Elementary Statistics and Computer Application

Internet works

• Internet is a collection of LANs connected by WAN.
• The real distinction between a subnet and a WAN is whether or not host is present.
• If the system within the closed curve contains only routers, it is a subnet.
• If it contains routers and host with their own users, it is a WAN. In case of a LAN, the cable and the host form the network. There is no subnet.
• Internetwork is formed when distinct networks are connected together. Connecting a LAN and a WAN or connecting two LANs forms an internetwork.
 
Router


• Device forwards data packets -networks.
• Router connected -at least two networks- two LANs or WANs or a LAN and its ISP’s network.
• Located at gateways-where two or more networks connect.
• Use headers and forwarding tables –determine best path for forwarding the packets
• use protocols- communicate with each other and configure the best route between any two hosts.
• Tasks -routing and forwarding, generally containing a specialized operating system.
• Routers operate in two different planes:
• Control Plane - learns the outgoing interface- appropriate for forwarding specific packets to specific destinations.
• Forwarding Plane-responsible for actual process of sending a packet received on a logical interface to an outbound logical interface.
• ROUTERS are completely different devices.
• Where a hub or switch is concerned with transmitting frames.
• Router's job, as its name implies, is to route packets to other networks.
• One of the key features of a packet is that it not only contains data, but the destination address of where it's going.
• Router use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.
 
Hub


• Common connection point for devices in a network.
• Hubs used to connect segments of a LAN.
• contains multiple ports.
• packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
• Do not manage any of the traffic that comes through them.
• Packet collisions result.
• Frames carry data.
• When a frame is received, it is amplified and then transmitted on to the port of the destination PC.
• Difference between these two devices is in the method in which frames are being delivered.
• In a hub, a frame is passed along or broadcast" to every one of its ports.
• The hub has no way of distinguishing which port a frame should be sent to.
• Passing it along to every port ensures that it will reach its intended destination.
• This places a lot of traffic on the network and can lead to poor network response times.
• one PC is broadcasting-access to the maximum available bandwidth.
• Multiple PCs are broadcasting- bandwidth will need to be divided among all of those systems, which will degrade performance.
• Hub -collisions -on individual ports-partition the port, disconnecting from the shared medium.
• status lights –hub-easily detected-coaxial cable.
• A compromise between a hub and a switch appeared known as a "dual speed hub".
• Two hubs (one of each speed) and a two port bridge between them.
• Devices were connected to the appropriate hub automatically based on their speed and the bridge handled inter-speed traffic.
 
Switches

• A switch, however, keeps a record of the MAC addresses of all the devices connected to it.
• In networks, a device that filters and forwards packets between LAN segments.
• Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol.
• Network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately.
• By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub.