Chapter 5: Network Hardware PDF

CHAPTER FIVE Network hardware 1  Repeaters As signals travel along a cable, they degrade and become distorted in a process called "attenuation.“ If a cable is long enough, attenuation will finally make a signal unrecognizable. Installing a repeate...

CHAPTER FIVE Network hardware 1  Repeaters As signals travel along a cable, they degrade and become distorted in a process called "attenuation.“ If a cable is long enough, attenuation will finally make a signal unrecognizable. Installing a repeater enables signals energetic to travel farther log distance.  How Repeaters Work A repeater works at the physical layer of the OSI Reference Model to regenerate the network's signals and resend them out on other segments. The following figure shows how repeaters regenerate weak signals. 2  For a repeater to work, both segments that the repeater joins must use the same access method. The two most common access methods are CSMA/CD and token passing. 3  As shown below, repeaters can move packets from one kind of physical media to another. Repeaters can connect different types of media 4  Implementing a repeater: This section summarizes what you need to consider when deciding whether to implement repeaters in your network.  Use a repeater to: Connect two segments of similar or dissimilar media. Regenerate the signal to increase the distance transmitted. Connect two segments in the most cost-effective manner.  Do not use a repeater when: – There is heavy network traffic. – Segments are using different access methods. – Data filtering is needed. 5  Hubs One network component that become standard equipment in networks is the hub. There are three types of hub:- 1. Active hub 2. Passive hub 3. Hybrid hub 1 – Active hub Most hubs are active; that is, they regenerate and retransmit signals in the same way as a repeater does. Because hubs usually have eight to twelve ports, they are sometimes called multi-port repeaters. 6 2- Passive Hubs Some types of hubs are passive. Examples include wiring panels or punch-down blocks. They act as connection points and do not amplify or regenerate the signal. The signals simply pass through the hub. 3 - Hybrid Hubs Advanced hubs that will accommodate several different types of cables are called hybrid hubs. The following figure shows a main hub (the hybrid) with three sub-hubs. 7  Hub Considerations  Hub-based systems are versatile and offer several advantages over systems that do not use hubs.  Hub-based topologies include the following benefits: Wiring systems can be changed or expanded as needed. Different ports can be used to accommodate a variety of cabling types. Monitoring of network activity and traffic can be centralized 8  A hub can be used as the central hardware component in a star topology. Hubs can also be used to expand the size of a LAN. Ethernet hubs connected Token-ring hubs in a series connected into one large ring 9  In a Token Ring network, the hub is known by several names that all mean the same thing. These include: MAU (Multi-station Access Unit). MSAU (Multi-station Access Unit). SMAU (Smart Multi-station Access Unit). Hub Capacity An IBM MSAU has 10 connection ports. It can connect up to eight computers. However, a Token Ring network is not limited to one ring (hub). Each ring can have up to 33 hubs. 10  Adding hubs while maintaining the logical ring 11  Switch In recent years, a new device, switch, has replaced the hub in popularity. It is sometimes referred to as a switching hub. Switches maintain MAC table in order to switch packets to the proper host. Switching is faster than routing! (why??) – Reads the frame header rather than the packet header. – No modification to the data packet. 12  Switch functions – Address learning From source MAC addresses – Forward / filter decisions Switching modes – Store and forward Frame will be stored in memory and will be check for errors. Frame will be discarded if it contains errors. Safest but with highest latency. – Cut-through The switch reads the frame until it learns the destination MAC. Once the destination MAC is known, the switch forwards the frame right away. No delay or error checking 13  Switches provide independent bandwidth on each port, unlike hubs. The following figure shows five hosts connected to a switch—all running 10Mbps half duplex to the server. Unlike a hub, each host has 10Mbps dedicated communication to the server. 14  Bridges  Bridge is a network device , which used to connect two or more LANs.  Functions of a Bridge The following figure illustrates the operation of a bridge between two LANs, A and B. The bridge performs the following functions: * Reads all frames transmitted on A, and accepts those addressed to stations on B. * Using the medium access control protocol for B, retransmits the frames onto B. * Does the same for B-to-A traffic. 15 16  Bridges work at the MAC sub-layer and are sometimes referred to as MAC-layer bridges.  A MAC-layer bridge: Listens to all traffic. Checks the source and destination addresses of each packet. Builds a routing table, as information becomes available. Forwards packets in the following manner:  If the destination is not listed in the routing table, the bridge forwards the packets to all segments.  If the destination is listed in the routing table, the bridge forwards the packets to that segment (unless it is the same segment as the source). 17  Creating the Routing Table Bridges build their routing tables based on the addresses of computers that have transmitted data on the network. Specifically, bridges use source addresses—the address of the device that initiates the transmission—to create a routing table. – When the bridge receives a packet, the source address is compared to the routing table. If the source address is not there, it is added to the table. The bridge then compares the destination address with the routing-table database. 18  If the destination address is in the routing table and is on the same segment as the source address, the packet is discarded. This filtering helps to reduce network traffic. 19  The routing table allows bridges to segment networks Therefore, bridges can use routing tables to reduce the traffic on the network by controlling which packets get forwarded to other segments. This controlling (or restricting) of the flow of network traffic is known as "segmenting network traffic." 20  Remote Bridges Bridge is powerful device in expanding and segmenting networks. They are often used in large networks that have widely dispersed segments joined by telephone lines. 21  Routers  Router is a networking device with: – Capable of knowing the address of each segment, – Determine the best path for sending data and – Filtering broadcast traffic to the local segment.  Routers work at the network layer of the OSI reference model. They can switch and route packets across multiple networks.  Routers have access to more information in 22 packets than bridges.  How Routers Work Routers maintain their own routing tables, usually consisting of network and host addresses. To determine the destination address for incoming data, the routing table includes: – All known network addresses. – Instructions for connection to other networks. – The possible paths between routers. – The costs of sending data over those paths. As shown below, a router uses its data-routing table to select the best route for the data based on costs and available paths. 23 Routers communicate with other routers, but not with remote  Note: computers. The routing table maintained by a bridge contains MAC- sub layer addresses for each node. The routing table maintained by a router contains network Addresses. 24  When routers receive packets destined for a remote network, they send them to the router that manages the destination network.  Since routers must perform complex functions on each packet, routers are slower than most bridges.  Routers do not look at the destination node address; they look only at the network address.  Since routers do not pass or even handle every packet, they act as a safety barrier between network segments. – This can greatly reduce the amount of traffic on the network. – The wait time experienced by users. 25  Choosing Paths - Unlike bridges, routers can accommodate multiple active paths between LAN segments and choose among redundant paths.  A router can listen to a network and identify which parts are busiest.  It uses this information to determine which path to send data over. Types of Routers The two major types of routers are: – Static – Dynamic 26  Static router It requires an administrator to manually set up and configure the routing table and to specify each route.  Dynamic router It is designed to discover routes automatically. 27  Characteristics of the Two Types of Routers Static routers Dynamic routers Manually set up and configure Manually configure the first all routes. route. Automatically detect additional networks and routes. Always use the same route, Can choose a route based on determined by a routing table factors such as cost and amount entry. of link traffic. Use a hard-coded route Can decide to send packets over (designed to handle only a alternate routes. specific situation), not necessarily the shortest route. Are considered more secure Can improve security by because the administrator manually configuring the router 28  Bridges work at the data-link layer MAC sub-layer. Routers work at the network layer. 29 30 Thank you!! 31