Table of Contents
Local Area Networks are interconnected through various network devices operating at different Internet model layers. These devices can be categorized into five groups based on the layer in which they function:
- Devices below the Physical Layer: Examples include Passive Hubs.
- Devices at the Physical Layer: Examples include Repeaters or Active Hubs.
- Devices at the Physical and Data Link Layers: Examples include Bridges or two-layer switches.
- Devices at the Physical, Data Link, and Network Layers: Examples include Routers or three-layer switches.
- Devices Operating at All Five Layers: Examples include Gateways, often functioning as routers.
In this section, we will explore network devices operating across various layers:
Hub
Hubs are vital in LAN connectivity, serving as central connection points. They operate by receiving signals from individual computers and broadcasting these signals to all other stations within the hub.
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| Hub |
Key Features:
- Hubs typically feature 4 to 24 RJ-45 ports for twisted-pair cabling.
- They include one or more uplink ports for connecting to other hubs.
- Indicator lights display port link status, collisions, and other essential information.
Types of Hubs:
1. Passive Hubs:
- Act as connectors, linking wires from different branches.
- In a star-topology Ethernet LAN, a passive hub serves as the collision point.
- Positioned below the physical layer in the Internet model.
2. Active Hubs:
- Amplify signals before transmitting to other computers.
- Function as Multiport Repeaters operating in the physical layer.
- Ideal for establishing connections in a physical star topology.
Switch
A switch serves as a critical network device responsible for determining the path or circuit through which a signal travels from its source to the destination. It plays a pivotal role in directing data to the appropriate adjacent network point.
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| CISCO Switch |
Switch Types:
1. Two-Layer Switch:
- Operates at the physical and data link layers.
- Functions as a bridge, connecting multiple LANs for enhanced performance.
2. Three-Layer Switch:
- Functions at the network layer, akin to a router.
- Routes packets based on logical addresses, facilitating efficient data transmission.
Switch Utilization:
- In smaller networks, switches may be optional.
- However, in expansive networks like the internet, where multiple routes are possible for transmitting a message, switches become essential.
- The primary purpose of a switch is to intelligently select the optimal path, effectively managing bandwidth in large-scale networks.
Router
A router serves as a sophisticated three-layer device, guiding packets based on their logical addresses. Typically linking Local Area Networks (LANs) and Wide Area Networks (WANs) on the internet, routers utilize dynamic routing tables to make informed decisions about the most efficient route.
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| Cisco Router |
Key Router Components:
- Routing Tables: These tables dynamically update through routing protocols, guiding the router in route decisions.
- Hardware: Physical interfaces connecting to various networks on the internet.
- Software: Comprising the operating system and routing protocols, essential for router functionality.
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| Working on Router, switch, Modem |
Router Functions:
- Path Determination: Routers excel in determining the optimal path for a particular transmission among available options.
- Logical and Physical Addressing: Utilizing logical and physical addressing, routers connect separate networks.
- Logical Network Segmentation: Organizing the extensive network into logical sub-networks allows for efficient data exchange.
- Packet Grouping: Data is organized into packets, each carrying both a physical device address and a logical network address.
- Store-and-Forward Technique: Routers temporarily store and then forward messages, implementing a store-and-forward technique to enhance transmission efficiency.
Repeater
Repeaters, functioning solely in the Physical Layer, play a critical role in preserving signal integrity within a network. As signals traverse a network, they encounter a limit to their travel distance before succumbing to attenuation and corruption. A repeater steps in just before this weakening point, receiving the signal, regenerating its original bit pattern, and sending forth a refreshed signal.
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| Matrox Veos Repeater |
Repeaters offer a strategic solution for expanding the physical reach of a network. By segmenting the cable into manageable sections, repeaters overcome cable length limitations. Installed between these segments, they operate as two-port nodes, receiving frames from one port, regenerating them, and forwarding them to the other port.
Repeater vs. Amplifier:
While an amplifier indiscriminately boosts all signals, including noise, a repeater distinguishes itself by not amplifying but regenerating the signal. It meticulously recreates a bit-for-bit copy of the original signal at its original strength. This selective regeneration ensures that the signal maintains its precision despite encountering some noise along the way.
The functionality of a Repeater:
The primary function of a repeater is to regenerate the original signal by creating an exact copy, bit for bit, at the original strength. Its crucial role lies in intercepting the signal before it degrades to a point where noise interferes with the meaning of its bits. Placing a repeater strategically on the network ensures it captures the signal before any degradation, allowing it to read the signal with enough precision to faithfully replicate the intended voltages. This precision is vital, as even slight alterations in bit voltage can impact the signal's accuracy without entirely compromising its identity.
Bridges
Bridges operate in both the physical and data link layers. In the physical layer, they regenerate signals, and in the data link layer, they examine MAC addresses (physical addresses) of the source and destination in frames. MAC stands for Media Access Control.
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| Bridges |
Unlike repeaters, bridges have filtering capabilities. They maintain a table mapping addresses to ports, allowing them to determine whether a frame should be forwarded or dropped based on its destination address. If forwarding is required, the bridge specifies the port for the transmission.
Gateway
A gateway is a versatile computer that operates across all five layers of the Internet or all seven layers of the OSI model. It manages messages, addresses, and protocol conversions necessary for delivering messages between networks. Essentially, a gateway interprets application messages and can serve as a connecting device between networks using different models.
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| Gateway |
Commonly, gateways connect a LAN and a Mainframe computer by adjusting protocols and transmitting packets between two distinct networks. For instance, a gateway can link a network following the OSI model with another using the Internet model. When a frame arrives from the first network, the gateway moves it up to the OSI application layer, extracting the message.
Gateways offer maximum flexibility in internetworking communications, allowing connections between networks with different models. However, this flexibility comes at the expense of a higher price, a more complex design, and increased demands for implementation, maintenance, and operation. Gateways also provide security features and can filter out unwanted application-layer messages.
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In comparison to other network devices, gateways are slower than routers, and routers are slower than bridges unless the processing capability is proportionately increased.
