I'm calling a URL to get json data from another web site in my Google App Engine application. Then i received bellow message.The Socket API will be enabled for this application once billing has  been enabled in the admin consoleSo I decided to enable billing, but I have a question: For Mail API, we can send 100 messages for a day for free. Is there any similar free default limit for Socket API ? 
Is there a free default limit for the Google App Engine Socket API?
google app engine;cost