Overview#IMessage is an Instant Messaging service by Apple and is supported by the Messages application in iOS 5 and later and OSX Mountain Lion and later.
IMessage protocol is based on the Apple Push Notification service (APNs)—a proprietary, binary protocol. IMessage sets up a Keep-Alive connection with the Apple servers. Every connection has its own unique code, which acts as an identifier for the route that should be used to send a message to a specific device. The connection is encrypted with TLS using a Client-side certificate, that is requested by the device on the activation of IMessage.