Network Management, Cryptography, and Client-Server Architecture
Network Management Functional Areas
Network management maximizes efficiency and productivity in a data network transparently to users. It performs various management tasks:
- Fault Management: Locating and correcting network problems and failures, including configuration adjustments.
- Configuration Management: Identifying and configuring critical devices, requiring an inventory to track updates.
- Security Management: Controlling access to information and data.
- Network Performance Management: Measuring the performance of network elements to ensure adequate operation.
- Accounting Management: Monitoring network resource usage to ensure sufficient resources and efficient utilization.
Key Cryptography Model
In a key cryptography model, parties A and B share the same key, such as a substitution pattern for letters. The Data Encryption Standard (DES) was a standard in the USA, using a 56-bit key and a 64-bit text input.
DES can now be deciphered due to the 2^56 possible combinations. To enhance security, 3DES (Triple DES) was developed, applying DES three times with three different keys. This increases the possible combinations to 2^168, making it computationally infeasible to decipher.
Transport Layer Control Flow (TCP)
Flow control prevents receiver saturation from multiple senders. It’s linked to error correction without limiting channel efficiency. Flow control involves:
- Error Detection: Detecting errors when sending frames to the receiver.
- Error Correction: Correcting identified errors by adding redundant bits for detection and retransmission.
Client-Server Architecture Features
In this architecture, communication occurs only between the client and the server, never client-to-client. The server is always running with a permanent IP address. Server farms, sets of PCs running the same program, are used for scaling.
The client initiates communication, connects to the server, and can connect intermittently with dynamic IP addresses (the IP should not change while expecting a response).
Email Sending Process and Protocols
Sending an email involves three components:
- User Agent: Composes, produces, and reads messages.
- Mail Servers: Stores incoming messages in the user’s inbox and queues outgoing messages.
- SMTP (Simple Mail Transfer Protocol): Sends mail messages between servers using TCP for reliable transfer.
SMTP operates in three stages: negotiation, transfer, and closure. Requests are in ASCII text, and responses include a status code and phrase. Messages must be 7-bit ASCII. The email message format includes a header (sender, recipient, subject line) and a body containing only ASCII characters.
For example, Alice uses a user agent to compose a message. Alice’s user agent sends the message to her mail server, placing it in a queue. The SMTP client opens a TCP connection with Bob’s mail server. The SMTP client sends Alice’s message over the TCP connection, and the mail server places the message in Bob’s inbox. Bob then uses his user agent to read the mail.