Document:

November 29, 1999

The Board of Directors of United Asset Management Corporation
c/o Norton H. Reamer, Chairman of the Board and Chief Executive Officer
United Asset Management Corporation
One International Place
Boston, MA  02110

Dear Members of the Board:

I hereby resign from my position as President and Chief Operating Officer of
United Asset Management Corporation ("UAM"), from my position as a Director of
UAM, from any position I may hold as an officer or director of any affiliate of
UAM, and from any other position that I may hold with any pooled investment
vehicle advised by an affiliate of UAM, all effective December 31, 1999.

We have agreed that my Employment Agreement (made as of March 1, 1998) is
amended so that the Term shall end on December 31, 1999. I understand that, in
all other respects, this Employment Agreement shall remain in full force and
effect without amendment. In particular, I acknowledge my obligations under
Section 5 (Confidentiality) under which I will remain obligated to UAM following
the termination of my employment.

Sincerely yours,

/s/  C.E. Haldeman, Jr.
Charles E. Haldeman, Jr.

Acknowledged, accepted and agreed:

UNITED ASSET MANAGEMENT CORPORATION

By:  /s/ Norton H. Reamer
     -------------------------------------------
         Norton H. Reamer, Chairman of the Board
         and Chief Executive OfficerSalary Continuation Plan

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

Plan for UAM        This table summarizes UAM's Salary Continuation Plan
Employees           benefits. The Salary Continuation Plan actually consists of
                    two Plans: one Plan covers officers; the other covers
                    employees other than officers. You will be notified of any
                    changes made to the Plans in the future.

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------------------------
                                                                         Details
---------------------------------------------------------------------------------------------------------------------------
<S>                            <C>
Qualifying event               Any involuntary termination by UAM, excluding any terminations for reasons related to job
                               performance
---------------------------------------------------------------------------------------------------------------------------
Who is eligible                All UAM employees who are paid directly by UAM and not its affiliates.
---------------------------------------------------------------------------------------------------------------------------
How  benefit is calculated     o    Exempt: Based on annual salary plus highest bonus paid for any of the last three
                                    calendar years (when applicable)
                               o    Non-exempt: Based on average of last 52 weeks wages
---------------------------------------------------------------------------------------------------------------------------
Base Salary Continuation Pay   Annual Cash Compensation               Base Salary Continuation Pay
                               (based on salary + bonus as above)
                               --------------------------------------------------------------------------------------------
                               o    Up to $50,000                          2 months pay
                               o    $50,001 - $100,000                     3 months pay
                               o    $100,001 - $150,000                    6 months pay
                               o    $150,000 +                             9 months pay
---------------------------------------------------------------------------------------------------------------------------
Additional Salary              o    One month pay for each year or partial year of service (measured from the
Continuation Pay                    employee's start date)
                               o    Maximum term of 24 months (includes base + additional pay)
                               o    Senior VP and above: minimum 24 months; maximum 30 months
---------------------------------------------------------------------------------------------------------------------------
Vacation Pay Out               Pay out all unused vacation and Paid Leave Bank time where applicable
---------------------------------------------------------------------------------------------------------------------------
Benefits                       Continue medical, dental, life insurance for full term of severance or until re-employed,
                               whichever is earlier (subject to the reasonable availability of continued coverage after
                               the 18 month COBRA period).
---------------------------------------------------------------------------------------------------------------------------
Options                        May be vested and/or extended at the Compensation Committee's discretion
---------------------------------------------------------------------------------------------------------------------------
Profit Sharing                 Immediately vests at 100%, in accordance with the terms of the Plan
---------------------------------------------------------------------------------------------------------------------------
Pay Out term                   Regular payroll (monthly)
                               NOTE: All payments under this Plan are subject to withholdings and other applicable
                               deductions
---------------------------------------------------------------------------------------------------------------------------
Terms of Salary                Continues for full term of salary continuation according to the above schedule; if annual
Continuation                   cash compensation from subsequent employment during the term is lower, UAM will payout
                               the difference between the Salary Continuation pay calculable above and the new cash
                               compensation.
---------------------------------------------------------------------------------------------------------------------------
Outplacement                   Reasonable outplacement services will be provided to all employees during the first three
                               months of severance.
---------------------------------------------------------------------------------------------------------------------------
</TABLE>

--------------------------------------------------------------------------------<PAGE>   1
                                                                 Exhibit 10.34.2

                               FIRST AMENDMENT TO
                              AMENDED AND RESTATED
                           REVOLVING CREDIT AGREEMENT

