Since the late 1990s, 10/100baseT Ethernet has become the de facto standard for local area networks. Here’s a look at the hardware components involved in using Ethernet in a 10/100baseT network, including cable pinouts and specs, network cards, hubs, and switches.

Some background on Ethernet
So you want to build an Ethernet LAN? Or maybe you’re wondering exactly what Ethernet is. Well, Ethernet (the name commonly used for IEEE 802.3 CSMA/CD—carrier sense multiple access, collision detection) is the dominant cabling and low-level data delivery technology used in local area networks (LANs). First developed in the 1970s, it was published as an open standard by DEC, Intel, and Xerox (or DIX) and later described as a formal standard by the IEEE. Following are some Ethernet features:

  • Ethernet transmits data at up to 10 million bits per second (10 Mbps). Fast Ethernet supports up to 100 Mbps. Gigabit Ethernet supports up to 1,000 Mbps (but that’s another story).
  • Currently, 10BaseT and 100BaseT (Fast Ethernet) Ethernets are the most common, and both can be built with twisted-pair cabling.
  • Data is transmitted over the network in discrete packets (frames), which are between 64 and 1,518 bytes in length (46 to 1,500 bytes of data, plus a mandatory 18 bytes of header and cyclical redundancy code [CRC] information).
  • Each device on an Ethernet operates independently and equally, precluding the need for a central controlling device.
  • Ethernet supports a wide array of data types, including TCP/IP, AppleTalk, IPX, etc.
  • To prevent the loss of data, when two or more devices attempt to send packets at the same time, Ethernet detects collisions. All devices immediately stop transmitting and wait a randomly determined period of time before they attempt to transmit again.

Phase 1: Preplanning
The first decision is a technology and cost decision. Will your network be 10BaseT or 100BaseT? Can you afford 100 Mbps from POP (Point of Presence, your connection to the outside world) to client or do you just need the higher bandwidth on your backbone? The following is a comparison of the two technologies.

Standard Ethernet (10BaseT)
Standard Ethernet (10BaseT) uses RJ-45 connectors on Unshielded Twisted Pair (UTP) or Shielded Twisted Pair (STP, also called Plenum) cable and operates at 10 Mbps. Using a Star topology, all computers connect to a Hub/Switch using patch cables with RJ-45 male connectors on both ends. These hubs can be linked to increase the number of ports available for patch cables; however, no more than three hubs should be linked together.

Sometimes these hubs/switches have “uplink” ports that allow them to be connected to each other using special cables that blend two hubs into one without daisy chaining. Both clients and hubs have RJ-45 female connections. Ideally, Category 5 patch cables should be used in 10BaseT (so that you can upgrade to 100BaseT without recabling). Specifications: 10BaseT networks are wired (within the plugs and ports) according to EIA/TIA 568B specifications. Maximum cable length is 100 meters. Maximum number of devices is 1,024, although performance would be unacceptable long before this number is reached.

Fast Ethernet (Also called 100BaseT)
This technology is essentially the same as 10BaseT in terms of specifications and limitations, but it has higher bandwidth. However, the network interface cards (NICs) and the ports on the hubs and switches operate at 100 Mbps. It is very common to have a 10BaseT LAN that runs from clients to a central switch or hub and a 100BaseT LAN as the backbone for your servers.

Phase 2: Plan
Building any network should begin with a physical plan. Draw your network out and measure the distance from the POP to each workstation. By having a physical reference for your network, you can determine how far your cable runs are going to be and where you will need to use switches and hubs to segment and extend your network.

The heart of an Ethernet network is the cable you use. One of the reasons for your physical plan is to ensure that your wiring plan will not violate the maximum cable length (100 meters for 10BaseT/100BaseT networks) for the type of wire you will use to connect your network. Currently, the majority of copper cable used for Ethernet is Category 5. This refers to a standard for cabling developed by the IEEE. Category 5 cable offers speeds up to 100 MHz and a data throughput rate up to 100 Mbps.

