network devices and their layers

Network devices are physical devices required for communication and interaction between hardware on a computer network. They work as a group and have a single purpose: to securely transfer data as fast as possible. Several network devices, such as repeaters, bridges, hubs, switches, and routers, are used to meet this goal.

Hub

Hub is one of the basic network devices that works at the physical layer and hence connects networking devices physically together. It is not used in modern networks. In networking, it is just studied because it is helpful to understand switches. If somebody understands it, then he can easily understand a switch.

A hub is a device that simply copies data received on any port to all its ports. So, if a packet of data arrives on interface 1 of a 5-port hub, it will blindly copy that data out to interfaces 2 through 5. The hub is a common connection point for network devices in a network. Different segments of LAN are commonly connected to it. It was a cheap and quick way to link up multiple computers in the early days.

The hub utilizes Carrier Sense Multiple Access with Collision Detect (CSMA/CD) to control Media access. The Ethernet hub communicates in a half-duplex mode, where data collisions are inevitable. The main issue with hubs is that only one computer can talk at a time.

So, if 2nd computers are going to talk at the same time, their traffic will join as it echoes out the other interfaces. This is called a collision, and it would corrupt the data being transmitted by both computers. So, each computer would have to try again after a random period. This becomes a real problem when the network gets busy or when more than a handful of computers are on a network. A switch solves the collision issue. Hub is a single broadcast and single collision domain. It has two types:-

Passive Hub

They Just point contact for the wires to be built into the physical network. They have nothing to do with modifying the signals.

Active Hub

Active hubs are smarter than passive hubs. They regenerate, concentrate, and strengthen the original signals before sending them to their destinations. Active hubs are also termed ‘repeaters’.

Repeater

A repeater is an electronic device that operates at the physical layer. It has two Ethernet ports. The repeater amplifies the received signal and retransmits it in the same network before it becomes too weak or corrupted, extending the length to which the signal can be transmitted over the same network. When the signal weakens, the repeater copies it bit by bit and regenerates it at its original strength.

Bridge

If a router connects two different types of networks, then a bridge connects two sub-networks as part of the same network. Bridges’ essential role in network architecture is storing and forwarding frames between the different segments that they connect.

Bridgeworks are at the Physical and Data Link Layer of the OSI Model. They connect different networks and develop communication between them. They connect two local-area networks, two physical LANs, into larger logical LANs or two segments of the same LAN that use the same protocol.

We can also use the bridge to divide larger networks into smaller sections by sitting between two physical network segments, managing the data flow, and reducing the broadcast between them.

Bridge uses MAC addresses for transferring frames. Bridges can forward the data or block it from crossing by looking at the MAC address of the devices connected to each segment. Bridges can also connect two physical LANs into a larger logical LAN. There are three main types of bridges:-

Transparent Bridge

A transparent bridge maintains a list of MAC addresses and appears transparently to other network devices. The other devices are ignorant of its existence. It only blocks or forwards data according to the MAC address. Transparent bridges also save and maintain the source-route addresses of incoming frames by listening to all the connected bridges and hosts. They use a transparent bridging algorithm to accomplish this.

Source Route Bridge

A form of routing is used to establish connections between pairs of nodes on different token rings. The source route bridge uses the path the packet takes through the network and is implanted within the packet.

Translational Bridge

Translational bridges reorder source and destination address bits when translating between Ethernet and Token Ring frame formats. They convert the data format of one networking system to another.

Switch

An Ethernet Switch is a device used to connect multiple computers and network devices within a LAN. It works at the OSI model’s Layer Two (Data Link Layer). Some switches also work at Layer 3( Network Layer). These switches are referred to as Layer 3 switches or multilayered switches.

The Basic Function of a Network Ethernet Switch and a Network Ethernet Hub is the same: forwarding Layer 2 packets (Ethernet frames) from the source device to the destination device. But a Network switch is more intelligent than a hub. An Ethernet switch uses MAC addresses to make forwarding decisions. It does not know about the protocol in the data portion, such as an IPv4 packet. The switch makes forwarding decisions based only on the Layer 2 Ethernet MAC addresses.

Unlike an Ethernet hub that repeats bits from all ports except the incoming port, an Ethernet switch consults a MAC address table to make a forwarding decision for each frame. The MAC address table is sometimes called a content addressable memory (CAM) table. Network switches for different input and output bandwidths are available. Today’s Ethernet Network Switches can have bandwidths of 10, 100, 1000, or 10,000 Megabits per second.

Switch Features and Advantages

• Connect network devices in a Local Area Network (LAN).
• It learns Layer 2 (MAC) addresses and forwards Layer 2 packets (Ethernet frames); to the exact destination with the help of the device’s MAC address.
• It’s control of who has access to various parts of the network.
• Provision to monitor network usage.
• High-end switches have pluggable modules.
• Allows to connect multiple devices and port can be managed VLAN can create security also can apply
• First broadcast; then unicast & multicast as needed.
• Switches use content-accessible memory CAM table, typically accessed by ASIC (Application Specific integrated chips).
• Half/Full duplex
• Connecting two or more nodes in the same network or a different network
• The switch has one broadcast domain [unless VLAN is implemented]

Router

The router is a network device that selects the best path for a data packet. It is located at any gateway (where one network meets another). It forwards data packets from one network to another based on the address of the destination network in the incoming packet and an internal routing table. It also determines which port (line) to send the packet (ports typically connect to Ethernet cables).

Routers also require packets formatted in a routable protocol, the global standard being TCP/IP, or simply “IP.” Routers operate at Layer 3 (network layer) of the OSI model, and they use the destination IP address in a data packet to determine where to forward the packet. The router stores the IP address in a Routing table and maintains an address on its own.

Gateway

Gateways usually work at the Transport layer and Session layer of the OSI model. It connects two networks that may work on different networking models. Gateway takes data from one system, interprets it, and transfers it to another. It is also a protocol converter and can operate at any network layer. Gateways are generally more complex than switches or routers. Gateway deals with numerous protocols and standards from different vendors. It performs all of the functions of routers. A router with added translation functionality is a gateway.

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