<PAGE>
                                                                    Exhibit 10.4

================================================================================

                          REGISTRATION RIGHTS AGREEMENT

                                  BY AND AMONG

                                    TEKELEC,

                              SANTERA SYSTEMS INC.,

                  CERTAIN STOCKHOLDERS OF SANTERA SYSTEMS INC.

                                       AND

                 AUSTIN VENTURES VI, L.P., AS THE REPRESENTATIVE

                           DATED AS OF APRIL 30, 2003

================================================================================

<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<S>                                                                                                                <C>
Article I Definitions............................................................................................   1
         1.1      Definitions....................................................................................   1
         1.2      Usage Generally, Interpretation................................................................   3

Article II Demand Registration...................................................................................   3
         2.1      Demand Rights..................................................................................   3
         2.2      Registration Requirements......................................................................   3
         2.3      Shares to be Included in Registration Statement................................................   4

Article III Incidental Registration..............................................................................   4

Article IV Registration Procedures...............................................................................   4
         4.1      Procedures.....................................................................................   4
         4.2      Period of Distribution.........................................................................   6
         4.3      Requirement to Furnish Information.............................................................   6
         4.4      Underwriting Agreement.........................................................................   6
         4.5      Suspension of Sales............................................................................   6

Article V Expenses...............................................................................................   7
         5.1      Registration Expenses..........................................................................   7
         5.2      Allocation.....................................................................................   7
         5.3      Expenses of Counsel............................................................................   7

Article VI Indemnification and Contribution......................................................................   7
         6.1      Indemnification by Santera.....................................................................   7
         6.2      Indemnification by Legacy Santera Stockholders.................................................   8
         6.3      Notices........................................................................................   8
         6.4      Relative Fault.................................................................................   8

Article VII Termination..........................................................................................   9

Article VIII Miscellaneous.......................................................................................   9
         8.1      Transfer or Assignment of Registration Rights..................................................   9
         8.2      Limitations on Subsequent Registration Rights..................................................   9
         8.3      Notices........................................................................................   9
         8.4      Remedies.......................................................................................  11
         8.5      Expenses.......................................................................................  11
         8.6      Binding Effect; Assignment.....................................................................  11
         8.7      Amendment and Waiver...........................................................................  11
         8.8      Counterparts...................................................................................  11
         8.9      Headings.......................................................................................  11
         8.10     Severability...................................................................................  11
         8.11     Governing Law..................................................................................  12
         8.12     Further Assurances.............................................................................  12
         8.13     Third Party Beneficiary........................................................................  12
</TABLE>

                                        i

<PAGE>

                          REGISTRATION RIGHTS AGREEMENT

         This REGISTRATION RIGHTS AGREEMENT (the "Agreement") is entered into
this 30th day of April, 2003 by and among Tekelec, a California corporation
("Tekelec"), Santera Systems Inc., a Delaware corporation ("Santera"), certain
of the stockholders of Santera on the date hereof (the "Legacy Santera
Stockholders") and Austin Ventures VI, L.P., a Delaware limited partnership, as
the Representative, as defined herein.

                                    RECITALS

         A.       Concurrently herewith, Merger Sub, Inc., a Delaware
corporation ("Merger Sub"), has merged with and into Santera, with Santera being
the surviving corporation, all pursuant to that certain Agreement and Plan of
Merger dated as of April 30, 2003 by and between Tekelec, Merger Sub, Santera,
certain of the Legacy Santera Stockholders and the Representative (the "Merger
Agreement").

         B.       Santera desires to provide the Legacy Santera Stockholders
certain rights to register shares of Series A Preferred Stock, par value $0.001
per share ("Series A Preferred Stock"), of Santera, and the Common Stock, par
value $0.001 per share ("Common Stock"), of Santera issuable upon conversion
thereof, in each case on the terms and subject to the conditions contained
herein.

         NOW, THEREFORE, in consideration of the conditions and provisions
contained herein, the parties hereto hereby agree as follows:

                                    ARTICLE I
                                   DEFINITIONS

         1.1      Definitions. The following terms shall, for purposes of this
Agreement, have the following meanings (terms defined in the singular or the
plural include the plural or the singular, as the case may be):

                  "Act" shall mean the Securities Act of 1933, as amended.

                  "Affiliate" shall mean a person or entity that directly or
indirectly, through one or more intermediaries, controls, is controlled by, or
is under common control with, the person or entity referred to. In this
definition, "control" shall mean the possession, direct or indirect, of the
power to direct or cause the direction of the management and policies of a
person or entity, whether through ownership of securities, by contract or
otherwise.

                  "Agreement" shall mean this Registration Rights Agreement, as
the same may be amended from time to time in accordance with the terms hereof.

