Document:

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                                                                   Exhibit 10.23

AMENDMENT NO. 1 TO AMENDED AND RESTATED CREDIT AGREEMENT AMONG IPC INFORMATION
  SYSTEMS, INC., AS PARENT BORROWER, IPC FUNDING CORP., AS SUB BORROWER, IPC
   COMMUNICATIONS, INC., AS A LOAN PARTY, THE LENDERS SIGNATORY THERETO, AS
  LENDERS, GENERAL ELECTRIC CAPITAL CORPORATION, AS ISSUING BANK, COLLATERAL
AGENT, ADMINISTRATIVE AGENT AND LENDER AND FIRST UNION CAPITAL MARKETS, INC., AS
                              DOCUMENTATION AGENT

          This Amendment No. 1 to Amended and Restated Credit Agreement, dated
as of July 1, 1999 (this "Amendment"), is entered into by and among IPC
Information Systems, Inc., a Delaware corporation (the "Parent Borrower"); IPC
Funding Corp., a Delaware corporation (the "Sub Borrower"); IPC Communications,
Inc., a Delaware corporation ("Holdings"), as a Loan Party; General Electric
Capital Corporation, as Lender, and as Agent for Lenders; and the other Lenders.

                                   RECITALS

     A.   Borrowers, Holdings, Agent, Lenders and First Union Capital Markets,
Inc., as Documentation Agent, are parties to that certain Amended and Restated
Credit Agreement, dated as of June 21, 1999 (the "Credit Agreement").

     B.   Borrowers, Holdings, Agent and Lenders are desirous of amending
Section 5.02(g) of the Credit Agreement, as and to the extent set forth in this
Amendment.

          NOW THEREFORE, in consideration of the premises and the mutual
covenants hereinafter contained, and of the loans or other extensions of credit
heretofore, now or hereafter made to, or for the benefit of, Borrowers by
Lenders, Borrowers, Holdings, Agent and Lenders hereby agree as follows:

          1.   Definitions.  Except to the extent otherwise specified herein,
               -----------
capitalized terms used in this Amendment shall have the same meanings ascribed
to them in the Credit Agreement.

          2.   Amendment.
               ---------

          2.1  Section 5.02(g) of the Credit Agreement is hereby amended by
deleting the words "twelve percent (12%)" in clause (D) and replacing them with
the following "twelve and three tenths percent (12.3%)(fourteen and one tenth
percent (14.1%) before giving effect to the initial public offering by IXnet
Holdings contemplated by clause (C), immediately preceding)".

          3.   Condition Precedent to Amendment.  The amendment contemplated by
               --------------------------------
Section 2 hereof is subject to the satisfaction of the following condition
precedent:

          3.1  Amendment.  This Amendment shall have been duly executed and
               ---------
delivered by each of Borrowers, Holdings, Agent and Required Lenders.
<PAGE>

          4.   Reference to and Effect Upon the Credit Agreement and other Loan
               ----------------------------------------------------------------
Agreements.
----------

          4.1  Except as specifically amended in Section 2 above, the Credit
Agreement, the Notes and each other Loan Document shall remain in full force and
effect and each is hereby ratified and confirmed.

          4.2  The execution, delivery and effect of this Amendment shall be
limited precisely as written and shall not be deemed to (i) be a consent to any
waiver of any term or condition, or to any amendment or modification of any term
or condition (except as specifically amended in Section 2 above), of the Credit
Agreement or any other Loan Document or (ii) prejudice any right, power or
remedy which the Agent or any Lender now has or may have in the future under or
in connection with the Credit Agreement, the Notes or any other Loan Document.
Each reference in the Credit Agreement to "this Agreement", "hereunder",
"hereof", "herein" or any other word or words of similar import shall mean and
be a reference to the Credit Agreement as amended hereby, and each reference in
any other Loan Document to the Credit Agreement or any word or words of similar
import shall be and mean a reference to the Credit Agreement as amended hereby.

