(a). Section 1(a) of the Rights Agreement is hereby amended by adding the following new
sentence: 
 “Notwithstanding the foregoing, neither Telefonaktiebolaget LM Ericsson (publ), nor any of its Affiliates or Associates
shall be deemed an Acquiring Person and none of a Stock Acquisition Date, a Distribution Date or a Flip-In Event shall be deemed to occur and the Rights will not separate from the Common Stock, in each case, by reason of the execution, delivery,
adoption, performance or consummation of the transactions contemplated pursuant to (i) the Agreement and Plan of Merger, dated as of 

 
December 19, 2006, by and among the Company, Telefonaktiebolaget LM Ericsson (publ) and Maxwell Acquisition Corporation (including any amendment or
supplement thereto, the “Merger Agreement”), and (ii) the Support Agreement (as defined in the Merger Agreement).” 
 4.
Amendment of Section 7. Section 7 of the Rights Agreement is hereby amended by adding the following provision immediately following clause (a)(iii) thereof: 
 “or (iv) the Effective Time (as defined in the Merger Agreement).” 
 5. Effective Date. This Amendment shall be deemed to be in force and effect immediately prior to the execution of the Merger Agreement and the
Support Agreement; provided, however, that this Amendment shall automatically terminate (if at all) and be of no further force or effect on the date on which the Merger Agreement is terminated in accordance with its terms. 
 6. Governing Law. This Amendment shall be governed by, construed and enforced in accordance with the laws of the State of Delaware without
reference to the conflicts or choice of law principles thereof. 
 7. Counterparts. This Amendment may be executed in separate
counterparts, each of which when executed and delivered is an original but all of which taken together constitute one and the same instrument. 
 8. Fax Transmission. A facsimile, telecopy or other reproduction of this Amendment may be executed by one or more parties hereto, and an executed copy of this Amendment may be delivered by one or more parties hereto by facsimile or
similar instantaneous electronic transmission device pursuant to which the signature of or on behalf of such party can be seen, and such execution and delivery shall be considered valid, binding and effective for all purposes. At the request of any
party hereto, all parties hereto agree to execute an original of this Amendment as well as any facsimile, telecopy or other reproduction thereof. 
 [signature page follows] 
  

 2 

 IN WITNESS WHEREOF, the Company and the Rights Agent have caused this Amendment to be duly executed as of
the day first above written. 
  

			
	REDBACK NETWORKS INC.
		
	By:	 	 /s/ Thomas L. Cronan III

	Name:	 	Thomas L. Cronan III
	Title:	 	Senior Vice President of Finance and Administration and Chief Financial Officer
	
	 U.S. STOCK TRANSFER CORPORATION
 as
Rights Agent

		
	By:	 	 /s/ William Garza

	Name:	 	William Garza
	Title:	 	Vice President

  

 3

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