At the hub of small business

Many consider the hub to be a technology consigned to the past. After all, why choose a hub when switch prices have fallen dramatically over the past few years? The answer is their simplicity. The sheer ease with which hubs are set up, configured and maintained means that the speed disadvantages are not necessarily enough to discourage the idea of a purchase.

Many small businesses and larger enterprises rely on the hub, and it is still the case that many of those thinking about networking a branch or small office could do a lot worse than investing in this stalwart piece of hardware.

Whichever hub you choose, the majority are simple to install. In most cases you simply turn them on, plug in the patch cables and retire to the pub for a quick pint. This makes it possible for just about anyone to get them to work.

Plan the network first
The only feasible problem that you may encounter is if you opt for a hub that operates at fast ethernet (FE) speeds, as it will only work with other 100Mbps FE devices. Plug in an ordinary ethernet (10Mbps) workstation and it won't be able to talk to anything else on the network.

So, if you want to deploy FE, look for hubs that can auto-sense the speed, and switch ports between 10Mbps and 100Mbps operation, or at least offer a mixture of the two types of connection. Dual-speed hubs are a better bet than dedicated 100Mbps FE products and they are not that much more expensive.

You should also opt for stackable hubs as they offer more flexibility, and, as with network interface cards (Nics), you are better off sticking with the big-brand names.

Some hubs will offer simple network management protocol (SNMP) and web-based management features, but bear in mind that these add to the cost and aren't needed for every device on the local area network (Lan).

If you want management features on anything other than the smallest of Lans, you're better off choosing hardware with SNMP management facilities. That way you can monitor and manage all the network hardware remotely from an SNMP console provided by network management software packages.

It is a good idea to plan your network upgrade in detail before you start to buy anything. Specialist vendors can help out in this respect with some of the direct-selling suppliers offering a complete design and installation service.

Network management is a big issue, so opt for SNMP support on all your networking hardware and consider buying a good SNMP management package.

A number of manufacturers now offer small business solutions that combine an ISDN router with a small network hub/switch, which makes setting up a Lan and connecting to the internet far easier. You can also get routers that act as remote access servers, allowing mobile users to gain access to the Lan.

Another thing when considering a hub purchase is what cable goes into it. The most popular form of network connection is unshielded twisted pair cable - commonly referred to as 10Base-T. The cable contains two pairs of twisted wires: one pair used for transmitting, the other for receiving. Each wire twist is through 180 degrees to cancel out electromagnetic interference while leaving the signal intact.

The wire in between each twist can act as an antenna and receive noise interference, so cable lengths are limited to 100m. To ensure transmission quality is maintained, the signal needs to be regenerated, a task carried out by the repeater or hub.

A matter of topology
Introducing a hub onto a network changes its topology. Thin ethernet resembles a bus topology where the co-axial cable is laid out in a single branch with workstations connected along its length. A hub creates a star topology where the hub is the central point with all connections radiating outwards. While the hub itself now represents a single point of failure that can affect the entire network, hub failures are extremely rare.

To allow distances between workstations to be increased beyond 10Base-T cable segment limitations, more hubs can be connected to ports on the first hub. Called cascading or daisy chaining, one port on each hub is used to connect the two devices together.

A special cable, with the send and receive wires crossed over, may be required but most hubs have a dual-function port. It can function as a normal port, or, with the flick of a switch, become a crossover port allowing a standard straight-through cable to be used to hook up a second hub.

There's no limit to the number of hubs that can be in a cascade, but as signal quality and timing cannot be maintained beyond a certain point, no two end-stations should be separated by more than four hubs or five wiring segments.

This could be a potential problem for companies that have used up all available ports on their hubs and want to expand further without violating these connection rules.

The simple solution is a stackable hub. These have a special connector on the rear panel allowing its back plane to be linked directly to another hub. When two or more are connected, they appear to the network as a single unit. It's an ideal method of expansion as you can add extra units without affecting the repeater count.

For most small companies with users swapping the occasional file and using shared printers, standard 10Mbps ethernet will provide all the bandwidth they need. However, the amount and variety of data being shunted around today's networks can soak this up, so the next option is FE.

Choose you cable with care
When it was first developed, 100Base-T Fast ethernet was used primarily as a backbone technology, linking Lan segments together and providing high-speed connections to servers and other important shared devices. However, price drops in the last few years have seen more and more implementations of FE right down to the desktop, particularly for the so-called power user running demanding video and multimedia applications.

As such, 100Base-T is now very much a commodity technology and is likely to displace 10Mbps altogether before long.

In order to deploy 100Base-T FE down to the desktop you need adapters and hubs that support this standard. Dual speed hubs are handy in that you can start out with a standard 10Mbps network and upgrade to 100Mbps very easily when the need arises.

Moreover, the latest adapters, hubs and switches can negotiate speeds with each other, and also select full-duplex operation if both ends of the connection support this option, thereby doubling the available bandwidth to 200Mbps.

For ease of management, you should also look for Nics with Wake-on-Lan support. This allows workstations to be powered up remotely for maintenance, software updates and so on.

If you install a standard ethernet network and use cheap Category 3 cable it's possible to get support (100Base-T4), with 100Mbps over multi-mode and single-mode fibre. But you may not be able to migrate all your users to FE as the cable is not of a sufficiently high quality to handle the faster signals.

It's far safer when specifying your wiring to choose Category 5 cable which will allow for the leap to gigabit ethernet in the future. As with normal ethernet, there are rules on connection for FE. Only two repeaters can be placed between workstations and the total cable length across the entire link cannot exceed 200m.

One of the biggest issues is maximum throughput, whether it's ethernet or FE. Essentially, ethernet is a connectionless service over shared media. When data is transmitted, it is sent to every other node on the network and only one packet of data can be on the wire at any one time. If two packets are transmitted simultaneously, they'll collide, with the consequence that each station must back off for a specific time and then re-transmit.

Thrashing will do no good
Ethernet networks use a method snappily called Carrier Sense Multiple Access/Collision Detection to deal with the collision problem.

Unfortunately, as more data is transmitted, the likelihood of a collision increases and the network can reach a stage known as thrashing, where there are so many colliding transmissions that no data is getting through to its destination. This usually occurs at around 80 per cent utilisation of the available bandwidth. FE solves this problem by the simple and effective expedient of throwing more bandwidth at it.

Buying a hub may not be the most difficult decision that you are going to make in your role as network manager, but this is not to say that it is any less important, and a great deal of forethought must still be put into the decision.