TCP/IP Review

In TCP/IP communications, why does each packet contain a sequence number?

• Computers use the sequence number to determine the original order of the packets.

• Routers use the sequence number to figure out where to send the packet next.

• Routers use the sequence number to figure out the final destination.

• Computers use the sequence number to identify which router sent the packet.

Why does each IP packet contain a destination address?

• Computers can look at the destination address to see if the packet has been hijacked along the way.

• Computers use the destination address to figure out how to reassemble IP packets in the correct order.

• Routers can see where a packet came from by examining the destination address, and make sure not to send it back.

• The web browser uses the destination address to decide what URL to show in the browser address bar.

• Routers use the destination address to decide where to send a packet next.

Computer A wants to send data to Computer B using the TCP/IP protocols.

What's the best description of how Computer A sends the data?

• Computer A splits the message into packets. It sends each packet to Computer B as fast as it can, and then closes the connection.

• Computer A creates two packets, one with the data, and the other with the metadata. Computer A first sends along the metadata and then sends along the actual data.

• Computer A splits the data into packets. It does a three-way handshake with Computer B to establish the connection, then sends each packet to the nearest router. If it detects packet loss, it re-sends the missing packets.

• Computer A splits the data into packets. It looks up the best routing path in a routing table, records the path in the packet, and sends it to the first router in the path. The packet follows the path until it gets to the final destination.

TCP/IP are protocols that move data around the Internet.

What are they each responsible for?

• TCP is responsible for giving addresses to each computer on the Internet. IP is responsible for mapping domain names to those addresses.

• TCP is responsible for reliable transmission of packets. IP is responsible for routing of packets from source to destination across the Internet.

• TCP is responsible for sending emails across the Internet. IP is responsible for preventing spam emails.

• TCP is responsible for the security of Internet connections. IP is responsible for checking that packets are sent on time.

Which of these tables is accurate about packet loss on the Internet?

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One problem with packet-based messaging systems like the Internet Protocol is that packets might arrive out of order.

TCP is a protocol that can deal with out-of-order packets. When used over IP, each IP packet contains a TCP segment with metadata and data.

Which part of the packet contains the sequencing information that's used by TCP to reassemble packets?

• IP metadata

• TCP metadata

• TCP data

• None of the above

The US postal service can serve as an analogy for Internet transport protocols.

The postal service offers various services:

• First class letter: the default service with no extras.

• Certified mail: sent using the standard route but provides the sender with proof that the letter was delivered.

• Registered mail: sent using secure mechanisms along the way (e.g. locked cages).

Similarly, there are multiple transport protocols that can be used on top of IP, with TCP and UDP being the most popular.

Which analogy between the transport protocols and USPS services makes the most sense?

• UDP is like the registered mail service and TCP is like the first class letter service.

• UDP is like the certified mail service and TCP is like the first class letter service.

• UDP is like the first class letter service and TCP is like the certified mail service.

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  UDP is like the first class letter service and TCP is like the registered mail service.