Network design
In a 10BASE2 network, each segment of cable is connected to the transceiver (which is usually built into the network adaptor) using a BNC T-connector, with one segment connected to each female connector of the T. At each physical end of the network a 50-ohm terminator is required. This is most commonly connected directly to the T-connector on a workstation though it does not technically have to be. A few devices such as Digital's DEMPR and DESPR had a built-in terminator and so could only be used at one physical end of the cable run.
When wiring a 10BASE2 network, special care has to be taken to ensure that cables are properly connected to all T-connectors, and appropriate terminators are installed. One, and only one, terminator must be connected to ground via a ground wire. Bad contacts or shorts are especially difficult to diagnose, though a time-domain reflectometer will find most problems quickly. A failure at any point of the network cabling tends to prevent all communications. For this reason, 10BASE2 networks could be difficult to maintain and were often replaced by 10BASE-T networks, which (provided category 5 cable or better was used) also provided a good upgrade path to 100BASE-TX. An alternative reliable connection has been established by the introduction of EAD-sockets.
Comparisons to 10BASE-T
10BASE2 networks cannot generally be extended without breaking service temporarily for existing users and the presence of many joints in the cable also makes them very vulnerable to accidental or malicious disruption. There were proprietary wallport/cable systems that claimed to avoid these problems (e.g. SaferTap) but these never became widespread, possibly due to a lack of standardization.
10BASE2 systems do have a number of advantages over 10BASE-T. They do not need the 10BASE-T hub, so the hardware cost is very low, and wiring can be particularly easy since only a single wire run is needed, which can be sourced from the nearest computer. These characteristics mean that 10BASE2 is ideal for a small network of two or three machines, perhaps in a home where easily concealed wiring may be an advantage. For a larger complex office network the difficulties of tracing poor connections make it impractical. Unfortunately for 10BASE2, by the time multiple home computer networks became common, the format had already been practically superseded. As a matter of fact, it is becoming very difficult to find 10BASE2-compatible network cards as distinct pieces of equipment, and integrated LAN controllers on motherboards don't have the connector, although the underlying logic may still be present.
Name origination
The name 10BASE2 is derived from several characteristics of the physical medium. The 10 comes from the maximum transmission speed of 10 Mbit/s (millions of bits per second). The BASE stands for baseband signalling, and the 2 represents the maximum segment length of 200, but the actual maximum is 185 meters because when the 10Base2 standard first came out they found that 200 meters was a bit too long and so they lowered the maximum to 185.
NOTE:
digital microdermabrasion system
没有评论:
发表评论