          5.   Counterparts.  This Amendment may be executed in any number of
               ------------
counterparts, each of which when so executed shall be deemed an original but all
such counterparts shall constitute one and the same instrument.

          6.   Costs and Expenses.  As provided in Section 8.04 of the Credit
               ------------------
Agreement, Borrowers shall pay the fees, costs and expenses incurred by Agent in
connection with the preparation, execution and delivery of this Amendment
(including, without limitation, reasonable attorneys' fees).

          7.   GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
               -------------
IN ACCORDANCE WITH THE INTERNAL LAWS (AS OPPOSED TO CONFLICTS OF LAW PROVISIONS)
OF THE STATE OF NEW YORK.

          8.   Headings.  Section headings in this Amendment are included herein
               --------
for convenience of reference only and shall not constitute a part of this
Amendment for any other purpose.

                           [Signature Pages Follow]
<PAGE>

          IN WITNESS WHEREOF, this Amendment No. 1 to Amended and Restated
Credit Agreement has been duly executed as of the date first written above.

IPC INFORMATION SYSTEMS, INC.,
as Parent Borrower

By: _________________________

Title:________________________

IPC FUNDING CORP.,
as Sub Borrower

By:__________________________

Its:__________________________

IPC COMMUNICATIONS, INC.,
as a Loan Party/1/

By:__________________________

Title:_________________________

________________
/1/ Not as a Borrower, but for purposes of the other provisions of this
Agreement
<PAGE>

GENERAL ELECTRIC CAPITAL
CORPORATION, as Agent and
Lender

By:__________________________

Title:_________________________

GENERAL ELECTRIC CAPITAL
CORPORATION, as Administrative Agent, Collateral Agent
and Issuing Bank

By:__________________________

Title:_________________________

FIRST UNION NATIONAL BANK, as a Lender

By: ___________________________

Title: _________________________

BNY FINANCIAL CORPORATION, as a Lender

By: _____________________________

Title: ___________________________<PAGE>

                                                                   Exhibit 10.24

 AMENDMENT NO. 2 TO AMENDED AND RESTATED CREDIT AGREEMENT AMONG IPC INFORMATION
   SYSTEMS, INC., AS PARENT BORROWER, IPC FUNDING CORP., AS SUB BORROWER, IPC
    COMMUNICATIONS, INC., AS A LOAN PARTY, THE LENDERS SIGNATORY THERETO, AS
   LENDERS, GENERAL ELECTRIC CAPITAL CORPORATION, AS ISSUING BANK, COLLATERAL
AGENT, ADMINISTRATIVE AGENT AND LENDER AND FIRST UNION CAPITAL MARKETS, INC., AS
                              DOCUMENTATION AGENT

          This Amendment No. 2 to Amended and Restated Credit Agreement, dated
as of August 12, 1999 (this "Amendment"), is entered into by and among IPC
Information Systems, Inc., a Delaware corporation (the "Parent Borrower"); IPC
Funding Corp., a Delaware corporation (the "Sub Borrower"); IPC Communications,
Inc., a Delaware corporation ("Holdings"), as a Loan Party; General Electric
Capital Corporation, as Lender, and as Agent for Lenders; and the other Lenders.

                                   RECITALS

     A.   Borrowers, Holdings, Agent, Lenders and First Union Capital Markets,
Inc., as Documentation Agent, are parties to that certain Amended and Restated
Credit Agreement, dated as of June 21, 1999 (as amended by Amendment No. 1
thereto, dated as of July 1, 1999, the "Credit Agreement").

     B.   Borrowers, Holdings, Agent and Lenders are desirous of amending
Section 5.02(g) of the Credit Agreement, as and to the extent set forth in this
Amendment.

