Sender ID is the alpha name or alpha-numeric name or number which appears on the mobile phone as the sender of a SMS (It is used to identify who's sending the message to the recipient). Sender ID can be a number (i.e. a Mobile Phone Number) or alpha-numeric term such as PLIVO, PLVSMS.
Sender ID is useful in uniquely identifying your business and helps with brand recall amongst your customers.
Why is registration required?
Registering your sender id in advance increases the delivery rate of your messages and reduces the chances of getting blocked by carriers.