Networking - Hardware - Devices

Another piece of knowledge we need to successfully troubleshoot problems with Macs is a general knowledge about networking hardware. In this article we will cover some of the most common pieces of networking hardware, the differences between them, and their varying uses.

Hubs are probably the most basic and common networking device you may encounter. Hubs are multiport devices used for distributing a single network connection to multiple computers or devices. Hubs work like a phone line splitter only for ethernet. Any data traffic that a hub receives, it passes on to all other ports of the hub. In a sense, it is a "dumb" device. A hub makes no effort to direct traffic to the correct port that corresponds with its final destination, it merely passes all data along to every port. For smaller networks, hubs work well and will not run into problems. However, on larger networks, or even small networks with high traffic loads, hubs can cause problems. Only one device connected to a hub can send traffic at any particular time. If multiple devices send data at the same time a data collision occurs. Collisons require one of the devices to resend data when it will not collide with another transmission. As you can see, with more than a few computers or with high traffic networks, this would quickly become a problem and render the network useless.

Switches, like hubs, have multiple ports to extend network connectivity to more devices. Switches however, differ from hubs in that they are "smart". Instead of directing traffic to all ports, a switch makes note of the ethernet hardware address (also known as a MAC address) of each device connected to it. When data traffic is received, the switch consults its table of MAC addresses and subsequently routes the traffic only to the correct port. If the address does not exist in the table, the data is forwarded to all ports but the one it came from. Using this more intelligent method of directing traffic, it is easy to see how switches would allow for more network capacity both in the number of hosts and in the overall bandwidth capacity of the network. Traffic being transmitted from port 1 to 5 can be taking place at the same time traffic can be going between port 3 and 7 without any of that traffic colliding and thus causing delays and retransmits. During work with networking hardware you may run into something called a bridge. A bridge is basically a 2 port switch designed for breaking up collision domains between hubs. Bridges are not very common anymore.

Another network device that is found working in conjuntion with switches, is a router. Routers take directing traffic one level higher than a switch. Routers examine the logical address information in data traffic and route based those addresses instead of physical addresses. Sometimes routers will need to change header information in the data being sent which allows traffic to be passed between dissimilar networks. Switches do not have this ability. Like switches, routers maintain tables to make their decisions on where to direct network traffic. However, routing tables maintain best path information so that traffic can be routed via the most efficient path based on various algorithms or static entries.