|Data Networks: Data networks developed as a result of business applications that were written for microcomputers. At that time microcomputers were not connected as mainframe computer terminals were, so there was no efficient way of sharing data among multiple microcomputers. It became apparant that sharing data through the use of floppy disks was not an efficient or cost-effective manner in which to operate business.|
|Businesses needed a solution that would successfully address the following three problems:|
|In the mid-1980s, new network technologies could not communicate with each other due to competition between companies. This often required old network equipment to be removed to implement new equipment.|
|One early solution was the creation of local-area network (LAN) standards. In a LAN system, each department of the company is a kind of electronic island. As the use of computers in businesses grew, it soon became obvious that even LANs were not sufficient. What was needed was a way for information to move efficiently and quickly, not only within a company, but also from one business to another. THe solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs). Because WANs could connect user networks over large geographic areas, it was possible for businesses to communicate with each other accross great distances.|
|The history of coputer networking is complex.|
|Some important dates:|
|Equipment that connects directly to a network segment is referred to as a device.
These devices are broken up into two classifications:|
|Host: The end-user can also be referred to as a Host.
Hosts allow users to share, create and obtain information.
Host devices are physically connected to the network media using a NIC.
Hosts use the NIC connection to perform the tasks of sending e-mails, printing reports, scanning pictures, or accessing databases.|
Repeater: network device used to regenerate a signal. Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuaation. A repeater does not perform intelligent routing like a bridge or a router.
Hubs: concentrate connections. They take a group of hosts and allow the network to see them as a single unit. Active hubs not only concentrate hosts, but they also regenerate signals.
Bridges: convert network transmission data formats as well as perform basic data transmission management. Bridges, as the name implies, provide connections between LANs. Not only do bridges connect LANs, but they also perform a check on the data to determin wheter it should cross the bridge or not. This makes each part of the network more efficient.
Switches: add more intelligence to data transfer management. Not only can they determine whether data should remain on a LAN or not, but they can transfer the data only to the connection that needs the data. Another difference between a bridge and a switch is that a switch does not convert data transmission formats.
Routers: have all the capabilities of the network devices mentioned above. Routers can regenerate signals, concentrate multiple connections, convert data transmission formants, and manage data transfers. They can also connect to a WAN, which allows them to connect LANs that are separated by great distances. Non of the other devices provide this type of connection.
|Network topology - Defines the structure of the network. Two parts to the topology are:
Commonly used Logical Topologies:
|Logical Topology of a network is how the hosts communicate across the medium. The two most common types of logical topologies are broadcast and token passing:
|These network rules are created and maintained by many different organizations and commmittees.
|Local-area Networks (LANs):|
LANs consist of the following components:
|LANs make it possible for businesses that use computer technology to locally share files and printers efficiently, and make internal communications possible. A good example of this technology is e-mail.|
Some common LAN technologies are:
|LANs are designed to:
|Wide-Area Networks (WANs):|
Wans are designed to...
|WANs interconnect LANs, which then provide access to computers or file servers in other locations. Because WANs connect user networks over a large geographical area, they make it possible for businesses to communicate across great distances. Using WANs allows computers, printers, and other devices on a LAN to share and be shared with distant locations. Wide-are networking has also created a new class of workers called telecommunicaters, people who never have to leave their homes to go to work.|
|Wans are designed to do the following:
|Some common WAN technologies are:
|Metropolitan-Area Networks (MANs)|
A MAN is a network that spans a metropolitan area such as a city or suburban area. A MAN usually consists of two or more LANs in a common geographical area.
|Storage-Are Networks (SANs)|
A SAN is a dedicated, high-performance network used to move data between servers and storage resources. Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers.
|Virtual Private Network (VPN)|
A VPN is a private network that is constructed within a public network infrastructure such as the global Internet. Usinv VPN, a telecommuter can access the network of the company headquarters through the Internet by building a secure tunnel between the telecommuter's PC and a VPN router in the headquarters.
