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Basic Home Networking-Hardware
by By Herbert Wong, Jr.,NOCCC Hardware SIG Leader, herbwong@primenet.com - February 20, 2000 at 01:51:15:
Home-computer networking has become very popular, recently. The reasons are simple. The advent of low-cost, high-performance computers has made multiple-computer households common. And, high band-width Internet connections, such as DSL and cable modem, have initiated the primordial networking event, the installation of network interface cards.General terminology—The most common networks are based upon the Ethernet standard defined by IEEE 802.3 (though some people may use IBM’s Token Ring). Standard Ethernet is designed for 10 megabits per second (Mbps). Fast Ethernet is designed for 100 megabits per second. The optional full duplex mode operation can double those speeds.
Open Systems Interconnect (OSI) Model—defines various layers for networking. At the lowest is the physical layer. The Ethernet standards define several physical layer standards that will be generally described herein. Their names are descriptive. The first portion can describe basic transmission rate (ex., 10 or 100 megabits per second). The second portion usually is either base (for baseband; a single channel or frequency operates on the cable) or broad (for broadband; multiple frequencies operate on the cable).
Ethernet operates using Carrier Sense Multiple Access with Collision Detection (CSMA/CD). A network interface card (NIC) attempts to transmit by first looking for a carrier signal. If no carrier signal is detected, the data are transmitted in packets. While transmitting, the NIC continues to monitor the signal for proper communication with the destination.
It is common for more than one station to attempt to transmit data at the same time. Such a situation causes a collision, which corrupts that data. One transmitter must then notify the other transmitter of the situation by sending a jam (a particular bit sequence). Each transmitter must wait a random period of time before it then retransmits its data. This operation is repeated as needed.
As you can see, a reasonable number of collisions are common in Ethernet networks. An extraordinary amount of collisions causes slow downs and ultimately can paralyze the network until the traffic is resolved. On a low traffic network, this is unlikely to happen.
10base2 (thin coax)—In the past, networks were often configured using thin coax (or 10base2) using RG-58 coaxial cables (at 50 ohms) with BNC connectors. RG-58 coaxial cable itself (not the connectors) is identical in appearance to the RG-59 coaxial cable used for home television (at 75 ohms).
Coaxial cable generally has a solid copper-wire core surrounded by an insulating jacket. Encasing the insulator is braided-wire mesh and/or a metal-foil that serves as a shield against electrical interference.
At every node (or junction), 10base2 requires the use of a T-connector. One connection is to the computer’s network interface card (NIC), one connection to the incoming cable, and the final connection to either an outgoing cable or a 50-ohm terminator.
The greatest advantage of 10base2 is that there is no need for an expensive network hub (that functions as a network-bus connection box). The 10base2 network bus was a simple chain of cables and computers with one 50-ohm terminator at each end.
The bus could be up to 200 meters long without using repeaters. Runs of about one thousand meters are possible with repeaters.
There are several disadvantages to 10base2 networks. Coaxial cable is not very flexible, so cable installation and storage is difficult. T-connectors are required, yet are not part of the cable itself. A single detached T-connector severs all nodes at that point. T-connectors are relatively expensive. Finally, it shares a total of 10-megabits per second across the entire bus.
Now that I’ve told you about it, forget about thin coax networks. You won’t likely use it at home. And, just about everything that follows doesn’t directly apply.
10baseT/100baseT (twisted pair)—The most common network configuration is now based upon unshielded twisted pair (UTP) cable either 10baseT or 100baseT. The 100baseT network can support up to 100 megabits per second (200 megabits per second in full duplex mode) for each segment compared to 10baseT’s 10 megabits per second (20 megabits per second in full duplex mode). Runs of up to 100 meters are possible.
The difference in cost between 10baseT and 100baseT equipment is now almost trivial. Except for very limited networks or where cost is paramount, get 100baseT components. The exception is that all cabling and connectors should be category 5 rated because when you do convert to 100baseT, you’ll have to reinstall category 5 components anyway.
Network Interface Cards— A network interface card (NIC) is the hardware that is required to connect a computer to a network. Every Ethernet NIC performs simple functions but better cards can be quite sophisticated. A single port NIC can cost from $15 to $170. A four port NIC (four connections in one card!) can cost $550! As always, get a PCI (and not an ISA) card.
If you have broadband Internet access, your cable modem or DSL box is usually connected to your computer by means of an Ethernet card. The access company will most likely install a 10-megabit per second Ethernet card using twisted pair (10baseT) in your computer and a 10-megabit per second cable modem or DSL box. This makes the grand promise of 30 megabits per second downloads seem unreasonable at best.
The best thing about Ethernet is that there is a fair degree of upward mobility and backward compatibility. If you buy 10/100 NICs, you can use them in 10baseT or 100baseT networks. The card will automatically attempt 200 megabits per second in full duplex operation (if it can), 100 megabits per second if that fails, and resort to 10 megabits per second if that fails.
On the installation bracket of the NIC you will see the connector (for RJ-45, BNC, AppleTalk, fiber optic, etc.) and as many as four LEDs (light emitting diodes). The LEDs are indicators for various functions. Sometimes they indicate 10 or 100-megabit mode, link, collision, transmit or receive, etc. The more LEDs the better.
