Network Connectivity Boxes

Here we take a look at the network connectivity hardware found on most wired networks. These are the boxes into which cables go, which allow computers and other devices to talk to each other. Often this extends to communicating with the rest of the world via the internet.

It is important to understand the differences between these devices, they all perform a similar task, but some are much more sophisticated than others..

Hubba hubba

The humble network hub has been around ever since we gave up on coax cable. Each computer or device plugs into the hub via a network cable, allowing it to communicate with every other device plugged into the hub. All that the hub does is repeat any signal which is sent to it, hence a hub is also known as a (multi port) repeater. It is this automatic repeating which lends hubs their greatest weakness; all signals going in on one port are automatically retransmitted out of all the other ports, even if the message was not intended for them.

This repeating of everything can ultimately lead to congestion on a busy network, as well as a significant security risk. It is for this reason that hubs are gradually being superceded by switches. Repeaters work at the Physical Layer of the OSI Model.

The 5:4:3 Rule of Ethernet dictates that a maximum of four repeaters can exist on the same network broadcast domain.

Bridging the Gaps..

Although less popular than they used to be on wired networks, a bridge is used to segment a network into smaller groups of computers. A bridge is more expensive than a repeater, but it learns which devices are on either side of it on the network. Thus it can intelligently filter traffic and only pass through what is intended for the other side.

When working out the best route, set the repeater count to zero if the data path goes through a bridge. As hubs are replaced with the more selective switches, bridges are becoming less common although they do still have a place in the world of wireless networking.

Maximum number of bridges on an Ethernet is seven. Most bridges have only two ports, however the use of multiport bridges can enable the maximum number of computers on an Ethernet network - 1024. Bridges are able to arrange themselves into a 'spanning tree', which prevents the occurrence of data loops within a network.

Bridges function at the Datalink Layer of the OSI Model.

Switching hands..

Visually, switches are virtually indistinguishable from hubs. A comparatively new kid on the block, the switch is a bit of an enigma with a variety of guises which make it harder to define than the others. Switches perform similar functions to bridges and routers and generally work at the network layer of the OSI Model, sometimes gaining for themselves the title of Layer 3 Switches.

Like routers, some switches can perform Media Access conversions - linking networks with not only differing protocols, but also different hardware, such as Ethernet and token ring. A big feature of switches for any sized network is that unlike hubs, a switch learns which device is connected to which of its ports. Any signals coming in are forwarded only to the port of the intended recipient. This ensures better security and a much faster network.

A switch can be used to segment a part of a network into a faster stream. Unlike a hub which broadcasts data from an incoming port out through all of its ports, a switch is able to dedicate incoming data out to a single destination port. What's more, it can do this at full bandwidth for each port. Thus the use of a switch can allow exclusive data throughput at max bandwidth, between two or more devices on the network, without sending out general broadcasts through all of its ports.

They're not Rooters!

Routers (row-ters) perform similar data filtering as bridges, but are able to interconnect totally different kinds of networks, including connecting LANs and WANs to the internet. Routers vary in their functionality. Most are able to create and maintain routing tables and databases of other routers and devices on the network and pass data packets on accordingly.

Routers are usually a hardware/software combination and may be a custom-designed 'box' or a PC with routing software installed. With the use of routers, there is no practical limit to the number of computers on a network (hence the internet). A router is able to connect two or more completely dissimilar networks, or to reduce a large network into smaller chunks. In these roles it is often referred to as a Gateway or the Default Gateway (usually meaning the closest gateway).

Additionally, routers usually have sets of rules regarding what traffic to let through and what traffic to block. In this common role a router may be referred to as a Firewall.

Traditionally visually unexciting flat boxes, CISCO the maker of 90% of the world's routers is working on it. Up until recently, these things were only owned by ISPs and large network operators. Now we have smaller cut down versions my makers of Linksys, Netgear, D-Link and the like, which can act as internet gateways for the home and small office.

Routers work at the Network Layer of the OSI Model.