Multiplexers, WAN, and LAN Network Technologies
Multiplexer Types
Frequency Division Multiplexer (FDM): Divides the bandwidth of a line among several channels. Each channel occupies a portion of the total frequency bandwidth.
Time Division Multiplexer (TDM): Each channel is assigned a specific time slot within the main channel. Time slots are shared equally among all channels. A disadvantage is that if a channel is unused, its time slot remains unused; other channels cannot utilize it. Padding bits are sent instead of data.
Statistical Time Division Multiplexer: Inactive channels are not allocated time slots, allowing for more efficient use of bandwidth. Priorities can be assigned to different channels.
Types of WAN Networks
Switched Circuit Networks: Communication requires establishing a call. Once the connection is made, users have a direct link through various network segments.
Message-Switched Networks: A computer (switch) manages traffic from connected computers and terminals. The computer examines the address in the message header to determine the destination Data Terminal Equipment (DTE). This technology allows for recording information for later retrieval. Users can delete, save, redirect, or automatically reply to messages.
Packet-Switched Networks: User data is divided into smaller pieces called packets. These packets are encapsulated with protocol information and travel through the network as independent entities.
Connection-Oriented Networks: These networks utilize the concept of multiplexed channels and ports, known as virtual circuits or channels. Users perceive a dedicated resource, but they share it with others due to the bursty nature of user traffic.
Connectionless Networks (Datagrams): These networks transition directly from an idle state to data transfer mode. They do not provide acknowledgments, flow control, or error recovery for the entire network, although these functions may exist for individual links. An example is the Internet.
Public Switched Telephone Network (PSTN): Originally designed for voice communication, this network uses switching systems. Switching establishes a connection based on a dialed number, corresponding to the destination’s identification number.
Local Area Networks (LANs)
Components
Network Interface Card (NIC): An electronic card that connects workstations to the network. It’s usually inserted into an expansion slot on the motherboard, providing direct memory access (DMA). NIC functions include:
- Packet formation
- Cable access
- Power conversion and speed adjustment
- Transmission and reception
- Error checking
- Serial/Parallel conversion
- Unique ID or address assignment
Workstations: PCs connected to the network, providing access to shared resources like disks, printers, and modems. They typically have a NIC, monitor, keyboard, and CPU.
Servers: Computers that provide services to workstations, such as disk storage, printer access, backup drives, and access to other networks or mainframes.
Repeater: Regenerates the signal from one cable segment and passes it to another, extending the connection length in a LAN without altering the signal’s content.
Bridges: Devices with two communication ports that create a memory table of MAC addresses on both ends. This restricts data traffic between segments, preventing packets from passing if the destination is on the same segment as the source.
Routers: Devices that connect multiple networks by referencing the network address of each segment. Routers restrict local network traffic, forwarding data only when it’s intended for a different network.
Brouters: Devices combining bridge and router functionality. Configuration determines whether they operate as a bridge or a router.
Hubs:
Switching Hub or Ethernet Switch: Divides the LAN into segments, limiting traffic to specific segments instead of broadcasting packets to all ports.