Skype Server 2015 and 2019 provide a way for Skype engineers and telephony administrators to manipulate call routing options. Calling number translation brings about a change that enables the Skype calling party to call the called party and display a number to be defined by a translation rule in the Skype dial plan to the called party representing the caller ID. A bit confusing I’m sure but I will break this down in a manner that allows you to make good use of the feature in Skype 2015 and 2019 enterprise voice capability.
Let’s start at the beginning; In Lync server 2010 within the trunk configuration you where able to modify the format of the dialed phone number using an outbound translation rule to ensure the format matched the type required by the PBX; the unfortunate thing is you could not do the same with the caller’s number.
Skype with enterprise voice requires that all dial strings be normalized to the E.164 format for the purpose of performing reverse number lookup (RNL) in order for the Skype server to route calls in a more efficient manner and lookup Skype clients based on their unique phone number.
Lync 2010 Outbound Number Translation
For example let’s say we are sending an outbound call from Lync to an IP-PBX via a sip trunk to the PSTN. (The reason we have a sip trunk is the sip peer is an IP-PBX instead of a legacy TDM PBX which would require a PSTN Gateway between the Lync Mediation server and the PBX.) In this scenario the IP-PBX prefers the numbers sent to it in a format that can be recognized, which is not always E.164; most IP-PBX’s prefers to do without the + in the digits it receives. So now we have the internal calling phone number +14255558585 and the called number +14253451212 normalization and reverse number lookup (RNL) being performed and being translated to 14253451212; notice the + being removed from called number; this is an example of the called number being translated in a format the IP-PBX prefers in this example. What Lync 2010 was not able to do was to manipulate the calling person’s number, which was +14255558585.
Figure 1: Called phone number going through reverse number lookup and removing the plus.
Skype 2015 and 2019 Outbound Number Translation
Skype Server 2015 and 2019 provides a way to have translation rules support calling numbers. The trunk peer (PBX) as I stated earlier may require that numbers be in a specific dialing format. To translate numbers from
E.164 format to another format, you can define one or more translation rules to manipulate the request URI (uniform resource indicator) before you route it to the trunk peer. Continuing from the example above, the caller +14255558585 makes a call to +14253451212 with normalization and reverse number lookup (RNL) taken place, due to the outbound routing translation that is within the Skype dial plan for the called party, the number has been formatted to 14253451212 (basically without the +) for the PBX. Now comes the interesting part, the caller ID for the called party appears as +14253455000 notices that last seven digits of the calling party’s DID have changed.
Note: I highlighted the last four digits to show the area that most organizations would consider changing with the “calling number translation” feature. So instead of the full seven digits like I did in figure 2, the last four for the translation would be 8585 to 5000.
Figure 2: Called phone number going through reverse number lookup and calling phone number going through translation pattern as well.
When configuring the calling party number translation rule, we need to go to Skype Control Panel, Voice Routing, and Trunk Configuration. Once in there is where the magic happens and we begin to create a translation rule that will tell the incoming number for the specific trunk what to translate to. Begin by clicking on New and then creating the Pattern to match and Translation pattern. In figure 3 below we see that my translation rule is fairly straight forward and tells the trunk that any call that contains ten digits and begins with a (+1) will append basically the entire ten digits with an addition of a country code of one to all numbers traveling to the next hop of the Skype Mediation server.
Figure 3: Configuring calling number translation rules in the Skype dial plan
Figure 4: Validation of the created test translation rule
Notes to take home
The evolution of Skype enterprise voice, specifically number translations brings about changes that will make life easier for administrators of PBX’s and Skype alike. The ability to configure and design dial plans that involve masking call routes from the Mediation server to the next hop which could be either the PBX or PSTN Gateway will allow more options for Skype administrators; rather than relying on the gateway appliance or PBXs to be responsible for the call manipulation of numbers from the called party. Keep in mind the called number translation feature is a subtle one that could go over looked for some existing Skype 2015 and 2019 deployments, in the sense that they might already be accounting for this capability through their current telephony infrastructure. The good news is, with Skype Server 2015 and 2019 you’re able to configure these changes on the Microsoft side of the house and take one less responsibility off the PBX or PSTN Gateway administrator.