Document:

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                                                                   EXHIBIT 10.1
                                                       to Agreement and Plan of
                                                      Merger and Reorganization

                          REGISTRATION RIGHTS AGREEMENT

         This Registration Rights Agreement (this "AGREEMENT"), dated as of
November 2, 2000, is entered into by and among Sonus Networks, Inc., a Delaware
corporation (the "COMPANY"), and the persons and entities listed on the
signature pages hereto under the heading "Stockholders" (each individually, a
"STOCKHOLDER", and collectively, the "STOCKHOLDERS").

                                   BACKGROUND

         WHEREAS, as of the date hereof, the Company, Storm Merger Sub, Inc., a
Texas corporation and wholly-owned subsidiary of the Company ("MERGER SUB"), and
telecom technologies, inc., a Texas corporation ("TARGET"), have entered into an
Agreement and Plan of Merger and Reorganization (the "MERGER AGREEMENT"),
pursuant to the terms of which, among other things, the Merger Sub will be
merged with and into Target (the "MERGER") and the outstanding shares of
Target's Class A common stock, no par value, and Class B common stock, no par
value, will be converted into the right to receive shares of Common Stock (as
defined below); and

         WHEREAS, it is a condition precedent to the obligations of the Company
and Target under the Merger Agreement that such parties execute and deliver this
Registration Rights Agreement;

         NOW, THEREFORE, in consideration of the mutual promises and covenants
contained in this Agreement, and for other valuable consideration, receipt of
which is hereby acknowledged, the parties hereto agree as follows:

                                    ARTICLE I
                                   DEFINITIONS

         As used in this Agreement, the following terms shall have the following
respective meanings:

                  "COMMISSION" means the United States Securities and Exchange
Commission, or any other federal agency at the time administering the Securities
Act.

                  "COMMON STOCK" means the common stock, $0.001 par value per
share, of the Company.

                  "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended, and the rules and regulations of the Commission issued under such Act,
as they each may, from time to time, be in effect.

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                                      -2-

                  "ORIGINAL REGISTRATION RIGHTS AGREEMENT" shall mean the Third
Amended and Restated Investor Rights Agreement, dated as of March 9, 2000, among
the Company and the Purchasers and Founders named therein.

                  "REGISTRATION STATEMENT" means a registration statement filed
by the Company with the Commission for a public offering and sale of Common
Stock by the Company or holders of shares of Common Stock (other than a
registration statement on Form S-8 or Form S-4, or their successors, or any
other form for a similar limited purpose, or any registration statement covering
only securities proposed to be issued in exchange for securities or assets of
another corporation).

                  "REGISTRATION EXPENSES" means the expenses described in
Section 4 of Article II below.

                  "REGISTRABLE SHARES" means (i) the Shares, and (ii) any other
shares of Common Stock issued in respect of such Shares (because of stock
splits, stock dividends, reclassifications, recapitalizations, or similar
events); PROVIDED, HOWEVER, that shares of Common Stock that are Registrable
Shares shall cease to be Registrable Shares upon any sale of such shares
pursuant to a Registration Statement or Rule 144 or Rule 145 under the
Securities Act.

                  "SECURITIES ACT" means the Securities Act of 1933, as amended,
and the rules and regulations of the Commission issued under such Act, as they
each may, from time to time, be in effect.

                  "SHARES" means the shares of Common Stock issuable to the
Stockholders in the Merger.

                                   ARTICLE II
                               REGISTRATION RIGHTS

         1.       INCIDENTAL REGISTRATIONS.

                  (a) Whenever the Company proposes to file a Registration
Statement at any time and from time to time, whether for its own account or the
account of other stockholders, it will, prior to such filing, give written
notice to each Stockholder of its intention to do so and, upon the written
request of any such Stockholder or Stockholders, given within ten 10 business
days after the Company provides such notice (which request shall state the
intended method of disposition of such Registrable Shares), the Company shall
use its reasonable best efforts to cause all Registrable Shares which the
Company has been requested by such Stockholder or Stockholders to register, to
be registered under the Securities Act to the extent necessary to permit their
sale or other disposition in accordance with the intended methods of
distribution specified in the request of such Stockholder or Stockholders;
PROVIDED, HOWEVER, that the Company shall have the right to postpone or withdraw
any registration effected pursuant to this Section 1 without obligation to any
Stockholder.

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                                      -3-

                  (b) In connection with any registration under this Section 1
involving an underwriting, the Company shall not be required to include any
Registrable Shares in such registration unless the holders thereof accept the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it. If in the opinion of the managing underwriter it is
desirable because of marketing factors to limit the number of Registrable Shares
to be included in the offering, then the Company shall be required to include in
the registration only that number of Registrable Shares, if any, which the
managing underwriter believes should be included therein; PROVIDED, HOWEVER,
that no persons or entities other than the Company, the Stockholders and other
persons or entities holding registration rights (including those persons holding
registration rights under the Original Registration Rights Agreement) shall be
permitted to include securities in the offering. If the number of Registrable
Shares to be included in the offering in accordance with the foregoing is less
than the total number of shares which the holders of Registrable Shares have
requested to be included, then the holders of Registrable Shares who have
requested registration and other holders of securities entitled to include them
in such registration shall participate in the registration pro rata based upon
their total ownership of shares of Common Stock (giving effect to the conversion
into Common Stock of all securities convertible thereinto). If any holder would
thus be entitled to include more securities than such holder requested to be
registered, then the excess shall be allocated among other requesting holders
pro rata in the manner described in the preceding sentence.

