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                                  EXHIBIT 10.43

                               SYNC RESEARCH, INC.
                              AMENDED AND RESTATED
                      CHANGE OF CONTROL SEVERANCE AGREEMENT


         This Amended and Restated Change of Control Severance Agreement (the
"AGREEMENT") is made and entered into by and between William K. Guerry (the
"EMPLOYEE") and Sync Research, Inc., a Delaware corporation (the "COMPANY"),
effective as of October 8, 1999.

                                    RECITALS


         A. It is expected that the Company from time to time will consider
the possibility of an acquisition by another company or other change of
control. The Board of Directors of the Company (the "BOARD") recognizes that
such consideration can be a distraction to the Employee and can cause the
Employee to consider alternative employment opportunities. The Board has
determined that it is in the best interests of the Company and its
stockholders to assure that the Company will have the continued dedication
and objectivity of the Employee, notwithstanding the possibility, threat or
occurrence of a Change of Control (as defined below) of the Company.

         B. The Board believes that it is in the best interests of the Company
and its stockholders to provide the Employee with an incentive to continue his
or her employment and to motivate the Employee to maximize the value of the
Company upon a Change of Control for the benefit of its stockholders.

         C. The Board believes that it is imperative to provide the Employee
with certain severance benefits upon Employee's termination of employment
following a Change of Control that provide the Employee with enhanced financial
security and incentive and encouragement to the Employee to remain with the
Company notwithstanding the possibility of a Change of Control.

         D. For the reasons set forth in these recitals, the Company and
Employee entered into a Change of Control Severance Agreement dated June 23,
1997 (the "PRIOR SEVERANCE AGREEMENT"). The Company and Employee desire to amend
and restate the Prior Severance Agreement in its entirety hereby.

         E. Certain capitalized terms used in the Agreement are defined in
Section 6 below.

         The parties hereto agree to amend and restate the Prior Severance
Agreement in its entirety as follows:

         1. TERM OF AGREEMENT. This Agreement shall terminate upon the date that
all obligations of the parties hereto with respect to this Agreement have been
satisfied.


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         2. AT-WILL EMPLOYMENT. The Company and the Employee acknowledge that
the Employee's employment is and shall continue to be at-will, as defined under
applicable law. If the Employee's employment terminates for any reason,
including (without limitation) any termination prior to a Change of Control, the
Employee shall not be entitled to any payments, benefits, damages, awards or
compensation other than as provided by this Agreement or as may otherwise be
available in accordance with the Company's established employee plans and
practices or pursuant to other agreements with the Company.

         3. STOCK VESTING ON CHANGE OF CONTROL.

                  (A) ACCELERATION UPON CHANGE OF CONTROL. Upon a Change of
Control, fifty percent (50%) of the Employee's options to purchase Common Stock
of the Company and/or shares of restricted stock of the Company that are
unvested as of the date of the Change of Control (the "UNVESTED SHARES") shall
immediately become vested.

                  (B) VESTING OF REMAINING UNVESTED SHARES. Upon a Change of
Control, the remainder of the Unvested Shares for which vesting was not
accelerated pursuant to Section 3(a) shall continue to vest at the same monthly
rate as prior to the Change of Control (i.e., if 200 shares vested per month
prior to the Change of Control, the remaining Unvested Shares will continue to
vest at the rate of 200 shares per month after the Change of Control) and in
accordance with the applicable stock option or restricted stock purchase
agreement.

