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Questions and Answers
What information does an identifier include for a process running on a host?
What is the port number commonly associated with an HTTP server?
In communication between processes, what does the app-layer protocol define?
What does an open protocol allow for in terms of communication?
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Which of the following is NOT an example of an application-layer protocol?
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What is the role of SMTP in the email communication process?
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Which protocol allows users to manipulate stored messages on the mail server?
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In the context of email communication, what does POP stand for?
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What is the purpose of DNS in a network environment?
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Which protocol is commonly used by web-based email services like Gmail and Yahoo! Mail?
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What kind of information is used by Internet hosts and routers for addressing datagrams?
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In the client-server architecture, what role does the server play?
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What is a characteristic of the P2P architecture?
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How do two processes within the same host communicate?
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What is the role of a server process in a network application?
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What does a socket represent in the context of network applications?
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What is the self-scalability characteristic of P2P architecture?
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How does a client process differ from a server process?
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What is the purpose of addressing processes in network applications?
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Study Notes
Application Layer
- Goals: understand conceptual and implementation aspects of network application protocols, transport-layer service models, client-server and peer-to-peer paradigms, and popular application-level protocols.
Network Applications
- Examples: e-mail, web, text messaging, remote login, P2P file sharing, multi-user network games, streaming stored video, voice over IP, real-time video conferencing, social networking, search.
Creating a Network App
- Run programs on different end systems that communicate over a network.
- No need to write software for network-core devices.
- Applications on end systems allow for rapid app development and propagation.
Application Architectures
- Client-server: always-on host, permanent IP address, data centers for scaling.
- Peer-to-peer (P2P): no always-on server, arbitrary end systems directly communicate, peers request service from other peers.
Processes Communicating
- Process: program running within a host.
- Processes in different hosts communicate by exchanging messages.
- Client process: initiates communication.
- Server process: waits to be contacted.
Sockets
- Process sends/receives messages to/from its socket.
- Socket is analogous to a door.
- Application process socket is controlled by the app developer.
- Transport socket is controlled by the OS.
Addressing Processes
- Process must have an identifier, including IP address and port numbers.
- Examples: HTTP server: 80, mail server: 25.
- To send an HTTP message to a web server, you need the IP address and port number.
App-layer Protocol
- Defines types of messages exchanged, message syntax, and message semantics.
- Examples: HTTP, SMTP.
- Open protocols are defined in RFCs and allow for interoperability.
- Proprietary protocols are used by applications like Skype.
Mail Access Protocols
- SMTP: delivery/storage to receiver's server.
- Mail access protocol: retrieval from server.
- Examples: POP, IMAP, HTTP.
DNS
- Domain Name System (DNS) maps between IP addresses and names.
- People use identifiers like SSN, name, and passport number.
- Internet hosts and routers use IP addresses.
- DNS is used to map between IP addresses and names, and vice versa.
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Description
Test your knowledge of network application protocols, including principles of network applications, Web and HTTP, FTP, electronic mail, P2P applications, socket programming with UDP and TCP, SMTP, POP3, IMAP, and DNS Application Layer. Explore conceptual and implementation aspects, transport-layer service models, client-server paradigm, and peer-to-peer paradigm.
