# Intro and Topologies

Video Activity
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Time
9 hours 49 minutes
Difficulty
Beginner
CEU/CPE
10
Video Transcription
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>> We'll continue on into
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Module 3 of our Network Plus course.
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Module 3 is going to cover network infrastructure.
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As we move into the objectives,
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I want to give a heads up that this is
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a lengthy section because there's
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so much network infrastructure.
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First, we'll discuss network topology.
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From a bird's eye view,
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that's how everything is connected together.
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The physical network topology.
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We'll cover logical topology as well,
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which is more about how data moves on the network
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and how individual systems are able to communicate.
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Then we'll focus on
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wired communication and media that we use.
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We'll discuss twisted pair
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coaxial cable and fiber optic as well.
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From there, we'll move into wireless communication
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and its specifics and wireless security.
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Next, we'll look at network connectivity devices,
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how we connect these elements together,
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and the fact that different devices are
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going to provide different functionality.
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We'll try to remove some of
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layer 3 switches, VLANs,
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and the various devices.
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We'll also get a little bit deeper into
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switch and VLAN configuration.
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Then we'll move on to looking at
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routing configuration, firewalls,
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and how if we create these network segments
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we protect traffic flowing from segment to segment.
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Last but not least,
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As promised, we'll jump right into network topology.
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First, we'll discuss physical topology which is how
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the systems are arranged on the network
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and how they communicate with each other.
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Then logical topology.
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We'll cover how they communicate,
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who gets time on the cable,
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when and how that's determined.
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Starting out with physical topology,
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we'll begin with the bus network.
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This was a topology that was
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common when I first got into networking.
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A bus network involves a central segment of cable or
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a central trunk and usually that was fixed coaxial table.
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You see the individual nodes are hosts connected
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directly into the cable and use devices called
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vampire taps that will literally pierce into
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the coaxial cable to provide
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the connection with the termination on each end.
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Termination was there to prevent
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something called signal balance,
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where the signal just stays on
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the line and balances throughout the network.
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We had to have a termination on our cable.
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When looking at this diagram,
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be sure to realize that
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everybody is connected into the cable.
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There is no central point of
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connectivity other than the cable.
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What that means is that if the cable goes down,
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our network goes down.
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One of the things about coaxial cable needing to be
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terminated is if there's any break in the cable,
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there's a break in the termination,
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and therefore you'd have a signal balance.
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A single break in the cable could
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send the entire network down.
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The other thing was, it was
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difficult to trace that break in the cable.
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You've got this long segment of cable and knowing
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where the break happened could be very challenging.
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As for how these hosts communicate,
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it was a free for all because
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there's no device to direct traffic,
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and this was with early Ethernet networks.
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If you'll remember from previous chapters,
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we said Ethernet uses
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a media access mode called CSMA/CD,
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Carrier Sense Multiple Access with Collision Detection,
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meaning every host is going to sense the cable,
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determine if somebody else is transmitting,
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and if so, put their message out there.
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But other nodes could be listening at
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the same time and everybody
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put their message on the keyboard at the same time.
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If that's the case, we have collisions.
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In this environment because we're all
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in one giant collision domain,
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we're going to have a lot of collisions.
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It was just something that we dealt
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with using bus topologies.
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In this diagram, we have a physical bus.
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You can tell it by the central strand of
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cable or the central trunk of cable.
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It's also a logical bus,
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and a logical bus means a single collision domain,
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everybody fighting for time on the cable.
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This is one of those few instances
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where the logical meets the physical.
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Moving into ring topology.
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It's not difficult to figure out why it's called a ring.
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It's because each node is connected to each other,
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and it's connected in a ring end, ring out fashion.
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Node 1 would connect to ring 1 on node 2.
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Then node 2 would use ring out to
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connect to node 3, and so on.
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In a triggering environment,
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any break in the cable would take the network
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down and so would any node that
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was malfunctioning because node's 1 job
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is to pass the ring to node 2.
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If we have a malfunctioning node that
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can also bring the network down,
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so that gets up very tricky.
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In most ring topologies,
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you have a single frame that traverses the network.
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A host has to grab or
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capture that frame in order to communicate.
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There's only one frame and you
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can't communicate without it,
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so typically we would have no collisions.
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Again, exactly as it is,
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this is a ring topology.
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Because there's a token traversing this ring,
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it's a ring from both the
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physical and logical perspective.
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A concern here is that there's way too
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much dependent on single points of failure.
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Often what we do is bring in a device
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called a multi-station access unit.
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Rather than physically connecting
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those nodes to this idea of a ring,
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we would connect it into the central device
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that when put in the middle, look like a star.
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If you can envision a device in
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the middle that all nodes connect directly to,
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that's node going to give you a star physically,
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but a ring logically.
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Here's our star. It looks
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like a star and you can see why.
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What we have is nodes connecting into
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a hub as our central point of connectivity.
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Here's the thing about a hub.
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It sends all data out all ports all the time.
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We really have a physical star,
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but a logical bus because
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we're one giant collision domain.
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If we change that device in the middle to a switch,
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then we would have a physical star
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and a logical star because
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the switch is going to direct traffic
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out of the appropriate ports.
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If you think about the main star bus ring,
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you have the physical topology,
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which I show they look in the diagram.
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Then you have the logical topology,
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which is really more about how traffic is directed.
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There are other types of topology, specifically mesh.
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With the mesh, every node is
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connected to every other node.
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That can be expensive,
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so many times for redundancy,
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we might use a partial mesh,
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which is going to allow multiple paths
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to get traffic from one spot to another.
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You can see partial mesh can pair
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to a full mesh and see,
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there's going to be a lot more expensive because we have
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all these connections from node to node to node.
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That's extremely fault tolerant.
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We might need that if we're talking about
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WAN connectivity for multiple offices,
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but as far as seeing something like that
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in LAN, probably not.
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We also have hybrid technologies.
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You might see a star bus or
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a star ring or any combination of the topologies.
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That will be considered a hybrid.
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best as far as how communication is going to happen.
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Word of realism, we don't really
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use a lot of the ring topologies today.
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That's back in the day when we had
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a token ring and that's
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something that's gotten off the LAN.
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You may still see some of
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the ring topologies for metropolitan area networks,
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but it's not really something we see on the LAN.
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The star technology is very popular of course
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because we have various devices connected into switches.
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Sometimes we might have
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a long trunk connecting switch to switch,
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which would be a star bus.
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The truth is somewhere in the middle,
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we mix and match topologies as we need them.
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The bottom line, don't forget physical and logical.
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I think on the exam, we'll
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ask you to know the difference.
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When you're looking at a diagram,
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the first thing you'll want to look
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at is its shape, so to speak.
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If it's a central trunk or cable, you've got a bus.
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If it's connected ring, you've got a ring.
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If you're connected to a central device,
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that's a physical star.
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When it comes to logical topology though,
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it's more about how data is moved
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on the network and how traffic is
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directed and controlled to provide
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access for the individual nodes.
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