Digital Modulation, Network Topologies and IP Addressing

Digital Modulation Techniques

FSK Modulation: Each set of bits is represented by a discrete frequency. In the simplest case, two frequencies are used: F0 and F1.

ASK Modulation: Each set of bits is represented by a discrete amplitude. Information is transmitted based on the amplitude of the carrier. If the bit is 0, it is sent as amplitude A0; if the bit is 1, it is sent as amplitude A1. In the case of ASK2, it reduces to phase modulation, as it changes the sign of the carrier (a 180-degree phase jump), which is the basis of QPSK.

PSK Modulation: Each set of bits is represented by a discrete phase of the carrier. Signaling 0 and 1 by sending the reference carrier and a 180-degree phase jump is commonly called BPSK modulation.

Voice Digitization and Switching

Digitizing Voice: A bit stream in both directions equals 64 Kbps. This value is derived as follows: 8,000 samples per second with 8-bit quantification results in 8 x 8,000 = 64,000 bits per second.

Digital telephony utilizes Time Division Multiplexing (TDM).

Circuit Switching: Switching equipment must establish a physical path between media prior to user connection. This pathway remains active during communication and is released upon termination (e.g., PSTN).

Network Topologies and MAN

MAN (Metropolitan Area Network): Designed for the interconnection of LANs within an urban area, typically covering a range of up to 100 km.

• Bus Topology: Elements are arranged in a linear series. Information issued by a node spreads throughout the bus. While simple to install and resilient to single-node failure, a bus breakdown renders the entire system futile.
• Star Topology: Centralized architecture where all elements connect point-to-point to a central node. All network traffic must pass through this hub; if the central node fails, the system goes down. A single cable failure only affects the associated node.

IP Addressing and Subnetting

Network Classes

• Class A: 0-126
• Class B: 128-191
• Class C: 192-223

Addressing Rules

• Network Address: Assigns 0 to the Host.
• First Host: The first available address (e.g., 131.47.0.1).
• Broadcast Address: 255 assigned to the Host.
• Subnet Mask: Converts the network portion to 255 and the Host portion to 0.
• Last Host: The last available address (e.g., 131.47.255.254).
• Following Network: The broadcast address plus 1 (e.g., 131.47.255.255 to 131.48.0.0).