Computer networking application protocols

Computer networking application protocols travel over computer networking end-to-end protocols to provide services meaningful to application programs residing in the endpoints. The application protocols differ in the kind of information they transfer (e.g., self-contained messages, computer files, remote procedure calls, digital voice, etc.). Note well that these are not directly accessible to a human user. To draw an analogy to postal mail, a person can drop an envelope into a mailbox, but has no access either to the mechanism between mailbox and post office, or post office to post office.

Application protocols also differ in their expectations of the performance end-to-end service below them. The application protocol may provide security, expect certain security services from the end-to-end or computer networking internetwork protocols over which they run, or both.

Classes of information transfer

Message

Messages are self-contained units of data, which may contain other types of data.

Message handling protocols are analogous to postal protocols. Different protocols run among mail clients that provide a human interface; message transfer agents analogous to post offices, possibly at multiple levels of a hierarchy; and and message stores, analogous to temporary mailboxes.

The major IETF message transfer paradigms and protocols include:

• Mail client to mail server: Post Office Protocol version 3 (POP3), in which the messages are transferred to the client, and Internet Mail Access Protocol (IMAP), in which copies of the messages go to the client but the master copies remain on the server, They use a client-server model
• Mail transfer agent to mail transfer agent: Simple Mail Transfer Protocol (SMTP) exchanges messages, on a peer-to-peer model, among mail transfer agents that either are part of mail servers, or pure mail exchangers.

File

Files are sequences of units of data.

Expectations of the end-to-end service

Performance

They may be tolerant or intolerant of impairments such as:

• Latency
• Bit errors
• Packet loss
• Sequencing of packets

Security

• Endpoint authentication
  • Client authentication
  • Server authentication
  • Peer authentication
• Data integrity
  • Atomic integrity
  • Sequential integrity
• Content confidentiality
• Traffic flow confidentiality
• Nonrepudiation