Networking Devices

Equipment can be divided into two types :

■ End user devices—Include computers, printers, scanners, and other devices that provide services directly to the user.

■ Network devices—Include all devices that connect the end-user devices to allow them to communicate.

Repeaters

´  Repeaters are networking devices that exist at Layer 1,  (physical layer), of the OSI reference model.

´   data  is transformed into either electrical or light pulses that pass along the networking medium. These pulses are called signals.

´  When signals leave a transmitting station, they are clean and easily recognizable.

´  However, the longer the cable length, the weaker and more deteriorated the signals become as they pass along the networking medium.

´  The purpose of a repeater is to regenerate and retime network signals at the bit level(0,1), allowing them to travel a longer distance on the medium.

Hubs

´  The purpose of a hub is to regenerate and retime network signals.

´  The characteristics of a hub are similar to those of a repeater.

´   A hub is a common connection point for devices in a network.

´  Hubs commonly connect segments of a LAN.

´  A hub contains multiple ports. When a packet arrives at one port, it is copied tocthe other ports so that all the LAN’s segments can see all the packets.

      Hub do  broadcast which increase a load on network.

´  Because hubs and repeaters have similar characteristics, a hub is also called a multiport repeater.

´  The difference between a repeater and a hub is the number of cables that connect to the device.

´  Whereas a repeater typically has only two ports, a hub generally has

´  from four to 20 or more ports.

´  Whereas a repeater receives on one port and repeats on the other, a hub receives on one port and transmits on all the other ports

´  The following are the most important properties of hubs:

´   

´  Hubs amplify signals.

´  Hubs propagate signals through the network.

´  Hubs do not require filtering.

´  Hubs do not require path determination or switching.

´  Hubs are used as network-concentration points.

Network Interface Cards

´  Network interface cards (NICs) are considered Layer 2 devices

´   NIC throughout the world carries a unique code, called a Media Access Control (MAC) address.

´  This address controls data communication for the host on the LAN.

´  The NIC controls the access of the host to the medium.

Bridges

´  A bridge is a Layer 2(data link layer) device designed to create two or more LAN segments, each of which is a separate collision domain.

´   In other words, bridges were designed to create more usable bandwidth. The purpose of a bridge is to filter traffic on a LAN to keep local traffic local yet allow connectivity to other parts (segments) of the LAN for traffic that is directed there.

´  Every networking device has a unique MAC address on the NIC.

´  The bridge keeps track of which MAC addresses are on each side of the bridge and makes forwarding decisions based on this MAC address list.

´  Bridges filter network traffic by looking only at the MAC address. Therefore, they can rapidly forward traffic representing any network layer protocol.

´  bridges look only at MAC addresses, they are not concerned with network layer protocols.

´    bridges are concerned only with passing or not passing frames, based on their destination MAC addresses.

´  Bridges are more “intelligent” than hubs. That is, they can analyze incoming frames and forward (or drop) them based on addressing information.

´   Bridges collect and pass packets between two or more LAN segments.

´  Bridges create more collision domains, allowing more than one device to transmit simultaneously without causing a collision.

´  Bridges maintain MAC address tables.

Layer 2 Switches

´  Layer 2 switches, also called LAN switches or workgroup switches, often replace shared hubs and work with existing cable infrastructures to ensure that the switches are installed with minimal disruption of existing networks.

´  Like bridges, switches connect LAN segments, use a table of MAC addresses to determine the segment on which a frame needs to be transmitted, and reduce traffic.

´  Switches operate at much higher speeds than bridges.

´  Switches are data link layer devices that, like bridges, let multiple physical LAN segments be interconnected into single larger networks.

´   Similar to bridges, switches forward and flood traffic based on MAC addresses.

´  Because switching is performed in hardware, it is significantly faster than the switching function performed by a bridge using software.

Routers

´  A router, is a type of internetworking device that passes data packets between networks based on Layer 3(network layer) addresses.

´   A router can make decisions regarding the best path for delivery of data on the network.

´   Layer 3 allows the router to make decisions based on network addresses instead of individual Layer 2 MAC addresses.

´  Routers also can connect different Layer 2 technologies, such as Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI).

´  Routers also commonly connect Asynchronous Transfer Mode (ATM) and serial connections.

´  However, because of their capability to route packets based on Layer 3 information,routers have become the backbone of the Internet and run the IP protocol.

´  The purpose of a router is to examine incoming packets (Layer 3 data), choose the best path for them through the network, and then switch them to the proper outgoing port.

´  Routers are the most important traffic-regulating devices on large networks.

´  Routers let virtually any type of computer communicate with any other computer anywhere in the world.