Network Devices : Routers | Repeaters | Bridges | Gateways

Network devices, also known as networking hardware, are physical devices that allow hardware on a computer network to communicate and interact with one another.

For example: Repeater, Hub, Bridge, Switch, Routers, Gateway and NIC, etc.

Routers in Computer Network

Routers are networking devices operating at layer 3 or a network layer of the OSI model. They are responsible for receiving, analysing, and forwarding data packets among the connected computer networks. When a data packet arrives, the router inspects the destination address, consults its routing tables to decide the optimal route and then transfers the packet along this route.

Features of Routers:

A router acts as the "air traffic controller" of a network, directing data to its correct destination across complex intersections.

1. Layer 3 Intelligence - A router operates at Layer 3 (the Network Layer) of the OSI model. Unlike switches that use MAC addresses to find local devices, routers use Logical Addressing (IP addresses) to communicate between entirely different networks.
2. Network Interconnectivity - The primary purpose of a router is to join disparate networks. This includes:

• Connecting a LAN (Local Area Network) to a WAN (Wide Area Network), such as connecting your home network to the Internet.
• Routing traffic between different subnets within a large enterprise.

3. Path Determination & Routing Tables - Routers do not guess where data goes; they make informed decisions:

• Routing Table: Every router maintains a dynamic database (Routing Table) containing a list of known routes.
• Routing Protocols: It uses protocols like OSPF, BGP, or RIP to share information with other routers, ensuring the table is always updated with the most efficient paths.
• Consultation: For every packet received, the router consults its table to find the "Best Path" based on metrics like distance, speed, or cost.

4. Broadcast Domain Isolation - One of the most important features of a router is its ability to break up broadcast domains. Unlike hubs or switches, which pass "broadcast" messages to every connected device, routers block these messages by default. This provides vital protection against broadcast storms, which can otherwise saturate a network and cause it to crash.
5. Data Encapsulation and Forwarding - Routers receive data in the form of IP Packets. They examine the destination IP, strip away the old Layer 2 header, and re-encapsulate the packet with new framing information suitable for the next physical link (e.g., switching from Ethernet to a Fiber-optic WAN link).
6. Security and Advanced Services - Because routers sit at the edge of a network, they often perform additional high-level tasks:

• NAT (Network Address Translation): Allowing multiple devices on a private LAN to share a single public IP address.
• Firewalling: Permitting or denying traffic based on security rules.
• Quality of Service (QoS): Prioritizing critical traffic, like voice or video calls, over less urgent data like email.

Hubs and Swithces in Computer Network

Hub:

A hub is a physical layer networking device which is used to connect multiple devices in a network. They are generally used to connect computers in a LAN.

A hub has many ports in it. A computer which intends to be connected to the network is plugged into one of these ports. When a data frame arrives at a port, it is broadcast to every other port, without considering whether it is destined for a particular destination or not.

Switches:

A switch is a data link layer networking device which connects devices in a network and uses packet switching to send and receive data over the network.

Like a hub, a switch also has many ports, to which computers are plugged in. However, when a data frame arrives at any port of a network switch, it examines the destination address and sends the frame to the corresponding device or devices. Thus, it supports both unicast and multicast communications.

Difference between Hub and Switch

Repeaters in Computer Network

A repeater is a dynamic network device used to reproduce the signals when they transmit over a greater distance so that the signal’s strength remains equal. It can be used to create an Ethernet network. A repeater that occurs as the first layer of the OSI layer is the physical layer.

Features of Repeaters:

A repeater is the simplest intermediary device, functioning primarily to overcome the physical limitations of transmission media.

1. Physical Layer Operation: Repeaters operate strictly at Layer 1 (Physical Layer) of the OSI model. They do not look at MAC or IP addresses; they only deal with electrical or optical bits.
2. Signal Regeneration: Instead of just "amplifying" (which also boosts noise), a modern repeater regenerates the signal. It receives a weakened bit-stream, reconstructs it to its original strength and shape, and retransmits it.
3. Distance Extension: Their primary purpose is to extend the physical reach of a network beyond the standard cable limits (e.g., extending Ethernet beyond 100 meters).
4. Transparency: Repeaters are transparent to the rest of the network. End devices do not know a repeater exists between them; it does not change the data in any way.

