Computer Networks Fundamentals

Videotex is an interactive information retrieval system that combines television technology for display, communication systems for transmission, and computer technology for data processing and storage. It allows users to access information from databases using a television set and a keypad/keyboard.

A Bulletin Board System (BBS) is a computer system equipped with software that allows users to connect and log in, post messages, read messages from other users, and exchange files. Unlike real-time communication, BBS allows asynchronous participation where users can check in at their convenience.

ISDN stands for Integrated Services Digital Network. It is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.

If communication software is the 'traffic cop' that manages data flow, the modem acts as a 'bridge' that connects the digital world of computers to the analog world of telephone lines, enabling communication between the two different environments.

If one character requires 10 bits to transmit and the transmission speed is 1,200 bits per second, then the number of characters transmitted per second is 1200/10 = 120 characters per second. This is a simple division calculation.

Computer ports serve as the physical interface between the CPU and peripheral devices, enabling data transfer through standardized connections. While modems, interfaces, and buffer memory play roles in communication, the port is the primary physical connection point. However, this answer is simplified - the actual data transfer involves complex bus systems and controller protocols.

Microprogramming involves programming the control unit of a CPU using microinstructions. Each machine instruction is broken down into micro-operations (microinstructions) stored in control memory. The control unit executes these microinstructions to perform the actual operations. It is not assembly language programming (which uses mnemonics), nor programming of microcomputers in general.

A spider network (also called centralized or star-network hybrid) has a central computer through which all activities must pass. All communications and processing are routed through this central hub. Ring networks have nodes connected in a circle, hierarchical networks have tree structures, and data control network is not a standard topology term.

The Presentation layer (Layer 6) transforms information from machine-readable format to human-understandable format. It handles data representation, encoding, formatting, encryption/decryption, and character set conversions. The Application layer provides user services, Session layer manages connections, and Physical layer handles raw bit transmission.

The Application layer (Layer 7) determines the interface of the system with the user. It provides network services directly to user applications and is the closest layer to the end user. Network layer handles routing, Data-link layer handles node-to-node communication, and Session layer manages session establishment and termination.

Layer 7 (Application layer) protocols are responsible for user and application program support including passwords, resource sharing, file transfer, and network management. This layer directly supports application-level services. Layers 6, 5, and 4 handle presentation, session management, and transport respectively, not these user-facing services.

Baseband transmission sends signals without modulation - the signal occupies its original frequency range. It uses the entire bandwidth of the medium for a single transmission. A signal with energy in a finite frequency range describes bandpass, not baseband. Simultaneous transmission to multiple stations is broadcasting, not baseband.

Broadcast transmission sends data simultaneously to multiple stations in a network. All stations receive the transmission. Bandwidth refers to frequency range capacity, aloha is a random access protocol, and analog transmission describes continuous signal transmission - none of which define simultaneous transmission to multiple stations.

Frame Check Sequence (FCS) is the error-detecting code added to data frames at the data link layer. It uses mechanisms like CRC (Cyclic Redundancy Check) to detect transmission errors. Checksum is a specific type of error-detecting code, but FCS is the broader, more accurate term for the field in network frames. Flow control is a separate function for managing data transmission rates, not error detection.

In a Class C network (which uses 24 bits for network address and 8 bits for host addresses), the total number of addresses is 256 (2^8). However, the network address (all zeros) and broadcast address (all 255s) are reserved, leaving 254 usable host addresses. This is a standard networking concept for IP address allocation.

RS-232C is a standard for serial communication. RTS (Request to Send) and CTS (Clear to Send) are used for hardware flow control. DSR (Data Set Ready) indicates the modem is ready. VDR is not a standard RS-232C signal - the correct signals are TD (Transmit Data), RD (Receive Data), RTS, CTS, DSR, DTR (Data Terminal Ready), DCD, and RI.

Mesh topology provides direct point-to-point connections between every pair of nodes. In a full mesh, each node has a bidirectional link to every other node, enabling direct communication and redundancy. Ring connects nodes in a circle, star has a central hub, and tree has a hierarchical structure - none of these support bidirectional links between ALL possible pairs.

BSC (Binary Synchronous Communication) uses ENQ (Enquiry) for multiple control functions. It's used to poll a station to check if it has data to transmit, to bid for control of the line, and to select a specific station for communication. Therefore, ENQ performs all three functions - polling, bidding, and selection.