A specific problem that must be solved in remote terminal access protocols such as Telnet is the
need to transmit exceptional events such as ‘kill signals’ from the ‘terminal’ to the host in advance
of previously-transmitted data. Kill signals should reach their destination ahead of any other
ongoing transmissions. Discuss the solution of this problem with connection-oriented and
connectionless protocols.

What will be an ideal response?

The problem is that a kill signal should reach the receiving process quickly even when there is buffer overflow
(e.g. caused by an infinite loop in the sender) or other exceptional conditions at the receiving host.
With a connection-oriented, reliable protocol such as TCP, all packets must be received and
acknowledged by the sender, in the order in which they are transmitted. Thus a kill signal cannot overtake other
data already in the stream. To overcome this, an out-of-band signalling mechanism must be provided. In TCP
this is called the URGENT mechanism. Packets containing data that is flagged as URGENT bypass the flow
control mechanisms at the receiver and are read immediately.
With connectionless protocols, the process at the sender simply recognizes the event and sends a
message containing a kill signal in the next outgoing packet. The message must be resent until the receiving
process acknowledges it.