Chapter 2

FTP = Application layer, transfer files SMTP = Application layer, send email IMAP = Application layer, retrieve email with more advanced features POP = Application layer, retrieve email

HTTP/1.1 = Persistent, keeps the connection open for multiple requests, reducing latency HTTP/1.0 = Non-Persistent, closes the connection after a single request-response pair

A = Map domain names to IP addresses MX = Indicate mail servers NS = Specify the DNS server for the domain

HTTP = Lacks built-in security, making data susceptible to interception HTTPS = Provides encryption and is more secure

Iterative = Client queries multiple DNS servers Recursive = DNS server queries others on behalf of the client, return the final answer

Cookie header line of HTTP response message = Part of the HTTP response that sets a cookie on the client Cookie header line in next HTTP request message = Part of the HTTP request that sends a cookie to the server Cookie file kept on user’s host, managed user’s browser = File stored on the user's device that contains cookie information Back-end database at Web site = Database that stores information related to cookies

RTT = Round Trip Time, the time it takes for a packet to travel from the source to the destination and back Persistent HTTP = HTTP/1.1, keeps the connection open for multiple requests Non-Persistent HTTP = HTTP/1.0, closes the connection after a single request-response pair Cookies = Small data files stored on user’s devices by websites

Root DNS server = The highest level in the DNS hierarchy, responsible for returning the IP address of the TLD server TLD servers = Responsible for returning the IP address of the authoritative DNS server Authoritative DNS servers = Responsible for providing the IP address of a specific domain or subdomain

Persistent = Multiple objects can be sent over single TCP connection between client and server Non-Persistent = At most one object sent over TCP connection, then closes connection

DNS server = Responsible for resolving domain names to IP addresses Name server = Part of the distributed database implemented in the hierarchy of many name servers Host = Communicates with name servers to resolve names

Client-server = Involves a central server serving multiple clients. Clients do not communicate with each other directly. Peer-to-peer = Nodes act both as clients and servers, sharing resources without a central control. Peers directly communicate with each other. Server = Always on and have a permanent IP address. Clients need to know how to contact the server. Client = Sends/requests data to/from servers. Clients may have dynamic IP address and be intermittently connected.

Communicating process = Program running within a host. Client process = Process that initiates communication. Server process = Process that waits to be contacted. Socket = An endpoint in communication, providing a mechanism for processes to send and receive data.

Visiting a website where your browser (client) requests data from a web server = Client-server Torrents, where files are shared directly between users = Peer-to-peer

Advantages: Centralized control, easier to manage and update = Client-server Advantages: Scalability, robustness as there is no single point of failure = Peer-to-peer Disadvantages: Less control, potential for security vulnerabilities = Peer-to-peer

Nodes act both as clients and servers = Peer-to-peer Clients do not communicate with each other directly = Client-server Always on and have a permanent IP address = Server Clients may have dynamic IP address and be intermittently connected = Client

Client process = Initiates communication Server process = Waits to be contacted

Advantages: Centralized control, easier to manage and update = Client-server Disadvantages: Centralized control, easier to manage and update = Client-server Advantages: Scalability, robustness as there is no single point of failure = Peer-to-peer Disadvantages: Less control, potential for security vulnerabilities = Peer-to-peer

Visiting a website where your browser (client) requests data from a web server = Client-server Torrents, where files are shared directly between users = Peer-to-peer

Nodes act both as clients and servers = Peer-to-peer Clients do not communicate with each other directly = Client-server Always on and have a permanent IP address = Server Clients may have dynamic IP address and be intermittently connected = Client

Client process = Initiates communication Server process = Waits to be contacted

Creating a socket = Initiate the network communication process by creating a socket using the socket() function Attaching the socket to the network = Bind the created socket to a specific IP address and port number with the bind() function Listening for incoming connections (for server) = Listen for incoming client connects using the listen() function Sending/receiving messages = Exchange data through the send() and recv() function or write() and read()

TCP = Provides reliable connection-oriented communication with features like flow control, congestion control, and secure TCP port number 443 UDP = Connectionless, faster, and requires fewer resources, but does not provide reliability, flow control, security, or connection setup

HTTP = HyperText Transfer protocol that governs web data transfer in a client/server model HTML = HyperText Markup language used for web content URL = Uniform Resource Locator that identifies web resources

