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Bridges, Hubs, and Switches

Bridges, Hubs, and Switches . Dijiang Huang. Extending the LAN. Why? Build larger (geographic) networks Communicate with more hosts Issues Signal Delay Signal Attenuation. Repeaters. A hardware device used to extend a LAN

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Bridges, Hubs, and Switches

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  1. Bridges, Hubs, and Switches Dijiang Huang

  2. Extending the LAN • Why? • Build larger (geographic) networks • Communicate with more hosts • Issues • Signal Delay • Signal Attenuation

  3. Repeaters • A hardware device used to extend a LAN • It connects directly to the physical medium (no access units used). • It amplifies all electrical signals that it receives.

  4. Repeaters • Limitations: • It amplifies all signals that it receives including noise (e.g. lightening) • Operates at physical layer. It does not recognize any protocols - so it copies packet collisions as well as valid packets. • A problem on one segment is propagated to all other segments. All segments are in one collision domain • No more than 4 repeaters in a LAN

  5. Repeaters - Application Segment on Floor 3 R3 Riser Segment Segment on Floor 2 R2 Segment on Floor 1 R1

  6. Bridges • Used to extend the range of LAN segments • Operates at Data Link level. Connects to segments just like nodes. • It propagates only complete / correct packets. Each segment becomes its own collision domain

  7. Bridge - Application • Packet forwarding regenerates data signal. Phase shifts, noise, etc. are removed. • As packets are forwarded, bridge “learns” which hosts are on each segment.

  8. Planning Bridged Networks • Bridges only propagate packets that are destined for other segments. • It thus allows simultaneous communications between hosts on the same segments. • Traffic studies can optimize the design of segments such that most communications happens within a segment, not between segments.

  9. Bridged Network Segment A Segment B Segment D Segment C Segment E Segment F Segment G Segment H

  10. Cycle of Bridges • Infinite transmission path loops may occur. • Bridges decide whether to forward packets based on a distributed spanning tree algorithm (DST)

  11. Hubs • Passive Hubs • Mechanical connection only (no amplification) • Active Hubs • Provides regeneration of signal • Intelligent Hubs (Switching Hubs) • Adds traffic routing • May add network management capabilities.

  12. Hubs (Active Hubs) • Used with xBaseT Ethernet technologies. • Hub regenerates each bit. • Operates at physical level and amplifies signal • Also known as multi-port repeaters • Signals are forwarded to all other ports on the hub.

  13. 10BaseT Hub • Used to interconnect Hosts on a LAN

  14. Backbone Hub • Used to interconnect LANs • All segments are part of the same collision domain

  15. Switched Hubs (Switches) • Each port “learns” which hosts are connected to it • Only packets destined for those hosts are forwarded to that port. • Lower traffic load means fewer collisions, so higher throughput. • Since it uses an xBaseT 4-wire interface, it may support full duplex transmission.

  16. Switched Hub Architecture

  17. Summary • Repeaters • Used to extend length of segment • Bridges • Used to forward packets between LANs • Hubs • Used to interconnect hosts • Switches • Used to forward packets between Hosts / LANs

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