Transcript IST 201
IST 201 Chapter 8 Environments • Shared- media • • • • • lots of hosts accessing same medium common collision domain 10Base2 10Base5 10BaseT – using hubs • Extended Shared-media • longer cable runs using hubs/repeaters • extended collision domain • Point to Point • Dial up connection • User to ISP • No collisions Indirectly Connected Networks • Circuit-switched • electrical circuits maintained for length of communication • bandwidth is dedicated point to point connection • no collisions • Packet switched • shared media but logical point to point connection Collision Domain Devices • Layer 2 and Layer 3 devices break up collision domains • Segmentation: process of breaking up collision domains 5-4-3-2-1 Rule • • • • • • • • 5 sections of media 4 repeaters/hubs 3 sections w/connected hosts 2 sections – extension purposes only 1 collision domain Repeater latency Propagation delay reasons for the 4 repeater rule NIC latency Late collisions • Violating 5-4-3 rule • Collision after 64 bytes of the frame are transmitted • NICs aren’t programmed to resend after late collisions • Add delay – called consumption delay • Decreases network performance Segmentation • Breaking up the collision domain into smaller segments • Created by layer 2 devices (layer 3 also) • Leads to more efficient network • More bandwidth is available to each host Problem • If there’s too much traffic between segments, the switch or bridge can become a bottleneck. Broadcast Radiation • Bridges & switches forward broadcasts and multicasts • Broadcast radiation – amount of traffic caused by all the bridges/switches on a network forwarding broadcasts/multicasts • Degrades network performance Sources of Broadcasts/Multicasts • Workstations • Routers • Multicast applications ARP-Address Resolution Protocol • Has IP address of destination host • Needs MAC address of destination host • Sends a broadcast to all hosts to get MAC address. Broadcast Domains • A network segment consisting of a number of collision domains • Routers (Layer 3) divide broadcast domains. • Routers do not forward broadcasts from one network to another. Data Flow Responsibility • Layer 1 – transmission across the medium • Layer 2 – collision domain management • Layer 3 = broadcast domain management Segment • Section of network bounded by bridges/switches/routers • In a bus network – the continuous circuit connected with repeaters • PDU @ the transport layer