VNet - it's a communication used in IT to talk within the organisation using a 6 digit dial in number......

Skype - it is also a communication used to just ping the person and it shows the status of the person,
available, busy, in meeting, do not disturb....ext...

And tagging a person in Skype will help us to know whenever they are coming to available status....

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If you guys have doubt with any terms that are used, kindly inline comment those, will help you out....