         4.       CONSULTING ARRANGEMENT.

                  (A) TERMINATION FOLLOWING A CHANGE OF CONTROL. If the
Employee's employment terminates as a result of Involuntary Termination other
than for Cause at any time within twelve (12) months following a Change of
Control, then, subject to Section 6, the Employee and the Company shall enter
into a consulting arrangement on the following terms:

                           (1) CONSULTING ENGAGEMENT. Effective as of the
Termination Date, and subject to the terms of this Agreement, the Company agrees
to retain the Employee as a consultant to perform such services (the "CONSULTING
SERVICES") for the Company as may be reasonably requested from time to time by
an officer of the Company (the "CONSULTING ARRANGEMENT"). The term of this
Consulting Arrangement shall commence on the Termination Date and expire on the
earlier of (i) the date the employee is working as a salaried employee of or
consultant to another person, company or entity which is actually or potentially
in competition with any business conducted by the Company, as determined by the
Company in its sole discretion, (ii) at the Employee's option, the date the
Employee is working as a salaried employee of or consultant to another person,
company or entity, or (iii) 24 months following the Termination Date. As
consideration for the Employee's services under the Consulting Arrangement, the
Company shall pay in cash to Employee an amount equal to 1/12th of the
Employee's Annual Compensation on the last day of each full month following the
Termination Date during which the Consulting Arrangement is in effect. The
Employee's stock options and/or restricted stock shall continue to vest during
the term of the Consulting Arrangement pursuant to Section 3(b). Notwithstanding
the foregoing, the Consulting Arrangement may be terminated earlier by either
party upon five days written notice of termination if the other party


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fails to cure any material breach of its obligations hereunder within 10 days
after receipt of notice specifying such breach.

                           (2) CONTINUED INSURANCE COVERAGE. Subject to the
provisions of this Section 4(a)(2), the Employee shall be entitled to one
hundred percent (100%) Company-paid health, dental and life insurance coverage
at the same level of coverage as was provided to such Employee immediately prior
to the Change of Control (the "COMPANY-PAID COVERAGE"). If such coverage
includes the Employee's dependents immediately prior to the Change of Control,
such dependents shall also be covered at Company expense. Company-Paid Coverage
shall continue until the earlier of (i) termination of the Consulting
Arrangement or (ii) the date that the Employee and his or her dependents become
covered under another employer's group health, dental or life insurance plans
that provide Employee and his or her dependents with comparable benefits and
levels of coverage. For purposes of Title X of the Consolidated Budget
Reconciliation Act of 1985 ("COBRA"), the date of the "qualifying event" for
Employee and his or her dependents shall be the date upon which the Company-Paid
Coverage terminates.

                  (B) VOLUNTARY RESIGNATION; TERMINATION FOR CAUSE. If the
Employee's employment terminates by reason of the Employee's voluntary
resignation (and is not an Involuntary Termination), or if the Employee is
terminated for Cause, then the Employee shall not be entitled to receive
payments for consulting services or other benefits under Section 4(a) except for
those (if any) as may then be established under the Company's then existing
severance and benefits plans and practices or pursuant to other agreements with
the Company.

                  (C) DISABILITY; DEATH. If the Company terminates the
Employee's employment as a result of the Employee's Disability, or such
Employee's employment is terminated due to the death of the Employee, then the
Employee shall not be entitled to receive payments for consulting services or
other benefits under Section 4(a) except for those (if any) as may then be
established under the Company's then existing severance and benefits plans and
practices or pursuant to other agreements with the Company.

                  (D) TERMINATION APART FROM CHANGE OF CONTROL. In the event the
Employee's employment is terminated for any reason, either prior to the
occurrence of a Change of Control or after the twelve-month period following a
Change of Control, then the Employee shall not be entitled to receive payments
for consulting services or other benefits under Section 4(a) except for those
(if any) as may then be established under the Company's existing severance and
benefits plans and practices or pursuant to other agreements with the Company.

         5. ATTORNEY FEES, COSTS AND EXPENSES. The Company shall promptly
reimburse Employee, on a monthly basis, for the reasonable attorney fees, costs
and expenses incurred by the Employee in connection with any action brought by
Employee to enforce his or her rights hereunder. In the event Employee is not
the prevailing party, determined without regard to whether or not the action
results in a final judgment, Employee shall repay such reimbursements.

