How did Fast Ethernet technology come about?
For a long time the ten-megabit network wasthe only way to connect computers. Although this technology had a number of features (stubs-terminators, signal collisions, correspondence of wave impedance), it was the one that got the most distribution.The equipment was relatively inexpensive, assembly- simple, and the speed of 1.25 MB / s suited everyone. However, the volume of transmitted data became more and more every year, and the requirements for network equipment became tougher. Therefore, in the 90s, the out-of-date solution was replaced by Fast Ethernet technology. When developing the wishes of users and manufacturers were taken into account, the "childhood diseases" of the 10-Mbit network were overcome.
Fast Ethernet. Description
The time of the origin of technology can be considered 1992year. It was then that a group of companies engaged in the creation of network equipment, including 3Com, SYNOptics and several others, created a special joint association called "Fast Ethernet Alliance". His task was to analyze the developments of various manufacturers, which could be used to create a high-speed information transfer solution.Moreover, the principles of the formation and transmission of data packets should not be too different from 10-Megabit networks. This was necessary to maintain compatibility with CSMA / CD access.
In the same year at the Institute of Standardization IEEEan association was formed, whose tasks included studying the solutions offered by companies for 100 Megabit access. This was the beginning of an unofficial confrontation between companies and their developments. Each developer sought to ensure that his decision was made for the standard.
As a result, as is often the case, manyhad to sacrifice, choosing a compromise option. For example, the proposed 100VG-AnyLAN technology from HP and AT & T, implementing a completely new principle of access to Demand Priority, was refused, as it was not backward compatible with the existing 10Base solution.
The result of the work was the recognition in 1995 of the 100-Megabit Fast Ethernet solution standard, which received the designation 802.3u.
The main difference between Fast Ethernet and its predecessor - 10 Mbit Base-T - was the change in physical implementation.
In addition to compatibility with the previous solution, the main advantages of this technology include:
- Increase the speed of data exchange to 12.5 MB / s (the very 100 Mbps);
- use of the random access method;
- the possibility of using the usual solutions, as the function of creating star-shaped networks was preserved, and it was possible to use classical conductors: twisted pair and fiber.
Since the Fast Ethernet packet frame formatdata has remained the same, this has allowed to achieve almost complete backward compatibility. So, even now all network solutions at 100 Mb and even 1 Gigabit provide for 10-megabit mode of operation (it can be set forcibly in the driver settings).
Nevertheless, there are differences. For example, the time intervals for the transmission of frames were reduced by almost 10 times (in fact, this allowed to achieve such a high speed).
Features of segments
As an Ethernet option that does not usecoaxial cable, 100Mbps Fast Ethernet requires connection to all ends of branches of receiving devices. These can be networked computer cards, hubs and hubs (HUBs). The length of the line is constrained depending on the type of conductor used. Thus, for a twisted pair of the fifth category, the permissible distance is 100 meters, but the optical fiber makes it possible to work from 400 m (half duplex) to 2 km.
Although the number of repeaters is also limited, this does not prevent the creation of complex network schemes due to the multiport nature of such devices.