TYPES OF NETWORKING DEVICES BYAMEYA KAMBLE

Networks using a Star topology require a central point for the devices to connect. Originally this device was called a concentrator since it consolidated the cable runs from all network devices. The basic form of concentrator is the hub.

 

As shown in Figure; the hub is a hardware device that contains multiple, independent ports that match the cable type of the network. Most common hubs interconnect Category 3 or 5 twisted-pair cable with RJ-45 ends, although Coax BNC and Fiber Optic BNC hubs also exist. The hub is considered the least common denominator in device concentrators. Hubs offer an inexpensive option for transporting data between devices, but hubs don't offer any form of intelligence. Hubs can be active or passive.

An active hub strengthens and regenerates the incoming signals before sending the data on to its destination.

Passive hubs do nothing with the signal.

Switches

Switches are a special type of hub that offers an additional layer of intelligence to basic, physical-layer repeater hubs. A switch must be able to read the MAC address of each frame it receives. This information allows switches to repeat incoming data frames only to the computer or computers to which a frame is addressed. This speeds up the network and reduces congestion.

Switches operate at both the physical layer and the data link layer of the OSI Model. 

Bridges

A bridge is used to join two network segments together, it allows computers on either segment to access resources on the other. They can also be used to divide large networks into smaller segments. Bridges have all the features of repeaters, but can have more nodes, and since the network is divided, there is fewer computers competing for resources on each segment thus improving network performance.

Bridges can also connect networks that run at different speeds, different topologies, or different protocols. But they cannot, join an Ethernet segment with a Token Ring segment, because these use different networking standards. Bridges operate at both the Physical Layer and the MAC sublayer of the Data Link layer. Bridges read the MAC header of each frame to determine on which side of the bridge the destination device is located, the bridge then repeats the transmission to the segment where the device is located.

Routers

Routers Are networking devices used to extend or segment networks by forwarding packets from one logical network to another. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines.

Routers work at the network layer (layer 3) of the Open Systems Interconnection (OSI) reference model for networking to move packets between networks using their logical addresses (which, in the case of TCP/IP, are the IP addresses of destination hosts on the network). Because routers operate at a higher OSI level than bridges do, they have better packet-routing and filtering capabilities and greater processing power, which results in routers costing more than bridges.

Routing tables

Routers contain internal tables of information called routing tables that keep track of all known network addresses and possible paths throughout the internetwork, along with cost of reaching each network. Routers route packets based on the available paths and their costs, thus taking advantage of redundant paths that can exist in a mesh topology network.

Because routers use destination network addresses of packets, they work only if the configured network protocol is a routable protocol such as TCP/IP or IPX/SPX. This is different from bridges, which are protocol independent. The routing tables are the heart of a router; without them, there's no way for the router to know where to send the packets it receives.

Unlike bridges and switches, routers cannot compile routing tables from the information in the data packets they process. This is because the routing table contains more detailed information than is found in a data packet, and also because the router needs the information in the table to process the first packets it receives after being activated. A router can't forward a packet to all possible destinations in the way that a bridge can.

• Static routers: These must have their routing tables configured manually with all network addresses and paths in the internetwork.
• Dynamic routers: These automatically create their routing tables by listening to network traffic.
• Routing tables are the means by which a router selects the fastest or nearest path to the next "hop" on the way to a data packet's final destination. This process is done through the use of routing metrics.
• Routing metrics which are the means of determining how much distance or time a packet will require to reach the final destination. Routing metrics are provided in different forms.
• hop is simply a router that the packet must travel through.
• Ticks measure the time it takes to traverse a link. Each tick is 1/18 of a second. When the router selects a route based on tick and hop metrics, it chooses the one with the lowest number of ticks first.

You can use routers, to segment a large network, and to connect local area segments to a single network backbone that uses a different physical layer and data link layer standard. They can also be used to connect LAN's to a WAN's.