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.

Microsoft Lync Server 2013 – Consolidated Edge Audio Issue

I was assisting a customer with the renewal of a Consolidated Edge external SSL certificate recently and upon applying the newly issued certificate to the server, audio calls with externally situated users or federated partners via the Consolidated Edge failed. Upon answering an audio call via the Lync Client, it immediately reported “Called Ended” and third party IP handsets would become stuck in a “Connecting” state once the call was answered by the remote party. While the latter error would have suggested perhaps an audio/video port issue at a firewall level, I was on the phone to the customer via a federated call when the certificate was assigned to the Consolidated Edge services, which in turn immediately caused the call to drop and as such I knew a firewall issue was not the root cause of this problem. On inspection of the Consolidated Edge servers event log, everything appeared to fine and all Consolidated Edge specific services were started, additionally all other functionality such as remote and federated instant messages were working as expected. However, upon a restart of the Consolidated Edge services the following event was logged:

The Access Edge Server failed to import a shared session key due to invalid signature.

In the past 1 minutes, the server rejected 1 shared session keys presented from the network due to an invalid signature. This suggests an incorrect certificate configuration. A large number of failures could indicate spoofed session key data sent by an attacker.

Cause: This is most likely to be a configuration problem in a server array.

Resolution: Ensure that all servers in an Access Edge Server Array have the same certificate configured for the external IP address on the Edge Interfaces tab. Inspect the serial number of each certificate. If the problem persists, use the Administrator Log to help identify the source of these messages.

Upon reading the error this immediately prompted me to inspect the certificate via the certificates MMC snap-in and upon reviewing the new SSL certificate everything appeared to be correct, the certificate chain was reporting as valid as was the private key. In this customers case a GoDaddy SSL certificate had been procured and while the certificate chain stated the implemented certificate was trusted, it transpired an intermediate GoDaddy certificate was missing. On adding the missing intermediate certificate into the Local Computer certificate store, which was also included in the downloaded certificates .zip file, the audio calling issue was resolved. In summary, always check intermediate SSL certificates for your chosen provider, specifically if you are not utilising one of the bigger SSL vendors such as VeriSign or Digicert. Hope this helps!