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Module 4.3: Repeaters, Bridges, & Switches

Module 4.3: Repeaters, Bridges, & Switches. Repeater Hub NIC Bridges Switches VLANs GbE. Hardware Components. Repeater Layer 1 device that provides physical and electrical connections.

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Module 4.3: Repeaters, Bridges, & Switches

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  1. Module 4.3: Repeaters, Bridges, & Switches • Repeater • Hub • NIC • Bridges • Switches • VLANs • GbE K. Salah

  2. Hardware Components • Repeater • Layer 1 device that provides physical and electrical connections. • It receives signals from one cable segment, regenerates, retimes, and amplifies them, and then transmits these “revitalized” signals to another cable segment. • Transmits in both directions • Joins two segments of cable • No buffering • No logical isolation of segments • Hub • Used to describe a repeater • Can be “repeater hub”, “switching hub”, bridging hub”. • NIC • Network Interface Card • Performs layer-2 functions: framing, error detection, and flow control. • Performs layer-1 functions by converting the bits into electrical signals using appropriate coding scheme. K. Salah

  3. Bridges • Layer 2 devices • Interconnects two or more individual LANs or LAN segments. • Desirable for separating traffic among segments. A segment is part of a LAN in which traffic is common to all nodes, i.e. it is a single continuous conductor, though it may include repeaters. • Split the segment with bridges/switches, if link utilization is more than 30%. • Store-and-forward devices. They capture the entire frame before deciding whether to filter or forward it. Frames with bad CRC are not forwarded. • Minimal buffering to meet peak demand K. Salah

  4. Bridges Standards • Transparent Bridges • Operate in promiscuous mode. • Bridging is transparent to stations, as if they are on one single LAN. • “plug and play” unit, learns addresses connecting to ports by examining source and destination addresses. • examines the destination address to forward or filter frames. • All broadcast and multicast frames are forwarded. • Source Routing Bridges • Sender provides routing information for frames. • Routing information includes local or remote destination address, and list of intermediate route designators. • A route designatorcontain 12-bit LAN number and 4-bit bridge number. • Every station has a map of the network (different routes to get to different destinations). • Routes can be configured manually or by performing route discovery. K. Salah

  5. Bridges Standards (cont.) Spanning Tree • Network loops can happen. Can cause broadcast storms that can bring the LAN down. • Spanning Tree algorithm resolves network loops. • Algorithm is based on graph theory. • Any connected graph, consisting of nodes and edges connecting pairs of nodes, there is a spanning tree of edges that maintains the connectivity of the graph but contains no closed loops. • Each LAN is a node and each bridge is an edge. • Specified in IEEE 802.1. It involves a brief exchange of messages among all bridges to discover the minimum-cost spanning tree. Whenever there is a change in topology, the bridges automatically recalculate the spanning tree. • Disabling B3-LAN4 port will result in a spanning tree. If B4 fails, the algorithm should enable this port again. K. Salah

  6. Switches • Switches can operate at different layers: layer 2, 3, 4, and 7.. • Basically a switch is hardware based, not software based. • Three types of layer 2 switches: • Store-and-Forward Switch • Similar to store-and-forward bridge. Store entire frame, check for errors, and then switch to the other ports, based on the destination MAC address. • Cut-Through Switch • The transmission of frame begins as soon as it reads the destination MAC address. Two switch fabric/matrix designs: • Crossbar • Backplane with bus speed > aggregate port speeds • Hybrid Switch • Reliability: store-and-forward. Turn ON when errors are high. • Low latency: cut-through. Turn ON when errors are low. K. Salah

  7. VLANs • VLAN is a logical grouping of nodes using Ethernet switches. Nodes don’t need to be connected physically to the same switch. A broadcast frame will be heard by all nodes within VLAN. • Benefits: • Isolates broadcasts • Frees up network from physical locations • Easily shares resources. A server can be part of multiple VLANs. • Performance. Easily can be enhanced by creating new VLANs. • Security. By containing who can listen to broadcast. • VLAN Membership (implicit tagging) • Port-based • MAC-based • Layer 3/IP • Combination of the above K. Salah

  8. Gigabit Ethernet • With GbE CSMA/CD • Network diameter shrinks to 25 meter. This is not a good option. • Therefore, minimum frame time was increased to 512 bytes. This give network diameter of 200 meter, but waste in bandwidth especially for small size data. • Most common use is point-to-point fame switching. • No CSMA/CD • We have now 10GbE that can go more than 50 km over SMF. K. Salah

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