         2.       REGISTRATION PROCEDURES. If and whenever the Company is
required by the provisions of this Agreement to effect the registration of any
of the Registrable Shares under the Securities Act, the Company shall:

                  (a) file with the Commission a Registration Statement with
respect to such Registrable Shares and use its best efforts to cause that
Registration Statement to become effective;

                  (b) as expeditiously as possible prepare and file with the
Commission any amendments and supplements to the Registration Statement and the
prospectus included in the Registration Statement as may be necessary to keep
the Registration Statement effective, in the case of a firm commitment
underwritten public offering, until each underwriter has completed the
distribution of all securities purchased by it and, in the case of any other
offering, until the earlier of the sale of all Registrable Shares covered
thereby or two years after the effective date thereof;

                  (c) as expeditiously as possible furnish to each selling
Stockholder such reasonable numbers of copies of the prospectus, including a
preliminary prospectus, in conformity with the requirements of the Securities
Act, and such other documents as the selling Stockholder may reasonably request
in order to facilitate the public sale or other disposition of the Registrable
Shares owned by the selling Stockholder; and

                  (d) as expeditiously as possible use its best efforts to
register or qualify the Registrable Shares covered by the Registration Statement
under the securities or Blue Sky laws of such states as the selling Stockholder
shall reasonably request, and do any and all other acts and things that may be
necessary or desirable to enable the selling Stockholder to consummate

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                                      -4-

the public sale or other disposition in such states of the Registrable Shares
owned by the selling Stockholder; PROVIDED, HOWEVER, that the Company shall not
be required in connection with this paragraph (d) to qualify as a foreign
corporation or execute a general consent to service of process in any
jurisdiction.

         If the Company has delivered preliminary or final prospectuses to the
selling Stockholders and after having done so the prospectus is amended to
comply with the requirements of the Securities Act, the Company shall promptly
notify the selling Stockholders and, if requested, the selling Stockholder shall
immediately cease making offers of Registrable Shares and return all
prospectuses to the Company. The Company shall promptly provide each selling
Stockholder with revised prospectuses and, following receipt of the revised
prospectuses, the selling Stockholder shall be free to resume making offers of
the Registrable Shares.

         As set forth in the next paragraph, notwithstanding the foregoing, each
selling Stockholder shall cease making offers or sales pursuant to a "shelf"
Registration Statement during any period (with the total of such periods not to
exceed ninety (90) days in any 12 calendar month period) in which the Company
determines, by notice to each selling Stockholder, that it is in possession of
material non-public information that, for valid business reasons, it wishes to
keep confidential.

         If, after a Registration Statement becomes effective, the Company
becomes engaged in any activity which, in the good faith determination of the
Company's Board of Directors, involves information that would have to be
disclosed in the Registration Statement but which the Company desires to keep
confidential for valid business reasons, then the Company may at its option, by
notice to such Stockholders, require that the Stockholders who have included
Shares in such Registration Statement cease sales of such Shares under such
Registration Statement for a period of time not to exceed 90 days and with the
total of such periods not to exceed ninety (90) days in any twelve (12) calendar
month period. If, in connection therewith, the Company considers it appropriate
for such Registration Statement to be amended, the Company shall so amend such
Registration Statement as promptly as practicable and such Stockholders shall
suspend any further sales of their Shares until the Company advises them that
such Registration Statement has been amended (subject to the same time
restrictions set forth in the preceding sentence). The time periods referred to
herein during which such Registration Statement must be kept effective shall be
extended for an additional number of days equal to the number of days during
which the right to sell shares was suspended pursuant to this paragraph.

         3. ALLOCATION OF EXPENSES. The Company will pay all Registration
Expenses of all registrations under this Agreement. For purposes of this Section
4, the term "Registration Expenses" shall mean all expenses incurred by the
Company in complying with Article II, Section 1, including, without limitation,
all registration and filing fees, exchange listing fees, printing expenses, fees
and expenses of one counsel to represent the selling Stockholder(s), state Blue
Sky fees and expenses, and the expense of any special audits incident to or
required by any such registration, but excluding underwriting discounts, selling
commissions and the fees and expenses of selling Stockholders' own counsel.

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         4.       INDEMNIFICATION AND CONTRIBUTION.

                  (a) In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, the Company will
indemnify and hold harmless the seller of such Registrable Shares, each
underwriter of such Registrable Shares, and each other person, if any, who
controls such seller or underwriter within the meaning of the Securities Act or
the Exchange Act against any losses, claims, damages or liabilities, joint or
several, to which such seller, underwriter or controlling person may become
subject under the Securities Act, the Exchange Act, state securities or Blue Sky
laws or otherwise, insofar as such losses, claims, damages or liabilities (or
actions in respect thereof) arise out of or are based upon any untrue statement
or alleged untrue statement of any material fact contained in any Registration
Statement under which such Registrable Shares were registered under the
Securities Act, any preliminary prospectus or final prospectus contained in the
Registration Statement, or any amendment or supplement to such Registration
Statement, or arise out of or are based upon the omission or alleged omission to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading; and the Company will reimburse such seller,
underwriter and each such controlling person for any legal or any other expenses
reasonably incurred by such seller, underwriter or controlling person in
connection with investigating or defending any such loss, claim, damage,
liability or action; PROVIDED, HOWEVER, that the Company will not be liable in
any such case to a seller, underwriter or controlling person to the extent that
any such loss, claim, damage or liability arises out of or is based upon any
untrue statement or omission made in such Registration Statement, preliminary
prospectus or final prospectus, or any such amendment or supplement, in reliance
upon and in conformity with information furnished to the Company, in writing, by
or on behalf of such seller, underwriter or controlling person specifically for
use in the preparation thereof.

