The two routers RTA and RTB are interconnected back-to-back using serial ports. The serial port of RTA is configured with HDLC protocol, and the serial port of RTB is configured with PPP protocol.
Both devices are configured with the correct IP address, then what will happen is ______. (Multiple choice)

The router S0/0 interface is connected to the network through frame relay, and the following interface information can be seen on this router:
[MSR]display interface Serial 0/0
Serial0/0 current state: UP
Line protocol current state: UP
Internet Address is 3.3.3.1/24 Primary
Link layer protocol is FR IETF
LMI DLCI is 0, LMI type is Q.933a, frame relay DTE
LMI status enquiry sent 91, LMI status received 69
LMI status timeout 22, LMI message discarded 1
Then you know ______. (Multiple choice)

It is the ______ of the OSI reference model that provides end-to-end reliable data transmission and flow control.

The default control protocol port used by FTP is ______.

In the process of establishing a PPP session, when authentication is set and the authentication is passed, the PPP link enters the ______ phase.