                  "Amended and Restated Certificate of Incorporation" shall mean
that certain Amended and Restated Certificate of Incorporation of Santera dated
_____________, 2003, as the same may be amended from time to time.

                  "Assignee" shall mean the transferee of at least 500 shares of
Registrable Securities, as adjusted for any stock dividends, combinations,
reverse stock splits, stock splits, recapitalizations,

                                        1

<PAGE>

reorganizations, reclassifications or other similar events with respect to such
shares (or a lesser number if such number represents one hundred percent (100%)
of the transferor's Registrable Securities).

                  "Commission" shall mean the Securities and Exchange
Commission.

                  "Common Stock" shall have the meaning set forth in the
recitals hereto.

                  "Exchange Act" shall mean the Securities Exchange Act of 1934,
as amended.

                  "Filings" shall have the meaning provided in Section 6.1.

                  "Legacy Santera Stockholders" shall have the meaning set forth
in the introduction hereto.

                  "Merger Agreement" shall have the meaning set forth in the
recitals hereto.

                  "Merger Sub" shall have the meaning set forth in the recitals
hereto.

                  "Preferred Stock" shall mean the Series A Preferred Stock and
the Series B Preferred Stock, collectively.

                  "Representative" shall mean Austin Ventures VI, L.P., who has
been appointed the representative of the Legacy Santera Stockholders, pursuant
to the terms of the Escrow Agreement, or any successor appointed pursuant to the
terms of the Escrow Agreement.

                  "Registrable Securities" shall mean (i) the Preferred Stock
and the Common Stock issuable upon conversion thereof, in each case held by the
Legacy Santera Stockholders or their Affiliates or Assignees and (ii) any Common
Stock of Santera issued as (or issuable upon the conversion or exercise of any
warrant, right or other security that is issued as) a dividend or other
distribution with respect to, or in exchange for, or in replacement of, the
shares references in (i) above.

                  "Registration Expenses" shall have the meaning provided in
Section 5.1.

                  "Santera" shall mean Santera Systems Inc., a Delaware
corporation.

                  "Series A Preferred Stock" shall mean the Series A Convertible
Preferred Stock, par value $0.001 per share, of Santera that is authorized on
the date hereof.

                  "Series B Preferred Stock" shall mean the Series B Convertible
Preferred Stock, par value $0.001 per share, of Santera that is authorized on
the date hereof.

                  "Stockholder" or "Stockholders" shall mean Tekelec, the Legacy
Santera Stockholders and any Person who becomes a Stockholder by Instrument of
Accession.

                  "Stock" shall mean the Common Stock and the Preferred Stock,
collectively.

                                       2

<PAGE>

                  "Tekelec" shall have the meaning set forth in the introduction
hereto.

                  "Stockholders' Agreement" shall mean that certain
Stockholders' Agreement dated as of April 30, 2003 among Tekelec, Santera, the
Legacy Santera Stockholders and the Representative.

         1.2      Usage Generally, Interpretation. Whenever the context may
require, any pronoun includes the corresponding masculine, feminine and neuter
forms. All references herein to articles, sections, subsections or paragraphs
shall be deemed to be references to articles, sections, subsections or
paragraphs of this Agreement unless the context otherwise requires. Unless
otherwise expressly provided herein, any agreement, instrument or statute
defined or referred to herein or in any agreement or instrument that is referred
to herein means such agreement, instrument or statute, as from time to time
amended, modified or supplemented, including (in the case of agreements or
instruments) by waiver or consent and (in the case of statutes) by succession of
comparable successor statutes and references to all attachments thereto and
instruments incorporated therein. Unless otherwise expressly provided herein,
all references to "as converted" or "as if converted" shall mean assuming
conversion of all then issued and outstanding shares of Preferred Stock
(including any of such shares that the holder thereof may not yet have the right
to convert into shares of Common Stock).

                                   ARTICLE II
                               DEMAND REGISTRATION

         2.1      Demand Rights. Beginning September 1, 2008 provided no call
right or put right under Article III of the Stockholders' Agreement or no notice
of redemption under Article Fourth, Section B.(ii)(I) or (II) of the Amended and
Restated Certificate of Incorporation has been delivered prior to March 1, 2008,
the Representative (on behalf of the Legacy Santera Stockholders) may request
Santera to register under the Act all or any portion of the Registrable
Securities for sale in the manner specified in the notice delivered to Santera
by the Representative, provided that the aggregate price to the public of such
public offering would exceed $35,000,000 and the per share price to the public
of such public offering would exceed $10. Any offering under this Section 2.1
must be a firm commitment underwritten public offering. In any firm commitment
underwritten public offering contemplated by this Section 2.1 or Article III,
Santera shall be entitled to require any shares of Series A Preferred Stock to
be converted into shares of Common Stock for sale to the underwriters, with such
conversion to take effect immediately prior to the closing of such sale to the
underwriters. Notwithstanding anything to the contrary contained herein, no
request may be made under this Section 2.1 within 120 days after the effective
date of a registration statement filed by Santera covering a firm commitment
underwritten public offering in which the holders of Registrable Securities
shall have been entitled to join pursuant to Article III.

