Ethernet - initially connecting technology based on a common bus to which computers are connected and «fighting» among themselves for the right to transfer package. The basic protocol - CSMA / CD (multiple access sensitive load and detect conflicts). The point is that if two stations simultaneously start the transfer, there is a situation of conflict, and the network for some time «waiting for», while «ulyagutsya» transients and again is «calm». 4Suschestvuet another method of access - CSMA / CA (Collision Avoidance) - the same, but with the exception of conflicts. This method is used in wireless technology Radio Ethernet or Apple Local Talk - before sending any packet network runs announcement that the transfer would happen now, and the station was no longer try to initsiirovat.2
Ethernet is half-duplex (Half Duplex), for all transmission media: the source and receiver «says waiting for» (classical connecting technology) and a full (Full Duplex), when two pairs of receiver and transmitter devices talk simultaneously. This mechanism works only on twisted pair (one pair for the transfer, one pair at the reception) and fiber (one pair for the transfer, one pair at the reception).
Ethernet is different for speed and methods of coding for different physical environment, as well as the type of packets (Ethernet II, 802.3, RAW, 802.2 (LLC), SNAP).
Ethernet is different speed: 10 Mbps, 100 Mbps, 1,000 Mbps (Gigabit). As the newly ratified standard Gigabit Ethernet to twisted pair category 5, we can say that for any Ethernet network can be used twisted pair, single (SMF) or multiple (MMF) fiber. Depending on this, there are different specifications:
• 10 Mbps Ethernet: 10BaseT, 10BaseFL, (10Base2 and 10Base5 exist for coaxial cable, and no longer apply);
• 100 Mbps Ethernet: 100BaseTX, 100BaseFX, 100BaseT4, 100BaseT2;
• Gigabit Ethernet: 1000BaseLX, 1000BaseSX (on optics) and 1000BaseTX (for the twisted-pair)
There are two options for the implementation of Ethernet to coaxial cable, called «fine» and «thick» Ethernet (Ethernet cable on a thin 0.2 inches thick and Ethernet cable to 0.4 inches). 1
Thin Ethernet cable uses a type of RG-58A / V (diameter of 0.2 inches). For a small network used by cable resistance of 50 ohms. Coaxial cable prokladyvaetsya from computer to computer. Each computer left small supply cable in the event of his possible move. The length of 185 m segment, the number of computers connected to the bus - to 30.
After the accession of all segments of the cable with BNC-connectors (Bayonel-Neill-Concelnan) to T-connector (the name is due to form the connector, similar to the letter «T») get a single cable segment. At its both ends are set terminator ( «cover»). Terminator constructively is a BNC-connector (he also put on the T-connector) with vpayannym resistance. The value of this resistance should correspond to the value of the wave resistance cable, that is need for Ethernet terminator resistance of 50 ohms.
Thick Ethernet - Network on thick coaxial cable with a diameter of 0.4 inches and wave impedance of 50 ohms. The maximum length of cable segment - 500 m.
Laying of the cable nearly the same for all types of coaxial cable.
To connect a computer to the thick cable used additional device, called the transceiver. Transceiver is connected directly to the network cable. It is special to your computer transiverny cable, the maximum length of 50 meters at both its ends are 15-DIX-contact connectors (Digital, Intel and Xerox). With a single connector to connect to the transceiver, with the help of another - to power the computer's motherboard.
Transceivers exempt from the need to lay the cable to each computer. The distance from the computer to the network cable is determined by the length transivernogo cable.
Creating a network using the transceiver's very convenient. It can be located anywhere in the literal sense «skip» cable. This simple procedure takes little time, while the connection is very reliable.
Cable does not cut into pieces, you can run without worrying about the exact location of computers and then install transceivers in the right places. Mounted transceiver, typically on the walls, provided that they are designed.
If you need to cover a local area network of more than allow the cable system applies additional devices - Repeaters (repeaters). Repeaters are 2-port performance, that is it can combine 2 segment of 185 m. The segment connects to a repeater, through T-connector. By the end of a T-connector plugs segment, and another is terminator.1
The network may be no more than four repeaters. This gives the network maximum length of 925 m.
There are 4-port Repeaters. One such repeater can be connected directly segment 4.
The length of the segment for Ethernet on a thick cable is 500 meters in one segment, you can connect up to 100 stations. If there transivernyh cables up to 50 meters in length, thick Ethernet can reach a segment of much more space than thin. These Repeaters are DIX-connectors and can connect transceivers, as the end of the segment or in any other place.
Very convenient combined Repeaters, ie suitable for thin and thick cable. Each port has a pair of connectors: DIX and BNC, but it can not be deployed simultaneously. If it is necessary to combine different segments on cable, a thin segment connects to a BNC-connector port repeater, as thick - to DIX-connector to another port.
Repeaters are very useful, but they should not be abused because they lead to a slowdown in the network.
Ethernet on twisted pair.
Twisted pair - are two insulated wires, twisted among themselves. For Ethernet using 8-wire cable, which consists of four twisted pairs. To protect the environment from the effects of cable has an external isolation blanket.
The main site for twisted pair - hub (in translation called drive, hub, or simply hub). Each computer must be connected to it through its cable segment. The length of each segment should not exceed 100 m. At the ends of cable segments are set RJ-45 connectors. A connector cable connects to the hub, the other - to the network adapter. RJ-45 connectors are compact, have a plastic shell and eight smaller sites.
Hub - a central device on the network on twisted pair, depends on it running. Have it should be in a readily accessible location so you can easily connect the cable and monitor decentralized ports.
Hubs are produced in different amounts of ports - 8, 12, 16 or 24. Accordingly, it can connect the same number of computers.
Technology Fast Ethernet IEEE 802.3U.
Technology Fast Ethernet standardized Committee of IEEE 802.3. The new standard called IEEE 802.3U. The speed of transmission of 100 Mbps. Fast Ethernet is organized by twisted pair or fiber.
In the Fast Ethernet network organized several domains of conflict, but given the mandatory class repeater used in the domain.
Repeaters Fast Ethernet (IEEE 802.3U) are two different classes and to delay in microseconds. Accordingly, the segment (logical) can be up to two repeaters Class 2 and a repeater class 1. For Ethernet (IEEE 802.3) network is subject to 5-4-3-2-1.
Rule 5-4-3-2-1 reads: between any two workstations there should be no more than 5 physical segments, 4 repeaters (hubs), 3 «human» natural segments, 2 «human» mezhrepiternyh Relations (IRL), and all This should constitute a conflict of domain (25.6 ms) .4
Physically, the hub of the «increasing» many wires, but logically it is all one segment of Ethernet and a conflicting domain, in connection with any malfunction of one station affects the other. Since all the stations are forced to «listen» other people's bags, a conflict occurs in the entire hub (in fact, at other ports sends a signal Jam, but it does not change the fact). Therefore, although the hub - this is the most inexpensive device, and it seems that it solves all the problems the customer, you might consider gradually abandon this method, especially in the context of the continuous growth of the requirements for resource networks, and move on switched networks. The network of 20 computers, gathered at the repeater 100 Mbps, can run slower than a network of 20 computers on the switchboard 10 Mbps. Where once considered «normal» presence in the segment up to 30 computers, the current networks, even 3 workstations can download the entire segment.