This tutorial explains the functions of the most common and essential networking devices such as Hubs, Switches, Routers, Bridges, Modems, NICs, Proxies, and Gateways.
Network Interface Card (NIC)
NIC stands on the top of the list of network devices. Networking cannot be done without this device. It is also known as a network adapter card, Ethernet card, or LAN card. A NIC allows a networking device to communicate with other networking devices.
A NIC converts data packets between two different data transmission technologies. A PC uses parallel data transmission technology to transmit data between its internal parts whereas the media that provides connectivity between different PCs uses serial data transmission technology. A NIC converts a parallel data stream into the serial data stream and a serial data stream into the parallel data stream.
The following image shows how a NIC works.
Typically, all modern PCs have integrated NICs. If additional NICs are required, they can be installed as add-on devices.
For desktop or server systems, they are available as adapters that can be plugged into an available slot on the motherboard. For laptops or other smaller-sized devices, they are available in PCMCIA (International Association of Personal Computer Memory Cards) card form that can be inserted into a PCMCIA slot.
Types of NICs
There are two types of NICs: media-specific and network design specific
Media Specific: - A media-specific NIC supports a particular type of media. For example, to connect a coaxial cable, you need a NIC that has the BNC port whereas to connect an Ethernet cable, you need a NIC that has the RJ-45 port.
Network Design Specific: - A network design-specific NIC supports a specific network topology. For example, FDDI, Token Ring, and Ethernet have their distinctive type of NIC cards. They cannot use other types of NIC cards.
The following image shows some common types of NICs.
Hub
A hub is a centralized device that connects multiple devices in a single LAN network. When a hub receives a data signal from a connected device on one of its ports, except for that port, it forwards those signals from the remaining ports to all other connected devices. Typically, a hub has one or more uplink ports that are used to connect it to another hub.
There are two types of the Hub.
Passive Hub: - A passive hub forwards data signals as it receives them. It does not change data signals in any manner.
Active Hub: - An active hub also forwards data signals. But, before forwarding them, it amplifies them. Due to this added feature, an active Hub is also called a repeater.
The following image shows an active hub and a passive hub.
Hubs are no longer used in computer networks.
MAU and Patch panel
An MAU and a patch panel look like a hub, but they are different. An MAU (Multi-Access Unit) is a replacement for a hub for a token ring network.
Differences between Hub and MAU are the following.
- Hub is used for Ethernet network while MAU is used for Token Ring network.
- Hub logically forms the star topology while MAU logically forms the ring topology.
The following image shows an MAU.
A patch panel is used to organize the UTP cables systematically. It doesn't interfere with the data signals.
The following image shows a patch panel.
Bridge
A bridge is used to divide a large network into smaller segments. The basic functions of a bridge are the following: -
- Breaking a large network into smaller segments.
- Connecting different media types such as UTP and fiber optic.
- Connecting different network architectures such as Ethernet and the Token ring.
The following image shows an example of a bridge.
A bridge can connect two different types of media or network architecture, but it cannot connect two different types of network layer protocols such as TCP/IP or IPX. It requires the same network-layer protocols across all segments.
There are three types of bridge:-
Local Bridge: - The Bridge directly connects two LAN segments. In Ethernet implementations, this is known as a transparent bridge. In the Token Ring network, this is called a source-routed bridge.
Remote Bridge: - This Bridge connects with another Bridge over the WAN link.
Wireless Bridge: - This Bridge connects with another Bridge without using wires. It uses radio signals for connectivity.
In networking models such as the OSI layers model and TCP/IP model, the functionalities of Bridges are defined in the physical layer and data link layer.
Just like a Hub, a Bridge is also no longer used in the computer network. Bridges have been replaced by switches.
Switch
Just like a hub and a bridge, a switch is also used to connect multiple devices in a LAN segment. A switch is the upgraded version of the bridge. Besides providing all the functionalities of a bridge, it also offers several additional features.
The biggest advantage of a switch is that it makes switching decisions in hardware by using application-specific integrated circuits (ASICs).
Unlike the generic processors that we use in our PC, ASICs are specialized processors built only to perform particular tasks. Usually, the ASICs in switches have a single task and that is switching the frames as fast as they can.
An ASIC occupied switch performs this task blazingly fast. For example, an entry-level 2960 Catalyst Switch can process 2.7 million frames per second.
Modem
In simple language, a modem is a device that is used to connect to the Internet. Technically, it is the device that enables digital data to be transmitted over telecommunication lines.
A Telco company uses entirely different data transmission technology from the technology that a PC uses for data transmission. A modem understands both technologies. When it receives signals from the PC, it converts them into the format that the Telco company understands. When it receives signals from the Telco company, it converts them into a format that the PC understands.
It enables communication between the PC (Known as the DTE device) and the Telecom company's office (Known as the DCE device).
The following image shows some common types of modems.
Gateway
Gateway is used to forward packets that originate from a local host or a local network and are intended for remote networks. If a data packet does not get its destination address in the local network then it takes the help of the gateway device to find the destination address in the remote network. The gateway device knows the path to the remote destination address. If necessary, it also encapsulates the packet so that it can travel through other networks to reach its destination address.
The following image shows a gateway device.
Examples of the Gateway
Email Gateway: - An email gateway translates SMTP e-mails in standard X.400 format before forwarding.
GSNW Gateway: - A GSNW gateway allows Windows clients to access resources from the NetWare server.
PAD Gateway: - A PAD gateway provides connectivity between a LAN network and an X.25 network.
Router
A router connects different network segments. It switches data packets between networks that are either located in different logical segments or constructed with different network-layer protocols.
When a router receives a data packet on any of its interfaces, it checks the destination address of that packet, and based on that destination address, forwards that data packet to the interface that is associated with the destination address.
To forward data packets to their destination, the router keeps a record of the connected network. These records are maintained in a database table known as the routing table. Routing tables can be created statically or dynamically.
The following image shows two routers.
The main functions of routers are the following: -
- To connect different network segments.
- To connect different network protocols such as IP and IPX.
- To connect several smaller networks into a large network.
- To break a large network into smaller networks.
- To connect two different media types such as UTP and Fiber optical.
- To connect two different network architectures such as Token Ring and Ethernet.
- To connect LAN network with Telco company's office.
- To access DSL services.
Transceiver
A transceiver is a small device that can send and receive both types of signals: analog and digital. Usually, it is inbuilt in the network interface card. But, it is also available as a separate device. It detects the type of signal from the network wire and converts the signal accordingly.
Let's take an example. A transceiver is attached to the device that transmits signals in digital form. Now suppose, this device is connected with the network wire that uses the analog form for data transmission. In this case, the transceiver converts digital signals into analog signals before placing them on the network wire.
The following image shows some transceivers.
Proxy
A proxy is used to hide the internal network from the outside world. It may be a dedicated device or maybe an application software. Once it is configured, all communication goes through it. Since external devices cannot directly access internal equipment, they cannot tamper with internal equipment.
The following image shows an example of a proxy.
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