                  (b) In the event of any registration of any of the Registrable
Shares under the Securities Act pursuant to this Agreement, each seller of
Registrable Shares, severally and not jointly, will indemnify and hold harmless
the Company, each of its directors and officers and each underwriter (if any)
and each person, if any, who controls the Company or any such underwriter within
the meaning of the Securities Act or the Exchange Act, against any losses,
claims, damages or liabilities, joint or several, to which the Company, such
directors and officers, underwriter or controlling person may become subject
under the Securities Act, Exchange Act, state securities or Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect thereof) arise out of or are based upon any untrue statement or alleged
untrue statement of a material fact contained in any Registration Statement
under which such Registrable Shares were registered under the Securities Act,
any preliminary prospectus or final prospectus contained in the Registration
Statement, or any amendment or supplement to the Registration Statement, or
arise out of or are based upon any omission or alleged omission to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading, if the statement or omission was made in reliance upon
and in conformity with information relating to such seller furnished in writing
to the Company by or on behalf of such seller specifically for use in connection
with the preparation of such Registration Statement, prospectus, amendment or
supplement; PROVIDED, HOWEVER, that the obligations of each such Stockholder
hereunder shall be limited to an amount equal to the net proceeds to such
Stockholder of Registrable Shares sold in connection with such registration.

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                                      -6-

                  (c) Each party entitled to indemnification under this Article
II, Section 5 (the "INDEMNIFIED PARTY") shall give notice to the party required
to provide indemnification (the "INDEMNIFYING PARTY") promptly after such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought, and shall permit the Indemnifying Party to assume the defense of any
such claim or any litigation resulting therefrom; PROVIDED, that counsel for the
Indemnifying Party, who shall conduct the defense of such claim or litigation,
shall be approved by the Indemnified Party (whose approval shall not be
unreasonably withheld); and, PROVIDED FURTHER, that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Article II, Section 5, unless
and except to the extent that the Indemnifying Party is prejudiced by the
failure of the Indemnified Party to provide timely notice. The Indemnified Party
may participate in such defense at such party's expense; PROVIDED, HOWEVER, that
the Indemnifying Party shall pay such expense if representation of such
Indemnified Party by the counsel retained by the Indemnifying Party would be
inappropriate due to actual or potential differing interests between the
Indemnified Party and any other party represented by such counsel in such
proceeding. No Indemnifying Party, in the defense of any such claim or
litigation shall, except with the consent of each Indemnified Party, consent to
entry of any judgment or enter into any settlement which does not include as an
unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect of such claim or
litigation, and no Indemnified Party shall consent to entry of any judgment or
settle such claim or litigation without the prior written consent of the
Indemnifying Party.

                  (d) In order to provide for just and equitable contribution to
joint liability under the Securities Act in any case in which either (i) any
holder of Registrable Shares exercising rights under this Agreement, or any
controlling person of any such holder, makes a claim for indemnification
pursuant to this Article II, Section 5 but it is judicially determined (by the
entry of a final judgment or decree by a court of competent jurisdiction and the
expiration of time to appeal or the denial of the last right of appeal) that
such indemnification may not be enforced in such case notwithstanding the fact
that this Article II, Section 5 provides for indemnification in such case, or
(ii) contribution under the Securities Act may be required on the part of any
such selling Stockholder or any such controlling person in circumstances for
which indemnification is provided under this Article II, Section 5; then, in
each such case, the Company and such Stockholder will contribute to the
aggregate losses, claims, damages or liabilities to which they may be subject
(after contribution from others) in such proportions so that such holder is
responsible for the portion represented by the percentage that the public
offering price of its Registrable Shares offered by the Registration Statement
bears to the public offering price of all securities offered by such
Registration Statement, and the Company is responsible for the remaining
portion; PROVIDED, HOWEVER, that, in any such case, (A) no such holder will be
required to contribute any amount in excess of the net proceeds to it of all
Registrable Shares sold by it pursuant to such Registration Statement, and (B)
no person or entity guilty of fraudulent misrepresentation, within the meaning
of Section 11(f) of the Securities Act, shall be entitled to contribution from
any person or entity who is not guilty of such fraudulent misrepresentation.

         5. INFORMATION BY STOCKHOLDER. Each Stockholder including Registrable
Shares in any registration shall furnish to the Company such information
regarding such Stockholder and

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                                      -7-

the distribution proposed by such Stockholder as the Company may reasonably
request in writing and as shall be required in connection with any registration,
qualification or compliance referred to in this Agreement.