         2.2      Registration Requirements. Following receipt of any notice
under Section 2.1, Santera shall use its commercially reasonable efforts to
effect within sixty (60) days of the date such request is given the registration
under the Act, for public sale, the number of shares of Registrable Securities
specified in such notice. In addition, Santera shall designate the managing
underwriter of such offering, provided that such managing underwriter shall be
reasonably acceptable to the Representative. Santera shall be obligated to
register the Registrable Securities pursuant to Section 2.1 on one (1) occasion
only, provided, however, that such obligation shall be deemed satisfied only
when a registration statement covering all Registrable Securities specified in
the notice received as

                                       3

<PAGE>

aforesaid, for sale in accordance with the method of disposition specified in
such notice, shall have become effective and all such shares shall have been
sold pursuant thereto.

         2.3      Shares to be Included in Registration Statement. Santera shall
be entitled to include in any registration statement referred to in Section 2.1,
for sale in accordance with Section 2.1, shares of Stock to be sold by Santera
for its own account. The number of shares of Stock to be included in such an
underwriting may be reduced if and to the extent that the managing underwriter
shall be of the opinion that such inclusion would adversely affect the marketing
of the securities to be sold therein; provided, however, that in no event shall
the number of Registrable Securities included in the offering be reduced unless
all of the other shares of Stock included in the offering are eliminated from
such offering completely. Except for registration statements on Form S-4, S-8 or
any successor thereto, Santera will not file with the Commission any other
registration statement with respect to its Stock, whether for its own account or
that of other stockholders, from the date of receipt of a notice from the
Representative pursuant to Section 2.1 until the later of (i) completion of the
period of distribution of the registration contemplated thereby or (ii) the
expiration of any "lock-up" period imposed by the underwriters in connection
with a registration under Section 2.1 hereof.

                                   ARTICLE III
                             INCIDENTAL REGISTRATION

         If, at any time beginning September 1, 2008 provided no call right or
put right under Article III of the Stockholders' Agreement or no notice of
redemption under Article Fourth, Section B.(ii)(I) or (II) of the Amended and
Restated Certificate of Incorporation has been delivered prior to March 1,
2006, Santera (other than pursuant to Article II) proposes to register any of
its securities under the Act for sale to the public, whether for its own account
or for the account of other security holders or both (except with respect to
registration statements on Forms S-4, S-8 or another form not available for
registering the Stock for sale to the public), each such time it will give
written notice to the Representative of its intention so to do. Upon the written
request of the Representative, received by Santera within thirty (30) days after
the giving of any such notice by Santera, to register any of the Registrable
Securities, Santera will use its commercially reasonable efforts to cause the
Registrable Securities as to which registration shall have been so requested to
be included in the securities to be covered by the registration statement
proposed to be filed by Santera, all to the extent requisite to permit the sale
or other disposition by the holders of Registrable Securities. In the event that
any registration pursuant to this Article III shall be, in whole or in part, an
underwritten public offering of Common Stock, the Registrable Securities to be
included in such an underwriting may be reduced (pro rata among the selling
stockholders according to the total number of securities requested to be
included therein by each such selling stockholder or in such other proportion as
shall be mutually agreed to by such selling stockholders) if and to the extent
that the managing underwriter shall be of the opinion that such inclusion would
adversely affect the marketing of the securities to be sold by Santera therein.

                                   ARTICLE IV
                             REGISTRATION PROCEDURES

         4.1      Procedures. If and whenever Santera is required by the
provisions of Article II or Article III to use its commercially reasonable
efforts to effect the registration of any Registrable Securities under the Act,
Santera will, as soon as reasonably practicable:

                  (a)      prepare and file with the Commission a registration
statement (which, in the case of an underwritten public offering pursuant to
Article II, shall be on Form S-1 or other form of

                                        4

<PAGE>

general applicability satisfactory to the managing underwriter selected as
therein provided) with respect to such securities and use its commercially
reasonable efforts to cause such registration statement to become and remain
effective for the period of the distribution contemplated thereby (determined as
hereinafter provided);

                  (b)      prepare and file with the Commission such amendments
and supplements to such registration statement and the prospectus used in
connection therewith as may be necessary to keep such registration statement
effective for the period specified in paragraph (a) above and comply with the
provisions of the Act with respect to the disposition of all Registrable
Securities covered by such registration statement in accordance with the
intended method of disposition set forth in such registration statement for such
period;

