# Why GSM module connects with same apn for different operator?

I'm using SIM868 in one of the GPS tracker that is being developed.

HTTP protocol is used in sending data to the server.I have tried this with SIM cards of 2 network operations,Vodafone and Airtel. AT+SAPBR=3,1,"APN","www" is the command I use to set the apn of the network, in here the apn of Vodafone is "www" and the apn of Airtel is "airtelgprs.com". However it is found that Airtel network also works with the apn of Vodafone and vice-versa. Both networks are able to connect and send data to the server(verified in the server side as well). How is it happening? Is apn not a mandatory parameter in connecting to internet?

Regards, Joe