         6. LIMITATION ON PAYMENTS. In the event that the payments and other
benefits provided for in this Agreement or otherwise payable to the Employee (i)
constitute


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"parachute payments" within the meaning of Section 280G of the
Internal Revenue Code of 1986, as amended (the "Code"), and (ii) but for this
Section 6, would be subject to the excise tax imposed by Section 4999 of the
Code (or any corresponding provisions of state income tax law), then the
Employee's benefits under Section 4(a) shall be either

                  (a)      delivered in full, or

                  (b)      delivered as to such lesser extent which would result
in no portion of such benefits being subject to excise tax under Section 4999 of
the Code,

whichever of the foregoing amounts, taking into account the applicable federal,
state and local income taxes and the excise tax imposed by Section 4999, results
in the receipt by the Employee on an after-tax-basis, of the greater amount of
benefits, notwithstanding that all or some portion of such benefits may be
taxable under Section 4999 of the Code. Unless the Company and the Employee
otherwise agree in writing, any determination required under this Section 6
shall be made in writing by the Company's independent public accountants (the
"ACCOUNTANTS"), whose determination shall be conclusive and binding upon the
Employee and the Company for all purposes. For purposes of making the
calculations required by this Section 6, the Accountants may make reasonable
assumptions and approximations concerning applicable taxes and may rely on
reasonable, good faith interpretations concerning the application of Sections
280G and 4999 of the Code. The Company and the Employee shall furnish to the
Accountants such information and documents as the Accountants may reasonably
request in order to make a determination under this Section. The Company shall
bear all costs the Accountants may reasonably incur in connection with any
calculations contemplated by this Section 6. In the event that subsection (a)
above applies, then Employee shall be responsible for any excise taxes imposed
with respect to such benefits. In the event that subsection (b) above applies,
then each benefit provided hereunder shall be proportionately reduced to the
extent necessary to avoid imposition of such excise taxes.

         7. DEFINITION OF TERMS. The following terms used in this Agreement
shall have the following meanings:

                  (A) ANNUAL COMPENSATION. "ANNUAL COMPENSATION" means an amount
equal to (i) Employee's Company salary for the twelve months preceding the
Change of Control, and (ii) Employee's maximum target bonus for the year in
which the Change of Control occurs.

                  (B) CAUSE. "CAUSE" shall mean (i) any act of personal
dishonesty taken by the Employee in connection with his or her responsibilities
as an employee and intended to result in substantial personal enrichment of the
Employee, (ii) Employee's committing and being convicted of a felony, (iii) a
willful act by the Employee which constitutes gross misconduct and which is
injurious to the Company or an act of fraud by Employee against the Company, or
(iv) following delivery to the Employee of a written demand for performance from
the Company which describes the basis for the Company's belief that the Employee
has not substantially performed his or her duties, continued violations by the
Employee of the Employee's obligations to the Company which are demonstrably
willful and deliberate on the Employee's part.

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                  (C) CHANGE OF CONTROL. "CHANGE OF CONTROL" means the
occurrence of any of the following events:

                           (i) Any "PERSON" (as such term is used in Section
13(d) and 14(d) of the Securities Exchange Act of 1934, as amended) is or
becomes the "BENEFICIAL OWNER" (as defined in Rule 13d-3 under said Act),
directly or indirectly, of securities of the Company representing 50% or more of
the total voting power represented by the Company's then outstanding voting
securities; or

                           (ii) A change in the composition of the Board
occurring within a two-year period, as a result of which fewer than a majority
of the directors are Incumbent Directors. "INCUMBENT DIRECTORS" shall mean
directors who either (A) are directors of the Company elected at the annual
meeting of stockholders of the Company to be held on June 13, 1997, or (B) are
elected, or nominated for election, to the Board with the affirmative votes of
at least a majority of the Incumbent Directors at the time of such election or
nomination (but shall not include an individual whose election or nomination is
in connection with an actual or threatened proxy contest relating to the
election of directors to the Company); or

                           (iii) The stockholders of the Company approve a
merger or consolidation of the Company with any other corporation, other than a
merger or consolidation which would result in the voting securities of the
Company outstanding immediately prior thereto continuing to represent (either by
remaining outstanding or by being converted into voting securities of the
surviving entity) at least fifty percent (50%) of the total voting power
represented by the voting securities of the Company or such surviving entity
outstanding immediately after such merger or consolidation or the stockholders
of the Company approve a plan of complete liquidation of the Company or an
agreement for the sale or disposition by the Company of all or substantially all
the Company's assets.