                  (c)      furnish to the Representative and to each underwriter
such number of copies of the registration statement and the prospectus included
therein (including each preliminary prospectus) and such other documents as such
persons reasonably may request in order to facilitate the public sale or other
disposition of the Registrable Securities covered by such registration
statement;

                  (d)      use its commercially reasonable efforts to register
or qualify the Registrable Securities covered by such registration statement
under the securities or "blue sky" laws of such jurisdictions as the
Representative or, in the case of an underwritten public offering, the managing
underwriter reasonably shall request, provided, however, that Santera shall not
for any such purpose be required to qualify generally to transact business as a
foreign corporation in any jurisdiction where it is not so qualified or to
consent to general service of process in any such jurisdiction;

                  (e)      use its commercially reasonable efforts to list the
Registrable Securities covered by such registration statement with any
securities exchange on which the Common Stock of Santera is then listed;

                  (f)      provide a transfer agent, registrar and CUSIP number
for all Registrable Securities covered by such registration statement, in each
case not later than the effective date of such registration;

                  (g)      immediately notify the Representative and each
underwriter under such registration statement, at any time when a prospectus
relating thereto is required to be delivered under the Act, of the happening of
any event of which Santera has knowledge as a result of which the prospectus
contained in such registration statement, as then in effect, includes an untrue
statement of a material fact or omits to state a material fact required to be
stated therein or necessary to make the statements therein not misleading in
light of the circumstances then existing;

                  (h)      if the offering is underwritten and at the request of
the Representative, use its commercially reasonable efforts to furnish on the
date that Registrable Securities are delivered to the underwriters for sale
pursuant to such registration: (i) an opinion dated such date of counsel
representing Santera for the purposes of such registration, addressed to the
underwriters and to the selling stockholders, stating that such registration
statement has become effective under the Act and that (A) to the knowledge of
such counsel, no stop order suspending the effectiveness thereof has been issued
and no proceedings for that purpose have been instituted or are pending or
contemplated under the Act, (B) the registration statement, the related
prospectus and each

                                        5

<PAGE>

amendment or supplement thereof comply as to form in all material respects with
the requirements of the Act (except that such counsel need not express any
opinion as to financial statements contained therein) and (C) to such other
effects as reasonably may be requested by counsel for the underwriters or by the
selling stockholders or their counsel and (ii) a letter dated such date from the
independent public accountants retained by Santera, addressed to the
underwriters and to the selling stockholders, stating that they are independent
public accountants within the meaning of the Act and that, in the opinion of
such accountants, the financial statements of Santera included in the
registration statement or the prospectus, or any amendment or supplement
thereof, comply as to form in all material respects with the applicable
accounting requirements of the Act, and such letter shall additionally cover
such other financial matters (including information as to the period ending no
more than five business days prior to the date of such letter) with respect to
such registration as such underwriters reasonably may request; and

                  (i)      make available for inspection by the Representative,
any underwriter participating in any distribution pursuant to such registration
statement, and any attorney, accountant or other agent retained by such
Representative or underwriter, all financial and other records, pertinent
corporate documents and properties of Santera, and cause Santera's officers,
directors and employees to supply all information reasonably requested by any
such Representative, underwriter, attorney, accountant or agent in connection
with such registration statement.

         4.2      Period of Distribution. For purposes of Section 2.3 and
Sections 4.1(a) and 4.1(b), the period of distribution of Registrable Securities
in a firm commitment underwritten public offering shall be deemed to extend
until each underwriter has completed the distribution of all securities
purchased by it, and the period of distribution of Registrable Securities in any
other registration shall be deemed to extend until the earlier of the sale of
all Registrable Securities covered thereby and 120 days after the effective date
thereof.

         4.3      Requirement to Furnish Information. In connection with each
registration hereunder, the Representative will furnish to Santera in writing
such information with respect to the Legacy Santera Stockholders and the
proposed distribution by the Legacy Santera Stockholders as reasonably shall be
necessary in order to assure compliance with federal and applicable state
securities laws.

         4.4      Underwriting Agreement. In connection with each registration
pursuant to Article II or Article III covering an underwritten public offering,
Santera and the Legacy Santera Stockholders agree to enter into a written
agreement with the managing underwriter selected in the manner herein provided
in such form and containing such provisions as are customary in the securities
business for such an arrangement between such underwriter and companies of
Santera's size and investment stature.

         4.5      Suspension of Sales. If Santera determines in good faith that
(i) sales of securities pursuant to the registration statement would have a
material adverse effect on Santera or its stockholders in relation to any
financing, acquisition or other corporate transaction or (ii) sales of
securities pursuant to the registration statement would require disclosure of
information Santera reasonably believes should remain confidential at such time
for a valid business purpose, in each case as evidenced by a certificate signed
by Santera's Chief Executive Officer, Santera shall be entitled to suspend all
sales under the registration statement and prospectuses related thereto for a
reasonable period of time, but not for more than an aggregate of ninety (90)
calendar days in any

                                        6

<PAGE>

360 day period (provided that any such suspension shall toll the period during
which Santera must maintain the effectiveness of such registration statement).

