These "virtual packets" allow heterogeneous networks to talk to each other using a common protocol.

A common protocol used in US hospitals includes the following:

A pair of programs that do not support a common protocol cannot communicate with each other.

It is the most common protocol which supports write-back cache.

In many gynecological exams a blood screen for thyroid is now a common protocol.

Historically, the most common protocol has been to place protected areas in the mountains, leaving the valleys to the timber industry.

When both teams' bands are present, it is common protocol for the visiting band to perform first.

Some of the common protocols for the data portion are listed below:

The technique is widely accepted today, and remains a common protocol in molecular biology labs.

So it's a way of writing code which uses not common protocols.