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Hubs and switches are key components of your Local Area Network (LAN). They connect network devices so data can flow from computer to computer, computer to printer, or computer to the Internet. Hubs and Switches look very similar and they perform the same basic functions. However, there are key differences that separate the two.

• Hubs do not perform “traffic control” on the local area network (LAN). Switches do.

• Many switches offer advanced configuration options such as the ability to create Virtual Local Area Networks. Some hubs have very basic management features, but most do not allow for any configuration.

• Computers connected to a switch can send and receive data at the same time, thus increasing the bandwidth. Hubs do not permit this.

Hubs

Let's look at how a hub operates. When a computer connected to a hub has data to transmit, it starts by getting the data packaged up for delivery. This happens at the Network Interface Card (NIC) in the computer. Once the data is packaged, it is sent out of the NIC onto the network medium. In most cases this medium is twisted-pair copper cable (LAN cable, Ethernet cable, CAT5, data cable). The signals travel along the cable until they reach the hub at the other end. At this point the hub takes the data package, now in the form of electrical signals, and retransmits it out of every one of its ports to devices at the other end.

When the data reaches each network device, that device's NIC will do a quick check of the data. If the data is not addressed for that device, it will immediately refuse delivery. The intended recipient will accept the data and process it further.

In the diagram, we see computer “A” sending a message to computer “B”. The arrows represent the data. The message leaves “A” and once it gets to the hub it is sent out to every computer on the network.

The key point here is that hubs retransmit the data out of every port. As a result, every device interacts with all data from every other device. Network devices connected by hubs spend a fair amount of time refusing data and waiting for a chance send their data. This makes things somewhat “noisy” on the network and can result in a slow network. This is not to say you should throw out your hubs. Hubs are perfect for smaller networks running the usual network services, such as file sharing and Internet services. It is when networks grow and network applications become more sophisticated that hubs may not be the best choice.

Switches

What if the hub knew which port serviced each network device? If the hub received data addressed to “bob's PC” and was able to send it out of the port that “bob's PC” was plugged into, then the other devices on the network would not have to contend with all of that extra traffic. This is what a switch does. It is the main difference between hubs and switches. A switch will learn which port services each network device. The switch builds a table for this information. When the switch receives data, it checks the destination on its table. When it finds a match, it sends the data out of the appropriate port.

In the diagram above, “PC a” is sending data to “PC b”. Again, the arrows represent the data. The data leaves “PC a” with a specified destination of “PC b”. When the data reaches the switch, the destination address is checked against the table the switch has built. The switch sees that “PC b” is located off of port 2 on the switch. The data is directed out of port 2. PCs c, d, and e are not interrupted by this exchange.

A popular analogy for the advantages of using switches is that of the busy road. If a driver is attempting to pull out on to a busy road, he will have to wait until there is a break in the traffic. Once the driver sees a break in traffic, he races into the opening and is off to his destination. If the driver had his own private road he could pull out and race off to his destination whenever he wanted. He would not have to wait because there are no other cars on the road. Connecting a computer to a switch is like giving it its own private road into the network. It can transmit and receive data whenever it wants.

Design options

In the example above, the switch ports and computers are on one-to-one connections. Each computer has its own switch port. This is fine if you have enough switch ports. If your PCs outnumber your switch ports, an option is to connect a hub to a single switch port. In such a scenario the switch would keep much of the traffic isolated to that segment. The switch will let traffic in and out of the segment according to the table it has built. In the diagram below, the switch connects several segments that were created by connecting a hub to the switch and then connecting hosts to the hub. The PCs on each hub will compete for bandwidth but the rest of the network is safe from most of their “noise.” You will also notice that the network server and Internet connection each have their own private connection to the switch. This is good design. The Internet connection and file server are shared and presumably heavily used resources. They need the bandwidth benefits of their own switch port.

Cost

Recent price drops have made switches a viable alternative to hubs in even the smallest networks. At these low prices many organizations can choose to replace aging hubs with switches as the hubs expire. A couple points to keep in mind about cost as you consider purchasing switches:

• Basic “non-managed” switches - that is, those with no software or hardware configuration options -- are very affordable. They often are priced the same (or lower!) than standard hubs. It may even be difficult to find a standard hub, as most vendors are now automatically including switching technology with their products. High-quality 24-port 10/100 switches can be purchased for less than $200.00. Prices are always going down.

• Important considerations at this price level are the warranty and replacement policy offered by the vendor. Many vendors offer limited lifetime warranties on their switches that cover everything but the power supply and fans, which of course, are the two parts most likely to malfunction.

• Entry-level "managed switches" from various vendors - the type that have an interface allowing the user to make hardware and software changes -- will generally cost between $21 and $30 per port. This means that a high-quality, 24-port managed switch can be purchased for between $500 and $750. Additional features, like expansion slots, extended support, and support of higher speeds or different media technologies (i.e. fiber) can increase this cost.

• Some high-end switches can cost tens of thousands of dollars or more. Do not be scared away by these prices. These switches are used in large corporate networks with hundreds or thousands of users. They are very likely not what you need.

• Remember that you are not limited to one computer per switch port. A hub, or even another switch, can attach to a switch port to expand the number of users on the switch.

Summary

In almost all instances, putting a switch at the core of your network will improve the performance of your network. Connecting your important or most heavily used devices directly into the switch (i.e., servers, routers, the director's computer), and connecting existing hubs into a switch port, will help alleviate congestion and improve performance of the network for a very low cost.

For the lowest cost, choose unmanaged switches to replace hubs in your network. For more control or manageability of your network, choose a managed switch as the core connection point of your network. This will allow you to perform more advanced troubleshooting of problems on your network.