                                    ARTICLE V
                                    EXPENSES

         5.1      Registration Expenses. All expenses incurred by Santera in
complying with Article II, Article III and Article IV hereof, including, without
limitation, all registration and filing fees, all underwriting discounts and
selling commissions, printing expenses, fees and disbursements of independent
public accountants for Santera, fees and expenses incurred in connection with
complying with state securities or "blue sky" laws, fees of the National
Association of Securities Dealers, Inc., transfer taxes, fees of transfer agents
and registrars and costs of insurance and fees, but excluding any fees and
expenses for counsel for the Legacy Santera Stockholders and fees and expenses
for counsel for Santera, are called "Registration Expenses".

         5.2      Allocation. Santera and the Legacy Santera Stockholders will
pay all Registration Expenses in connection with registrations under Article II
and Article III pro rata in proportion to the number of shares sold by Santera
(to the extent Santera is a seller) and each of the Legacy Santera Stockholders.

         5.3      Expenses of Counsel. In connection with registrations under
Article II and Article III, each of Santera and the Legacy Santera Stockholders
will pay their own expenses for counsel.

                                   ARTICLE VI
                        INDEMNIFICATION AND CONTRIBUTION

         6.1      Indemnification by Santera. In the event of a registration of
any of the Stock under the Act pursuant to Article II or Article III, Santera
will indemnify and hold each seller of such Stock thereunder and each person, if
any, who controls such seller within the meaning of the Act and each of their
respective directors, officers and agents harmless for any loss, claim, damage
or liability (joint or several) or action (including reasonable attorneys fees)
to which any of the foregoing persons may become subject under the Act or other
applicable securities laws, insofar as such loss, claim, damage, liability or
action arises out of or is based upon any of the following statements, omissions
or violations: (i) any untrue statement or alleged untrue statement of a
material fact contained in a registration statement, including any preliminary
prospectus or final prospectus contained therein or any amendments or
supplements thereto (collectively, the "Filings"), (ii) the omission or alleged
omission to state in the Filings a material fact required to be stated therein,
or necessary to make the statements therein not misleading or alleged untrue
statement, or omission, or alleged omission, of material fact made in the
Filings, or (iii) any violation or alleged violation by Santera of the Act, the
Exchange Act, any state securities law or any rule or regulation promulgated
under the Act, the Exchange Act or any state securities law with respect to the
offering of the securities pursuant to the Filings other than, in any such case,
for such untrue statement, or alleged untrue statement, or omission, or alleged
omission, of material fact or violation or alleged violation made in reliance
upon and in conformity with information furnished or confirmed to Santera by
such Stockholder, or by any agent thereof, specifically for use in the
preparation of the Filings

                                       7

<PAGE>

         6.2      Indemnification by Legacy Santera Stockholders. In the event
of a registration of any of the Stock under the Act pursuant to Article II or
Article III, each seller of such Stock thereunder agree to indemnify and hold
harmless Santera, its directors, officers and agents harmless for any loss,
claim, damage, liability or action that arises out of or is based upon any
untrue statement, or alleged untrue statement, or omission, or alleged omission,
of material fact made in the registration statement or any preliminary
prospectus or prospectus contained therein or any amendment or supplement
thereto in reliance upon and in conformity with written information furnished or
confirmed to Santera by such Stockholder, or by any agent thereof, specifically
for use in the preparation of such registration statement; provided, however,
that the foregoing indemnity obligations shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability or action if such
settlement is effected without the consent of the Stockholder (which consent
shall not be unreasonably withheld) and, provided further, that in no event
shall the foregoing indemnity obligations exceed the net proceeds from such
offering received by such Stockholder.

         6.3      Notices. Promptly after receipt by an indemnified party
hereunder of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect thereof
is to be made against any indemnifying party hereunder, deliver to the
indemnifying party a written notice of the commencement thereof and the
indemnifying party shall have the right to participate in, and, to the extent
the indemnifying party so desires, but only if such indemnifying party shall
have unconditionally acknowledged to each indemnified party in writing the
obligation of the indemnifying party to indemnify the persons entitled to be
indemnified hereunder with respect to such claims, jointly with any other
indemnifying party similarly noticed, to assume the defense thereof with counsel
mutually satisfactory to the parties; provided, however, that an indemnified
party (together with all other indemnified parties that may be represented
without conflict by one counsel) shall have the right to retain one separate
counsel, with the fees and expenses to be paid by the indemnifying party, 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 such indemnified party and any other party represented by such
counsel in such proceeding. The failure to deliver written notice to the
indemnifying party within a reasonable time of the commencement of any such
action shall, to the extent such failure is prejudicial to the indemnifying
party's ability to defend against any such action, relieve such indemnifying
party of any liability to the indemnified party hereunder to the extent thereto,
but the failure to deliver written notice to the indemnifying party will not
relieve it of any liability that it may have to any indemnified party otherwise
than hereunder.