Advantages:

1. Cost-Effectiveness: They are significantly cheaper than hubs, switches, or routers because they require very little processing power.
2. Simplicity: They are "Plug-and-Play" devices requiring no configuration or software management.
3. Signal Integrity: By regenerating the signal at intervals, they ensure that data reaches its destination without becoming unreadable due to attenuation (signal fading).
4. No Performance Overhead: Because they don't "process" data or make routing decisions, they add almost zero latency to the transmission.

Disadvantages:

1. Noise Amplification: While they regenerate digital signals, if the incoming signal is too distorted, the repeater may incorrectly interpret "noise" as a "bit," effectively propagating errors.
2. Single Network Limitation: A repeater cannot connect two different types of networks (e.g., it cannot connect a Token Ring network to an Ethernet network).
3. Collision Domain Extension: Repeaters do not filter traffic. They forward everything, including collisions and errors, which can increase congestion in a large network.
4. The "5-4-3 Rule" (Legacy): In older Ethernet networks, you can’t daisy-chain infinite repeaters. Using too many creates propagation delay, where the signal takes so long to travel that it interferes with the network's timing (leading to "late collisions").
5. Limited Intelligence: They cannot perform tasks like traffic filtering, security, or path finding.

Bridges in Computer Network

Bridges are used to connect two subnetworks that use interchangeable protocols. To be precise, bridges connect segments that use the same protocol (e.g., Ethernet to Ethernet). They operate at Layer 2 (Data Link), so they cannot translate between fundamentally different protocols like a Gateway or Router can. They treat the data as "interchangeable" because the framing remains consistent across the bridge. It combines two LANs to form an extended LAN. The main difference between the bridge and repeater is that the bridge has a penetrating efficiency.

Working of Bridges:

Bridges work in the following ways: -

1. MAC (Media Access Control) Address Learning –

When a frame arrives at the bridge, it reads the source MAC address of the sender and adds this information to its internal MAC address table. 

2. Filtering and Forwarding –

The bridge then looks at the destination MAC address in the frame.

1. Local Traffic: If the destination MAC address is on the same network segment as the sender, the bridge will not forward the frame to other segments, as it knows it would only cause unnecessary traffic.
2. Remote Traffic: If the destination MAC address is on a different segment, the bridge will forward the frame only to that specific segment.
3. Unknown Destination: If the destination MAC address is not in its table, the bridge will broadcast the frame to all segments (except the one it arrived from) to find the device.

3. Segmentation –

By forwarding traffic only where it's needed, the bridge creates separate collision domains, effectively dividing a larger network into smaller, more manageable segments with reduced overall traffic and improved network performance. 

Uses of Bridges:

Primary uses of bridges are: -

1. Network Segmentation (Traffic Management) - The most common use of a bridge is to divide a large, congested network into smaller, manageable collision domains. By acting as a filter, the bridge ensures that local traffic stays within its own segment. This reduces "packet collisions" and prevents unnecessary data from flooding the entire network, significantly increasing overall performance and bandwidth availability.
2. Physical Network Extension - Standard networking cables (like Ethernet) have strict length limits before the signal degrades. Bridges allow you to:

• Extend the Reach: By connecting two segments, a bridge effectively doubles the maximum distance of the network.
• Overcome Connection Limits: It allows for the addition of more nodes (devices) than a single cable segment could physically or electrically support.

3. Connecting Disparate Locations (Remote Bridging) - Bridges can be used to link LANs that are geographically separated. Using a "half-bridge" setup, two LAN segments can be connected over a long-distance link (such as a leased line, fiber optic link, or a high-speed synchronous connection).This makes two physically separate offices appear as one single, seamless local network to the users.
4. Protocol Transparency - Bridges provide a way to expand the network without requiring complex software configurations on the end devices. Since they operate at the Data Link Layer (Layer 2), they are "transparent," meaning computers on either side can communicate as if they were on the exact same wire, regardless of the physical media used (e.g., bridging a fiber segment to a copper segment).