         6. "STAND-OFF" AGREEMENT. Each Stockholder, if requested by the Company
and the managing underwriter of an offering of Common Stock or other securities
of the Company pursuant to a Registration Statement, shall agree not to sell
publicly or otherwise transfer or dispose of any Registrable Shares held by such
Stockholder for a specified period of time (not to exceed 90 days) following the
effective date of such Registration Statement, subject to customary exceptions
and other customary terms; PROVIDED:

         (a)  the Company provides notice to each Stockholder no less than 7
              days from the Closing and such period terminates no later than 180
              days from the Closing that such limitations on transfer are being
              requested by the Company (the "STAND-OFF NOTICE"), which such
              Stand-Off Notice shall (i) include a representation by the Company
              that it has used its reasonable best efforts to obtain the
              agreement of the managing underwriter of such offering that such
              limitations on transfers by the Stockholders are not necessary for
              the completion of the offering; and (ii) be delivered to each
              Stockholder no more than 20 days prior to the reasonably
              anticipated effectiveness of such Registration Statement and which
              such limitations called for therein shall take effect no earlier
              than 10 trading days following the delivery of such Stand-Off
              Notice; and

         (b)  all executive officers, directors, and holders of shares of Common
              Stock who have acquired such shares directly from the Company in a
              transaction that was not registered under the Securities Act and
              hold as many or more shares of Common Stock as were originally
              issued to such Stockholder in the Merger (collectively with
              respect to such Stockholder, the "Covered Persons") of the Company
              have agreed to limitations on transfers with respect to their
              shares of Common Stock or other securities of the Company at least
              as extensive as those set forth called for by such Stand-Off
              Notice, which such agreement the Company shall certify in the
              Stand-Off Notice sent to each Stockholder;

and, PROVIDED, FURTHER, that (i) in the event that any Stockholder other than
Anousheh Ansari or Hamid Ansari requests the inclusion of fifty percent (50%) or
more of the Registrable Securities then owned by it in the offering in
accordance with Section 1(a), and the Company is unable to include at least
fifty percent (50%) of the Registrable Shares held by such Stockholder, any
lock-up or similar agreement entered into by such Stockholder pursuant to this
Section 6 shall immediately terminate; (ii) in the case of Anousheh Ansari or
Hamid Ansari, the Company shall comply with its registration obligations set
forth herein; and (iii) if the Company releases any Covered Person from its
limitations under the agreements described in (c) above, such release shall
apply the same extent to each Stockholder, and the Company shall promptly inform
each Stockholder thereof.

         7. LIMITATIONS ON SUBSEQUENT REGISTRATION RIGHTS. The Company shall
not, without the prior written consent of Stockholders holding 66 2/3% of the
Registrable Shares held by all

<PAGE>

                                      -8-

Stockholders, enter into any agreement (other than this Agreement), or amend any
outstanding agreements with any holder or prospective holder of any securities
of the Company which would allow such holder or prospective holder to include
securities of the Company in any Registration Statement upon terms which are
more favorable to such holder or prospective holder than the terms on which
holders of Registrable Shares may include shares in such registration, PROVIDED,
HOWEVER, that nothing in this Agreement shall be deemed to limit the existing
rights and obligations of the Company and the Purchasers and Founders named
therein under the Original Registration Rights Agreement.

         8. RULE 144 REQUIREMENTS. Until such time that there shall no longer be
any Registrable Securities, the Company agrees to:

             (i) comply with the requirements of Rule 144(c) under the
Securities Act with respect to current public information about the Company;

             (ii) use its best efforts to file with the Commission in a timely
manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act (at any time after it has become subject to
such reporting requirements); and

             (iii) furnish to any holder of Registrable Shares upon request (A)
a written statement by the Company as to its compliance with the requirements of
said Rule 144(c), and the reporting requirements of the Securities Act and the
Exchange Act (at any time after it has become subject to such reporting
requirements), (B) a copy of the most recent annual or quarterly report of the
Company, and (C) such other reports and documents of the Company as such holder
may reasonably request to avail itself of any similar rule or regulation of the
Commission allowing it to sell any such securities without registration.

                                   ARTICLE III
                                     GENERAL

         1.  NO TRANSFER OF RIGHTS.

             This Agreement, and the rights and obligations of the Stockholders
and the Company hereunder, may not be assigned by any party hereunder.

         2.  SEVERABILITY. The provisions of this Agreement are severable, so
that the invalidity or unenforceability of any provision of this Agreement shall
not affect the validity or enforceability of any other term or provision of this
Agreement, which shall remain in full force and effect.

         3.  GOVERNING LAW. This Agreement shall be governed by, and
construed and enforced in accordance with, the laws of the State of Delaware
(without reference to the conflicts of law provisions thereof).

         4. NOTICES. All notices, requests, consents, and other communications
under this Agreement shall be in writing and shall be delivered by hand, sent
via a reputable nationwide

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                                      -9-

overnight courier service or mailed by first class certified or registered mail,
return receipt requested, postage prepaid:

         If to the Company, at Sonus Networks, Inc., 5 Carlisle Ave, Westford,
MA 01886, Attn: President, or at such other address or addresses as may have
been furnished in writing by the Company to the Purchasers, with a copy to
Bingham Dana LLP, 150 Federal Street, Boston, MA 02110, Attn: David L. Engel,
Esq. and Johan V. Brigham, Esq.;

         If to a Stockholder, at its address as set forth the signature pages
hereto, or at such other address or addresses as may have been furnished to the
Company in writing by such Stockholder, with a copy to Wachtell, Lipton, Rosen &
Katz, 51 West 52nd Street, New York, NY 10019, Attn: Andrew J. Nussbaum, Esq.;
or

         Notices provided in accordance with this Article III, Section 4 shall
be deemed delivered upon personal delivery, one (1) business day after being
sent via a reputable nationwide overnight courier service, or five (5) business
days after deposit in the mail.