|There are three types of VPNS: Access VPNs, Intranet VPNs, and Extranet VPNs.|
|Intranets and Extranets|
|One common configuration of a LAN is an Intranet. Intranet Wreb servers differ from public Web servers in that the public must have the proper permissions and passwords to access the Intranet of an organization.|
|Extranets refer to applications and services that are Intranet based, and use extended, secure access to external users or enterprises. Therefore, an Extranet is the extention of two or more Intranet strategies with a secure interaction between participant enterprises and their respective intranets.|
|Bandwidth is defined as the amount of information that can flow through a network connection in a given period of time. It is limited by physics and technology, is not free, and is crucial to network performance.|
|Bandwidth is finite. In other words, regardless of the media used to build the network, there are limits on the capacity of tht network to carry information. Bandwidht is limited by the laws of physics and by the technologies used to place information on the media. For example, the bandwidth of a conventional modem is limited to about 56kbps by both the physical properties of twisted-pair phone wires and by modem technology. However, the technologies employed by DSL also use the same twisted-pair phone wires, yet DSL provides much greater bandwidth than is available with conventional modems. So, even the limits imposed by the laws of physics are soetimes difficult to define. Optical fiber has the physical potential to provide virtually limitless bandwidth. Even so, the bandwidth of optical fiber cannot be fully realized until technologies are developed to take full advantage of its potential.|
|Bandwidth is not free. It is possible to buy equipment for a local-area network (LAN) that will provide nearly unlimited bandwidth over a long period of time. For WAN connections, it is almost always necessary to buy bandwidth from aservice provider. In either case, an understanding of bandiwdth and changes in demand for bandwidth over a given time can save an individual or a business a significant amount of money. A network manager needs to make the right decisions about the kinds of equipment and services to buy.|
|Bandwidth is a key factor in analyzing network performance, designing new networks, and understanding the internet. A networking professional must understand the tremendous impact of bandwidth and throughput on network performance and design. Information flows as a string of bits from computer to computer throughout the world. These bits represend massive amounts of information flowing back and forth across the globe in seconds or less.|
|The demand for bandwidth is ever increasing. As soon as net network technologies and infratstructures are built to provide greater bandwidth, new applictions are created to take advantage of the greater capacity. The delivery over the network of rich media content, including streaming video and audio, requires tremendous amounts of bandwidth. IP telephony systems are now commonly installed in place of traditional voice systems, which further adds to the need for bandwidth. The successful networkiung professional must anticipate the need for increased bandwidth and act accordingly.|
|Analogies of Bandwidth|
|Bandwidth is like the width of a pipe. A network of pipes brings fresh water to homes and businesses and carries waste water away. This water network is made up of pipes of different diameters. The main water pipes of a city may be two meters in diameter, while the pipe to a kitchen paucet may have a diameter of only two centimeters. The width of the pipe determines the amount of flow possible. The water is like data.|
|Bandwidth is like the number of lanes on a highway. A network of roads serves every city or town. Large highways with many traffic lanes are joined by smaller roads with fewer traffic lanes. These roads lead to even smaller, narrower roads, which eventually go to the driveways of homes and businesses. When fewer cars are on the road, they may move freely, but as traffic increases, congestion develops and the cars take longer to reach their destinations.|
|Measurement of Bandwidth|
|In digital systems, the basic unit of bandwidth is bits per second (bps). Bandwidth is the measure of how much information, in bits, can flow from one place to another in a given amount of time (seconds). Network bandwidth is typically described as thousands (kbps), millions (Mbps), billions (Gbps), and trillions (Tbps) of bits per second.|
|Limitations of Bandwidth|
|Typical Media||Maximum Theoretical Bandwidth||Maximum Theoretical Distance|
|50-Ohm Coaxial Cable|
(10BASE2 Ethernet; Thinnet)
|10 Mbps||185 m|
|50-Ohm Coaxial Cable|
(10BASE 5 Ethernet; Thicknet)
|Cat 5 Unshielded Twisted Pair (UTP)|
|10 Mbps||100 m|
|Cat 5 Unshielded Twisted Pair (UTP)|
|Cat 5 Unshielded Twisted Pair (UTP)|
|Multimode Optical Fiber (62.5/125mm)|
|Multimode Optical Fiber (62.4/125mm)|
|Multimode Optical Fiber (50/125mm)|
|WAN Service||Typical User||Bandwidth|
|DSL||Individuals, telecommuters, small businesses||128kbps - 6.1Mbps|
|ISDN||Telecommuters, small businesses||128kpbs|
|Frame Relay||Small institutions (schools), reliable WANs||56kbps - 44.736Mbps (US) or 34.368Mbps (Europe)|
|Throughput of Bandwidth|
|Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network.|
|Variables That May Affect Throughput|
|The following are some of the factors that determine throughput:
|Transfer Time Calculation|
|Best Download: T = (S/BW)|
Typical Download: T = (S/P)
|BW: Maximum theoretical bandwidth of the "slowest link" between the source host and destination host|
P: Acutal throughput at the moment of transfer
T: Time for transfer to occur (seconds)
S: File size in Bits
|Digital vs. Analog|
|Radio, television, and telephone transmissions have, until recently, been sent through the air and over wires using electromagnetic waves. These waves are called analog because they have the same shapes as the light and sound waves produced by the transmitters. As light and sound waves change size and shape, the electrical signal that carries the transmission changes proportionally. In other words, the electromagnetic waves are analogous to the light and sound waves.|
|Analog bandwidth is measured by how much of the electromagnetic spectrum is occuppied by each signal. The basic unit of analog bandwidth is hertz (Hz), or cycles per second. Typically, multiples of the basic unit of analog bandwidth are used, just as with digital bandwidth. Units of measurement that are commonly seen are KHz, MHz, and GHz.|
|While analog signals are capable of carrying a variety of information, they have some significant disadvantages in comparison to digital transmissions. The analog video signal that requires a wide frequency range for transmission cannot be squeezeed into a smaller band.|
|It is important to understand the differences and similarities between digital and analog bandwidth. Both types are regularly encountered in the field of IT. However, this course is primarily concerned with digital networking, so 'bandwidth' will refer to digital bandwidth.|