Network Devices

 Introduction :

• Network device is also called Networking Hardware which are physical devices that allow hardware on a computer network to communicate and interact with one another.
• before learning to Network device we need to know the OSI(Open Systems Interconnection ) Model .

What is OSI Model ?

• OSI model describes seven layers that computer systems use to communicate over a network. It was the first standard model for network communications, adopted by all major computer and telecommunication companies in the early 1980s.
• OSI model is a conceptual model created by the International Organization for Standardization which enables diverse communication systems to communicate using standard protocols.
• Lets have a look on the seven standard layers which enables the communication  system:

👉 Physical Layer : NIC , RJ-45, Modem, Repeater.

👉Data Link Layer : Hub, Bridge, Switch.

👉Network Layer: Router, Gateway.

The physical layer:

• The physical layer is the first and lowest layer of the Open System Interconnection Model (OSI Model.)
• The physical layer (also known as layer 1) deals with bit-level transmission between different devices and supports electrical or mechanical interfaces connecting to the physical medium for synchronized communication.
• This layer plays with most of the network’s physical connections—wireless transmission, cabling, cabling standards and types, connectors and types, network interface cards, and more —as per network requirements.

      The physical layer provides the following services:

• Modulates the process of converting a signal from one form to another so that it can be physically transmitted over a communication channel.
  
• Bit-by-bit delivery.
• Transmission mode control.
• Signal equalization to ensure reliable connections and facilitate multiplexing.
  
• Forward error correction/channel coding such as error correction code.
  
• Bit interleaving to improve error correction

→let's brifely discuss about some hardware of physical layer which is mentioned above: 

NIC(Network Interface Card) :

– NIC or network interface card is a network adapter that is used to connect the computer to the network. It is installed in the computer to establish a LAN.  It has a unique id that is written on the chip, and it has a connector to connect the cable to it. The cable acts as an interface between the computer and the router or modem. NIC card is a layer 2 device which means that it works on both the physical and data link layers of the network model. 

Types of network interface cards

While the standard NIC is a plastic circuit board that slides into a computer to connect with the motherboard, there are multiple ways this connection can occur:

• Wireless. These are NICs that use an antenna to provide wireless reception through radio frequency waves. Wireless NICs are designed for Wi-Fi connections.

• Wired. These are NICs that have input jacks made for cables. The most popular wired LAN technology is Ethernet.

• USB. These are NICs that provide network connections through a device plugged into the USB port.

• Fiber optics. These are expensive and more complex NICs that are used as a high-speed support system for network traffic handling on server computers. This support could also be accomplished by combining multiple NICs.

 Register Jack-45 (RJ45):

network connectors are most commonly found at either end of an Ethernet (wired internet) connection. At first glance, they appear similar to the familiar telephone plugs and jacks which connect landlines to walls or switchboards. However, RJ45 connectors are typically slightly larger.

The term RJ45 connector is widely used today to describe both male RJ45 plugs and female RJ45 sockets. The plugs, sometimes called modular connectors, are usually found on the end of Ethernet cables. The sockets or jacks are generally embedded in the device that is being hooked up or mounted to a fixed wall panel.

Modem(modulator/demodulator) :

Short for modulator/demodulator, a modem is a hardware device that allows a computer to send and receive information over telephone lines. When sending a signal, the device converts ("modulates") digital data to an analog audio signal, and transmits it over a telephone line. Similarly, when an analog signal is received, the modem converts it back ("demodulates" it) to a digital signal.

    Types of Modem:

• Onboard modem - Modem built onto the computer motherboard. These modems cannot be removed, but can be disabled through a jumper or BIOS setup.

• Internal modem - Modem that connects to a PCI slot inside a newer desktop computer, or ISA slot on an older computer. The internal modem shown above is an example of a PCI modem.

• External modem - Modem in a box that connects to the computer externally, using a serial port or USB port. The picture is an example of an external USRobotics modem.

• Removable modem - Modem used with older laptops PCMCIA slot and can be added or removed as needed.

Repeater : 

A repeater is a network device that retransmits a received signal with more power and to an extended geographical or topological network boundary than what would be capable with the original signal.

A repeater is implemented in computer networks to expand the coverage area of the network, repropagate a weak or broken signal and or service remote nodes. Repeaters amplify the received/input signal to a higher frequency domain so that it is reusable, scalable and available.

Repeaters were introduced in wired data communication networks due to the limitation of a signal in propagating over a longer distance and now are a common installation in wireless networks for expanding cell size.

Repeaters are also known as signal boosters.

2. Data Link Layer: 

• The data link layer is the protocol layer in a program that handles the moving of data into and out of a physical link in a network. The data link layer is Layer 2 in the Open Systems Interconnection (OSI) architecture model for a set of telecommunication protocols.
• Data bits are encoded, decoded and organized in the data link layer, before they are transported as frames between two adjacent nodes on the same LAN or WAN. The data link layer also determines how devices recover from collisions that may occur when nodes attempt to send frames at the same time.
• The data link layer has two sublayers: the logical link control (LLC) sublayer and the media access control (MAC) sublayer.

