Chapter 4
1973 Xerox Develops Ethernet
Carrier Sense Multiple Access/Collision Detection (CSMA/CD)
Preamble
Bus topology
Dominates Today's Networks
3 Mdps
Developed off of the Sneakernet Methods
1979 Xerox looks for Partners
Digital-Intel-Xerox (DIX)
Digital Equipment Corporation (DEC)
Origins of Ethernet
Coaxial Cable
10 Mbps
Creates IEEE 802.3 (Ethernet)
Standard is still controlled today
Recipient MAC
Sender MAC
Type
Data
Pad
Frame Check Sequence FCS
7 byte series, followed by a 1 byte start frame
Gives the receiving NIC time to respond
MAC Address
Each NIC is often refereed as a Node in terns of MAC Addressing
Gives the NIC a unique address
Hubs will broadcast the MAC across the network, the computer with the correct MAC from the frame will receive the message.
Network Interface Controller NIC
48-bit/6 byte binary address identifys the MAC Address
.
This leaves a security vulnerability, because data is sent to all computers on the Ethernet network
Helps the receiving computer interpret the frame contents
Does not tell the receiving computer if higher level data is included, aka. emails or web pages
Contains the actual payload of the frame
Used to bring the frame of data up to 64 bytes if the frame is small
Makes sure the data transfer is not corrupted
Makes sure the network is 'free' before sending the frame
The Ethernet is a first-come first-served basis
If there is a collision the data is broken and the frame is sent a random number of seconds later to get it across the ethernet
Serves as the connection between the computers on the network
There are a certain group of 'nodes' on the network that are collision domains
This means that they can send at the same time across the network
The last true bus topology used 10Base2 ot Thinnet
Limited to 185 Meters in length on coaxial cable RG-58
10BaseT becomes the most popular bus topology in 1990
10BaseT Hubs use 'ports' as connections between computers on the network
Can have around 4 to 48 ports
The 'T' refers to the cabling (Unshielded Twisted Pair or UTP)
Needs CAT 3 cabling or higher
Introduces the RJ-45 connector
10BaseFL
2000 meter transmit limit
No more than 1024 nodes per hub
Uses multmode fiber-optic cabling