AudioCodes E-SBC – Removing ;ext= From An INVITE Header

Recently I was performing an integration between Microsoft Lync Server 2013 and an Alcatel OmniPCX phone system at a customer site. The existing PBX already had an element of VoIP via a separate platform called OpenTouch which allowed users to have multiple devices associated with a single extension. For an unknown reason when calling OpenTouch users via Lync Server 2013, which caused the call to be sent to an AudioCodes Virtual E-SBC and then onto the Alcatel PBX via a direct SIP trunk, the users handset would not ring. After working with the customers Alcatel vendor, it transpired the OpenTouch platform did not like INVITE’s that were sent with a from destination of +441234567890;ext=7890 for example, and the ;ext= element was causing the issue. In order to remove this aspect from an INVITE the ;ext= element needed to be stripped from the INVITE header using a Message Manipulation on the AudioCodes E-SBC, as with Sonus devices a regular expression is required in order to remove any parts of an INVITE we do not need. On an AudioCodes devices running version 6.8 of the firmware, the following was performed.

1. When logged into the device and expand VoIP -> SIP Definitions -> Msg Policy & Manipulations and then select Message Manipulations.

2. In the Message Manipulations table, click add and provide an Index number, such as 1 if this is your first manipulation and then proceed to configure the manipulation as per the provided screenshot below.

Message Manipulation 1024x96 AudioCodes E SBC   Removing ;ext= From An INVITE Header

3. To understand how Message Manipulation works, in the condition section this where we look for specific information within the INVITE. In this case we are using a regular expression to place each part of the INVITE header into a variable. For example the (.*) part of the condition places the value into variable $1, this would be the +441234567890 part of the number only, the next part of the regular expression (;ext=) would be placed in variable $2 which would only be the (;ext=) part of the header and so on and so forth. By placing each part of the header into variable we can then control the manipulation by specifying an Action Value, this Action Value constructs the header using only specific parts that we wish to use. For example, to gain a result that removes the ;ext= element, we would use $1 (+441234567890) and then $4 (@) and then $5 (domain.com) to construct a header that displays +441234567890@domain.com.

4. Once this is complete, expand VoIP -> VoIP Network -> IP Group and then edit the IP Group you wish to apply the message manipulation to. When the properties of the manipulation opens, enter the Manipulation Set ID that you entered in step 2 into either the inbound or outbound manipulation set ID dialog boxes depending on the direction in which you need to apply the manipulation, as illustrated below.

SBC Manipulation Set AudioCodes E SBC   Removing ;ext= From An INVITE Header

That’s it, when performing a debug trace on the gateway you should now see the ;ext= element has now been removed from the INVITE header.

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