What is Ethernet

ETHERNET local area computer networks. General principles, types of frameworks and structures of ETHERNET networks.

802,3 IEEE-Ethernet
PARC ETHERNET, before 1970, is created initially in the form of a corporate standard for coaxial cable and speed 10Mbit. On the basis of them creates a DIx Ethernet. The projects are being developed by IEEE 802. In these access method is used in a transmission medium CSMA/CD.

Principle of operation of Ethernet:
WS (Work Station) or when the server wishes to transmit, originally the official transmission medium, tracks have a normal broadcast signal (50ms a time for the transmission of information or 900bit ≈ 62.5 octets (1 byte) if it finds that the transmission medium is free it begins to transmit the frame that has the following expected transmission response from the Subscriber that contains the acknowledgement of correctly adopted framework. The answer expected. If you do not answer arrives , repeat the frame. If so, if there is a next transmit frame. The beginning of the next frame must not be late more in time for the transmission of 96bit. If you do not comply with the other stations will feel that the transmission medium is released. In the event that the transmission medium is occupied by the workstation that you want to transmit starts waiting. She waits in the course of time allocated in the exponential law. After the expiry of the waiting WS audition again transmission medium and performs all the procedures listed above. In Ethernet are possible adverse events (conflicts, collisions).Expansion is an event in which two or more stations are starting to transmit at the same time.In such simultaneous work on the transmission medium is aggregating some discrete signals.The proper acceptance is impossible. WS who participated in the conflict, register the conflict on the basis of this confusion in the line. They do not receive a response. The stations, which are in conflict with the first sequence sent a special structure in the transmission medium.Notify the other stations that conflict. After you submit the procedure to resolve the conflict.Trace the conflict: each station involved in the conflict selects the waiting time {Ti}. Make 16 conflict resolution experience. When you first choose 1 of 2 times. The second selects 1 of 4, 1 in 8, and the next 1 of 16. On subsequent always chooses 1 of 16. The transmission of several attempts to 16 is necessary because in the random selection of waiting times is possible two or more of the parties to the conflict to choose the same time. As a result of which enter the next conflict. This theoretically does not give permission, but in practice gives a completely satisfactory results.

The development of Ethernet-since 1998. be increasing the speed of Exchange, providing the duplex mode, perfection of methods of access to the transmission medium. The rate is raised from 10Mbit/s Ethernet 100Mbit/-, s-, fast 1000Mbit Ethernet/Gigabit Ethernet-s.

In Ethernet clearly distinguishable levels 2 and 1. To have a global network and parts of level 3 of the OSI model. Level 2, in accordance with detailed specifications for the Ethernet level and contains two functional elements: MAC and LLC-Logical Link Control and Media Access Control.They provide:

  • Accepting and processing framework and recognition of MAC addresses.
  • Audit for detecting errors and protocols for re-submission of open error.
  • Maintain interface with upper and lower levels.
  • Control of the integrity of the data within one framework.
  • Ensure compatibility with other architectural LAN.

In the above level 2 protocols of the other levels go transparent. MAC is the lower-level component provides the interface functions with the physical layer 1. This sublevel takes place the very formation of the structure of the framework. Level 1 features: this physical level is divided Into 4 components. Each component is: podsloj PLS, AUI, MDI, PMA:

  • PLS-physically signals. Form signals to be transmitted over the cable. Interface to the transmission medium;
  • AUI-interface (actual) with a transmission medium. Standardize the funkciiite here the final signal equipment;
  • PMA-the physical transmission medium. Standardize the characteristics of the transmission medium;
  • MDI-depends on the Middle interface. Regulate only interfaces in terms of transmission medium. Has 3 parts:

I part numbers-bit rate in Mbit/s; Part II-BASE technology, an honor all baseband bandwidth is provided to AB to transmit data; Part III-or maximum length of LAN in hundreds of feet, or the type of transmission medium.

Ethernet Standards:

  • 10Base2-10Mbit/s total bandwidth-maximum length of LAN-200m;
  • 10Base5-10Mbit/s total bandwidth-maximum length of LAN-500m. In organizing the LAN using network segments. The number of domains is kolizijnite from 3 to 5;
  • -pair 10BaseT twister -2 twisted pairs of inverse differential signals, signal, which is transmitted in the second wire;
  • -10Mbit/s 10BaseFL fiber optic cable mnogomodov Used (better noise immunity), maximum length 2 km;
  • 10BaseFOIRL-singlemode fiber optic cable 8.3 μm;
  • 100BaseTX -cub twisted 2ki, FTP, UTP cat 5 STP;
  • 100BaseFX fiber optic cable-, mnogomodov, -1000 400 m;
  • 100BaseT4 -short range, 4 vdojki, duplex mode;
  • 1000BaseLX optical cables-400-500-3000 m mnogomodov-Singlemode;
  • 1000BaseCX-shielded, twisted pairs, coaxial cable up to 25 m;
  • 1000BaseT-may be shielded, unshielded UTP-20 m.

Be used through Internetdict.com in Gigabit Ethernet frames: 3 main Base Frame, Frame, LLC LLC snap frame

  • Base Frame–used when carrying out a co-axial socket exchange within one Ethernet network or Ethernet network between the great distances;
  • LLC Frame-when interacting heterogeneous networks;
  • LLC snap frame-heterogeneous networks and different protocols at a high level.

And the 3 frames are informational. The frame has a specific structure in which individual fields are formed. Each field has a fixed place in the structure of the framework, specific location and purpose. There are mandatory fields: an introductory Header that has 7 octets; the frame delimiter 1 octet address field 18bit, for recipient-6 octets, the address field for the sender to 6 octets, the length field of the frame-2 octets; checksum field; data field-length promeliva with limitations on the top and bottom.

The following two types of information frames are received using basic framework immediately before the corresponding Header-and-SNAP header, LLC header, and reduces the upper limit of the broadcast. Headera LLC consists of three fields with length 1 octet. The first field is the DSAP (port for access to the service recipient); SSAP-port to access the data source; control box-contains the ednobitovi flag-general purpose-provide 1 octet compatibility between different LAN. When the networks are not only raznotipni, but also work with a variety of protocols at a high level is added and the SNAP header, which provides coordination with different protocols of higher level.

Gallery

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