While setting up a network, you will come across different types of hardware used. The commonly used hardware are hubs, switches and routers.
A hub is a device that connects multiple computers using a twisted-pair cable. Hubs operate at Layer 1 (Physical). The number of computers that can be connected to a hub depends on the number of parts available (typically 4 to 8). Whenever it receives data from one port, the hub broadcast data to all thedevices connected to it, leading to collisions. Hence hubs are referred to as multiport repeaters. Since the evolution of SOHO routers and network switches,hubs are rarely used and considered obsolete.
Bridge is a device that can connect network segments and separate network traffic based on broadcasts. Bridges examine the frames and selectively transfer frames according to their MAC address. Bridges operate at Layer 2 of the OSI Model.
Switch is a device that allows multiple computers to be connected using twisted pair cable. Switches (operating at Level 2 OSI) manage traffic based on MAC (Media Access Control) addresses and are efficient in large networks. Switches are intelligent as they can build a table of MAC Addresses of all the devices connected to ports on the switch and create a virtual circuit for each attached device. Once a packet is received, it is analysed and forwarded to only the destined station with matching MAC address based on the table.
Using switches can eliminate collision as each part in the switch acts as a collision domain. Since switches isolate collision domains, they are referred to as multiport bridges. When forwarding frames, switches use Store and forward, cut through, Fragment free or Adaptive switching methods.
Unlike a hub that uses half-duplex communication, a network switch can send and receive at the same time (full-duplex mode) resulting in faster performance.
Number of computers that you can connect to a switch depends on the number of ports available (Typically 4 or 8 on SOHO switches designed for use in home and small business networks and 8 – 32 or 64 on switches designed for use in an enterprise network.). The networks can be extended by adding additional switches usually cascaded from the primary switch. Switches designed for larger networks are cascaded through a special port called the Uplink port.
Categories of switches include:
- Unmanaged switches are network switches used typically for homes or small offices requiring no administrative configuration.
- Managed switches are widely used in enterprise networks and ISP’s. These need to be configured by the network administrator before it is used in a network.
A single layer-2 network can be partitioned to create multiple distinct broadcast domains, enabling data to be exchanged only between the computers within the domain. This is referred to as VLAN or Virtual LANs. This is created for two primary reasons:
- To reduce collisions
- To implement security.
For example if all the computers in an organization are connected to a single switch, you can isolate them by creating VLAN’s for each department resulting in restricted access across departments with maximum access between computers within departments. VLANS can be configured only on Managed switches.
Power over Ethernet (PoE)
PoE describes a standardized system to provide electrical power supply through Ethernet cables; generally, UTP cables carry only signals necessary for data communication. Switches that have support for PoE are generally expensive and in some cases only limited number of Ethernet ports are capable of supporting PoE. Advantages of PoE include the ability to provide power up to 25 watts and distance factor that allows devices to be connected up to 100 meters from the switch.
Routers are Layer 3 devices that allow packets to be routed to different logical networks. Routers can discover and transfer packets based on routing table that are pre-determined or self-discovered. Routing tables are either managed by an administrator by manually defining the routes or automated through special configuration to exchange the routing tables with other routers on a logical network. Most common type of routers includes the SOHO router used at home or small office for sharing Internet connection; sophisticated routers are widely used in enterprise networks and ISP’s. Similar to SOHO switches, SOHO routers do not need to be configured and routers designed for use in large networks require to be configured before they can be used.
In general, a combination of several routers and switches are used in large networks. Notable manufacturers of routers include Cisco, Nortel Networks, Avaya, HP, Dell, Huawei, etc.
Routing is the process of selecting paths in a network when sending receiving packets across computers or devices. Imagine if you are planning to send a parcel to someone; the parcel will travel through different offices, change routes if roadblocks are detected and finally be delivered to the recipient. Similarly when you browse the internet or send an email, packets take different routes (from your computer to your ISP, from your ISP to the next ISP, etc.) until it reaches its destination.
Also referred to as a residential gateway, SOHO (Small Office Home Office) routers are devices designed for use in small to medium sized networks. Most SOHO routers have combinations of a switch, DSL or cable modem and an access point for Wi-Fi connectivity. These devices are used for two primary purposes
- Connecting desktops & laptops across home or office.
- Sharing a single Internet connection across desktops & laptops.
Some models include support for connecting peripherals such as printers, USB hard disk drives, etc. through USB ports.
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