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Written by Administrator
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Saturday, 11 July 2009 04:09 |
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Page 3 of 15 LAN media Access technologiesEthernet It uses share media employing carrier sense multiple access with collision detection (CSMA/CD). It supports full-duplex on twisted-pair and coaxial media. It is defined by IEEE 802.3 standard. - 10base2 implementation: ThinNet, uses coaxial cable, maxlength 185 meters, provides 10 Mbps.
- 10base5 implementation: ThickNet, uses coaxial cable, maxlength 500 meters, provides 10 Mbps.
- 10base-T implementation: Uses twisted-pair wiring provides 10 Mbps, usually implemented in star topology.
- Fast Ethernet implementation: Uses twisted-pair wiring provides 100 Mbps.
Token ring It uses a token passing technology with a physically star configured topology. - Each computer is connected to a central hub, Multi-station Access Unit (MAU).
- It operates with transmission speeds at 16 Mbps.
- It has an active monitor that removes frames that are continuously circulating on the network.
- Beaconing - If a computer detects a problem with the network, it sends a beacon frame. This will generate a failure domain where computers and devices will attempt to reconfigure certain settings to try and work around the detected fault.
FDDI—Fiber Distributed Data Interface It is a high speed token-passing media access topology. - It transmits data at 100 Mbps.
- It provides fault tolerance by providing a second counter rotating fiber ring.
- It enables several tokens to be present on the ring at the same time.
Important TermsMaximum Transfer Unit (MTU) It is a parameter that indicates how much data a frame can carry on a specific network. MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). Token passing It is a 24-bit control frame used to control which computers communicate at what intervals. The token grants a computer the right to communicate. Do not cause collisions because only one computer can communicate at a time.
CSMA Carrier sense multiple access CSMA/CD (collision detection) - Monitor the transmission activity or carrier activity on the wire so that they can determine when would be the best time to transmit data. Computers listen for the absence of a carrier ton on the cable, which indicates that no one else is transmitting date at the same time. - Contention - The nodes have to compete for the same shared medium
- Collision - Happens when two or more frames collide.
- Back-off algorithm - All stations will execute a random collision timer to force a delay before they attempt to transmit data.
- CSMA/CA (collision avoidance) - Is an access method where each computer signals its intent to transmit data before it actually does so.
Collision Domains It is a group of computers that are contending or competing for the same shared communication medium. Collection of hubs represents a single collision domain.
Polling Some systems are configured to be primary stations and others are secondary stations. At predefined intervals, the primary station will ask the secondary station if it has anything to transmit.
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Last Updated on Friday, 28 August 2009 05:02 |
