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Exhibit 4.31

Nortel Networks Agreement No. 011449
Nortel Networks Amendment No. 011449(5)

# AMENDMENT #5

# TO

# OEM PURCHASE AND SALE
AGREEMENT NO. 011449 (Agreement)

# BETWEEN SELLER
CORPORATION AND NORTEL NETWORKS LIMITED

This Amendment #5 to OEM Purchase and
Sale Agreement No. 011449 by and between Nortel Networks Limited, a Canada corporation
with offices located at 8200 Dixie Road, Suite 100, Brampton, Ontario, Canada L6T 5P6
(Nortel Networks) and AudioCodes Ltd., an Israeli corporation with offices located at 1
Hayarden Street, Airport City, 70100 Lod, Israel (Seller), will be effective as of January
1, 2005 (Amendment #5 Effective Date),

WHEREAS, Nortel Networks and Seller
entered into an OEM Purchase and Sale Agreement dated April 28, 2003
(Agreement); and

WHEREAS, Nortel Networks and Seller
wish to amend certain provisions relating to support of the Products in Exhibit C of the
Agreement and for revising the terms and conditions of the Agreement;

NOW, THEREFORE, in consideration of
the premises and the promises set forth herein, the parties agree as follows:

|1. | Nortel
Networks and Seller agree to amend the following sections of Exhibit C of           the
Agreement as follows:
|-- | --------------------------------------------------------------------------------------------------------------------

| | 1.1 | Delete
the existing section 1.1 and replace by:
| | --- | -----------------------------------------------

| | Remote Technical
Services  At Nortel Networks request Seller will provide Nortel Networks
with remote technical support services, as described in Section 3 of Exhibit H to this
Agreement, under (a) Sellers Standard Support Package (b) Sellers Enhanced
Support Package (c) Sellers Standard Support Package with 24x7 support (24x7
Support Package), or (d) Sellers Premium Support Package.
| | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | 1.2 | Delete
the existing section 1.1.1 and replace by:
| | --- | -------------------------------------------------

| | Support Package
Charges Sellers basic charges for the support packages described in
Section 1.1 will be calculated at the end of each calendar quarter during the Term. As of
the last day of the calendar quarter, for each support package and each Product group
(e.g., Mediant products) (and in the case of 24X7 and Premium Support Packages in each
control protocol) supported under a package, Seller will calculate the total Price of all
Products in the Product group (and, if applicable, each control protocol under each
Product group) purchased by Nortel Networks since the Effective Date (Product Group
Cumulative Volume).
| | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



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| | (a) | Standard
and Enhanced For the Standard Support Program and the                Enhanced
Support Program Seller will apply the Product Group Cumulative Volume                to
the matrix in Subsection 1.1.2 below to determine the percentage to be used
               in calculating the technical support charges that will apply retroactively
for                the calendar quarter just ending. Seller will divide the resulting
effective                annual dollar charge by 4 to calculate the quarterly charge to
invoice. For                example, as of the end of the third quarter of the second
year of the Term, if                Nortel Networks Product Group Cumulative Volume
for Mediant Product                supported under the Standard Support Package were [*]
and the Product Group                Cumulative Volume for Mediant Products supported
under the Enhanced Support                Package were [*] million, then the applicable
percentages to be used would be                [*] and [*] respectively. Applying the
percentages in the examples, the basic                charges Seller would invoice Nortel
Networks for the quarter would be [*] for                the Standard Support Package and
[*] for the Enhanced Support Package (i.e., the                effective annual charge
divided by [*]).
| | --- | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | (b) | 24X7
and Premium Support Packages For the 24X7 and Premium Support
               Packages only, Nortel Networks agrees that the applicable support charges
will                be determined by applying the Product Group Cumulative Volume on a
per control                protocol basis (i.e., a separate calculation for each of [*],
[*] and [*]). In                that regard if the Product Group Cumulative Volume for
one protocol for Mediant                Products were [*] million then Seller would
invoice Nortel Networks for [*] for                the 24x7 Support Package for the
calendar quarter just ending (i.e., the                effective annual charge divided by
4), based on the greater than               requirement in the applicable
matrix column in Subsection 1.1.2.
| | --- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | 1.3 | Delete
the existing section 1.1.2 and replace by:
| | --- | -------------------------------------------------