         5.  COMPLETE AGREEMENT; AMENDMENTS.

             (a) This Agreement constitutes the full and complete agreement of
the parties hereto with respect to the subject matter hereof.

             (b) This Agreement may be amended and the observance of any term of
this Agreement may be waived (either generally or in a particular instance and
either retroactively or prospectively) at any time by a written instrument
signed by the Company and Stockholders holding at least 66 2/3% of the
Registrable Shares. No waivers of or exceptions to any term, condition or
provision of this Agreement, in any one or more instances, shall be deemed to
be, or construed as, a further or continuing waiver of any such term, condition
or provision.

         6.  PRONOUNS. Whenever the content may require, any pronouns used in
this Agreement shall include the corresponding masculine, feminine or neuter
forms, and the singular form of nouns and pronouns shall include the plural, and
vice versa.

         7.  COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which shall be deemed to be an original, and all of which
together shall constitute one Agreement binding on all the parties hereto.

         8.  CAPTIONS. Captions of sections have been added only for
convenience and shall not be deemed to be a part of this Agreement.

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         IN WITNESS WHEREOF, this Agreement has been executed as an instrument
under seal as of the date first above written.

         COMPANY

         By:      ____________________________________
                  President

         STOCKHOLDERS:

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

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

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

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         ----------------------------------<PAGE>

                                                                    EXHIBIT 10.2

                              SONUS NETWORKS, INC.

                               2000 RETENTION PLAN

<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<S>                                                                     <C>
1.  Purpose.............................................................1

2.  Definitions.........................................................1

3.  Term of the Plan....................................................2

4.  Stock Subject to the Plan...........................................2

5.  Administration......................................................3

6.  Authorization and Eligibility.......................................3

7.  Expiration of Awards................................................4

8.  Adjustment Provisions...............................................4

9.  Settlement of Awards................................................5

10. Unfunded Status of Plan.............................................7

11. Non-Transferability of Awards.......................................7

12. Reservation of Stock................................................7

13. No Special Employment or Other Rights...............................7

14. Nonexclusivity of the Plan..........................................7

15. Termination and Amendment of the Plan...............................8

16. Governing Law.......................................................8
</TABLE>

<PAGE>

                              SONUS NETWORKS, INC.

                               2000 RETENTION PLAN

1.       PURPOSE

         This Plan is intended to encourage retention of TTI employees and to
provide additional incentive for them to promote the success of the business of
the Company and TTI This Plan is the "Retention Plan" contemplated by Section
12.7 of the Agreement and Plan of Merger and Reorganization by and among Sonus
Networks, Inc., TTI, and Storm Merger Sub, Inc., a Texas corporation and a
wholly-owned subsidiary of Sonus Networks, Inc., dated as of November 2, 2000
(the "Merger Agreement"), and shall at all times be administered and operated in
accordance therewith and the terms of the Plan.

2.       DEFINITIONS

         As used in this Plan, the following terms shall have the following
meanings:

         2.1. ADMINISTRATOR means so long as the obligations of the Company
under Section 10.8 of the Merger Agreement remain in effect (the "Management
Period"), the "Manager" as such term is defined in the Merger Agreement (the
"TTI Administrator"); PROVIDED, such term shall also include the Committee to
the extent the Committee has administrative responsibilities under the Plan
pursuant to Section 5; PROVIDED, further, that the Chief Executive Officer of
the Company (the "Company Administrator") and the TTI Administrator shall
administer the Plan jointly (not severally) under certain circumstances provided
under the Plan. Following the end of the Management Period, the Company
Administrator (and the Committee, if so provided under Section 5) shall
administer the Plan, unless otherwise agreed to by the Company Administrator and
the TTI Administrator.

         2.2. AFFILIATE means a corporation or other entity controlled by,
controlling or under common control with the Company.

         2.3. AWARD means an award made hereunder of Common Stock vesting upon
and only to the extent provided in the Vesting Conditions.

         2.4. AWARD AGREEMENT means an agreement between the Company and a
Participant pursuant to which an Award is made.

         2.5. BOARD means the Company's Board of Directors.

         2.6. CODE means the Internal Revenue Code of 1986, as amended from time
to time.

         2.7. COMMITTEE means the Compensation Committee of the Board, or if
such Committee does not consist solely of two (2) or more "outside directors"
(as defined in

<PAGE>

                                      -2-

Section 162(m) of the Code and applicable guidance thereunder), a subcommittee
thereof satisfying such condition.

         2.8.  COMMON STOCK or STOCK means common stock, par value $0.001
per share, of the Company.

         2.9.  COMPANY means Sonus Networks, Inc., a corporation organized
under the laws of the State of Delaware, and its successors.

