A user's perception of how good a network is will generally be based on two main factors: speed and reliability. These demands, coupled with the need to accommodate ever more bandwidth-hungry applications, means that network administrators are under continual pressure to provide a faster and more reliable system. So how do you give your growing Ethernet LAN a performance boost, without implementing complicated upgrades that could affect the stability of your network? One common strategy is to replace existing 10BaseT Ethernet hubs with switches. In this article, we'll look at how Ethernet switches can make your network faster and examine what factors you should consider before purchasing.
Ethernet switches are not a new technology, having been popular in corporate environments for a number of years. In such environments, where speed is a priority over cost, switches are pretty much the standard. However, in smaller LANs, and LANs that have been in place for some time, Ethernet hubs are still working away, albeit slowly.
Replacing your Ethernet hubs with switches can yield massive improvements in performance. Not only are switches capable of making same-speed transmissions faster than hubs, they can also unleash performance improvements in equipment that you already have. For example, many older hubs have transmission speeds of only 10Mbps, but many newer PC's have network cards with 100Mbps capability. Plug a 100Mbps network card into a 10Mbps hub, and you will have a 10Mbps connection. Plug the same 100Mbps network card into a 100Mbps switch, and it is possible to achieve data transmission speeds of 200Mbps, as well as gaining the speed improvements provided by the basic process of switching.
How switches improve performance
|Layer 2 and Layer 3 switches
Layer 2 switches: Because switches make their forwarding decisions by using the MAC address, they are often referred to as Layer 2 switches in reference to the second layer of the OSI data model.
Layer 3 switches: You can also buy Layer 3 switches, which have the capability to make their decisions based on the network address or service as defined by the third layer of the OSI model. Some high-end switches use a combination of methods, switching at the most appropriate layer depending on the configuration. The high level of flexibility found in switches means that they can also be used for other network configuration tasks, such as the establishment of virtual LANs (VLANs).
To understand how using switches can make such a difference in performance, let's quickly review how Ethernet networks function. When a computer connected to an Ethernet network wants to send data, it listens for any other traffic on the network segment; when the computer determines the media is clear, it attempts to transmit. Because Ethernet is a base-band technology, only one signal can use the cable at a time. So, if two machines attempt to talk at exactly the same time, their transmissions collide, damaging the data.
The network cards of the sending PCs sense the collision, wait for a random time period, and then attempt to resend the data. If the cable is clear this time, the transmission is completed. If it isn't, and another collision occurs, the re-transmit process repeats. This collision-based system means that the more devices connected to an Ethernet segment, the more likely collisions are to occur, degrading performance exponentially. Switching provides vast improvements in speed by literally preventing these collisions.
In a switched network, each station has its own dedicated segment. The sending PC doesn't have to consider that another device may be using the segment, which eliminates the possibility of collisions. The isolation of devices in this way is known as microsegmentation. With a switch in place, when the PC wants to send data, it transmits directly to the switch without having to wait. The switch examines the data, determines from the destination Media Access Control (MAC) address which other port on the switch to send the data to, and forwards it to that port.
Eliminating the need to worry about collisions provides a further opportunity for switches to improve performance, by allowing communication to occur in full-duplex mode. When a PC and a switch communicate in full-duplex mode, they send and receive data on the cable at the same time. This is possible because in a full-duplex communication, the two connected devices drop the standard Ethernet communication system (which by its nature caters to multiple accesses of the media) in favor of a more direct one-to-one method. Full-duplex communication can deliver double the throughput--a 100Mbps connection running in full-duplex will effectively become a 200Mbps connection.
Buying a switch
When you're buying a switch, you need to consider a number of factors:
- How many ports do you need on the new device? Consider not just your current needs, but your future requirements, as well.
- Look at the speed at which the ports on the switch operate. Switches described as 10/100 models can accommodate both speeds, and usually have the ability to detect the speed at which a connection can be made. This feature, known as auto-negotiation, is also how the switch determines whether full duplex communication is possible.
- Consider whether you need management capabilities. Managed switches will often have features such as port mirroring and remote monitoring, which can be useful if you are troubleshooting network devices or measuring bandwidth utilization.
Managed devices have the ability to communicate with a network management system, usually via Simple Network Management Protocol (SNMP), or are capable of communicating with proprietary network management systems.
- Check how much memory is available for buffering data on the switch. The size of the buffer can play a large part in the overall performance. Look carefully at manufacturers' specifications, because some quote figures for the entire switch, whereas others quote on a per-port basis.
- Ascertain whether there is an opportunity for expansion. Some switches have the ability to accept plug-in expansion modules to provide high-speed uplink capabilities, or media conversion options. Again, consider your current as well as your future requirements.
Once you have decided on the features you need, it's time to go shopping. When you start to look around for switches, you may notice that prices vary a great deal. With switches, as with any other type of networking equipment, the name makes quite a difference. Products from manufacturers such as Cisco or Nortel are likely to cost more than those from some of the smaller and less well known manufacturers. That doesn't mean a device from a smaller company may not be suitable for your needs. If it has the features, backup, and support you're looking for, then it may be the switch for you. As always, shop around and compare features and prices.
Whether you go with one of the big names or buy from a smaller manufacturer is a matter of personal and business preference. From a price perspective, the biggest influence is likely to be whether the unit has management capabilities. For an unmanaged switch, costs can be as low as few hundred dollars for an eight-port unit. For a larger, managed unit from a major manufacturer, you can expect to pay between $75 and $125 per port.
A risk-free upgrade
Perhaps the most attractive feature of using a switch as an upgrade is that doing so is almost risk free. The implementation of a new switch generally has no effect on other networking components, such as cabling, network cards or other network devices. Depending on which switch you purchase, in many cases, the actual upgrade is as simple as connecting a power cord to the new switch, unplugging the cables from an existing hub, and plugging the cables into the switch. If you are looking for a quick, easy and reliable way to improve the performance of your Ethernet LAN, switches represent what could be the easiest network upgrade you ever do. //
Drew Bird (MCT, MCNI) is a freelance instructor and technical writer. He has been working in the IT industry for 12 years and currently lives in Kelowna, BC., Canada. You can e-mail Drew at firstname.lastname@example.org.