         6.4      Relative Fault. If the indemnification provided for in this
Article VI is held by a court of competent jurisdiction to be unavailable to an
indemnified party with respect to any loss, claim, damage, liability or action
referred to therein, then the indemnifying party in lieu of indemnifying such
indemnified party hereunder, shall contribute to the amount paid or payable by
such indemnified party as a result of such loss, claim, damage, liability or
action in such proportion as is appropriate to reflect the relative fault of the
indemnifying party on the one hand and of the indemnified party on the other in
connection with the statements or omissions or alleged statements or omissions
that resulted in such loss, liability, claim, liability or action as well as any
other relevant equitable considerations. The relative fault of the indemnifying
party and of the indemnified party shall be determined by reference to, among
other things, whether the untrue or alleged untrue statement of a material fact
relates to information supplied by the indemnifying party or by the indemnified
party and the parties' relative intent, knowledge, access to information and
opportunity

                                       8

<PAGE>

to correct or prevent such statement or omission. In no event shall any
Stockholder be required to contribute an amount in excess of the net proceeds
from the offering received by such Stockholder.

                                   ARTICLE VII
                                   TERMINATION

         This Agreement shall terminate upon the occurrence of any of the
following events:

                  (a)      the written agreement of Santera, the Representative
and Tekelec;

                  (b)      the date on which only one Person (or its wholly
owned subsidiaries) owns shares of Stock of Santera;

                  (c)      the date on which Tekelec acquires all Stock as a
result of the consummation of a transaction pursuant to the exercise of the call
right or the put right contained in Article III of the Stockholders' Agreement
or the date on which Santera redeems all Stock pursuant to Article Fourth,
Section C(1)(ii)(a)(I) or (II) of the Amended and Restated Certificate of
Incorporation; or

                  (d)      the dissolution of Santera.

                                  ARTICLE VIII
                                  MISCELLANEOUS

         8.1      Transfer or Assignment of Registration Rights. The rights to
cause Santera to register Registrable Securities pursuant to this Agreement may
be transferred or assigned, but only with all related obligations, by a holder
of Registrable Securities to an Assignee; provided that (i) prior to such
transfer or assignment, Santera is furnished with written notice stating the
name and address of such Assignee and identifying the securities with respect to
which such registration rights are being transferred or assigned, (ii) such
Assignee agrees in writing to be bound by and subject to the terms and
conditions of this Agreement and (iii) such transfer or assignment shall be
effective only if immediately following such transfer or assignment the further
disposition of such Registrable Securities by the Assignee is restricted under
the Act.

         8.2      Limitations on Subsequent Registration Rights. From and after
the date of this Agreement, Santera shall not, without the prior written consent
of Legacy Santera Stockholders holding at least a majority of the Registrable
Securities then outstanding, enter into any agreement with any holder or
prospective holder of any securities of Santera which would allow such holder or
prospective holder (a) to include such securities in any registration filed
under Article II or Article III, unless under the terms of such agreement, such
holder or prospective holder may include such securities in any such
registration only to the extent that the inclusion of such holder's or
prospective holder's securities will not reduce the amount of the Registrable
Securities of the Legacy Santera Stockholders or any Assignees which is included
or (b) to make a demand registration that could result in such registration
being declared effective prior to the dates set forth in Section 2.1.

         8.3      Notices. All notices, consents, approvals, requests and other
communications hereunder shall be in writing and shall be deemed given when
delivered personally, one (1) day after being delivered to an overnight courier
or when telecopied (with a confirmatory copy sent by overnight courier) to the
parties at the following addresses (or at such other address for a party as
shall be specified by like notice):

                                        9

<PAGE>

         If to Santera, to:

         Santera Systems Inc.
         3601 East Plano Parkway, #100
         Plano, Texas 75704
         Attention: President
         Facsimile No.: (972) 461-7512

         with copies to:

         Munsch Hardt Kopf & Harr P.C.
         1445 Ross Avenue, Suite 4000
         Dallas, Texas 75202
         Attention: A. Michael Hainsfurther
         Facsimile No.: (214) 855-7584

         If to Tekelec, to:

         Tekelec
         26580 West Agoura Road
         Calabasas, California 91302
         Attention: President
         Facsimile No.: (818) 880-0176

         with copies to:

