It is mentioned in the Altel website that its prepaid pay-per-use data rate is 5 sen per MB or per session.

What is meant by 'per session'?

Most probably it means that if you only use 8kb, let's say u sent a text via whatsapp and then you stop using the phone; no data in or out, then you will be charge for that session which is 5 sen.

What?

Just send a whatsapp message costs 5 sen?

Can't be.

Cos your session is just 8Kb for example. Per session; in that session, you only use or text once. Otherwise you continue to use until or before you reach 1 MB, but how are you going to monitor your usage and also maybe that time you have no need to use or to send message to anyone.

How do you define 'per session' then?

Per session means the total period your phone is connected to the data network. Some smartphone will cut off data in sleep mode.

Thanks for the explanation.

So if I keep my mobile data connection on as long as possible, say for 3 hours, that 3 hours is counted as one session?

If your smartphone doesn't cut off the connecion then yes. Usually they charge per session or per certain amount of data whichever comes first