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Ethernet or CSMA/CD
CSMA/CD means Carrier Sense with Multiple Access and Collision Detection. Here are the rules that make CSMA/CD work.
- All computers stay quiet if another computer is talking.
- Any computer that wants to talk must listen to see if the network is silent, they must wait a predetermined time based on the time it takes for a message to travel the length of the network.
- If after waiting, if the network is silent, then a computer may talk.
- If two computers wait and both talk together, a collision is said to occur.
- Other computers recognise the collision and re-enforce it by talking.
- Then all computers stop talking.
- Each computer picks a random number and counts backward to zero.
- Hopefully one of the two computers that wanted to talk finishes first and begins talking causing the other computers to wait.
In the diagram above you can see that all computers are connected to a common pathway. The original ethernet cable (pathway) was a coax cable. This also means that ethernet is a bus topology. All computers share a common pathway, the bus. Ethernet has gone through a number of migrations to more sophisticated cabling styles and has had some major increases in data rates. Here is a list of the variations in Ethernet.
| Short Name |
Expanded Name |
Equipment |
Code Used |
Connector Type |
Cable Type |
Distance |
| 10BASE5 |
10MB/s Baseband 5x100m |
Controller card at PC, AUI cable, Transducer |
Manchester Encoding |
Male N type coax, Vampire Clamps, Female N type 50W terminators |
Coax 50W |
500m may be repeated up to 2,500m |
| 10BASE2 |
10MB/s Baseband 2x100m |
NIC at PC |
Manchester Encoding |
Male BNC type coax, BNC T adaptors, Female BNC 50W terminators |
Coax 50W |
185m |
| 10BASET |
10MB/s Baseband Twisted Pair |
NIC at PC, HUB |
Manchester Encoding |
RJ45 male/female connectors, Cat 3 cable, 100W balanced |
UTP 100W+/-15W |
90m plus 10m patching |
| 100BASET4 |
100MB/s Baseband Twisted Pair 4 pairs used |
NIC at PC, HUB |
8B/10B Encoding |
RJ45 male/female connectors, Cat 3 cable, 100W balanced |
UTP 100W+/-15W |
90m plus 10m patching |
| 100BASETX |
100MB/s Baseband Twisted Pair 2 pairs used |
NIC at PC, HUB or Switch |
MLT3 Encoding |
RJ45 male/female connectors, Cat 5 cable, 100W balanced |
UTP 100W+/-15W |
90m plus 10m patching |
| 1000BASET |
1000MB/s Baseband Twisted Pair 4 pairs used |
NIC at PC, HUB/Switch |
4D PAM5 Encoding |
RJ45 male/female connectors, Cat 5e/6 cable, 100W balanced |
UTP 100W+/-15W |
90m plus 10m patching |
| 100BASESX |
100MB/s Baseband 850nm Short wavelength 2 fibers |
Point to Point, HUB's, Switches |
FLP Fast Link Pulse |
ST, SC, MT-RJ |
62.5/125mm Multimode |
300m on Multimode |
| 100BASELX |
100MB/s Baseband 1300nm Long wavelength 2 fibers |
Point to Point, HUB's, Switches |
Pulsed |
ST, SC, MT-RJ |
SM or MM |
3Km on singlemode, 460m on multimode |
| 1000BASESX |
1000MB/s Baseband 850nm Short wavelength 2 fibers |
Point to Point, HUB's, Switches |
8B/10B Serial |
SC/PC, MT-RJ |
MM 62.5/125mm or MM 50/125mm |
300m (62.5m) 550m (50m) |
| 1000BASELX |
1000MB/s Baseband 1310nm Long wavelength 2 fibers |
Point to Point, HUB's, Switches |
8B/10B Serial |
SC/PC, MT-RJ |
MM 62.5/125mm or SM 9/125mm |
550m MM or 3Km SM |
| 10GBASEXX |
10,000MB/s Baseband XX=many variations |
Backbone Fiber only |
64/66b encoding |
various |
MM or SM |
up to 40Km |
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