         2.10. EFFECTIVE TIME means the Effective Time (as defined in the Merger
Agreement).

         2.11. FAIR MARKET VALUE means the average of the closing price for
shares of Common Stock on the Nasdaq Stock Market or other principal exchange or
market on which or in which the Common Stock is traded for the most recent
trading day prior to the date on which such determination is made.

         2.12. PARTICIPANT means any holder of an outstanding Award under the
Plan.

         2.13. PLAN means this 2000 Retention Plan, as amended from time to
time.

         2.14. RETENTION SHARES means any shares of Common Stock issued pursuant
to an Award and subject to the Vesting Conditions thereof.

         2.15 TTI means telecom technologies, inc., a corporation organized
under the laws of the State of Texas, and its successors, including the
"Surviving Corporation" (as defined in the Merger Agreement).

         2.16 VESTING CONDITIONS means the conditions under which a Participant
will be entitled to the Stock subject to an Award, if ever, as set forth on
EXHIBIT A attached to the Award.

         2.17 VESTING DATE means January 1, 2003.

3.       TERM OF THE PLAN

         Awards will be granted under this Plan only in the period commencing on
the Effective Time and ending immediately prior to the Vesting Date.

4.       STOCK SUBJECT TO THE PLAN

         At no time shall the number of shares of Common Stock issued pursuant
to or subject to outstanding Awards granted under the Plan exceed three million
(3,000,000) shares of Common Stock and at least three million (3,000,000) shares
of Common Stock shall be granted initially under the Plan; SUBJECT, HOWEVER, to
the adjustment provisions of Section 8 of the Plan. For purposes of applying the
foregoing limitation, if any Award is forfeited, the shares of Stock subject to
such forfeited Award shall again be available for Awards to be granted under the
Plan. Shares of Common Stock issued pursuant to the

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                                      -3-

Plan may be either authorized but unissued shares or shares held by the Company
in its treasury.

5.       ADMINISTRATION

         The Plan shall be administered by the TTI Administrator; PROVIDED,
HOWEVER, that the Committee shall exercise the powers and responsibilities
assigned the Administrator under the Plan insofar as it pertains to the grant of
Awards to any "covered employee" (as defined in Section 162(m) of the Code and
applicable guidance thereunder), but only if such exercise of powers and
responsibilities is necessary to preserve the deductibility of such Awards under
Section 162(m) of the Code. Subject to the provisions of the Plan, the TTI
Administrator shall have complete authority, in its discretion, to make or to
select the manner of making all determinations with respect to each Award to be
granted by the Company under the Plan including the employee to receive the
Award, PROVIDED, that the reallocation or regrant of Common Stock subject to
forfeited Awards shall be as determined by the TTI Administrator and proposed by
the TTI Administrator to the Company Administrator for and subject to its
consent, which consent shall not be unreasonably withheld, and PROVIDED FURTHER,
that the Company Administrator may withhold consent with respect to the regrant
of any Awards or Retention Shares originally issued to Anousheh Ansari and Hamid
Ansari for any reason or no reason, in its sole discretion. In making such
determinations, the Administrator may take into account the nature of the
services rendered by the employees, their present and potential contributions to
the success of the Company and its subsidiaries, and such other factors as the
Administrator in its discretion shall deem relevant. Subject to the provisions
of the Plan and Award Agreements, the Administrator shall also have complete
authority to interpret the Plan, to prescribe, amend and rescind rules and
regulations relating to it, to determine the terms and provisions of the
respective Awards (which need not be identical), and to make all other
determinations necessary or advisable for the administration of the Plan. The
Administrator's determinations made in good faith on matters referred to in this
Plan shall be final, binding and conclusive on the Company and on all persons
having or claiming any interest under this Plan or an Award made pursuant to
hereto. Unless otherwise approved by the Company Administrator, the TTI
Administrator shall not have authority to change the Vesting Conditions of any
Award or make any other amendments to any Award or the Plan that have material
adverse accounting consequences on the Company, which would otherwise not have
occurred in the absence of such change or amendment. Notwithstanding the other
provisions of this Section 5, the Company Administrator shall at all times have
the authority and discretion to waive and/or accelerate the satisfaction of any
Vesting Conditions applicable to any Award.

6.       AUTHORIZATION AND ELIGIBILITY

         6.1. GENERAL. The Administrator may grant from time to time and at any
time prior to the termination of the Plan one or more Awards, either alone or in
combination with any other Awards, to any employee of TTI. Each grant of an
Award shall be subject to all applicable terms and conditions of the Plan, and
such other terms and conditions, not inconsistent with the terms of the Plan, as
the Administrator may prescribe, and shall

<PAGE>

                                      -4-

be evidenced by an Award Agreement or other document delivered to the
Participant and in such form as the Administrator may specify.

         6.2. SPECIFIC GRANTS. As of the Effective Time, the TTI Administrator
shall grant the Awards described on EXHIBIT A attached hereto.

         6.3. GRANT OF SHARES OF STOCK SUBJECT TO FORFEITED AWARDS. If any Award
is forfeited prior to the Vesting Date, such forfeited Award shall be granted to
other Participants or employees of TTI, as determined by the TTI Administrator,
subject to the consent of the Company Administrator, as described in Section 5
above; PROVIDED, that in no event shall the Company or TTI have an obligation
hereunder to reallocate or regrant any Retention Shares that are forfeited by
Anousheh Ansari or Hamid Ansari.