If everything always works, you don’t need the LEDs. In my world, nothing ever seems to work right, so the LEDs serve as the only diagnostic tools I have for the physical connection. A little LED can tell you that your computer isn’t even connected to the server, is at 10 megabits instead of 100 megabits, is not transmitting data when it should, isn’t even seated in its slot, etc.
Okay, a few LEDs can’t replace a Fluke OnTouch 10/100, Fluke DSP-4000, Microtest OMNIScanner2 (all about $5000), Microtest DTS1463, etc. as a diagnostic tool. But until the kind folks at Fluke or Microtest or B&K etc. give me such a tool, LEDs will have to do.
Twisted Pair Cables—Due to the higher bandwidth demands of 100baseT, category 5 (also known as cat-5) cables are required instead of 10baseT’s category 3 (cat-3) cables. All new cabling should conform to at least category-5 standards since the parts’ cost is trivial compared to the installation cost.
The cables can be constructed with either solid-core wire or stranded wire. Stranded cables are more flexible and are used in shorter runs as patch cables (or patch cords). The stiffer solid core cables are best used inside walls where flexibility is not important. Remember to specify fire retardant Plenum cables that conform to commercial fire codes for office-wall wiring.
Unshielded twisted pairs (UTP) of wires are used to improve electrical characteristics of the cables. The twisted pairs of wires are twisted at a specific number of times per given length. Contrast this to a shielded twisted wire-pair cable where the inner wires are covered by a braided wire mesh and/or metal-foil shield.
Eight wire RJ-45 plugs and jacks are used as the connectors. They look like larger versions of standard four wire telephone connectors. Beware! Even the connectors must be capable of 100 megabits operation.
Normal operation requires two pairs of wires. Pairs are wires one and two (transmit plus and minus, respectively) and three and six (receive plus and minus, respectively) are used. Full duplex operation makes use of all eight wires in four pairs; two pairs for transmission and two for receiving.
The wires in a normal cable go straight through from one connector to the other. Pin one is attached to pin one (using orange/white wire), pin two is connected to pin two (using orange wire), pin three is connected to pin three (using green/white wire), etc. Wires four through eight are blue, blue/white, green, brown/white, and brown, respectively.
Crossover cables are used to join two computers together without a hub. A crossover cable can is also used to unify one hub with another hub via uplink ports. A crossover cable connects pin one to three, pin two to six, pin three to one, and pin six to two. Other pins are not normally used.
Hubs—A hub allow you to connect two or more network interface cards together. A simple hub is quite stupid and won’t allow you to upgrade your network. A slightly more expensive hub or even a switch may be all you ever need.
A simple hub might only support standard Ethernet at 10 megabits per second. Another simple hub might support Fast Ethernet at 100 megabits per second. You wouldn’t be able to mix the two data rates.
A slightly more sophisticated autosensing hub could automatically detect a 10 or 100 megabits per second NIC connection and use the maximum speed. However, if different ports were at different speeds, a problem develops. If there is only a single speed permitted, the hub must revert to the slower speed.
A hub with a switch (or switched hub) allows one segment to operate at 10 megabits per second and a second segment to run at 100 megabits per second. The switch will facilitate data transfer between the two segments so that data are not lost!
A hub broadcasts its transmissions to every port in the hub, which is very inefficient. A hub shares its maximum bandwidth between all of the ports. In other words, ten equally active ports will get only ten percent of fast Ethernet’s 100 megabits per second.
Switches—A switch is a very intelligent device. Most switches autosense 10 or 100 megabits per second speeds and allow every port’s connection to operate at its maximum speed (i.e., every 10/100 NIC operates at 100 megabits per second). Switches create efficient direct routes between ports so that the data are not broadcast to every other port. Switches maintain full bandwidth between every connection!
Switches are now relatively inexpensive. The prices have fallen drastically in the past few years. A switch is only a little more expensive than a hub. Buy a switch rather than a hub if your network requires multiple users at high bandwidth.
Recommendations—Get network interface cards from reliable manufacturers so that you can get new device drivers as needed. Device drivers are critical for NICs when it comes to performance, reliability, compatibility, and stability. Don’t think that cheap is okay; and don’t forget the LEDs.
It is possible to connect two NICs with a crossover cable. With normal (straight through) UTP cables, a hub or switch is required. New, short length, no-name brand, category 5 cables can be purchased at computer swap meets for as little as $1.75 each. Some stores charge $5 to $10 for similar cables, so shop around. Look for no-snag boots on the RJ-45 connector plugs to protect the little plastic tab from breakage if you frequently disconnect the network cable.
At the least, get a hub with a switch so that you can mix existing 10 megabits per second and 100 megabits per second devices. If you must have high performance while several ports are in use, get a switch.
Simple network kits are commonly available. They include two 10/100 network interface cards, two cables, and a five-port hub or a five-port switch. The price for a kit with a hub is about $120. The same kit with a switch is about $150.
Resources: Ethernet FAQ at http://www.faqs.org/faqs/LANs/ethernet-faq/.
Linksys Networking Basics at http://www.linksys.com/support/faqs/howbuild/whatis.htm.
IBM Building an e-business at http://www.networking.ibm.com/primer/infrastructure2.html.
3Com The Intelligent Server NIC at http://www.3com.com/technology/tech_net/white_papers/503041.html.
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