Question about open interest and volumes

I am confused by my concept of volumes and open interest. I had read that Open Interest is the total number of outstanding contracts that are held by market participants at the end of each day. For example, if both parties to the trade are initiating a new position ( one new buyer and one new seller), open interest will increase by one contract. If both traders are closing an existing or old position ( one old buyer and one old seller) open interest will decline by one contract. The third and final possibility is one old trader passing off his position to a new trader ( one old buyer sells to one new buyer). In this case the open interest will not change.

So either which way the volume is the same as Open interest or more never less. The nseindia options page shows open interest changes much more than volume. For example now the 4300 Call has a decrease in OI by 5000 and the volume is 138. I have also noticed this in the nseindia bhavcopy.

Any explanation where I am wrong on my concept of OI and volume? Thanks in advance.

Probably you ignored the fact that OI / change in OI is in multiple of 50 whereas Volumes are not.
i.e. Volume = number of contract traded.
OI = actual qty..i.e contract * lot size.

for for 138 volumn, impacted OI is 138*50 = 6900.. If OI is 5000, then 1400 units got exchanged in mkt between old player and new player (3rd type of txn in your example) without impact any new OI.

hope this helps..
Happy Trading