The bits required to fill up the 64kbps channel must be added in a systematic
way so that the receiving device can remove the bits using exactly the same
methodology to retain the information being transmitted.
There are
two protocols commonly used that define systems to insert and remove extra bits:
You will use either one or the other, depending on the protocol required by
the service you are calling.
Rate Adaptation is usually implemented in a Terminal Adapter. The activity
happens within the B channel and is an end-to-end protocol. The ISDN is
therefore unaware of this and the call type will be Unstructured Data.