IAM(Initial Address Message)contains the information

requried for setup call.For a basic call it is a first

message send to Destination.

SAM(subsequent address message)exactly it is overlap calls

address.

SAM message has to be sent in the scenario when suppose a

subscriber dialed a number 9321353536.

SSP send the IAM message to there destination without

reading the 353536. I.e originating SSP looks 9321 and

sends the IAM message to their respective Destination.

And SAM to be send with rest dialed digit.