What is the difference between TCP Keepalive and HTTP Keep-Alive?

1. A Both protocols are conceptually identical and are used interchangeably by various modern browsers and web-servers to manage the persistent state of a user's session.
2. B TCP Keepalive reuses high-level application headers to maintain the connection, while HTTP Keep-Alive relies on low-level sequence number synchronization at the transport layer.
3. C TCP Keepalive is a low-level 'heartbeat' used to detect if a connection is still alive; HTTP Keep-Alive is an agreement to reuse the same TCP socket for multiple sequential requests.
4. D The HTTP-level Keep-Alive mechanism has been fully deprecated in modern web browsers in favor of the more efficient and secure 128-bit transport-layer alternative.