Will the other person see that I am online if I call them on WhatsApp - briefly?
Yes, the other person will see that you are online when you call them on WhatsApp. This is because WhatsApp displays your online status to the recipient during a call.
Will the other person see that I am online if I call them on WhatsApp - in detail?
When you make a voice or video call on WhatsApp, the recipient will immediately be able to see your status as "online" or "calling." This is due to the nature of real-time communication protocols used by WhatsApp, which require immediate feedback and acknowledgment of the call initiation.
WhatsApp uses a combination of Internet Protocol (IP) and User Datagram Protocol (UDP) for voice and video calls. When you place a call, your device sends a request to WhatsApp's servers, which then forward this request to the recipient's device. The recipient's device receives this request and updates their status to indicate that someone is trying to reach them. This status change is reflected in both the chat window with your contact and in the main WhatsApp interface where active statuses are displayed.
In addition, if the recipient has notifications enabled for WhatsApp calls, they will receive an alert indicating that you are calling them. This notification includes your profile picture and a message stating "Calling" or "Missed Call," depending on whether they answered the call or not.
It is important to note that even if the recipient does not answer the call, their status will still show that you tried to reach them. The "Last Seen" timestamp will update to reflect the time of your call attempt, and it will remain visible until the recipient either changes their privacy settings or manually updates their status.
In summary, making a voice or video call on WhatsApp automatically makes your online presence visible to the recipient through various indicators such as status updates and notifications.