         Ronald W. Buckly
         Tekelec
         26850 West Agoura Road
         Calabasas, California 91302
         Facsimile: (818) 880-0176

         and

         Bryan Cave LLP
         One Metropolitan Square
         211 North Broadway, Suite 3600
         St. Louis, Missouri 63102
         Attention: J. Mark Klamer and Katherine F. Ashton
         Facsimile: (314) 259-2020

         If to the Legacy Santera Stockholders, to the Representative:

         Austin Ventures VI, L.P.
         2435 North Central Expressway
         Suite 1600

                                       10

<PAGE>

         Richardson, Texas 75080
         Attention: Edward E. Olkkola
         Facsimile No.: (972-892-3701

         with a copy to:

         Wilson, Sonsini, Goodrich & Rosati Professional Corporation
         8911 Capital of Texas Highway North
         Westech 360, Suite 3350
         Austin, Texas 78759
         Attention: Paul R. Tobias
         Facsimile: (512) 338-5499

         8.4      Remedies. The Stockholders will be entitled to enforce their
rights under this Agreement specifically (without posting a bond or other
security), to recover damages by reason of any material breach of any provision
of this Agreement and to exercise all other rights existing in their favor. The
parties hereto agree and acknowledge that money damages may not be an adequate
remedy for any breach of the provisions of this Agreement and that any
Stockholder may in its sole discretion apply to any court of law or equity of
competent jurisdiction for specific performance and/or injunctive relief in
order to enforce or prevent any violation of the provisions of this Agreement.
In the event of any dispute involving the terms of this Agreement, the
prevailing party shall be entitled to collect reasonable fees and expenses
incurred by the prevailing party in connection with such dispute from the other
parties to such dispute.

         8.5      Expenses. Except as otherwise provided in this Agreement or
the Merger Agreement, each party hereto will pay its own costs and expenses
incurred in connection with the negotiation, execution and performance of this
Agreement and the transactions contemplated hereby.

         8.6      Binding Effect; Assignment. This Agreement shall be binding
upon and inure to the benefit of the respective successors and permitted assigns
of the parties hereto.

         8.7      Amendment and Waiver. No modification, amendment or waiver of
any provision of this Agreement will be effective against Santera or the
Stockholders unless such modification, amendment or waiver is approved in
writing by Santera and the holders of a majority of Registrable Securities. The
failure of any party to enforce any of the provisions of this Agreement will in
no way be construed as a waiver of such provisions and will not affect the right
of such party thereafter to enforce each and every provision of this Agreement
in accordance with its terms.

         8.8      Counterparts. This Agreement may be executed in counterparts,
each of which shall be deemed to be an original, but all of which shall
constitute one and the same instrument.

         8.9      Headings. The headings of the various sections of this
Agreement have been inserted for convenience of reference only and shall not be
deemed to be a part of this Agreement.

         8.10     Severability. If any provision of this Agreement shall be
determined to be illegal or unenforceable, the remaining provisions of this
Agreement shall remain in full force and effect, and

                                       11

<PAGE>

this Agreement shall be construed as if the illegal or unenforceable provision
were not a part hereof, so long as the remaining provisions of this Agreement
shall be sufficient to carry out the overall intent of the parties as expressed
herein.

         8.11     Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of Delaware, without regard
to its conflicts of law doctrine. All claims brought hereunder are required to
be brought and maintained in the any Federal or state court in the district in
which Dallas, Texas is located. Any and all counterclaims in any action must be
brought in the same court in which the related proceeding was initiated in
accordance with the foregoing provisions. The parties hereto agree that such
courts shall have exclusive jurisdiction and venue over all disputes between the
parties hereto.

         8.12     Further Assurances. Each party hereto shall perform all other
acts and execute and deliver all other documents as may be necessary or
appropriate to carry out the purposes and intent of this Agreement.

         8.13     Third Party Beneficiary. Nothing set forth in this Agreement
shall be construed to confer any benefit to any third party who is not a party
to this Agreement.

         [The remainder of this page has been left blank intentionally.]

                                       12

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed as of the date first written above.

                           SANTERA SYSTEMS INC.

                           By: /s/ David Heard
                              _________________________
                           Name: David Heard
                                _______________________
                           Title: President and CEO
                                 ______________________

                           TEKELEC

                           By: /s/ Frederick M. Lax
                              _________________________
                           Name: Frederick M. Lax
                                _______________________
                           Title: President and CEO
                                 ______________________

                           By: /s/ Paul J. Pucino
                              _________________________
                           Name: Paul J. Pucino
                                _______________________
                           Title: CFO
                                 ______________________

                           AUSTIN VENTURES VI, L.P., as Representative

                           By: AV Partners VI, L.P., its general partner

                                By: /s/ Edward E. Olkkola
                                   _________________________
                                Name: Edward E. Olkkola
                                     _______________________
                                Title: General Partner
                                      ______________________

                           AUSTIN VENTURES VI, L.P.