      This FIRST AMENDMENT TO AMENDED AND RESTATED REVOLVING CREDIT AGREEMENT
AND WAIVER (this "First Amendment") is made as of February 1, 2000, by and among
ADVANCED FIBRE COMMUNICATIONS, INC., a Delaware corporation (with its successors
and permitted assigns, the "Borrower"), the LENDERS from time to time parties
hereto (including their Assignees), BANQUE NATIONALE DE PARIS, a French banking
association, as arranger and administrative agent (the "Administrative Agent"),
and BANK OF AMERICA, N.A. (formerly known as Bank of America National Trust and
Savings Association), a national banking association, as syndication agent (the
"Syndication Agent").

      WHEREAS, the Borrower, the Lenders, the Administrative Agent and the
Syndication Agent are parties to that certain AMENDED AND RESTATED REVOLVING
CREDIT AGREEMENT, dated as of July 29, 1999 (as amended, modified or otherwise
supplemented prior to the date hereof, the "Agreement"); and

      WHEREAS, the parties desire to amend the Agreement as hereinafter set
forth;

      NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained, the parties hereby agree as follows:

      SECTION 1. DEFINED TERMS. Capitalized terms that are used in this First
Amendment without definition shall have the same meanings herein as in the
Agreement.

      SECTION 2. CHANGE IN AGGREGATE REVOLVING CREDIT COMMITMENT. Effective from
and after February 1, 2000, the Aggregate Revolving Credit Commitment
(representing the amount available for borrowing under the Agreement, subject to
the terms and conditions of the Agreement) shall be reduced from $50,000,000 to
$30,000,000; and the definition of "Aggregate Revolving Credit Commitment"
contained in Exhibit A to the Agreement shall be changed accordingly. Also
effective from and after February 1, 2000, the Revolving Credit Commitment for
each of Banque Nationale de Paris and Bank of America N.A. shall be reduced from
$25,000,000 to $15,000,000. The preceding reductions are subject to the
condition that as of the close of business (New York time) on January 31, 2000,
the aggregate Available Revolving Credit Commitment (after reduction for any
then pending requests for Loans or for issuance of Letters of Credit) shall be
not less than $20,000,000.

      SECTION 3. AMENDMENT TO SUBSECTION 3.1(b). Subsection 3.1(b) of the
Agreement shall be amended to read in its entirety as follows:

            (b) Unless otherwise approved by the Issuing Lenders with respect to
      a Letter of Credit, each Letter of Credit shall (i) be denominated in
      Dollars; (ii) be in a minimum dollar amount of $100,000; (iii) if a

                                      -1-
<PAGE>   2
      Standby Letter of Credit, be issued to support obligations of the Borrower
      or any of its Subsidiaries, contingent or otherwise, or to finance the
      working capital and business needs of the Borrower or any of its
      Subsidiaries in the ordinary course of business; (iv) if a Standby Letter
      of Credit, expire no later than two years after the date of its issuance;
      and (v) if a Commercial Letter of Credit, expire no later than ninety days
      after the date of its issuance.

      SECTION 4. CASH COLLATERALIZED LETTERS OF CREDIT. Except as otherwise
provided in part (c) below, the Borrower may, at its option, provide cash
collateral in the form of assignment of a time deposit of funds (as more fully
set forth below) for any Letter of Credit hereafter issued on its account by an
Issuing Lender pursuant to Article 3 of the Agreement. Fees in connection with
any Letter of Credit arrangement which satisfies the cash collateral
requirements of Section 4 of this First Amendment shall be as provided in part
(e) below.

            (a) Notice. The Borrower shall irrevocably notify the Issuing Lender
of its intent to provide cash collateral for a requested Letter of Credit at the
time that the Borrower submits its Application for such Letter of Credit.