7.       EXPIRATION OF AWARDS

         Each Award shall be forfeited, to the extent the Vesting Conditions
applicable thereto have not theretofore been satisfied, immediately following
the Vesting Date or, if earlier, on termination of the Participant's employment
if so provided in the applicable Award Agreement. Neither the Company nor TTI
shall have any liability or obligation in respect of forfeited Awards.

8.       ADJUSTMENT PROVISIONS

         8.1. ADJUSTMENT FOR CORPORATE ACTIONS. All of the share numbers set
forth in the Plan reflect the capital structure of the Company as of November 2,
2000. If subsequent to November 2, 2000, the outstanding shares of Common Stock
(or any other securities covered by the Plan by reason of the prior application
of this Section) are increased, decreased, or exchanged for a different number
or kind of shares or other securities, or if additional shares or new or
different shares or other securities are distributed with respect to shares of
Common Stock or other securities, through merger, consolidation, sale of all or
substantially all the property of the Company, reorganization, recapitalization,
reclassification, stock dividend, stock split, reverse stock split, or other
distribution with respect to such shares of Common Stock, or other securities,
an appropriate, equitable and proportionate adjustment will be made, to preserve
the value of outstanding Awards, in (i) the maximum numbers and kinds of shares
provided in Section 4 and (ii) the numbers and kinds of shares or other
securities subject to Awards.

         8.2. RELATED MATTERS. Any adjustment in Awards made pursuant to this
Section 8 shall be determined and made, if at all, by the Administrator and
shall include any correlative modification of terms which the Administrator may
deem necessary or appropriate so as to ensure the rights of the Participants in
their respective Awards are not diminished nor enlarged as a result of the
adjustment and corporate action. No fraction of a share shall be deliverable
upon settlement of an Award, but in the event any adjustment hereunder of the
number of shares covered by an Award shall cause such number to include a
fraction of a share, such number of shares shall be adjusted to the nearest
smaller whole number of shares, with fractional shares to be paid in cash based
on the Fair Market Value of a share of Common Stock on the date of payment.

<PAGE>

                                      -5-

9.       SETTLEMENT OF AWARDS

         9.1. DELIVERY OF STOCK. Upon satisfaction of the Vesting Conditions
applicable to an Award, the Company shall deliver to the Participant holding
such Award a certificate representing the shares of Common Stock described
therein. The Company shall file, as of the Effective Time, a registration
statement on a Form S-8 (or other appropriate form) under the Securities Act (as
defined in the Merger Agreement) to register the shares of Common Stock issuable
under the Plan, and shall cause such registration statement to remain effective
until the delivery of all shares under the Plan.

         9.2. VIOLATION OF LAW. Notwithstanding any other provision of the Plan,
if, at any time, in the reasonable opinion of the Company, the issuance of
shares of Common Stock covered by an Award may constitute a violation of law,
then the Company may delay such issuance and the delivery of a certificate for
such shares until (i) approval shall have been obtained from such governmental
agencies, other than the Securities and Exchange Commission, as may be required
under any applicable law, rule, or regulation and (ii) in the case where such
issuance would constitute a violation of a law administered by or a regulation
of the Securities and Exchange Commission, one of the following conditions shall
have been satisfied:

         (a) the shares are at the time of the issue of such shares effectively
registered under the Securities Act of 1933, as amended; or

         (b) the Company shall have determined, on such basis as it deems
appropriate (including an opinion of counsel in form and substance satisfactory
to the Company) that the sale, transfer, assignment, pledge, encumbrance or
other disposition of such shares or such beneficial interest, as the case may
be, does not require registration under the Securities Act of 1933, as amended
or any applicable State securities laws.

The Company shall use its reasonable best efforts to bring about the occurrence
of said events.

         9.3. TAX WITHHOLDING. Whenever shares of Stock are issued or to be
issued pursuant to Awards granted under the Plan, or the Vesting Conditions with
respect to such Retention Shares are satisfied in whole or in part, the Company
shall have the right to require the recipient to remit to the Company an amount
sufficient to satisfy federal, state, local or other withholding tax
requirements if, when, and to the extent required by law (whether so required to
secure for the Company an otherwise available tax deduction or otherwise) prior
to the delivery of any certificate or certificates for such shares. The
obligations of the Company under the Plan shall be conditional on satisfaction
of all such withholding obligations and the Company shall, to the extent
permitted by law, have the right to deduct any such taxes from any payment of
any kind otherwise due to the recipient of an Award. In the sole discretion of
the Company Administrator, the Participant may be permitted to satisfy any such
withholding by surrendering shares of Common Stock otherwise receivable under
the Plan, based on the Fair Market Value of a share of Common Stock on the date
on which the withholding is made, PROVIDED the

<PAGE>

                                      -6-

amount so withheld does not exceed the minimum withholding allowed and satisfies
any other conditions necessary to avoid material adverse accounting consequences
to the Company, which would otherwise not have occurred in the absence of such
withholding.

         If Participants are not permitted to satisfy withholding obligations by
the surrender of shares otherwise receivable under the Plan, the Company shall
provide that payment of the withholding taxes may in full or in part be made by
delivering a notice to the Company, together with a copy of irrevocable
instructions to a broker to deliver promptly to the Company the amount of sale
proceeds necessary to pay the amount of any federal, state, local or foreign
withholding taxes. To facilitate the foregoing, the Company shall enter into
agreements for coordinated procedures with one or more brokerage firms.

