Human Communication Data Conversion: A Deep Dive

Posted on Nov 28, 2024 in Computers

Human Communication Data Conversion

Seven Steps of Data Conversion

  1. User enters data via hardware interface.
  2. Software/hardware converts data to digital format.
  3. Application services initiate data transfer.
  4. OSI layers encapsulate data (downstack).
  5. Encapsulated data is conveyed to destination.
  6. Destination OSI layers decapsulate data (upstack).
  7. Data is ready for processing.

Application Layer Software

Application layer software has two forms:

  1. Applications: Interact directly with users, providing an interface between people and hardware. Data transfer starts when the user initiates an action (e.g., pressing “Send”).
  2. Services: Background programs performing specific network functions. Invoked by devices or applications; generally invisible to the end-user. They connect applications to the network.

Client-Server Roles in Data Networks

In data communication, the data source is the server, and the receiver is the client. Client and server processes are application-layer services enabling network connectivity.

Servers are information reservoirs (text, databases, images, etc.), often managing real-time communication (e.g., a university student registration system).

The server process (or “server daemon”) typically runs in the background. It “listens” for client requests.

Client processes allow users to request data from a server. Client software is usually user-initiated. The client initiates communication, sending requests; the server responds with data. Data transfer from client to server is uploading; from server to client is downloading.

Examples of client-server services include DNS, FTP, HTTP, and Telnet.

Client-Server vs. Peer-to-Peer Data Transfer

Client-server transfer uses a centralized server and multiple clients. Peer-to-peer transfer uses devices that act as both client and server within the same communication. Both ends can initiate communication; devices are considered equal. Unlike client-server’s centralized data, peer-to-peer networks have distributed data. Data isn’t processed by another network device in the application layer.

Five Application Layer Protocol Functions

  1. Communication endpoint processes: Data handling and protocol data unit structuring.
  2. Message types: Application, receipt, data, status, and error messages.
  3. Message syntax: Expected order of information (fields) in a message.
  4. Field meaning: Consistent field meanings for proper interpretation.
  5. Message dialogues: Response to each message, invoking services and enabling data transfer.

Application Layer Protocols: Specific Objectives

These protocols use client-server processes:

  • DNS (Domain Name System): Resolves resource names and email domains to numerical network addresses.
  • HTTP (Hypertext Transfer Protocol): Transfers data in hypermedia information systems (e.g., the World Wide Web).
  • SMB (Server Message Block): Shares network resources (directories, files, printers).
  • SMTP (Simple Mail Transfer Protocol): Transfers outgoing email to mail servers.
  • POP (Post Office Protocol): Delivers email from mail server to client.

Comparing Application Layer Protocol Messages

These protocols use client-server request/response messages:

  • DNS: Uses a single message format for queries, responses, errors, and resource record transfers.
  • HTTP: Uses request/response messages. A client (e.g., web browser) sends a request; the server responds.
  • SMB: Uses a common format for session control (start, authenticate, terminate) and message sending/receiving.
  • SMTP: Uses commands and responses for login, mail transactions, forwarding, mailbox verification, and list expansion.
  • POP: A client-server protocol where the client initiates the connection to retrieve email.

While users interact with applications using HTTP, SMB, and SMTP/POP, DNS operates transparently in the background.