When networking with Ethernet, it is highly recommended that you use Category 5 (or Category 5e) cable. You may not have switches/hubs that support 100-Mbps connections to the desktop. But having the ability to upgrade that switch/hub without the expense and time associated with rewiring your network is enough reason to justify the additional cost of Category 5 rated wire.

Your wiring should begin from the heart of your network—your data center or server room—and fan out to the clients.

Phase 3: Buy
Network interface cards
NICs connect a client/host device to your network. Cheap NICs can introduce chatter and collisions. They can deny bandwidth and cause endless hours of troubleshooting. The same is true with hubs and switches. Find a good NIC that is within your price range and use that type of card consistently throughout your network.

Plan for a failure rate of 1 in 100 and purchase additional cards when you are populating your network. When a NIC fails and cuts a client or server off your network (or disables your network with chatter), that’s not the time to learn how to install a NIC.

Hubs are used to connect multiple hosts to one segment of wire, and all hosts share the same bandwidth—meaning one large collision domain. Use hubs at points where you would deploy a network sensor. That way, the hubs can see all the traffic on their portion of the network.

Switches transfer data between different ports based on the destination MAC addresses. Each segment or port connection is its own collision domain, but all ports are in the same broadcast domain. You can use switches to connect multiple ports to the same destination (that is, multiple uplink ports), but only one port can be active at a time.

If cost allows, use “intelligent” switches that offer port spanning. This will enable you to place a network sensor on that switch and let it inspect all of the traffic regardless of destination. When buying hubs or switches, plan on 50 to 100 percent growth rate. So, for example, if you currently need to connect only 12 hosts to a switch, buy a switch with 24 ports. This allows for growth as well as potential port failure.

Phase 4: Build
Once you’ve planned properly and bought the hardware, it’s time to build out your Ethernet hardware. Whether you outsource the cabling job or do it yourself, here are some tips to follow:

  • When you place your servers, hubs, and switches, remember to allow for the proper ventilation and cooling in your data center or server room.
  • Don’t skimp on cable layout. Make cable runs from switches and hubs to a patch panel, preferably in your data center/server room. Then, run the cable through your walls from the patch panel to the wall mounts and run a separate cable from the wall mounts to the client devices. Never run cable from an intermediate device (switch/hub) directly to a client device. This can result in troubleshooting and design problems.
  • Do not run Ethernet cable alongside power cables. If costs allow, buy cable ducting and use it to route and protect your cables.
  • After installation, test your cables with data testing equipment or known good devices.

If you are the network manager, you should have a firm understanding of the layout (also called pinouts) of the RJ-45 connectors on your Ethernet data cables. There are two standards for cable ends: EIA/TIA 568A (Figure A) and EIA/TIA 568B (Figure B).

Figure A

Figure B

When looking at an RJ-45 wall jack (female), contact 1 is on the left, and contact 8 is on the right. When looking at the RJ-45 connector on the end of a cable (male) with the tab on the bottom and the contacts on the top, contact 8 is on the left, and contact 1 is on the right.

I would recommend using one standard throughout your network. The most popular is 568B. It doesn’t matter which standard you use; just be consistent.

Also, remember the following:

  • To connect two similar devices (two clients, two hubs, etc.), you should make one end of your cable 568A and the other 568B. This is often called a crossover cable.
  • To connect two different devices (client/server to a hub or switch), your cable should have the same wiring scheme on both connectors.

Summing up
Now you have the information you need to decide what type of Ethernet network (10baseT or 100baseT) you’ll need, how to plan, what to buy, and how to build. In my next article, I’ll cover the protocols that can run over your Ethernet LAN and explain what your data looks like “on the wire,” as well as offer some helpful troubleshooting tips specific to Ethernet LANs.

How is Ethernet implemented in your network?

We look forward to getting your input and hearing about your experiences regarding this topic. Join the discussion below or send the editor an e-mail.