|Product GroupCumulative Volume perSupport Package                       | [*] | [*] | [*] | [*]
|----------------------------------------------------------------------- | --- | --- | --- | ---
|Standard Support Program                                                | [*] | [*] | [*] | [*]
|Enhanced Support Program                                                | [*] | [*] | [*] | [*]
|                                                                       
|Product GroupCumulative Volume (perControl Protocol) perSupport Package | [*] | [*] | [*] | [*]
|24x7 Support Package                                                    | [*] | [*] | [*] | [*]
|Premium Support Package                                                 | [*] | [*] | [*] | [*]

* Confidential



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| | 1.4 | Delete
the existing section 1.1.3 and replace by:
| | --- | -------------------------------------------------

| | Cumulative Total
Support Program Charge Notwithstanding Subsection 1.1.1 above, during the
Term, if the total of all Product Group Cumulative Totals for the Standard or Enhanced or
24x7 Support Package exceeds [*], and until the total of all Product Group Cumulative
Totals for the same support package equals [*], Nortel Networks will not be obligated to
pay (i) more than [*] in support charges in each future calendar quarter for Standard
Support Package; or, (ii) more than [*] in total support charges for all control
protocols in each future calendar quarter for the 24X7 Support Package. Notwithstanding
Subsection 1.1.1 above, during the Term, if the total of all Product Group Cumulative
Totals for the Premium Support Package exceeds [*] million, and until the total of all
Product Group Cumulative Totals for the same support package equals [*], Nortel Networks
will not be obligated to pay more than [*] in total support charges for all control
protocols in each future calendar quarter for the Premium Support Package. When the total
of all Product Group Cumulative Totals for each of the Support Packages equals [*], the
parties will agree on the applicable percentage to be used to calculate future support
charges for the applicable support package.
| | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|2. | Nortel
Networks and Seller agree to amend the following sections of Exhibit H of           the
Agreement as follows:
|-- | --------------------------------------------------------------------------------------------------------------------

| | 2.1 | Add
new section 3.10A to read:
| | --- | ------------------------------

| | In
addition to Sellers obligations under this Exhibit H for providing its Premium
Support Package, the Premium Support Package will include Sellers providing Nortel
Networks with Major Software Version releases that include performance enhancements as
well as additional features.
| | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

| | 2.2 | Add
new section to read:
| | --- | ------------------------

| |  | Premium
Support Payment Exclusions:
| | - | -----------------------------------

| |  | TP610
for Centrex IP (No upgrades)
| | - | ----------------------------------

| |  | Lab
equipment, PI equipment, R&R inventory
| | - | ------------------------------------------

| |  | Account specific free labs equipment that is used for initial lab testing
potential Service Provider customers. Free Labs does not include equipment
that will be later used in a network deployment.
| | - | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|3. | This
Amendment will serve as notice under the Agreement that Sellers           address
is now at 1 Hayarden Street, Airport City, Lod 70100, Israel.
|-- | -----------------------------------------------------------------------------------------------------------------------------------------------------

|4. | Except
for this Amendment No. 5, in all other respects the Agreement shall           remain
unchanged.
|-- | ------------------------------------------------------------------------------------------------------

* Confidential



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IN WITNESS WHEREOF, the parties have
caused this Amendment No. 5 to the Agreement to be signed by their duly authorized
representatives.

|NORTEL NETWORKS LIMITEDBy: /s/ Nancy Scott
Print Name: Nancy ScottTitle: SR Mgr. Supply Mgmt.Date: May 6, 2005 |  | AUDIOCODES LTD.By: /s/ Ben Rabinowitz
Print Name: Ben RabinowitzTitle: VP Marketing and Sales, NADate: April 27, 2005
|---------------------------------------------------------------------------------------------------------------------------- |  | -----------------------------------------------------------------------------------------------------------------------------------



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