            (b) Form of Deposit, Term of Deposit, Interest Rate. Not later than
the date on which a Letter of Credit that is to be cash collateralized is
issued, the Borrower shall deposit with the Issuing Bank an amount of Dollars
(in available funds) equal to the maximum amount available under such Letter of
Credit. Such deposit shall be in the form of an irrevocable time deposit for a
term equal to the term of such Letter of Credit plus 30 days. The amount on
deposit shall bear interest at the CD Rate (as defined below) from the day
immediately following the date of the deposit until the day on which the deposit
is terminated as provided in part (f) below. The term "CD Rate" shall mean, for
each CD Interest Period (as defined below), the annual rate of interest equal to
(i) the LIBO Rate for a one month period determined by the Issuing Lender on the
first day of each CD Interest Period (ii) minus 0.125 percent (the "CD Rate").
The term "CD Interest Periods" shall mean, with respect to each deposit, the
approximately one month period beginning on the date of the deposit and ending
on the same date of the succeeding month (or, if the succeeding month does not
have such a date, then on the last day of the succeeding month), and thereafter
the approximately one month periods from the day after the previous CD Interest
Period to the same date of the succeeding month (or, if the succeeding month
does not have such a date, then on the last day of the succeeding month),
provided, that the final CD Interest Period shall end on the termination date
for the applicable deposit as provided in part (f) below. Interest earned on a
deposit shall be paid by the Issuing Lender to the Borrower immediately
following the last day of each CD Interest Period; and the obligation to pay
interest with respect to a deposit shall be solely the obligation of the Issuing
Lender holding such deposit of not of any other Lender.

            (c) Non-Dollar Denominated Letters of Credit. The Issuing Lenders
shall not be required to accept a cash deposit in connection with a Letter of
Credit denominated in a currency other than United States Dollars. An Issuing
Lender may condition its acceptance of a cash deposit in connection with a
non-Dollar denominated Letter of Credit upon such terms as it deems appropriate,
including, without limitation, (i) maintenance of a deposit in Dollars equal to
some percentage greater than 100 percent of the maximum Letter of Credit amount
as converted

                                      -2-
<PAGE>   3
at current exchange rates into Dollars, (ii) application of a different interest
rate (which may be 0 percent) than the CD Rate to such deposit, and (iii)
application of an administrative fee.

            (d) Security Interest. The Borrower hereby irrevocably grants to the
Issuing Lender, for the equal and ratable benefit of all the L/C Participants, a
security interest in each deposit (including the cash deposited, accrued
interest, the deposit account and all proceeds thereof) made hereunder in
connection with the issuance of a Letter of Credit, in any instrument, document
or other evidence of such deposit (whether certificated or otherwise), and in
the products and proceeds thereof, which security interest shall secure all
obligations (both payment and performance obligations) of the Borrower to the
Lenders under this Agreement, including, without limitation, the obligation of
the Borrower to reimburse the Issuing Lender for any payment made by the Issuing
Lender in connection with the Letter of Credit issued upon the delivery of such
deposit. The Borrower shall take such additional actions as the Issuing Lender
or the Administrative Agent may require to evidence, perfect or maintain a first
priority interest in such security interest. The Issuing Lender shall also have
such lien in and against the deposited funds and the deposit account as are
provided by statute. Upon any payment by the Issuing Lender upon the Letter of
Credit for which a deposit was made, which payment is not reimbursed on the date
of such payment the Issuing Lender may (and, at the request of the
Administrative Agent, shall), without prior notice to the Borrower or other
action on the part of the Issuing Lender, apply the deposit to reimbursement of
such payment (or to reimbursement of the L/C Participants if the L/C
Participants have advanced funds to reimburse the Issuing Lender). Upon the
occurrence and during the continuation of any Event of Default the Issuing
Lender may (and, at the request of the Administrative Agent, shall) apply the
deposit as provided in Article 8 of the Agreement.

            (e) Fees. For all L/C Obligations which are secured by a cash
deposit as provided in this Section 4 of this First Amendment (hereafter, the
"Secured L/C Obligations"), the Borrower shall pay to the Administrative Agent
for the ratable account of the Issuing Lender and the L/C Participants a letter
of credit fee equal to 0.50 percent (rather than equal to the Applicable Margin
for LIBO Loan, which at present is 1.50 percent) on the average daily
outstanding Secured L/C Obligations during each applicable calculation period.
All other fees, charges and expenses with respect to Secured L/C Obligations,
including issuance fees payable to the Issuing Bank, shall be identical to fees,
charges and expenses applicable to other L/C Obligations.

            (f) Termination of Deposit. A deposit with respect to any Letter of
Credit, together with the security interest in such deposit, shall terminate and
the amount of the deposit together with any accrued and unpaid interest thereon
shall be paid by the Issuing Lender to the Borrower upon the earlier of (A) (i)
payment in full of the amount of any payment by the Issuing Lender with respect
to such Letter of Credit, (ii) and termination of any additional obligations of
the Issuing Lender with respect to such Letter of Credit, and (iii)
reimbursement to the Issuing Lender (and to the L/C Participants to the extent
that the L/C Participants have advanced funds to the Issuing Lender) of all
amounts reimbursable by the Borrower with respect to such Letter of Credit, or
(B) thirty days following expiration of such Letter of Credit without any
payment having been made thereunder by or on behalf of the Issuing Bank;
provided, however, that no deposit shall terminate, no security interest shall
terminate, and no deposited funds shall be returned to the Borrower if a Default
or an Event of Default has occurred and is continuing.

