Module 11 – Transport Layer Services Quiz Answers

1. Why is UDP well suited as the transport layer protocol for video applications?

  • UDP has low overhead.
  • UDP provides flow control using windows.
  • UDP provides acknowledgment of received data.
  • UDP provides a reliable session.

Explanation: UDP is a stateless protocol that provides no reliability or flow control. Because of its low overhead, UDP is well suited for delay sensitive applications such as VoIP.

2. Which transport layer information is added to both the TCP and UDP headers?

  • acknowledgment flag
  • IP addresses
  • window size
  • port numbers

Explanation: IP addresses are added to an Internet (IP) header. The ACK flag and window components are only added to a TCP header.

3. What type of applications are best suited for using UDP?

  • applications that are sensitive to packet loss
  • applications that need reliable delivery
  • applications that are sensitive to delay
  • applications that require retransmission of lost segments

Explanation: UDP is not a connection-oriented protocol and does not provide retransmission, sequencing, or flow control mechanisms. It provides basic transport layer functions with a much lower overhead than TCP. Lower overhead makes UDP suitable for applications which are sensitive to delay.

4. What protocol header information is used at the transport layer to identify a target application?

  • port number
  • sequence number
  • MAC address
  • IP address

Explanation: The TCP/IP transport layer uses port numbers to identify target applications. Each network application (server or client) has a port number assigned to the application.

5. A client device has initiated a secure HTTP request to a web browser. Which well-known port address number is associated with the destination address?

  • 404
  • 110
  • 443
  • 80

Explanation: Port numbers are used in TCP and UDP communications to differentiate between the various services running on a device. The well-known port number used by HTTPs is port 443.

6. Which number or set of numbers represents a socket?

  • 01-23-45-67-89-AB
  • 21

Explanation: A socket is defined by the combination of an IP address and a port number, and uniquely identifies a particular communication.

7. Open the PT activity. Perform the tasks in the activity instructions and then answer the question.

What is the application layer service being requested from Server0 by PC0?

CCNA 1 System Test Course (Version 1.1) - System Test Exam PT

  • HTTP
  • SMTP
  • FTP
  • DNS

Explanation: From the PDU, the destination port is 443, which means the service requested is HTTPS.

8. What information is used by TCP to reassemble and reorder received segments?

  • acknowledgment numbers
  • port numbers
  • fragment numbers
  • sequence numbers

Explanation: At the transport layer, TCP uses the sequence numbers in the header of each TCP segment to reassemble the segments into the correct order.

9. What type of port number is assigned by IANA to commonly used services and applications?

  • private port
  • registered port
  • well-known port
  • dynamic port

Explanation: Well-known ports (0 to 1023) are reserved for common applications and services. Registered ports (1024 to 49151) are assigned to user processes and applications. Dynamic, private, or ephemeral ports (49152 to 65535) are assigned to client applications when initiating a connection.

10. Which protocol operates at the transport layer of the TCP/IP model and ensures reliable delivery of IP packets?

  • TCP
  • IP
  • HTTP
  • UDP

Explanation: Transmission Control Protocol (TCP) operates at the transport layer of the TCP/IP model. TCP ensures that IP packets are delivered reliably.

11. What is a characteristic of UDP?

  • It provides unreliable delivery of segments.
  • It establishes sessions with a three-way handshake.
  • It adds 20 bytes of overhead to application layer data.
  • It uses sequence numbers to reassemble segments.

Explanation: UDP is a connectionless protocol that provides unreliable delivery of segments.

12. What is the well-known port address number used by DNS to serve requests?

  • 25
  • 60
  • 110
  • 53

Explanation: Port numbers are used in TCP and UDP communications to differentiate between the various services running on a device. The well-known port number used by DNS is port 53.

13. Which action is performed by a client when establishing communication with a server via the use of UDP at the transport layer?

  • The client sends a synchronization segment to begin the session.
  • The client sets the window size for the session.
  • The client sends an ISN to the server to start the 3-way handshake.
  • The client randomly selects a source port number.

Explanation: Because a session does not have to be established for UDP, the client selects a random source port to begin a connection. The random port number selected is inserted into the source port field of the UDP header.

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