Distributed Programming Concepts

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Questions and Answers

Which statement best describes the fundamental method of communication between computers?

Computers communicate through direct hardware connections.

All communications depend on local data storage.

Communication is achieved by sending network messages to each other. (correct)

Internet protocols are the only means of communication.

What distinguishes packet switching from circuit switching in network communication?

Circuit switching supports variable quality of service for all transmissions.

Packet switching requires a constant circuit for each communication.

Circuit switching allows for messages to be split into packets.

Packet switching transmits messages as independent packets. (correct)

What is a disadvantage of circuit switching compared to packet switching?

Circuit switching allows for better fault tolerance.

Circuit switching eliminates the need for dedicated circuits.

Quality of service is less consistent in circuit switching.

Resource utilization can be inefficient during idle periods. (correct)

Which of the following is a characteristic of packet-switched networks?

They use shared network infrastructures among users. Signup and view all the answers

In terms of quality of service (QOS), how does packet switching typically perform?

It provides variable QOS, with the possibility of out-of-order delivery. Signup and view all the answers

What is the purpose of the listen() function in a TCP socket?

It converts a client socket to a server socket. Signup and view all the answers

Which of the following TCP-based protocols is NOT mentioned?

DNS Signup and view all the answers

What does the backlog parameter in the listen() function signify?

The buffer size for pending connections. Signup and view all the answers

During the TCP three-way handshake, which of the following is the second step?

The client sends a SYN-ACK packet to the server. Signup and view all the answers

What return value signifies success when using the listen() function?

0 Signup and view all the answers

What does the bind() function accomplish in TCP socket programming?

It specifies the address of a socket. Signup and view all the answers

Which of the following statements about TCP sockets is correct?

Server sockets must be created to accept incoming connections. Signup and view all the answers

What is the default state of TCP sockets upon creation?

They are client sockets unable to accept connections. Signup and view all the answers

What does the function 'accept' return if the connection establishment fails?

-1 Signup and view all the answers

What is the significance of checking the return value of the 'write' function?

To ensure all requested bytes were sent Signup and view all the answers

What happens when 'read()' returns a value of 0?

The end-of-file (EOF) has been reached Signup and view all the answers

Which of the following is NOT a parameter of the 'write' function?

timeout Signup and view all the answers

What is the behavior of 'read()' when it has less data available than the requested size?

It returns only the available data Signup and view all the answers

What is the purpose of the 'buf' parameter in the 'read' function?

To specify where to store the incoming data Signup and view all the answers

Which of the following statements about writing to a socket is true?

It may send fewer bytes than requested Signup and view all the answers

In the context of socket programming, what does 'blocking' mean when reading data?

The process will stop executing until data is available Signup and view all the answers

What is the main function utilized for converting domain names to IP addresses in the provided content?

gethostbyname() Signup and view all the answers

What does the struct hostent's h_addr_list represent?

A null-terminated array of network addresses for the host. Signup and view all the answers

Which statement accurately describes why domain names are used instead of IP addresses?

Domain names are easier for humans to remember than numerical IP addresses. Signup and view all the answers

What happens if the gethostbyname() function fails to resolve a domain name?

It returns NULL and prints an error message. Signup and view all the answers

What is the purpose of the h_length field in the struct hostent?

To define the length of the address being used. Signup and view all the answers

Which of the following is NOT a component of the struct hostent?

h_address Signup and view all the answers

What is the role of the Domain Name Service (DNS) in the context of domain names?

To resolve domain names into IP addresses. Signup and view all the answers

Which of the following statements regarding the interaction of network protocols with domain names is correct?

Domain names must be resolved to IP addresses before use by network protocols. Signup and view all the answers

What is the role of the connect() function in initiating a TCP connection?

It binds the client's socket to a random unused port. Signup and view all the answers

What does the accept() function do upon receiving an incoming connection?

It creates a dedicated socket for that connection. Signup and view all the answers

What is the expected return value of the connect() function upon success?

0 Signup and view all the answers

What happens to the original socket after a call to accept()?

It is ready to accept more connections. Signup and view all the answers

What parameters must be specified when using the connect() function?

sockfd, serv_addr, addrlen Signup and view all the answers

In the context of TCP, what does the addrlen parameter represent in the accept() function?

The length of the client's socket address. Signup and view all the answers

What is the consequence of calling listen() with a negative return value?

The server socket cannot accept connections. Signup and view all the answers

What does the accept() function block while waiting for?

An incoming client connection. Signup and view all the answers

What does the close() function do when called on a TCP socket?

It sends an EOF message to the other party. Signup and view all the answers

What is the result of a read operation after an EOF has been received on a TCP socket?

It returns 0 bytes. Signup and view all the answers

What is the purpose of the shutdown() function in TCP socket programming?

To allow one side to finish sending data before closing. Signup and view all the answers

Which method allows a program to monitor multiple file descriptors without blocking?

Employing non-blocking I/O techniques. Signup and view all the answers

What happens after executing shutdown(fd, SHUT WR) on a TCP socket?

The socket can still read data but not write. Signup and view all the answers

Which function blocks a program until one of multiple file descriptors is ready for reading or writing?

select() Signup and view all the answers

When is it appropriate to use the poll() function over the select() function?

When additional information about streams is needed. Signup and view all the answers

What can be inferred about the effect of the close() function on a TCP connection?