         9.4. RIGHTS PENDING ISSUANCE. Subject to Section 11 of the Plan, the
Participant shall have, with respect to the shares of Common Stock underlying an
Award, the rights of a stockholder of the Company holding the class or series of
Common Stock that is the subject of the Award, including, if applicable, the
right to vote the shares and the right to receive any cash dividends, provided
that cash dividends on the class or series of Common Stock that is the subject
of the Award shall be automatically deferred and held by the Company on behalf
of the Participant subject to the vesting of the underlying Award and shall be
payable in cash upon, but only upon, the vesting of the underlying Award.

         9.5. AWARDS AND CERTIFICATES. Awards shall be evidenced in such manner
as the Company Administrator may deem appropriate, including book-entry
registration or issuance of one or more stock certificates. Any certificate
issued in respect of Retention Shares prior to the satisfaction of the Vesting
Conditions with respect to such Retention Shares shall be registered in the name
of such Participant and shall bear an appropriate legend referring to the terms,
conditions, and restrictions applicable to such Award, substantially in the
following form:

                  "The transferability of this certificate and the shares of
                  stock represented hereby are subject to the terms and
                  conditions (including forfeiture) of the Sonus Networks, Inc.
                  2000 Retention Plan and the applicable Award Agreement
                  thereunder. Copies of such Plan and Agreement are on file at
                  the offices of Sonus Networks, Inc. "

The Company Administrator may require that the certificates evidencing the
Retention Shares be held in custody by the Company until the restrictions
thereon shall have lapsed and that, as a condition of any Award of Retention
Shares, the Participant shall have delivered a stock power, endorsed in blank,
relating to the Common Stock covered by such Award.

<PAGE>

                                      -7-

10.      UNFUNDED STATUS OF PLAN

         The Plan is intended to constitute an "unfunded" plan for incentive
compensation, and the Plan is not intended to constitute a plan subject to the
provisions of the Employee Retirement Income Security Act of 1974, as amended.
With respect to any payments not yet made to a Participant by the Company,
nothing contained herein shall give any such Participant any rights that are
greater than those of a general creditor of the Company. In its sole discretion,
the Committee may authorize the creation of trusts or other arrangements to meet
the obligations created under the Plan to deliver Stock or payments with respect
to Awards hereunder, provided, however, that the existence of such trusts or
other arrangements is consistent with the unfunded status of the Plan.

11.      NON-TRANSFERABILITY OF AWARDS

         Awards shall not be transferable, and no Award or interest therein may
be sold, transferred, pledged, assigned, or otherwise alienated or hypothecated,
other than by will or by the laws of descent and distribution. During the
Participant's life, all of a Participant's rights in any Award may be exercised
only by the Participant or the Participant's legal representative. Common Stock
with respect to which the Vesting Conditions are satisfied shall not be subject
to the transfer restrictions set forth in this Section.

12.      RESERVATION OF STOCK

         The Company shall at all times during the term of the Plan and any
outstanding Award granted hereunder reserve or otherwise keep available such
number of shares of Stock as will be sufficient to satisfy the requirements of
the Plan (if then in effect) and the Awards and shall pay all fees and expenses
necessarily incurred by the Company in connection therewith.

13.      NO SPECIAL EMPLOYMENT OR OTHER RIGHTS

         Nothing contained in the Plan or in any Award shall confer upon any
recipient of an Award any right with respect to the continuation of his or her
employment or other association with the Company or TTI or interfere in any way
with the right of the Company or TTI subject to the terms of any separate
employment or consulting agreement or provision of law or corporate charter,
certificate or articles, or by-laws, to the contrary, at any time to terminate
such employment or consulting agreement or to increase or decrease, or otherwise
adjust, the other terms and conditions of the recipient's employment or other
association with the Company or TTI.

14.      NONEXCLUSIVITY OF THE PLAN

         The adoption of the Plan by the Board shall not be construed as
creating any limitations on the power of the Board to adopt such other incentive
arrangements as it may deem desirable, including without limitation, the
granting of stock options and restricted stock other than under the Plan, and
such arrangements may be either applicable generally or only in specific cases.

<PAGE>

                                      -8-

15.      TERMINATION AND AMENDMENT OF THE PLAN

         The Board may at any time terminate the Plan or make such modifications
of the Plan as it shall deem advisable, subject to the prior written consent of
the TTI Administrator. No amendment of the Plan may adversely affect the terms
of any Award outstanding on the date of such amendment. The Board may not
terminate the Plan if such termination shall adversely affect outstanding Awards
or shall result in there being less than 3,000,000 shares of Common Stock
(subject to adjustment as provided in Section 8 of the Plan) being subject to
Awards under the Plan. Subject to the terms of Section 5 of the Plan, the
Administrator may amend the terms of any Award theretofore granted,
prospectively or retroactively, PROVIDED that the Award as amended is consistent
with the terms of the Plan, but no such amendment shall adversely affect the
rights of the recipient of such Award without his or her consent.

16.      GOVERNING LAW

         The Plan and all Awards and actions taken thereunder shall be governed,
interpreted and enforced in accordance with the laws of the State of Delaware,
without regard to the conflict of laws principles thereof.

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