Ethernet Basics
Ethernet is the IEEE 802.3 standard based on the CSMA/CD access method. It’s good balance of speed, cost and ease of use has established Ethernet as one of the most popular LAN technologies.
CSMA/CD
The Ethernet standard is based on the way the individual computers access the network and talk to each other.
Nodes access the network using a set of rules called CSMA/CD or Carrier Sense Multiple Access with Collision Detection. Ethernet is a baseband transmission, meaning that all the computers ( nodes ) share access to the network at the maximum allowable bandwidth.
This basically means that computer's are either listening/receiving or sending information. On Ethernets, only one computer is allowed to talk at a time. Before a computer sends out any information it checks to see if anybody else is talking. If all is clear, it sends out its information to every computer in the vicinity (network segment). The other computers ignore the data except the one computer that is the intended target of the information. The target computer then signals that it has received the data and the whole process starts over again.
Collisions
Collisions occur if two computers believe the network is quiet and they both begin talking at the same time. The first computer that senses that a collision has occurred sends out a signal called a JAM. This 32-bit stream helps stop the computers from transmitting. After an arbitrary delay the computers attempt to resend their information. The delay must be random otherwise the collision state would keep reoccurring endlessly. Collisions are a normal occurrence in ethernets. The more computers are on a segment, the higher the probability of collisions occurring. There seems to be no hard rule for how many collisions are too many. However, there is no doubt that a certain type of collision known as a late collision is unwanted and shows poor network design. Late collisions occur when two computers don't realize that they are talking at the same time. This usually happens because they are so far away from each other that they send out their whole message before they receive the jam signal.
In other words, if it takes longer for a packet to reach the far side of a segment than it does to put the packet on the segment a late collision will likely occur.
Collision Domain
A collision Domain is a single CSMA/CD network that produces a collision if two computers transmit at the same time. Routers and switches separate networks into collision domains.
MAC Address
Another important aspect of ethernets is the MAC address, also known as hardware address. A hardware address is a unique number associated with the ethernet card that distinguishes it from all the other cards on the network. The MAC address is a six byte number that is usually represented is hex format as follows: 12:34:45:67:89:10. The number can be found printed directly on the green PCB board of the ethernet card. To reduce the chances of two cards having the some MAC, the first three bytes are unique to a particular manufacturer and the next three are unique to the card.
10 base 5
The first 10Mbps Ethernets were the 10base5 's or thick Ethernets. They required a special cable to connect the Ethernet card to a transceiver, which in turn was connected to the segment line. The minimum distance between transceivers along the trunk line is 2.5m. The extra equipment lead to higher costs for implementing this network.
10 base 2
10base2 had the transceiver integrated into the Ethernet card. This eliminated the need for an external one and the extra connector cable. Computers hooked up to the segment line by means of a "T" connector. The segment had to be capped at both ends with a 50-Ohm terminator to prevent signal reflection.
100 base T
100 Mb networks adopt a star pattern (topology) with all the computers attached to a hub centered in the middle of the pattern. Fast Ethernets have the ability to autonegotiate the speed between 10 and 100 Mbps, allowing dual speed hubs and flexibility when incorporating older equipment.
Overview10 Mbps ( 10 Mega bit ) Ethernets
Overview 100 Mbps ( 100 Mega bit ) Ethernets
CSMA/CD
The Ethernet standard is based on the way the individual computers access the network and talk to each other.
Nodes access the network using a set of rules called CSMA/CD or Carrier Sense Multiple Access with Collision Detection. Ethernet is a baseband transmission, meaning that all the computers ( nodes ) share access to the network at the maximum allowable bandwidth.
This basically means that computer's are either listening/receiving or sending information. On Ethernets, only one computer is allowed to talk at a time. Before a computer sends out any information it checks to see if anybody else is talking. If all is clear, it sends out its information to every computer in the vicinity (network segment). The other computers ignore the data except the one computer that is the intended target of the information. The target computer then signals that it has received the data and the whole process starts over again.
Collisions
Collisions occur if two computers believe the network is quiet and they both begin talking at the same time. The first computer that senses that a collision has occurred sends out a signal called a JAM. This 32-bit stream helps stop the computers from transmitting. After an arbitrary delay the computers attempt to resend their information. The delay must be random otherwise the collision state would keep reoccurring endlessly. Collisions are a normal occurrence in ethernets. The more computers are on a segment, the higher the probability of collisions occurring. There seems to be no hard rule for how many collisions are too many. However, there is no doubt that a certain type of collision known as a late collision is unwanted and shows poor network design. Late collisions occur when two computers don't realize that they are talking at the same time. This usually happens because they are so far away from each other that they send out their whole message before they receive the jam signal.
In other words, if it takes longer for a packet to reach the far side of a segment than it does to put the packet on the segment a late collision will likely occur.
Collision Domain
A collision Domain is a single CSMA/CD network that produces a collision if two computers transmit at the same time. Routers and switches separate networks into collision domains.
MAC Address
Another important aspect of ethernets is the MAC address, also known as hardware address. A hardware address is a unique number associated with the ethernet card that distinguishes it from all the other cards on the network. The MAC address is a six byte number that is usually represented is hex format as follows: 12:34:45:67:89:10. The number can be found printed directly on the green PCB board of the ethernet card. To reduce the chances of two cards having the some MAC, the first three bytes are unique to a particular manufacturer and the next three are unique to the card.
10 base 5
The first 10Mbps Ethernets were the 10base5 's or thick Ethernets. They required a special cable to connect the Ethernet card to a transceiver, which in turn was connected to the segment line. The minimum distance between transceivers along the trunk line is 2.5m. The extra equipment lead to higher costs for implementing this network.
10 base 2
10base2 had the transceiver integrated into the Ethernet card. This eliminated the need for an external one and the extra connector cable. Computers hooked up to the segment line by means of a "T" connector. The segment had to be capped at both ends with a 50-Ohm terminator to prevent signal reflection.
100 base T
100 Mb networks adopt a star pattern (topology) with all the computers attached to a hub centered in the middle of the pattern. Fast Ethernets have the ability to autonegotiate the speed between 10 and 100 Mbps, allowing dual speed hubs and flexibility when incorporating older equipment.
Overview10 Mbps ( 10 Mega bit ) Ethernets
| name | 10 BASE 5 | 10 BASE 2 | 10 BASE T | 10 BASE F |
| speed | 10 Mbps | 10 Mbps | 10 Mbps | 10 Mbps |
| connector | AUI | BNC | RJ-45 | ST |
| cable | Thick coaxial | Thin coaxial | Twisted pair | Fiber optic |
| segment length |
500 M | 186 M | 90 M | 2000 M |
| nodes per segment |
100 | 30 | 1024 | 1024 |
| topology | bus | bus | star | star |
Overview 100 Mbps ( 100 Mega bit ) Ethernets
| name | 100 BASE T4 | 100 BASE TX | 100 BASE FX |
| speed | 100 Mbps | 100 Mbps | 100 Mbps |
| connector | RJ-45 | RJ-45 | ST |
| cable | 4 pair twisted | 2 pair twisted | Fiber optic |
| segment length |
100 M | 100 M | 2000 M |
| topology | star | star | star |
