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Computer Networks

Published on June 2016 | Categories: Documents | Downloads: 5 | Comments: 0
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TCP/IP Reference Model Defined after the advent of Internet. Service interface and protocols were not clearly distinguished before TCP/IP supports Internet working Loosely layered Protocol Dependant standard More Credible TCP reliably delivers packets, IP does not reliably deliver packets

OSI Reference Model Defined before advent of internet. Service interface and protocols are clearly distinguished Internet working not supported Strict layering Protocol independent standard Less Credible All packets are reliably delivered

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What is a Hub?
Guest Author - Cathy Spearmon One of the most commonly used networking hardware devices are hubs. However, the inexpensive switch is rapidly replacing the hub. Anyway, hubs serve as central connection points for local area networks (LANs) that typically embrace the star topology. The basic hub contains no active electronics and cannot be used to extend a LAN past its cabling distance specifications. Yet, hubs organize your cables and relay data signals to all computers that exist on your LAN. Hubs are used on networks where twisted-pair cabling is used. The ports, which are available on the hub, provide connection points for the devices on the network. Computers and devices are connected to the hub via network cables to individual ports. In cases where a LAN outgrows the size of its hub, a new hub can be attached by daisy-chaining them together using a short connection cable, which is often referred to as a rattail. Hubs come in many different shapes and sizes and are available in a wide range of prices. The more ports available on the hub, the more expensive the hub. Also, hubs that support faster varieties of Ethernet, for example Fast Ethernet, will also cost more.

What is a Switch?
Guest Author - Cathy Spearmon A switch is another internetworking device used to manage bandwidth on a large network. Switches are rapidly becoming one of the most used internetworking devices from connecting even smaller networks because they allow you to have some control over the use of the bandwidth on the network. A switch, which is referred to as a "bridge on steroids" controls how data flows by using the MAC addresses that are placed on each data packet. Remember that this MAC address on the data packet is the same MAC address on the network card of that particular computer.

Switches divide networks into what is known as a Virtual LAN or VLAN. The best thing about a VLAN, which is also a logical grouping of computers on a network into what is described as some sort of communication group, is that the computers really do not have to be in close proximity or even on the same floor. This is because it allows the computers to be grouped by the similarities in the types of users in the VLAN. Switches use a combination of software and hardware to switch packets between computers and other devices on the network. This software is the switches operating system. And, because switches offer a higher density of connection ports, they can easily replace hubs on the network. This means that each computer on the network can be connected to its own port on the switch. When the computers are directly connected to the switch, the switch can supply each of the computers with a dedicated amount of bandwidth. For example, say users are on a 100Mbps Ethernet network via a switch. Each user can realize a bandwidth of 100Mbps and don't have to compete for the bandwidth the way computers do on a network via a hub because each port on the switch has a dedicated 100Mbps. This is why switches are rapidly replacing hubs. Inexpensive switches are even available to accomodate small networks and home network markets. Some of the switch hardware can also take advantage of full-duplex access to the network media, which allows for the sending and receiving of data simultaneously. Essentially, this provides access to an Ethernet network that is collision free, when an Ethernet network is pretty much known to have data collisions. A computer existing on a Fast Ethernet network, typically running at 100Mbps, would see a 200Mbps throughput because sending and receiving would occur simultaneously on a fullduplex media. Since switches are becoming very popular on both the small and large networks, they have all but replaced bridges as the internetworking devices for conserving network bandwidth and expanding LANs into larger corporate internetworks. But, they are also making hubs a device of the past for smaller networks.

What is a Repeater?
Guest Author - Cathy Spearmon Different types of network cabling have their own maximum distance that they can move a data signal. In cases where a LAN must be extended beyond it maximum run for its particular cabling type, repeaters are used. Repeaters take the signal that it receives from the computers and other devices on the LAN and regenerates the signal in order for the signal to maintain its integrity while traveling along a longer media run that is normally possible. Repeaters do not have any capability of directing network traffic or deciding what particular route that certain data should take, they are simply devices that sit on the network and boost the data signal that they receive. The problem with repeaters is that they amplify the entire signal that they receive, including any line noise. In the worst case scenario, they pass on data traffic that is barely discernable from the background noise on the line.

Introduction to Data Communications 15. Transmission Media - Guided

15. Transmission Media - Guided There are 2 basic categories of Transmission Media: Guided and Unguided. Guided Transmission Media uses a "cabling" system that guides the data signals along a specific path. The data signals are bound by the "cabling" system. Guided Media is also known as Bound Media. Cabling is meant in a generic sense in the previous sentences and is not meant to be interpreted as copper wire cabling only. Unguided Transmission Media consists of a means for the data signals to travel but nothing to guide them along a specific path. The data signals are not bound to a cabling media and as such are often called Unbound Media. There 4 basic types of Guided Media: Open Wire Twisted Pair Coaxial Cable Optical Fibre

15a. Open Wire Open Wire is traditionally used to describe the electrical wire strung along power poles. There is a single wire strung between poles. No shielding or protection from noise interference is used. We are going to extend the traditional definition of Open Wire to include any data signal path without shielding or protection from noise interference. This can include multiconductor cables or single wires. This media is susceptible to a large degree of noise and interference and consequently not acceptable for data transmission except for short distances under 20 ft.

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