1. Which of the following protocols are connection-oriented? Answer: A and B
2. Which of the following protocols are reliable? Answer: B
3. PC1 is using TCP, has a window of 4, and sends four segments numbered 2, 3, 4, and 5 to PC2. PC2 replies with an acknowledgment number 5. What should PC1 do next?
Which of the following are not features of a protocol that is considered to match OSI Layer 4?
Which of the following flow-control methods let the receiver tell the sender how much data the sender is allowed to send before the sender must wait for an acknowledgment?
Which of the following header fields identifies which TCP/IP application gets data received by the computer?
Answer: E and F
Which of the TCP connection-establishment flows sets both the SYN and ACK flags in the TCP header?
Which of the following is not a typical function of TCP?
Answer: D and E
Which of the following functions is performed by TCP and UDP? Answer: C
Data that includes the Layer 4 protocol header, and data given to Layer 4 by the upper layers, not including any headers and trailers from Layers 1 to 3, is called what?
Answer: C and G
Describe the features required for a protocol to be considered connectionless.
Answer: Unordered low-overhead delivery of data from one host to another is the service provided in most connectionless protocol services.
Answer: LLC Type 1, UDP, IPX, and IP are some examples of connectionless protocols. Remember, Frame Relay, X.25, and ATM are connection oriented, regardless of whether they define error recovery.
3. Describe the features required for a protocol to be considered connection oriented.
Answer: Either the protocol must exchange messages with another device before data is allowed to be sent, or some pre-established correlation between the two endpoints must be defined. TCP is an example of a connection-oriented protocol that exchanges messages before data can be sent; Frame Relay is a connection-oriented protocol for which a pre-established correlation between endpoints is defined.
4. In a particular error-recovering protocol, the sender sends three frames, labeled 2, 3, and 4. On its next sent frame, the receiver of these frames sets an Acknowledgment field to 4. What does this typically imply?
Answer: Frames through number 3 were received successfully. The receiver might have not received Frame 4, or Frame 4 might not have passed the FCS check.
Answer: TCP, SPX, LLC Type 2, and X.25 are some examples of connection-oriented protocols that provide error recovery. ATM and Frame Relay are also connection oriented, but without error recovery.
6. Describe how TCP performs error recovery. What role do the routers play?
Answer: TCP numbers the first byte in each segment with a sequence number. The receiving host uses the Acknowledgment field in segments that it sends back to acknowledge receipt of the data. If the receiver sends an acknowledgment number that is a smaller number than the sender expected, the sender believes that the intervening bytes were lost, so the sender resends them. The router plays no role unless the TCP connection ends in the router—for example, a Telnet into a router. A full explanation is provided in the section "Error Recovery (Reliability)."
7. How many TCP segments are exchanged to establish a TCP connection? How many are required to terminate a TCP connection?
Answer: A three-way connection-establishment sequence is used, and a four-way connection-termination sequence is used.
8. Describe the purpose of the Port Number field in a TCP header. Give one example.
Answer: The port numbers are used to help computers multiplex received data. For instance, a PC with two web browsers open can receive an IP packet. The destination TCP port number identifies which of the two browsers should receive the data.
9. List the components of a TCP socket.
Answer: A socket consists of three things: an IP address, a transport layer protocol (TCP or UDP), and the TCP or UDP port number.
10. How many TCP segments must be sent to establish a TCP connection? How many are used with normal TCP connection termination?
Answer: Three TCP segments are needed to establish the connection, and four are needed to tear it down under normal operation.
11. How many UDP segments must be sent to establish a UDP connection? How many are used with normal UDP connection termination?
Answer: UDP does not establish connections because it is not connection oriented.
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