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TTL-expired packet. When Tracert receives this response, it notes the address of the second
router. This continues until the packet reaches the intended IP address.
Protocols at the Internetwork Layer
47. How does TCP provide flow control and reliability?
TCP sets a maximum number of bytes to transmit before it must receive an acknowledgment
of receipt from the receiving station. If it does not receive an acknowledgment within a
certain period, it assumes an error has occurred and begins to retransmit the data since the
last acknowledgment was received.
TCP: The Reliable Transport Layer
48. Briefly describe the three-way handshake that TCP uses to establish a connection.
When a client computer makes a request, TCP begins the session by sending the receiving
computer, which is typically a server, a SYN segment. If the server is not busy, then it sends
back an ACK-SYN packet acknowledging the creation of the session. Then the client
computer sends back an ACK segment to finalize the connection.
TCP: The Reliable Transport Layer
49. What is the function of DNS, and at which layer does it operate?
DNS allows computers to contact other computers using a familiar name instead of a hard-to–
remember IP address. DNS keeps records of which name corresponds to which IP address in
a DNS cache so that a frequently accessed address can be resolved quickly. DNS is an
Application layer protocol.