Call Classification: OnNet vs OffNet

Call Classification in Cisco Unified Communications Manager (CUCM) is the practice of labelling a call to be either "OnNet" or "OffNet".   This is also a topic that you should understand well if you are pursuing CCNA Collaboration or CCNP Collaboration certifications.  You could go into quite a bit of depth when researching the various features and interactions related to Call Classification, but my goal with this post is provide some useful reference material and get your studies off in the right direction.

Why is Call Classification important?   It has direct impact on the features listed below:

• Directory Number Call Forward Settings:  Forwarding paths are configured differently for OnNet calls (Ex., Forward Busy Internal) and OffNet calls (Ex., Forward Busy External).  Internal calls can be forwarded to a manager or team member while OffNet calls are preferred to forward to voicemail when the party is unavailable.
• Drop Conference When No OnNet Party Remains:  A toll fraud feature, this requires that an internal party be on a conference to ensure that the conference stays open.  
• Toll Fraud Control (Block OffNet to OffNet Transfer):  Another toll fraud feature, this prevents you from forwarding your friend's calls to their family member in Costa Rica.  I'm sure that she's a nice lady, but your company shouldn't be paying for your friend's calls.  

Call Classification Configuration:

1. Route Pattern Configuration, Cisco Unified Communications Manager Administration Guide
2. Gateway Configuration, Cisco Unified Communications Manager Administration Guide
3. Trunk Configuration, Cisco Unified Communications Manager Administration Guide
4. Service Parameter Configuration, Cisco Unified Communications Manager Administration Guide
5. Conference Bridges, Cisco Unified Communications Manager System Guide

Additional interactions related to Call Classification:

• Call Data Records (CDR):  Many reports will break data down by OnNet/Internal or OffNet/External calls.   The value of these reports will depend upon understanding exactly what types of calls could contribute to each sum.  
• Dialed Number Analyzer (DNA):   DNA will reference the call classification when possible and is a useful tool for troubleshooting and testing various call flows.  
• Bulk Administration:   Call Classification is a configurable value when using this tool to administer trunks and gateways.

Definition:  OnNet vs OffNet

"OnNet" typically refers to calls made within your own network of telephony devices.   Within a CUCM cluster of devices, this typically means calls between devices that are configured by the cluster itself.   

"OffNet" conversely refers to calls made to devices outside of your local network of devices.  For example, if you are calling from your cluster to any external PSTN device (like a cell phone) - it's an OffNet call.

So, somebody is going to ask - "But what if my company has multiple clusters?"  That's a very good question!  The trouble with this question is that it depends!  Calls between clusters could be either OffNet or OnNet depending on how you've designed the telephony network.  

Perhaps, these are entirely different business units that function quite independently of one another?  I would love to have some readers share their experiences on this topic in the comments below. 

Toll Fraud Considerations

Drop Conference When No OnNet Party Remains

The system drops the active conference when the last on-network party in the conference hangs up or drops out of the conference. Cisco Unified Communications Manager releases all resources that are assigned to the conference.

Be thoughtful when enabling this feature!  To use the additional functionality that advanced ad hoc conferencing provides, Cisco recommends that you set this service parameter to "Never." Any other setting can result in unintentional termination of a conference.

Block OffNet to OffNet Transfer

The Cisco Unified Communications Manager clusterwide service parameter "Block OffNet to OffNet Transfer" allows administrators to prevent users from transferring external calls to another external number. This parameter specifies values as "True" or "False". 

Setting the parameter to "True" blocks external calls from being transferred to another external device. The default value specifies False. You modify the "Block OffNet to OffNet Transfer" service parameter by using the Service Parameter Configuration window.

When a user tries to transfer a call on an OffNet gateway or trunk when the service parameter "Block OffNet to OffNet Transfer" is set to "True", a message displays on the user phone to indicate that the call cannot be transferred.