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Architech: Future-proofing your network means getting the right system, hubs and cabling installed now - before it's too late

For most of us, using a network is second nature. We copy files from one machine to another and rely on the server to store, organise and back up our work. The prospect of setting up your own network may seem a little daunting; the benefits, however, even if you only have a few desktop PCs, are great. Here we look at some of the basic issues relating to designing and setting up your own local area network, (LAN). The most common network topologies are explained and their relative merits discussed.

Daisy chain

Inexpensive and technically simple to install, daisy-chain networks provide an easy introduction to networking. They allow you to run the full range of networking services - such as printer sharing, file serving and electronic mail - that large professional networks also run.

It is possible to run Ethernet and Apple's LocalTalk (or Farallon's PhoneNet) as daisy chain networks.

Limitations - really only suitable for a small network of about six devices on back-to-back desks. The main danger is that it is easy to disrupt the network by breaking the daisy-chain. The effectiveness of the network depends on the integrity of the cable; if cables trail and get walked on, or twisted and flexed frequently, this leads to internal and invisible damage to the copper core, resulting in reduced network performance.

Backbone

A more professional installation, the backbone cable is installed in ducting or secured to skirting and accessed thorough wall-sockets. This allows you to plug in to or unplug from the network without disrupting the network signal on the backbone. This type of network is also known as a trunk network.

It is possible to run Ethernet and LocalTalk or PhoneNet as backbone networks.

Limitations - as your network expands, you may want to install a router to divide the network into two zones and improve the overall performance. With a continuous backbone cable, wherever you place the router, all devices to the left will be in one network and those to the right in the other. In real life, however, it is rare that this works out - just because people happen to be at one end of a wire does not mean that they work together - indeed they may work primarily with people or servers at the other end of the network. A backbone is fine for networks up to about 15 devices. However, if you are planning a network of 10+ devices where expansion of devices, network services and speed have to be taken into account, a star topology would be a better solution.

Star topology

A star topology network - sometimes referred to as a structured cabling system or premises distribution system (pds) - represents one of the major developments in networking design over the last few years. It is a cross- platform, protocol-independent cabling system. For the AppleTalk environment the advantages are even greater. Not only do you have all the advantages of easier management and fault-finding, and a better way to expand your network and move people around on the network without recabling, you can also install your cabling system without worrying in advance who will require LocalTalk and who will require Ethernet. The cable is capable of running both.

In a star topology, each wall socket has an individual cable containing eight wires (four pairs). Of these wires, two pairs are used for Ethernet, one pair is used for LocalTalk (PhoneNet), and the remaining pair can be used for telephones (at least in the us). Each wall-socket's cable is joined to the others at a central point usually by a device called a hub (sometimes referred to as a concentrator or star controller).

Unmanaged hubs

Unmanaged hubs allow you to create star topology networks and hence gain greater reliability for your network. This is because each port on the hub has its own cable - so if one cable is damaged, the rest of the network is unaffected - and because the hub is capable of automatically disconnecting faulty devices on a port (a technique known as auto-partitioning).

Managed hubs

While being reliable and cost-effective for the job that they do, unmanaged hubs do not offer any facilities for diagnosing problems, a limitation which becomes more of a constraint as the size of your network increases. It is because of this that managed hubs have been introduced.

Managed hubs have their own processor which monitors all the ports and makes available information on traffic levels, error rates, device addresses and so on to a network manager.

This can be done either using a proprietary scheme (for example Farallon's StarControllers and StarCommand software), or using the defacto standard of SNMP (simple network management protocol). By far the majority of managed Ethernet hubs now use SNMP; even Farallon now has SNMP support in some of its Ethernet hubs, in addition to its proprietary scheme.

SNMP was originally developed for managing TCP/IP routers over The Internet but can be used to manage virtually any network device including PCs, Macs and, of course, hubs.

I-Beam managed hubs

EtherSmart hub

This Ethernet hub has 12 built-in 10baseT ports (no patch panel is required) and both thin and thick ports for connecting to backbones. The twelfth 10baseT port can also be configured as a cross-over port for interconnecting hubs.

It also has two 50-pin amphenol connectors for creating a stack of hubs. Up to 16 of these units can be interconnected in this way giving you a total of 192 10baseT ports.

The built-in power supply is an autosensing universal power supply. The units can either be stacked on a desk or shelf, or mounted in a rackmount cabinet using the included brackets.

EtherSmart management module

The management module provides SNMP capabilities for up to 16 cascaded EtherSmart hubs.

As only one management module is required for up to 16 EtherSmart Hubs, significant cost savings can be achieved over other products which sometimes require you to pay for the management capabilities each time you buy an additional hub.

The management module has two 50-pin amphenol connectors for linking to a stack of EtherSmart hubs. It also has two serial ports, one of which can be used with a computer or terminal (possibly via a modem) to allow out-of-band management. Software upgrades can also be downloaded to the management module via this port from a PC.

EtherSmart management hub

This new unit is basically identical to the EtherSmart Hub but has the management capabilities of the EtherSmart management module built in to the same box. This offers convenience and cost savings, and takes up less space in your cabinet.

It has the same connectors, and can manage an additional 15 EtherSmart hubs (making the same total of 16 as the EtherSmart management module).

The first step in designing a future-proof network is to choose a network topology. Most network systems work with a star topology cabling system, indeed some will only work with this topology (also known as a structured wiring system). A star topology system is a good start in future-proofing a network.

The next step is to choose the correct type of cable and wall sockets.

All major network systems can work over category 5 unshielded twisted pair (UTP) cable. In the past, this used to cost a lot more than category 3 cable but as supplies have increased along with its popularity, so the price has dropped.

The difference between category 3 and category 5 is the transmission speed each can support without generating excessive noise. For category 3 cable this is rated at 20MHz - sufficient for using PhoneNet, Ethernet, or Token Ring. Category 5 is rated at up to 100Mhz and is therefore also suitable for 100Mbps Ethernet networks.

Category 5 cable achieves this extra transmission capacity by having a greater number of twists in the wires in the cable which helps reduce interference.

In order to fully benefit from category 5 cable, you must also remember to use category 5-rated wall sockets, fly-leads, and patch panels.

RJ45 wall sockets (Category 5 ones, of course) should be used, as all of the listed networks will work with these. Although PhoneNet uses RJ11 fly-leads (and patch panels) this is still compatible with RJ45 wall sockets. This is because RJ45 sockets were designed to be backwards compatible with RJ11 plugs which can simply fit into the middle part of the RJ45 socket.

PhoneNet uses pins 3 and 6 on an RJ45 socket which aline with pins 1 and 4 on an RJ11 plug. It is not necessary to make special RJ11 to RJ45 adaptor cables.

Besides being able to support all the network standards, a star topology category 5 network can also support Full Duplex Ethernet, Packet Switching hubs and also up-and-coming ones such as asynchronous transfer mode (ATM).

Upgrading from PhoneNet to Ethernet

Cabling installed as detailed on this page (ie a star topology with RJ45 wall sockets) will make upgrading from PhoneNet to Ethernet simply a matter of unplugging the wall socket cable from the PhoneNet hub, and plugging it into an Ethernet hub.

All the user then has to do is replace the PhoneNet connector and flylead with an Ethernet card and flylead.

The beauty of this is that it is not necessary to install new cabling or wall sockets.

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