Sem 2 Networking Week 10-2 UDP

Questions and Answers

What does an 'open' port indicate about a server application?

It is actively listening for incoming data. (correct)

It is temporarily disabled for maintenance.

It is no longer accepting data.

It is reserved for future use.

Which statement is true regarding port number assignment for server applications?

Port numbers are interchangeable between applications.

Port numbers have no relevance in identifying services.

Each port number is unique to a particular application. (correct)

Multiple services can share the same port number.

How does a server process an incoming client request?

By relying on the TCP segment's source address only.

By using the client's hostname.

By checking the server's IP only.

By matching the IP address and port number of an open socket. (correct)

What signal does a client send to indicate it has finished sending data?

FIN flag Signup and view all the answers

What is the purpose of using a specific port number in TCP connections?

To identify which application should handle incoming traffic. Signup and view all the answers

What occurs when a server application is actively listening on a port?

The port is open. Signup and view all the answers

What is the primary purpose of the ACK flag in TCP?

Acknowledges the receipt of data Signup and view all the answers

During the TCP three-way handshake, which packet does the client send after receiving the SYN-ACK from the server?

ACK Signup and view all the answers

What is the function of the PSH flag in a TCP segment?

Instructs immediate processing of data Signup and view all the answers

What is ensured by the TCP handshake process?

Synchronization and agreement on connection parameters Signup and view all the answers

How does TCP ensure data reliability during transmission?

Through flow control and error checking mechanisms Signup and view all the answers

What process is used to terminate a TCP connection?

Four-step process involving FIN and ACK Signup and view all the answers

What is the primary purpose of the source and destination ports in a UDP datagram?

To identify the applications on the sending and receiving devices Signup and view all the answers

Which field in the UDP header is specifically used for error-checking?

Checksum Signup and view all the answers

In which scenario would UDP be a suitable choice for communication?

Applications requiring low latency and can tolerate some data loss Signup and view all the answers

What are well-known ports used for?

For standard services and applications to connect easily Signup and view all the answers

What is the range of registered ports as assigned by IANA?

1,024 to 49,151 Signup and view all the answers

Which type of applications typically utilizes unidirectional communication and manages reliability themselves?

Network management applications Signup and view all the answers

What is the maximum segment size (MSS) calculated for a default Ethernet MTU of 1500 bytes?

1460 bytes Signup and view all the answers

What is one of the primary purposes of establishing an MSS during a TCP connection?

To ensure efficient data transmission Signup and view all the answers

During the TCP three-way handshake, how is the MSS determined?

Each device sends its preferred MSS and the lower value is used Signup and view all the answers

What is the role of 'Slow Start' in TCP flow control?

It initiates the exponential increase of the congestion window Signup and view all the answers

Which of the following best describes 'Congestion Avoidance' in TCP?

The congestion window increases linearly after reaching a threshold Signup and view all the answers

What happens during the 'Fast Retransmit' phase in TCP?

Lost packets are quickly retransmitted upon receiving duplicate acknowledgments Signup and view all the answers

What does the server send after acknowledging the client's FIN with an ACK segment?

A FIN segment to terminate its own data flow Signup and view all the answers

What is the purpose of the client's initial SYN packet?

To verify the server's presence and availability Signup and view all the answers

Which segment does the server send in response to the client's SYN packet?

SYNACK segment indicating readiness to connect Signup and view all the answers

What does the ACK segment sent by the client after receiving the server's FIN signify?

The client acknowledges the termination of the connection Signup and view all the answers

What does the TCP three-way handshake primarily ensure?

A reliable and established connection between client and server Signup and view all the answers

What is the significance of a clean and orderly shutdown in TCP connections?

To allow both sides to finish ongoing transmissions before closing Signup and view all the answers

Study Notes

UDP Header Fields

Source Port: 16-bit field identifying the source application via port number.
Destination Port: 16-bit field identifying the destination application via port number.
Length: 16-bit field indicating the total length of the UDP datagram (header + data).
Checksum: 16-bit field for error-checking of the UDP header and data.

Applications that Use UDP

Live Video and Multimedia: Require low latency and can tolerate some data loss (e.g., VoIP, live streaming).
Simple Request and Reply: Handle simple transactions with minimal overhead (e.g., DNS, DHCP).
Reliability Managed by Applications: Unidirectional communication where the application handles reliability (e.g., SNMP, TFTP).

Port Numbers and Socket Pairs

Socket: Combination of an IP address and port number used for identifying specific processes or services.
Source and Destination Ports: Included in segments for routing and managing data between applications.
Encapsulation: Segments containing port numbers are encapsulated within IP packets for transmission.

Purpose of Sockets

Distinguish multiple processes on clients and differentiate multiple connections to servers.

Port Number Groups

Well-known Ports (0 to 1,023): Reserved for common services (e.g., HTTP, FTP, SMTP) for easy identification by clients.
Registered Ports (1,024 to 49,151): Assigned by IANA for specific processes requested by entities (e.g., Cisco's RADIUS server on port 1812).

Active Connections

Monitoring active connections helps identify services communicating with the machine, e.g., TCP connections with various local and foreign addresses.

TCP Connection Establishment

Port Number Assignment: Each server application uses a specific port number to identify incoming network traffic.
Unique Port Assignment: No two services can listen on the same port within the same transport layer.
Open Ports: Indicates that a server application is ready to accept incoming data.
Handling Incoming Requests: Client requests directed to a socket (IP address + port number).

Session Termination Steps

Client initiates termination with a FIN segment when no more data is to be sent.
Server acknowledges the FIN with an ACK segment confirming receipt.
Server initiates its termination by sending its own FIN segment.
Client acknowledges the server's FIN with an ACK segment, ensuring an orderly shutdown.

TCP Three-Way Handshake

Establish Device Presence: Client sends a SYN packet to initiate the connection.
Verify Service Availability: Server responds with a SYN-ACK packet confirming it’s listening on the specified port.
Inform of Connection Intent: Client sends an ACK packet to confirm readiness for data transmission.

Connection Termination Process

Utilizes a four-step process (FIN and ACK) ensuring both parties agree to close the session without data loss.

Reliability Function

TCP ensures synchronization and agreement on connection parameters through the handshake, contributing to reliable data transfer.

Control Bit Flags in TCP Header

URG: Indicates urgent data needing immediate processing.
ACK: Acknowledges receipt of data; set in all segments post-initial SYN.
PSH: Instructs immediate processing of received data without delay.

Maximum Segment Size (MSS)

Default Ethernet MTU is 1500 bytes; TCP and IP headers consume 40 bytes, leading to an MSS of 1460 bytes.
MSS ensures efficient data transmission by setting a limit to avoid fragmentation.
MSS negotiation occurs during the three-way handshake, with the lower of two preferred values used.

TCP Flow Control and Congestion Avoidance

Slow Start: Initiates with a small congestion window, increasing exponentially until a threshold is reached or packet loss occurs.
Congestion Avoidance: After threshold, congestion window increases linearly to avoid overload.
Fast Retransmit and Recovery: Quickly retransmits lost packets upon duplicate ACKs, adjusting congestion window as needed.
Congestion Control Algorithms: Variants like TCP Tahoe and TCP Reno optimize data flow based on network conditions.

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Description

This quiz focuses on the various fields in the UDP header, including source and destination ports, UDP length, and checksum. Each field's function and importance in networking are highlighted to enhance your understanding of UDP protocols.