We use many different devices to connect our enterprise networks. In this video, you’ll learn about switches, routers, access points, cable modems, and other common networking devices.
A hub is a basic form of Ethernet connectivity. This is a picture of a very small, four-port hub. Sometimes you’ll hear hubs referred to as a multi-port repeater, because anything you put into one port on that particular hub will be repeated to all of the other interfaces on that hub. Because of that, we often refer to a hub as an OSI Layer 1 device, because it’s not really making any intelligent decision about where it’s sending that data, it’s simply receiving information on one interface and sending that data to every other interface on that hub.
If you’re using a hub, then everything connected to this hub is operating at half duplex. This means that you can either send information to the hub, or receive information from the hub, but you can’t do both of those at the same time. This also means, as the activity and traffic on the network increases, the efficiency of the network decreases because you are not able to send traffic while anyone else is sending traffic. You’ll find hubs that are available at 10 megabit per second and 100 megabit per second speeds, but you won’t find any gigabit or higher speed hubs available. In fact, hubs themselves are difficult to find these days. If you did manage to find a hub, then you’ve probably found it on a secondary market, or on some third party site, on eBay. Most of the time, we’re using switches instead of hubs in our networks today.
Before the advent of switches, though, we still were able to separate networks, and send traffic between those networks, based on destination MAC address. And we did that by using a technology called a bridge. You can think of this as a switch that has a limited number of ports on it– usually two to four ports on a traditional bridge– and most of the decisions on where data is forwarded take place in the software of that bridge. Bridges can connect networks that are similar to each other, or they may be connecting two different topologies together. Because the bridge is commonly making a forwarding decision based on a MAC address, we refer to this as an OSI Layer 2 device. If you were looking for a more modern version of a bridge, you can look to a Wireless Access Point, which is bridging between a wired Ethernet connection, and an 802.11 wireless connection.
Another modern type of bridge is a switch. This is effectively doing exactly the same function as a bridge, because it’s making forwarding decisions based on the destination MAC address of the data. One of the most significant differences between the traditional software-based bridge and today’s modern switches is that switches are able to make these decisions in hardware. More specifically, in ASIC, which is Application-Specific Integrated Circuit.
As we mentioned, our modern switches are making forwarding decisions based on that MAC address, so these would be OSI Layer 2 devices. Another significant difference between traditional bridges and today’s modern switches is that we can have tens or even hundreds of interfaces on our switches. It’s common to see these switches not only in the core of our networks, but in the edges of the networks as well. These switches also can provide additional features. For example, many switches will provide Power over Ethernet, or PoE, so that you can simply plug-in an access point, or Voice-over-IP phone, and have that device powered through the switch.
Some manufacturers have improved on a switch by adding routing functionality within the switch as well. So instead of having a separate switch and a separate router, they’ve taken all of that functionality and put it into the same physical device. You’ll often hear these devices referred to as a marketing term of Multilayer Switch, although these devices truly are partly switch and partly router, all within the same physical component.
This routing functionality can be very useful if you need to connect two different IP subnets. To be able to perform this, we need a router, which makes decisions based on the IP address, or the OSI Layer 3 address, of the network traffic. Although we don’t refer to them as routers, if you have a device that is both a switch and a router, you’ll sometimes see those devices referred to as a Layer 3 switch. These devices actually have a switch inside, operating at Layer 2, and they also have a router inside that operates at Layer 3.
It’s very common to use routers to also connect different types of networks across different IP subnets. So you may use a router to connect a LAN to a WAN, or perhaps between copper and fiber connections. In our homes, we commonly have a wireless router that has both a Wireless Access Point and a router and a switch inside of the same device. In our enterprise, we usually let the routers do the routing, and for wireless connectivity, we use an access point. As we mentioned earlier, our wireless access point is a bridge. So we are able to bridge between our wired ethernet and our wireless 802.11 networks. These access points are making the forwarding decisions between the wired and the wireless network based on the MAC address; therefore we refer to these as an OSI Layer 2 device.
If you’re using a cable company for your internet connectivity, then you probably have a cable modem. This is connecting to a broadband network. That means you’re transmitting information across this network over multiple frequencies. This means that you can have many different traffic types, or even television channels, using different frequencies on the same cable that you’re connecting to the cable modem. The data frequencies on that cable are separated out by the cable modem in a standard called DOCSIS, that stands for Data Over Cable Service Interface Specification. And these DOCSIS standards can support a wide range of speeds. It’s common to see cable networks that are running at 4 Megabit through 250 Megabits, and these days you might even find cable networks that are providing Gigabit speed connectivity or higher. Some cable modems will also support video and voice connectivity, along with the internet connection.
If you’re not using a cable modem for your internet connection, you might be using a DSL modem. DSL stands for Digital Subscriber Line, and this is commonly an Asymmetric Digital Subscriber Line, or ADSL. ADSL uses existing telephone lines to provide this internet connection, using a DSL modem. The A in ADSL is Asymmetric, which means that the download speeds are going to be faster than your upload speeds. And those speeds are going to vary based on how far away you are from the central office. Usually, there’s about a 10,000 foot limitation for receiving a DSL signal in your home. Normally, you’ll find DSL speeds that range around 52 Megabits downstream and 16 megabits upstream, but you might get even faster speeds if you happen to be closer to the central office.
If you need to extend a network connection beyond the standard range, then you might want to use a repeater. A repeater receives a signal, regenerates the signal, and sends that signal out another interface. This means that the repeater is not making any forwarding decisions, it’s simply taking data into one interface and sending it out another. Repeaters are commonly used to boost the signal over a copper or fiber connection, but they might also be used to connect one type of media to the other. For example, this particular repeater is connecting a 100 Megabit fiber connection to a 100 Megabit copper connection.
This conversion process is occurring at the physical layer, or OSI Layer 1. If you are repeating a signal over very long distance, and changing the type of topology you’re using, then it would be more accurate to call this a converter rather than a repeater. For example, you might have fiber that you’ve run between two buildings over a very long distance, and you need to connect a switch that only has copper ports. Well, if you use one of these converters in the middle, you can convert between fiber to copper, and then plug that copper connection into your switch. Although you can’t see it in this picture, there’s usually a power connection in the back so that it can perform that conversion between the different media types.