          NOW THEREFORE, in consideration of the premises and the mutual
covenants hereinafter contained, and of the loans or other extensions of credit
heretofore, now or hereafter made to, or for the benefit of, Borrowers by
Lenders, Borrowers, Holdings, Agent and Lenders hereby agree as follows:

          1.   Definitions.  Except to the extent otherwise specified herein,
               -----------
capitalized terms used in this Amendment shall have the same meanings ascribed
to them in the Credit Agreement.

          2.   Amendment.
               ---------

          2.1  Section 5.02(g) of the Credit Agreement is hereby amended by
deleting the figure "$100,000,000" from the first proviso of clause (iii)(C) and
replacing it with the figure "$80,000,000";

          2.2  Section 5.02(g) of the Credit Agreement is hereby further amended
by deleting from clause (iii) (D) the words "twelve and three tenths percent
(12.3%)" and replacing them with the words "twelve and six tenths percent
(12.6%)".
<PAGE>

          3.   Condition Precedent to Amendment.  The amendment contemplated by
               --------------------------------
Section 2 hereof shall be effective when this Amendment shall have been duly
executed and delivered by each of Borrowers, Holdings, Agent and Required
Lenders.

          4.   Reference to and Effect Upon the Credit Agreement and other Loan
               ----------------------------------------------------------------
Agreements.
----------

          4.1  Except as specifically amended in Section 2 above, the Credit
Agreement, the Notes and each other Loan Document shall remain in full force and
effect and each is hereby ratified and confirmed.

          4.2  The execution, delivery and effect of this Amendment shall be
limited precisely as written and shall not be deemed to (i) be a consent to any
waiver of any term or condition, or to any amendment or modification of any term
or condition (except as specifically amended in Section 2 above), of the Credit
Agreement or any other Loan Document or (ii) prejudice any right, power or
remedy which the Agent or any Lender now has or may have in the future under or
in connection with the Credit Agreement, the Notes or any other Loan Document.
Each reference in the Credit Agreement to "this Agreement", "hereunder",
"hereof", "herein" or any other word or words of similar import shall mean and
be a reference to the Credit Agreement as amended hereby, and each reference in
any other Loan Document to the Credit Agreement or any word or words of similar
import shall be and mean a reference to the Credit Agreement as amended hereby.

          5.   Counterparts.  This Amendment may be executed in any number of
               ------------
counterparts, each of which when so executed shall be deemed an original but all
such counterparts shall constitute one and the same instrument.

          6.   Costs and Expenses.  As provided in Section 8.04 of the Credit
               ------------------
Agreement, Borrowers shall pay the fees, costs and expenses incurred by Agent in
connection with the preparation, execution and delivery of this Amendment
(including, without limitation, reasonable attorneys' fees).

          7.   GOVERNING LAW.  THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
               -------------
IN ACCORDANCE WITH THE INTERNAL LAWS (AS OPPOSED TO CONFLICTS OF LAW PROVISIONS)
OF THE STATE OF NEW YORK.

          8.   Headings.  Section headings in this Amendment are included herein
               --------
for convenience of reference only and shall not constitute a part of this
Amendment for any other purpose.

                           [Signature Pages Follow]
<PAGE>

          IN WITNESS WHEREOF, this Amendment No. 2 to Amended and Restated
Credit Agreement has been duly executed as of the date first written above.

IPC INFORMATION SYSTEMS, INC.,
as Parent Borrower

By: _________________________

Title:________________________
<PAGE>

IPC FUNDING CORP.,
as Sub Borrower

By:__________________________

Title:__________________________

IPC COMMUNICATIONS, INC.,
as a Loan Party

By:__________________________

Title:_________________________

GENERAL ELECTRIC CAPITAL CORPORATION,
as Administrative Agent, Collateral Agent, Issuing Bank and Lender

By:__________________________

Title:_________________________

FIRST UNION NATIONAL BANK,
as a Lender

By: ___________________________

Title: _________________________

GMAC COMMERCIAL CREDIT LLC,
as a Lender

By: _____________________________

Title: ___________________________

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