Networking

Networking Notes

• Definition of router

         A Router is a device that connects two networks - frequently over large distances. It understands one or more network protocols, such as IP or IPX. A Router accepts packets on at least two network interfaces, and forwards packets from one interface to another.

Router's may be programmed to filter out some packets, and to dynamically change the route by which packets are routed.

Router's often use different media on each interface. For instance, a router might have one Ethernet port and one ISDN port.
Definition of: WAN

• (Wide Area Network) 

          A long-distance communications network that covers a wide geographic area, such as a state or country. The telephone companies and cellular carriers deploy WANs to service large regional areas or the entire nation. Large enterprises have their own private WANs to link remote offices, or they use the Internet for connectivity. Of course, the Internet is the world's largest WAN. 

• WANs, LANs and MANs

         A LAN (local area network) is contained within a building or complex. A MAN (metropolitan area network) generally covers a city or suburb. Following is a bandwidth comparison between major LAN and WAN technologies. See LAN, MAN and personal area network.

LAN Cable

• Serial cable

Almost nothing in computer interfacing is more confusing than selecting the right RS232 serial cable. These pages are intended to provide information about the most common serial RS232 cables in normal computer use, or in more common language "How do I connect devices and computers using RS232?"

• What are Ethernet Cables?

Ethernet cables connect network devices such as modems, routers, and adapters. They transmit data using the Ethernet protocol. (See the bottom for variations.) NETGEAR Ethernet cables have RJ-45 jacks on both ends, each with 8 pins. (They look similar to telephone jacks, which use 4 pins or 6 pins.)

• Equipment using an Ethernet cable is referred to as wired.

• Wireless equipment uses radio waves in place of some (or all) Ethernet cables. A network device that uses both Ethernet and wireless connections is usually called just wireless.
The Physical Ethernet Cables

• Use Cat 5 cables. (Cat 5 is a measure of quality, meaning that it supports traffic up to 100 MB / sec.) These are also called 10/100 Base-T Cat 5 cables.

• Some Ethernet cable wires criss-cross internally, others are straight through, meaning that pin 1 is wired to pin 1 on the other end, etc. A port (socket) for a straight through Ethernet cable is sometimes called an uplink port. If you aren't sure about a cable, and you can see the inside wires' colors, hold the two ends of the plugs up, so the same side of the plug is facing you.

If the wire colors are in the same order in both, it is a straight through cable. Otherwise, it's probably a crossover cable.

• Cables are crossover where the wire for pin 1 attaches on the other end to pin 8, etc. This is used, for example, to connect two computers directly, without a hub or switch. Manuals will tell you whether to use a crossover cable.

• Using a crossover cable instead of a straight through one won't hurt anything — but it won't work, unless you have...

• Auto Uplink technology, where the equipment figures out which kind of cable you have actually attached to it.

• What Travels over the Ethernet Cable

You might need these terms, which relate to what travels over the cable:

• Full duplex. Data can travel both directions at once.

• Half-duplex (aka semi-duplex). Data can only travel one direction at any instant. This is slower than full duplex. Attaching a network device that can only do half-duplex to one that can only do full duplex will cause terrible performance — if they connect at all.

• Auto-negociation. This is when the network devices figure out whether both on either end of an Ethernet cable are full duplex. Rarely, the auto-negociation fails, so sometimes in debugging, it is turned off.

Variations on Using the Ethernet Protocol on Ethernet Cables

• Powerline products use regular electrical power cords in place of Ethernet cables. This useful (and easy to install!) technology is often overlooked in situations where Ethernet cabling is inconvenient.

• Power Over Ethernet products use Ethernet cables to transmit small amounts of power to Ethernet equipment (as well as data). This is useful where running power cords is inconvenient.