LAN
1. Ethernet The IEEE has standardized a number of LAN and MAN under the name of IEEE 802. Ethernet is the most popular lower-layer protocol used in LANs. There have been several enhancements to the original version of Ethernet, and the current versions support network transmission speeds ranging from 10 Mbps to 1,000 Mbps.
Ethernet uses a technique called the Carrier Sense Multiple Access/Collision Detection (CSMA/CD), also known as IEEE 802.3 to provide media access to devices on the network. A carrier is a signal containing some specific data. CSMA/CD works in the following manner.
(a) The device that needs to send data checks the cable for any signals. This is called Carrier Sense.
(b) If no carrier is found, the device accesses the medium and transmits data signals, but it is possible that multiple devices start transmitting signals simultaneously. This is called Multiple Access.
(c) When multiple devices transmit signals simultaneously, a collision occurs. The device nearest to the point of collision detects the collision and informs all the devices about the collision, which is called Collision Detection. The devices then wait for a random period of time before retransmitting the data.
2. Ethernet Cabling
|
Name
|
Cable
|
Max.seg
|
Nodes/seg
|
Advantages
|
|
10Base5
|
Thick coax
|
500m
|
100
|
Original cable; now obsolete
|
|
10Base2
|
Thin coax
|
185m
|
30
|
No hub needed
|
|
10Base-T
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Twisted pair
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100m
|
1024
|
Cheapest system
|
|
10Base-F
|
Fiber optics
|
2000m
|
1024
|
Best between building
|
The common names for various types of Ethernet are interpreted based on the following format:
<data rate><transmission method><maximum length of cable/type of cable>
Some types of Ethernet cables
(a) 10 Base-T 10Base-T means that the cable has a data rate of 10Mbps, uses baseband, and perform data transmission using twisted-pair cable. The maximum length of a 10Base-T segment is 100 meters. Repeaters can be used to extend the maximum cable length. The minimum cable length between computers is about 8 feet. A 10BaseT LAN can support up to 1024 computers. 10BaseT solution provides the advantages of a star-wired topology. The 5-4-3 rule for Ethernet states that an Ethernet can have a maximum of five segments with a maximum of four repeaters, and out of the five segments only three segments can have nodes attached to them.
(b) 10Base2 10Base2 means that the cable has a data rate of 10 Mbps, uses base band transmission, and has a maximum cable length of 185 meters per segment, each of which can handle only 30 machines. The minimum distance between two nodes in this type of Ethernet is 16.5 feet.
(c) 10Base5 10Base5 popularly called thick Ethernet means that the cable has data rate of 10 Mbps, uses baseband transmission, and has a maximum cable length of approximately upto 500 meters. It can support a maximum of 100 computers in a given segment. Thus, 300 nodes can be connected in an Ethernet network implemented using thickest cables. In addition, the minimum distance between two nodes should be 8.25 feet.
(d) 10BaseF The 10BaseF which uses Fiber optics. This alternative is expensive due to the cost of the connectors and terminators, but it has excellent noise immunity. It offers good security since wire tapping Fiber is much more difficult than wire tapping copper wire. It allows a maximum distance of 1.3 mile per segment. You can connect up to 1024 nodes on such a network.
(e) 100BaseX (Fast Ethernet) The Fast Ethernet standard supports speed of 100Mbps and uses the same frame formats as the 10 Mbps Ethernet. The 100 denotes 100 Mbps data speed. There are three categories in 100BaseX Ethernet: 100BaseT4, 100BaseTX, and 100BaseFX. The 100baseT4 uses category 3, 4, or 5 UTP cable. The 100BaseTX Ethernet uses category 5 STP or UTP cable and 100BaseFX uses fiber optic cable. The distance between a computer and a hub con not be greater than 330 feet. The 5-4-3 rule is not applicable to fast Ethernet. Fast Ethernet is the most popular Ethernet because of high speed and cost-effectiveness.
(f) 1000BaseT IEEE 802.ab describes Gigabit Ethernet using Cat-5e cables. These networks can transfer data at 1 Gbps rate.
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COMPUTING KNOWLEDGE
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