Application Layer Computer Networking: Chapter 2 Quiz

Identifying Processes on a Host

• A process is a program running within a host and can communicate with other processes using inter-process communication (defined by OS) within the same host.
• Processes in different hosts communicate by exchanging messages.

Process Identifiers

• A process needs an identifier to receive messages, but an IP address of the host on which the process runs is not enough to identify the process.
• An identifier includes both the IP address and port numbers associated with a process on a host.
• Examples of port numbers: HTTP server (80), mail server (25).

Application Layer Protocols

• Application layer protocols define the types of messages exchanged, message syntax, and message semantics.
• Examples of application layer protocols: HTTP, SMTP, FTP.
• Open protocols are defined in RFCs, allowing for interoperability between different systems.
• Proprietary protocols, such as Skype, do not allow for interoperability.

HTTP

• An HTTP client initiates a TCP connection to an HTTP server (process) at a specific port number (usually 80).
• The HTTP client sends an HTTP request message into the TCP connection socket.
• The HTTP server receives the request message, forms a response message containing the requested object, and sends the message back into its socket.

Network Applications

• Network applications can be categorized into two main architectures: client-server and peer-to-peer (P2P).
• In a client-server architecture, the server is always-on and has a permanent IP address.
• In a P2P architecture, arbitrary end systems directly communicate with each other, and peers request service from other peers and provide service in return.

Sockets

• A socket is a door through which a process sends and receives messages.
• A process sends messages to its socket, and the socket relies on the transport infrastructure to deliver the message to the receiving process.

Electronic Mail

• Electronic mail (email) involves mail servers, mail clients, and the SMTP protocol.
• Mail servers have a mailbox containing incoming messages for users and a message queue of outgoing mail messages.
• SMTP is a protocol for exchanging email messages between mail servers using TCP, usually on port 25.
• The SMTP protocol involves three phases of transfer: handshaking, transfer of messages, and closure.

Mail Message Format

• An email message consists of header lines (e.g., To:, From:, Subject:), a blank line, and the message body.
• The message body consists of ASCII characters only.

Mail Access Protocols

• Mail access protocols, such as POP and IMAP, allow users to retrieve email messages from a mail server.
• POP and IMAP are mail access protocols, whereas HTTP is used for web-based email services like Gmail, Hotmail, and Yahoo!.

Test your knowledge on principles of network applications, Web and HTTP, FTP, electronic mail, P2P applications, peer-to-peer applications, and DNS as covered in Chapter 2 of the book 'Computer Networking: A Top Down Approach' by Jim Kurose and Keith Ross.