What You Should Know about Wired LANs to Get a Networking Job - dummies

What You Should Know about Wired LANs to Get a Networking Job

By Peter H. Gregory, Bill Hughes

As long as you stay within your own property, you can network using LANs. As a rule, LAN technology is much cheaper and faster than WAN technology. An organization needs to use WAN technology when it must connect two LANs across some public right-of-way such as a street or a river.

With some exceptions, pretty much every wired LAN is a variation of Ethernet. Four kinds of hardware elements are part of Ethernet data networking:

  • Network interface card (NIC): This card goes into a PC, laptop, or smartphone.

  • Hub: The hub connects Ethernet cables from multiple devices so that they can all communicate. This simple, unintelligent connection option is economical, particularly for a small office or a home network.

  • Switch: An Ethernet switch combines a hub with a little bit of intelligence. Whereas the hub has each NIC card listen to each message and determine whether or not the packet is meant for it, an Ethernet switch will figure out which PC the message is for and not bother every NIC card with every message.

  • Router: The term router applies to a range of equipment to manage an Ethernet LAN and interact with WANs. These devices range in complexity from routers in a small home office up to carrier-class devices that control the universe (or at least the digital part of the universe).

Some manufacturers incorporate a wireless LAN access point into a router. Other manufacturers don’t. It is easy to be confused.

Ethernet technology has the lion’s share of the installed base of LANs. The different flavors of Ethernet are based on cable and nominal speed.

Ethernet Name Cable Connector Nominal Speed
Ethernet 10BASE-T 10 Mbit/s
Fast Ethernet 100BASE-TX 100 Mbit/s
Gigabit Ethernet 1000BASE-T 1 Gbit/s
10-gigabit Ethernet 10GBASE-X 10 Gbit/s
40-gigabit Ethernet 40GBASE-X 40 Gbit/s
100-Gggabit Ethernet 100GBASE-X 100 Gbit/s

Although this information looks straightforward, there are several opportunities for confusion. First, some people refer to the 10Mb per second local area network as Ethernet. Others refer to the technology that includes all the options in the table as Ethernet. Both are correct, but the terminology can be confusing.

To distinguish among them, many people refer to the cable connector, such as 10BASE-T. However, the cable connector is also called RJ-45. On top of that, the cable can be called Cat-5 or Cat-6 cable. The best advice is to ask for clarification on the Ethernet speed only if it matters.

Another source of confusion is the speed of the Ethernet. There are two reasons why Ethernet speed issues can get confusing. A cool feature of this technology is that it will “dumb itself down” to accommodate the slowest technology. For example, your router and wiring may accommodate Gigabit Ethernet. However, if the NIC can work with only 10Mb per second, the technology will operate at the slower speed.

The problem is that the technology will never tell you that it is operating below what it’s capable of. You have to know to ask. The 10/100/1000 specification indicates that the equipment is happy to work at any of those speeds and will default to the highest possible.

Another side of Ethernet speed is that 10Mb per second is the nominal speed. TCP/IP is chatty. By chatty, we mean that the respective ends of the connection spend a fair amount of time making sure that the other end is ready to receive the transmission, that it received the transmission correctly, and that it has finished sending. These tasks are important to ensuring an accurate transmission, but they require bandwidth. You, as a user, get only a percentage of the nominal speed.

Ethernet LANs are the most common type of LAN. The hardware is inexpensive and readily available. Plus, many people know how to support it.

There are many options for non-Ethernet LANs. They are typically used in special applications, such as when exceptional security is required.

Token-ring LANs, for example, were heavily promoted by IBM in the 1980s. Eventually, IBM gave up and accepted that Ethernet had the dominant market share. As the name implies, a token-ring LAN has all PCs on a logical ring. The PCs on a given LAN ring are in communication with the PC that is logically to its left and to its right. When it receives the token from the PC to its right, it looks to see if that token has a message that belongs to it.

If it does, it takes that message and hands off the token to the PC on its left. If the token does not have a message for that PC, it passes the token along with the message to the next PC on the left. This process happens very fast.

This architecture feels more reliable compared to the Ethernet, where all the PCs essentially repeat until a message is acknowledged.

Another alternative to Ethernet is Fiber Distributed Data Interface (FDDI). This technology operates at a nominal rate of 100 Mbit/s. Whereas Ethernet uses copper wire, FDDI employs fiber-optic cabling. In addition, each PC is connected back to the central router in a star topology. These two features make FDDI more secure than Ethernet. (Note, however, that some Ethernet LANs use fiber-optic cable.)