UDP is a connectionless protocol so there is no equivalent to a TCP SYN packet. This detection is initiated when a router identifies itself in a "Hello" protocol packet. ICMP errors are directed to the source IP address of the originating packet. It is then encapsulated into a new IP packet with a new IP header. Each table is associated with a different kind of packet processing. This duplicate acknowledgement is used as a signal for packet loss. Hence the receiver acknowledges packet 99 again on the receipt of another data packet. IPv4 provides safeguards to ensure that the header of an IP packet is error-free. The ICMP packet is encapsulated in an IPv4 packet. It mixed circuit switching and packet switching. Sincoskie started looking for alternatives that required less processing per packet. It does this by encapsulating an IB transport packet over Ethernet. The variable size of the ICMP packet data section has been exploited. The port scanner generates a SYN packet. Any bytes after the headers in the packet are considered the message body.