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Another copper cable you may come across is a direct attachment cable or DAC cable.

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This cable comes in various lengths up to 15 meters.

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Uses Copper Twin X and has tsps on each end.

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An SFP or small form factor.

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Pluggable is a hot pluggable transceiver and may support various media types such as fibre or copper.

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This replaces G, bics or gigabit interface converters and the one shown here is an enhanced small form

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pluggable or SFP plus that supports data rates up to ten gigabits per second.

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So a DAC cable is inserted into an SFP plus slot and allows for a ten gigabit per second connection

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between two devices.

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Other SFP or SFP pluses will support fibre that can go to greater lengths.

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But this cable allows for ten gigabit copper connectivity between two devices over a short distance,

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such as seven metres.

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A roll over cable is a special cable used to connect to the consoles of networking devices.

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It allows you to connect from the serial port on your PC or laptop to the console of a router or switch.

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So if you've got a serial port or comm port on your PC, you can connect directly to the console of

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a router or switch using a rollover cable.

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However, a lot of modern day PCs don't have serial ports, so you'll need to get a USB to serial port

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converter, which has a USB connection on one side and a db9 male connector on the other side.

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This would allow you to connect a DB nine female console cable to your PC with either a RJ 45 connector

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on the other side or another DB nine connector.

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Most Cisco switches and routers use an RJ 45 connector, but you may come across some devices from other

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vendors such as HP that use a DB nine connector for the console port.

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So a DB nine serial would connect to your PC and either an RJ 45 or DB nine Serial would be connected

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to the console of the networking device that you want to configure in a rollover cable.

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All pins are inverted or rolled over, so pin one is connected to PIN eight, PIN two is connected to

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PIN seven, 3 to 6 and so forth and so on until you get to PIN eight, which is connected to pin one.

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You could use a standard Cat five or Cat six cable as a rollover cable, and then just change the peanuts

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on the ends from straight through to rollover.

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But typically this is not required as most networking devices are shipped with console cables.

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This video has explained a lot about Ethernet and data flows.

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In the next video, we'll look at how traffic is forwarded by hubs, bridges, switches and routers.

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Now that we've looked briefly at cabling, I'd like to explain how network devices operate and the first

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device that we're going to look at is a hub.

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A hub is a layer one device in the AC model and you would use a Cat five unshielded twisted pair cable

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with an RJ 45 connector to connect your laptop as an example to a port on a hub hubs onto very popular

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today and have been superseded by switches and I'll explain in a few minutes why but for now, let's

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assume that you are connecting your PC to a hub.

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It's important that you understand how a hub operates, however, because wireless operates in the same

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way, like a physical hub would.

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So when you connect to a wireless network, you'll often encounter the same issues that you would encounter

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when connecting to a physical hub.

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So for now, let's assume that you're connecting your PC physically to a hub.

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Hubs have multiple ports, and thus multiple devices can be connected to a hub at the same time.

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The number of ports available depends on the hub model.

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But as you can see in both of these examples, a hub has various ports that you can connect devices

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to.

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So in this topology, let's assume that you have four devices connected to a hub on ports, 1 to 4.

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It's important to realize that a hub is a physical layer device.

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It's not intelligent and does not understand the frames going through it.

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It's basically a multi port repeater and it will amplify or repeat the frames that it receives on one

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port out of all other ports.

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So it's once again simply a multi port repeater with no intelligence.

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The physical topology of a hub is a star topology.

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In a star topology you have a central device which in this case is a hub and devices hanging off that

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central device as spokes which resemble the spokes in a bicycle wheel.

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Each spoke device is connected to the central device with its own cable, and all transmission or communications

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between devices are through the central device.

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In other words, if A wants to communicate with sea, the traffic will flow through the hub and will

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not flow directly between the two devices.

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There were some major advantages to using hubs and UTP rather than ten based two.

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The first advantage is a cable break.

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If a cable broke in this topology, it would only affect device A and it would not affect the rest of

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the network.

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In ten bays two.

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If a cable broke, it would affect all devices in that network here.

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However, other devices such as C and B can still communicate, even though the cable is broken to device

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A, another advantage is that you can extend distances easily.

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A bus topology is limited in size in a ten based T environment such as this, the distance between a

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device such as A and the hub needs to be 100 meters.

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But you can extend the distance by adding another hub.

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In other words, you add another multiport repeater and repeat or regenerate the signal to extend the

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distance of the network to distances greater than 100 meters.

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So in this example, E could be 100 meters away from its hub, and the two hubs could be 50 meters apart.

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So in this example, we've extended the network further than the restriction of 100 meters.

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So device E could be 100 meters from its hub.

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It could be a cable length of 50 meters between the two hubs.

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An A could be 100 meters away from its hub.

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Our network now has a length of 250 meters, which is well over the limitation of 100 meters.

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Now there are restrictions on the number of hubs that you can daisy chain together, but the point is

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it's possible to extend the topology by adding more hubs and more devices to the network.

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These were therefore great reasons to move away from ten based two and ten based five and implement

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UTP or untrusted pair networks using hubs.

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Another advantage is that UTP cabling is cheaper and easier to manage and therefore it became common

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to use hubs and ten based rather than ten based two or ten based five in the past.