                           By: AV Partners VI, L.P., its General Partner

                           By: /s/ Edward E. Olkkola
                              ___________________________________
                               Edward E. Olkkola, General Partner

                           AUSTIN VENTURES VI AFFILIATES FUND, L.P.

                           By: AV Partners VI, L.P., its General Partner

                           By: /s/ Edward E. Olkkola
                              ___________________________________
                               Edward E. Olkkola, General Partner

                           AUSTIN VENTURES VIII, L.P.

                           By: AV Partners VIII, L.P., its General Partner

                           By: /s/ Edward E. Olkkola
                              ___________________________________
                               Edward E. Olkkola, General Partner

                          REGISTRATION RIGHTS AGREEMENT
                                 Signature Page

<PAGE>

                           REDPOINT VENTURES II, L.P., by its General
                           Partner, Redpoint Ventures II, LLC

                           By: /s/ R. Thomas Dyal
                               _______________________________________
                               R. Thomas Dyal, Managing Director

                           REDPOINT ASSOCIATES II, LLC, as nominee

                           By: /s/ R. Thomas Dyal
                               _______________________________________
                               R. Thomas Dyal, Managing Director

                           REDPOINT TECHNOLOGY PARTNERS Q-I,
                           L.P., by its General Partner, Redpoint Ventures I,
                           LLC

                           By: /s/ R. Thomas Dyal
                               _______________________________________
                           Name: R. Thomas Dyal
                                 _____________________________________
                           Title: Managing Director
                                  ____________________________________

                           REDPOINT TECHNOLOGY PARTNERS A-I,
                           L.P., by its General Partner, Redpoint Ventures I,
                           LLC

                           By: /s/ R. Thomas Dyal
                               _______________________________________
                           Name: R. Thomas Dyal
                                 _____________________________________
                           Title: Managing Director
                                  ____________________________________

                           MERITECH CAPITAL PARTNERS L.P.

                           By: Meritech Capital Associates L.L.C.
                                 its General Partner

                           By: Meritech Management Associates L.L.C.
                                 a managing member

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           MERITECH CAPITAL AFFILIATES L.P.

                           By: Meritech Capital Associates L.L.C.
                                 its General Partner

                           By: Meritech Management Associates L.L.C.
                                 a managing member

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                          REGISTRATION RIGHTS AGREEMENT
                                 Signature Page
<PAGE>

                           SEQUOIA CAPITAL FRANCHISE FUND, L.P.

                           By: SCFF Management, LLC
                           A Delaware Limited Liability Company
                           General Partner

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           SEQUOIA CAPITAL FRANCHISE PARTNERS,
                           L.P.

                           By: SCFF Management, LLC
                           A Delaware Limited Liability Company
                           General Partner

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           SEQUOIA CAPITAL VIII, L.P.

                           By: SC VIII Management, LLC
                           A California Limited Liability Company
                           General Partner

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           SEQUOIA INTERNATIONAL TECHNOLOGY
                           PARTNERS VIII, L.P.

                           By: SC VIII Management, LLC
                           A California Limited Liability Company
                           General Partner

                           By: /s/ Mark Stevens
                               _______________________________________

                           Name: Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                          REGISTRATION RIGHTS AGREEMENT
                                 Signature Page
<PAGE>

                           SEQUOIA INTERNATIONAL TECHNOLOGY
                           PARTNERS VIII (Q), L.P.

                           By: SC VIII Management, LLC
                           A California Limited Liability Company
                           General Partner

                           By:   /s/ Mark Stevens
                               _______________________________________
                           Name:    Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           SEQUOIA 1997

                           By:   /s/ Mark Stevens
                               _______________________________________
                           Name:    Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           CMS PARTNERS LLC

                           By:   /s/ Mark Stevens
                               _______________________________________
                           Name:    Mark Stevens
                                 _____________________________________
                           Title: ____________________________________

                           INSTITUTIONAL VENTURE PARTNERS VIII,
                           L.P., by its General Partner, Institutional Venture
                           Management VIII, LLC

                           By:   /s/ R. Thomas Dyal
                               __________________________________________
                                 R. Thomas Dyal, Managing Director

                           IVM INVESTMENT FUND VIII, LLC, by its

                           Manager, Institutional Venture Management VIII,

                           LLC

                           By:   /s/ R. Thomas Dyal
                               __________________________________________
                                 R. Thomas Dyal, Managing Director

                           BROADBAND FUND, L.P., by its General Partner,
                           BBF Management, LLC, by its Manager,
                           Institutional Venture Management VIII, LLC

                           By:   /s/ R. Thomas Dyal
                               __________________________________________
                                 R. Thomas Dyal, Managing Director

                          REGISTRATION RIGHTS AGREEMENT
                                 Signature Page