Introduction to LAN Switching LAN segmentation 4.2.1 This page will explain LAN segmentation. A network can be divided into smaller units called segments. Figure shows an example of a segmented Ethernet network. The entire network has fifteen computers. Of the fifteen computers, six are servers and nine are workstations. Each segment uses the CSMA/CD access method and maintains traffic between users on the segment. Each segment is its own collision domain. Segmentation allows network congestion to be significantly reduced within each segment. When data is transmitted within a segment, the devices within that segment share the total available bandwidth. Data that is passed between segments is transmitted over the backbone of the network through a bridge, router, or switch. The next page will discuss bridges LAN segmentation wit 4.2.2 This page will describe the main functions of a bridge in a LAN. Bridges are Layer 2 devices that forward d...
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The benefits of using repeaters 4.1.8 This page will explain how a repeater can be used to extend the distance of a LAN. The distance that a LAN can cover is limited due to attenuation. Attenuation means that the signal weakens as it travels through the network. The resistance in the cable or medium through which the signal travels causes the loss of signal strength. An Ethernet repeater is a physical layer device on the network that boosts or regenerates the signal on an Ethernet LAN. When a repeater is used to extend the distance of a LAN, a single network can cover a greater distance and more users can share that same network. However, the use of repeaters and hubs adds to problems associated with broadcasts and collisions. It also has a negative effect on the overall performance of the shared media LAN. The Interactive Media Activity will teach students about the Cisco 1503 Micro Hub. The next page will discuss full-duplex technology. Full-duplex tr...
Network latency 4.1.6 This page will help students understand the factors that increase network latency. Latency, or delay, is the time a frame or a packet takes to travel from the source station to the final destination. It is important to quantify the total latency of the path between the source and the destination for LANs and WANs. In the specific case of an Ethernet LAN, it is important to understand latency and its effect on network timing as it is used to determine if CSMA/CD will work properly. Latency has at least three sources: First, there is the time it takes the source NIC to place voltage pulses on the wire and the time it takes the destination NIC to interpret these pulses. This is sometimes called NIC delay, typically around 1 microsecond for a 10BASE-T NIC. Second, there is the actual propagation delay as the signal takes time to travel through the cable. Typically, this is about 0.556 microseconds per 100 m for Cat 5 ...
Network congestion 4.1.5 This page will discuss some factors that create a need for more bandwidth on a network. Advances in technology produce faster and more intelligent desktop computers and workstations. The combination of more powerful workstations and network intensive applications has created a need for greater network capacity, or bandwidth. All these factors place a strain on networks with 10 Mbps of available bandwidth and that is why many networks now provide 100 Mbps bandwidth on their LANs. The following are types of media that have increased in transmission over networks: Large graphics files Full-motion video Multimedia applications There is also an increase in the number of users on a network. As more people utilize networks to share larger files, access file servers, and connect to the Internet, network congestion occurs. This results in slower response times, longer file transfers, and less productive network users. To relieve ne...
Half-duplex networks 4.1.4 This page will explain how collisions occur on a half-duplex network. Originally Ethernet was a half-duplex technology. Half-duplex allows hosts to either transmit or receive at one time, but not both. Each host checks the network to see whether data is being transmitted before it transmits additional data. If the network is already in use, the transmission is delayed. Despite transmission deferral, two or more hosts could transmit at the same time. This results in a collision. When a collision occurs, the host that detects the collision first, sends out a jam signal to the other hosts. When a jam signal is received, each host stops data transmission, then waits for a random period of time to re-transmit the data. The back-off algorithm generates this random delay. As more hosts are added to the network, collisions are more likely to occur. Ethernet LANs become saturated because users run network intensive software, such as client/server appli...
Factors that impact network performance 4.1.2 This page will describe some factors that cause LANs to become congested and overburdened. In addition to a large number of network users, several other factors have combined to test the limits of traditional LANs: The multitasking environment present in current desktop operating systems such as Windows, Unix/Linux, and Mac OS X allows for simultaneous network transactions. This increased capability has lead to an increased demand for network resources. The use of network intensive applications such as the World Wide Web has increased. Client/server applications allow administrators to centralize information and make it easier to maintain and protect information. Client/server applications do not require workstations to maintain information or provide hard disk space to store it. Given the cost benefit of client/server applications, such applications are likely to become...
Introduction to Ethernet/802.3 LANs 4.1.1 Ethernet/802.3 LAN development This page will review the devices that are found on a network. The earliest LAN technologies used either thick Ethernet or thin Ethernet infrastructures. It is important to understand the limitations of these infrastructures, as shown in Figure , in order to understand the advancements in LAN switching. The addition of hubs or concentrates into the network offered an improvement on thick and thin Ethernet technology. A hub is a Layer 1 device and is sometimes referred to as an Ethernet concentrate or a multi-port repeater. Hubs allow better access to the network for more users. Hubs regenerate data signals which allows networks to be extended to greater distances. Hubs do not make any decisions when data signals are received. Hubs simply regenerate and amplify the data signals to all connected devices, except for the device that originally sent the signal. Ethernet is fundamentally a sh...
Module 4: Switching Concepts Overview LAN design has evolved. Network designers until very recently used hubs and bridges to build networks. Now switches and routers are the key components in LAN design, and the capabilities and performance of these devices continue to improve. This module describes the roots of modern Ethernet LANs with an emphasis on the evolution of Ethernet/802.3, the most commonly deployed LAN architecture. A look at the historical context of LAN development and various network devices that can be utilized at different layers of the OSI model will help students better understand the reasons why network devices have evolved as they have. Until recently, repeaters were used in most Ethernet networks. Network performance suffered as too many devices shared the same segment. Network engineers then added bridges to create multiple collision domains. As networks grew in size and complexity, the bridge evolved into the modern switch which allows microsegmentat...