It signifies that the connection can no longer be used by anyone. Signup and view all the answers

Study Notes

Distributed Programming with Sockets

This presentation covers distributed programming concepts using sockets.
The specific date is September 29, 2019.

Overview

The presentation outlines five main topics:
- A brief introduction to computer networks
- IP addressing and name resolution
- TCP (Transmission Control Protocol)
- I/O multiplexing
- Server structures

A Very Brief Introduction to Computer Networks

Two types of computer networks: circuit switching and packet switching.
- Circuit switching: a dedicated electrical circuit for communication. Example: traditional phone networks. Inefficient resource usage, fixed quality of service, wastes resources during periods of silence.
- Packet switching: messages split into packets. Packets can take different routes, multiple users share the same infrastructure. Example: the Internet, more efficient resource utilization with fault tolerance.
All computer programs communicating over networks send/receive messages. Sockets are the fundamental way programs communicate through message exchange.

Internet Protocol (IP)

Most networks use IP (Internet Protocol). IP sends packets of limited size. Maximum Transmission Unit (MTU) is a key concept, defining the maximum size of packets acceptable on each network link.
Packets can be fragmented or dropped if MTU is too low.
IP addresses are 32-bit integers.
Dotted string notation makes them easier to read for humans. A common example would be 10.5.55.87.
IP offers no guarantees (e.g., packets can get lost, reordered, delivered multiple times or corrupted in transit).
IP addresses are used by other protocols on top of it, not directly by programs.

UDP: User Datagram Protocol

UDP is similar to IP. It sends packets, similar to IP packets.
UDP datagrams are identified by IP address and port number. Port numbers allow simultaneous programs to use the network, distinguishing messages.
UDP offers no guarantee.

TCP: Transmission Control Protocol

TCP establishes connections between machines.
Users perceive reliable, ordered data flow, with no lost data.
Data transferred in a structured manner using packets. Sequential numbers are assigned to the packets.
The receiver confirms the correct sequence of the packets through acknowledgments.
Retransmission of lost packets ensures data reliability ensuring the whole message is delivered correctly.
Communication is bi-directional.

A Very Simplified View

A simplified model shows how various protocols interact.
User programs use TCP for reliable communication.
TCP fragments data into packets the IP protocol handles routing.
The packets are transmitted via Ethernet.

IP Addressing and Name Resolution

IP addresses are 32-bit integers. They are machine-readable.
Dotted strings (e.g., 130.37.20.38) are user-readable.
DNS uses human-readable names (e.g., www.aait.edu.et) to translate into IP addresses.

Big/Little-endian Network Ordering

Computers represent numbers in different orderings.
Converting numbers between host and network byte order using functions like htons, htonl, ntohs, ntohl.

sockaddr_in: Unix Network Addresses

Unix represents network addresses using a sockaddr_in struct.
Contains fields for address family, port number, and IP address.

Domain Names

IP addresses are difficult for humans to remember.
Domain names (e.g., www.aait.edu.et) are easier to remember.
DNS translates domain names to IP addresses to allow network communication.

Converting Domain Names to IP

gethostbyname() is a crucial function for converting domain names to IP addresses.
gethostbyname() returns a structure (struct hostent) containing host information, including a list of IP addresses (h_addr_list).

TCP Sockets

TCP sockets are defined in RFC 793.
Common TCP-based protocols like TELNET, FTP, SMTP, HTTP, and SSH.

TCP Socket Functions

Core socket functions include socket(), connect(), write(), read(), close().

listen() Setting a Server Socket

Server sockets maintain more state and handle incoming connections.
listen() sets up the socket to accept incoming connections, and specifies the buffer size.

Initiating a TCP connection

connect() initiates a connection to a server, including sending the destination IP address and port number to connect to the server.

Waiting for an Incoming Connection

accept() waits for an incoming connection request and creates a new socket for this client.

Example Use of accept

Demonstrates using accept() to handle incoming connections.

Writing Data to a Socket

write() sends data to a socket.
It returns the number of bytes actually sent.
Insufficient bytes sent could require resending.

Reading Data from a Socket

read() receives data from a socket.
It blocks until it has received the expected number of bytes.

Closing a TCP Socket

close() terminates communication on a socket.
Sends an end-of-file (EOF) signal.

Asymmetric Disconnection

shutdown() allows stopping sending or receiving data, but to allow the other party to finish without immediate disruption.

I/O Multiplexing

Techniques like select() and poll() are used to handle multiple file descriptors (sockets) concurrently, allowing programs to interact with multiple sockets efficiently.

Server Structures

Various server structures are employed depending on the intended concurrency, such as iterative models, one-child-per-client, or preforked models.

Iterative Servers

The server handles one client request at a time.
Offers simple resource utilization but may block on receiving a request if other requests are still in progress.

One Child per Client

A new process is created for each client connection.
Enables handling multiple clients concurrently.

Preforked

Pool of processes is created. The server immediately can start handling new connection without having to spawn additional processes.
Suitable for highly concurrent servers.

Select Loop

A single process manages multiple connections, managing all incoming requests.
Implements stages and maintains a data structure containing the status of each client connection.

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Description

This quiz covers key concepts of distributed programming using sockets. It includes topics such as computer networks, IP addressing, TCP, I/O multiplexing, and server structures, offering a comprehensive overview suitable for students and professionals alike.