Hub –  A hub is a basically multi-port repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices.  In other words, the collision domain of all hosts connected through Hub remains one.  Also, they do not have the intelligence to find out the best path for data packets which leads to inefficiencies and wastage. 

Bridge – A bridge operates at the data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of the source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

Types of Bridges 

• Transparent Bridges:- These are the bridge in which the stations are completely unaware of the bridge’s existence i.e. whether or not a bridge is added or deleted from the network, reconfiguration of the stations is unnecessary. These bridges make use of two processes i.e. bridge forwarding and bridge learning.
• Source Routing Bridges:- In these bridges, routing operation is performed by the source station and the frame specifies which route to follow. The host can discover the frame by sending a special frame called the discovery frame, which spreads through the entire network using all possible paths to the destination.

Switch – A switch is a multiport bridge with a buffer and a design that can boost its efficiency(a large number of ports imply less traffic) and performance. A switch is a data link layer device. The switch can perform error checking before forwarding data, which makes it very efficient as it does not forward packets that have errors and forward good packets selectively to the correct port only.  In other words, the switch divides the collision domain of hosts, but the broadcast domain remains the same.

Types of  Switch

1. Unmanaged switches: These switches have a simple plug-and-play design and do not offer advanced configuration options. They are suitable for small networks or for use as an expansion to a larger network.
2. Managed switches: These switches offer advanced configuration options such as VLANs, QoS, and link aggregation. They are suitable for larger, more complex networks and allow for centralized management.
3. Smart switches: These switches have features similar to managed switches but are typically easier to set up and manage. They are suitable for small- to medium-sized networks.
4. Layer 2 switches: These switches operate at the Data Link layer of the OSI model and are responsible for forwarding data between devices on the same network segment.
5. Layer 3 switches: These switches operate at the Network layer of the OSI model and can route data between different network segments. They are more advanced than Layer 2 switches and are often used in larger, more complex networks.
6. PoE switches: These switches have Power over Ethernet capabilities, which allows them to supply power to network devices over the same cable that carries data.
7. Gigabit switches: These switches support Gigabit Ethernet speeds, which are faster than traditional Ethernet speeds.
8. Rack-mounted switches: These switches are designed to be mounted in a server rack and are suitable for use in data centers or other large networks.
9. Desktop switches: These switches are designed for use on a desktop or in a small office environment and are typically smaller in size than rack-mounted switches.
10. Modular switches: These switches have modular design, which allows for easy expansion or customization. They are suitable for large networks and data centers.

3.Network Layer :

• The Network Layer is the third layer of the OSI model.
• It handles the service requests from the transport layer and further forwards the service request to the data link layer.
• The network layer translates the logical addresses into physical addresses
• It determines the route from the source to the destination and also manages the traffic problems such as switching, routing and controls the congestion of data packets.
• The main role of the network layer is to move the packets from sending host to the receiving host.

The main functions performed by the network layer are:

• Routing: When a packet reaches the router's input link, the router will move the packets to the router's output link. For example, a packet from S1 to R1 must be forwarded to the next router on the path to S2.
• Logical Addressing: The data link layer implements the physical addressing and network layer implements the logical addressing. Logical addressing is also used to distinguish between source and destination system. The network layer adds a header to the packet which includes the logical addresses of both the sender and the receiver.
• Internetworking: This is the main role of the network layer that it provides the logical connection between different types of networks.
• Fragmentation: The fragmentation is a process of breaking the packets into the smallest individual data units that travel through different networks.

---

Services Provided by the Network Layer

• Guaranteed delivery: This layer provides the service which guarantees that the packet will arrive at its destination.
• Guaranteed delivery with bounded delay: This service guarantees that the packet will be delivered within a specified host-to-host delay bound.
• In-Order packets: This service ensures that the packet arrives at the destination in the order in which they are sent.
• Guaranteed max jitter: This service ensures that the amount of time taken between two successive transmissions at the sender is equal to the time between their receipt at the destination.
• Security services: The network layer provides security by using a session key between the source and destination host. The network layer in the source host encrypts the payloads of datagrams being sent to the destination host. The network layer in the destination host would then decrypt the payload. In such a way, the network layer maintains the data integrity and source authentication services.

Router:

The router is a physical or virtual internetworking device that is designed to receive, analyze, and forward data packets between computer networks. A router examines a destination IP address of a given data packet, and it uses the headers and forwarding tables to decide the best way to transfer the packets. There are some popular companies that develop routers; such are Cisco, 3Com, HP, Juniper, D-Link, Nortel, etc. Some important points of routers are given below:

• A router is used in LAN (Local Area Network) and WAN (Wide Area Network) environments. For example, it is used in offices for connectivity, and you can also establish the connection between distant networks such as from Bhopal to
• It shares information with other routers in networking.
• It uses the routing protocol to transfer the data across a network.
• Furthermore, it is more expensive than other networking devices like switches and hubs.

A router works on the third layer of the OSI model, and it is based on the IP address of a computer. It uses protocols such as ICMP to communicate between two or more networks. It is also known as an intelligent device as it can calculate the best route to pass the network packets from source to the destination automatically.

Gateway:

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.

Types of Gateways

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

• 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.
• 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 −

• 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.

• 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.
• 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).
• 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.
• 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.