While the term "Bridge" is still used to describe the function, in modern hardware, these tasks are almost exclusively handled by Switches. A switch is essentially a "multi-port bridge" that can create a separate segment for every single device connected to it.

Gateways in Computer Network

A gateway is a network node that forms a passage between two networks operating with different transmission protocols. The most common type of gateways, the network gateway operates at layer 3, i.e. network layer of the OSI (open systems interconnection) model. However, depending upon the functionality, a gateway can operate at any of the seven layers of OSI model. It acts as the entry – exit point for a network since all traffic that flows across the networks should pass through the gateway. Only the internal traffic between the nodes of a LAN does not pass through the gateway.

Features of Gateways:

A Gateway is a network point that acts as an "entrance" to another network, often involving a change in protocol or architecture.

1. Protocol Translation (The Core Role) - The defining feature of a gateway is its ability to act as a protocol converter. It can take data formatted for one protocol suite (e.g., AppleTalk or IPX/SPX) and translate it into another (e.g., TCP/IP). This ensures compatibility between two fundamentally different systems.
2. Multi-Layer Operation - Unlike routers (Layer 3) or switches (Layer 2), a gateway is OSI Layer agnostic. It can operate at any level, from the Physical Layer all the way up to the Application Layer (Layer 7). This allows it to inspect the actual data content, not just the addresses.
3. Edge Boundary Management - A gateway typically sits at the edge of a network. It acts as the "choke point," managing all inbound and outbound traffic. This centralized position makes it the perfect location for:

• Security: Acting as a Firewall.
• Privacy: Acting as a Proxy Server.
• Traffic Control: Monitoring and filtering content.

4. Intelligent Routing - Gateways maintain information regarding the internal paths of their own network as well as the paths of the external networks they connect to. They use packet-switching techniques to ensure data is handed off to the correct destination after translation.
5. Hardware and Software Versatility - In large enterprises, gateways are often dedicated physical nodes equipped with multiple NICs (Network Interface Cards) to bridge different physical media. A gateway can also be a software application installed on a standard server or computer that handles the translation logic between networks.
6. Address Translation and Protection - Modern gateways frequently handle NAT (Network Address Translation), allowing an entire private internal network to hide behind a single public IP address, providing an essential layer of security and IP conservation.

Types of Gateways:

Gateways can be categorised on the following two bases: -

On basis of direction of data flow, gateways are broadly divided into two categories - 

1. Unidirectional Gateways − They allow data to flow in only one direction. Changes made in the source node are replicated in the destination node, but not vice versa. They can be used as archiving tools.
2. Bidirectional Gateways − They allow data to flow in both directions. They can be used as synchronization tools.

On basis of functionalities, there can be a variety of gateways, the prominent among them are as follows -

1. Network Gateway − This is the most common type of gateway that provides as interface between two dissimilar networks operating with different protocols. Whenever the term gateway is mentioned without specifying the type, it indicates a network gateway.
2. Cloud Storage Gateway − It is a network node or server that translates storage requests with different cloud storage service API calls, such as SOAP (Simple Object Access Protocol) or REST (Representational State Transfer). It facilitates integration of private cloud storage into applications without necessitating transfer of the applications into any public cloud, thus simplifying data communication.
3. Internet-To-Orbit Gateway (I2O) − It connects devices on the Internet to satellites and spacecraft orbiting the earth. Two prominent I2O gateways are Project HERMES and Global Educational Network for Satellite Operations (GENSO).
4. IoT Gateway − IoT gateways assimilates sensor data from IoT (Internet of Things) devices in the field and translates between sensor protocols before sending it to the cloud network. They connect IoT devices, cloud network and user applications.
5. VoiP Trunk Gateway − It facilitates data transmission between plain old telephone service (POTS) devices like landline phones and fax machines, with VoIP (voice over Internet Protocol) network.