                  (D) DISABILITY. "DISABILITY" shall mean that the Employee has
been unable to perform his or her Company duties as the result of his or her
incapacity due to physical or mental illness, and such inability, at least 26
weeks after its commencement, is determined to be total and permanent by a
physician selected by the Company or its insurers and acceptable to the Employee
or the Employee's legal representative (such Agreement as to acceptability not
to be unreasonably withheld). Termination resulting from Disability may only be
effected after at least 30 days' written notice by the Company of its intention
to terminate the Employee's employment. In the event that the Employee resumes
the performance of substantially all of his or her duties hereunder before the
termination of his or her employment becomes effective, the notice of intent to
terminate shall automatically be deemed to have been revoked.

                  (E) INVOLUNTARY TERMINATION. "INVOLUNTARY TERMINATION" shall
mean (i) without the Employee's express written consent, the significant
reduction of the Employee's duties, authority or responsibilities, relative to
the Employee's duties, authority or responsibilities as in effect immediately
prior to such reduction, or the assignment to Employee of such reduced duties,
authority or responsibilities; (ii) without the Employee's express written
consent, a substantial reduction, without good business reasons, of the
facilities and prerequisites (including office space and location) available to
the Employee immediately prior to such reduction; (iii) a


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reduction by the Company in the base salary of the Employee as in effect
immediately prior to such reduction; (iv) a material reduction by the Company
in the kind or level of employee benefits, including bonuses, to which the
Employee was entitled immediately prior to such reduction with the result
that the Employee's overall benefits package is significantly reduced; (v)
the relocation of the Employee to a facility or a location more than thirty
(30) miles from the Employee's then present location, without the Employee's
express written consent; (vi) any purported termination of the Employee by
the Company which is not effected for Disability or for Cause, or any
purported termination for which the grounds relied upon are not valid; (vii)
the failure of the Company to obtain the assumption of this Agreement by any
successors contemplated in Section 8(a) below; or (viii) any act or set of
facts or circumstances which would, under California case law or statute,
constitute a constructive termination of the Employee.

                  (F) TERMINATION DATE. "TERMINATION DATE" shall mean (i) if
this Agreement is terminated by the Company for Disability, thirty (30) days
after notice of termination is given to the Employee (provided that the Employee
shall not have returned to the performance of the Employee's duties on a
full-time basis during such thirty (30)-day period), (ii) if the Employee's
employment is terminated by the Company for any other reason, the date on which
a notice of termination is given, provided that if within thirty (30) days after
the Company gives the Employee notice of termination, the Employee notifies the
Company that a dispute exists concerning the termination or the benefits due
pursuant to this Agreement, then the Termination Date shall be the date on which
such dispute is finally determined, either by mutual written agreement of the
parties, or by a final judgment, order or decree of a court of competent
jurisdiction (the time for appeal therefrom having expired and no appeal having
been perfected), or (iii) if the Agreement is terminated by the Employee, the
date on which the Employee delivers the notice of termination to the Company.

         8.       SUCCESSORS.

                  (A) COMPANY'S SUCCESSORS. Any successor to the Company
(whether direct or indirect and whether by purchase, merger, consolidation,
liquidation or otherwise) to all or substantially all of the Company's business
and/or assets shall assume the obligations under this Agreement and agree
expressly to perform the obligations under this Agreement in the same manner and
to the same extent as the Company would be required to perform such obligations
in the absence of a succession. For all purposes under this Agreement, the term
"COMPANY" shall include any successor to the Company's business and/or assets
which executes and delivers the assumption agreement described in this Section
8(a) or which becomes bound by the terms of this Agreement by operation of law.

