Once you login to TMAC and went available, one can see the dummy call on hard phone. This dummy call is nothing but the Nailer call or in other-words can say that the agent is nailed up.
This call is sent by POM if the agent is logged in as POM agent in TMAC. This call will not be there for an ACD agent. This can be seen only for POM Outbound agent who is in 'Available' state.
The call will be connected throughout starting from agent login to logout, only then the outbound calls are fired from POM to TMAC. If nailer call is disconnected or dropped, POM will not send any call to TMAC since there is communication link breakage. Hence nailer call acts as a communication medium between TMAC and POM. All the call controls in TMAC will fail if the nailer call is disconnected by any means.