Advantages: Reliable, error checking. Disadvantages: Overhead due to acknowledgements, slower than UDP = TCP Advantages: Faster, Less overhead. Disadvantages: No guaranteed delivery or sequence = UDP

Browsing a website, where lost data could disrupt the page = TCP Streaming a video, where occasional lost data (a few frames) is preferable to delay = UDP

socket() = Creates a socket and returns a socket descriptor bind() = Attaches the created socket to a specific IP address and port number listen() = Used by servers to listen for incoming client connections send() and recv() = Used to exchange data between client and server

Reliability = File transfer, web applications need 100% reliable data transfer Throughput = Some apps, like multimedia and real-time audio/video, require a minimum amount of throughput to be effective Timing = Some apps, like multimedia and real-time audio/video, require low delay to be effective Security = Encryption, data integrity, etc

An app might make a system call to access the file system and read a file = System call A print spooler communicates with a printer driver to manage print jobs from various applications = Inter-process communication Browsing a website, where lost data could disrupt the page = TCP Streaming a video, where occasional lost data (a few frames) is preferable to delay = UDP

Pipes = One-way communication between related processes Message queues = Messages are stored on the queue until they are retrieved by the receiving process Shared memory = Processes can share data by mapping a shared memory segment into their address space

socket() = Creates a socket and returns a socket descriptor, representing an endpoint for data transfer bind() = Binds the created socket to a specific IP address and port number listen() = Listens for incoming client connects close() = Closes the socket to release system resources

Client-server involves a central server serving multiple clients, while peer-to-peer nodes act both as clients and servers, sharing resources without a central control.

Advantages: centralized control, easier to manage and update. Disadvantages: centralized control, easier to manage and update.

Advantages: scalability, robustness as there is no single point of failure. Disadvantages: Less control, potential for security vulnerabilities.

Visiting a website where your browser (client) requests data from a web server.

Torrents, where files are shared directly between users.

A process that initiates communication.

A process that waits to be contacted.

An endpoint in communication, providing a mechanism for processes to send and receive data.

A client process initiates communication, while a server process waits to be contacted.

Sockets provide a mechanism for processes to send and receive data.

TCP

2RTT + K*RTT with pipelining: 2RTT +RTT

2RTT+k(2RTT) RTT

Cookies are small data files stored on user’s devices by websites to remember user preferences and track user behavior.

1. Cookie header line of HTTP response message
2. Cookie header line in next HTTP request message
3. Cookie file kept on user’s host, managed by user’s browser
4. Back-end database at Web site

FTP (File Transfer Protocol) is used to transfer files over the application layer.

SMTP (Simple Mail Transfer Protocol) is used to send email over the application layer.

IMAP (Internet Message Access Protocol) and POP (Post Office Protocol) are used to retrieve email from a server.

DNS (Domain Name System) is used to translate domain names to IP addresses, making web navigation simpler.

The basic DNS record types are 'A', 'MX', and 'NS' resource records.

The socket() function is used to initiate the network communication process by creating a socket. It returns a socket descriptor, representing an endpoint for data transfer.

Binding the socket to a specific IP address and port number is crucial for servers as it allows them to listen for incoming connections on a predefined port.

The listen() function is used to listen for incoming client connections, while the accept() function is used to accept these incoming connections. The accept() function returns a new socket descriptor for the individual client connection.

Data can be exchanged through the send() and recv() functions, or through the write() and read() functions.

Once the communication is complete, the socket should be closed to release system resources. The close() function is used to accomplish this.

Inter-process communication (IPC) is when two processes communicate with each other within the same host. It enables processes to exchange data, which is vital for multi-process applications.

Some methods of inter-process communication include pipes, message queues, and shared memory.

Some of the transport services provided by the transport layer include data transfer, reliability, and flow control.

Applications may require reliability for file transfer or web applications, throughput for multimedia and real-time audio/video, timing for low delay in multimedia and real-time audio/video, and security through encryption and data integrity.

TCP provides reliable connection-oriented communication with advantages such as reliability and error checking, but with the disadvantage of overhead due to acknowledgements. UDP, on the other hand, provides faster and connectionless communication with advantages such as less overhead, but lacks reliability and guarantees delivery or sequence.