                                      -3-
<PAGE>   4
Unless otherwise required by applicable law, no penalty or other charge shall be
payable by the Borrower in connection with termination of a deposit prior to its
initial term.

            (g) Default. Upon the occurrence and during the continuation of an
Event of Default, any deposit or deposit account existing under this Section 4
of this First Amendment shall, from and after the date on which the Borrower
receives written notice of the Event of Default from the Administrative Agent,
be deemed to be deposits under the second paragraph of Article 8 of the
Agreement, and interest shall no longer be payable with respect to such
deposits.

            (h) Post-Termination Date Letters of Credit. Any cash-collateralized
Letter of Credit having an expiration date later than the Termination Date
shall, from and after the Termination Date, be governed by the terms of Section
3.9 of the Agreement and not by Section 4 of this First Amendment.

      SECTION 5. REPRESENTATIONS AND WARRANTIES. The Borrower hereby represents
to the Lenders, the Administrative Agent and the Syndication Agent that:

            (a) Representations and Warranties. Its representations and
warranties contained in Article VIII to the Agreement are true and correct as of
the date hereof (unless stated to relate solely to an earlier date, in which
case such representations and warranties are true and correct as of such earlier
date).

            (b) Enforceability. The execution and delivery by this First
Amendment, and the performance of its obligations under this First Amendment and
the Agreement, as amended hereby, are within its corporate powers and have been
duly authorized by all necessary corporate action on its part. This First
Amendment and the Agreement, as amended hereby, are its valid and legally
binding obligations, enforceable in accordance with their terms, except as
enforceability may be limited by bankruptcy, insolvency, reorganization or other
similar laws affecting the enforcement of creditors' rights generally and by
general principles of equity, regardless of whether such enforceability is
considered in a proceeding in equity or at law.

            (c) No Default. No Default or Event of Default has occurred and is
continuing.

      SECTION 6. EFFECT OF AMENDMENT. Except as expressly amended and modified
by this First Amendment, all provisions of the Agreement shall remain in full
force and effect. After this First Amendment becomes effective, all references
in the Agreement (or in any other Credit Document) to "this Agreement",
"hereof", "herein" or words of similar effect referring to the Agreement shall
be deemed to be references to the Agreement as amended by this First Amendment.
This First Amendment shall not be deemed to expressly or impliedly waive, amend
or supplement any provision of the Agreement other than as set forth herein.

      SECTION 7. EFFECTIVENESS. This First Amendment shall become effective as
of the date hereof upon receipt by the Administrative Agent of counterparts of
this First Amendment (whether by facsimile or otherwise) executed by each of the
other parties hereto.

                                      -4-
<PAGE>   5
      SECTION 8. GOVERNING LAW. This First Amendment shall be governed by, and
construed in accordance with, the internal laws of the State of California
without regard to any otherwise applicable principles of conflicts of law.

      SECTION 9. COUNTERPARTS. This First Amendment may be executed in any
number of counterparts and by different parties on separate counterparts, and
each counterpart shall be deemed to be an original, and all such counterparts
shall together constitute but one and the same instrument.

      SECTION 10. SECTION HEADINGS. The various headings and sub-headings of
this First Amendment are inserted for convenience only and shall not affect the
meaning or interpretation of this First Amendment or the Agreement or any
provision hereof or thereof.

      IN WITNESS WHEREOF, the parties hereto have caused this First Amendment to
be duly executed and delivered by their proper and duly authorized officers as
of the day and year first above written.

Advanced Fibre Communications, Inc.,    Bank of America, N.A.,
as Borrower                             as Lender and Syndication Agent

/s/    Keith E.Pratt                    /s/    Ronald J. Drobny
----------------------------------      ----------------------------------------
By:    Keith E. Pratt                   By:    Ronald J. Drobny
Title: Vice President & CFO             Title: Vice President

Banque Nationale de Paris,
as Lender and Administrative Agent

/s/    Jennifer Cho
----------------------------------
By:    Jennifer Cho
Title: Vice President

/s/    Michael McCorriston
----------------------------------
By:    Michael McCorriston
Title: Vice President

                                      -5-

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