                  (B) EMPLOYEE'S SUCCESSORS. The terms of this Agreement and all
rights of the Employee hereunder shall inure to the benefit of, and be
enforceable by, the Employee's personal or legal representatives, executors,
administrators, successors, heirs, distributees, devisees and legatees.

         9.       NOTICE.

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                  (A) GENERAL. Notices and all other communications contemplated
by this Agreement shall be in writing and shall be deemed to have been duly
given when personally delivered or five (5) days after being mailed by U.S.
registered or certified mail, return receipt requested and postage prepaid. In
the case of the Employee, mailed notices shall be addressed to him or her at the
home address which he or she most recently communicated to the Company in
writing. In the case of the Company, mailed notices shall be addressed to its
corporate headquarters, and all notices shall be directed to the attention of
its Secretary.

                  (B) NOTICE OF TERMINATION. Any termination by the Company for
Cause or by the Employee as a result of a voluntary resignation and any
Involuntary Termination shall be communicated by a notice of termination to the
other party hereto given in accordance with Section 9(a) of this Agreement. Such
notice shall indicate the specific termination provision in this Agreement
relied upon, shall set forth in reasonable detail the facts and circumstances
claimed to provide a basis for termination under the provision so indicated, and
shall specify the termination date (which shall be not more than 30 days after
the giving of such notice). The failure by the Employee to include in the notice
any fact or circumstance which contributes to a showing of Involuntary
Termination shall not waive any right of the Employee hereunder or preclude the
Employee from asserting such fact or circumstance in enforcing his or her rights
hereunder.

         10.      MISCELLANEOUS PROVISIONS.

                  (A) NO DUTY TO MITIGATE. The Employee shall not be required to
mitigate the amount of any payment contemplated by this Agreement, nor shall any
such payment be reduced by any earnings that the Employee may receive from any
other source, subject to the termination provisions of Section 4(a)(1).

                  (B) WAIVER. No provision of this Agreement shall be modified,
waived or discharged unless the modification, waiver or discharge is agreed to
in writing and signed by the Employee and by an authorized officer of the
Company (other than the Employee). No waiver by either party of any breach of,
or of compliance with, any condition or provision of this Agreement by the other
party shall be considered a waiver of any other condition or provision or of the
same condition or provision at another time.

                  (C) WHOLE AGREEMENT. The Prior Severance Agreement is hereby
terminated, and this Agreement supersedes the Prior Severance Agreement in its
entirety. This Agreement represents the entire agreement between the Employee
and the Company with respect to the matters set forth herein. No agreements,
representations or understandings (whether oral or written and whether express
or implied) which are not expressly set forth in this Agreement have been made
or entered into by either party with respect to the subject matter hereof.

                  (D) CHOICE OF LAW. The validity, interpretation, construction
and performance of this Agreement shall be governed by the laws of the State of
California as applied to agreements entered into and performed within California
solely by residents of that state.


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                  (E) SEVERABILITY. The invalidity or unenforceability of any
provision or provisions of this Agreement shall not affect the validity or
enforceability of any other provision hereof, which shall remain in full force
and effect.

                  (F) WITHHOLDING. All payments made pursuant to this Agreement
will be subject to withholding of applicable income and employment taxes.

                  (G) COUNTERPARTS. This Agreement may be executed in
counterparts, each of which shall be deemed an original, but all of which
together will constitute one and the same instrument.


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         IN WITNESS WHEREOF, each of the parties has executed this Agreement, in
the case of the Company by its duly authorized officer, as of the date set forth
above.

COMPANY:                                             SYNC RESEARCH, INC.


                                                     By: /s/ GREG REYES
                                                         --------------------
                                                     Title: BOARD CHAIRMAN
                                                           ------------------


EMPLOYEE:                                            /s/ WILLIAM K GUERRY
                                                     ------------------------
                                                     Signature

                                                     WILLIAM K. GUERRY
                                                     ------------------------
                                                     Please print name



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